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ECCS EUROPEAN CONVENTION FOR CONSTRUCTIONAL STEELWORK CECM
CONVENTION EUROPEENNE DE LA CONSTRUCTION METALLIQUE E K S
EUROPAISCHE KONVENTION FR STAHLBAU
ECCS - Technical Committee 7 - Cold Formed Thin Walled Sheet
Steel Technical Working Group 7.6 - Composite Slabs
Design Manual for Composite Slabs
FIRST EDITION
1995 N87
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'I ECCS EUROPEAN CONVENTION FOR CONSTRUCTIONAL STEELWORK CECM
CONVENTION EUROPEENNE DE LA CONSTRUCTION METALLIQUE E K S InI
EUROPAISCHE KONVENTION FR STAHLBAU
ECCS - Technical Committee 7 - Cold Formed Thin Walled Sheet
Steel Technical Working Group 7.6 - Composite Slabs
Design Manual for Composite Slabs
FIRST EDITION
1995 N87
-
2 Design Manual for Composite Slabs
ISBN : 92-9147-000-8
Copyright 1995 by the European Convention for Constructional
Siceiwork All rights reserved. No part of this publication may be
reproduced, stored in a retrieval system, or transmitted in any
form or by any means, electronic, mechanical, photocopying,
recording, or otherwise, without the prior permission of the
Copyright owner: ECCS General Secretariat CECM Avenue des Ombrages,
32/36 bte 20 EKS 8-1200 BRUSSEL (Belgium)
Tel. 32/2-762 04 29 Fax 32/2-7620935
ECCS assumes no liability with respect to the use for any
application of the material and information contained in this
publication.
ECCS N 87
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Summary - Rsum - Zusammenfassung 3
SUMMARY This design manual has been produced for engineers as
well as project managers in design offices, for engineers in steel
construction companies and for engineers concerned with the
manufacture of profiled steel sheets for composite construction. It
contains a collection of the current knowledge for the design,
calculation and construction of composite slabs with profiled steel
sheeting. The manual is based on Eurocode 4, part 1.1, chapters 7,
10 and Annexe E which deals with composite construction, as well as
Eurocode 3, part 1.3 which considers the design of profiled steel
sheeting. It also contains complementary information on certain
aspects of composite construction not covered in the Eurocodes.
After a general introduction to composite slabs, in Chapter 1, the
manual presents Chapter 2 of the complementary document "Good
Construction Practice for Composite Slabs" making the link between
construction and design. Chapters 3 and 4 describe the conception,
the predesign and the detailing of structures using composite
slabs. The main part of the manual (Chapters 5-9) is devoted to the
design approaches for profiled steel sheeting and composite slabs,
giving, in particular, data relating to materials, to loads and to
the verification of the limit states. Finally, Chapter 10 presents
a series of numerical examples covering the predesign, the design
of the profile at the construction stage, the design of composite
slabs and designs for special situations.
RESUME Le present manuel de dimensionnement a t rdig pour les
ingnieurs en tant qu'auteurs de projet dans les bureaux d'tudes,
les ingnieurs des entreprises de construction mtallique et les
ingnieurs des unites de production des tles profiles pour dalles
mixtes. Ii constitue l'ensemble des connaissances actuelles dans le
domaine de Ia conception, du calcul et de la construction des
planchers mixtes avec tles profiles. Le manuel est base sur
l'Eurocode 4, partie 1.1, chapitres 7, 10 et annexe E, pour ce qui
concerne La construction mixte, ainsi que sur l'Eurocode 3, partie
1.3, pour ce qui concerne la tle profile. Ii contient galement des
informations complmentaires sur les sujets non traits dans ces
Eurocodes. Aprs une introduction gnerale sur les dalles mixtes
(chapitre 1), le manuel reprend intgralement le chapitre 2 du
document parallle "Good Construction Practice for Composite Slabs',
faisant le lien entre construction et dimensionnement. Les
chapitres 3 et 4 constituent une base de conception, de
prdimensionnement et d'tude des details des structures comportant
des planchers mixtes. La partie principale (chapitres 5 a 9) est
consacre au calcul des tles profiles et dalles mixtes, comprenant
en particulier les donnes relatives aux matriaux, aux charges et
aux verifications des tats limites. Finalement le chapitre 10
prsente des exemples numriques couvrant le prdimensionnement, le
dimensionnement de la tle au stade de btonnage, le dimensionnement
des dalles mixtes et des dimensionnements particuliers.
ECCS N 87
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4 Design Maiusal for Composite Slabs
ZUSAMMENFASSUNG Dieser Leitfaden zur Bemessung von Verbunddecken
wendet sich an Lngenieure und Projektleiter, die sowohi in
IngenieurbUros und Stahibaufirmen als auch in der Herstellung von
Profilbiechen fr den Verbundbau tAtig sind. Er enthAlt eine
Zusammenstdllung des aktuellen Wissensstandes Uber Entwurf,
Berechnung und Konstruktion von Verbunddecken mit
Profilbiechen.
Der Leitfaden basiert auf den Regelungen des Eurocode 4
"Bemessung und Konstruktion von Verbundtragweiten aus Stahl und
Beton", Teil 1.1, Kapitel 7, 10 und Anhang E sowie Eun)code 3, Tell
1.3, der sich mit der Bemessung von Profliblechen befaBt. Weiterhin
sind erganzende Informationen enthalten. die nicht in den Eurocodes
behandelt wenlen. Nach einer ailgemeinen Einftthrung in die
Verbunddeckenbauweise (Kapitel 1), steilt der vorliegende Leitfaden
das Kapitel 2 der ergnzenden Broschre "Good Constniction Practice
for Composite Slabs" vor und vethindet daxnit Konstniktion und
Bemessung. Die Kapitel 3 und 4 beinhalten den Entwurf, die
Vorbemessung sowie die Betrachtung verschiedener
Konstruktionsdetails bei der Anwendung von Verbunddecken.
Der Hauptteil dieses Leitfadens (Kapitel 5-9) ist den
Nachweisverfahren fUr Profilbieche und Verbunddecken gewidmet. Dazu
werden insbesondere Angaben zu Werkstoffen, Lastannabmen und dem
Nachweis von Grenzzustnden gemacht. SchlieBlich steilt Kapitel 10
eine Reihe von Rechenbeispielen vor, die die Vorbemessung, den
Nachweis der Proffibleche im Bauzustand, die Bemessung der
Verbunddecke und sogar Nachweisverfahren fr verschiedene
Sondeffitile beinhalten.
ECCS N 87
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Preface 5
Preface
The first edition of the EUROPEAN RECOMMENDATIONS FOR THE DESIGN
OF COMPOSITE FLOORS WiTH PROFILED STEEL SHEET was published in
September 1974 by the ECCS Committee 11 "Multi-Storey Buildings".
This ECCS document No. 14 was subsequently used as a reference
publication for Section 15 of the "Model Code for Composite
Structures" prepared by the Joint Committee on Composite Structures
(CEB-ECCS-FIP-IABSE) and published under the title COMPOSITE
STRUCTURES by the Construction Press, London, in 1981. The Model
Code was finally used as a draft format for the preparation of
Eurocode 4 "Design of Composite Steel and Concrete Structures",
1985.
In 1987 a technical group TWO 7.6 "Composite Slabs" was created
within the ECCS Technical Committee TC 7 (Cold-formed thin-walled
sheet steel in building), with the following tasks:
- To propose comments to Eurocode 4 (1985). - To revise the
document ECCS No. 14 (1974). - To coordinate research efforts in
the field of composite slabs.
The first part of the revision has been published as ECCS
document No 73, entitled "Good Construction Practice for Composite
Slabs". It contains practical information for construction site
personnel. The present document represents the second part of the
revision of ECCS document No. 14, concerning the design of
composite slabs. It will be completed by a separate document
concerning the way how to present load tables and diagrams for
practical design and will be entitled "Standard ECCS Product
Presentation for Composite Slabs". The working group TWO 7.6 is at
present composed of the following members:
BEGUIN Philippe France BLAFFART Henri Belgium BODE Helmut
Germany CRISINEL Michel (Chairman) Switzerland KOUKKARI Hell
Finland VELJKOVIC Milan Sweden OLEARY David (Tech. Sec.) Great
Bntain SCHUSTER Reinhold Canada STARK Jan Netherlands TSCHEMMERNEGG
Ferdinand Austria
Corresponding members are: BAEHRE Roif Germany BREKELMANS Jan
Netherlands DANIELS Byron Netherlands ENGEL Pierre France JANSS Jos
Belgium MAGNIEZ Georges France MELE Michele Italy MOREAU Gerard
France PATRICK Mark Australia PORTER Max USA SAUERBORN Ingeborg
Germany
ECCS N 87
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6 Design Manual for Composite Slabs
SOKOL Leopold France WOELFEL Eilhard Germany WRIGHT Howard Great
Britain
Principal contributions were provided by the following
members:
Philippe BEGUIN, CI1CM, St-Rezny-les-Chevreuse, France Henri
BLAFFART, Metal Pmfil Belgium, Liege, Belgium Dr Byron J. DANIELS,
TNO Building and Construction Research, Deift, Netherlands Dr
Pierre ENGEL, PAB-Sollac, Nanterre, France Mrs Hell KOUKKARI, VTF
Finland David OLEARY, Civil Engineering Department, University of
Salford, Great Britain Dr Leopold SOKOL, PAB-Sollac, Nanteire,
France Mrs Ingeborg SAUERBORN, University of Kaiserslautem,
Germany. Thanks are also due to many more colleagues who took part
in working group meetings or offered suggestions.
