COMPOSITE SLABS AND BEAMS USING STEEL DECKING: BEST

MCRMA

18 MERE FARM ROAD

PRENTON

WIRRAL

CHESHIRE

CH43 9TT

TEL: 0151 652 3846

FAX: 0151 653 4080

www.mcrma.co.uk

Composite Slabs and Beams Using Steel Decking: Best Practice for Design and Construction

THE METAL CLADDING & ROOFING MANUFACTURERS ASSOCIATION

in partnership with

THE STEEL CONSTRUCTION INSTITUTE

COMPOSITE SLABS AND BEAMS

USING STEEL DECKING:

BEST PRACTICE FOR DESIGN

AND CONSTRUCTION

MCRMA Technical Paper No. 13

SCI Publication P300

CI/SfB

Nh2(23)

MARCH 2009

THE STEEL CONSTRUCTION INSTITUTE

SILWOOD PARK

ASCOT

BERKSHIRE

SL5 7QN

TEL: 01344 636525

FAX: 01344 636570

www.steel-sci.org

cyan plate magenta plate yellow plate black plate

REVISED EDITION

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SCI (The Steel Construction Institute) is the leading, independent provider of technical expertise and

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The Metal Cladding and Roofing Manufacturers Association represents the major manufacturers in the

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The Metal Cladding And Roofing Manufacturers Association Limited

18 Mere Farm Road, Prenton, Wirral, Cheshire CH43 9TT

Tel: +44 (0) 151 652 3846

Fax: + 44 (0) 151 653 4080

www.mcrma.co.uk

MCRMA Technical Paper No. 13

SCI Publication No. P300

Composite Slabs and Beams using

Steel Decking:

Best Practice for Design and

Construction

(Revised Edition)

J W Rackham BSc (Build Eng), MSc, DIC, PhD, CEng, MICE

G H Couchman MA, PhD, CEng, MICE

S J Hicks

B Eng, PhD (Cantab)

Published by:

The Metal Cladding & Roofing Manufacturers Association

in partnership with

The Steel Construction Institute

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 2009 The Steel Construction Institute and The Metal Cladding & Roofing Manufacturers Association

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Publications supplied to the Members of the Institute at a discount are not for resale by them.

Publication Number: MCRMA Technical Paper No 13; SCI P300 Revised Edition

ISBN 978-1-85942-184-0 .

A catalogue record for this book is available from the British Library.

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FOREWORD

Composite construction has proven popular because it combines structural efficiency with

speed of construction to offer an economic solution for a wide range of building types.

Applications include commercial, industrial and residential buildings.

This guide covers the design and construction of composite slabs and beams, and

addresses the good practice aspects of these activities. It updates the previous

MCRMA/SCI guide, which was published in 2000. The update reflects the latest

guidance for good practice and gives information on design to the Eurocodes, but omits

most of the advice given previously on construction practice for decking, as this is now

covered comprehensively in separate BCSA documents Guide to the installation of deep

decking, Publication No. 44/07, and Code of Practice for metal decking and studwelding,

Publication No. 37/04.

Design and construction guidance related to Slimdek construction is dealt with in a

separate part of the guide because of the significant number of differences from

‘traditional’ composite beam and slab construction.

The principal authors of this publication were Dr J W Rackham, Dr G H Couchman, and

Dr S J Hicks (all from The Steel Construction Institute). They were part of a

collaborative group responsible for the content of the publication, other members of

which were:

Mr A J Shepherd Richard Lees Steel Decking Ltd

Mr J Turner Structural Metal Decks Ltd

Mr A Wallwork Corus Panels and Profiles Ltd

Mr D St Quinton Kingspan Structural Products Ltd

Mr D Mullett Studwelders Ltd

Mr D E Simpson The Concrete Society

Further information was provided by Dr W I Simms and Mr A Way, both from

The Steel Construction Institute.

The preparation of this document was funded and commissioned by the Metal Cladding

and Roofing Manufacturers Association (MCRMA).

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CONTENTS

Page No.

FOREWORD iii

SUMMARY vi

1 INTRODUCTION 1

1.1 Benefits of composite construction 2

1.2 Applications 3

1.3 Scope of this publication 3

2 THE DESIGN AND CONSTRUCTION TEAM 4

2.1 Team members 4

2.2 Roles in design and construction 5

2.3 Design and construction sequences 8

3 INFORMATION TRANSFER 10

3.1 Design stage 10

3.2 Construction stage 11

4 DESIGN OF DECKING AND SLABS 15

4.1 Steel decking 15

4.2 Composite slabs 26

4.3 Acoustic insulation 48

4.4 Health & Safety 51

4.5 Further reading 52

5 DESIGN OF COMPOSITE BEAMS 54

5.1 Construction stage 55

5.2 Composite stage 56

5.3 Shear connection 63

5.4 Further reading 72

6 CONSTRUCTION PRACTICE - CONCRETE 75

6.1 Concrete supply design 75

6.2 Placing concrete 76

6.3 Loads on the slab during and after concreting 81

6.4 Further reading 83

7 SLIM FLOOR CONSTRUCTION 85

7.1 Introduction 85

7.2 Design 88

7.3 Construction practice 100

7.4 Further reading 104

8 REFERENCES 105

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SUMMARY

This guide covers the design and construction of composite floors, paying particular

attention to the good practice aspects. Following a description of the benefits of

composite construction and its common applications, the roles and responsibilities of the

parties involved in the design and construction process are identified. The requirements

for the transfer of information throughout the design and construction process are

described.

The design of composite slabs and beams is discussed in detail in relation to the

Eurocodes and BS 5950. In addition to general ultimate and serviceability limit state

design issues, practical design considerations such as the formation of holes in the slab,

support details, fire protection, and attachments to the slab are discussed. Guidance is

also given on the acoustic performance of typical composite slabs. The obligations of

designers according to the CDM Regulations are identified and discussed.

The practical application of Slimdek construction, which normally utilises deep decking

and special support beams, is also covered. Typical construction details are illustrated,

and guidance is given on the formation of openings in the beams and the slab.

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1 INTRODUCTION

Composite slabs consist of profiled steel decking with an in-situ reinforced

concrete topping. The decking not only acts as permanent formwork to the

concrete, but also provides sufficient shear bond with the concrete so that, when

the concrete has gained strength, the two materials act together compositely.

Composite beams are normally hot rolled or fabricated steel sections that act

compositely with the slab. The composite interaction is achieved by the

attachment of shear connectors to the top flange of the beam. These connectors

generally take the form of headed studs. It is standard practice in the UK for the

studs to be welded to the beam through the decking (known as ‘thru-deck’

welding) prior to placing the concrete. The shear connectors provide sufficient

longitudinal shear connection between the beam and the concrete so that they act

together structurally.

Composite slabs and beams are commonly used (with steel columns) in the

commercial, industrial, leisure, health and residential building sectors due to the

speed of construction and general structural economy that can be achieved.

Although most commonly used on steel framed buildings, composite slabs may

also be supported off masonry or concrete components.

A typical example of the decking layout for a composite floor is shown in

Figure 1.1. The lines of shear connectors indicate the positions of the composite

beams.

Figure 1.1 A typical example of composite floor construction,

showing decking placed on a steel frame

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1.1 Benefits of composite construction

Composite construction has contributed significantly to the dominance of steel

frames in the commercial building sector in the UK. The main benefits of

composite construction are:

Speed of construction

Bundles of decking can be positioned on the structure by crane and the

individual sheets then installed by hand. Using this process, crane time is

minimal, and in excess of 400 m

of decking can be installed by one team in a

day, depending on the shape and size of the building footprint. The use of the

decking as a working platform speeds up the construction process for following

trades. Minimal reinforcement is required, and large areas of floor can be

poured quickly. Floors can be concreted in rapid succession. The use of fibre

reinforced concrete can further reduce the programme, as the reinforcement

installation period is significantly reduced.

Safe method of construction

The decking can provide a safe working platform and act as a safety ‘canopy’ to

protect workers below from falling objects.

Saving in weight

Composite construction is considerably stiffer and stronger than many other

floor systems, so the weight and size of the primary structure can be reduced.

Consequently, foundation sizes can also be reduced.

Saving in transport

Decking is light and is delivered in pre-cut lengths that are tightly packed into

bundles. Typically, one lorry can transport in excess of 1000 m

of decking.

Therefore, a smaller number of deliveries are required when compared to other

forms of construction.

Structural stability

The decking can act as an effective lateral restraint for the beams, provided that

the decking fixings have been designed to carry the necessary loads and

specified accordingly. The decking may also be designed to act as a large floor

diaphragm to redistribute wind loads in the construction stage, and the

composite slab can act as a diaphragm in the completed structure. The floor

construction is robust due to the continuity achieved between the decking,

reinforcement, concrete and primary structure.

Shallower construction

The stiffness and bending resistance of composite beams means that shallower

floors can be achieved than in non-composite construction. This may lead to

smaller storey heights, more room to accommodate services in a limited ceiling

to floor zone, or more storeys for the same overall height. This is especially

true for slim floor construction, whereby the beam depth is contained within the

slab depth (see Section 7).

Sustainability

Steel has the ability to be recycled repeatedly without reducing its inherent

properties. This makes steel framed composite construction a sustainable

solution. ‘Sustainability’ is a key factor for clients, and at least 94% of all steel

construction products can be either re-used or recycled upon demolition of a

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building. Further information on sustainability of composite flooring systems is

given in Composite Flooring Systems: Sustainable construction solutions

[1]

Easy installation of services

Cable trays and pipes can be hung from hangers that are attached using special

‘dovetail’ recesses rolled into the decking profile, thereby facilitating the

installation of services such as electricity, telephone and information technology

network cabling. These hangers also allow for convenient installation of false

ceilings and ventilation equipment (see Section 4.2.8).

The above advantages (detailed in more depth in SCI publication Better Value in

Steel: Composite flooring

[2]

) often lead to a saving in cost over other systems.

SCI publication Comparative structure cost of modern commercial buildings

[3]

shows solutions involving composite construction to be more economical than

steel or concrete alternatives for both a conventional four storey office block

and an eight storey prestigious office block with an atrium.

1.2 Applications

Composite slabs have traditionally found their greatest application in steel-

framed office buildings, but they are also appropriate for the following types of

building:

 Other commercial buildings

 Industrial buildings and warehouses

 Leisure buildings

 Stadia

 Hospitals

 Schools

 Cinemas

 Housing; both individual houses and residential buildings

 Refurbishment projects.

1.3 Scope of this publication

This publication gives guidance on the design and construction of composite

slabs and composite beams in order to disseminate all the relevant information

to the wide and varied audience involved in the design and construction chain.

Guidance is given on design and construction responsibilities, and requirements

for the effective communication of information between the different parties are

discussed.

The principal aim of the design guidance given in this publication is to identify

relevant issues. The reader is directed elsewhere, including to British Standards

and Eurocodes, for specific design guidance. Summary boxes are used to

highlight how to achieve economic, buildable structures through good practice

in design.

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2 THE DESIGN AND CONSTRUCTION

TEAM

The aim of this Section is to identify typical activities and responsibilities for

the team members involved in the design and construction of a building using

composite components. Clearly, the precise delegation of responsibilities will

depend on the details of the contract for a specific project, with which all

parties need to be familiar.

As an overriding principle, the CDM Regulations

[4]

state that ‘Every person on

whom a duty is placed by these Regulations in relation to the design, planning

and preparation of a project shall take account of the general principles of

prevention in the performance of those duties during all stages of the project’.

A similar requirement applies for the responsibilities during construction: ‘Every

person on whom a duty is placed by these Regulations in relation to the

construction phase of the project shall ensure as far as is reasonably practicable

that the general principles of prevention are applied in the carrying out of the

construction work’. Guidance on the specific details of the responsibilities of

each of the relevant parties under the CDM Regulations may be found in

Reference 5.

2.1 Team members

In recognition of the different types of contract that may be employed, the

following generic terminology has been adopted for the key parties involved:

The Client is the person (or organisation) procuring the building from those

who are supplying the components and building it.

The Architect is the person (or practice) with responsibility for the integration

of the overall design of the building, and with a particular responsibility for the

building function and aesthetics.

The Structural Designer is the person (or organisation) who is responsible for

the design of the structural aspects of the permanent works. This role could, for

example, be fulfilled by a Consultant, a ‘Design and Build’ Contractor, or a

Steelwork Sub-contractor. In many cases the Structural Designer will delegate

some of the design responsibility. For example, a Consultant may effectively

delegate some of the design work by using data supplied by a decking

manufacturer. The manufacturer then becomes a Delegated Designer, with

responsibility for certain aspects of the decking and, perhaps, the slab design.

Where applicable, this must be clearly communicated to the manufacturer along

with all relevant design information required early in the project design process.

A Delegated Designer is a person (or organisation) who, because of specialist

knowledge, carries out some of the design work on behalf of the Structural

Designer. This may be achieved by supplying design information such as

load-span tables for composite slabs.

The Main Contractor is the organisation responsible for the building of the

permanent works, and any associated temporary works.

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The CDM co-ordinator has obligations with regard to the safety aspects of a

project. This is a role defined in the CDM Regulations (see Section 2.2,

Safety).

2.2 Roles in design and construction

Form of floor construction

The choice of floor construction and the general beam and column arrangements

are the responsibility of the Architect and the Structural Designer. The Architect

will be concerned with more general and spatial aspects of the building form,

such as the column locations, the construction depth of the floors, and the soffit

appearance (if it is to be exposed).

The Structural Designer will determine the general loads to be considered in the

design of the structure, based on the type of occupancy for each area specified

by the Architect/Client. Details of any specific loads, for example due to

services, may need to be supplied by others. The Structural Designer will also

undertake scheme designs to identify beam and slab solutions with spanning

capabilities to suit the Architect’s requirements.

Composite beams

The detailed design of the composite beams (Section 5) is the responsibility of

the Structural Designer, who should recognise that there is an interaction

between the beam and slab design, particularly with the decking and transverse

reinforcement. In designing the composite beams, due consideration should be

given to the construction stage load case.

Although it may be necessary to consult the decking manufacturer for practical

advice on shear connector configurations, it is the responsibility of the structural

designer to specify the shear connector type and quantities required.

When considering composite beams, the designer should be aware of practical

considerations such as the access requirements for using stud welding equipment

(see Section 5.3.1) and minimum practical flange widths for sufficient bearing

of the decking (see Section 4.1.4). These requirements may have serious

implications on the economy of the chosen solution.

Composite slab

The design of the composite slab (Section 4) is the responsibility of the

Structural Designer. Particular attention should be paid to areas where there are

special loads, such as vehicle loads and loads from solid partitions and tanks.

Construction stage loads should also be considered, with particular attention to

any concentrated loads from plant or machinery required to carry out the safe

erection of the building and its structure. When designing and detailing any

reinforcement, the Structural Designer should ensure that the specified bars can

be located within the available depth of slab and that the correct reinforcement

covers for the design durability conditions can be achieved. (Recognise any

other space constraints that may exist on site.)

It is recommended that the Structural Designer prepares general arrangement

drawings for the slab (in addition to the steelwork general arrangement

drawings). In particular, these drawings should define the edges and thickness

of the slab, and they should form the basis of the decking layout drawings and

the reinforcement drawings.

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The Structural Designer should also produce a reinforcement layout drawing for

each bay of each floor. The reinforcement grade, location, lengths, minimum

overlaps and minimum concrete cover should be shown (and appropriate

information about fibres if they are to be used). On site, these drawings will be

used to check that all the reinforcement has been fixed correctly (or fibres

correctly incorporated).

Designing a concrete mix to provide the required structural and durability

performance is normally the responsibility of the Main Contractor.

Choice of Decking

The choice of decking and its general arrangement is the responsibility of the

Structural Designer. The design must consider the fire resistance of the slab

(which may depend on the decking type), the ability of the decking and

composite slab to resist the applied loading, the propping requirements, and the

deflections at both the construction and in-service (composite) stages. As well as

influencing all of these, the choice of decking profile may have implications for

the composite beam design.

Design data provided by a decking manufacturer will normally be used to select

the decking, as its performance is complex and is best determined from tests.

The Structural Designer must be satisfied with the information supplied in this

form by the Delegated Designer (decking supplier/manufacturer), and ensure

that it is not used ‘out of context’. Consultation with the decking

supplier/manufacturer is recommended if there is any doubt. Where decking is

specified for unusual applications, the ‘standard’ design information may not be

directly applicable (see Section 4).

Decking arrangement and details

The decking layout drawings (Section 3.2) are normally prepared by a decking

sub-contractor acting as a Delegated Designer. Details should be checked by the

Structural Designer, who should advise the Delegated Designer of any special

requirements, such as the need for extra fixings when the decking is required to

act as a wind diaphragm, or of any particular requirements concerning the

construction sequence. The Structural Designer should check that the proposed

bearing details and the interfaces with the other elements of construction are

practicable, and that they permit a logical, buildable sequence.

In preparing the decking layout drawings, the decking sub-contractor may find it

beneficial to refine the design. For example, it may be necessary to change

some of the continuous spans to simple spans for practical reasons. This may

have implications on the propping requirements during construction.

The loads that may be applied to the decking in the construction condition, both

as a temporary working platform and as formwork, should be clearly indicated

on the decking layout drawings or general notes. The loads that may be applied

to the composite slab should also be shown on the decking layout drawings, and

on the appropriate concreting drawings (these will be included in the Health and

Safety File for reference throughout the lifetime of the building). It is therefore

essential that all loading assumptions and design criteria are communicated to

the decking sub-contractor.

Temporary works

Propping should be avoided wherever possible, as it reduces the speed of

construction and therefore affects the construction sequence and economy. When

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propping is unavoidable, it is usually necessary to prop through several floors to

support the prop loads. This can prevent other operations over a large area.

However, when the construction sequence permits, propping does increase the

spanning capability of the decking. Determining the propping requirements is

generally the responsibility of the Structural Designer (normally using

information supplied by a Delegated Designer), although local propping needs

may change when the Delegated Designer details the decking layout. The

decking should be checked by the Structural Designer to ensure that it can

withstand the concentrated loads from the propping arrangement.

The location of lines of props or other temporary supports should be shown on

the decking layout drawings. The design and installation of the propping system

is the responsibility of the Main Contractor, but propping systems should be

braced appropriately. Removal of props should not be carried out before the

concrete has reached its specified strength, or, when specified in the contract,

before the Structural Designer gives explicit approval.

In addition, the Structural Designer should supply the Main Contractor with the

propping loads, and the dead load that has been considered, to help him/her to

draw up the propping scheme. When devising the scheme, consideration must

be given to the fact that floors will need to be designed to carry the

concentrated loads from props (see Section 6 for advice on possible loading).

Further advice on propping is given in Section 4.2.7.

Fire protection

The Architect is normally responsible for determining the fire resistance period

required for the building, and for choosing the type of fire protection. The

Structural Designer, in many cases represented by a Delegated Designer

(specialist sub-contractor), is responsible for the specific details of the fire

protection. The Structural Designer should also make it clear on the drawings

when any voids between the profiled decking and the steel beams have to be

filled (see Section 5.2.3).

Safety

Whilst all parties involved in the design and construction process are required to

consider construction safety, the CDM co-ordinator has some specific

obligations under the CDM Regulations

[4,5]

. [It is to be noted that the post of

Planning Supervisor established under the previous Regulations has been

revoked and replaced by the post of CDM co-ordinator.] These obligations

include the creation of the Health & Safety Plan and the Health & Safety File.

The aim of the first of these documents is to inform others of potential health

and safety issues; the Structural Designer should supply, for example, details of

any risks that may be foreseen during construction for inclusion in this plan.

The Health and Safety File is intended to assist persons undertaking

maintenance work, and will include information such as as-built drawings. The

Structural Designer should inform the contractor of any ‘residual hazards’ (those

that the contractor will manage during the construction) associated with any

unorthodox method of construction, and the provisions made to help the

contractor to manage them. It is the CDM Co-ordinator’s responsibility to

provide advice and assistance, to ensure that designers fulfil their obligations, to

consider health and safety issues, to co-operate with others, and to supply all

appropriate information.

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2.3 Design and construction sequences

The following flowcharts describe typical design (Figure 2.1) and construction

(Figure 2.2) sequences for composite floor construction.

Choose type of floor

construction, e.g. slimfloor,

composite beam + slab,

non-composite beam + slab

Choose concrete type and

grade, slab depth

Consider likely decking, slab

and beam span capability

Consider construction depth,

service requirements, need for

an exposed soffit?

Consider fire resistance period,

availability of concrete type

durability

Design as composite

beam?

Choose type of connector

and when to be welded

Building arrangement

chosen by Client/Architect

Choose column grids/beam

arrangement

Design beams

Design reinforcement at

openings in slab

Check composite slab and

design reinforcement

For composite beams:

Determine shear connector layout and

design transverse reinforcement

Consider:

Fire resistance period

In-service loading, e.g. solid partitions,

concentrated loads

Temporary construction loading, e.g. from

MEWPs

Consider:

Construction loading, dead weight

Concrete ponding deflections

Propping, effects of propping on fall arrest

system

Single or continuous spans

Consider:

Access for welding equipment

Electrical earthing

Economic No. of shear connectors

Can top flange of beams be left unpainted?

Alternatives to stud connectors

Site or shop welding

Design floor decking and

check at construction stage

Yes

Figure 2.1 Sequence of design activities

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Remove props

Install fall arrest system

Position floor deck edge trims

and end closures and fix to

steelwork

Fix shear connectors, if any

Are props required

prior to casting

slab?

Fix reinforcement

Form slab

construction joints

Place concrete

Prepare slab surface

Install props

Install fall arrest

system (nets not

appropriate)

Install props

Fix:

Reinforcement at slab openings

and cantilevers, transverse

reinforcement, mesh

reinforcement, and ‘fire’

reinforcement, as necessary

Limit potential for grout loss

Consider concrete strength

Carry out additional cube tests?

Consult structural designer?

Are props required

prior to placing

decking?

Yes

Offload and hoist packs into

place

Erect steel frame

Including fibre reinforcement,

when specified

Figure 2.2 Sequence of construction activities

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3 INFORMATION TRANSFER

Clear and timely communication of information is important given that several

parties are involved in the building design process (see Section 2 for

identification of typical responsibilities). There are also obligations placed on

the key parties under the CDM Regulations

[4]

to exchange information during

both design and construction.

3.1 Design stage

The design of composite beams and slabs is clearly influenced by spanning

requirements, and the loads that are to be supported. In addition to grid layouts,

it is therefore important that accurate details of all the loads are established at

an early stage. Unfortunately, some information, such as the loads due to the

services, is often unavailable when needed, and the Structural Designer has to

use conservative values in order to give flexibility when the services are

designed at a later stage.

Knowledge of the position of services is also important, because it enables

account to be taken of any opening requirements in the beam webs and/or slabs.

Openings can have a significant effect on the resistance of a member.

The following list is a guide to the information required to design the composite

slabs and beams:

 Column grid and beam general arrangement

 Position of slab edges

 Static and dynamic imposed loads (to include consideration of any

temporary concentrated loads from plant/machinery that may be required

during construction)

 Services and finishes loads

 Special loads (e.g. walls, wind diaphragm loads)

 Fire resistance period

 Decking type (shallow or deep, re-entrant or trapezoidal)

 Slab depth limitations

 Minimum mass requirements (for acoustic performance)

 Location of openings

 Requirements for soffit appearance and general exposure

 Requirements for service fixings

 Requirements for cladding attachments (which may affect the slab edge

detailing)

 Construction tolerances

 Deflection limits

 Propping requirements or restrictions

 Any known site restrictions on the use of thru-deck welding.

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In order to prepare the decking layout drawings, a Delegated Designer will also

need to know the:

 Concrete type and grade

 Shear connector layout and details

 Cladding support method (for edge trim design, etc.)

There are also specific issues of information transfer that arise because the

design of the decking and composite slabs often relies on the use of information

presented in decking manufacturers’ literature. It is important that the tabulated

data and explanatory information is comprehensive. For example, in load-span

tables the following points should be clear:

 Are the loads that are given nominal values or design values?

 What allowances, if any, have been made for services loads etc.?

 What fire performance do the tables relate to?

 Do specified reinforcement requirements imply any crack control

capability?

 Do the tables imply adequate serviceability behaviour as well as resistance,

and if so what limiting criteria have been assumed?

If the Structural Designer chooses to delegate some of the slab design to the

design service of a decking manufacturer (Delegated Designer), it is essential

that there is clear communication of all relevant design information.

3.2 Construction stage

An absence of essential information transfer between the design and construction

teams can lead to delays or, at worst, incorrect or unsafe construction.

The site personnel should check the information provided and confirm that it is

complete, passing any relevant information to appropriate sub-contractors. Any

variations on site that might affect the design should be referred to the

Structural Designer.

Decking layout drawing

Decking layout drawings should be available for those lifting the decking, so

that the bundles can be positioned correctly around the frame. Clearly, they

should also be available for the deck laying team.

Although different decking contractors’ drawing details may vary slightly, the

drawings should show (in principle) each floor divided into bays, where a bay is

an area that is to be laid from a bundle as one unit. Bays are normally indicated

on the drawing using a diagonal line. The number of sheets and their length

should be written against the diagonal line. The bundle reference may also be

detailed against this diagonal line. Further construction notes for the bay can be

referenced using numbers in circles drawn on the diagonal lines, as shown in

Figure 3.1. This figure shows an example of a decking layout drawing, but with

the shear connectors and fastener information omitted for clarity. Decking

contractors’ literature should be referenced for exact details.

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Stairs by others

Temporary propline

Symbol

defining

one bay

Edge Trim

A 150,50

Edge Trim

A 150,100

Edge Trim

A 150,100

Indicator start

point for

laying of panels

distance of edge

from C of beam

Edge

trim

height

Reference

number for

special

comments

Orientation of

decking ribs

Edge Trim

Reference

for edge trim

Number of

panels

B 150,100

Panel lengths

Bundle identification code

Figure 3.1 Typical decking layout drawing (shear connector and

fastener information omitted)

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The approximate starting point for laying the decking should be given on the

drawings, together with the direction in which laying should proceed. All

supports (permanent or temporary) should be identified, and whether they

should be in place prior to laying the decking. The letters TP on the drawings

typically indicate lines of propping. Column positions and their orientation

should also be shown. The decking type, thickness and material strength should

be indicated on the drawing.

