Stability of buildings Part 3: Shear walls
March 2015
Author A Gardner MEng(Hons) MA(Cantab) CEng MIStructE (The Institution of Structural Engineers) Consultees P Perry BSc(Hons) CEng MIStructE MICE MHKIE (CH2M Hill) Chairman of the Reviewing Panel E Bennett MEng (Arup) O Brooker BEng CEng MIStructE MICE MCS (Modulus) Dr A S Fraser BEng(Hons) PhD CEng MIStructE MICE (Arup) J Guneratne BSc(Hons) CEng MIStructE (CH2M Hill) R Marshall BEng(Hons) MIPENZ (Buro Happold) Acknowledgements The use of Arup internal guidance documents in developing this Guide is gratefully acknowledged. Photographs and digital imagery have been supplied by courtesy of and are published with the permission of the following organisations and individuals: Figures 2.4, 3.1, 6.7, 6.8, 7.2: Arup Figure 7.11a: The Structural Timber Association Figures 7.11b, 7.14: Milner Associates Figure 8.2b: ‘Reinforced concrete frame with brick masonry infill walls, India’ by A. Charleson (GEM Nexus website [or http://www.nexus.globalquakemodel.org]) is licensed under CC BY 3.0 (http://creativecommons.org/licenses/by/3.0/) Box 3.2: J.K. Nakata, United States Geological Survey Box 3.3: Halcrow Atkins Joint Venture Box 6.3: SKM anthony hunts Boxes 7.1, 7.5, 7.6b: Arup Box 7.3: Wellcome Images Box 7.4: P Buffett Box 7.6a: Frank P Palmer All other photographs and all hand illustrations: A Gardner Published by The Institution of Structural Engineers, 47–58 Bastwick Street, London EC1V 3PS, United Kingdom Telephone: þ44(0)20 7235 4535 Fax: þ44(0)20 7235 4294 Email:
[email protected] Website: www.istructe.org First published 2015 ISBN 978-1-906335-27-4 # 2015 The Institution of Structural Engineers
The Institution of Structural Engineers and those individuals who contributed to this Guide have endeavored to ensure the accuracy of its contents. However, the guidance and recommendations given in the Guide should always be reviewed by those using the Guide in the light of the facts of their particular case and specialist advice obtained as necessary. No liability for negligence or otherwise in relation to this Guide and its contents is accepted by the Institution, the author, the consultees, their servants or agents. Any person using this Guide should pay particular attention to the provisions of this Condition. No part of this publication may be reproduced, stored in a retrieval system or transmitted in any form or by any means without prior permission of The Institution of Structural Engineers, who may be contacted at 47–58 Bastwick Street, London EC1V 3PS, United Kingdom.
Contents
Foreword vi
7 7.1 7.2 7.3 7.4
Part 3: Shear walls
7.5
Glossary
iv
Notation
v
Introduction
2 2.1 2.2 2.3 2.4 2.5 2.6 2.7 2.8 2.9 2.10
Design overview 4 Form and configuration 4 Resistance and force transfer 4 Failure mechanisms 5 Materials 6 Monolithic and jointed construction 6 Coupled behaviour 6 Buckling and buckling restraint 6 Slenderness and effective heights 7 Limit state philosophy and initial wall sizing References 10
3 3.1 3.2 3.3 3.4 3.5 3.6 3.7 3.8
Requirements of walls 11 Introduction 11 Wall locations 11 Non-structural partitions and non-loadbearing panels 11 Cores 12 Vertical access and transportation 12 Service risers and distribution 14 Insulation and compartmentalisation 15 References 15
4 4.1 4.2 4.3 4.4 4.5 4.6
Elastic theory of thin-walled sections 16 Introduction 16 Complementary shear 16 Torsion 16 Warp and warp restraint 16 Lintel beams in sections subject to torsion 18 Centroid and shear centre 19
5 5.1 5.2 5.3
Modelling and analysis 21 Introduction 21 Modelling simplifications 21 Modelling vertical stability structures 22 5.3.1 1-dimensional element models 22 5.3.2 Grillage models 26 5.3.3 2-dimensional finite element models 28 Modelling horizontal stability systems 30 Manually apportioning actions between vertical stability systems 31 Modelling boundary conditions 31 Elastic and plastic analysis 32 References 32
5.6 5.7 5.8 6 6.1 6.2 6.3 6.4 6.5 6.6 6.7 6.8
8 8.1 8.2 8.3 8.4
Shear infill panels 53 Introduction 53 Common characteristics of infill systems 53 Masonry infill panels 54 References 56
7.6 7.7 7.8
1
5.4 5.5
7.9
Non-monolithic shear wall construction 40 Introduction 40 Precast construction 40 Precast reinforced concrete wall construction 42 Hybrid precast in situ reinforced concrete wall construction 43 Timber and light gauge steel ‘platform’ frame construction 45 Mass timber 47 Loadbearing masonry 49 Steel plate diaphragm walls in steel framed buildings 51 References 52
1
9
Monolithic reinforced concrete shear wall construction 33 Introduction 33 Modelling the stiffness of concrete 33 Ultimate and serviceability limit state design of reinforced concrete sections 34 Concrete classes 35 Minimum wall thickness 35 Reinforcement and embedments 35 Construction 36 References 39 The Institution of Structural Engineers Stability of buildings Part 3
iii
Glossary
The following definitions are provided to explain how the listed terms are used specifically in this Guide. They may differ to definitions found in other documents. Term
Definition
Action or load
An influencing effect, normally external to the structure, that causes movement, deformation and/or internal stresses. The two terms are largely interchangeable; ‘action’ is favoured by the Eurocodes while ‘load’ is more common throughout the design codes of English-language countries. Both terms are used herein.