Michel CRISINEL Prof. Michael DAVIES Swiss Federal Institute of
Technology (EPFL) Civil Engineering Department Institute for Steel
Structures (ICOM) University of Salford, Lausanne, Switzerland
Salford, Great Britain
Chairman of TWG 7.6 Chainnan of TC7
Lausanne and Salford, November 1995.
Figures The figures have been graciously placed at our disposal
by the following companies and institutions: - Ecole polytechnique
f&Irsle de Lausanne (EPFL), Construction mtallique (ICOM),
Lausanne (CR):
1.1 1.3/3.1 + 3.4 / 7.1 / 8.1 / 8.4 + 8.6 / 8.9 / 8.11
/8.12/10.4.1 -'- 10.4.4. - Schweizerische Arbeitsgemeinschaft fr
Holzftrschung (SAH), Lignuxn, ZUrich (CR):
3.20 - Umversitt Kaiserslautern, Bauingenieurwesen, Fachgebiet
Stahlbau, Kaiserslautern (D):
8.13 + 8.15 / 10.3.1 + 10.3.10 / 10.5.1 + 10.5.5. - Produils
Btiment de Sollac (PAB-Sollac), Nanteire (F):
3.15 + 3.19 / 3.21 + 3.25 / 3.29 / 4.7 / 7.2 /7.3 / 9.1 / 9.5 +
9.24 /10.1.1 / 10.2.1. - Centre Technique Industriel de la
Construction M&allique (CTICM), Saint-Rmy-ls-Chevreuse (F):
4.14.6/4.8+4.11/4.13/8.3. - Steel Construction Institute (SC!),
Ascot (UK):
2.1 /22 / 2.3 / 3.5 3.14 / 3.26 + 3.28 / 4.12(a). Schweizerische
Zentralstelle fr Stahlbau (SZS), ZUrich (CR):
4.12 (b) HiBond by Metecno, London (UK):
8.2 - Comit Eumpeen de Nonnalisation (CEN), Bruxelles (B):
6.1 / 8.7 / 8.8 / 8.10. The manuscript of this document has been
prepared at the Swiss Federal Institute of Technology (EPFL),
Institute for Steel Structures (ICOM), Lausanne, Switzerland.
ECCS N 87
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Conteius 7
CONTENTS
Page
SCOPE OF THE PUBLICATION 9
NOTATION 10
1 INTRODUCTION 13 1.1 State-of-the-art 13 1.2 Behaviour 17 1.3
Design requirements 20
2 LIST OF ESSENTIAL CONSTRUCTION SITE INFORMATION 23 2.1 General
23 2.2 Decking bundle identification 23 2.3 Information for steel
sub-contractors 24 2.4 Information for concrete sub-contractors 25
2.5. Construction loads 25
3 PRELIMINARY CONSIDERATIONS AND PRE-DESIGN 29 3.1 Introduction
29 3.2 Possible composite action with beams 29 3.3 Column layout
and the various beam arrangements 31 3.4 Renovation and
refurbishment schemes 39 3.5 Shallow floor construction 43 3.6
Pre-design 45
4 DETAILING REQUIREMENTS 49 4.1 General conditions for steel
sheeting and composite slab 49 4.2 Construction stage 50 4.3
Composite stage 54
5 PROPERTIES OF MATERIALS 59 5.1 PrOfiled steel sheeting 59 5.2
Concrete 60 5.3 Reinforcing steel 61 5.4 Structural steel 61 5.5
Partial safety factors for resistance and material properties
62
6 LOADS AND ACTIONS 63 6.1 General 63 6.2 Loads for the
construction stage 63 6.3 Loads for the composite stage 64
ECCS N 87
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8 Design Manual for Composite Slabs
7 BASIS OF DESIGN - CONSTRUCTION CONDITION .67 7.1 Design
procedure 67 7.2 Cross-sectional design resistances 69 7.3
Ultimatelimitstate 71 7.4 Serviceabilitylimitstates 74
8 BASIS OF DESIGN - COMPOSITE CONDITION 77 8.1 Design procedure
77 8.2 Cross-sectional resistances 83 8.3 Deflections 89 8.4
Verification. 91
9 SPECIAL DESIGN CONSIDERATIONS 97 9.1 Diaphragm effect 97 9.2
Fire design 100 9.3 Openings and penetration holes 105 9.4
Concentrated loads 114 9.5 Sound insulation 116 9.6 Corrosion
protection 119
10 DESIGN EXAMPLES 121 10.1 Preliminary design example 121 10.2
Verification of the sheeting as shuttering 123 10.3 First typical
design example 131 10.4 Second typical design example 143 10.5
Special design example 152 10.6 Design example for moving
concentrated load 158 10.7 Design of composite slab with additional
reinforcement carrying moving concentrated
load 162
BIBLIOGRAPHY 167
ECCS N 87
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Scope of the publication 9
SCOPE OF THE PUBLICATION The purpose of this publication is to
present information on the design of composite slabs carried Out in
accordance with Eurocode 4. The design and construction process for
these slabs involves basically two stages: the temporary stage -
when the profiled steel sheeting (hereafter referred to as
decking), acting as a
one-way spanning element, carries the weight of the wet concrete
and associated construction loads, the permanent stage - when the
one-way spanning composite slab carries the imposed loads and a
percentage of the dead load dependent on the mode of
construction. The publication is intended to complement Eurocode 4
"Design of Composite Steel and Concrete Structures" (particulary
Chapters 7, 9, 10 and Annex E) and has been produced by the ECCS
Technical Committee 7, Working Group 7.6 "Composite Slabs". In
addition to the presentation of the normal design criteria for the
ultimate and serviceability limit states, attention is given to the
special design considerations of fire resistance, the treatment of
openings, in-plane bracing and the effects of concentrated loads.
Further information particular to the implementation of good site
practice for composite slabs is available in the ECCS document
"Good Construction Practice for Composite Slabs" which lists
amongst other things the information which should be passed on from
the designer/architect to site personnel. Another reference is the
ECCS publication No 72 "Composite Beams and Columns to Eurocode 4"
produced by the ECCS Technical Committee 11 "Composite
Structures".
ECCS N 87
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10 Design Manual for Composite Slabs
NOTATION
Notation is presented in detail, including subscripts to
symbols. Reference should also be made to Eurocode 4 Part 1.1.
Symbols Latin letters A : Cross-sectional area B : width b :
width C : perimeter, coefficient c : coefficient D : orthogonal
bending stiffeness d : pitch of corrugation E : modulus of
elasticity (Youngs modulus) e : distance F strength of fastener f :
ultimate strength of a material 0 : self weight, permanent action g
: self weight, permanent action h : thickness, depth, height I :
moment of inertia, second moment of area k : factor, constant,
coefficient L : span length, length 1,1, span length, length,
horizontal distance M internal bending moment, bending resistance m
: coefficient N : axial force n : number, ratio P point load,
concentrated load p : pitch of fasteners, unifonn distributed load
Q imposed load, variable action q imposed load, variable action,
uniform load R : resistance, support reaction r : radius S action
effect s : construction load t sheet thickness V : vertical shear,
shear resistance, shear buckling strength W : section modulus w :
beam spacing x,y,z : coordinates x : position of neutral axis z :
leverarm
ECCS N 87
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Notation
Greek letters
a coefficient B coefficient T partial safety factor 6
deflection
strain Ti degree of shear connection o rotation
slenderness p factor, density, reinforcement ratio o normal
stress sp web inclination
shear stress x buckling coefficient
Subscripts
1,2,3 : number a structural steel, bearing adm : admissible,
allowable ap : decking steel b : bottom c : concrete, compression
corn : compressive cr : critical d : design value e elastic,
effective eff : effective end end support f : full shear
connection, floor finishes G : permanent action g : permanent
action, global h haunch i number mt intermediate k characteristic
1, : longitudinal, local M : material m mean, effective,
constniction stage max maximum mm minimum o reference value,
ovethang p plastic, profiled sheeting, plane element, point load,
punching Q : variable action q : variable action R resistance r
reduced, relative S internal forces or moments
ECCS N 87
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12 - Design Manual for Composite Slabs
s reinforcement, shear, shrinkage, stiffener ser service
internal forces or moments span span sup superior, upper, suppoit T
thermal t : tensile, total, top test experimental, test value u :
ultimate, uncracked alt : ultimate v : vertical, steel - concrete
connection, shear w : web x,y,z : coordinates y : yieldofsteel a :
normal stress
ECCS N 87
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Introduction 13
1 INTRODUCTION 1.1 STATE-OF-THE-ART
1.1.1 The development of composite slabs A composite slab
comprises steel decking, reinforcement and cast-in situ concrete
(Figure 1.1). The combination of the different elements is such
that both structural and economic advantages are achieved.
Initially the decking acts as both a platform for construction and
as shuttering for the wet concrete. Secondly, when the concrete has
hardened the decking carries some or all of the tensile forces in
the slab caused by a load which is subsequently imposed. The
concrete carries the compressive and shear forces in the composite
slab and provides the sound insulation and fire resistance for the
structure. The surface and shape of the decking is formed in such a
way that at the interface between the decking and concrete
horizontal shear forces can be transmitted. This is necessary to
ensure the composite action between steel and concrete.