The location of all openings trimmed with steelwork, and all slab perimeters,

should be given relative to the permanent supports. This may be in the form of

a reference box titled ‘Edge Trim’, with a reference number (for details shown

elsewhere), the slab depth, and the distance from the edge of the slab to the

centre line of the nearest permanent support, but decking contractors’ literature

should be referred to for the exact drawing details.

The shear connector layout should also be shown on the decking drawings, or

on separate drawings for reasons of clarity. The information should include the

type of shear connector, its length, orientation (if shot-fired) and position

relative to the ribs. The minimum distance between the centre-line of the shear

connector and the edge of the decking should be given. Details of preparation,

fixing and testing of shear connectors should be available on site. For more

information on shear connection, refer to Sections 5.3 and BCSA publication

37/04

[6]

Fastener information should be given on the drawings. The fastener type for

both seams and supports should be given, along with maximum spacings (or

minimum number of fasteners per metre). Where the Structural Designer has

designed the decking to act as an effective lateral restraint to the beams and

additional fasteners to the manufacturer’s normal fixing arrangement are

necessary, this should be clearly indicated on the decking layout drawing and/or

general notes.

The general notes should include the design loads that the decking can support

in the construction condition. Guidance on avoidance of overload prior to

placing the concrete is given in the BCSA publication 37/04

[6]

A copy of the decking layout drawings must be given to the Main Contractor so

that checks can be made that the necessary propping is in place. The Main

Contractor will also need to refer to these drawings for details of the maximum

construction loading and any special loading.

Decking bundle identification

An identification tag should be attached to each bundle of decking delivered to

site. The tag will normally contain the following information:

 Number of sheets, their lengths and thickness

 Total bundle weight

 Location of floor to receive bundle

 Deck type

 Bundle identification.

Product information on the decking should also be available on site, including

the height of the ribs and their spacing, and other technical information.

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Information required for laying the reinforcement, casting the slab and

its use thereafter

A reinforcement layout drawing should be prepared for each bay of each floor

by the Structural Designer. The location, length, minimum overlap and

minimum concrete cover of all reinforcement should be indicated. The grade of

all reinforcement should also be noted. This grade can be checked against the

identification tag for each reinforcement bundle delivered to site. Appropriate

information about fibres should be given, if they are to be used.

Important reinforcement details (such as at construction joints, support

locations, openings and edges) should be referenced and placed on this drawing.

The floor slab general arrangement drawings (or the Specification) should

include the concrete performance requirements or mix details (including any

details for fibre reinforcement), surface finish requirements, level tolerances and

any restrictions on the location of construction joints. They should also identify

the minimum concrete strength at which temporary supports may be removed,

the minimum concrete strength at which temporary construction loads may be

applied, and, where appropriate, the maximum allowable vehicular axle weight

(for punching shear). Minimum concrete strengths may be given in terms of

days after concreting.

Propping Information

As mentioned in Section 2.2, the Structural Designer should supply the Main

Contractor with the floor dead load value to allow a propping solution to be

developed.

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4 DESIGN OF DECKING AND SLABS

This Section provides information about design principles and procedures,

codified design rules, and guidance on good practice in design and detailing.

Along with Section 5, it is aimed primarily at the Structural Designer, and any

Delegated Designers. Summary boxes are used to highlight particular issues of

good practice, or areas where particular attention is needed

4.1 Steel decking

The steel decking has two main structural functions:

 During concreting, the decking supports the weight of the wet concrete and

reinforcement, together with the temporary loads associated with the

construction process. It is normally intended to be used without temporary

propping.

 In service, the decking acts ‘compositely’ with the concrete to support the

loads on the floor. Composite action is obtained by shear bond and

mechanical interlock between the concrete and the decking. This is

achieved by the embossments rolled into the decking – similar to the

deformations formed in rebar used in a reinforced concrete slab - and by

any re-entrant parts in the deck profile (which prevent separation of the

deck and the concrete).

The decking may also be used to stabilise the beams against lateral torsional

buckling during construction, and to stabilise the building as a whole by acting

as a diaphragm to transfer wind loads to the walls and columns (where it is

designed to do so, and in particular where there are adequate fixings

[7]

. The

decking, together with either welded fabric reinforcement placed in the top of

the slab or steel/synthetic fibres throughout the slab (see Section 6.2.1), also

helps to control cracking of the concrete caused by shrinkage effects.

A.1.1 Decking profiles

Decking profiles are produced by a number of manufacturers in the UK.

Although there are similarities between their profiles, the exact shape and

dimensions depend on the particular manufacturer. There are two generic types

of shallow decking; re-entrant (dovetail) profiles and trapezoidal profiles.

Examples of re-entrant profiles are shown in Figure 4.1. Examples of

trapezoidal profiles with a shoulder height of up to 60 mm (excluding the crest

stiffener) are shown in Figure 4.2, and similar profiles deeper than this are

shown in Figure 4.3.

The traditional shallow decking profiles are between 45 to 60 mm high, with a

rib spacing usually of 150 to 333 mm. This type of decking typically spans 3 m,

leading to frame grids of 9 m  9 m or similar dimensions, using secondary

beams at 3 m spacing, for which temporary propping is usually not required.

Profiles up to 95 mm high overall have been developed which can achieve over

4.5 m spans without propping. Normally, the decking is laid continuously over

a number of spans, which makes it stronger and stiffer than over a single span.

More recently, a 160 mm (overall) profile has been developed which can span

6 m unpropped as a simply supported member.

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Deep decking profiles, which are over 200 mm deep, are also available. These

are mainly used in slim floor construction, which is considered separately in

Section 7 of this guide.

51mm

152mm

51mm

150mm

51mm

150mm

149 mm

Multideck 50

R51

ComFlor

Holorib

MetFloor 55

55mm

Figure 4.1 Examples of re-entrant deck profiles used for composite

slabs, supplied by:

1. Richard Lees Steel Decking Ltd.

2. Corus Panels and Profiles

3. Kingspan Structural Products Ltd.

4. Structural Metal Decks Ltd.

5. CMF Ltd.

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46 mm

10 mm

50 mm

300 mm

225 mm

Ribdeck AL

TR60

333 mm

12 mm

60 mm

Chevron embossments

Vertical embossments

Sloping and

horizontal

embossments

ComFlor 46

15 mm

300 mm

Multideck 60

Sloping embossments

60 mm

323 mm

9 mm

ComFlor 60

Embossments

60 mm

MetFloor 60

300 mm

15 mm

Figure 4.2 Examples of trapezoidal deck profiles up to 60 mm deep

(excluding the top stiffener) used for composite slabs,

supplied by:

1. Richard Lees Steel Decking Ltd.

2. Corus Panels and Profiles

3. Kingspan Structural Products Ltd.

4. Structural Metal Decks Ltd.

5. CMF Ltd.

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300 mm

80 mm

10 mm

Ribdeck 80

12 mm

K shaped embossments

Sloping and

horizontal

embossments

300 mm

TR80

300 mm

80 mm

Sloping embossments

Multideck 80

9 mm

300 mm

ComFlor 80

Embossments

80 mm

MultiDeck 146

80 mm

15 mm

80 mm

145 mm

MetFloor 80

300 mm

Figure 4.3 Examples of trapezoidal deck profiles greater than 60 mm

deep (excluding the top stiffener) used for composite

slabs, supplied by:

1. Richard Lees Steel Decking Ltd.

2. Corus Panels and Profiles

3. Kingspan Structural Products Ltd.

4. Structural Metal Decks Ltd.

5. CMF Ltd.

The grades of steel used for decking are specified in BS EN 10326

[8]

. The

common grade in the UK is S350 (the designation identifies the yield strength of

the steel in N/mm

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Decking is generally rolled from 0.9 to 1.2 mm thick strip steel. The spanning

capability of a given decking profile clearly increases as the steel thickness

increases, but not in direct proportion to the strength. The steel is galvanized

before forming, and this is designated in the steel grade by the letters GD,

followed by a number corresponding to the number of grammes of zinc per m

The normal specification is GD

275, i.e. 275 grammes of zinc per m

, which

results in a thickness of approximately 0.02 mm per face (sufficient to achieve

an excellent design life in internal applications with mild exposure conditions).

Thicker galvanized coatings of 350

g/m

, and up to 600 g/m

, are available for

special applications where improved durability is needed, but specifications

other than 275

g/m

will be difficult to obtain and are likely to require a large

minimum order. ‘Thru-deck’ welding may also be affected. For this reason,

polyester paints are sometimes applied over the galvanizing to provide a longer

service life. Advice should be sought from the supplier/manufacturer when

decking is to be used in a moderate or severe environment. Further advice on

the use of composite construction in an aggressive environment is given in

AD 247

[9]

Standard thickness galvanizing (275 g/m

) will give an excellent design life

in most internal applications. Non-standard thicknesses of galvanizing are

difficult to obtain and should not therefore be considered as a practical way

of increasing durability.

4.1.2 Design for resistance

The temporary construction load usually governs the choice of decking profile.

When designing to Eurocodes, the construction loading that should be

considered in the design of the decking is defined in BS EN 1991-1-6

[10]

and its

National Annex. Unfortunately, the provisions are a little unclear; the following

is understood to be the recommended construction loading, which should be

treated as a variable load:

(i) 0.75 kN/m

generally

(ii) 10% slab self weight or 0.75 kN/m

, whichever is greater, over a

3 m  3 m ‘working area’. This area should be treated as a moveable patch

load that should be applied to cause maximum effect

This is shown diagrammatically in Figure 4.4.

3m square working area

Clear span + 0.075m

Self weight



Construction load

0.75 kN/m²

Construction load

inside 'working area'

= 10% slab self weight

0.75 kN/m²

Figure 4.4 Loading on decking at the construction stage to

BS EN 1991-1-6

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When designing to BS 5950-4

[11]

, the construction loading is defined as:

 A uniformly distributed load of 1.5 kN/m

acting over one span. For spans

less than 3 m, the load should be increased to 4.5/L

, where L

is the

effective span of the decking.

 A reduced load of 0.5 kN/m

on adjacent spans.

In both these cases, the construction loads are in addition to the self weight of

the slab (usually 2 to 3 kN/m

), which may need to include an allowance for

‘ponding’ of the concrete (see Section 4.1.3). When concrete is poured using

the ‘flood’ technique, care must be taken that the assumptions made in respect

of the concrete thickness are reflected in the calculation of deflections of the

slab and the supporting beams. The above load values allow for construction

operatives, impact, the heaping of concrete during placing, hand tools, and

small items of equipment and materials for immediate use. The loads are not

intended to cover excessive impact or excessive heaping of concrete, pipeline or

pumping loads.

In the Eurocodes, densities of the wet weight of reinforced concrete are given in

BS EN 1991-1-1

[12]

, and the data is classified as ‘informative’. The data is for

heavily reinforced construction associated with conventional reinforced concrete

structures. The UK NA states that those values may be used, but it is

recommended that the density of dry concrete used in composite floor

construction should be 24 kN/m³ for normal weight concrete and 19 kN/m³ for

lightweight concrete, increased to 25 kN/m³ and 20 kN/m³ respectively for wet

concrete. The weight of the reinforcement should be added separately. The self

weight of the wet concrete is treated as a variable load for the construction

condition, but the reinforcement may be considered as a permanent load.

In BS 5950-4, wet densities are given as 2400 kg/m

and 1900 kg/m

for normal

and lightweight concrete respectively, and similarly 2350 kg/m

and 1800 kg/m

for dry concrete. The self weight of the wet concrete is treated as a dead load.

The design of shallow decking is covered in BS EN 1991-1-3

[13]

. The moment

resistance of the section is established using an effective width model to take

account of the thin steel elements in compression. Stiffeners (in the form of

folds) are often introduced into the decking profile to increase the effectiveness

of the section. The effective width approach is relatively conservative because

the section behaviour is very complicated owing to local buckling, and so the

section properties can be predicted neither easily nor accurately. The design of

the decking is also covered in BS 5950-4 and BS 5950-6

[11]

, where a similar

approach is given.

As an alternative to analytical procedures, the Standards also allow the use of

testing in order to determine the performance of the decking. Spans 10% to

15% in excess of the limits predicted by simple elastic analysis using effective

section models are possible. For this reason, manufacturers often provide load-

span tables based on tests rather than on an elastic analysis approach.

In addition to tests under simulated uniform loading, further tests are normally

carried out to check the resistance of the decking to localised loading. This

provides information on the resistance to local loading from above as well as on

the maximum allowable prop and support forces.

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Decking design based on testing is more economical than design based on

analytical models. Manufacturer’s (empirical) information should therefore

be used whenever possible.

Empirical information must not be used for designs outside the scope of the

tests on which it is based. Load-span tables will generally only cover

uniformly distributed loading.

4.1.3 Design for serviceability

It is necessary to limit the deflections at the construction stage to limit the

volume of concrete that is placed on the decking; excess deflections will lead to

‘ponding’ of the concrete, and this will increase the dead loads on the structure.

Deflection limits for the decking are given in BS EN 1994-1-1

[14]

, and in

BS 5950-4. According to BS EN 1994-1-1, if the central deflection of the

sheeting δ is greater than 1/10 of the slab thickness, ponding should be allowed

for. In this situation the nominal thickness of the concrete over the complete

span may be assumed to be increased by 0.7δ.

For the serviceability limit state, the recommended value of the deflection δ

s,max

of steel sheeting under its own weight plus the weight of wet concrete is L/180

in BS EN 1994-1-1 (where L is the effective span between supports). In

BS 5950-4, the limit on the residual deflection of the soffit of the deck (after

concreting) is also given as span/180 (but not more than 20 mm), which may be

increased to span/130 (but not more than 30 mm) if the effects of ‘ponding’ are

included explicitly in the design.

The standard limits may be increased ‘where it can be shown that greater

deflections will not impair the strength and efficiency of the slab’, although this

is rarely applied. As a further check, it is recommended that the increased

weight of concrete due to ponding should be included in the design of the

support structure if the predicted deflection, without including the effect of

ponding, is greater than one tenth of the overall slab depth.

The requirement for verification of the profiled sheeting at SLS in BS EN 1994-

1-1 is expressed simply in terms of deflection under the weight of wet concrete

and there is no requirement to check that such deflection should be elastic.

However, it is recommended that there is also a check to ensure that there is no

premature local buckling of the profile under the weight of wet concrete and the

construction loading, to prevent irreversible deformation. This applies

particularly to the intermediate support regions of continuous spans.

Excess deflections of the decking (and beams) may lead to ‘ponding’ of the

concrete and therefore increased self weight of the slab. The decking and

propping requirements should be chosen to minimise ponding.

4.1.4 Supports

Minimum bearing length

The bearing length is the longitudinal length of decking or slab in direct contact

with the support. In each case, this length should be sufficient to satisfy the

following relevant criterion. For decking, it should be sufficient to avoid

excessive rib deformations, or web failure, near the supports during

construction. For the slab, it should be sufficient to achieve the required load

carrying capacity of the composite slab in service.

The recommended minimum bearing lengths shown in Figure 4.5 should be

observed. The values given in this figure are based on the requirements of

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BS EN 1994-1-1, but similar requirements are given in BS 5950-4. These limits

should also be respected for temporary supports. The limits given represent

nominal values that should be considered in the design and detailing, i.e. they

include an allowance for construction deviations leading to slightly reduced

values on site.

The recommended bearing lengths and support details differ depending upon the

support material (steel, concrete, etc.), and they are different for interior and

exterior (end) supports. Typical values and details are given in Figure 4.5 for

the following:

 Steel or concrete supports - Composite slabs on steel or concrete supports

should have minimum bearing lengths of 75 mm for the slab, and a

minimum end bearing length of 50 mm for the decking (see Figure 4.5(a)

and Figure 4.5(b)). For continuous decking, the minimum overall bearing

length should be 75 mm.

 Masonry and other support types - Composite slabs on supports made of

materials other than steel and concrete should have a minimum bearing

length of 100 mm for the slab and a minimum end bearing length of 70 mm

for the decking (see Figure 4.5(c) and Figure 4.5(d)). For continuous

decking, the minimum overall bearing length should be 100 mm.

The flange width of supporting steel beams should be sized to supply the

minimum bearing, by assuming that erection tolerances sum up unfavourably.

Details of how the decking should be fixed to supports are given in BCSA

Publication No. 37/04

[6]

If ‘thru-deck’ welding of the studs is to be used to anchor the decking, so that it

contributes to the transverse shear reinforcement (see Section 5.3.2), the

dimensions specified in Figure 4.5 may need to be increased (see Figure 5.9).

In cases where the slab must transfer the wall loads from one storey to the next

(rather than simply sitting on the top of a wall), the relatively lower volume of

voids in a slab formed using a re-entrant profile means it may be better able to

satisfy the design requirements.

Minimum 50 mm

edge distance for

screwed and

plugged fixings

a) b)

c) d)

Masonr

and other materials

Steel or concrete

100

Figure 4.5 Minimum bearing lengths for permanent supports

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Recommended support details

In addition to the ‘standard’ detail of a slab bearing on a steel beam or wall,

there are a number of other commonly occurring support conditions which need

to be considered at the design stage in order to avoid problems or delays on

site. Some typical details are shown in Figure 4.6.

There are two basic cases at the interface of the decking with beams; where end

support is required (Figure 4.6(a)), and where side support is required

(Figure 4.6(b)). In both cases a steel ‘shelf angle’ is normally detailed as the

decking support, and it is preferable to fix this during fabrication. Angle

flashing is not suitable. To enable fixing of the decking, particularly in the case

of an end support, it is important that the leg of the angle extends at least

50 mm beyond the flange of the beam. The support angles should be continuous

and extend as close as is practical to beam connections, to minimise the

unsupported length of the decking.

Support is also required when the decking interfaces with a concrete wall. This

may be provided by attaching a steel angle, flashing, or timber batten to the

wall, preferably by using cast-in fixings (Figure 4.6(c)). Provision may need to

be made to achieve reinforcement continuity between the wall and slab.

The decking should not cantilever beyond a support more than 600 mm (or ¼

of the span, if less) when spanning perpendicular to it. When the decking is

spanning in a parallel direction, no cantilever is possible without extra support

being provided – although the edge trim may cantilever a short distance (see

Section 4.2.6)

The decking may also need to be supported around penetrations which reduce,

or prevent, the effective bearing. Supports should be provided as part of the

permanent steelwork, for example in the form of cleats or angles. Examples of

when such supports are necessary include when the decking is penetrated by

columns greater than 250 mm wide (without incoming beams on both axes), or

by columns supported off beams. Figure 4.7 shows a recommended detail using

a shelf angle to support the decking around a column.

50 min.

Discrete lengths of shelf

angle to support decking

and to prevent grout loss

a) End support at a beam web

(decking ribs perpendicular to beam)

b) Side support at a beam web

(decking ribs parallel to beam)

c) Side support at a concrete wall

Decking

Discrete lengths of

steel angle or timber batten

fixed to concrete wall

Shelf angle to project 50 mm min.

from toe of flange for

fixing accessibility

Figure 4.6 Decking support details at a beam web and at a concrete

wall

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A less common detail is one in which the column is supported by a beam, in

which case special detailing may be required to achieve sufficient bearing for

the decking around the perimeter of the column. Where the deck is spanning in

a direction perpendicular to the beam, the minimum bearing of 50 mm required

to support the end of the decking may not be available because of the presence

of the column base plate. Therefore, the beam flange may need to be extended

by welding plates to the sides at the column position, as shown in Figure 4.8(a).

If the column position does not coincide with a butt joint in the decking, the

continuous decking sheet may have to be cut to fit around it. At this position,

the decking should then be treated as if it was simply supported, and props

maybe required locally. A similar situation may arise when flange splice plates

are fixed to the top of the steel section, as shown in Figure 4.8(b).

Supports may also be needed if the decking is to be penetrated by temporary

works structures (depending on the size of the penetration). To avoid problems

in such situations, it is vital that there is good communication between the Main

Contractor, who is responsible for the temporary works, and the Structural

Designer, who should specify the appropriate steelwork.

The decking should be cut to fit around any penetration. A typical detail, with a

column, is shown in Figure 4.9.

If temporary propping is proposed as a support around a penetration, this will

clearly only be present during the construction stage, i.e. to support the

decking. The completed slab may then need to include additional reinforcement,

as might be necessary around any untrimmed opening in a reinforced concrete

slab (see Section 4.2.6), in order to support the in-service loads. This

reinforcement should be specified by the Structural Designer.

Sheet lengths

The tolerance in the sheet lengths for shallow decking is normally specified as

+0 mm and –3 mm. A zero positive tolerance is used to avoid accumulations in

length when sheets are butted in a long run. Long sheets could lead to the butt

joint positions becoming increasingly displaced thus giving inadequate bearing

for the sheets near the end of a run. Cutting on site might be needed to

overcome this problem. It is, therefore, easier for the decking to be installed

when sheets are slightly short. A small gap between sheets above the supporting

beams is of no structural significance.

Shelf angle or plate required

Shelf angles

Figure 4.7 Decking support details at a column web

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Decking cut away

for clarity

Decking cut away

for clarity

PLAN PLAN

Extension to

beam flange

Extension to

beam flange

Decking

a) Column support off beam b) Beam flan

e splice plate

Flange splice plate

50 mm min. required

for decking bearing

(extend flange if necessary)

50 mm min. required

for decking bearing

(extend flange if necessary)

Figure 4.8 Decking details where a column is supported off a beam

and where a beam flange plate occurs

Figure 4.9 Typical detail of decking installation around a column

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4.2 Composite slabs

Composite slabs are normally used to span between 3 m and 4.5 m onto

supporting beams or walls. The ability of the decking to support the

construction loads, without the need for temporary propping, generally dictates

such spans (longer spans are possible when props are used). Slab thicknesses are

normally in the range 100 mm to 250 mm for shallow decking, and in the range

280 mm to 320 mm for deep decking.

When the concrete has gained sufficient strength, it acts in combination with the

tensile strength of the decking to form a ‘composite’ slab. It can be considered

as a reinforced concrete slab, using the decking as external reinforcement.

The load carrying capacity of composite slabs is normally dictated by the shear

bond, enhanced by interlock, between the decking and the concrete, rather than

by yielding of the decking. From tests, it is known that this shear bond

generally breaks down when a ‘slip’ (relative displacement between the decking

and the concrete) of 2 to 3 mm has occurred at the ends of the span. In

practice, this will not occur below ultimate load levels. An initial slip, which is

associated with the breakdown of the chemical bond, may occur at a lower level

of load. The interlock resistance is therefore due to the performance of the

embossments in the deck (which cause the concrete to ‘ride-over’ the decking),

and the presence of re-entrant parts in the deck profile (which prevent the

separation of the deck and the concrete).

Information on improving the bending resistance of composite slabs by

providing additional reinforcement, or end anchorage in the form of shear

connectors, can be found in BS EN 1994-1-1

[14]

and BS 5950-4

[11]

If the slab is unpropped during construction, the decking alone resists the self-

weight of the wet concrete and construction loads. Subsequent loads are applied

to the composite section. If the slab is propped, all of the loads have to be

resisted by the composite section. Surprisingly, this can lead to a reduction in

the imposed load that the slab can support, because the applied horizontal shear

at the decking-concrete interface increases. However, for both unpropped and

propped conditions, load resistances well in excess of loading requirements for

most buildings can be achieved.

Composite slabs are usually designed as simply supported members in the

normal condition, with no account taken of the continuity offered by any

reinforcement at the supports. Two methods of design are generally recognised,

both of which use empirically derived information on the ‘shear bond’ resistance

of the slab from uniformly distributed loading arrangements. The more

traditional method, and one which is given in both BS EN 1994-1-1 and

BS 5950-4, is the so-called ‘m and k’ method (see Section 4.2.3). However, this

method has limitations and is not particularly suitable for the analysis of

concentrated line and point load conditions. An alternative method of design is

included in the Eurocode, which is based on the principles of partial shear

connection. This method provides a more logical approach to determine the

slab’s resistance to applied concentrated line or point loadings. It is not

normally necessary for designers to understand the design methodology in

detail, as manufacturers normally present the design data in the form of load-

span tables, but these are only applicable for uniformly loaded conditions.

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4.2.1 Concrete

Concrete types

Both normal weight concrete and lightweight concrete are used in composite

slabs, but in the Eurocodes these are now referred to as normal concrete and

lightweight aggregate concrete respectively. Normal concrete is made using

dense aggregates from natural sources

[15]

. Lightweight aggregate concrete

contains artificially produced aggregates such as expanded pulverised fuel ash

pellets. The cement and water contents are higher in lightweight concrete

because of the absorption of water by the aggregate. For normal weight

concrete, strength classes C25/30, C28/35 or C32/40 are normally chosen; for

lightweight concrete, strength classes LC25/28, LC28/31 or LC32/35 are

typical.

Lightweight concrete is commonly used because the obvious advantage of

(typically) 25% weight saving can provide economic benefit for the overall

design of the structure and its foundations (see Section 4.1.2 for concrete

densities used for design). Lightweight concrete also has better fire insulating

qualities than normal weight concrete, and so thinner slabs may be possible

when the ‘fire condition’ governs the slab design (see Section 4.2.5).

Unfortunately, lightweight concrete is not always readily obtainable in all areas

of the UK. Also, it may not be appropriate if it is to be used in trafficked areas;

to achieve a good wearing surface, the finishing process must cover the particles

of lightweight coarse aggregate with an adequate, well-trowelled dense surface

mortar layer. It also has poorer sound insulation properties than normal weight

concrete.

Lightweight concrete offers several performance advantages, but it is not

available in all parts of the UK.

Concrete grade

The Structural Designer chooses a concrete specification that is suitable for the

intended application. This specification is normally chosen on the basis of the:

 overall structural requirements

 flooring finish, if any, to be laid on the slab

 exposure conditions.

The concrete strength class designations according to BS EN 206-1

[16]

and

BS 8500

[17]

relate to the characteristic strength (95% probability of being

exceeded) achieved after 28 days, based on cylinder or cube tests. The cylinder

strength is about 80% of the strength of a 150 mm cube. Design standards

provide rules that relate the design strength to the concrete grade.

As a minimum standard, concrete of strength class C25/30 or LC25/28 should

be specified. In the case of concrete used as a wearing surface, the minimum

strength class should be C28/35 (although C32/40 is preferred).

