CC

IP-030D

esign of Hybrid C

oncrete Buildings

R. W

hittle MA (Cantab) CEng M

ICE H. Taylor FREng, BSc, PhD

, CEng, FICE, FIStructE

Design of Hybrid Concrete Buildings

This design guide is intended to provide the structural engineer with essential guidance for the design of structures that combine precast and in-situ concrete in a hybrid concrete structure. It introduces the options available for hybrid concrete structures, and goes on to explain the key considerations in the design of this type of structure.

Bearings, interface details, consideration of movement, composite action, robustness and the effects of prestressing are all explained in this guide and design examples are included where appropriate. The importance of overall responsibility and construction aspects are also described.

CCIP-030 Published January 2009 ISBN 978-1-904482-55-0Price Group P

© The Concrete Centre

Riverside House, 4 Meadows Business Park,Station Approach, Blackwater, Camberley, Surrey, GU17 9ABTel: +44 (0)1276 606 800 www.concretecentre.com

CI/Sfb

UDC624.072.33:624.012.3/.4

Robin Whittle has extensive knowledge and experience of designing all types of concrete buildings. He regular contributes to concrete industry publications and is a consultant to Arup. He was a member of the project team which drafted Eurocode 2.

Howard Taylor has extensive knowledge and experience of designing precast concrete elements and buildings, including developing alternative production methods. He is a past president of the Institution of Structural Engineers and is currently chairman of the British Standards Institution Building and civil engineering structures Technical Committee B/525.

Design of Hybrid Concrete BuildingsA guide to the design of buildings combining in-situ and precast concrete

A cement and concrete industry publication

R. Whittle MA (Cantab) CEng MICE

H. Taylor FREng, BSc, PhD, CEng, FICE, FIStructE

Hybrid cov-.indd 1Hybrid cov-.indd 1 29/01/2009 16:43:3729/01/2009 16:43:37

A cement and concrete industry publication

Published by The Concrete CentreRiverside House, 4 Meadows Business Park, Station Approach, Blackwater, Camberley, Surrey GU17 9AB Tel: +44 (0)1276 606800 Fax: +44 (0)1276 606801 www.concretecentre.com

CCIP-030Published January 2009 ISBN 978-1-904482-55-0Price Group P© The Concrete Centre

Cement and Concrete Industry Publications (CCIP) are produced through an industry initiative to publish technical guidance in support of concrete design and construction.

CCIP publications are available from the Concrete Bookshop at www.concretebookshop.com Tel: +44 (0)7004 607777

All advice or information from The Concrete Centre is only intended for use in the UK by those who will evaluate the signifi cance and limitations of its contents and take responsibility for its use and application. No liability(including that for negligence) for any loss resulting from such advice or information is accepted by The Concrete Centre or their subcontractors, suppliers or advisors. Readers should note that the publications from The Concrete Centre are subject to revision from time to time and should therefore ensure that they are in possession of the latest version.

Cover photo: Courtesy of Outinord International Ltd.Printed by Information Press Ltd, Eynsham, UK

AcknowledgementsThe authors would particularly like to thank the following people for their support in the development of this design guide:

Tony Jones ArupIan Feltham Arup

The contributions and comments from the Concrete Society Design Group and also from the following people are gratefully acknowledged:

John Stehle Laing O’RourkeGraham Hardwick John Doyle Construction LtdPeter Kelly Bison Concrete Products LtdAlex Davie ConsultantDavid Appleton Hanson Concrete ProductsKevin Laney Strongforce Engineering PlcNorman Brown British Precast Concrete Federation Ltd

Type 1Precast twin wall and lattice girder slab with

in-situ concrete

Type 2Precast column and edge beam with in-situ

fl oor slab

Type 3Precast column and fl oor units with cast in-situ

beams

Type 4In-situ columns or walls and beams with precast

fl oor units

Type 5In-situ column and structural topping with precast

beams and fl oor units

Type 6In-situ columns with lattice girder slabs with

optional spherical void formers

Typical hybrid concrete options.Please note this diagram is a repeat of Figure 2.1, page 8.