Figure 1.1 - Composite slab
Composite slab systems were first developed in the late 1930's
for tall building applications. At that tune the technique brought
a considerable dead-load reduction and it was essentially seen as a
substitute for traditional reinforced concrete slabs. Because of
their efficiency and advantages, composite slabs were soon used for
a wide range of construction projects invariably based on
structural steel framing (high rise, low rise and industrial
buildings). During the late 1980's the introduction of fastrack
construction methods brought a new interest in steel design and
consequently a logical use of composite flooring. This change in
mentality, coupled with the search by the manufacturers to use
composite slabs with other framing materials, marked a new period
of expansion for the technique. Steel decking is now used in
conjunction with steel frames but also with concrete, prestressed
concrete and timber structures.
ECCS N 87
secondary beam
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14 Design Manual for Composite Slabs
Composite floors are employed in a great variety of
applications. The overall depth of composite slabs generally varies
between 80 mm and 250 mm with a bare metal thickness of steel sheet
between 0.7 and 1.5 mm (Fig. 1.2). The robustness of composite
floors identifies them for the construction of thin slabs (80 rum
to 120 mm) with moderate loading or medium span requirements. Other
regular types of slabs (130 mm to 250 mm) with heavy loading or
long span requirements axe also possible.
4 150 = 600 4 z 183 732
38.1 1373 B 89
4 x 150 600 I- 5x200= 1000 -l A ___'
___ B L1_J - L'.-I B L_.J t.2.J i 55 4 x 150 95 750 x 150
600
4x183= 732 3x190570
_1122WT' 5xl76=880 l
3x1O4312
J\J'UEjkJfl1 Figure 1.2 - Examples of decking used in composite
slabs
1.1.2 The use of composite slabs Decking and composite slabs
predominantly carry imposed vertical loads in bending and shear.
Because both the decking and the composite slab do not have the
same geometry in each direction (non- isotropic) a two-way design
is complicated. To simplify this situation, design procedures
consider only the bending and shear resistances along the
longitudinal axis (in the direction of the ribs). This results in
conservative estimates of actual load carrying capacity. Decking
used in combination with concrete (composite slabs) have been
designed especially for this purpose. It is thus not advisable to
use cladding or roofing profiles as composite slab decking. Most
decking manufacturers have produced table or charts with all the
necessary cross-sectional properties. This simplifies the designers
task as decking geometries can be quite complicated. Standard
protection against corrosion of decking is normally a thin layer of
galvanizing. This protection is generally sufficient for the most
common use of composite floors (dry interior atmosphere). For more
severe applications, other types of protection are available and an
adequate layer must be provided.
ECCS N 87
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!nLroduction 15
Composite slab design is normally both simple and straight
forward. Minimum slab thicknesses have been established to ensure
that significant two-way load distribution can occur. Non-standard
bay geometries and large openings represent cases for which special
consideration must be given. Lastly, heavy concentrated loads,
cyclical and dynamic loads must be treated with caution. Some
examples of the widespread use of composite slabs in various
branches of the construction industry are now described.
a) Office and administrative buildings Long span steel
structures associated with composite slabs offer architects and
their clients a greater free space for offices, administrative and
commercial buildings. The beams are usually of sufficient depth for
the primary service ducts to be accommodated by providing holes in
the beam webs. The services may be directly suspended, with
possibly a false ceiling, from the deck which is generally provided
with a convenient suspension system.
b) Renovation schemes Renovation schemes often require
irregularly shaped slabs and access to the construction site is
difficult. Often the low carrying capacity of the existing
foundation requires a severe limitation of the dead load. Composite
floors are lighter in weight than conventional reinforced concrete
slabs by up to 1.0 kN/m2 and are therefore very economical for
these applications.
C) Housing and community service buildings There are many
examples of family houses, housing schemes, schools, hospitals and
other community buildings whose construction is based on the use of
composite flooring. The satisfactory performance of composite slab
systems in terms of fire resistance, acoustic and thermal
insulation properties provide the high performance criteria
required for such premises.
d) Car park units Composite floors may be used for car park
construction built either as underground structures (diaphragm
walling) or as multi-storey aerial platforms (framed structures).
In both cases the speed and ease of erection coupled with the good
span/strength capacity and reliable composite action offered by
these floors lead to very competitive solutions.
e) Warehouse and storage buildings Warehouse and storage
facilities are essentially buildings which are purpose designed to
store various types of goods. Generally the layout is made as open
as possible to allow flexibility of use. They are invariably
characterised by heavy loads applied to the floors. The distributed
and point-loads transmitted to the floor by pallet racks and/or
fork-lift trucks may require special design attention.
Nevertheless, composite slabs may provide a solution. There is also
the advantage that the sprinkler fire devices and other piping
networks may be suspended.
f) Industrial buildings and processing plants Composite floors
may be designed to carry loadings met in industrial buildings. High
uniformly distributed loads, in conjunction with punching forces
and/or fork-lift trucks axles up to 30 kN, can be accommodated. For
these buildings the steel deck is most often associated with steel
framed structures. The panels are quickly and easily fastened onto
the steel beams with shot-fired pins. Slabs may be attached to the
beams by mean of shear connectors in order to transmit the in-plane
forces providing an
ECCS N 87
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16 Design Manual for Composite Slabs
efficient form of bracing to static and dynamic loading. The
stiffness of composite slabs is also beneficial for testing
laboratories where deflections and vibrations must be as small as
possible.
1.1.3 The main advantages of composite slabs Composite floors
are now the popular choice for a wide range of structures, offering
the designer and his client the following advantages:
Working platform Before concreting, the decking provides an
excellent safe working platform which speeds the construction
process for other trades.
Permanent shuttering The steel deck spans from beam to beam,
forming permanent formwork to the concrete, the need for temporary
props is often not necessary. The decking constitutes a good vapour
barrier. The soffit remains clean after concreting and the use of
colour-coated steel sheets can give an attractive aesthetical
aspect to the ceiling.
Steel reinforcement The steel reinforcement provided by the
cross-section of the deck is usually sufficient to resist positive
moments. Additional fabric reinforcement may be provided in the
slab to resist shrinkage or temperature movements or to provide
continuity over intermediate supports (hogging moments). Composite
action is obtained by the profile shape or by mechanical means
provided by indentation or embossment of the steel proffle.
Concrete and steel saving The hollow shape of the proffle steel
decking produces a saving of concrete which is variable with the
deck type (up to 40 litres/rn2). This reduction in of the slab
self-weight produces a significant reduction of the dead load (up
to 1.0 kN/m2) carried by the structure and the foundations.
Composite slabs are usually thinner than conventional reinforced
concrete slabs because the relatively high steel area in the deck
(between 1000 to 1500 mm2/metre width) is working at lower
stresses.
Speed and simplicity of construction The unique properties of
the steel deck combining high rigidity and low weight, ease
considerably the transportation and the storage of the material on
site. Often one lorry is capable of carrying up to 1500 rn2 of
flooring. A team of four men can set up to 400 m2 of decking per
day. Panels are light, pre-fabricated elements that are easily
transportated and set in place by two or three men.
Quality controlled products Steel deck proffles are manufactured
under factory controlled conditions. This allows the establishment
of strict quality procedures and less random work on the
construction site. This results in a greater accuracy of
construction, assisting the following trades.
Service and building flexibility Composite floors are adaptable.
They may readily be modified during the life of the building. This
is especially true when the slab is used with framed structures. It
is then always possible to create a new staircase between two
floors by just simply adding the necessary trimmer beams. ECCS N
87
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!ntrodziction 17
Recent developments and changes in communications, information
and computing technology have shown the importance of being able to
modify quickly the building services arrangement. Because of the
present rate of change, it is not possible to predict precisely
what further developments may occur at the time the building is
constructed.
Furthermore, in commercially let buildings or in multi-shared
properties it must be possible to modify the services without
violating the privacy of the other occupants. In order to solve
this problem, engineers have to choose between several solutions.
There are generally three: Accommodation in the ceiling
Accommodation within a false floor Accommodation in coffer box
running along the walls The two last solutions are limited to
specific services and they may cause a loss of space or result in
poor appearance. Composite floors are rarely used without a false
ceiling beneath the beams usually for aesthetical reasons. The gap
between the soffit and the bottom flange constitutes an ideal zone
in which services may be hidden. Many "dove-tailed" decks have
slots or pre-formed tags to connect hanger wires. It is therefore
possible to suspend new cable networks and piping without
undertaking costly and noisy drilling attachments during building
maintenance.
Temporary bracing of the steel structures The fastening of the
steel deck to the structure prior to concreting provides a stiff
and reliable floor bracing. Diaphragm action, which is produced by
the capacity of the steel deck to resist distorsion in its own plan
readily obviates the need for temporaiy horizontal bracing during
construction.
Composite beam construction Shear connectors are generally used
to provide connection between the underlying steel beam and the
composite slab. This composite beam configuration increases
considerably the strength of the structure, using the same beams or
more efficiently smaller beams. The beam height but also the weight
of the steel beam (between 15 and 30%) are effectively reduced (see
also ECCS publication No 72).
1.2 BEHAVIOUR
1.2.1 BehavIour of the steel decking (construction stage) At the
construction stage, when the concrete is wet, the decking alone
resists the external loads. The behaviour is then comparable to the
behaviour of the profiles for roofing. The decking is subjected
mainly to bending and shear. Compression due to bending of the
profile may arise in either the flanges and in parts of the webs.