Surface finishes

There are two basic performance conditions; concrete to be used as a wearing

surface, and concrete that is to be covered by raised floors, screeds, carpets,

tiles, sheet vinyl, etc. When the concrete is to be used as a wearing surface, the

concrete is first power floated. The specification should then require the slab to

be allowed to stiffen for a short time prior to power trowelling, which

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compresses and polishes the surface material, resulting in a harder and more

durable surface. Recommendations for power floating and power trowelling are

given in BS 8204

[18]

and Concrete Society Technical Report No.34

[19]

When the concrete is not to be used as the wearing surface, it is recommended

that a wood floated, skip floated or power floated finish is specified.

Drying

Because the concrete is only exposed on one surface of a composite floor, it can

take a longer period than a traditional reinforced concrete slab to dry out. If

moisture sensitive floorings and/or adhesives are to be applied, many months

may be needed before the slab is sufficiently dry to accept them. Measures such

as the specification of special concrete, dewatering or surface vapour-proof

membranes, may need to be considered if inadequate time for drying is allowed

in the contract programme.

If surface vapour-proof membranes are used, moisture will be trapped in the

slab. This trapped moisture will not be detrimental to the concrete or the

decking, as the steel in contact with the concrete is prevented from corrosion by

its high pH. The provision of small holes, perforations, in the decking to aid

drying is ineffective; the area represented by the holes is insufficient to have

any significant effect on drying times.

AD 163

[20]

provides additional guidance on provisions for water vapour release.

Level and flatness

It is recommended that a precisely level and flat concrete floor is not specified

unless it is absolutely necessary, as it is difficult to achieve because the tamping

rails are usually positioned along the support beams, which deflect under the

self weight of the finished floor. To achieve greater accuracy, it is necessary to

estimate the central deflection of the beams and to set the tamping rails along

each beam to allow for this deflection. This can result in errors because, in

practice, the beams may not deflect as much as expected (e.g. because of the

stiffness of the beam-column connections). It is reasonable to set the rails on the

basis that the beams will deflect 30% less than predicted by simple theory.

In propped construction, further deflection occurs on removal of the props.

Subsequent deflections will be greater the earlier the props are removed (due to

the lower stiffness of the ‘immature’ concrete). Therefore, props should not be

removed until the concrete has gained its design strength.

As deviations in level are dependent on the deflection of the composite slab and

the supporting beams, tolerances within which these deviations must lie should

only be specified at points where there is negligible deflection of the supporting

structure, i.e. at columns. The Main Contractor will be able to do little to

correct matters if deviations exceed tolerances specified at other points.

The following tolerances are recommended:

Top surface of concrete, level to datum ± 15 mm

Top surface of supporting steel beams, level to datum ± 10 mm

For the reasons discussed above, a thickness tolerance should only be specified

at the column locations. If it is really necessary to specify absolute levels for the

top surface, the thickness tolerance should be calculated by combining the top

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and bottom level tolerances using a method given in BS 5606

. This results in a

slab thickness tolerance of ± 18 mm. To achieve slightly tighter tolerances on

thickness, the level of the concrete should be specified relative to the level of

the supporting steelwork.

Owing to the accumulative deflections of the deck and beams, it is not practical

to specify tight flatness tolerances on composite slabs. BS 8204

[18]

gives three

tolerances for floor flatness, as shown in Table 4.1. The deviation is determined

by measuring the maximum gap beneath a 3 m straight edge laid on the surface.

For composite slabs, the straight edge must always be positioned parallel to the

supporting beams, i.e. perpendicular to the decking span.

Table 4.1 Surface flatness tolerances

BS 8204

Flatness

Designation

Maximum gap (mm)

below a 2 m

straight edge laid on

the surface

Comments

SR1 3

(1 in 667)

Not achievable on suspended floors of any

construction.

SR2 5

(1 in400)

May be achievable on parts of a composite floor,

but will not be achievable over all of a floor, owing

to deflections. This is a tight flatness tolerance and

high levels of workmanship are required to achieve

SR2 on any type of suspended floor.

SR3 10

(1 in 200)

May be achievable over most of a floor, depending

on the deflections of the supporting beams.

4.2.2 Reinforcement

Bar reinforcement

Types and details

The bar reinforcement in composite slabs usually takes the form of a relatively

light welded fabric, commonly supplemented by some bar reinforcement. The

fabric reinforcement is required to perform a number of functions:

 Provide bending resistance at the supports of the slab in the fire condition

(this reinforcement is usually ignored under ‘normal’ load conditions).

 Reduce and control cracking at the supports, which occurs because of

flexural tension and differential shrinkage effects.

 Distribute the effects of localised point loads and line loads.

 Strengthen the edges of openings (see Section 4.2.6).

 Act as transverse reinforcement for the composite beams (see

Section 5.3.2).

The most common fabric sizes are A142 and A193 (using designations

according to BS 4483

[22]

), with the numbers indicating the cross-sectional area

(mm

) of reinforcing bars per metre width. The fabric is normally manufactured

in ‘sheets’ that are 2.4 m wide and 4.8 m long. ‘A’ type fabric has layers of

bars equally spaced in both directions (known as ‘square’ fabric) and is most

commonly used. It is possible to order special fabric with heavier wires or

closer spacing in one direction, such as ‘B’ or ‘C’ type fabrics. ‘B’ type

‘structural’ fabrics have longitudinal bars at 100 mm centres and transverse bars

at 200 mm centres. These can be used when highly reinforced areas are

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required for structural or fire resistance purposes. ‘C’ type ‘highway’ fabrics

are intended for highway use and have only very light reinforcement in the

transverse direction. C type fabrics should not be used in composite floors.

Fabric sizes less than A142 are not recommended because of their poor

performance as fire reinforcement and inability to control shrinkage, and are

considered as non-structural.

Bar reinforcement may be used to supplement the fabric:

 To achieve longer fire resistance periods.

 To reinforce the slab around significant openings.

 When additional transverse reinforcement is needed.

 To achieve greater crack control.

Reinforcement should comply with BS 4483

[22]

(fabric) or BS 4449

[23]

(bars), and

the detailing of it should be in accordance with BS EN 1992-1-1

[24]

BS 8110

[30]

and BS 8666

[25]

. Bar reinforcement is produced in three ductility

grades; A, B or C. In the UK, bar reinforcement of ductility grade B is

normally used, but most fabric is supplied with ductility grade A. The ductility

grade of the reinforcement has no effect on the lap and anchorage lengths. The

bars in fabric supplied to BS 4483 are ribbed, and this will reduce the required

anchorage lengths compared to plain bars. BS EN 1992-1-1 assumes that bars

are ribbed, but BS 8110 allows for the use of ribbed and plain bars.

In shallow composite slabs, the reinforcement should be supported sufficiently

high above the top of the decking to allow concrete placement around the bars.

The required top cover depends on the concrete class and the exposure.

Recommendations are given in Tables NA.2 and NA.3 to BS EN 1992-1-1;

these present the same information as in BS 8500-1

[17]

but in a more compact

form. The Structural Designer should determine the relevant exposure condition

for the top of the floor. The following exposure conditions apply:

 For a floor in a dry protected environment, e.g. in enveloped buildings such

as offices, the exposure class for the concrete is XC1.

 For an external floor exposed to high levels of humidity, the exposure class

for the concrete would be XC3 or XC4.

 For a floor exposed in a marine environment, the exposure class would be

XS1, XS2 or XS3.

 For a floor that is exposed to freeze-thaw cycles, the exposure class would

be XS (see BS 8500-1 for recommendations for this class).

Table NA.2 in BS EN 1992-1-1 applies where the intended working life is 50

years and Table NA.3 applies where the intended working life is 100 years (not

normally applicable to buildings).

In car parks, where the slab is exposed to chlorides and freeze/thaw attack, the

exposure class is XD3 or, if the intended design life does not exceed 30 years,

the exposure class is XF3 or XF4, provided that the concrete surface is

protected by an effective, durable and long-lasting waterproof membrane. (Any

membrane should be a waterproof coating that prevents the ingress of water

containing dissolved de-icing salts into the concrete, including at any joints and

cracks in the concrete.)

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Recommended covers for XC1 and XC3/4 exposure classes are given in

Table 4.2. Refer to BS 8500-1 for covers and concrete specifications for other

exposure classes.

The recommendations for durability in this section only relate to the concrete

and reinforcement. The corrosion protection of the metal decking is covered in

Section A.1.1

Table 4.2 Minimum reinforcement covers for various levels of

exposure

Aggregate Type Normal weight Lightweight

Concrete Strength

Class

C25/30

C28/35

C32/40

C35/45

C40/50

LC25/28

LC28/31

LC32/35

Max Water cement

ratio

0.65 0.60 0.55 0.50 0.45 0.65 0.60 0.55

Min cement

content for 20 mm

aggregate (kg/m

)

260 280 300 320 340 260 280 300

Min cement

content for 14 mm

aggregate (kg/m

)

280 300 320 340 360 280 300 320

Min cement

content for 10 mm

aggregate (kg/m

)

300 320 340 360 360 300 320 360

Nominal cover in mm to reinforcement according to the exposure level:

XC1

25 25 25 25 25 25 25 25

XC3/4

45 40 35 35 30 45 40 35

Notes:

(a) These values are taken from BS 8500-1

[17]

and BS EN 206-1

[16]

(b) The exposure conditions are defined in BS 8500-1. For internal floors in a watertight heated

building, with dry conditions the exposure condition would be XC1. For floors subject to

high humidity or cyclical wet and dry conditions the exposure condition would be XC3/4.

More severe exposure conditions may be applicable in some conditions, e.g. car parks.

listed in Table 4.2 are the minimum covers given in BS 8500-1 plus a fixing tolerance (Δc)

of 10 mm. The covers listed are for an intended working life of 50 years. For an intended

working life of 100 years no change is required to the XC1 exposure class covers, and 15

mm should be added to the XC3/4 covers.

(d) In practice, nominal covers less than 30 mm with light fabrics are not recommended owing

to practical difficulty in supporting the light fabric in the correct location.

(e) The listed covers are for durability purposes. Greater covers may be needed for fire

resistance considerations.

Recommended tension laps and anchorage lengths for welded fabric and bars for

design to BS 8110 are given in Table 4.3, and for design to BS EN 1992-1-1 in

Table 4.4.

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Table 4.3 Recommended tension laps and anchorage lengths for

welded fabric and bars to BS 8110

Aggregate Type Normal Lightweight

Strength Class

C25/28 C28/30 C28/31 LC28/35 LC32/35 LC32/40

Reinforcement

Type

Wire/Bar Type

Grade 500 Bar of

diameter d

Deformed Type 2

44d 40d 38d 56d 54d 50d

A142 Fabric

(6 mm wires at

200 centres)

Deformed Type 2

275 250 250 350 325 300

A193 Fabric

(7 mm wires at

200 mm centres)

Deformed Type 2

300 275 275 400 375 350

A252 Fabric

(8 mm wires at

200 mm centres)

Deformed Type 2

350 325 300 450 425 400

A393 Fabric

(10 mm wires at

200 mm centres)

Deformed Type 2

440 400 375 550 550 500

Notes:

(a) Table 4.3 is based on information given in BS 8110-1

[30]

, assuming fully stressed bars/fabric.

It should be noted however that the recommendations determined in accordance with

BS EN 1992-1-1 (as shown in Table 4.4, below) may differ from the above.

(b) Where a lap occurs at the top of a section and the minimum cover is less than twice the size

of the lapped reinforcement, the lap length should be increased by a factor of 1.4.

which protrude beyond the main round part of the bars/wires. There may be longitudinal

ribs. Note: The majority of deformed high yield reinforcement available in the UK is Type 2.

(d) The minimum Lap/Anchorage length for bars and fabric should be 300 mm and 250 mm

respectively.

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Table 4.4 Recommended tension laps and anchorage lengths for

welded fabric and bars to BS EN 1992-1-1in C25/30

concrete

Reinforcement in tension, bar diameter,



(mm)

Bond

condition

8 10 12 16 20 25 32 40

Good 230 320 410 600 780 1010 1300 1760

Straight bars

only

Poor 330 450 580 850 1120 1450 1850 2510

Good 320 410 490 650 810 1010 1300 1760

Anchorage

length, l

Other bars

Poor 460 580 700 930 1160 1450 1850 2510

Good 320 440 570 830 1090 1420 1810 2460

50% lapped in

one location

(



6 = 1.4)

Poor 460 630 820 1190 1560 2020 2590 3520

Good 340 470 610 890 1170 1520 1940 2640

Lap

length, l

100% lapped

in one location

(



6 = 1.5)

Poor 490 680 870 1270 1670 2170 2770 3770

Notes

1 Nominal cover to all sides and distance between bars ≥ 25 mm (i.e. 

2 < 1).

2 It is assumed that the coefficients to allow for factors effecting the anchorage (defined in BS EN 1992-1-1, clause

8.4.4.) 

1 = 3 = 4 = 5 = 1.0.

3 Design stress has been taken as 435 MPa. Where the design stress in the bar at the position from where the

anchorage is measured, 

sd, is less than 435 MPa the figures in this table can be factored by sd/435. The

minimum lap length is given in clause 8.7.3 of BS EN 1992-1-1.

4 The anchorage and lap lengths have been rounded up to the nearest 10 mm.

5 Where 33% of bars are lapped in one location, decrease the lap lengths for ‘50% lapped in one location’ by a

factor of 0.82.

6 The reinforcement ductility class has no effect on lap and anchorage lengths.

7 In slabs up to 250 mm thick all horizontal reinforcement can be considered to have Good Bond conditions.

8 In slabs over 250 mm thick horizontal reinforcement in the bottom 250 mm can be considered to have Good Bond

conditions. Reinforcement in the top zone (above 250 mm from the bottom) can be considered to have Poor Bond

conditions.

9 The information in this table is taken from How to design concrete structures to Eurocode 2

[26]

. This publication

should be consulted for other concrete classes or for further guidance.

Concrete class

C20/25 C28/35 C30/37 C32/40 C35/45 C40/50 C45/55 C50/60

Factor

1.16 0.93 0.89 0.85 0.80 0.73 0.68 0.63

Fibre reinforcement

Fibre reinforcement consists of short fibres made from steel, polypropylene or a

combination of both, which are mixed into the concrete prior to placement.

Under controlled circumstances, fibres may be substituted for some or all of the

fabric reinforcement. Use of fibre reinforcement results in a three dimensional

reinforced concrete composite slab.

The performance of fibre reinforcement is verified empirically, specifically for

fire resistance and for longitudinal shear transfer, using the same testing regimes

that are used to validate the use of traditional reinforcement within steel deck

composite floors.

Considerable benefits can be achieved using fibre reinforcement, including a

reduction in labour costs and a saving on the construction programme. The

requirement for longitudinal shear reinforcement, in the form of bars or fabric,

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can be dramatically reduced and only a minimal amount of fabric reinforcement

need be purchased, transported and stored. There is less usage of the crane as

there are fewer lifting operations. The installation of the floor is easier and safer

because there is less reinforcement to obstruct the floor working area and to

handle, fix and check, and this can reduce installation times by up to 20%.

Independent testing has shown that fibre reinforcement systems can provide an

equivalent or superior performance to traditional welded wire fabric solutions,

although local reinforcement may be necessary in locations of concentrated

loads. Fibre reinforcement provides resistance to plastic shrinkage, settlement

cracking and toughness, but the performance is related to the specific fibre.

BS EN 14889

[27]

covers the requirements for fibres used as concrete

reinforcement. Part 1 covers steel fibres, and Part 2 polymer fibres. Care

should be taken with the selection of polymer fibres, as only Class 11 (macro)

fibres in accordance with BS EN 14889 are suitable as a replacement for

traditional fabric reinforcement in steel deck composite slabs.

It is very important to note that fibre reinforced composite slabs are not a

generic product. A specific type and dosage of fibres must be used according to

the fibre manufacturer’s specification for the particular deck, and other deck or

fibre types cannot be substituted.

When using a fibre reinforcement solution, it is still general practice to use

U-bars on composite edge beams, bar reinforcement around openings in the

slab, and fabric or bar reinforcement at construction joints, or where the

composite slab cantilevers beyond a support.

More information on fibre reinforcement is given in Section 6.2.1. Further

guidance on the use of steel or macro-synthetic fibre-reinforced concrete can be

found in Concrete Society Technical Reports No. 63

[40]

and 65

[41]

respectively.

Fiber reinforcement is provided within the concrete that is delivered and

ready to pump on site. This can reduce installation times by up to 20%.

4.2.3 Design for resistance

The performance of a composite slab with a particular decking profile can only

be assessed readily by testing. Test procedures are set out in both

BS EN 1994-1-1

[14]

and BS 5950-4

[11]

. The tests must cover the complete range

of the key design parameters (usually slab depth and span). The specimens are

first subject to dynamic load (5,000 load cycles up to 1.5 times the working

load are specified in BS EN 1994-1-1, but 10,000 cycles are required by

BS 5950-4). Following this, a static load is applied and increased until failure

occurs. The objective of the dynamic part of the test is to break any adhesion

bond, so that only the more stable mechanical interlock remains.

The test procedure is such that all loads are applied to the composite section to

simulate a uniformly loaded condition. The test results are then presented in

terms of empirical constants, either (m and k) or Tau (τ), that can be used to

quantify the interaction between the steel and concrete.

As far as slab design is concerned, the Structural Designer will not undertake

tests to determine the m and k or Tau (τ) factors. These constants are used by

the decking manufacturers themselves in order to present designers with a range

of load-span tables for uniformly loaded conditions for their specific products.

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Specific checks are necessary where there are concentrated line or point loads

whose effect is normally greater than that of a nominal uniformly distributed

blanket load.

The vertical shear resistance of a reinforced composite slab using bar or fabric

is assessed as for a reinforced concrete slab, using guidance given in

BS EN 1992-1-1

[24]

or BS 5950-4. ‘Punching’ shear resistance, against localised

loads, should also be assessed using these Standards. When fibre reinforcement

is used, designers should seek guidance from the manufacturers.

Manufacturers’ load-span tables for slabs are normally based on testing (in

order to minimise conservatism). Designers should take care to ensure that

they do not use this information for situations that are not covered by the

scope of the testing especially if concentrated line or point loads are

applied to the slab.

4.2.4 Design for serviceability

Crack control

There is a risk of cracking in the concrete in all composite slabs due to the

restraint to drying shrinkage provided by the steel decking and primary

steelwork, even though the decking effectively acts as reinforcement and helps

to distribute the shrinkage strains so that large cracks do not form. However,

cracks do not normally pose a durability or serviceability hazard. Only where

the surface of the slab is used as a wearing surface, or where terrazzo or other

‘rigid’ floor coverings are to be used, may specific reinforcement (in addition to

the ‘standard’ fabric) be required in order to control the cracking. When

cracking is an issue, reinforcement percentages in excess of 0.3% will normally

be required in order to limit crack widths to the recommended limit. Fabric,

rather than bars, is generally used to control cracking.

According to BS EN 1994-1-1, when continuous slabs are designed as simply-

supported, the minimum cross-sectional area of the anti-crack reinforcement

within the depth of the concrete cover to the decking should be as follows:

 0.2% of the cross-sectional area of the concrete above the ribs for

unpropped construction

 0.4% of the cross-sectional area of the concrete above the ribs for propped

construction.

It is possible that larger crack widths will occur over the intermediate supports

with propped construction, because the full self-weight of the slab is applied in

the composite slab on removal of the props, which explains the higher minimum

percentage reinforcement required.

The above amounts do not automatically ensure that the crack widths are less

than the typical value of 0.3 mm given in BS EN 1992-1-1 (and the UK

National Annex to this code) for certain exposure classes. If the exposure class

(or the floor finish) is such that cracking needs to be controlled, the slab should

be designed as continuous, and the crack widths in hogging moment regions

evaluated according to BS EN 1992-1-1.

Experience shows that the greatest risk of cracking is over supporting beams,

owing to the combination of restrained drying shrinkage and flexural action

[28]

‘Induced’ joints may be used to reduce the risk of random cracking at these

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locations. Such joints can be formed by sawing the slab, but clearly, care is

needed to prevent the reinforcement required for fire resistance and longitudinal

shear resistance from being damaged or severed. However, where cracking has

to be controlled, a more reliable measure is to use additional crack control

reinforcement at the support.

When fibre reinforcement is to be used in place of bar/fabric reinforcement the

suppliers of the fibres should be consulted regarding crack control measures.

Deflections

Deflections due to loading applied to the composite member should be

calculated using elastic analysis, neglecting the effects of shrinkage. For an

internal span of a continuous slab, where the shear connection is achieved by

either mechanical or frictional interlock, or end anchorage by through-deck

welded studs, the deflection may be determined using the average value of the

cracked and uncracked second moment of area may be taken. This applies both

for design to the Eurocodes and design to BS 5950, but the modular ratio for

long-term and short-term effects is calculated slightly differently in

BS EN 1994-1-1 and BS 5950-4 (which refers to BS 5950-3).

BS EN 1994-1-1 permits calculations of the deflection of the composite slab to

be omitted if both the following conditions are satisfied for external or simply-

supported spans:

 the span/depth ratio of the slab does not exceed certain limits specified in

BS EN 1992-1-1 for lightly stressed concrete (shown here in Table 4.5);

and

 the load causing an end slip of 0.5 mm in the (long span) tests on

composite slabs exceeds 1.2 times the design service load.

Table 4.5 General rules for the slab maximum span-to-depth

ratios in accordance with BS EN 1992-1-1

Normal concrete

Lightweight

concrete

Single spans 20 18.8

End spans 26 24.5

Internal spans 30 28.3

For cases where the end slip exceeds 0.5 mm at a load below 1.2 times the

design service load, two options exist for the designer:

(i) end anchors should be provided; or

(ii) deflections should be calculated including the effect of end slip.

Should the behaviour of the shear connection between the sheet and the concrete

not be known from tests on composite slabs with end anchorage,

BS EN 1994-1-1 permits a tied-arch model to be used. Guidance for designers

on this case can be found in the Designer’s guide to BS EN 1994-1-1

[29]

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For design to BS 5950-4, there are also simple design rules to ensure adequate

deflection behaviour of a composite slab. Calculation of deflections is not

necessary when designing to this code if the span-to-depth ratios are not greater

than those given in Table 4.7. Confirming that the slab satisfies these limits will

ensure that excessive deflections are avoided. The effective span of the decking

is defined in BS 5950-4 as the smaller of:

 the distance between the centres of the supports, and

 the clear span between the supports plus the effective depth of the

composite slab.

The values in Table 4.7 apply to slabs under uniformly distributed loading, with

nominal continuity reinforcement (0.1%) over the intermediate supports, i.e.

they are designed as simply supported. For slabs with full continuity

reinforcement over the supports, reference should be made to BS 8110

[30]

Deflections should be calculated explicitly for slabs that fail to satisfy the span-

to-depth ratio or reinforcement limits. BS 5950-4 recommends that the

deflection of the composite slab should not normally exceed the limits in

Table 4.6.

Table 4.6 Recommended limits for the maximum deflection of

composite slabs given in B S5950-4

Criterion Recommended Limit

Deflection due to the imposed load

/350 or 20 mm, whichever is

the lesser

Deflection due to the total load less the

deflection due to the self-weight of the

slab plus, when props are used, the

deflection due to prop removal

L/250

The stiffness of slabs reinforced with conventional fabric reinforcement can be

determined using ‘normal’ reinforced concrete design rules (assuming fully

effective bond between the decking and the concrete). When fibre reinforced

concrete is used, advice on the slab stiffness should be sought from the

manufacturer.

Table 4.7 General rules for the slab maximum span-to-depth ratios in

accordance with BS 5950-4

Normal

concrete

Lightweight

concrete

Single spans 30 25

End spans 35 30

Internal spans 38 33

Values apply to supported spans

with nominal continuity

reinforcement, subject to

uniformly distributed loading

Dynamic sensitivity

The dynamic sensitivity of composite slabs is not normally critical, because they

are relatively stiff compared with the beams, although the dynamics of the

whole floor should be considered, as explained in Section 5.2.2.

Cracking of internal concrete surfaces will generally not compromise the

structural performance of a building, so for economic design its

consequences may often be ignored.

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4.2.5 Design for fire resistance

The required fire performance of floor slabs is defined by the Approved

Document B to the National Building Regulations. The Approved Document

requires the slab performance to be assessed based on criteria for insulation ‘I’,

integrity ‘E’ and load bearing capacity ‘R’. For design to the Eurocodes,

BS EN1994-1-2

[31]

and the UK National Annex to BS EN1994-1-2

[32]

provide

guidance on how composite slabs may be designed to meet these criteria. For

UK design, guidance is available in BS 5950-8

[11]

The insulation criterion is satisfied by providing adequate slab thickness to

ensure that the temperature of the unexposed surface of the slab does not exceed

140

C. BS 5950-8 and the UK National Annex to EN1994-1-2 provide a table

of recommended concrete thicknesses to satisfy the insulation criterion for

common periods of fire resistance. The minimum thickness of concrete required

to satisfy the insulation requirements is shown in Table 4.8 for trapezoidal decks

and Table 4.9 for re-entrant decks. Figure 4.10 shows that the insulation depth

depends on the type of profile, and it is the concrete cover to the main crest of

the deck for trapezoidal profiles and the full slab depth for re-entrant profiles.

Table 4.8 Minimum thickness of concrete, measured above the steel

deck, for trapezoidal profiled steel deck exposed to the

standard fire

Minimum thickness of concrete (mm) for a fire

resistance period (mins) of:

Concrete type

30 60 90 120 180 240

Normal concrete

(All cases)

60 70 80 90 115 130

Lightweight concrete

(All cases)

50 60 70 80 100 115

Table 4.9 Minimum thickness of slab for re-entrant profiled steel

sheets exposed to the standard fire

Minimum thickness of concrete (mm) for a fire

resistance period (min) of:

Concrete type

30 60 90 120 180 240

Normal concrete 90 90 110 125 150 170

Lightweight concrete 90 90 105 115 135 150

EN1994-1-2 permits the designer to calculate the bending resistance and

insulation properties assuming that composite slabs fulfil the integrity criterion.

Insulation

depth

Insulation

depth

Trapezoidal steel deck Re-entrant steel deck

Figure 4.10 Minimum insulation depth measurement

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Fire tests have been carried out on slabs with conventional fabric reinforcement,

and on fibre reinforced slabs.

