复合楼板强度设计

Design of Composite Slabs for Strength

Design Booklet DB3.1

OneSteel Market Mills
Composite Structures Design Manual

February 2001

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Composite Slabs Design of Composite Slabs for Strength

Published by

OneSteel Manufacturing Pty Limited

ABN 42 004 651 325

Produced by the

Centre for Construction Technology & Research

University of Western Sydney

Contributors

Dr. Mark Patrick *

Centre for Construction Technology & Research

Dr. Chong Chee Goh *

Mr. David Proe *

Mr. Rodney Wilkie *

* Formerly BHP Melbourne Research Laboratories

Reviewed by

Prof. Russell Bridge

Centre for Construction Technology & Research

Mr. Rennie Darmanin

Scott Wilson Irwin Johnston Pty Ltd

Endorsed by

BHP Building Products

Stramit Industries

Woodroffe Industries Pty Ltd

Edition 1.0 - May 1998

Edition 2.0 - February 2001

Disclaimer

While every effort has been made and all reasonable care taken to ensure the accuracy of the material contained herein, the contributors, editors and publishers of this booklet shall not be held liable or responsible in any way whatsoever, and expressly disclaim any liability or responsibility for any loss or damage, cost or expenses, howsoever incurred by any person whether the user of the booklet or otherwise including without limitation, loss or damage, costs or expenses incurred as a result of or in connection with the reliance, whether whole or partial by any person as a foresaid upon any part of the contents of this booklet. Should expert assistance be required, the services of a competent person should be sought.

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Foreword

OneSteel is a leading manufacturer of steel long products in Australia after its spin-off from BHP Pty Ltd on the 1st November 2000. It manufactures a wide range of steel products, including structural, rail, rod, bar, wire, pipe and tube products and markets welded beams.

OneSteel is committed to providing to design engineers, technical information and design tools to assist with the use, design and specification of its products. This design booklet “Design of Composite Slabs for Strength” was one of the first two design booklets of the Composite Structures Design Manual, which is now being completed and maintained by OneSteel.

The initial development work required to produce the design booklets was carried out at BHP Melbourne Research Laboratories before its closure in May 1998. OneSteel Market Mills is funding the University of Western Sydney’s Centre for Construction Technology and Research in continuing the research and development work to publish this and future booklets.

The Composite Structures Design Manual refers specifically to the range of long products that are manufactured by OneSteel and plate products that continue to be manufactured by BHP. It is strongly recommended that OneSteel sections and reinforcement and BHP plate products are specified for construction when any of the design models in the design booklets are used, as the models and design formulae including product tolerances, mechanical properties and chemical composition have been validated by detailed structural testing using only OneSteel and BHP products.

To ensure that the Designer’s intent is met, it is recommended that a note to this effect be included in the design documentation.

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Contents

Preface v

1. SCOPE AND GENERAL

1.1 Scope 1

1.2 General 1

2. TERMINOLOGY

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3. DESIGN CONCEPTS

3.1 Shear Connection 5

3.2 Slab in Bending 7

3.3 Vertical Shear 10

3.4 Sheeting Support Conditions 10

3.5 Curtailment of Positive Tensile Reinforcement 11

3.6 Preventing Sudden Collapse 12

3.7 Effects of Propping 13

4. DESIGN MODELS

4.1 General 14

4.2 Positive Moment Capacity 14

4.3 Positive Vertical Shear Capacity 17

4.4 Negative Moment Regions 18

4.5 Effective Span 18

5. DESIGN APPROACH

5.1 General 20

5.2 Definition of Design Situation 20

5.3 Identification of Potentially Critical Cross-Sections 20

5.4 Calculation of Design Action Effects 22

5.5 Design of Negative-Moment Regions 23

5.6 Design of Positive-Moment Regions 26

6. DESIGN RULES

6.1 Design Objectives 28

6.2 Limit State Requirements for Strength 28

6.3 Application 28

6.4 Design Loads 29

6.5 Methods of Structural Analysis 30

6.6 Moment Redistribution 30

6.7 Negative-Moment Regions 30

6.8 Positive-Moment Regions 31

7. WORKED EXAMPLES

7.1 General 33

7.2 Definition of Design Situation 33

7.3 Identification of Potentially Critical Cross-Sections 34

7.4 Design of Negative-Moment Regions 35

7.5 Design of Positive-Moment Regions 37

8. REFERENCES

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APPENDICES

A Referenced Australian Standards 44

B Notation 45

C Strength Design Information for Proprietary Profiled Steel Sheeting Products 48