Shear occurs essentially near the supports. The thin component
plate elements which make up the decking may buckle prior to yield
under these compressive and shear stresses, thereby reducing its
load can-ying capacity and stiffness. The current design procedures
rely on the concept of effective width to provide a method for the
calculation of this type of thin walled members. Clearly, the
effective width of the compression flange depends upon the maximum
stress imposed on the flange, which in turn depends on the location
of the neutral axis of the cross-section. As the effective area of
the flange decreases under increasing bending moment, the neutral
axis of the proffle is lowered and the extreme fibre stresses will
change accordingly. Iterative design becomes necessary for strength
and serviceability calculations. It is also possible to determine
design characteristics and methods by tests.
ECCS N 87
-
18 Design Manual for Composite Slabs
1.2.2 BehavIour of composite slabs (permanent stage) The
behaviour of composite slabs is different to that of other similar
fonns of composite construction, such as reinforced concrete and
composite beams of steel and concrete. In reinforced concrete,
composite action is achieved as a result of the bond resistance of
the reinforcement due generally to the cross section of the
deformed bars used. This bond resistance, verified by tests, is
equal to the ultimate tensile resistance of the reinforcement which
ensures that the slab may always develop the full flexural
resistance. In composite beams, composite action is achieved by
connectors fixed to the top flange of the steel beam. The design of
such connections is based on the assumption that the beam attains
ultimate bending resistance (full connection). If the number of
connectors is smaller that required for full connection then the
connection is partial. In this case the ultimate resistance to
bending depends essentially on the number of connectors, the span
of the beam and the method of construction. The composite slab with
decking has elements of both systems. On one hand decking with
embossments or anchorages compares to reinforcement, whereas on the
other hand decking is an element with bending rigidity similar to
steel beams. The difference results from the fact that decking, and
similary the embossments, can be deformed. Also, unlike
reinforcement, decking does not benefit from being totally embedded
in concrete. Such deformation behaviour depends on numerous
parameters, which makes the analysis of the actual behaviour of
composite slabs more complicated. A composite slab behaves in
normal loading conditions usually as a cracked structure bent in
the longitudinal direction of the sheet. 1) When the loads are
small, the slab might be uncracked. The composite action between
the parts is
full, and the stresses of the sheet and concrete are linearly
dependent on the strains. 2) The cracking in the concrete in
tension reduces the stiffiess of the structure and increase of
loads
causes greater deflections of the slab than in uncracked state.
The adhesion between the sheet and the concrete is capable of
transferring the shear force between the cracks. It may happen that
in the ends of the slab the adhesion fails.
3) When a composite slab is experimentally or accidentally
loaded by higher loads than the design loads, its behaviour greatly
depends on the type of the steel sheet. In all composite slabs some
relative slip may take place between the elements when the shear
stresses between them is greater than the strength of the
joint.
4) Composite slabs have different failure modes depending not
only on the sheet type but also on the dimensions of the structure.
There are types of proffle which fail quickly if the load is larger
than the first slip load (brittle or non-ductile behaviour). Some
types of sheet can undergo great deflections before failure when
the loads are gradually increased, although the relative slip
increases at the same time (ductile behaviour). The failure of a
composite slab may occur at the interface between the steel sheet
and the concrete as a shear bond failure or as material failure in
one element.
For the case when the slab has been propped during construction,
the slab will deflect instantly after the removal of the props.
This initial loading can cause cracking in concrete. Permanent and
transient moving loads on the slab cause instant changes in
deflection. The concrete will also creep for several years which
will gradually increase the deflections of the slab. The manner in
which a composite slab behaves during a loading test enables the
basic information for the design of a particular type of the sheet
to be developped. Because there are a great variety of the sheet
types and there are no common design formula, all sheet types must
be subjected to tests. Two modes of behaviour can be identified
using Figure 1.3 from a loading test where the load was gradually
increased by displacement controlled jacks; At first the
load-deflection curve is approximately linear for all types of
slabs which corresponds to the behaviour of a composite element
bonded at the interface by chemical adhesion and/or friction. ECCS
N 87
-
Introduction 19
Mode 1 - brittle behaviour The load suddenly decreases at a
certain point where the relative slip is such that the surface bond
is broken. All the shear force must be taken up by friction and
embossments. The decrease in load depends on the quality of the
mechanical embossments. With further deformation of the slab the
load increases again slightly without ever reaching the level of
the initial phase. None of the mechanical connections in the slab
are capable of assuring a composite effect superior to that of
simple surface adhesion. It should be noted that the decrease of
the load is not due to the sudden opening of tension cracks in the
concrete, because this is prevented by the decking, but by relative
slip between the concrete and the decking.
Load P (kN)
50
40
30
20
10
Deflection
Figure 1.3 - Two typical behaviour modes of composite slabs
Mode 2- ductile behaviour The mechanical connection is capable
of transferring the shear force until failure occurs. Failure is
produced either by bending, corresponding to total connection, or
by longitudinal shear, corresponding to partial connection.
Acconling to the Eurocode 4, the behaviour is classified as
ductile if the failure load exceeds the load causing first recorded
end slip by more than 10%. The load causing first recorded end slip
is the load at which the slip at any end of the slab is greater
than 0.5 mm. Otherwise, the behaviour is classified brittle (or
non-ductile). Eurocode 4 takes into account of the ductile or
non-ductile behaviour of a composite slab by means of different
partial safety factors applied to the failure load.
ECCS N 87
Slip at first end
2
P P
Slip at second end
20 30 40 6 [mm]
-
20 Design Manual for Composite Slabs
1.3 DESIGN REQUIREMENTS
1.3.1 Structural stages A distinctive characteristic of
composite slabs is the two structural states that exist: firstly,
the temporary stage of construction when only the decking resists
the applied loads and secondly, the permanent stage when the
concrete is bonded to the steel allowing composite action. For the
both structural stages, it shall be verified that no relevant limit
states are exceeded: Profiled sheeting as shuttering Verifications
at the ultimate limit state and the serviceability limit state are
required for the safety and the serviceability of the proffled
sheeting acting as formwork for the wet concrete. The effects of
props (if used) shall be taken into account in this design
situation. Composite slabs Verifications at the ultimate limit
state and the serviceability limit state are required for the
safety and the serviceability of the composite slab after composite
behaviour has commenced and any props have been removed.
1.3.2 Verification conditions for the ultimate limit states The
resistance of the decking (temporary stage of construction) or the
composite slab (pemianent stage) must be sufficient to resist the
external actions. Each section or member must be capable of
resisting the internal forces determined by the analysis of the
structure. When considering a limit state of rupture or excessive
deformation, it shall be verified that:
Sd Rd
Sd : design value of action effects Rd : design value of the
resistance Combination of actions For each load case, design values
for the effects of actions shall be determined from combination
rules involving design values of actions, as identified by Table
1.1. The most unfavourable combinations are considered at each
critical location of the structure, for example, at the points of
maximum negative or positive moment, In Table 1.1 a combination
factor of 0.9 is taken into account. Eurocodes permit the use of
other combination factors, if reliable load data is available.
1.3.3 VerIfication conditions for the serviceability limit
states The behaviour of the decking under its self-weight and the
weight of the wet concrete must fall within accepted limits. The
following verifications shall be made: deflection is within the
admissible limit, marks on the sheet due to the props should be
avoided. The behaviour of the composite slab under permanent loads
and variable service loads must fall within accepted limits.
ECCS N 87
-
introduction
Table 1.1 - Combinations of actions for the ultimate limit
state
21
2. 1G 1.35
Gk+0.9.'yQ.Qk (*) G + 0.9 1.50
The following verifications shall be made: Concrete cracking in
hogging moment regions is within a limited width. Deflection, or
variation of deflection, auairiing the admissible limit. Vibrations
above a limiting value. Combination of actions For each load case,
design values for the effects of actions shall be determined fmm
combination rules involving design values of actions as identified
by Table 1.2.
TabLe 1.2 - Combinations of actions for the serviceability limit
state
Load combinations to be considered: Parameters defined in Table
1.1 1. GkQk,max
2. Gk + O.9Ql
ECCS N 87
Load combinations to be considered: YGGk+YQQkmaX
1. 1.35Gk+l.5OQk,max (*)
= permanent actions, eg. self weight
Qk = variable actions, eg. imposed loads on floors, snow loads,
wind loads
(*) If the dead load G counteracts the variable action Q:
= the variable action which causes the largest effect at a
given
= 1.00
location
If a variable load Q counteracts the dominant loading:
= partial safety factor for permanent actions
YQ actions
= partial safety factor for variable
-
Page blank in original
-
Consiruction site information 23
2. LIST OF ESSENTIAL CONSTRUCTION SITE INFORMATION 2.1 GENERAL
This chapter contains the minimum amount of information that the
designer and/or architect should supply to construction site
personnel. Most of the information contained in this chapter is
used by the designer and/or architect when calculating decking and
composite slab resistances. Ignorance of this information by field
personnel can lead to situations that the designer and/or architect
has not forseen. Any variations from the conditions specified by
the designer and/or architect should be brought to their
attention.