The load bearing resistance of the slab at elevated temperatures can be

determined by calculation in accordance with the principles given in EN1994-1-

2. The UK National Annex provides additional guidance on determining design

temperatures for UK decking geometries.

Depending on the span required, an increased size of fabric may need to be

used, or extra bars may need to be placed in the troughs of the deck, to satisfy

the load bearing criteria (R) for the fire condition. In either case, the additional

reinforcement is used to compensate for the loss of strength of the (exposed)

decking at elevated temperatures. Design guidance covering this aspect is

normally given by the decking manufacturers in their design tables. These

design tables are based on the extended application of fire test results and

provide product specific guidance which will result in the most economic

solutions for fire design. The extended applications of the fire test results are

based on a design model for plastic resistance that is in accordance with the

principles of EN1994-1-2 §4.3.1 and the recommendations of the UK National

Annex to EN1994-1-2.

In the UK National Annex, the use of Informative Annex D of EN1994-1-2 is

rejected as many UK decking profiles are outside the limits of the field of

application. It was found that when the methods in Annex D were applied to

these decking geometries, unusable answers were obtained. For projects in other

European countries where the use of Annex D is recommended, it is likely that

the manufacturer’s fire design tables will be the only valid method of design for

UK decking profiles.

Slab designs that comply with the recommendations of EN1994-1-1 for room

temperature design are deemed to have 30 minutes fire resistance, when

assessed under the load bearing criteria ‘R’, but these slabs still need to be

checked for compliance with the insulation criteria.

Further information on the calculation of load bearing resistance of composite

slabs can be obtained from P375

[33]

4.2.6 Openings and edges

Openings

Openings can be accommodated readily in composite slabs. Some advice as to

limits on the size of openings, and the provision of any extra reinforcement that

may be required, is normally given in the notes accompanying a decking

manufacturer’s load-span tables. Further advice is given here on issues relating

to design with shallow decking (deep decking is covered in Section 7), and

advice relating to the construction of openings is given in the BCSA Code of

practice for metal decking and stud welding

[6]

Openings may be categorised by their size:

 Small - openings up to 300 mm square - unlikely to present a problem

structurally and do not normally require additional reinforcement.

 Medium - openings between 300 mm and 700 mm square - normally

require additional reinforcement to be placed in the slab. This is also the

case if the openings are placed close together.

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 Large - openings greater than 700 mm square - should be trimmed with

addition permanent steelwork back to the support beams.

It should be noted that slightly different dimensions from those given above may

be quoted in a manufacturer’s literature for specific profiles, in which case the

manufacturer’s guidance should be followed.

For small and medium size openings, normal practice is for the Main

Contractor to form an opening by ‘boxing-out’ an area of decking using timber

or polystyrene inserts before concreting, as shown in Figure 4.11. The decking

should not be cut until the concrete has gained 75% of its design strength. Then

it may be cut or burnt away to form the opening, and the cut edges bent up or

ground off. If cutting the deck prior to casting is unavoidable, temporary

propping is likely to be required. This may have implications on the slab

design, and the Structural Designer should be consulted.

For large openings, the supporting trimming steel should be in positioned prior

to placing the decking. The opening should then be trimmed prior to casting the

slab, as shown in Figure 4.12.

Timber shutter Dense polystyrene block

Figure 4.11 Typical examples of boxing out openings

Figure 4.12 A typical trimmed opening (immediately after deck laying,

prior to fixing the edge protection and reinforcement

around the opening)

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Cutting the slab after concreting (post-forming the openings) may cause a loss

of bond between the concrete and the decking, and is not recommended. When

post-forming is unavoidable, non-percussive cutting methods such as diamond

core drills/saws should be adopted, so that the disturbance to the mechanical

interlock between the decking and the concrete is kept to a minimum. The

structural implications of the location and size of the opening need careful

consideration, and should always be referred to the Structural Designer.

The need for extra reinforcement in the slab, or additional trimming steelwork,

depends on the size of the opening. Requirements should be determined by the

Structural Designer, who may be represented by a slab or steelwork specialist.

The Structural Designer will identify reinforcement requirements on the contract

drawings, and should be consulted if there are any doubts about the location of

openings or the amount of reinforcement needed. Any additional reinforcement

that may be required should be designed in accordance with BS EN 1992-1-1

[24]

or BS 8110

[30]

. Site operatives should be made aware that additional

reinforcement is required around medium sized openings. This often takes the

form of bars placed in the troughs of the decking adjacent to the opening, with

additional transverse bars used to ‘smooth out’ the load transfer around the

opening (see Figure 4.14). The distance between an opening and an unsupported

edge should not be less than the greater of either 500 mm and the width of the

opening. If the opening falls within the usual ‘effective breadth’ of concrete

flange of any composite beams (typically span/8 each side of the beam centre

line), the beam resistance should be checked assuming an appropriately reduced

effective breadth of slab.

In the absence of any specific manufacturer’s guidance on the provision of extra

reinforcement, it may be assumed that an effective system of ‘beam strips’ span

the perimeter of the opening, as shown in Figure 4.13. The effective breadth of

the beam strips should be taken as d

/2, where d

is the width of the opening in

the direction transverse to the decking ribs. Only the concrete above the ribs is

effective. The transverse beam strips are assumed to be simply supported, and

span a distance of 1.5 d

. The longitudinal beam strips are designed to resist the

load from the transverse beam strips, in addition to their own proportion of the

loading. Extra reinforcement is provided within the ‘beam strips’ to suit the

applied loading. This reinforcement often takes the form of bars placed in the

troughs of the decking (see Figure 4.14). Additional transverse or diagonal bars

may be used to improve load transfer around the opening. Reinforcement bars

in these beam strips will need to extend at least an anchorage length beyond the

centre line of the supporting beam.

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Multiple openings in a floor may need to be considered as equivalent to one

large opening, and the reinforcement should be designed accordingly.

Slab edges

The edges of the floor are usually formed using ‘edge trims’ made from pressed

strips of light gauge galvanized steel. Edge trim is delivered to site to the

required depth and normally in standard 3.0 m long strips. The thickness of the

steel used may vary with location, but is normally no more than 2 mm. The

strips are cut to length on site to suit column centres. The trim is usually set out

from the edge beam centre line (rather than the grid lines, which cannot be set

out easily on site), as shown in Figure 4.15. The trim should be fixed in the

same way as the decking. It should not be used as a tamping rail because it may

be damaged.

d /2

C Floor beam

Deck

span

d /2

Longitudinal reinforce

concrete beam strips

Transverse reinforced

concrete beam strip

Effective span

of transverse

beam strips

= 1.5 d

Figure 4.13 Load paths and beam strips around medium to large

openings

Section A - A Section B - B

Opening

Extra bars in troughs

Extra bars

in slab

(over the deck)

Extra bars in troughs

Extra bars over deck

Fabric

reinforcement

Fabric

reinforcement

Figure 4.14 Typical reinforcement detailing around an opening

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Straps are always specified to tie back the upper part of the trim at 0.6 m to

1 m spacing, depending on the slab depth and overhang. Typical details are

given in Figure 4.16, covering two distinct cases. Where the decking (with

transverse ribs) runs over the edge beam and cantilevers out a short distance,

the edge trim can be fastened in the manner suggested in Figure 4.16(a). The

cantilever projection should be no more than 600 mm, depending on the depth

of the slab and deck type used.

The more difficult case is where the decking ribs run parallel to the edge beam,

and the finished slab is required to project a short distance, so making the

longitudinal edge of the sheet unsupported Figure 4.16(b). When the slab

projection is more than approximately 200 mm (depending on the specific

details), the edge trim should span between stub beams attached to the edge

beam, as shown in Figure 4.16(c). These stub beams are usually less than 3 m

apart, and should be designed and specified by the Structural Designer as part

of the steelwork package. If stub beams are not provided in this case, then

additional support to the edge of the decking, such as by propping from the

floor beneath, may be required and this information must be highlighted in the

information passed to the contractor. Non-standard edge trims (for example

those used to support cladding, or those forming a curved edge) will require

more accurate setting out procedures than standard trim.

Trims fixed to a curved edge are normally formed by cutting and bending the

standard lengths to form a continuous faceted ‘curve’ with, typically, 300 mm

straight sides.

Further information on how edge trims should be attached and supported is

given in Reference 6.

Achievable tolerances for the position of the top of standard edge trims relative

to the steelwork (after concreting) are ±10 mm horizontally, and ± 5 mm

vertically (see Figure 4.15). Tighter tolerances than these may need to be

specified for edge trims that incorporate housings for cladding supports. It will

also be necessary to ensure that these trims do not deflect excessively during

concreting. The Structural Designer must specify requirements for any such

‘non-standard’ trims.

Decking

C Beam

Edge trim should be set out from

centre line of beam (not grid)

Figure 4.15 Setting out of edge trim

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4.2.7 Temporary supports

Decking is usually designed to be unpropped for spans up to 3 m for profiles up

to 60 mm deep, and up to 4.5 m for profiles 80 mm deep. For longer spans

temporary propping may be required, but this will depend on the depth of the

concrete, the profile used and whether the decking is multiple or single

spanning. The limitations of a particular decking should be checked with the

manufacturer at an early stage so that any propping requirement can be planned.

The structural designer should check whether beam deflections during

construction and the method of levelling of the slab would lead to significant

additional concrete loads (from concrete ponding) that have not been allowed for

in the design of the structure and decking (see Section 4.1.3). Propping may be

necessary to minimise ponding.

In general, traditional ‘shallow’ decking spanning greater than 4 m will require

the propping system to be in place, braced and levelled, before placing the

decking. SD225 deep decking will generally require such propping for spans

greater than 7.5 m. Propping will reduce the deflections from the self-weight of

the decking, which would otherwise be difficult to remove if props were

installed after laying the decking. It will also minimise the risk of overloading

the decking under loads during construction, e.g. from operatives and storage,

but the implications of using design which requires propping should be

Fixing to top

of edge trim

U-bars required to prevent

longitudinal splitting

Fixing

Restraint straps at

600 mm c/c approx.

Max. 200 mm

Stub cantilever

specified by

structural designer

> 200 mm

Steel deck cut on site

to suit edge detail

Additional U-bars required to

resist longitudinal splitting

Restraint straps at

600 mm c/c approx.

Mesh reinforcement

Restraint strats at

600 mm c/c approx.

Minimum 114 mm

(for 19 mm studs)

Maximum 600 mm

cantilever (or 1/4 of

adjacent span, if less)

Additional U-bars required to

resist longitudinal splitting

a) Typical end cantilever

(decking ribs transverse to beam)

b) Typical edge detail

(decking ribs parallel to beam)

c) Side cantilever with stub bracket

(decking ribs parallel to beam)

Figure 4.16 Typical edge details

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considered at an early stage, because it can have sequence and programming

implications, and can preclude the use of safety netting. When temporary

propping is positioned after the decking is placed, it is particularly important to

check that the props are set in accordance with the Structural Designer’s

requirements, and that the increased weight due to concrete ponding is allowed

for in the design of the propping system.

There may be small areas in a building where propping is necessary, even when

the main areas of the floor remain unpropped. These propped areas may include

bays that are in-filled after the removal of climbing cranes, or lift shafts which

have non-standard span lengths. The decking layout drawings should show the

extent and lines of temporary supports.

Normally, props are placed at either mid-span (one line of props) or at third

points (2 lines of props) within a span. Isolated props should not be used, and

all props should be suitably braced (in the direction of the line of the props and

perpendicular to this) to prevent dislodgement during construction operations.

Props normally consist of lengths of timber and/or steel plates supported by

adjustable length steel tubes (‘Acrows’). The minimum bearing length of the

timber and/or plates depends upon the thickness of the slab, the span length and

the decking rib geometry. Bearing lengths are typically in the 75 to 100 mm

range. The timber bearer should be continuous, and should extend the full width

of the bay. The decking sheets should never be interrupted (cut) at the location

of a temporary support, and the decking should not be fastened to the temporary

supports. It is good practice to carry out a final check of the propping system

before pouring the concrete.

A typical temporary support is shown in Figure 4.17. Props of this nature are

normally placed about 1 m apart, according to the Structural Designer’s

requirements.

Props may be supported off the floor directly beneath the floor being concreted,

but the designer should check that the design capacity of the lower floor is not

exceeded (the supporting floor should achieve its design strength before props

Figure 4.17 Temporary support using an ‘Acrow’ props

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are installed). If the lower floor does not have sufficient resistance, further

‘back’ propping will be needed (i.e. using props to support the floor that is

supporting the props). Props should never be placed directly on the decking

alone as this could result in localised buckling of the deck. Further guidance on

back propping can be found in Reference 34.

Props should not be removed until the floor has reached 75% of its design

strength. This is normally achieved in 7 to 8 days, but the Structural Designer

should be consulted specifically before removal, unless general guidance has

already been given. Where crack control is essential, props should not be

removed until the floor has achieved its specified strength.

Other temporary support details may be needed for special situations, such as

end supports in refurbishment projects or where there are concrete encased

beams. Particular care should be taken with non-standard details to ensure that

the sequencing of the construction is practicable. A typical detail for the

temporary support of the decking at an encased beam is shown in Figure 4.18.

In this case, the decking is supported initially off the steel beam, and a

temporary prop is inserted under the decking close to the beam. This must be of

sufficient width to avoid crushing of the decking during concreting (see

Section 4.1.4). The decking is then cut back to allow access for the

reinforcement and the shuttering to be positioned, and the concrete to be

poured. This detail is only suitable for re-entrant decking because the decking

can interlock into the concrete by the ‘dovetails’, without needing support

underneath in the permanent condition. The decking cannot contribute to the

shear resistance of the finished slab. Use of this detail should be confirmed by

the Structural Designer and indicated on the drawings.

4.2.8 Attachments

Hangers

The best way to eliminate the hazardous activity of post-drilling concrete to

attach services is to use hangers, and designers are encouraged to specify them.

Many decking profiles have re-entrant slots into which proprietary wedges can

be inserted to receive threaded rods. The rods serve as hangers to the services,

and they have a safe load-carrying capacity of, typically, 100 kg to 200 kg

each. Some examples of these attachments are shown in Figure 4.19.

Beam

Timber shutter

Re-entrant steel deck

initially supported on

steel beam, then cut back

after prop installed

Temporary prop installed

to support decking

during construction

Supporting timber

Reinforcement

Crack control mesh

Hairpin tie bar/transverse

reinforcement

Figure 4.18 Special temporary support detail for re-entrant decking on

a concrete-encased beam

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Designers or Architects wishing to make use of these attachments should seek

information, including safe load capacities, from the decking supplier. For

services that are too heavy for the capability of the hangers, it may be necessary

to use drilled expanding anchor fixings into the composite slab (taking care to

ensure that the resistance of the fixing is appropriate for this type of use).

For detailed information on the interface between the services and the floor,

refer to Interfaces: Design of Steel framed buildings for service integration

[35]

Cladding supports

Brackets cast in to the edge of the slab may be used to support the cladding.

These may form part of a proprietary edge trim. Even though this may need to

be set out more accurately on site than the standard edge trim, the support

system should be co-ordinated early during the design process to allow for

horizontal deviations in the edge of slab position of at least ± 25 mm (more for

high rise buildings). Such an allowance is necessary because not only may the

allowed tolerances for the cladding be considerably more stringent than those

for the frame, but also that the brackets may move during concreting. An

example of a typical stainless steel brickwork support arrangement is shown in

Figure 4.20.

As an alternative to cast-in brackets, drilled fixings may be used to achieve

greater accuracy and require the use of power tools. Drilling for these fixings

may, however, be more time-consuming. For further information on cladding

attachments see Interfaces: Curtain wall connections to steel frames

[36]

A wedge attachment

An alternative wedge attachment

Figure 4.19 Examples of fixings for ceilings and services

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Cladding fixing brackets should be provided with provision for adjustment,

in recognition of different tolerance requirements for the slab edge and the

cladding. This may avoid problems and additional cost on site.

4.3 Acoustic insulation

Building designers should consider two basic ‘types’ of sound transmission;

airborne and impact. The acoustic insulation (attenuation) of both types of

sound, and particularly airborne sound, is partly related to the mass (or weight)

of the element through which the sound is passing. It is also affected by the

presence of any ‘soft’ layers, which increase the sound absorption.

High levels of sound insulation are typically required in:

 Multi-occupancy residential buildings

 Hotels

 Schools and other education-related buildings

 Hospitals and other health-related buildings.

For composite floors with shallow decking, a bare composite slab will normally

provide about the same degree of acoustic insulation as a reinforced concrete

slab with a thickness equal to the average thickness of the composite slab.

However, the floor should not be considered as an element in isolation because

the acoustic performance of the walls, and the junction details between the walls

and floors, also need consideration. The junctions need to be detailed to

minimise sound which may travel around the floor; known as flanking sound.

Further guidance on this is provided in SCI Publication P372

[37]

. Approved

Document E to The Building Regulations

[38]

requires residential buildings to

undergo pre-completion acoustic testing to demonstrate compliance unless the

walls, floors and their interfaces have been constructed in accordance with

‘Robust Details’

[39]

Enhancing the acoustic performance of the floor by adding mass is not very

efficient and is not always practical. This is particularly true for impact sound.

Embedded channel and anchor

(part of proprietry edge trim)

Brickwork

support angle

Serrated U bar bolted

to embedded channel

Fabric reinforcement

Spacer bar

L bar to prevent

pull-out of anchor

Reinforcement bar

parallel to edge trim

110 typ

(depends on trim channel size)

Figure 4.20 Typical steel brickwork support

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A much more effective means of enhancing sound attenuation is by the use of

layers above and below the floor slab. A ‘resilient layer’ of material applied

above the bare slab and beneath the walking surface is an effective way of

reducing the impact sound transmission through the floor. The walking surface

material, such as a screed or chipboard, forms a ‘floating layer’ above the

resilient layer; the sound energy is absorbed by the resilient layer rather than

being transmitted through the floor. A ceiling layer suspended below the floor

slab will reduce airborne and impact sound transmission. In addition, the impact

sound transmission can be reduced by suspending the ceiling on resilient bars,

which reduces the sound transfer from the slab. A wide range of proprietary

acoustic floor and ceiling systems are available which incorporate these features.

As a guide to the acoustic performance of typical composite floor constructions,

the attenuation that can be expected is given in Table 4.10. All the values given

in the table are for normal weight concrete, which is recommended for

dwellings and buildings where acoustic insulation is important. Lightweight

concrete will generally give slightly less sound insulation than normal weight

concrete.

Details of a shallow deck composite floor and a deep deck composite floor that

both comply with Robust Details are shown in Figure 4.21 and Figure 4.22

respectively.

4.4 Health & Safety

Revised CDM Regulations came into force in 2007 and were published with an

associated Approved Code of Practice (ACoP)

[4]

. The ACoP should be read in

conjunction with the Regulations, as it has special legal status and gives advice

on how to comply with the law. These are the most important new regulations

affecting safety in construction to be published in recent years. Their primary

thrust is to ensure that structures can be constructed, used and demolished

safely. ‘Use’ in this context relates to operations such as maintenance,

redecoration, repair and cleaning.

One of the most significant features of the Regulations is that designers are now

required to concern themselves with construction safety. They must give

adequate regard to ‘foreseeable’ hazards and, by implication, the designer is

expected to have a sound appreciation of the hazards that may be involved in

the project. This does not mean that the designer is expected to take

responsibility for all hazards that will eventually arise on site. A designer cannot

prevent unsafe practices taking place, and the word ‘foreseeable’ acknowledges

that some hazards cannot be anticipated. The Contractor remains responsible for

health and safety on site and this responsibility is not diminished by the

designer’s regard to the foreseeable hazards.

Another area where the designer has significant influence is in the specification

of components, which falls within the definition of design according to the

Regulations. The selection of materials, equipment, etc. must be given equal

attention to that of the construction method itself.

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Table 4.10 Site test data for composite floors

Sound pressure level (dB)

Form of Floor Construction

Airborne Sound

Attenuation

nT,w

+Ctr

(dB)

Impact Sound

Level

L’

nT,w

(dB)

Approved Document E requirement for purpose

built dwellings

[38]

≥ 45 ≤ 62

Shallow Deck Floors

An 18 mm chipboard walking surface over

25 mm of dense mineral wool over a 175 mm

slab on a 60 mm trapezoidal deck. A 12.5 mm

plasterboard ceiling suspended from the slab on

a metal framed grid.

55 43

An 18 mm MDF walking surface over a 10 mm

dense fibre resilient layer over a 200 mm slab on a

re-entrant deck. A 30 mm (2 x 15) plasterboard

ceiling suspended from the slab on a metal

framed grid.

56 34

A 70 mm screed on 5 mm foam resilient layer

over a 150 mm slab on 50 mm re-entrant deck.

A 12.5 mm plasterboard ceiling suspended from

the slab on a metal framed grid with 85 mm of

mineral wool in the ceiling void.

56 40

A 18 mm chipboard walking surface supported

on softwood timber battens on a 25 mm

acoustic quilt over a 150 mm slab on a re-

entrant deck. A 25 mm (2 x 12.5) plasterboard

ceiling suspended from the slab on a metal

framed grid.

60 34

Deep Deck Floors

An 18 mm chipboard walking surface supported

on softwood timber battens with resilient strips

over a 13 mm mineral fibre quilt over a 300 mm

deep slab. A 12.5 mm plasterboard ceiling fixed

to timber battens fixed to the underside of the

slab.

54 48

An 18 mm chipboard walking surface over

30 mm of dense mineral wool over a 300 mm

deep slab. A 12.5 mm plasterboard ceiling

suspended from the slab on a metal framed grid.

54 43

An 18 mm chipboard walking surface supported

on softwood timber battens with resilient strips

over a 300 mm deep slab. A 12.5 mm

plasterboard ceiling suspended from the slab on

a metal framed grid.

55 42

A 55 mm screed over a 5 mm foam resilient

layer over a 300 mm deep slab. A 12.5 mm

plasterboard ceiling suspended from the slab on

a metal framed grid.

57 45

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approx



Softwood timber battens

with resilient strips.

300

Normal weight concrete slab with

Shallow decking

Single skin 12.5 mm (8 kg/m²) plasterboard

suspended ceiling

130

18 mm thick tongued and grooved

chipboard walking surface

Figure 4.21 Typical shallow composite slab with a battened resilient floor

system (classified as a Robust Detail)



Dense mineral wool

( 25 mm)

225

18 mm thick tongued

and grooved chipboard

walking surface

approx.



300

Resilient

bars

Single skin 12.5 mm (8 kG/m³)

plasterboard suspended ceiling

Normal weight concrete

floor slab with

SD225 deep decking

Figure 4.22 Composite slab with deep decking and a layered resilient floor

system (classified as a Robust Detail)

The designer is obliged to follow the same hierarchy of measures whether

considering the construction process or the specification of components, namely

to avoid hazards, reduce their impact, or protect people from their

consequences. Designers may assume (as indeed the ACoP requires) that

contractors will be competent, i.e. not only capable of providing quality work,

but also experienced in the day-to-day hazards associated with that work. For

example, designers may assume that decking layers are experienced specialists

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who are aware of the hazards of working at height, and used to managing the

associated risks by adopting best practice in laying techniques.

Nevertheless, designers must consider whether there are any features of the

design itself, or the way in which it would be constructed, which are unusual,

or unduly onerous, for operatives. Features falling into one of these categories

may include the specification of items which are difficult to handle and locate,

such as excessively long and heavy decking sheets. Such features may be

avoided by changing the steelwork layout, propping arrangements, etc. Another

feature falling into this category is the need for propping of the decking during

construction. If, on the basis of information given in a load-span table, the

designer knows that there will be a need to prop the chosen decking in order to

satisfy the load and span requirements, this information must be clearly

communicated to the relevant parties, preferably on the drawings.

A number of ways to reduce ‘general’ risks and afford greater protection to

those working at height during the deck installation are recommended in the

good practice guidance given in Reference 6. They include such measures as

edge protection and the use of fall arrest equipment. A list of common hazards

that are more specific to floor construction using steel decking, and the

measures to control the risks associated with them, are shown in Table 4.11.

Table 4.11 Common hazards associated with floor construction using

metal decking and potential design and site control

measures

Hazard Design/Site Control Measures

Falling through decking -

due to inadequate

resistance of decking

Check the decking for the erection case.

Falling through decking -

due to inadequate

support

Allow for adequate bearing. Minimise the

use of propping. Highlight the need to

ensure the propping arrangement is in

place and of adequate construction.

Supply propping loads

Falling through penetrations in decking

Create openings by ‘boxing out’ and

cutting out later. Minimise penetration

(liaise with services engineer)

Contact with hot particles during stud

welding

Wear appropriate protection when stud

welding, and barrier and/or screen areas

below or in proximity

Collapse of decking from overload during

concreting

Check decking for erection loads given in

BS EN 1991-1-6 or BS 5950-Part 4

Collapse of decking due to overload from

bad storage of materials.

Place stored materials directly over, or

close to, support beams, and distribute

their weight over the decking ribs using

timbers

4.5 Further reading

The references given below mainly relate to slab design. See Section 5.4 for

additional design guidance related more to beams. (For information on authors

and publishers, see Section 8, References.)

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Concrete Society Technical Report No. 63, 2007 - Guidance for the design of

steel-fibre-reinforced concrete

[40]

This publication summarises the range of applications for steel-fibre-reinforced

concrete and includes practical aspects such as production and quality control.

Concrete Society Technical Report No. 65, 2007 - Guidance on the use of

macro-synthetic fibre reinforced concrete

[41]

This publication reviews the current range of applications for Macro-synthetic

Fibre Reinforced Concrete and gives guidance on quality control.

Interfaces: Curtain wall systems for steel frames (P101)

[36]

This outlines the main considerations in the design of a curtain wall attachment

system, and reviews some of the systems available for steel framed buildings.

Interfaces: Composite floor systems (P166)

[42]

This book provides information on most aspects relating to the design of

composite floors. It is particularly useful in that it covers both conventional

composite floors with shallow decking and slim floors (with deep decking). A

comprehensive set of worked examples of the design of floor beams is included.

Design of composite slabs and beams with steel decking (P055)

[43]

This provides the theoretical aspects of the design of composite beams with

shallow decking. It includes a comprehensive series of design tables for

common loading and span arrangements, and a worked example.