Hybrid cov-.indd 2Hybrid cov-.indd 2 29/01/2009 16:43:5429/01/2009 16:43:54

Design of Hybrid Concrete Buildings

Contents

1. Introduction 5 1.1 Single point of responsibility 5 1.2 Design considerations 6 1.3 Best practice procurement guidance 6

2. Overview of hybrid solutions 7 2.1 Type 1: Precast twin wall and lattice girder slab with in-situ concrete 7 2.2 Type 2: Precast column with in-situ fl oor slab 9 2.3 Type 3: Precast column and fl oor units with cast in-situ beams 10 2.4 Type 4: In-situ columns or walls and beams with precast fl oor units 12 2.5 Type 5: In-situ column and structural topping with precast beams and fl oor units 13 2.6 Type 6: In-situ columns with lattice girder slabs with optional spherical void formers 14

3. Overall structural design 15 3.1 Robustness 15 3.2 Stability 18 3.3 Diaphragm action 18 3.4 Shear at interface of concrete cast at different times 19 3.5 Interface shear 22 3.6 Shear and torsion design 25 3.7 Long-line prestressing system 26 3.8 Secondary effects of prestressing and the equivalent load method 29 3.9 Temperature effects 29 3.10 Differential shrinkage 29 3.11 Designing for construction 33

Design of Hybrid Concrete Buildi1 1Design of Hybrid Concrete Buildi1 1 29/01/2009 16:47:3229/01/2009 16:47:32

4. Bearings and movement joints 34 4.1 Horizontal forces at bearings 34 4.2 Restrained bearings 35 4.3 Movement joints 36 4.4 Actions and restraints 36 4.5 Design considerations 37 4.6 Allowance for anchorage of reinforcement at supports 37 4.7 Bearings that allow limited movement 38 4.8 Connections between precast fl oors and in-situ concrete beams 42

5. Structural elements and connections 43 5.1 Twin wall construction (type 1) 43 5.2 Precast columns, edge beams and in-situ slabs (type 2) 52 5.3 Biaxial voided slabs 55 5.4 Prestressed hollowcore units 58 5.5 Double tee beams 68 5.6 Stairs 74 5.7 Corbels, nibs and half joints 82

6. Construction issues 87 6.1 Method of construction 87 6.2 Composite action between precast units and in-situ structural topping 89 6.3 Specially shaped standard units 89 6.4 Long and short units adjacent to each other 89 6.5 Differences of camber in double tees 91 6.6 Method of de-tensioning double tee units 91 6.7 Checking strand or wire pull-in for hollowcore units 91 6.8 Placing hollowcore units into the correct position 91 6.9 Production tolerances 92

7. Special structures - case studies 93 7.1 Lloyd’s of London 93 7.2 Bracken House 100

References 104

Design of Hybrid Concrete Buildi2 2Design of Hybrid Concrete Buildi2 2 29/01/2009 16:47:4429/01/2009 16:47:44

List of worked examples

Worked example 1 Hollowcore fl oor acting as a diaphragm 20Worked example 2 Interface shear between hollowcore slab and edge beam 23Worked example 3 Upwards camber on slab due to temperature gradient 30Worked example 4 Differential shrinkage 31Worked example 5 Bearing of a hollowcore unit 41Worked example 6 Vertical tie 56Worked example 7 Anchorage length of longitudinal tie bar 65Worked example 8 Dowel bar for connection of precast stairs 80Worked example 9 Corbel design 84

Design of Hybrid Concrete Buildi3 3Design of Hybrid Concrete Buildi3 3 29/01/2009 16:47:4429/01/2009 16:47:44

Design of Hybrid Concrete Buildi4 4Design of Hybrid Concrete Buildi4 4 29/01/2009 16:47:4529/01/2009 16:47:45