2.2 DECKING BUNDLE IDENTIFICATION An identification tag should
be attached to each decking bundle delivered to the job site. An
example tag is shown in Figure 2.1. Tags may look somewhat
different but should contain the following information: Total
bundle weight Deck type, surface condition, thickness Bundle
identification code The number, length and thickness of each panel
The bundle identification code will also appear on the decking
layout plan, and can thus be used to identify the bay(s) for which
the bundle is designated. A product description including the
following should be available on site or from the decking
manufacturer's technical information service: Rib height Embossment
depths The yield strength of the core material The type of coatings
(if any) and coating thickness
Job No. Deck type Galvanised id1e identification / o 0 XYPD 01
43000 - MARK: AZI 0 Q GRD FLR LVL 1.00 mm Q
o 4x7295.0 o lOx 10075.0
o 3x3335.0 Bundle weight o 0.967 tonnes
0 0
" 0 V
Thickness (mm)
Figure 2.1 - Example decking bundle identification
ECCS N 87
Location
N I
No. of sheets Length (mm)
-
24 Design Manual for Composite Slabs
2.3 INFORMATION FOR STEEL SUB-CONTRACTORS The steel
sub-contractor should be provided with a decking layout drawing
which divides the floor into bays. A bay consists of panels from
the same decking bundle that are to be laid Out and fixed to the
underlying frame as one unit. Each bay of each floor with composite
slabs should be contained in this drawing. Information not included
in this chapter may also be specified in this drawing. Such
information may be necessary because of variations from standard
practices. All such variations should be clearly indicated
(highlighted) by the designer and/or architect.
2.3.1 Decking layout drawing
Bay definition
Bays may be defined using dashed lines and a diagonal solid
line, such as are shown in Figure 2.2. A reference number may be
placed in a circle on the diagonal line to indicate that special
bay instructions are given elsewhere on the drawing. The
approximate location of the first panel to be placed in each bay
and the direction in which layout should continue is indicated.
Other information given for each bay is: Decking rib orientation
The number of panels The bundle identification code The panel
length
Columns and supports The location and orientation of each column
should be indicated as shown in Figure 2.2. All supports (permanent
or temporary) should be included. Permanent supports are drawn
using a solid line, temporary supports are drawn using a dashed
line and the letters TP (Temporary Prop-line). The minimum width of
the temporary support in contact with the decking should be given
(the minimum bearing width) together with the line load reaction
[kN/m] on the props.
Openings and edges The location and orientation of all openings
and edges with respect to permanent supports should be given. This
includes both permanent and temporary edges. Such information
should be indicated in boxes identified by the words "Edge trim",
see Figure 2.2. There may be more than one reference box for each
edge. The following information should be contained in each
reference box: A reference letter (or number) for details which
appears elsewhere The decking rib height The distance between the
edge of the decking and the centreline of the nearest permanent
support. Details should be available for all exterior edges and
edges next to openings. Details may also be necessary for temporary
edges. Temporary edges include changes in the orientation of the
decking ribs and edges between concretings. Examples of support and
edge details are given in the document "Good Construction Practice
for Composite Slabs" (Figures 17 and 19 of Chapter 6, and in
Figures 24 and 25 of Chapter 8).
Panel fastening Panels may be fastened only to permanent
supports and to adjacent panels (seam fasteners). Fastening should
be undertaken immediately after each panel or bay has being laid
out. For each bay special fastener information may be given.
Fastener information is indicated on the decking layout drawing
using infonnation boxes identified by the word "Fasteners", as
shown in Figure 2.3. Each information box should contain the
following: ECCS N 87
-
Construction site information 25
Fastener type Number of fasteners needed to fix each panel to
each support, or the minimum number of seam
fasteners per metre length.
2.3.2 Shear connectors Shear connectors are normally shown on
structural drawings for composite beams. This information need only
be included in the decking layout drawing if holes must be cut in
the decking, or if shear connectors are to be installed using
through deck welding or through deck shot-firing. In these cases
the location, type and length of each shear connector should be
indicated on the decking layout drawing. The orientation and
location of the shear connector relative to decking ribs should be
clearly indicated.
The minimum distance between the centreline of the shear
connector and the edge of the decking should be given. Installation
and quality control procedure information from the shear connector
supplier should be available on site.
2.4 INFORMATION FOR CONCRETE SUB-CONTRACTORS A reinforcement
layout drawing should be made available to the appropriate
contractor for each bay of each floor. The location, length,
minimum overlap and minimum concrete cover of all reinforcement in
the composite slab should be indicated. The specified grade of all
reinforcement should also be indicated on this drawing. This grade
should be checked against the identification tag for each
reinforcement bundle. Important reinforcement details (such as near
supports, openings and edges) should be referenced and placed on
this drawing or on the decking layout drawing. Any special
preparation needed to ensure that excessive leakage does not occur
during concrete should be indicated. The concreting work should be
started above the permanent supports of the slab and proceed
towards the middle areas of the sheets. The height from which
concrete falls should be as low as possible. The order of the work
should be clearly shown in the drawings for the building site.
Information concerning the concrete mix should be provided in the
same manner as for other reinforced concrete components. Minimum
necessary concreting information includes the following: The
minimum concrete compressive strength Maximum aggregate size Types
of admixtures : it is necessary to check if the admixtures used are
compatible with the coating
of the profiled sheets. For example, the use of antifreeze-type
admixtures is prohibited because they are definitely not compatible
with zinc coatings.
2.5 CONSTRUCTION LOADS The design load that may be carried by
the decking as a temporary working platform, as shuttering and by
the composite slab should be clearly indicated on the decking
layout drawings and on appropriate concreting drawings (in kN/m2).
Special loading limitations should be clearly indicated for each
bay. In addition the following values may be necessary: The minimum
concrete compressive strength at which temporary supports may be
removed (can be
given in terms of days after concreting) The minimum concrete
compressive strength at which temporary construction load may be
applied
(can be given in terms of days after concerting) The maximum
allowable vehicular axle weight.
ECCS N 87
-
I I
til (. z 0 00
Tem
pora
ry p
ropl
ine
Bund
le id
entif
icatio
n
0
I
Ref
eren
ce fo
r D
eck
edge
det
ail
nb
draw
ings
he
ight
ln
dica
tor s
tart
poi
nt fo
r la
ying
of p
anel
s
No m
ere
than
(4) w
ork
men
al
low
ed on
deck
ing.
A
ncho
rage
s pro
vide
d at
supp
orts.
No
mpo
rsry
pr
op.lo
.ds a
llow
ed pr
ior t
o co
ncr
etin
g.
Tape
joints
betw
een
Bay
s (1)
and (
2).
No s
peci
al lo
ad
rest
rictio
ns.
-
Construction site information
1.. U C
(1 Id
1., >.. U
27
Figure 2.3 - Exa,nple decking layout drawing (Fasteners details
only)
ECCS N 87
UVC
03 z.g&
C U
. U
U 4)
.C U
-
Page blank in original
-
Prelijninary considerations and pre-design 29
3 PRELIMINARY CONSIDERATIONS AND PRE-DESIGN
3.1 INTRODUCTION This chapter has been written for architects
and engineers and more generally for all those who have to produce
a quick but sound pre-design for a composite floor. This might be
required for either a preliminary project or a cost estimation
exercise. Experience often shows that the architects must be given
a realistic estimation of the floor system depth including slabs,
suppoiting beams and ceiling. This is necessary because the overall
depth of the floor has a direct influence on the total building
height. This parameter which is usually fixed by urban planners may
be restricted for a specific area. The building height depends
directly on the floor arrangement and therefore it is not an
exageration to state that the simple pre-design estimate of the
composite slab thickness is meaningless for a project if the
designer does not consider the beam spacing, the beam span, the
total acceptable depth of the floor system (beam + slab) and also
the column layout.
3.2 POSSIBLE COMPOSITE ACTION WITH BEAMS The use of composite
beams follows naturally from the use of composite slabs in the
transverse direction. Shear connectors are generally used to
provide shear connection between the underlying steel beam and the
concrete slab. The resulting in-span behaviour of these components
is an optimum use of the two materials where the concrete works in
compression and the steel beam mainly in tension (see Figure 3.1).
In a composite beani the resulting centroid of the composite
section is usually positioned in the vincinity of the top flange of
the steel beam. The area of the steel beam in compression is
therefore significantly reduced, and may even be zero. This so
called 'composite beam' arrangement increases considerably the
strength of the element. The beam height but also the weight of the
steel beam is effectively reduced by 15% to 30% (see also Figure
3.2). Recent fire tests carried out in France and the U.K. have
shown that it is possible to obtain a fire stability of 30 minutes
for unprotected composite steel beams. Composite beam arrangements
also make the structure stiffer and more ductile. Finally this type
of structure has a improved resistance to seismic forces. The
numerous beam solutions applicable to the composite slabs are
outhned in section 3.3.2a).
3.2.1 Composite beams with welded shear connectors Welded shear
connectors can be attached on site or in the workshop. The studs
are welded directly onto the beam (welded in the shop) or directly
through the steel deck (welded on site). Welded stud connectors
were initially used for composite bridges. These connectors have
various diameters between 12 and 22 mm (see Figure 3.3). 3.2.2
Composite beams with nailed shear connectors Cold formed angle
connectors made of light-gauge steel are connected to the beam
through the deck by using shot fired nails. This technique is very
practical on site because the tools are light and easy to use. The
top flange can be painted and the presence of moisture between the
deck and the beam flange does not affect the performance of the
system. However the number and the capacity of this type of
connector to resist the shear forces is limited compared to the
welded headed studs. Nailed shear connectors (Figure 3.4) are
mainly used for small and medium size contracts or when the access
to site for a generator is difficult.