Acoustic detailing for steel construction (P372)

[37]

This guide explains the principles of acoustics in a very readable way. Sound

insulation values are given for many examples of floor and wall construction,

and typical details are recommended which are compatible with the Robust

Details Handbook

[39]

Advisory Desk

The following ‘Advisory Desk’ items, published in New Steel Construction and

available on www.steelbiz.org, provide further information relevant to this

Section:

AD 150, Vol 1, December 1993

[45]

, Composite floors - wheel loads for fork lift

trucks. This note gives a procedure for checking the behaviour of slabs under

heavy point loading.[ Further advice is given in BS EN 1994-1-1, clause 9.4.3.]

AD 163, Vol 2, December 1994

[20]

, Provision for water vapour release in

composite slabs. This note explains the problems sometimes associated with

water vapour release in composite roof slabs. It is suggested that perforated roof

felt may be used, but the use of perforated decking is not recommended.

AD 247, Vol 9, March 2001

[9]

, Use of composite construction in an aggressive

environment. This note gives advice on improving the corrosion resistance of

decking and beams for an aggressive environment. It recommends using coated

steel or additional paint protection for decking, and discusses the advantages and

disadvantages of using shot-fired studs or pre-welded studs for beams.

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5 DESIGN OF COMPOSITE BEAMS

This Section provides information about design principles and procedures,

codified design rules, and guidance on good practice in design and detailing. It

(along with Section 4) is aimed primarily at the Structural Designer, and any

Delegated Designers. Summary boxes are used to highlight particular issues of

good practice, or things that the designer should beware of.

Composite beams typically consist of steel ‘I’ sections acting structurally with a

concrete slab by means of shear connectors attached to the top flange of the

steel section, as shown in Figure 5.1. An effective width of slab is taken as

acting as part of the composite section on either side of the centreline. Fabric

reinforcement is ideally placed below the head of the studs; its main role,

possibly supplemented by individual bars, is to act as transverse reinforcement

in order to transfer the forces between the shear connectors and the slab.

Alternatively, fibre reinforcement may be used to fulfil this role. Fabric or fibre

reinforcement may also serve as a means of controlling crack widths. The

beams are generally designed to be simply supported.



Steel section

Transverse

reinforcement

In-situ concrete

Voids left unfilled

for fire resistance

periods 90 mins

Profiled

steel decking

Shear stud

connector

Mesh

Figure 5.1 Typical cross-section through a composite beam

The composite action developed between the steel beam and concrete slab

significantly increases the load carrying capacity and stiffness of the beam by

factors of up to 2 and 3.5 respectively

[46]

. These benefits can result in significant

savings in steel weight and/or structural floor depth.

It is often found that the size of the steel section is governed by serviceability

considerations because composite beams tend to be used for long span

applications (in excess of 9 m). This makes deflection and dynamic criteria

more likely to be critical. Controlling deflections is particularly important where

brittle ceiling finishes are specified, or for edge beams, where excessive

deflections can damage the cladding.

Designers should note that where edge beams are designed as composite beams,

care is required to ensure that the decking, edge trim, shear connector, slab

edge and reinforcement details are practicable. Edge beams are sometimes

designed non-compositely to avoid transverse reinforcement requirements, which

may result in problems of reinforcement congestion.

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5.1 Construction stage

The steel sections are normally designed to be unpropped during construction,

and must be sized to support the self-weight of the slab, and other construction

loads, in their non-composite state. Design is generally in accordance with

either BS EN 1993-1-1

[47]

or BS 5950-1.

The weight of extra concrete from ponding of the slab should be allowed for in

the design of the beams when the deflection of the decking under the wet weight

of the concrete exceeds one tenth of the depth of the slab, in accordance with

both BS EN 1994-1-1 and BS 5950-4. Careful consideration should be given to

the correct allowance for the weight of the concrete when ‘mass flood’ levelling

techniques are adopted – see Section 6.2.1. As well as checking the resistance

of the steel beams, this will involve an assessment of their stiffness. Beams that

are not suitably stiff will deflect excessively during concrete placement, and the

extra concrete should be allowed for in the design.

When designing to the Eurocodes, the construction load is defined in

BS EN 1991-1-6 and is taken as the same construction load as for designing the

decking, as described in Section 4.1.2. The self weight of the wet concrete is

treated as a variable load. The construction loading is significantly more

onerous for beams than previous UK practice and, at the time of writing,

consideration is being given to address this.

When designing to BS 5950, the construction load should be taken as an

‘imposed load’ of not less than 0.5 kN/m

applied uniformly over the supported

area. The construction loading should be applied in addition to the self weight

of the concrete, reinforcement and decking. This non-composite check may

dictate the final choice of section size if subsequent imposed loads are low.

To use a steel beam economically, the top (compression) flange needs to be

restrained laterally. The restraint provided by the decking to the beams depends

on the decking orientation and the fixings. The restraint provided by decking

spanning in a direction parallel to a beam is normally assumed to be negligible,

but decking spanning perpendicularly to a beam can provide restraint if it is

adequately connected. In this latter case, continuous lateral restraint occurs

when thru-deck welded shear connectors are provided (irrespective of other

fixings), but when there are no shear connectors, restraint is limited by the

resistance of the fixings. This will depend not only on the shear resistance of an

individual fixing (typically, 0.8 kN to 4.0 kN, according to the type of fixing),

but also on their spacing along the beam. The Structural Designer should ensure

that the restraint assumed in the design is provided by the fixing arrangement;

guidance on the force that must be resisted is given in the SCI publication

Lateral stability of steel beams and columns

[48]

and BS EN 1993-1-1 (or

BS 5950-1).

Check that the steel beam size chosen is capable of supporting the wet

weight of the concrete, and other construction loads, in its non-composite

state.

Check that beam deflections during construction will not lead to significant

additional concrete loads (due to ponding) that have not been allowed for in

the design.

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The decking will only provide lateral restraint to the beams during

construction if the resistance of the fixings is adequate, and where the

decking ribs run perpendicular to the beams.

5.2 Composite stage

5.2.1 Design for resistance

Composite beams are generally designed in accordance with either

BS EN 1994-1-1 or BS 5950-3. In both cases, the bending resistance of the

section is normally evaluated using ‘plastic’ principles (provided the cross

section will not be subject to local buckling). The calculated resistance is then

independent of the order of loading, i.e. whether the beam is propped or

unpropped during construction. The resistance should be adequate for the

maximum total design moment at the ultimate limit state.

The plastic moment resistance is calculated using idealised rectangular stress

blocks, as shown in Figure 5.2. In BS EN 1994-1-1 it is assumed that stresses

of f

and 0.85 f

can be achieved in the steel and concrete respectively, where

(=f



) is the design yield strength of the steel and 0.85f

is the bending

compression resistance of the concrete. It is 0.85 times the design cylinder

strength of the concrete f

, where f



. Equivalent strengths in BS 5950

are p

for the design yield strength of the steel and 0.45 f

for the design

bending compression strength of the concrete (where f

is the cube strength of

the concrete).

The plastic neutral axis may fall within the depth of either the slab or steel

section, depending on the relative areas of these two components.

The area of concrete in compression is limited by its effective breadth. This

breadth varies along the length of a beam, as shown schematically in

Figure 5.3. Its form depends on the type of loading, and the end conditions

(simply supported or continuous). However, a simpler form may be assumed for

design. In BS EN 1994-1-1, the effective breadth is defined as constant for the

middle portion of the span and tapering towards each end, as shown in

Figure 5.3. The distance between centres of pairs of shear connectors, b

, is

also included. However, for the serviceability limit state, a constant effective

breadth can be assumed to act over the entire span, based on the mid-span

value. In BS 5950-3, the effective breadth is a constant value for a simply-

supported beam with decking perpendicular to the beam. For both BS 5950-3

Secondary

beam

Shear

connector

Concrete

Decking

Plastic neutral

axis

Idealised stress

distribution

0.85f

Figure 5.2 Plastic analysis of composite section (using

BS EN 1994-1-1 notation)

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and BS EN 1994-1-1 the maximum value of the effective breadth is span/8 on

each side of the centre-line of the beam for both serviceability conditions and

for the ultimate limit state. As well as considering this limit, the width assumed

in design must not exceed the actual slab width available. This is particularly

relevant for edge beams and beams adjacent to openings, where there may be

only a narrow width of slab on one side.

The compressive area of the concrete also depends on the orientation of the

decking. When the decking ribs run perpendicular to the beam, the concrete

contained within the depth of the decking must be neglected (see Figure 5.4(a)).

When the decking ribs run parallel to the beam, the total cross-sectional area of

the concrete may be considered, provided that it lies above the neutral axis of

the composite section (Figure 5.4(b)).

The stress blocks that can be generated in the steel and concrete, and used to

calculate the moment resistance, may be limited by the amount of longitudinal

shear force that can be transferred between the materials at their interface. If

this limit governs, it is called ‘partial interaction’ (see Section 5.3.3).

It is assumed that in both BS EN 1994-1-1 and BS 5950-3 all of the vertical

shear force applied to the beam is resisted by the steel section alone. Design

checks should therefore be in accordance with BS EN 1994-1-1 or BS 5950-3,

which give guidance on the consideration of combined bending and shear. In

addition, the width of the top flange of the steel section must be sufficient to

ensure that the decking does not fail in bearing over the beam.

Figure 5.3 Effective breadth profile of a simply supported beam

according to BS EN 1994-1-1

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The concrete adjacent to the steel beam forms a structural flange, and the

presence of openings in the slab will therefore influence the performance of

the beam.

Avoid placing slab openings next to beams (within the effective flange

width) wherever possible. If such openings cannot be avoided, their effect

must be included in the beam design.

5.2.2 Design for serviceability

Deflections

Composite beams are generally shallower (for any given span and loading) than

non-composite beams, and they are used commonly in long span applications.

Consequently, deflections are often critical. BS EN 1990

[49]

(and BS 5950-1)

recommends that deflections should not affect the appearance, the comfort of

users or the functioning of the structure.

In addition to the ‘traditional’ deflection check under imposed loads, it is also

prudent to check deflections due to the following:

 Total (in-service) loads – the combined dead and imposed loads should be

considered to ensure that floor curvatures will not be unacceptable (see

comments below on deflection limits). This is particularly important for

long spans if there is limited depth available in the zone for under-floor

services.

 Construction loads – although not a serviceability deflection limit, it is

necessary to check that excessive concrete ponding will not apply

significant extra loading to the structure.

For edge beams supporting cladding, it is important that the deflections are

checked under cladding and imposed floor loads to ensure that the deflection of

the beams does not compromise the performance of the cladding.

‘Uncracked’ elastic section properties should be used to calculate the deflection

of simply supported beams (the total area of concrete within the effective flange

width is considered, even that part which in reality will be cracked in tension).

A transformed section is used; the effective width of the slab is reduced using a

Secondary

beam

Deck

Shear

connector

Effective breadth Effective breadth

Secondary

beam

Primary

beam

Idealised available

compressive area of slab

(

)

(

)

Figure 5.4 Composite beams incorporating composite slabs. (a) Deck

perpendicular to secondary beam. (b) Deck parallel to

primary beam

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modular ratio equal to the elastic modulus of the steel divided by that of the

concrete. The effect of creep of the concrete is taken into account by choosing a

modular ratio between one based on short term concrete properties and one

based on long term properties, according to the mix of long and short term

When designing to BS EN 1994-1-1, the increased flexibility of the composite

beam caused by greater slippage between the concrete slab and the steel section

when using partial shear connection may be ignored if the degree of shear

connection is not below 50%. However, BS 5950-3 requires an additional

deflection to be included using a modification factor.

For the calculation of deflections where props are used, all the loads are applied

to the composite section.

Deflection limits for beams subject to imposed load are recommended in the

National Annex to BS EN 1993-1-1 (or BS 5950-1). As a more comprehensive

guide, the deflection limits given in Table 5.1 may be considered in design.

Table 5.1 Suggested deflection limits for composite beams

Beam Type Load Case Limit

Absolute Limit

(mm)

Imposed load Span/360 To suit finishes

Total load Span/200 To suit finishes

Internal beams

Dead load at construction

stage

–

‡

Imposed load Span/500 To suit cladding

Imposed load + cladding

Span/360 To suit finishes

Edge beams

supporting both

floor and cladding

Total load Span/250 To suit cladding

Edge beams

supporting cladding

only

Cladding weight Span/500 To suit cladding

Notes:

‡ Although not a serviceability criterion, this is to limit the additional load due to ponding of the

concrete, consequent on beam deflection.

Where dead load deflections are excessive, pre-cambering may be appropriate

(this is normally only adopted for beams longer than 10 m). However, the

pre-camber required may be difficult to determine accurately; for example, the

stiffening effect of the end connections may be significant, so some pre-camber

may remain after casting, and the depth of the slab may not be as intended at

the critical point of mid-span. Therefore, a general rule of thumb is to design

any pre-cambering to eliminate no more than two thirds of the dead load

deflection. In some situations, large amounts of pre-camber may possibly hinder

the laying of decking.

Further information on methods of calculating deflections are given in Design of

composite slabs and beams with steel decking

[43]

. For the assessment of beam

with web openings, additional guidance may be found in Design of beams with

large web openings for services

[50]

The deflection limits used in design should be chosen to suit the building

details.

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Pre-cambering can be used to limit beam deflections under dead load.

Assessing the amount of pre-camber needed may prove difficult, and

calculations should take into account the likely stiffness of the connections.

Irreversible deformation

In BS EN 1994-1-1 there is no specific requirement to limit stresses at the

serviceability limit state (see clause 7.2.2). In BS 5950-3, the stresses in simply

supported composite beams at the serviceability limit state, calculated using

elastic principles, are limited to p

in the bottom fibres of the steel section, and

0.5 f

in the concrete slab. Full shear connection, with negligible slip, may be

assumed when calculating these stresses. Any part of the concrete in tension

should be neglected when calculating stresses (‘cracked’ section properties

should be assumed – unlike the procedure for calculating deflections, when

uncracked properties may be assumed). A similar limitation could be applied

when designing to BS EN 1994-1-1, whereby the steel stress would be limited

to f

and the concrete stress

to 0.63 f

In unpropped construction, the stresses should be calculated first for the

non-composite section subjected to the loading at the construction stage, and

then those for the composite section should be added. In propped construction,

the stresses due to the construction loading are often ignored.

Dynamic sensitivity

Traditionally, the parameter used to assess the dynamic sensitivity of a floor is

its natural frequency. This allows a simple assessment of what is, in reality,

very complex behaviour. A frequency of 4 Hz is a commonly accepted lower

limit for the natural frequency of an individual composite floor beam, as this

will generally mean that the frequency of the entire floor system is greater than

3 Hz, and therefore ensure that excitation activities do not occur at a frequency

that coincides with that of the floor. A higher frequency limit may be

appropriate for applications such as dance floors and gymnasia.

The natural frequency of a floor beam may be determined from the approximate

formula f = 18/√, where



is the static deflection (in millimetres) resulting

from the application of the self-weight of the floor, plus that of the ceiling and

finishes, plus 10% of the imposed loading applied to the composite beam.

Partitions tend to increase the damping and stiffness of the structure, and are not

included in the loading.

Floors are likely to be more ‘lively’ in situations where there is a grid of

primary beams and secondary beams. In these cases, the cumulative deflection

of the slab, secondary beams and primary beams (i.e. the total deflection in the

middle of the slab) should be assessed, and a combined floor frequency

calculated. A method for determining the combined frequency is set out in

Design of floors for vibration: A new approach

[51]

. This publication also includes

methods for determining the likely accelerations of a floor when subjected to

vibration, in terms of Response Factors, and it is recommended that this more

detailed analysis is used to assess the dynamic sensitivity of a floor.

Long span applications, for which composite beams are often used on account

of their excellent resistance and stiffness characteristics, often have a relatively

low natural frequency. However, they also tend to have a high effective mass.

The consequence of this is that the inertia of the floor relative to the impacting

dynamic loads is large, so that floor accelerations (which are what dictate

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occupant comfort) remain acceptably low. This means that even if the natural

frequency limit is not satisfied, a full calculation of the floor response may show

it to be satisfactory. Further information may be found in Reference 51.

5.2.3 Design for fire resistance

Typically, composite beams are design to achieve the required fire resistance by

applying fire protection materials. Three methods of protection are commonly

used; boards, sprays and intumescent coatings. Fire protection adds to the cost

of the structural frame and has implications on the construction programme, as

another trade has to be accommodated in the construction programme. There are

alternative methods of design available which limit the extent of fire protection

required on composite floor plates, as described in SCI publication, P288

[52]

It is also possible to take the fire protection operations for beams off-site.

Off-site intumescent coatings are becoming increasingly popular because, unlike

traditional forms of protection (which are applied on site), the operation is not

on the critical path and is not affected by the weather. Although better handling

and storage of the sections is required with offsite coatings, any slight damage

can be touched up easily. Through-deck stud welding on site will have an affect

on the intumescent coating, but does not prohibit the use of off-site protection of

composite beams. Further information is available in Structural fire design:

Offsite applied thin film intumescent coatings

[53]

For composite beams that are to be fire protected, a ‘critical temperature’ needs

to be established in order to enable the required thickness of fire protection to

be determined. Methods of determining the failure temperatures are provided in

BS EN 1994-1-2

[28]

and BS 5950-8

[11]

. The terminology used to describe these

methods is different in each Standard but they both provide a calculation model

for determining the relationship between beam failure temperature and the load

applied in fire conditions. The thermal properties of proprietary fire protection

systems are not readily available in the public domain. However, Table 5.2

provides an initial estimate for the critical temperature for composite beams

subject to bending. More comprehensive information is given in the NA to

BS EN 1994-1-2 and in BS 5950-8. The load level at the fire limit state η

should be calculated as follows:

td,fi,





where

fi,d,t

is the design value of the effects of actions at the fire limit state and

is the design resistance at normal temperature.

For beams designed to the Eurocodes, it is recommend that the resistance of the

composite beam is verified by calculation of the moment resistance

fi,Rd

using

the procedure given in BS EN1994-1-2 §4.3.4.2, which is described in more

detail in P375

[30]

. The temperature of the steel for this calculation should be

based on the value of critical temperature obtained from Table 5.2. Table 5.2

has been calculated on the basis of a uniform temperature for the steel section.

There is no limitation on the depth of the section that may be designed using the

temperatures from Table 5.2, and the temperatures are appropriate for all values

of shear connection. For beams designed to BS 5950-8, the use of the limiting

temperature method is recommended.

Beams with web openings present a particular problem as far as the

specification of fire protection is concerned, as the critical mode of failure may

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be related to buckling of the web posts between the openings rather than global

bending at the point of maximum applied moment. The performance of the fire

protection material has also been found to influence the critical temperature.

The critical temperatures given in Table 5.2 should not be applied to beams

with web openings. Further guidance on fire protection of cellular beams is

given in RT1187

[54]

Table 5.2 Critical temperatures for composite downstand beams

Critical Temperature (ºC) for a load level η

of:

Description of member

0.7 0.6 0.5 0.4 0.3 0.2 0.1

Unprotected or protected

composite members in

bending supporting concrete

slabs or composite slabs

535 567 600 641 680 738 838

When the ribs of the profiled steel decking run across the steel beams, voids are

created between the decking and the top flange of the steel (see Figure 5.4).

Although additional heat enters into the steel beam via these voids,

BS EN1994-1-2 recommends that the voids are ignored if at least 85% of the

surface of the top flange is in contact with the slab. This means that for re-

entrant decks the voids do not need to be filled. However, for trapezoidal decks

the voids must be filled - or the effect of the voids on the beam temperature

must be considered when determining the critical temperature of the section.

This is beyond the scope of the simple thermal model given in BS EN1994-1-2.

Therefore, if the voids are to be unfilled, the temperature of the beam must be

determined from tests or advanced analysis.

Fire tests in accordance with BS 476

[55]

have shown the effects of unfilled voids

on structural performance

[56]

. As UK Building Regulations still recognise the

BS 476 test methods, this guidance may still be used in the UK - although this

situation may change in the future. Guidance in accordance with P109

[56]

given in Table 5.3 to identify when special measures must be taken because of

these voids, and what they should be. In some cases it may be necessary to

increase the thickness of fire protection to compensate for the adverse effect of

the voids, or they may be filled.

It should nevertheless be remembered that, for all beams forming part of a fire

compartment, the voids should always be filled to avoid affecting the integrity

of the compartment wall.

Where the voids have to be filled, it is not necessary to use the same material as

that used to protect the beam; any non-combustible material will suffice.

For beams with decking orientated parallel to them, the edges of the top flange

must be protected; when board protection is used, the boards should be taken

past the edge of the flange to abut the underside of the decking.

It is not always necessary to fire protect the voids between the steel flange

and decking. Specifying such protection unnecessarily will lead to increased

costs.

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Table 5.3 Recommendations for fire protection of voids between

profiled steel decking and steel beams in composite floor

construction

Trapezoidal deck

Fire Resistance (minutes)

Beam Type

Fire Protection

on Beam

Up to 60 90 Over 90

Composite

Insulating

sprays and

boards

(assessed at

550̊ C)

No increase in

thickness

Increase

thickness by

10 % or assess

thickness using

A/V increased

by 15%*

Fill voids

Intumescent

coatings

(assessed at

620̊ C)

Increase thickness

by 20% or assess

thickness using

A/V increased by

30%*

Increase thickness

by 30% or assess

thickness using

A/V increased by

50%

Fill voids

Non-composite All types Fill voids

Dovetail deck

Fire Resistance (minutes)

Beam Type

Fire Protection

on Beam

Up to 60 90 Over 90

Any All types

Voids may be left unfilled for all periods of fire

resistance

* The least onerous option may be used (A/V=heated surface area per unit volume of the steel

section)

5.3 Shear connection

The longitudinal shear connection between the steel section and the concrete is

provided by shear connectors, which normally take the form of studs welded to

the top of the steel section. All connectors should be capable of resisting uplift

forces caused by the tendency for the slab to separate from the beam as it

bends. In the case of shear studs this is achieved by the head of the stud.

Although shear connectors ensure adequate fixing of the decking to the beam,

they are not needed simply to achieve this. They should only be used when it is

desired to achieve composite action between the slab and the steel beam, or to

tie the slab at edge beams when the floor acts as a diaphragm.

5.3.1 Connectors

The most common type of shear connector used in composite beams for

buildings is a 19 mm diameter by either 100 mm or 125 mm long welded stud.

For thru-deck welding (see below), this is the only stud diameter that can be

used practically, because it is the only one for which suitable ferules are

available. Although other heights are available, they are not so easy to obtain.

There are a number of other forms of shear connector available, such as angles

welded to the top flange. However, most lack a practical application in

composite beams, with the exception of shot-fired connectors. These should be

considered for smaller projects, those where beams need to be galvanized or top

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flanges painted for reasons of durability, or indeed any project where the

provision of power for stud welding is a problem. They may be particularly

appropriate for refurbishment projects, where there is either limited access or no

earthing facility. The most common shot-fired shear connector is that produced

by Hilti, which is available in heights of 95 mm to 140 mm. It should be noted

that a shot-fired connector has less resistance than a welded stud. Design

guidance and design values of the shear resistance should be obtained from the

supplier.

It should be noted that a shot-fired connector has less resistance than a

welded stud. Design guidance should be obtained from the supplier.

Resistance

Design resistances of shear studs are given in BS EN 1994-1-1 and BS 5950-3,

based on standard push-out tests on samples with ‘standard’ fabric

reinforcement. However, tests have also been carried out on specimens with

fibre reinforcement, and these results show they perform at least as well as

those with fabric reinforcement. The design resistance is a function of the:

 shape of the decking profile

 size, strength and number of connectors per decking trough

 concrete properties

 the sheet thickness (according to BS EN 1994-1-1)

In BS EN 1994-1-1, the resistance of a stud in a solid slab is calculated directly

from formulae which include terms for the concrete strength and modulus. The

concrete modulus can be found in BS EN 1992-1-1

[24]

, where the value for

normal concrete (

) is given in Table 3.1, and the value for lightweight

aggregate concrete (

lcm

) is given in Table 11.3.1. The presence of shallow

cracking above a beam does not necessitate a reduction in the design resistance

of the shear connectors, because of the presence of the transverse reinforcement

or steel fabric reinforcement.

In BS 5950-3, the design resistance of a stud in a solid slab in normal weight

concrete is given in Table 5, according to concrete strength and stud

dimensions. These values are reduced by 10% when lightweight concrete is

used.

The reason why the efficiency of the shear connectors is reduced when the

decking is orientated with the ribs transverse to the beam is because the force

transferred through the shear connector into the slab relies on a small localised

area of concrete immediately in front of the stud. For this orientation of the

decking, this area of concrete is limited in size by the presence of the profile, as

shown in Figure 5.5. Reduction formulae are given in BS EN 1994-1-1 and

BS 5950-3 to allow for this by considering the relative geometry of the stud and

the decking rib.

As well as the shape and thickness of the decking, the position of the stud in the

trough is important; tests have shown that the integrity of this local area of

concrete can break down if the stud is positioned close to the decking. The

formulae given in BS EN 1994-1-1 and BS 5950-3 assume that studs are located

centrally in the troughs, or are alternated between the ‘favourable’ and

‘unfavourable’ side of the trough. Recommended practice is to place the studs in

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the ‘favourable’ side (see Figure 5.5). This means that, for single studs on

simply supported beams with symmetric loading, the position of the stud in a

trough with a central stiffener must change at mid-span.

The number of studs placed transversely (across the width of the beam) in each

trough also affects their resistance. A reduction factor should be applied to the

design resistance when two studs are present. Note that the design resistances

given in BS EN 1994-1-1 explicitly do not cover more than two studs per

trough. For further information, reference should be made to the Designer’s

guide to BS EN 1994-1-1

[26]

and the Commentary on BS 5950: Part 3:

Section 3.1 Composite beams

[46]

Attachment of studs

‘Thru-deck’ welding is generally used, particularly in the UK, to attach the

shear studs to the steel beams. This process welds the stud, decking and steel

section effectively together in a single operation. A typical run of thru-deck

welded shear studs is shown in Figure 5.7. The Structural Designer should

recognise the following practical limitations before specifying thru-deck

welding:

Cracking

Crushing

Concrete

Moment

on head

Force distribution

in concrete

Force distribution

in concrete

Crushing

Weld

Force

Force Force applied

to slab

c) Off-centre welding of shear connector

a) Shear connector in plain slab

b) Shear connector fixed through profiled sheeting

End of

beam

End of

beam

End of

beam

Unfavourable side Favourable side

Figure 5.5 Shear connector forces in composite slabs

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 The galvanized steel decking should not exceed 1.25 mm thick, and the

total galvanizing thickness should not exceed 0.04 mm.