D Design Positive Moment Capacity Tables for Proprietary Profiled Steel Sheeting Products 50

E Design Positive Vertical Shear Capacity Tables for Proprietary Profiled Steel Sheeting Products 55

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Preface

This design booklet forms part of a suite of booklets covering the design of simply-supported and continuous composite beams, composite slabs, composite columns, steel and composite connections and related topics. The booklets are part of the OneSteel Market Mills' Composite Structures Design Manual which has been produced to foster composite steel-frame building construction in Australia to ensure cost-competitive building solutions for specifiers, builders and developers.

Composite slabs have a long history of use in Australia dating back to the mid-1960's when John Lysaght (Australia) was promoting Bondek as a "new release composite slab structural floor decking". Local bond stress was calculated using the SAA Code for Concrete Buildings AS CA2-1963 and was not to exceed 40 psi (0.27 MPa). It was understood at the time that bond between the galvanised sheeting and the concrete was achieved by virtue of chemical adhesion of the cement paste to the zinc coating. The maximum span that could be used in practice was determined from uniformly-loaded slab tests, with the aim of ensuring that sufficient safety remained against bond failure, noting that load-carrying capacity, and therefore the bond stress at failure, reduced as span increased.

Considerable research into the behaviour of composite slabs has been performed at BHP Melbourne Research Laboratories in subsequent years. New types of profiled steel sheeting have been developed which no longer depend on adhesion bond for their anchorage. Mechanical and frictional resistance have now been identified as the major contributors to the bond developed by these products, similar to deformed reinforcing bars. Estimates of these resistances can be derived from a newly-developed Australian test called the Slip-Block™ Test, for which an Australian Standard is being prepared. Alternatively, slab tests can be used to estimate the strength of the mechanical resistance. This research has allowed this design booklet covering the design of composite slabs for strength to be written. A unified approach is presented, whereby, for the first time in Australia, all the major types of profiled steel sheeting currently produced in this country can be designed by the same methods.

A method of design for bending strength is presented. The method is based on partial shear connection strength theory, and is very similar to that used to design simply-supported composite beams for bending strength (see Design Booklet DB1.1). Data about the shear connection performance of proprietary sheeting products must be obtained from either slab tests or the Slip-Block Test. The mechanical resistance must at least by assumption be ductile.

A method of design for vertical shear is also presented.

For products which develop ductile mechanical resistance of sufficient magnitude, use of the design rules contained in this booklet can lead to very significant improvements in economy compared with the designs obtained currently. Owing to the high tensile capacity of the sheeting in positive-moment regions, a major saving can result by allowing moment redistribution from negative to positive moment regions in continuous composite slabs, leading to a significant reduction in the amount of top-face reinforcing steel.

The design rules presented in this booklet are being used as a basis for one of the strength design methods in a new Australian Standard on composite slabs currently being prepared, noting that a method will also be provided for products with either weak or non-ductile mechanical resistance. The slabs may be either simply-supported or continuous, while the loading must be essentially static in nature and uniformly-distributed. Partial shear connection strength theory can be used to design slabs with line loads perpendicular to the span, and this feature is used in the method of design for vertical shear. The rules are presented entirely in limit state format, and the design principles on which they are based are in harmony with the latest European design provisions. Design for other limit states such as serviceability (e.g. deflection and cracking), durability and fire resistance will be covered in later design booklets.

Edition 1.0 was published by BHP in May 1998. Edition 2.0 contains changes as a result of the move to 500 MPa reinforcing steels, some minor corrections to the first edition, and is published by OneSteel.

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