ECCS N 87
-
30 Design Manual for Compose Slabs
Without connection : M = Mp,a fy Za
Figure 3.1 - The principle of composite beams
Self-weight (slab and profile) : 91 + 92 Weight of floor
finishes : g = 1 kN/m2 Variable imposed load : q = 4 kN/m2
140 t999WW 9299 J h L 2500
With connection
Plastic design Connection :40% Connection: 100%
ECCS N 87
Figure 3.2 - Possible weight saving with composite beams
I iE74 IY
With connection: M = fy Z
I
I
7500 _
Without connection
Plastic design Elastic design
Depth h[mm] ::
:500 J_ 440 j 410
Section IPE 400 IPE 360 IPE 300 IPE 270
Weight of profile [kg/m] 66.3 57.1 42.2 36.1 Number of studs
&g[mmj
10
13019 12
12019 24
25019 33
shnnk (mm) 6 7 7
q[mmJ 8 3 10 6
-
Preliminary consideralions and pre-design 31
111 .. :j
* + + -.i_
Figure 3.3 - Welded shear studs
.i i Figure 3.4 - Nailed shear connectors
3.3 COLUMN LAYOUT AND THE VARIOUS BEAM ARRANGEMENTS The pattern
of the column layout is certainly the first parameter to consider
when designing a building structure. The distance between the
columns and the beam/column arrangement define directly the beam
spans and consequently the depth of the floor members.
3.3.1 Short to medium span structures Short/medium span
structural arrangements are used when the building flexibility is
not critical and/or when the beam depth is limited. These
structures do not always use the composite beam approach as
discussed earlier in this chapter. The decision whether a beam
should or should not be composite (i.e connected to the slab)
depends of national practice and can result in savings in beam
weight in regards with the cost of connection between the slab and
the beam. These siructures are usually based on "square grid" have
a higher number of columns. Figure 3.5 shows a possible option.
3.3.2 Long span structures using composite beams The initial
development of the use of composite construction was as a
substitution for the traditional reinforced concrete frame. Thus
grids are square or nearly square with column spacing in the range
of 6 to 9 metres. Such span layout does not take full advantage of
some of the composite beam's inherent benefits. In particular it
does not recognize that a composite floor is essentially an overlay
of one way structural elements. The floor spans between the
secondary beams, which span transversely on to the primary beams;
the latter in turn span to the columns. This set of loads paths
lends itself to rectangular grids and it becomes feasible to
increase the span in at least one direction to 12, 15 or even 20
metres and more.
ECCS N 87
Figure 3.5 - First type of column layout structure
-
32 Design Manual for Conzposue Slabs
The depth of the long span beams will clearly increase in order
to achieve economy but now the beams are of sufficient depth for
the primary service ducts to be accomodated readily within their
depth, so that the overall floor depth does not necessarily
increase significantly. The ducts may be accomodatecj by providing
holes in the beam webs, or, by tapering the beams near their ends.
Modem buildings are generally designed to have a life of not less
than 50 years. Recent developments and changes in communications,
information technology and manufacturing methods have already had a
profound influence on commercial and industrial practice and
consequently on various type of building arrangements. Therefore it
is not possible to predict precisely what further developements may
occur during the life of a building that is designed currently.
Today there is no evidence that the rate of change of office and
industrial technology or social habits will slacken and developers
must expect profound changes in requirements for modern building
during their life. While many of these changes will influence
services requirements, others will primarily affect the partition
layout. The best way to maximise flexibility of internal planning
is to minimise the number of columns. Figure 3.6 shows typical
examples of ways in which "long span" primary beams can reduce or
eliminate the number of internal columns. The cost of the floor
will increase but this can be partly offset by saving from the
reduction in the number of foundations and some savings in speed
and cost of erection. In any case the net increase in the
structural cost may well be no more than 10 % and this represents a
much smaller proportion of the total development cost. This is a
very small premium to pay if proper account is taken of the
potential future benefits because the structure is less likely to
become obsolete.
a) Structural options for long span beams This section describes
the various options for achieving the twin aims of long spans and
ready incorporation of services within normal floor zones.
Beams with web openings In this method of construction, the beam
depth is selected so that sufficiently large, usually rectangular-
shaped openings can be cut into the web (see Figure 3.7). For
general guidance, it is suggested that the openings should form no
more than 70% of the depth of the web, where horizontal sliffeners
are welded above and below the opening. Typically, the length of
the openings should be no more than twice the beam depth. The best
location for the openings is in the low shear zone of the beams. A
modified form of construction is the notched beam where the lower
part of the web and flange of the section is cut away over a short
distance from the support. This method is not usually practical
unless the cut web is stiffened.
ECCS N 87
Figure 3.6 - Long span primary beams
-
Casteflated beams can be used effectively for lightly serviced
buildings or for aesthetic reasons where the structure is exposed
(see Figure 3.8). Composite action does not significantly increase
the strength of the beam but does increase their stiffness
significantly. Castellated beams have limited shear capacity and
ate best used as secondary beams.
db'6boo Composite tnisses
Figure 3.8 - Castellated floor beams
Trusses are frequently used in multi-stoity building in North
America and are best suited for very long spans, where the truss is
designed to occupy the full depth of the floor zone (see Figure
3.9). The cost of fabrication can be high in relation with the
material cost. Little benefit is gained for composite action apart
improving the stiffness of the truss. The modified Warren truss is
the most common form as it offers the maximum zone for service
between bracing members.
Stub girders Architectural demand for square column-grids with
spacings of 10 to 12 metres led to the development of stub girder
construction in North America. The stub girder comprises a bottom
chord which acts in tension and a series of short beam sections (or
stubs) which connect the bottom chord to the concrete slab.
Secondary beams span across the bottom chord and can be designed as
continuous members. Voids are created adjacent to the stubs for
services. This is illustrated in Figure 3.10.
ECCS N 87
Preliminary considerations and pre-d esign 33
Reinforcern1nt
Stiffener Opening for services
Castellated beams
Figure 3.7 - Web openings in floor beams
Figure 3.9 - Composite trusses with composite floors
-
Parallel beam grillage systems This system is different from the
other previouly described in that continuity can be developed in
both the secondary and primary beams. The secondary beams are
designed to act compositely with the concrete slab, and are made
continuous by passing over the primary beams. The primary beams are
arranged in pairs and pass on either side of the columns to which
they are attached by shear resisting brackets. These primary beams
are non-composite. The method of construction is illustrated in
Figure 3.11. Dual beam systems are ideally suited to accomodated
large service ducts in orthogonal directions.
Haunched beams Haunched beams are designed by forming a rigid
moment connection between the beams and columns. The depth of the
haunch is selected primarily to provide an economic method of
transferring moment into the column; the length of the haunch is
selected to reduce the depth of the beam to a practical minimum.
The extra service zone created beneath the beam between the
haunches offers flexibility in service layout. At edge columns, it
would be normal to develop additional continuity through the slab
reinforcement, but this is only an option at internal columns. This
form of construction can be used for sway frames, i.e. where
vertical bracing or concrete shear walls or cores are not provided.
This is practical for buildings up to 5 storeys in height. An
example of a haunched composite beam is shown in Figure 3.12.
34 ____ ___
Design Manual for Composite Slabs
Figure 3.10 - Stub girder system with composite slab
secordary beam
Figure 3.11 - Composite slab and parallel beam grillage
systems
4- Shear connectors r, 7-.Tr-r,---r
C(mposite secondary bea"ms
Figure 3.12 - Composite floor with haunched beams
ECCS N 87
-
Preliminary considerations and pre-design 35
b) Structural arrangements with built-up sections Figure 3.13
shows three typical floor arrangements for a one-bay long-span
structure. Wider, multi-bay buildings would simply be repetitions
of these single-bay arrangements, although the 6 in column spacing
that is shown along the building would be likely to increase for
internal columns. Figure 3.13a shows the fabricated beams acting as
the primary beams, supporting light hot-rolled, composite,
secondary beams between 2 and 5 m centres, which depends on whether
the sheet is supported or not during concreting. In Figure 3. 13b
the fabricated sections are themselves placed at 2.4 to 3.6 m
centres and are supported directly by the columns or by composite
haunched beams. In multi-bays schemes the haunched internal beams
would be replaced by primary beams or internal columns lines.
Figure 3.13c is only applicable to one-bay structures, with beams
on the center-lines of the mullion columns. Choice of arrangement
will depend on the overall structural form. Type Cc) would only be
used if mullion columns were required at centres of between 2.4 and
3.6 in to support the building envelope. Where the column spacing
is greater than 3.6 in along the building, some form of grillage is
required if conventional composite decking is used. Propping of the
steel decking may also be used in this case. The choice between a)
and b) is not clear cut. For conventional construction, b) would be
generally favoured. However, layout b) does have a greater number
of fabricated sections, which inherently more expensive per tonne
than rolled sections. In addition the lightly loaded fabricated
sections of b) are likely to be less efficient than the heavier
fabricated sections of a). For example the webs of the former may
be governed by minimum thickness criteria. Even if that is not the
case their greater slenderness will reduce strength. Conversely,
the number of connections in a) are greater than b) thus increasing
erection and fabrication costs for the former.
Figure 14 shows a range of profiles for tapered beams. 3.3.3
Structural options with other materials Composite slabs are now
widely used with reinforced, prestressed concrete and timber
structures. They may lead to material saving and increased speed of
erection. These applications are now discussed.
a) Reinforced and prestressed concrete structures The use of
composite slabs in conjunction with reinforced concrete beams
appeared in the mid 1980's. A large vanety of buildings ranging
from an underground car park (a typical detail is given in Figure
3.15) to a tail building with a tubular core (a typical detail is
given in Figure 3.16) were built using composite slab flooring.