 The thickness of the top flange of the steel section must not be less than 0.4

times the stud diameter (i.e. 7.6 mm for a 19 mm stud) to prevent localised

bending of the flange at ultimate loading.

 Small numbers of studs are uneconomic because of the amount and expense

of the equipment needed.

 A clear height above a beam of at least 450 mm is necessary to carry out

the process of stud welding, i.e. to give room for the operative and

equipment. (A typical example of where a problem can occur is when there

is a change in the floor level, as shown in Figure 5.6.) In these situations

it may also prove difficult to fix the slab edge trim.

 The need to keep the top of the beam flange free of paint is generally not a

problem (in an internal environment having an exposed, unprotected top of

flange in the ‘voids’ is acceptable). Thru-deck welding may however blister

any paint applied, and required, on the underside of the flange. Remedial

measures may be required for aesthetic, if not corrosion protection,

reasons. An intumescent coating on the underside of the flange might also

be damaged, but would not normally need remedial work other than for

aesthetic reasons.

 A minimum flange width is needed to provide sufficient bearing for the

decking on both sides, end distance from the stud to the sheet when

anchorage from the stud is required (for decking design and to enable the

decking to be included as transverse reinforcement and shear reinforcement),

and transverse distance between studs. Consequently, when the decking is

perpendicular to the beam, flange widths less than 125 mm are not

recommended (see below for advice when pre-welded studs are used).

Further limitations, related to site practice, are discussed in Section 6.5.

450 mm min.

required for

stud fixing

Figure 5.6 Minimum height clearance for stud welding

Thru-deck welding is significantly more economical than the alternative of pre-

welding the studs to the steel beams in the factory, although it is not possible

when the beam has to be galvanized. Problems associated with using pre-welded

studs include:

 Erection becomes more hazardous and therefore slower.

 Decking has to be laid in single spans between the lines of studs, which

requires beams with a sufficient flange width (≥133 mm) to provide the

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minimum safe bearing for the decking on each side of the beam, and the

decking is less efficient as a single-spanning member.

 Alignment of the troughs in decking perpendicular to the beam with

pre-welded studs can be difficult. The flange width should be specified so

that, should they not align, at least 50 mm concrete encasement is provided

beyond the transverse spacing of the studs to the edges of the decking. The

stud resistance may be reduced when studs do not align with the troughs,

and it should be calculated using the reduction factor for ribs parallel to the

beam using the width of encasement provided, rather than the reduction

factor for ribs perpendicular to beam.

Holes may be cut in the decking to avoid these problems, but this leads to other

complications trying to align the studs and holes. Decking placement will

become more hazardous because of the need to slot the studs through the holes,

and so this method is not recommended.

Detailing rules

The following detailing rules apply to the positioning of stud shear connectors,

and are illustrated in see Figure 5.9:

 BS EN 1994-1-1 requires that nominal height (before welding) of the shear

studs should be at least 2

d (where d is the stud diameter) above the top of

the decking. The corresponding requirement in BS 5950-3 is 35 mm. (Note

that the ‘top of the decking’ refers to the height of the shoulder, i.e.

excluding any small stiffening ribs in the crest of the decking.) Studs that

are longer than is necessary to meet these requirements will not have a

greater resistance.

 To avoid damaging the decking, the studs should be located along pre-

determined lines marked on it.

Figure 5.7 A typical run of stud shear connectors

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 The distance between the edge of the shear connector and the edge of the

steel flange should not be less than 20 mm.

 The minimum longitudinal spacing of the studs should be 5d.

BS EN 1994-1-1 states that the maximum spacing should not exceed the

lesser of 800 mm and six times the slab depth. The limit given in

BS 5950-3 is 450 mm, and this latter value is recommended in the light of

recent test evidence

[57]

. It should be noted that studs are often required at

larger spacings than these on non-composite beams for other purposes, such

as restraint of the beam.

 The transverse stud spacing should not be less than 2.5d in sold slabs and

d in other cases.

 Studs should normally be placed uniformly along the length of the beam;

one (or a pair) in every trough of the decking, or one in alternate troughs.

Any additional studs noted on the drawing that cannot be placed in equal

numbers in all the troughs should be positioned symmetrically about the

mid-span of the beam, working from the supports inward (assuming

uniformly distributed loading).

 When the decking has a central stiffener in the trough (which makes it

impossible to attach the stud centrally), the studs should be attached on the

favourable side of the trough. For symmetrically loaded beams, this will

involve a changeover of position of the stud at mid-span.

 At discontinuities in the decking, the studs should anchor both sheets. The

minimum distance from the centre of the stud to the edge of each sheet

should be 30 mm. Because of this, beams with flange widths less than

125 mm are not recommended – see notes on attachment of studs, above.

[Note that studs should never be welded through two layers of decking. At

joints, it is recommended the decking should be butted, and when studs are

in single lines they should be welded alternately on one sheet then the

other, and when in pairs they can be welded one on each.]

 Studs attached to edge beams should be placed no closer than 6d (from the

stud centre-line) to the slab edge, as shown inFigure 5.8. Where the slab

edge is less than 300 mm from the line of the studs, ‘U’ bars should be

specified around the studs in accordance with BS EN 1994-1-1 (or

BS 5950-3) to prevent bursting of the concrete near the slab edge.

edge distance

(flange)

20 mm

edge distance

(decking)

30 mm

50 mm

edge trim

bearing

Figure 5.8 Shear connector detailing at an edge (for 19 mm diameter

studs)

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a) Single shear connector per trough in staggered pattern

Stiffener

ELEVATION

Mesh



b) Pairs of shear connectors per trough in staggered pattern

Decking trough

Beam



Beam

Shear connector

to stud centreline

20 mm



to edge of stud

e) Shear connectors on decking laid parallel to beam

Beam

c) Correct positioning of pairs of studs not in a staggered pattern

Shear connector



End of

span

End of

span

d) Butt joint in decking (correct positioning of single stud per trough)

Stiffener

To end

of span

Beam

To mid-span

Non-beneficial side Beneficial side

25 mm



Butt joint

in decking



20 mm

95 mm

76 mm

57 mm



30 mm

95 mm

Figure 5.9 Detailing of shear connectors (19 mm diameter) welded

through decking

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5.3.2 Longitudinal shear

Composite beams may be designed plastically if the shear connectors are

sufficiently ductile. This enables a plastic shear connection resistance to be

assumed, whereby the maximum resistance in each connector is assumed to

occur simultaneously down the length of the beam. BS EN 1994-1-1 states that

19 mm diameter studs with a ‘length as welded’ greater than 76 mm may be

assumed to satisfy this requirement. The total longitudinal shear force that can

be transferred across the steel-concrete interface is the sum of the resistances of

the shear connectors positioned within the length between a support and the

point of zero bending moment. Where the loading is asymmetric, the lesser of

the resistances totalled either side of the point of zero bending should be used.

Transverse reinforcement

The longitudinal shear resistance of the concrete slab must be checked to ensure

that the force from the shear connectors can be transferred into the slab without

splitting the concrete. This requires the provision of transverse reinforcement

(perpendicular to the beam centre-line). It is usually found that fabric or fibre

reinforcement is sufficient for the design of secondary beams, where the

decking ribs run perpendicular to the beam (as shown in Figure 5.10(a)). For

beams where the ribs run parallel to the beam (Figure 5.10(b)) additional bar

reinforcement is likely to be required. Potential shear planes through the slab lie

on either side of the shear connectors (Figure 5.10). However, plane b-b need

not be checked for composite slabs with decking because characteristic stud

resistances are determined from tests which allow for this type of failure. The

shear resistance per unit length of shear plane along the beam is a function of

the concrete strength and the amount of reinforcement provided.

For edge beams, ‘U’ bars should be positioned as low as possible but with

sufficient bottom cover for the aggregate to flow (BS 5950-3 states that the bars

should be placed at least 15 mm below the head of the stud, although there is no

such requirement in BS EN 1994-1-1).

The decking may also act as part of the transverse reinforcement to contribute

to the longitudinal shear resistance. The full resistance of the decking can be

used when it is placed transverse to the beams and is continuous. In situations

where the decking is discontinuous, the anchorage force that can be developed

by the shear connectors limits this action, but the decking contribution may be

Cover width of decking

Mesh reinforcement

ccd

)

Figure 5.10 Potential failure planes through the slab in longitudinal

shear (a) Decking perpendicular to beam

(b) Decking parallel to beam

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included, provided that there is sufficient end distance of the decking beyond the

centre line of the studs. Guidance on the anchorage resistance is given in

BS EN 1994-1-1 (clause 9.7.4(3)) and in BS 5950-4 (clause 6.4.3), but

minimum values are quoted as 1.65 times stud diameter in the former and 1.7

times stud diameter in the latter.

The contribution of the decking should always be neglected where it is not

properly anchored at discontinuities, or where the decking ribs run parallel to

the beam. In theory, when the decking is parallel to the beam and properly

anchored, some contribution to the longitudinal shear resistance could be

included. However, including this contribution is not recommended because the

decking resistance is affected by the (unpredictable) presence of laps on site;

this approach is consistent with BS EN 1994-1-1. Studs fixed in a single line at

a butt joint in the decking do not provide sufficient anchorage for the decking to

contribute to the transverse reinforcement. Further guidance on transverse

reinforcement can be found in AD 192

[58]

and AD 266

[59]

Transverse reinforcement is always needed to ensure adequate

performance of the shear connection. Fabric may be sufficient, but a check

is always necessary, particularly for primary beams. Fabric is preferred

because it minimises the need for steel fixers to work in a bent position.

The contribution of the decking to the transverse reinforcement can only be

included if it is properly anchored, and this depends on a number of factors

- continuity of the decking, decking rib orientation, and laps in the decking.

The contribution of the decking should always be neglected where the ribs

run parallel to the beam.

Bending resistance envelope

The bending resistance of a composite beam depends on the shear transfer

between the beam and the slab. Consequently, the resistance increases away

from the supports; the resistance at a given point is a function of the resistance

moment of the bare steel beam and the number of connectors between that point

and the nearest support.

For a beam subject to uniformly distributed load, the maximum design moment

is at mid span. It is only necessary for the Structural Designer to check the

moment resistance at this point, and determine the total number of connectors

needed to transfer the load into the slab (see Section 5.2.1 and Figure 5.3);

these connectors may be evenly distributed between the support and mid-span.

For beams subject to point loads, it is necessary to check the resistance moment

at intermediate points, not just the point of maximum design moment. For

example, Figure 5.11 shows a beam with four point loads, the applied bending

moment diagram, and a resistance moment that is just sufficient at each of the

four load positions. To achieve the required resistance at the intermediate point

‘A’, the number of connectors between that point and the nearest support must

enable sufficient force to be transferred to the slab to achieve the required

resistance

. With a heavy point load close to the support, it may not be

possible to accommodate the required number of studs over that short length.

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5.3.3 Degree of shear connection

The maximum longitudinal shear force that is required to be transferred from

the steel to the concrete is the lesser of the compressive force to cause concrete

crushing, and the force that would cause yielding of the steel section in tension.

If sufficient shear connectors can be provided to transfer this force, the full

plastic resistance moment of the composite section can be achieved. This is

known as providing ‘full shear connection’ (sometimes referred to as full

interaction).

‘Partial shear connection’ refers to situation in which fewer shear connectors are

provided. In this case, the stress block method used for calculating the

resistance moment (see Section 5.2.1) must be modified to take into account the

reduced longitudinal force that can be transferred. The use of partial interaction

often results in improved economy, especially where the number of shear

connectors is limited by the spacing of the ribs in the decking.

Deformation of the shear connectors allows slip between the concrete and the

steel section. This slip is zero at the point of maximum bending moment (often

at mid-span) and increases towards the supports; the longer the beam span, the

greater the slip at the supports. For partial shear connection, because there are

fewer shear connectors, there will be more slip for a given load than with full

shear connection. To avoid any adverse effects arising from excessive slip, a

minimum limit to the degree of shear connection is specified in BS EN 1994-1-1

and BS 5950-3, although the rules differ between them slightly.

Further guidance on the degree of shear connection can be found in AD 266

[59]

5.4 Further reading

The references given below relate particularly to beam design - see Section 4.5

for additional design guidance related more to slabs. (For information on

authors and publishers, see Section 8, References.)

Interfaces: Design of steel framed buildings for service integration (P166)

[35]

This design guide outlines the various services that have to be integrated into

the floor zone of a building and illustrates how this may be achieved with

several different structural steel floor framing systems, many of which

incorporate composite floors.

N = (N +N )

Resistance moment

envelope (M )

Total No. of connectors

Intermediate

load point

Applied load (M)

Number of connectors between load points

PP P P

M( M )



Steel section

resistance

moment

(M )

Figure 5.11 Shear connector distribution for beams subject to point

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Designer’s guide to BS EN 1994-1-1

[29]

This guide provides the detailed background to the clauses to Eurocode 4. It

includes many worked examples that show the application of the individual

clauses. It is a standard reference for designers of composite beams to EC4.

Commentary on BS 5950: Part 3: Section 3.1 Composite beams (P078)

[46]

This is a comprehensive guide that provides the background to the clauses in the

BS 5950-3. It discusses the relevant research, and includes a worked example of

the design of a composite beam. It is an essential reference for designers of

composite beams in the UK.

Design of beams with large web openings for services (P355)

[50]

This guide provides a design method for both composite and non-composite

beams with web openings. A model for the complex force distribution around

an opening is explained, from which a simplified method for stiffened and

un-stiffened openings is derived. Guidance on the positioning and size of

openings is included.

P354: Design of floors for vibration: A new approach (P354)

[51]

This guide examines the theoretical aspects of vibrations in buildings caused by

people walking. It shows how floors may be analysed for their dynamic

sensitivity, and suggests acceptance criteria for the floor response.

Fire protection for structural steel in buildings (4th Edition)

[60]

This publication explains the basic aspects of fire protection and fire protection

appraisal procedures. It gives application details for most of the products

available, and protection thickness required for different beam and column

exposure conditions. This is the standard design reference for fire protection of

structural steel.

Structural fire design: Off-site applied thin film intumescent coatings (2

edition)

(P160)

[53]

This publication describes the design and specification issues relating to off-site

applied thin film intumescent coatings. An example of a calculation for the

determination of the coating thickness for a steel member is presented. A

‘model’ Specification is also included.

Managing construction for health and safety - Construction (Design and

Management) Regulations, 2007. Approved Code of Practice L144 (ACoP)

[4]

This document contains the Regulations themselves, together with an

explanatory commentary for each requirement. It is an essential source

document.

P178: Design for construction (P178)

[61]

This guide highlights the effects of basic design decisions on the overall

buildability and cost of a building. It is aimed at engineers primarily, but has a

relevance to all those having a design input. It includes a section on the 1994

CDM Regulations.

Advisory Desk

The following ‘Advisory Desk’ items, published by the SCI in New Steel

Construction and on the SCI Steelbiz web site www.steelbiz.org, provide

further information relevant to this Section:

AD 174,

Shear connection along composite edge beams

[62]

. This note outlines a

method for checking the bending resistance of composite edge beams in existing

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buildings where the shear connectors have not been properly fixed, or the

transverse reinforcement has been omitted.

AD 175,

Diaphragm action of steel decking during construction

[7]

. A method is

given in this note for checking the adequacy of the decking to stabilise the

structure by providing diaphragm action. Fixing requirements are given.

AD 192,

Transverse reinforcement in composite T-beams

[58]

. A detailed

description of the principles of longitudinal shear, and the role of transverse

reinforcement, is given in this note. The background to the relevant clauses in

BS 5950-3 is explained.

AD 266,

Shear connection in composite beams

[59]

. This note discusses the basis

for effective breadth rules, the minimum degree of shear connection rules and

transverse reinforcement calculations.

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6 CONSTRUCTION PRACTICE -

CONCRETE

This Section provides information concerning good practice in relation to the

site activities associated with the procurement, placement and finishing of in-

situ concrete. It is aimed at all personnel involved in the site activities.

Guidance on concrete mix design is included, but guidance is not given on

access requirements for concrete mixers, checking of concrete delivery notes

etc. These issues are considered to be general site practice, and not appropriate

for inclusion in a guide on composite construction.

6.1 Concrete supply

Concrete supply is normally the responsibility of the Main Contractor, who

should make sure that it is specified, supplied and assessed in accordance with

BS 8500-1

[17]

to meet the strength grade specified by the Structural Designer.

Basic details for some typical concrete mixes are given in Table 6.1.

Table 6.1 Concrete specifications (extracted from BS 8500)

Aggregate Type Normal weight Lightweight

Strength class

C25/30

C28/35

C32/40

C35/45

C40/50

LC25/28 LC28/31 LC32/35

Maximum water

cement ratio

0.65 0.60 0.55 0.50 0.45 0.65 0.60 0.55

Minimum cement

content (kg/m

)

260 280 300 320 340 260 280 300

Notes:

1. BS 8500-1 does not give universal relationships between strength class and water cement

ratio and minimum cement content. The relationships depends upon the exposure class and

cement types used. The relationships shown in table 6.1 are those given in BS 8500-1 for XC

exposure conditions. Other strength class/water cement ratio/cement content relationships are

listed in BS 8500-1 for other exposure conditions.

2. The minimum cement contents listed are for 20 mm aggregate. Generally minimum cement

contents would need to be increased by 20 kg/m3 for 14 mm aggregate and 40 kg/m3 for

10 mm aggregate

To ensure the quality control of the concrete mix, it should be obtained from a

plant providing concrete in accordance with an approved quality assurance

scheme.

Aggregate types and size

Most composite slabs are constructed with a normal aggregate, but lightweight

aggregate is available.

When normal concrete is specified, the maximum size of the aggregate needs to

be limited to ensure that the concrete may be placed easily into the decking ribs

and between the reinforcing bars.

The nominal dimension of the largest aggregate, which has an angular nature,

should not exceed the smallest of the following limits (see Figure 6.1).

 40% of the concrete cover above the ribs.

 The average width of the decking ribs (trapezoidal decking).

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 One third of the minimum rib width (dovetail decking).

It is recommended that 20 mm aggregate is used whenever possible. When

smaller aggregates are used, the required cement content will increase, and the

shrinkage performance of the concrete will be adversely affected.

With lightweight concrete, aggregate size is not a problem because of the small

rounded nature of the pellets.

Consistence

To ensure that the concrete is sufficiently workable to allow it to be pumped

with the correct flow, and to achieve adequate compaction around the

reinforcement, in the troughs of the decking and around the steel beams in slim

floors, a minimum consistence class of S3 should be specified in line with

BS 8500-1.

Concrete mixes with low consistence should not be used as this can lead more

readily to heaping of the concrete and overloading of the steel deck.

6.2 Placing concrete

6.2.1 Preparation

Prior to beginning work on the decking, guard rails should be in position at all

perimeters, internal edges and voids. The positions of any props (and back

props) should be checked against the details shown on the decking layout

drawings to ensure that the required support has been provided.

Cleaning the decking

The surface of the decking should be reasonably free of dirt, oil, etc. prior to

concreting. The slight surface grease that is present on the decking when it is

delivered to site does not affect the interaction between the concrete and steel,

Height of

concrete

above ribs

Height of

concrete

above ribs

a) Open profile

b) Dovetail (re-entrant)

rofile

Average

trough width

Minimum

trough width

Figure 6.1 Nominal cross-sectional dimensions used to determine

maximum concrete aggregate size

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and therefore need not be removed. Though recommended, it is not essential to

clean out all the broken ceramic ferrules from stud welding.

Construction joints

Typical pour sizes are up to 1000 m

/day, although there is no technical

limitation to the area that may be concreted. Where the limits of the pour do not

coincide with permanent slab edges, construction joints (day joints) are used to

define the extent of the pour.

Where possible, the construction joints should be located close to butt joints in

the decking. For conventional composite beams, it is preferable to create the

joint to one side of the line of the shear connectors, to ensure sound concrete

around the studs. This does not affect the resistance of the shear connectors. If

the construction joint cannot be made near a butt joint, it is suggested that no

more than one-third of the decking span from a butt joint should be left

unpoured, as shown in Figure 6.2. Concreting should not be stopped within a

sheet length with more than this left unpoured because excessive deflections

might occur when the loads on a continuous decking sheet are not balanced

either side of the intermediate support beam.

Stop ends, usually in the form of timber or plastic inserts, are used to create the

construction joints. As with all the joints and ends of the decking, they should

be checked for potential grout loss.

A construction joint will form a discontinuity in the slab, so it is important that

continuity reinforcement is provided across the joint. When fibre reinforcement

is used, continuity reinforcement in the form of conventional reinforcing bars or

a strip of steel fabric will be required at construction joints. The decking

supplier should be consulted regarding the continuity reinforcement required in

fibre reinforced slabs. The occurrence of cracking in the concrete adjacent to

day joints is normal, and does not affect the structural performance. If the size

of the crack at the construction joint is important, e.g. when brittle finishes are

being used, the reinforcement should be sized to control the crack width by the

structural designer. Alternatively, there are commercial systems for decoupling

brittle finishes from the underlying composite concrete slab, and guidance on

their use should be sought from the supplier.

Bar and fabric (mesh) reinforcement

All bar/fabric reinforcement should be properly supported so that it does not

become displaced during concreting. Plastic stools, loops or preformed fabric

may be used as ‘chairs’, but not plastic channels, which can induce cracking.

Chairs should be robust, because operatives will need to use the floor as a

working platform for themselves and their equipment. In particular, the handling

1/3 max

Span

Deck

Intermediate decking

orts

Concrete

Dec

butt

joint

Construction joint

preferred position

Construction joint

alternative position

Figure 6.2 Recommended positions for construction joints in the

concrete slab

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and movement of concrete-filled pipes during pumping can cause significant

local impacts on the fabric reinforcement. Although a slight depression (up to

15 mm) of the fabric may occur during concreting, the performance of the slab

is not affected significantly by this. An example of a floor with the

reinforcement in place and ready for casting is shown in Figure 6.3.

The reinforcement that has been fixed should be checked against the slab

reinforcement drawing. Particular attention should be given to checking any

additional bar reinforcement, such as may be needed around openings, across

composite beams and U-bars for composite edge beams.

Fibre reinforcement

When steel or polymer fibres are used, they are added to the concrete mix at the

batching plant, or directly in to the mixer on site. Fibre reinforced concrete can

be pumped to elevated floors, as shown in Figure 6.4. When using a fibre

reinforcement solution, it is still general practice to use U-bars on composite

edge beams, bar reinforcement around openings in the slab, and fabric or bar

reinforcement at construction joints, or where the composite slab cantilevers

beyond a support. When preparing for concreting, the site team should ensure

that any such bars/fabric are present.

Grout loss

The decking joints should be closely butted and exposed ends should be

‘stopped’ with proprietary filler pieces to avoid grout loss. Gaps greater than

5 mm should be sealed, but gaps smaller than this do not need any special

provision normally. Small gaps may be spray-filled with expanding polyurethane

foam.

Figure 6.3 Decking and fabric reinforcement – ready for casting the

concrete

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Tamping rails

Tamping rails should be placed close to the beam centre-lines, to avoid

excessive deflection during concreting. The level of the concrete top surface will

then tend to reflect the deflected shape of the beams.

Mass flood technique

Where a ‘mass flood’ technique of casting (whereby the concrete is poured and

the whole floor levelled to a fixed datum) is used, considerably more concrete

will be needed and thicker slabs will result from deflections of the steelwork

and decking. Levelling to a fixed datum should not be adopted without first

confirming with the Structural Designer that the extra weight of concrete

‘ponding’ has been allowed for in the design.

6.2.2 Placement

The concrete should be well compacted, particularly near and around any shear

connectors. This can be done using a vibrating beam, which will require

adequate supports at both ends, or by an immersion poker vibrator. Hand

tamping is not recommended as a way of compacting the concrete.

Concrete can be placed when the air temperature is 5°C or above. In cold

weather, it may be necessary to make provision to maintain this temperature

during at least part of the curing period (see below).

Concrete pumping

Pumping has become the normal way of placing concrete, and can be adopted

for both normal and lightweight aggregate mixes. Flow rates in the order of 0.5

to 1 m

of concrete per minute can be achieved, although, clearly, the longer

the pump lines and the higher the concrete is to be pumped, the slower the

operation. A pump can normally ‘lift’ the concrete up to 30 m. Secondary

pumps, placed at intermediate levels, may be necessary for higher lifts.

Figure 6.4 Pumping of fibre-reinforced concrete

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Pump lines are normally 150 mm in diameter and are assembled in segments.

Because the force exerted at bends can be significant, straight line pumping is

preferred. The lines should be supported on timber blocks at intervals of 2 to

3 m. Resetting of pump lines is required at frequent intervals as the pour

progresses. This means that the outlet pipe should be moved frequently and

carefully so that concrete heaping is minimised. A minimum of two operatives

are necessary for this operation, one to hold and manoeuvre the outlet pipe, the

other to shovel away excess concrete. No more than 4 workmen should be

present around the pipe outlet during pumping, because of the potential for

overloading the decking. The concrete should not be dropped from the outlet

pipe onto the decking from a height of more than about 1 m.

Any low quality concrete (the first part of each lorry load, or after flushing out

pipeline blockages) should be discarded.

Skip and barrow

Ideally, concrete should always be placed by pump, but there will be occasions

when small areas need to be concreted where placing by pump is not practical.

Considerable care is needed if a skip and barrows are to be used, to ensure the

decking is not overloaded. It would be preferable to discharge concrete into

barrows on previously constructed areas, to avoid concrete being discharged

directly from a skip onto decking. Placing concrete from a skip hung from a

crane may be difficult because of obstructions from beams and decking at higher

floor levels. However, despite being time consuming (progress rates rarely

exceed 5 m

per hour), it is sometimes efficient to use the skip and barrow

technique for small infill bays.

Skips should have a means of controlling the rate of discharge, and should not

be discharged from more than 0.5 metres above the decking or barrow. When

discharging into a barrow, the barrow should be supported by thick (30 mm)

boards covering a 2 m by 2 m area, or by a finished part of the slab. Either

provision limits impact loads. Barrows should be run over thick boards placed

on the fabric reinforcement, which should be supported locally.

Testing

The concrete should normally be tested in accordance with the requirements of

BS EN 12350

[63]

. At least two cubes will need to be taken from every 20 m

delivered and batched, or two cubes per day if the quantity used that day is less

than 20 m

. The cubes are crushed at 28 days, and the average of the two cubes

strengths becomes the individual 28 day result for the batch sampled. Additional

cubes may be taken for testing at 7 days, or other ages, for the determination of

early strengths.

6.2.3 Finishing, curing and drying

The concrete surface finish is normally specified by the Structural Designer

(Section 4.2.1). If power-floating is to be carried out, this should be done

within 2-3 hours of casting. This allows time for the concrete to sufficiently

harden.

Experience shows that there is a high risk that well trowelled surfaces will

exhibit crazing

[64]

. Crazing is the term used to describe an irregular polygonal

pattern of fine interconnected cracks which often occur on power trowelled

concrete surfaces. Crazing should not be considered a defect and it generally

has no adverse effect on the performance of the floor surface.

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Although concrete normally gains strength relatively quickly, it is necessary to

keep temperatures above 5°C for at least 3 days after pouring. When concreting

during the winter months, loss of heat, such as by radiation from the lower

surface of the decking at night, can be significant. It may then be necessary to

use space-heaters to maintain the temperature. Some heat is generated during

setting, or ‘hydration’, of the concrete (this raises the temperature by 3 to 5°C,

typically).

The moisture in the concrete should not be allowed to evaporate too early,

otherwise the surface may lose its integrity, forming dust and possibly cracking,

and it will not have a good abrasion resistance. The slab therefore needs to be

‘cured’ by covering the surface with polythene sheeting for 3 to 7 days,

depending on the weather (this is particularly important in warm or windy

weather). Alternatively, the concrete may be sprayed with a proprietary curing

compound.

Because the concrete is only exposed on one surface of a composite floor, it can

take longer than a traditional reinforced concrete slab to dry out. The preferred

method of checking the moisture content of the slab is the insulated hygrometer

method given in BS 8203

[65]

6.3 Loads on the slab during and after concreting

6.3.1 Loads during concreting

Loads during concreting arise mainly from the weight of the operatives,

concrete, pump-lines and impact forces. Loads to be taken into account for

design during concreting are specified in BS EN 1991-1-6 and in BS 5950-3,

and are outlined in Section 4.1.2. The self weight of the finished slab (typically

2 to 3 kN/m

) and local loading (caused by normal localised heaping of the

concrete) are included. This is usually not critical because adjacent areas of

decking are unloaded, or only partially loaded.

The following list describes the loads that usually arise during concreting, and

that will normally have been allowed for by the Structural Designer:

 A concrete gang consisting of 5 or 6 men (only 4 of whom are within 2 m

of the pump outlet).

 Concrete that is poured from no higher than knee level above the decking

(to avoid excessive impact loading).

 A 150 mm diameter pipeline full of concrete. [The weight of the line

should be adequately spread across the decking by using suitable timbers to

avoid local damage to the deck.]

 A cone of heaped concrete of approximately 0.2 m height and 1 m base. It

will have been assumed that the pump line outlet will be moved frequently

to avoid excessive heaping (or, if a skip is used, the discharge will be

carefully controlled).

Additional concrete may be placed because of deflections of both the decking

and the steel frame, particularly if the slab is finished to ‘absolute’ (datum)

levels. The Structural Designer must be consulted to confirm whether the

resultant increased loads have been allowed for in the design. Levelling the top

of slab to achieve a uniform thickness, rather than a ‘level’ top surface is

recommended and will avoid this problem.

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6.3.2 Construction loads after concreting

Construction loads are often applied to the slab soon after concreting. Examples

of commonly occurring loads are bags of fire protection, skips of debris, pallets

of blocks and other equipment. If these loads are no more than 1.5 kN/m

(over

a 3 m by 3 m area), the construction load used in the design of the decking,

then the slab is clearly not overloaded (provided there is no additional,

unforeseen load due to ‘ponding’). For loads above this, the concrete strength

will need to be relied upon. Props should not be removed, nor additional loads

applied, until the concrete has reached 75% of its design strength, as indicated

by ‘control’ concrete compression tests. If the slab is to be loaded before 28

days after concreting, its strength at the time of loading needs to be established

(possibly by testing cubes or cylinders early), and an effective ‘design strength’

agreed with the Structural Designer.

The following list gives examples of typical construction loads. Items are

assumed to be placed on pallets, which should always be positioned directly

over the support beams:

 Concrete blocks: a 1 m high pallet of blocks applies a load up to 10 kN/m

 Bricks: a 1 m high pallet of bricks can exert a load of over 15 kN/m

 Bags of fire protection: a bag of fire protection material normally weighs

25 kg. A 1 m high pallet of bags can be equivalent to a load of 2.5 kN/m

 Bags of cement: bags of cement weigh 25 kg each. A standard pallet of

these weighs 1,400 kg (12 kN/m

The application of very heavy construction loads should always be referred to

the Structural Designer. When considering the location of such loads, it is best

to position them over the beams wherever possible. Examples of such loads are:

 Generators: welding generators can apply a load of 50 kN.

 Fork lift trucks: fork lift trucks can exert a load up to 100 kN, not

including their live load. In general, vehicles with axle weights above

3 tonnes should be used only if the slab has been designed/checked

specifically for that purpose.

 Crane counter weights: each counter weight is marked clearly with the

value of its weight.

 Mobile access platforms: The potential loading imposed by any mobile

access platforms used to install services, finishes, etc should be checked.

A procedure for checking the adequacy of the slab to support heavy point loads,

such as the wheel loads from forklift trucks, is given in AD 150

[44]

Care is needed if a composite floor is to be used in situations where there could

be frequent vehicle movements. Designing such floors just for uniformly

distributed loads may not be satisfactory. The fatigue effects of the repeated

dynamic loading from vehicles on the slab and supporting beams must be

considered by the Structural Designer. The suitability of the floor design (beams

and slab) for dynamic loading from vehicles should be checked.

Where the concrete is to be used as a wearing surface, or where bonded finishes

are specified, the concrete surface should be protected from oil spillage and

damage from moving plant.

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6.4 Further reading

The references given below relate particularly to this Section. (For information

on authors and publishers, see Section 8, References.)

ACIFC and Concrete Society Good Concrete Guide No. 5 – Composite concrete

slabs on steel decking – Guidance on construction and associated design

considerations

[66]

This Guide is intended to provide an overview of the factors which should be

considered in the design of composite slabs with steel decking.

Concrete Society Technical Report No.34, 1994 - Concrete industrial ground

floors

[19]

This document provides comprehensive guidance on the design, specification,

construction and finishing of industrial concrete ground floors. The guidance on

concrete quality requirements for durability, and on finishing procedures, is also

relevant to suspended composite slabs.

Concrete Advisory Service Data Sheets

These are produced and published by The Concrete Advisory Service, a

subsidiary of the Concrete Society. They provide theoretical and practical advice

on matters pertaining to concrete. The sheets referred to in this Section are:

No.8, 1997 Crazing: power trowelled concrete floor slabs

[64]

No.14, 1997 Cracking in composite concrete/corrugated metal decking floor

slabs

[28]

The manual and advisory safety code of practice for concrete pumping

[67]

This a specialist guide for concrete pumping contractors which covers in detail

both the theoretical and practical sides of pumping concrete.

Guide to steel erection in windy conditions

[68]

This guide provides advice to designers concerning the effect of wind on

steelwork during erection. It also explains the role of management and

supervision in controlling work as wind freshens, as well as giving comparative

information concerning weather forecasts that might be used to plan steel

erection.

Guide to the erection of multi-storey buildings

[69]

This document is a code of practice for Steelwork Contractors erecting multi-

storey steel-framed buildings. The principles included also apply to high-rise

structures generally. The code also provides guidance to Clients, CDM

co-ordinators, Principal Contractors and Designers. It describes the management

procedures and methods to be adopted when drafting site- and project-specific

Erection Method Statements. The document contains advice on the safety

aspects of site management; site preparation; delivery, stacking and storage of

materials; structural stability; holding down and locating arrangements for

columns; lifting and handling; and interconnection of components.

Good construction practice for composite slabs

[70]

This document covers much of the information included in the current guide,

but has a bias towards the European market.

National structural steelwork specification for building construction

[71]

This is the industry ‘standard’ for the quality of workmanship associated with

the fabrication and erection of steel framed buildings and will often form one of

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the contract documents. It includes procedures for shear stud welding and

testing.

Health and Safety Executive Guidance Note GS28: Safe erection of structures

[72]

This publication relates to the 1994 CDM Regulations and is currently

withdrawn, but an update is awaited. It is expected to provide essential

information on safety from the initial planning stage through to site management

and procedures, and will help users interpret the Regulations more readily.

Health and Safety in Construction HS(G)150

[73]

This is a comprehensive guide giving practical advice for achieving healthy and

safe construction sites. It helps to identify many common hazards and explains

control measures. It also deals with planning and management issues, including

risk assessment and the Method Statement. It is an essential reference.

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7 SLIM FLOOR CONSTRUCTION

This Section describes slim floor construction and outlines its benefits. Aspects

of design that differ from those of ‘traditional’ composite slabs and beams

(described in Sections 4and 5) are highlighted. The construction process is

described, as are typical construction details. The guidance is aimed at both

design and construction personnel.

Boxes are used to highlight issues of good practice in design, or things that the

designer should be aware of. They are also used to highlight issues of safety

during construction.

7.1 Introduction

Slim floor is a generic term used to describe a form of construction where the

supporting beams are contained within the depth of the concrete slab. This is

achieved by supporting the slab off the bottom flanges of the beams. Although

this concept is not new, it has been significantly refined in recent years, with

considerable development work undertaken in the UK by Corus (formerly,

British Steel). This work led to

Slimdek construction, a form of slim floor

construction using hot rolled beams together with composite slabs using deep

decking. Older forms of slim floor construction, using precast concrete planks

to form the slab, are less effective in a number of ways (such as ease of service

integration), and are not considered in this document.

Slim floor construction using deep decking is suitable for building layouts

requiring the decking, and subsequently the slab, to span up to 9 m. For typical

applications, spans vary between 5.5 m and 6.5 m, and the decking does not

need propping during construction. This spanning capability means that

secondary beams are not normally needed.

The role and structural behaviour of deep decking are similar to those of

shallow decking (Section 4), except that the composite resistance of the slab

needs to be enhanced by reinforcing bars located in the decking troughs.

A range of beam sections is available (Section 7.1.2). Some of these sections

can achieve composite interaction with the slab as a result of the shear bond at

the interface between the steel and concrete components, with no need for

additional shear connectors.

7.1.1 Benefits

The benefits of composite construction listed in Section 1.1 all apply to slim

floor construction using steel decking. It is particularly beneficial in providing

the following:

 Shallow floor depth. This may lead to savings in cladding cost, or help to

meet overall building height restrictions.

 Ease of service integration. There is a potential to accommodate the

services within the slab depth (between the ribs of the decking).

 Inherent fire resistance. A fire resistance of 60 minutes can be achieved

without fire protection.

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7.1.2 Slim floor components and systems

The most recent slim floor development produced by Corus is the Slimdek

system. This system comprises

Slimflor beams and ComFlor 225 deep decking.

Three different types of

Slimflor beam are produced: Slimflor Fabricated Beams

(SFB), Asymmetric

Slimflor Beams (ASB), and Rectangular Hollow Slimflor

Beams (RHSFB).

Slimflor Beams

Slimflor Fabricated Beam consists of a Universal Column section with a wide

flange plate welded to its underside. This plate supports the slab. Sections

ranging from 152 mm to 356 mm nominal depth may be used. Shear connectors

can be fixed to the top flange of the beam to achieve composite interaction with

the slab. Thin gauge closure pieces, known as ‘end diaphragms’, are fixed to

the flange plate to stiffen the ends of the decking (particularly during

concreting), and to form the concrete around the SFB. This type of construction

is shown in Figure 7.1.

An Asymmetric

Slimflor Beam is a hot rolled section with a narrower top flange

than bottom flange. The slab is supported off the upper surface of the bottom

flange. Composite interaction can be, and usually is, achieved by partial

encasement of the section (see Section 7.2.2). Two types of ASB are produced

by Corus, one of which has a thicker web. The thicker web type, known as

ASB(FE), can be used without fire protection for up to 60 minutes fire

resistance. In total, ten different ASB sections are produced by Corus

[74]

ranging from a 280 ASB 74 (272 mm deep, 74 kg/m) to a 300 ASB (FE) 249

(340 mm deep, 249 kg/m)). Construction using an ASB is shown in Figure 7.2.

A Rectangular Hollow

Slimflor Beam is fabricated from a rectangular hollow

section with a flange plate welded to its lower face. These beams are more

efficient than either SFBs or ASBs in resisting unbalanced loading, and so are

ideal for use at the edges of a building. Composite interaction can be achieved

by welding studs to the upper flange of the hollow section. Hollow sections up

to 500 mm deep may be used, with typical sizes ranging from 200 mm to

300 mm depth. Construction using a RHSFB is shown in Figure 7.3.

Figure 7.1 SFB with deep decking (non-composite beam)

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ComFlor 225 deep decking

The

ComFlor 225 profile is the most recent form of deep decking, and it may

be used with any of the beam types described above. Its cross-section is

illustrated in Figure 7.4; the profile includes provision for special attachment

points for services and/or a suspended ceiling. A cut-out is included at the top

of each rib to ease concrete placement around the beams. The decking is

produced in 600 mm wide units, normally from 1.25 mm thick grade S350

galvanized steel. Typical floor construction using

ComFlor 225 decking is

shown in Figure 7.5.

Figure 7.2 ASB with deep decking (composite beam)

Figure 7.3 RHSFB with deep decking (non-composite beam)

600

400100

238

100

Attachment hanger

(typical detail)

195

Figure 7.4 Cross-section of ComFlor 225 deep decking profile,

showing a typical service attachment detail.

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7.2 Design

Detailed methods for the design of all the components in the Slimdek system are

presented in References 75, 76 and 77, as well as being summarised in the

Corus Slimdek Manual

[74]

. Design software for the beams and decking, Slim

Floor Integrated Design Software

– SIDS®

[78]

, is available from Corus at

www.corusconstruction.com. The software designs and analyses flooring

solutions utilizing both

Slimflor® Fabricated Beams (SFB) and Asymmetric

Slimflor Beams (ASB).

There are two distinct stages for which the elements of the

Slimdek system must

be designed. The first is the construction stage, during which the beams and

decking support the loads as non-composite sections. The second is the final

stage, during which the decking and concrete act together compositely, as do

(generally) the ASBs and slab. SFBs and RHSFBs will act compositely if shear

studs have been provided. A summary of the key design considerations for both

of these stages is given below.

Figure 7.5 View of Slimflor construction using ComFlor 225 decking.

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The sequence of design activities generally follows that given in Figure 2.1. The

following two points should be noted:

 Consideration of the required spans will allow the depth of the beams to be

estimated.

 Consideration of the required fire resistance will allow the depth of slab to

be estimated, as a function of the cover required for the beams and the

decking.

Having established these scheme design parameters, detailed design of the

beams and slab can be undertaken. The following slab depths should be

considered as typical:

 280 ASB sections ~ 290-320 mm deep slab

 300 ASB sections ~ 315-340 mm deep slab.

These depths will enable adequate cover to the ASB for it to act compositely

with the slab. For SFBs a greater range of slab depths may be considered for a

given depth of beam; the slab depth requirement will depend on whether shear

studs must be accommodated to make the SFB act compositely.

7.2.1 Construction stage

Beam design

Design of the beams at the construction stage is essentially the same as for

conventional steel beams. It may control the size of the beam when the

in-service imposed loads are small. The one significant difference arises from

the fact that in

Slimdek construction the bottom flange (or flange plate) is loaded

by the weight of the wet concrete and construction loads. The flange (or plate)

must be designed to carry this loading in ‘transverse’ bending, at the same time

as acting in tension as part of the beam section.

Out-of-balance loading from one side during construction results in torsion

being applied to the beam. This is resisted by the beam and its end connections.

Two load conditions should be considered:

 uniformly distributed load on one side of the beam, causing maximum

torsion in the beam

 uniformly distributed load over the entire supported area, causing maximum

bending moment in the beam.

Check that the steel beam size chosen is capable of supporting the wet

weight of the concrete, and other construction loads, in its non-composite

state.

Check for the worst case combination of ‘transverse’ and ‘longitudinal’

bending. Loading on one side of the beam only will often dictate the

required section size.

Decking design

In addition to considering the self weight of the slab, the design of the deep

decking should take into account temporary construction loads. It is

recommended that the construction loads specified in the Eurocodes are used for

the design of deep decking, and not those specified in BS 5950-4, which are

considered unduly onerous for long span decking. The specified loads are the

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same as for shallow decking, and are explained in detail in Section 4.1.2. They

include a 3 m length construction load of 1.5 kN/m

, which may be placed

anywhere for the most onerous effect, and adjacent loads of 0.75 kN/m

The effect of concrete ponding should be taken into account (by increasing the

self weight of the slab) if the deflection under self weight alone exceeds the

lesser of span/180 or 20 mm.

If temporary props are used to support the decking during construction, the 3 m

length construction load of 1.5 kN/m

should be applied in the most onerous

positions for the prop and the decking design, although, for design simplicity, a

constant load could be considered across the span for these ‘propped’ design

conditions.

It is likely that deep decking will require propping during construction if it is

required to span more than about 6.5 m. The precise limit depends on whether

lightweight or normal weight concrete is used. The spacing of the props is

governed by the ability of the decking to resist combined bending and shear in

the hogging (negative) moment regions over the lines of props. It is

recommended that the spacing between the props should be relatively close, so

that local loads do not cause damage to the decking (2.5 m to 3.5 m spacing

depending on the slab weight

[79]

). A 100 mm wide by at least 40 mm thick

timber bearer should be used to distribute the load at these points.

The nominal end bearing of the sheets should be specified as 50 mm. The

flange widths are such that this bearing can be achieved, whilst still allowing the

sheets to be dropped vertically into position (i.e. without having to ‘thread’

them between the top and bottom flanges). It should be noted that a nominal

bearing length of 50 mm has been justified

[74]

by recent testing (earlier

publications suggested that 75 mm was necessary).

It is not necessary for the deep decking to be designed to support

1.5 kN/m

over its entire span. Half this value may be considered outside

the ‘middle 3 m’, although when the slab is propped it may be prudent to

design for a constant 1.5 kN/m

Allow for increased self weight due to concrete ponding when deflections

are substantial.

Specify an end bearing length of 50 mm. Any less would be insufficient to

achieve the necessary resistance to local loading, any more would make

the decking sheets more difficult to drop into position.

7.2.2 Final stage

Beam design

ASBs will in most cases be designed to act compositely in the final stage.

Composite action is developed by the shear bond between the steel and concrete

around the beam, and this is enhanced by the raised pattern rolled into the top

surface of the beam. The bond is sufficient to satisfy the minimum degree of

shear connection required by BS 5950-3. Only in unusual cases, for example

when there is less than 30 mm concrete cover over the top flange, will a

non-composite design be necessary. This will mean that section sizes may have

to be increased for given span and loading requirements.

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SFBs may be designed either non-compositely or compositely. Composite action

can be achieved by the use of shear studs welded to the top flange. These studs

are usually 19 mm diameter and 70 mm as-welded height.

RHSFB edge beams may be designed either non-compositely or compositely. As

for SFBs, composite action can be achieved by the use of ‘short’ shear studs

welded to the top flange. Sufficient transverse reinforcement looped around the

shear connectors is required in order to transfer the shear force into the slab

[75]

For ASBs, SFBs and RHSFBs, the minimum concrete cover required for the

beams depends on the beam size, exposure conditions, the concrete specification

and composite interaction is required.

The plastic stress blocks assumed when calculating the moment resistance of a

composite ASB section are shown in Figure 7.6. The resistance model for a

composite SFB or RHSFB is basically the same as that for a ‘traditional’

composite beam (Section 5.2.1), with a requirement to consider the ability of

the shear studs to transfer the envisaged longitudinal force.

For edge beams, or beams adjacent to openings in the slab, out-of-balance

loading occurs during both the construction and final stages. This may be taken

into account by a rigorous analysis combining the longitudinal bending effects

with the torsional effects. A method is presented in Reference 79.

If possible, sufficient concrete cover should be provided to allow composite

interaction between the beams and slab. This will generally allow the beam

sizes to be reduced.

Slab design

The design of composite slabs using deep decking differs from that for shallow

decking (Section 4.2) in the following ways:

 The ultimate load resistance of the slab is increased by placing bar

reinforcement in the troughs of the decking. The benefit of these bars is

considered in both the ‘normal’ and fire conditions.

 The slab depth may need to be chosen not only to satisfy the structural,

durability and fire resistance requirements of the slab itself (see

Compression in concrete

Plastic

neutral

axis

Cross sectional stresses

in com

osite section

Plastic neutral axis

in web below slab

Effective breadth of slab B



0.85f /



f /

ya a



f /

ya a

ck u

Figure 7.6 Assumed stress blocks for ASB design (using

BS EN 1994-1-1 notation)

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Sections 4.2.3, 4.2.4 and 4.2.5), but also to provide appropriate cover over

composite beam sections (Section 7.2.2).

The reinforcing bars in the troughs of the decking provide additional tensile area

to that provided by the decking, and thus enhance the bending resistance of the

composite slab (Figure 7.7). Diameters range from 16 mm to 32 mm,

depending on the span and fire resistance requirements.

Straight bars may be used to achieve 60 minutes fire resistance (provided that

shear stresses are low

[74]

. In other cases, L bars (see Figure 7.8) should be used

to provide sufficient end anchorage in fire conditions. Detailing rules are

summarised in Table 7.1 and Figure 7.8.

Table 7.1 Detailing requirements for deep composite slabs

Fire Resistance (min)

Detailing Requirement

≤60 90 120

Minimum bar dia (mm)

- unpropped 16 20 25

- propped 20 25 32

Cover to bar (mm) 70 90 120

Bar type Straight L-bar L-bar

Min fabric in topping A142 A193 A252

The minimum anchorage details depend on the level of applied shear and the diameter of the main

reinforcing bars in the rib, which in turn depends on the fire resistance period and whether or not

the slab is propped. For 60 minutes fire resistance, when the level of applied shear is less than

0.5 times the available shear resistance, straight bars may be used without extra anchorage bars -

in accordance with BS 8110-1:2005

[30]

, clause 3.12.9.4. However, anchorage bars are

recommended even for low values of applied shear at 90 and 120 minutes fire resistance periods.

For more details see Reference 74.

Slip between

deck and concrete

Support

Longitudinal

shear bond

Concrete in

compression

Tension in

decking and

bar reinforcement

Stress

distribution

Vertical

reaction

Mid-span

Bar reinforcement

Figure 7.7 Action of composite slab with reinforcement in ribs

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Additional reinforcement may be required to fulfil the following roles:

 Transverse reinforcement adjacent to shear connectors.

 U-bars at composite edge beams.

 Additional crack control reinforcement (see below).

 Strengthening around openings.

 Strengthening at positions of concentrated loads.

One of the principal considerations governing the choice of slab depth is the

required fire resistance period. Minimum depths are given in Table 7.2

[74]

as a

function of the concrete type and fire resistance required.

Table 7.2 Minimum concrete depth above decking for adequate fire

insulation

Concrete Depth Above

Decking (mm)

Fire Resistance (mins)

Normal

concrete

Lightweight

concrete

60 70 60

90 80 70

120 90 80

Note: Depths given are the

minimum for fire insulation

purposes. Greater thicknesses

may be required for spanning

capability, or to achieve

adequate beam cover.

The slab depth may also be governed by structural resistance requirements.

However, as for shallow decking (Section 4.2.3), the performance of a

composite slab using deep decking can only be accurately determined by testing.

Detailed design procedures have been developed based on appropriate tests

[74]

and should be used to determine the depth of slab needed to satisfy structural

requirements.

It is normal for some cracking to occur in the slab over the beams. These

cracks run parallel with the beams and are not detrimental to the structural

behaviour of the slab. They may be controlled by fabric reinforcement provided

across the tops of the beams. Guidance on the detailing of reinforcement to

control cracking may be found in the Corus

Slimdek manual

[74]



100 mm100 mm



Figure 7.8 Detailing of bar reinforcement in slabs (need for L bars

depends on level of shear stress)

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7.2.3 Service integration

There are three opportunities for service integration in the Slimdek system:

 Partial integration: Major services pass below the slab and beams and the

space between the ribs is used for small pipes and fitments, such as lighting

units. This allows for cross-overs of ducts or pipes. The absence of

downstands provides for greater flexibility of service distribution and

reduces the depth of the structure-services zone.

 Full integration: Circular or elongated openings formed in the webs of the

beams for ducts and pipes located between and within the depth of the ribs

to pass through the beams. (Alternatively, the space between the ribs can

act as a duct in itself, which again continues through the openings in the

beams.)

 Slab penetrations: Services can pass vertically through openings (up to

400 mm wide by 1 m long) in the concrete topping between the ribs.

Larger openings can be formed, but require more detailed design.

In certain areas where spans are relatively short (< 3.5 m), shallower floors

may be created locally, using a composite slab of 120 to 150 mm depth

comprising more traditional decking of 50 to 60 mm depth. This is particularly

useful in, or adjacent to, core areas where duct cross-overs and horizontal bends

are required without deepening the ceiling-floor zone excessively.

Web openings

Full integration of services can be achieved by providing openings through the

beam web midway between the ribs of the deep decking. During fabrication, an

opening (usually circular or oval) is cut in the web. The same sized openings

are also cut in the diaphragms that fit between the ribs and a ‘sleeve’ is placed

through the beam and diaphragms before the concrete is placed. The elements

that form the opening are shown in Figure 7.9. Flat, oval or circular ducts may

be placed inside the sleeve and sealed externally.

End diaphragm

Sleeve

20 minimum

160 maximum

Duct

Figure 7.9 Forming openings through ASB

Maximum acceptable sizes, and positions, for openings in the webs of ASBs

have been established by full-scale tests:

ASB sections:

 Provide elongated openings up to 160 mm deep by 320 mm long centrally

between the ribs over the middle half of the beam span, but not within

1500 mm from the supports.