Single span sheets are used at each support, the slab and the beams
may be linked using mesh reinforcement to ensure longitudinal shear
connection. There are several possible ways to use these
techniques, one of which is shown in Figure 3.17. Steel decks are
easily adapted to the concrete support providing the minimum edge
distances can be satisfied. The stability of the steel sheet must
be assured during construction. The fastening of the steel deck may
be carried out by various ways as shown in Figure 3.18. For
prestressed concrete beams the deck is locked/clamped or fixed
using shot fired fasteners. A minimum edge distance must be
respected in order to avoid splitting or a steel plate should be
inserted in order to provide a fastener base. The Fdration
internationale de la prcontrainte (FIP) is preparing a Guide to
good practice Precast composite floor structures, which gives
general rules and recommendations for construction composite
structures with prefabricated elements.
ECCS N 87
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36 Design Manual for Composite Slabs
-6m-- hot-rolled secondary beam
fabricated primary beam
fabricated beam
composite haunched beam
mullion column
Figure 3.13 - Structural arrangements with built-up sectio
Lj111111111111 (a) Straight taper
(b) Semi-taper
ECCS N 87
(C) Cranked taper
Figure 3.14 - Fabricated beams alternative shapes
(a) Type A
(b) Type B
(C) Type C
-
Preliminary considerations and pre-dthgn
____________________________________ 37
/.
Figure 3.15 - Composite slab and reinforced concrete beams
ECCS N 87
5cm
temporary prop
Figure 3.16 - Europe's tallest building has composite floor
(Messeturm in Franlfurt/Main, Germany)
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38 Design Manual for Composite Slabs
steel mesh / steel decking
b) Timber structures
Figure 3.17 - Other construction details for concrete frames
P ' length 150 mm e=5h
Figure 3.18 - Various way to connect the deck on concrete
The timber beam option for flooring can be either a structural
or an architectural choice. Floors made with composite slabs are
well suited to this type of structure because of the reduced slab
weight The fastening of the sheets onto the beams is carried out by
mean of nails or screws (see Figure 3.19). When adequately fasten,
the deck can be used to improve the structural stability for both
the temporary and permanent stages. Typical construction details
for timber structures are given in Figure 3.20.
ECCS N 87
.
shear bars
h
L L HI
-
Pre1iminay considerazwnsandpre-design 39
Figure 3.19 - Fcteners for timber structures
3.4 RENOVATION AND REFURBISHMENT SCHEMES
V
I
Composite slabs are versatile and can very often be used for
renovation of existing structures. The use of composite slabs in
this particular context is not very different from current
applications but the uniqueness of such projects may lead to
problems compared with conventional design. This section outlines
briefly the various possibilities in these situations. Depending
with the nature and/or the importance of the renovation scheme
composite floors can be placed on various type of beams including
steel beams (Figure 3.21) reinforced concrete beams (Figure
3.22)
wooden or timber beams (Figure 3.23) prestressed concrete beams
(Figure 3.24) reinforced concrete walls (Figure 3.25)
ECCS N 87
Figure 3.20 - Typical construction details on timber
structures
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40 Design Manual for Composite Slabs
ECCS N 87
+
concrete slab
Fi2ure 3.21 - Renovation and refurbishment schemes steel
beams
tile
steel joist
/1 composite __/' slab with NWC
Connected steel joist
/ composite I' slab with LWC
5000 to 8000 mm 5000 to 8000 mm
S S I
Figure 3.22 - Renovation and refurbishment schemes reinforced
concrete beams
-
Preliminary considerations and pred esign 41
Existing floor Renovated floor
unsawn timber beam
composite slab tire bar
timber beam level
Figure 3.23 - Renovation and refurbishment schemes on wooden or
timber beams
Figure 324 - Renovation and refurbishment schemes on prestressed
concrete beams
ECCS N 87
timber floor 100 - 140 mm thick slab I h stable to fire
SLA 4O
p.
grout
shutter
prestressed concrete beam
slab 4 composite existing
wall
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42 Design Manual for Composite Slabs
The number of renovation projects where composite slabs can be
used is very large. Examples range from very simple projects with a
new slab cast onto the existing steel beams to major refurbishment
schemes where only the facade of the building has been retained. It
is difficult to produce here a complete list of these multi-purpose
applications but they include the following: Re-modelling
Strengthening Extension
Composite flooi avoid the setting of costly and voluminuous
formwork which slows down construction progress. Generally the low
or unknown carrying capacity of the existing foundations places a
severe limitation on the dead load. Lightweight composite slabs are
beneficial because they are easy to handle and up to 1.0 1rN/m2
lighter than conventional reinforced concrete flooring. The
installation of composite floor panels for renovation schemes does
not require the use of a procedure which is different to new
construction. Steel decking available on the market offers a large
variety of solutions to tackle the problems of partial or total
renovation. Renovation schemes are often characterised by the
irregular shape of the slabs. The use of the conventional slab
techniques (i.e.: cast-in place, pre-cast or hollow core slabs) is
often difficult. Composite floors are generally useful in these
situations, the pre-cut panel elements are cut on site to the exact
shape of the building using simple tools such as grinders and
nibblers. The flexibility and the lightness of the panels allows
quick but efficient installation of the elements. The steel sheets
may be manually positioned by 2 or 3 men. When the access to the
construction site is difficult with the conventional lifting
equipment the passage of the panels through the door or existing
windows is possible without the need to dismantle the roof.
ECCS N 87
Figure 3.25 - Example of floor construction
-
Preliminary consideraJions and pre-desgn
3.5 SHALLOW FLOOR CONSTRUCTION
43
Shallow floor construction incorporates light gauge steel
decking as part of a composite slab (see Figure 3.26). The system
has the benefits of slim floor construction but possesses
additional advantages over the traditional concrete option (i.e.
lighter weight of the slab, ease and speed of erection). Shallow
floors made of composite slabs usually span between 5 to 9 metres,
the total thickness of the slab is usually set between 180 and 350
mm. All types of steel deck can be used providing they can achieved
the required deflection and strength criteria. However, deep steel
decking presents another advantage, the size of the corrugations
allows light services to run within the floor depth parallel to the
corrugation and through the beams webs (see Figure 327).
600
= 210
210 deep deck x 1.25 thk.
Figure 3.26 - Shallow floor arrangement with composite slab
3.5.1 Shallow floor with deep steel decking The slab is hidden
within the beam height which is generally a compact section. The
use of deep steel decking is therefore an efficient solution,
because the deck rests directly on a plate welded to the bottom
flange of the beam. The deck openings are closed by stop end
accessories which prevent concrete leakage. The top flange of the
beam is covered by a concrete topping (70 to 100mm) which houses
the steel fabric for hogging moments and the shear connectors when
the beam is designed for composite action. This topping constitutes
the compression part of the slab within the current span. The fire
stability of the beam is brought up to 1 hour and the use of
lightweight concrete allows to span up to 6 metres without
props.
ECCS N 87
B = span/4 Transverse reinforcement
DI'
A4JL Cross-section through composite 'Slimfior' beam - Type
B
Section A - A
I
600
-
Design Manual for Composite Slabs
Services
3.5.2 Shallow floor for long-span beams The steel beams for
longer spans are rarely made of compact sections. The beam depth is
clearly increased in order to achieve economy and the slab is not
supported on the bottom flange of the beam. However it is still
advantageous to use the shallow floor technique in order to reduce
the total floor height and improve the fire stability of the beams.
In this arrangement the slab rests on brackets or packings whose
purpose are to maintain the steel sheet during the construction
stage. All or part of the slab is contained within the beam depth
as is shown in Figure 3.28. Any conventional steel decking can be
use for this arrangement, providing that the design and propping
requirements are met. The fire stability of the beams varies with
the way they have been integrated within the slab.
ECCS N 87
In-situ concrete
Figure 3.27 - Floor service with shallow floor
Figure 3.28 - Shallow floor arrangement for long span
structures
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Preliminary consideradns and pre-design 45
3.6 PRE-DESIGN
3.6.1 Major information In order to carry out a realistic
pre-design exercise it is necessary for the designer to gather a
minimum amount of information about the project. This vital
pre-design information will include all or a number of the
following: Slab depth compatible with the fire rating Limiting
slenderness ratio for slab Slab depth compatible with the sound
insulation Accepted propping conditions on site The possible span
of the slab and the beams Permanent or short temi imposed load
applied to the floor.
a) Slab depth compatible with the fire rating This criterion
fixes the minimum slab thickness necessary to achieve
satisfactorily the required fire rating. The minimum slab thickness
is variable and depends on the type of decking and the technique
used to solve the fire problem. Two main techniques are available:
Fire protection of the soffit using either applied or screened
material (no minimum slab thickness
imposed by the fire design) The use of steel bar reinforcement
for fire resistance (a minimum slab thickness is compulsory,
see
also Section 8.2) The minimum slab depth for this fire
resistance is a direct consequence of this choice. For a fire
rating of two hours the steel reinforcement solution is efficient
and cost effective. The first solution is generally preferred when
the fire rating has been set above two hours.
b) Limiting slenderness ratio for slab The slenderness ratio is
given by the span length (L) divided by the effective depth of the
slab (dp). This number usually lies between 20 (heavy loads) and 40
(light loads). For typical structures this slenderness ratio may be
taken as not greater than 32 to comply the serviceability
requirement. Such limitation of the slenderness ratio also
influences the dynamic response of the slab.
C) Slab depth compatible with the sound insulation The acoustic
performance of composite slabs is described by the "mass law"
equation. The performance of slabs are normally given in
manufacturer's brochures. In certain circumstances the composite
slab is not sufficiant for sound insulation and in this case a
system involving an additional layer of insulation must be used. It
is important to estimate the minimum thickness of the concrete slab
in conjunction with the technique of insulation chosen for the
construction as described in Section 8.6.
d) Accepted propping conditions on site The use of props may
either depend on the method of construction and/or the conditions
on site. Their use always induces extra-cost for the setting and
removal of these devices. However one or two lines of props enables
larger spans to be achieved.
ECCS N 87
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46 Design Manual for Composite Slabs
e) The possible span of the slab and the beams The beam spacing
in a floor using composite slab is a critical decision. There are
two cases: Beam spacing and column layout are imposed Beam spacing
and column layout are free In the first case the designer has
little freedom only the spacing of the secondary members requires
determination.
The early decision whether constiuction is with or without
propping is critical because the criterion "no props" limits the
choice of the deck type or forces the designer to use shorter
spans. Therefore the mmiinum required thickness of the slab will be
dictated by the spanning limits of the deck. In the second case the
designer has more design choices. A good way to stait the
pre-design is to use the minimum slab thickness as explain before
and then estimate the maximum span with or without props. The
spacing of the secondary beams is then known and therefore their
section depth can be estimated.
f) Total dead and Imposed load applied on the floor The majority
of design charts given by manufacturers gives permissible loads for
maximum spans (or vice versa). For a typical range of buildings
imposed loading varries between 2 kN/m2 and 5 kN/m2 for light loads
and up to 10 kN/m2 for heavy loads.
3.6.2 Pre-design procedure Pre-design of floors using composite
slabs by architects or engineers is greatly simplified by the
manufacturers design charts. Recently these charts are sometimes
accompagned by software packages whose level of refinement is
variable. These packages may provide safe load tables or more
refined analyses. Their use is particular to each manufacturer and
therefore will not be considered here since the design charts are
universal.
Most brochures produced by the manufactures have a double entry
system considering both the construction stage (number of props)
and the loading stage (total slab depth, steel reinforcement for
hogging and sagging). These two stages will be considered
separately.
a) Temporary or construction stage The designer must first
consider the construction stage and select a deck type compatible
with the site requirement (props or no props). In many cases the
site layout decision influences the choice of profile and also the
form of the slab construction.
Clearly the allowable deck span is influenced by: The support
conditions Sheet lengths can be used to span one or more spans
(single or multi span). When investigating larger unpropped span
the designer is advised to arrange a multi-span layout of the deck.
This is more economical for both the unpropped span length and the
site layout. The decking strength The deck carrying capacity is
mainly influenced by the inertia which is in turn directly linked
to the rib depth of the profile and the thickness of the metal
sheet (smaller influence). ECCS N 87
-
Preliminary considerations aizdpre-design 47
A crude stereotyped approach for a typical office building slab
would be:: deck with rib height of 40 mm spans up to 2.70 m deck
with rib height of 60 mm spans up to 3.30 m
deckwithribheightoflOmmand+spansupto3.70m specific decking for
large span up to 6.5 m (no prop) The possible span depends of
course of the finished slab depth but also with the type of
concrete (normal or light weight).
b) Permanent or service stage As a guide the minimum depth of
the slab is given: the limiting slenderness ratio L/dp 32 (see also
3.6.1 b) the minimum depth for fire rating and/or sound
insulation.
The decking shape and properties can be obtained once this
minimum slab depth has been set together with the possible span
layout (single or multi-span, number of props accepted). All the
data are normally computed using conventionnal hypothesis such as
the average concrete strength, the deflection at service and other
current parameters. These values are always given with the data and
should be specified for the final design. Special calculations for
the fire reinforcement or other special loading condition are
usually not relevant to this stage of the project. They are carried
out later by the design office.
3.6.3 Summary Table 3.1 gives an overview of the different
alternatives for the choice of a composite floor system.
Table 3.1 - Different alternatives for the choice of a composite
floor system
Feature Alternatives
Structural system Single or continuous span beam.
Floor beam length 6 to 20 m. Floor beam centres or spacing (slab
span length)
1.80 to 5.0 m.
Steel decking Trapezoidal profiles, re-entrant profiles,, types
embossments end anchorage.
of indentations or
Fire protection Thickness of the slab, additional reinforcement,
(suspended ceilings, sprayed material).
protection system
Shear connection Stud connectors, welded through the sheet or
welded to the beam with holed sheet. Nailed shear connectors.
Degree of shear connection (beam)
Partial to full (40 to 100%)
Concreting (slab) Unpropped or propped slab.
ECCS N 87
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Page blank in original
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Detailing requirementr 49
4 DETAILING REQUIREMENTS The following detailing requirements
should be respected whatever conditions of design are considered as
a minimum. More information may be found in the ECCS document No
73: "Good Construction Practice for Composite Slabs". Two specific
design situations must be considered: Construction stage Composite
stage
4.1 GENERAL CONDITIONS ON STEEL DECKING AND COMPOSITE SLABS
4.1.1 Decking and slab It is recommended that the nominal
thickness of the steel decking should not be less than 0.75 mm.
Zinc coating should be provided on each face with a minimum of 0.02
mm per face. This rule is for corrosion protection. The depth of
the steel sheeting t'p should not be less than 35 mm and the depth
of the composite slab not be less than 80 mm. This is a minimum
condition for fire resistance and sound insulation.
The span to effective depth ratio of the slab should be less
than or equal to 32 for simple supported slabs and 36 for
continuous slabs. This is a condition for slab rigidity and comfort
(see EC 2). The thickness hc of concrete above the ribs of the
decking shall be greater than 40 mm. If the slab acts compositely
with a beam or is used as a diaphragm, the minimum total slab depth
h is 90 mm and the minimum concrete thickness hc above the decking
is 50 mm.
;: T ' . h ______
___f jh 4hp h bb bh
re-rentrant trough profile open trough profile Figure 4.1 -
Minimum conditions : decking and composite slab
4.1.2 Concrete The minimum characteristic resistance in
compression of the concrete is 20 N/mm2 (Class C20). Concrete may
be Normal Weight Concrete (NWC) or Light Weight Concrete (LWC). The
nominal size of agregate depends on the smallest dimension on the
structural element within which concrete is poured, and shall not
exceed the least of: 0.4 h where h is the depth of concrete above
the ribs b>/3 where b0 is the mean width of the rib (minimum
width for re-entrant profiles) 31.5 mm.
ECCS N 87
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50 Design Manualfor Composite Slabs
4.2 CONSTRUCTION STAGE The stage during the erection of the
structure is one of the most critical. Specific details must be
complied at this design stage.
4.2.1 Bearing During construction, the steel sheeting is acting
as shuttering. It is placed on permanent supports and
supports, the props. Figure 4.2 shows the minimum values for
bearing sometimes, on specific temporary lengths on permanent
supports.
1
beanng on other materials such as brick or block
(c) jj F
0
Figure 4.2 - Minimum bearing lengths for permanent supports (7.3
of EC4) For design calculations, it is convenient to consider that
the decking is supported on the centre line of the bearing.
Temporary supports shall be checked in accordance with part 1.3 of
EC 3. Figure 4.3 gives the minimum values for the temporary bearing
lengths (props). All interior panel ends shall be centered over
permanent supports. During construction cantilevers shall be
temporary supported. Note: EC 4 allows reduction of minimum bearing
lengths given above if special care is considered in the design
(see EC 4 for more information). 4.2.2 Fasteners Each panel should
be connected at least twice at each end to the permanent supports
and the decking shall be butted to each other or overlapped. The
longitudinal overlapping depends of the shape of decking. Generally
profiles overlap on one or half of one rib. When used, the minimum
transversal overlapping on supports are 50 mm on steel supports and
70 mm on supports made of others materials (see Figure 4.2)
ECCS N 87
bearing on steel or concrete
- I
0 ., 3 - .0
(b) j L (d)
iooj.
-
Detailing requirements 51
SLAB DEPTH mm
SPAN m
MINIMUM TIMBER BLOCKSIZE
mm
HEIGHT WIDTH
120 130 150 200
3.25 3.75 4.25 4.75
175 200 225 225
50 50 50 75
Figure 4.3 - Minimum bearing lengths of temporary supports
Panels shall be seamed together. Minimum distance between seams
is 500 mm for single spans and 1000 mm for continuous decking. Seam
fasteners between panels are particulary important if heavy
construction loads are expected or if the decking spans more than 3
metres. If the decking is acting as a diaphragm, the number and the
placement o;f the fasteners must meet the relevant design
specification. A 600 mm interval between fasteners is considered as
a minimum. Figure 4.4 shows typical arrangement for fastening,
overlapping and seaming. In any case, during construction,
cantilevers shall be temporarely supported. Figure 4.5 shows
typical cantilever situations.
Edge trims or angles shall be fixed to edges to contain the
fresh concrete. The thickness of the trim depends on the expected
slab thicknesses and are not specifically designed. Table 4.1 gives
good practice values for trim thicknesses. Lateral edges trim
deflection may be reduced by ties backs. Ties back spacing are
typically between 250 mm and 1.0 metre.
Table 4.1 - Trim thicknesses
h [mm]
X [mm]
t [pjJ 200
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52 Design Manual for Composite Slabs
ECCS N 87
r
Figure 4.5 - Cantilever situations
Sean, fe
Figure 4.4 - Fastening, overlapping and seaming
1 L.
M secUon
-
Detailing requirements 53
4.2.3 Edges treatment Edges are classif