 Alternatively, provide circular openings up to 160 mm diameter, but not

within 1000 mm from the supports.

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 Ensure that the base of all openings is 20 mm above the bottom flange,

independent of their depth. This avoids the root radius of the section and

fits the openings within the decking shape.

ASB (FE) sections:

 Provide elongated openings up to 160 mm deep by 320 mm long centrally

between the ribs, but not within 450 mm from the supports.

 Alternatively, provide circular openings up to 160 mm diameter.

 Ensure that the base of all openings is 20 mm above the bottom flange,

independent of their depth. This avoids the root radius of the section and

fits the openings within the decking shape.

Detailing rules for web openings are summarised in Figure 7.10.

320 65

600

400

160

ComFlor 225

decking









320 x 160 max.

dimensions

of opening

75 typ.

195

a) Maximum size of opening



Support

Thick web ASB

Thin web ASB

450

1000

Span/4 1500

b) Location of openings

Figure 7.10 Detailing rules for web openings in ASB a) maximum size

of openings b) location of openings

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Maximum acceptable sizes, and positions, for openings in the webs of SFBs

have also been established by testing. The base of all openings should be

detailed approximately 20 mm above the top of the bottom flange of the UC.

Combinations of elongated openings up to160 mm deep by 240 mm long, and

circular openings up to 160 mm in diameter, may be accommodated in different

parts of a span. Full details of maximum sizes and allowable positions are given

in Figure 7.11.

Web openings affect the shear resistance, the bending resistance, and the second

moment of area of a beam. Empirical formulae for predicting revised properties

for ASB and SFB sections, as a function of the opening geometry, may be

found in Reference 74. Design allowing for openings is also included in design

software available from Corus.

Openings may also affect the fire resistance of a section. ASB sections with

openings invariably require fire protection to the bottom flange for 60 minutes

fire resistance (and above) for economic design. However, for 30 minutes fire

resistance, ASB sections with openings do not require fire protection.

One of the major benefits of the Slimdek system is its ability to

accommodate services. Substantial web openings may be formed in the

beams, but the designer must adhere to strict empirical rules concerning

the position and size of the openings, and their influence on beam

behaviour.

Openings in the slab

Provision for vertical service openings within the floor slab will necessitate

careful design and planning. The following list summarises the options that are

available to the designer (see Figure 7.12):

 Openings up to 300 mm  300 mm can be accommodated anywhere in the

slab over a crest section of the deck, normally without needing additional

reinforcement.

Side view

End view

55 - t

D 160mm

in rest of span

a) Detailing of openings in sections

b) Maximum size of openings in Slimflor sections

160 for

t 20





Circular openings permittedOval openings permitted in middle half of beam span

240

D 1.5D





Figure 7.11 Detailing rules for web openings in SFB a) maximum size of

openings b) location of openings

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 Openings up to 400 mm wide  1000 mm long may be taken through the

crest of the

ComFlor 225 decking. Additional reinforcement, which should

be designed in accordance with BS EN 1992-1-1

[24]

(or BS 8110

[30]

), may be

required around the opening.

 Openings up to 1000 mm wide  2000 mm long may be accommodated by

removing one rib (maximum) of the decking, fixing suitable edge trims and

providing additional reinforcement to transfer forces from the discontinuous

rib. The slab should be designed as a ribbed slab in accordance with

BS EN 1992-1-1 (or BS 8110), with the decking being used as permanent

formwork. Guidance may be found in the Corus

Slimdek Manual

[74]

 Larger openings will generally require trimming by secondary beams.

 Openings required in the slab should be made using shuttering or void-

formers, and the decking cut after curing – unless properly supported

during construction or permanently trimmed.

If an opening greater than 300 mm

 300 mm lies within the effective width of

slab adjacent to a beam (L/8), the beam should be designed as non-composite.

A close grouping of penetrations transverse to the span direction of the decking

should be treated as a single large opening.



ASB beam

Minimum A142 mesh

throughout

400



Opening

beam span/16*500



1000





beam span/16*





beam span/16*

* for composite beam design

Edge trim

fixed as 'box'

Curtailed bar

Transverse

bar

Edge trim

fixed as 'box'

End diaphragm Transverse bar

Temporary prop Temporary prop

Section A - A

Section B - B

T12 bar x 1500 long

Centre-line

of ribs

Additional bottom

reinforcement to

adjacent ribs

(by engineer)

Opening

1000

300

2000

Additional top

reinforcement

Figure 7.12 Details of small and medium size openings in the slab.

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A range of possibilities exist for passing services vertically through the

slab. The designer should recognise that some of these have implications

for the permanent works design, e.g. the need to specify additional

reinforcement and/or trimming steel.

Service attachments

The

ComFlor 225 decking facilitates the fixing of services and suspended

ceilings. Hangers can be used to support services running either parallel or

perpendicular to the decking span.

The new adjustable Lindapter

Slimdek 2 fixing clip

[80]

can achieve a safe

working load of 1.0 kN per fixing. These allow service pipes to be suspended

directly from the decking between the ribs. Alternatively, self-drilling self-

tapping screws may be used to attach hangers to the decking after the concrete

has been placed but care is required when attaching fixings to ensure that the

bond between the decking and concrete is not impaired.

Service integration is covered in detail in

Service integration in the Slimdek

system

[35]

7.2.4 Construction details

Ends of decking

Often, it is necessary to use part width sheets of decking, particularly at tie

beams or at slab edges. When a part width is specified, a Z section is needed to

provide local support to the decking, as shown in Figure 7.13. This should be

identified on the decking layout drawing (Section 3.2).

Slab edges

There are various alternatives for edge beams in

Slimdek construction. These

are:

 Conventional downstand beams

 Rectangular Hollow Section Slimflor Beams

 Asymmetric Slimflor Beams.

Tee section

cut from UC

section

ASB bottom

flange

Decking cut to

suit setting-out

requirement

Mesh reinforcement

Reinforcement

bar

600

Figure 7.13 Z section to support edge of decking at a tie beam

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Typical details for edge beams are shown in Figure 7.14. There are some

critical dimensions that should be noted:

 In detail (a) the concrete cover to the RHSFB should either be zero or

greater than or equal to 40 mm

 In detail (b) the concrete cover to the composite RHSFB should be at least

15 mm greater than the as-welded height of the studs (85 mm for 70 mm

long studs)

 In detail (c) the minimum distance from the edge trim to the top flange of

the beam should be 125 mm (to allow access for a fixing tool) and

maximum overhang of the trim from the bottom flange should be 150 mm.

Column ties

Tie members are required between columns, perpendicular to the main beams,

in order to provide:

 Stability during construction.

 Robustness and stability of the completed construction.

 Transfer of forces (e.g. due to wind action).

The tie members may be of various forms, as illustrated in Figure 7.15, the

most common being:

 T sections in which the flange of the T provides support to the decking.

 RHS sections with a bottom plate to support the decking.

Mesh





U bar

10 mm dia. (min)

a) Non composite RHSFB b) Composite RHSFB

L bar

End diaphragm

L bar

c) Composite ASB d) Downstand beam

Figure 7.14 Typical edge beams.

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 Lighter ASB sections, especially adjacent to openings.

 Fire protected RHS sections not encased in the slab.

Advice on tying requirements for robustness may be found in Reference 81.

Connecting decking to the bottom flange of I beams often presents practical

difficulties on site because the fixing tool cannot be fitted in the space between

the web of the decking and the beam flange. Therefore, the use of an ASB

beam or a RHS with welded bottom plate is preferred. Where the T or RHS

members are encased in the slab, a shelf plate should be welded to the column

web to provide local support to the decking.

7.3 Construction practice

Good practice for receiving, storing, and placing bundles of deep decking on the

steel frame is essentially the same as for shallow decking. However, because of

the use of end diaphragms, there is a significant difference in the procedure

adopted for placing and fixing the decking.

Slimdek designers and installers

should refer to the

BCSA Guide to the installation of deep decking

[82]

. This

publication carries detailed description of safe installation procedures.

Planning

Deep decking is similar to shallow decking in that good planning on the part of

the designers is essential for the success of the project. In particular, with deep

decking it is quite common for designers to show details that are impossible to

install; these of course should be avoided and the Corus standard details

(available for download from the Corus website) always used. Some typical

details to avoid are shown in Figure 7.16. In the figure, details (a) and (b) are

possible with an appropriate steel angle or timber support (see Figure 4.6).

Detail (c) is not possible when the clearance between the top flange of the ASB

and the edge trim is less than 110 mm because of inadequate access to fix the

trim on the bottom flange. This can be remedied by detailing the trim and slab

to cantilever slightly. Welding a flange plate to the section on which to support

the decking is one option to avoid the problems caused by detail (d). Detail (g)

is not possible because of inadequate access to fix the trim on the section bottom

flange. A solution is to extend the flange plate (by at least 110 mm) to enable

a) Tee section b) Encased RHS with shelf plate

c) ASB d) Exposed RHS

Figure 7.15 Alternative forms of tie members

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the edge trim to be fixed directly to it. The table of the angle in detail (h) needs

to be extended to provide the access needed (see Figure 4.6). The problems

associated with detail (j) can be overcome by adding a flange plate to the RHS

member and setting it at a level where the decking can be supported either side

of it on the flange plate.

Other important planning points include:

 Ground conditions - it is even more important for deep decking than for

shallow decking that there is a hard, flat, well-compacted surface for the

decking installer to work from within the building footprint. This is because

a) Abutting masonry wall without

support

b) Abutting beam flange without

support

<125 mm

c) Inadequate access to fix edge trim

to beam flange

d) Inadequate access to fix decking to

beam flange

e) Inadequate access to fix diaphragms

and decking to beam flange

f) Inadequate access to fix zed trim to

beam flange

g) Inadequate access to fix lower

flange of edge trim to beam flange

and insufficient access for concrete

h) Inadequate access to fix diaphragms

and decking to shelf angle

i) Decking not laterally restrained

(from spreading at edge)

) Decking cannot be stitched on

longitudinal seam because of

presence of tie

Figure 7.16 Unsuitable decking details

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deep decking uses diaphragms that are generally fitted from a work

platform or MEWP (see below).

 The location of the perimeter edge protection needs to be considered at an

early stage, and should be fitted at an offset from the perimeter beams

because the deckers need to work from these to lay the decking sheets.

 Decking bundles must be correctly positioned as indicated on the Decking

Contractor’s drawings, to minimise unnecessary manual handling and the

need for operatives to traverse open steelwork.

Placement and fixing of decking

Following erection of the permanent steelwork, the following procedure should

be adopted for installing and fixing a panel of deep decking on

Slimflor beams.

The end diaphragms are fixed first, as shown in Figure 7.17. These are supplied

in lengths of 1800 mm, which equates to three sections of

ComFlor 225

decking. They are fixed to the edges of the lower flanges of the beams on both

sides (except for edge beams), using at least two shot-fired pins for each length.

The diaphragms should be installed from a work platform wherever reasonably

practicable. Access systems such as MEWPs or Mobile Scaffold Work

Platforms can be used if the ground conditions are adequately levelled and

compacted, including the areas around the column bases.

Decking installation should only commence once the end diaphragms and safety

net (or alternative) fall arrest system are in place. The decking sheets are then

manually lowered individually onto the beams. The nominal end bearing of the

sheets should be 50 mm; the flange widths are such that this can be achieved,

whilst still being able to drop the sheets vertically into position (i.e. without

having to ‘thread’ them between the top and bottom flanges). The bearing length

should never be less than 40 mm. As it is often not possible to straddle the

steelwork once the end diaphragms are in place, decking operatives will usually

stand on the top flange of the beam at either end of the first bundle of decking

to cut open the steel banding and lift the first decking sheet out onto the

steelwork and over the pre-fitted diaphragms. Decking sheets should always be

positioned by a minimum of two operatives. Where sheets are longer than 6 m,

decking should be positioned preferably by two operatives at each end of the

sheet using an extended handlebar lifting device, unless mechanical lifting

systems are available.

Once the sheets for the whole bay are in place, they are secured to the beam

lower flanges using heavy duty shot-fired fixings, and to the top of the

diaphragms using self drilling self tapping screws.

Light steel edge trim is used to form the edges of the slab and to infill where

the 600 mm profile of the decking does not align with the parallel supports.

These sections are custom manufactured for each project, and will be detailed

on the decking layout drawing (Section 3.2).

The decking forms a part of the slab reinforcement, with the remainder being

supplied by a bar in each trough of the decking and a fabric placed near to the

top of the slab. Reinforcement should be fixed in accordance with the

requirements of the Structural Designer (or Delegated Designer). Normally,

spacers are used to position the bars 70 mm from the base of the trough. This

distance will increase to 90 or 120 mm (respectively) when 90 or 120 minutes

fire resistance are required. There may be additional fabric or bar reinforcement

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to fix adjacent to supports or edge beams, or above beams for crack control

purposes.

Having fixed the reinforcement, the Main Contractor completes the floor slab

by providing any necessary temporary propping and finally concreting the slab.

It is important to ensure that the concrete is properly compacted, and a poker is

needed to ensure proper concrete flow around the beams, beyond the ends of

the decking.

Any shear studs that are required (to make SFBs or RHSFBs composite) may

be welded to these sections during fabrication, because they do not interfere

with the decking. If they are to be welded on site, the precautions and

procedures outlined in Section 6.5 should be considered.

Propping

For long spans the decking should be propped; requirements will have been

identified by the Structural Designer and indicated on the decking layout

drawings. Props should be in place prior to placing the decking, for spans of

7.5 m or more; the props will provide an additional support point for the sheets

when they are being lowered into position on the beam flanges. In all cases

props should be stable without relying on friction with the decking for lateral

stability. The end props in a row should be self supporting and braced to the

internal props.

If it is necessary to prop the beams, the supports should be much more robust

than those used to support decking. Generally, a ‘Tri-shore’ or braced propping

system will be required. These props should be placed at a minimum of 3 m

spacing along the beams. It will often be necessary to prop to two levels below

the supported beam to avoid creep-induced deflections of the supporting beam.

Very short lengths of decking

Where the beam spacing demands a length of decking of 1 m or less, especially

where the beams are not parallel, it is far more efficient to use a shallow

composite floor deck. This eliminates the need for close spaced diaphragms and

complicated cutting of very short pieces of

ComFlor 225.

Shot fired fixing

Figure 7.17 Fixing of end diaphragms at ASB

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7.4 Further reading

The references given below relate particularly to this Section. (For information

on authors and publishers, see Section 8, References.)

Corus Slimdek Manual

[74]

This is an essential reference as it covers all aspects relating to the design and

construction of the

Slimdek system.

BCSA Guide to the installation of deep decking

[82]

This publication carries a detailed description of safe installation procedures for

deep decking.

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8 REFERENCES

1 Composite Flooring Systems: Sustainable construction solutions

MCRMA, 2003

2 Better value in steel - Composite flooring - floors using steel decking

(P285)

The Steel Construction Institute, 2001

3 HICKS, S.J, LAWSON, R.M, RACKHAM, J.W, and FORDHAM, P.

Comparative structure cost of modern commercial buildings - Second

Edition (P137)

The Steel Construction Institute, 2003

4 Managing health and safety in construction

Construction (Design and Management) Regulations 2007. (CDM)

Approved Code of Practice (Series code L144).

HSE Books, 2007

5 BROWN, D.G.

The Construction (Design and Management) Regulations 1994:

Advice for designers in steel (P162)

The Steel Construction Institute, 1997

6 Code of Practice for metal decking and stud welding (Ref 37/04).

BCSA, 2004

7 AD 175: Diaphragm action of steel decking during construction

Advisory Desk, in New Steel Construction, Vol 3 (4), Aug 1995

8 BS EN 10326: 2004 Continuously hot-dip coated strip and sheet of

structural steels. Technical delivery conditions

BSI

9 AD 247: Use of composite construction in an aggressive environment.

Advisory Desk, in New Steel Construction, Vol 9(2), March 2001

10 BS EN 1991-1-6:2005 Eurocode 1. Actions on structures. General

actions. Actions during execution

BSI

11 BS 5950: Structural use of Steelwork in Building:

BS 5950-1:2000 Structural use of steelwork in building. Code of

practice for design. Rolled and welded sections

BS 5950-3.1:1990 Design in composite construction. Code of practice

for design of simple and continuous composite beams

BS 5950-4:1994 Structural use of steelwork in building. Code of

practice for design of composite slabs with profiled steel sheeting

BS 5950-6:1995 Structural use of steelwork in building. Code of

practice for design of light gauge profiled steel sheeting

BS 5950-8: 2003 Code of practice for fire resistant design

BSI

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12 BS EN 1991-1-1:2002 Eurocode 1. Actions on structures. General

actions. Densities, self-weight, imposed loads for buildings

BSI

13 BS EN 1993-1-3:2006 Eurocode 3. Design of steel structures. General

rules. Supplementary rules for cold-formed members and sheeting

BSI

14 BS EN 1994-1-1:2004 Eurocode 4. Design of composite steel and

concrete structures. General rules and rules for buildings

BSI

15 BS 882:1992 Specification for aggregates from natural sources for

concrete

BSI

16 BS EN 206-1:2000 Concrete. Specification, performance, production and

conformity

BSI

17 BS 8500-1:2006 Concrete. Complementary British Standard to BS EN

206-1. Method of specifying and guidance for the specifier

BSI.

18 BS 8204-2:2003 Screeds, bases and in situ floorings. Concrete wearing

surfaces. Code of practice

BSI

19 Concrete industrial ground floors - A guide to their design and

construction. Third Edition (TR34)

The Concrete Society, 2003

20 AD 163: Provision for water vapour release in composite slabs

Advisory Desk, in New Steel Construction, Vol 2 (6), December 1994

21 BS 5606: 1990 Guide to accuracy in building

BSI

22 BS 4483:2005 Steel fabric for the reinforcement of concrete.

Specification.

BSI

23 BS 4449:2005 Steel for the reinforcement of concrete. Weldable

reinforcing steel. Bar, coil and decoiled product. Specification.

BSI

24 BS EN 1992-1-1:2004 Eurocode 2: Design of concrete structures.

General rules and rules for buildings

BSI

25 BS 8666:2005 Scheduling, dimensioning, bending and cutting of steel

reinforcement for concrete. Specification.

BSI

26 BOND, A.J., HARRISON T., BROOKER O., MOSS R.,

NARAYANAN, R. and WEBSTER, R.

How to design concrete structures using Eurocode 2 (CCIP-006)

The Concrete Centre, 2007

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27 BS EN 14889 Fibres for concrete:.

BS EN 14889-1:2006 Steel fibres. Definitions, specifications and

conformity.

BS EN 14889-2:2006 Polymer fibres. Definitions, specifications and

conformity

BSI

28 Cracking in composite/corrugated metal decking floor slabs (CAS13)

The Concrete Society, 2003

29 JOHNSON, R.P. and ANDERSON, D.

Designer’s Guide to BS EN 1994-1-1

Eurocode 4: Design of composite steel and concrete structures

Part 1.1 General rules an rules for buildings

Thomas Telford, 2004

30 BS 8110-1:1997 Structural use of concrete. Code of practice for design

and construction

BSI

31 BS EN 1994-1-2:2005 Eurocode 4. Design of composite steel and

concrete structures. General rules. Structural fire design

BSI

32 NA to BS EN 1994-1-2:2005 UK National Annex to Eurocode 4. Design

of composite steel and concrete structures. General rules. Structural fire.

design

BSI

33 SIMMS, W.I., KIRBY, B.R., BAILEY, C.G. and BURGESS, I.W.

Steel building design: Fire resistance design (P375)

The Steel Construction Institute, 2008.

34 Backpropping Flat Slabs by Eur Ing Pallett Bsc Eng FICE FCS –

PFP/136 (23/08/04): Pallett Temporary

Works Ltd

35 McKENNA, P.D. and LAWSON, R.M.

Interfaces: Design of steel framed buildings for service integration (P166)

The Steel Construction Institute, 1997

36 OGDEN, R.G.

Interfaces: Curtain wall connections to steel frames (P101)

The Steel Construction Institute, 1992

37 WAY, A.G. and COUCHMAN, G.H.

Acoustic Detailing for Steel Construction (P372)

The Steel Construction Institute, 2008

38 DEPARTMENT OF LOCAL GOVERNMENT AND COMMUNITIES

The Building Regulations 2000

Approved Document E: Resistance to the passage of sound

The Stationery Office, 2003

39 Part E Robust Details Handbook 3

edition

Robust Details Ltd, 2007

40 Guidance for the design of steel-fibre-reinforced concrete (TR63)

The Concrete Society, 2007

41 Guidance on the use of macro-synthetic fibre reinforced concrete (TR65)

The Concrete Society, 2007

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42 MULLETT, D.L.

Composite floor systems

Blackwell Science and The Steel Construction Institute, 1998

43 LAWSON, R.M.

Design of composite slabs and beams with steel decking (P055)

The Steel Construction Institute, 1989

45 AD 150, Composite floors - wheel loads from forklift trucks

Advisory Desk, in New Steel Construction, Vol 1(7), Dec 1993

46 LAWSON, R.M.

Commentary on BS 5950: Part 3: Section 3.1 ‘Composite Beams’ (P078)

The Steel Construction Institute, 1990

47 BS EN 1993-1-1:2005 Eurocode 3. Design of steel structures. General

rules and rules for buildings

BSI

48 NETHERCOT, D.A. and LAWSON, R.M.

Lateral stability of steel beams and columns (P093)

The Steel Construction Institute, 1992

49 BS EN 1990:2002 Eurocode. Basis of structural design

BSI

50 LAWSON, R.M. and HICKS, S.J.

Design of beams with large web openings for services (P355)

The Steel Construction Institute, to be published 2009

51 SMITH, A.L., HICKS, S.J. and DEVINE, P.J.

Design of floors for vibration: A new approach (P354)

The Steel Construction Institute, 2007

52 NEWMAN, G.M., ROBINSON, J.T. and BAILEY, C.G.

A new approach to multi-storey steel-framed buildings.Second Edition

(P288)

The Steel Construction Institute, 2006.

53 NEWMAN L C, DOWLING, J.J. and SIMMS, W I.

Structural fire design: Offsite applied thin film intumescent

coatings.Second Edition (P160)

The Steel Construction Institute, 2005.

54 RT1187: Guidance on the fire protection of beams with web openings The

Steel Construction Institute, 2005.

55 BS 476-21:1987 Fire tests on building materials and structures. Methods

for determination of the fire resistance of loadbearing elements of

construction

BSI

56 NEWMAN, G.M. and LAWSON, R.M.

Fire resistance of composite beams (P109)

The Steel Construction Institute, 1991

57 HICKS, S.J.

Strength and ductility of headed stud connectors welded in modern

profiled steel sheeting,

The Structural Engineer, Vol. 85(10), May 2007, pp 32-38

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58 AD 192, Transverse reinforcement in composite T-beams

Advisory Desk, in New Steel Construction, Vol 5 (1), Feb/Mar 1997

59 AD 266, Shear connection in composite beams

Advisory Desk, in New Steel Construction, Vol 11 (4), July 2003

60 Fire protection for structural steel in buildings (4th edition)

ASFP/ FTSG/ SCI, 2007.

61 CIMSTEEL

Design for Construction

The Steel Construction Institute, 1997

62 AD 174, Shear connection along composite edge beams

Advisory Desk, in New Steel Construction, Vol 3 (3), June 1995

63 BS EN 12350-1:2000 Testing fresh concrete. Sampling

BSI

64 Crazing: power trowelled concrete for floor slabs (CAS8)

The Concrete Society, 2003

65 BS 8203: 1996 Code of Practice for installation of resilient floor

coverings.

66 Composite concrete slabs on steel decking - GCG5 (CS161)

The concrete Society, 2008

67 The Manual and Advisory Safety Code of Practice for concrete pumping

BCPA, 1990

68 Guide to steel erection in windy conditions (ref 39/05)

BCSA, 2004

69 Guide to the erection of multi-storey buildings (ref 42/06)

BCSA, 2006

70 Good construction practice for composite slabs

Publication No. 73, European Convention for Constructional Steelwork

Technical Committee 7 - Working Group 7.6

ECCS, 1993

71 National Structural Steelwork Specification for Building Construction (5

edition)

BCSA and SCI, 2007

72 Guidance Note GS28: Safe Erection of Structures

HMSO, 1984 (currently withdrawn, awaiting update)

73 Health and safety in construction (3

Edition))

HSG 150, HSE Books, 2006

74 CORUS

Slimdek Manual (http://www.corusconstruction.com)

75 MULLETT, D.L.

Design of RHS

Slimflor® edge beams (P169)

The Steel Construction Institute, 1997

76 LAWSON, R.M., MULLETT, D.L., and RACKHAM, J.W.

Design of Asymmetric

Slimflor® Beams using deep composite decking

(P175)

The Steel Construction Institute, 1997

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77 MULLETT, D.L., and LAWSON, R.M.

Design of

Slimflor® fabricated beams using deep composite decking

(P248)

The Steel Construction Institute, 1999

78 Slim Floor Integrated Design Software (SIDS)

Corus (http://www.corusconstruction.com)

79 NETHERCOT, D. A., SALTER, P. R. and MALIK, A. S.

Design of members subject to combined bending and torsion (P057)

The Steel Construction Institute, 1989

80 Lindaptor International, Brackenbeck Road, Bradford, West Yorkshire

BDN 2NF

81 WAY, A.J.

Guidance on meeting the robustness requirements in Approved Document

A (P341)

The Steel Construction Institute, 2005

82 BCSA Guide to the Installation of Deep Decking

Publication number 44/07

BCSA, 2007

MCRMA

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CHESHIRE

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www.mcrma.co.uk

Composite Slabs and Beams Using Steel Decking: Best Practice for Design and Construction

THE METAL CLADDING & ROOFING MANUFACTURERS ASSOCIATION

in partnership with

THE STEEL CONSTRUCTION INSTITUTE

COMPOSITE SLABS AND BEAMS

USING STEEL DECKING:

BEST PRACTICE FOR DESIGN

AND CONSTRUCTION

MCRMA Technical Paper No. 13

SCI Publication P300

CI/SfB

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MARCH 2009

THE STEEL CONSTRUCTION INSTITUTE

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