Braced
Stabilised in sway by other connected elements or systems such that the subject element does not experience a significant sway moment. Structural elements or systems that are not braced are ‘unbraced’. The term braced is not to be confused with ‘bracing’ which is a type of structural component.
Centroid
The point on a cross-section, defined by the intersection of the neutral axes, through which a pure axial load will result in a uniform stress.
Coupled
Two or more elements with joints that resist longitudinal shear and make the flexural stiffness of the system greater than the sum of the parts.
Deflection head
A detail that allows differential vertical movement at the top of a non-loadbearing wall/panel. The detail may or may not provide in- and/or out-of-plane shear resistance.
Effective height
The length of an ideal pin ended wall that would have the same buckling load as the actual wall to which it relates.
Force
A type of action, causing both stresses and strains within a resisting static structure.
Horizontal stability system
An element, frame or assembly orientated in a horizontal or near horizontal plane that transfers lateral actions through the structure (generally connecting the fac¸ade to the vertical stability systems).
Hybrid system
A structure that contains more than one type of vertical stability system. This is usually with a combination of shear walls, framed bracing or portalisation.
In-plane
Characteristics (e.g. stiffness) or effects (e.g. actions) considered in a vertical plane that are orthogonal to a wall’s or wall system’s major axis. For a planar wall, these are the characteristics or effects in the plane of the wall. Out-of-plane characteristics or effects are those orthogonal to a system’s minor axis.
Insulated sandwich panels
Also known as ‘structural insulated panel systems’ (SIPS), a pre-cast composite wall element combining layers of materials to deliver structural and insulation (acoustic and/or thermal) performance. The structural component is typically either reinforced concrete or timber.
Lateral loadThe total structural system that acts to resist lateral loads comprising both horizontal and vertical stability resisting system systems together with fac¸ade elements (windposts, cladding rails, etc.) and the substructure. Length
The longer plan dimension of a wall. For planar walls, this is orthogonal to the major axis.
Loadbearing
A wall that resists vertical actions. Walls that resist in-plane lateral forces but not vertical actions are defined as ‘non-loadbearing’ herein. Meanwhile partitions and fac¸ade elements that only resist out-of-plane local pressures are defined as ‘non-structural’.
Load path
The complete route by which any applied or induced stress is transmitted through a structure to the foundations via a system of interconnected elements.
Modular ratio
The ratio of moduli of elasticity for two composite materials. In the context of reinforced concrete, it is the ratio of the steel modulus divided by the concrete modulus.
Non-structural
An element that can be removed without detrimental impact on the retained structure.
Precast
Used generically for any construction process that is not completed in situ. This includes processes that are more accurately described as pre-formed or pre-assembled.
Secant modulus The average gradient (stiffness) plotted as a straight line between two defined points on a stress–strain curve. It of elasticity differs to the tangent stiffness which is the gradient of a tangent to the stress–strain curve at a given point on the curve. Shear centre
The longitudinal axis through which a transverse shear will cause a linear displacement without twist, and about which a torque will cause pure rotation.
Slender
An element that is prone to buckling at a load less than the material strength would imply. Structural elements that are not slender are ‘stocky’.
Soft storey
Those storeys that have undergone ill-conceived structural alterations leading to a structural system that is particularly highly utilised and vulnerable to failure.
U-value
The thermal transmittance of a material, it is a measure of the power loss per metre squared per degree Kelvin temperature gradient (standard units W/m2/K). It is the inverse of the thermal resistivity.
Vertical stability system
An element, frame or assembly orientated in a vertical or near vertical plane that transfers lateral actions through the structure (generally down towards the ground). These systems form part of the lateral load-resisting structure.
iv
The Institution of Structural Engineers Stability of buildings Part 3
Notation
The following notation is used for hand drawn figures: An applied force An applied bending moment A movement/displacement An out-of-plane surface pressure Centre of stiffness Lateral restraint Solid wall section Structural lintel beams across wall openings Components of stiffness
The following notation is used in equations. Further notation is defined in the body text and within figures where used. A E G I J L Le b k t
e s t
Cross-section area Young’s modulus of elasticity Shear modulus Section second moment of area Section torsion constant Wall height Effective wall height Wall cross-section length on plan Stiffness Wall cross-section thickness Strain Normal stress Shear stress
The Institution of Structural Engineers Stability of buildings Part 3
v
Foreword
Following on from Stability Parts 1 and 2: General philosophy and framed bracing, this Guide seeks to explain and simplify the design concepts, thoughts and detail surrounding the shear wall as a stability element. With the advent of various products – many of which are proprietary – this Guide talks through the issues from the initial concept of a scheme, through preliminary, scheme and detailed design. Even if a product is to be used, such as a type of precast wall, the development of the stability provision must be understood and protected as it is constructed, recorded and maintained. This will be increasingly important as more and more ’engineered’ buildings of the last century come to the end of their intended function, many to be remodelled and renovated. Coordination is vital to ensure that concepts are developed correctly and the Institution encourages young engineers to pick up this challenge as well as incorporate the ability to design the particular stability provision that is a shear wall. This Guide has been written to assist structural engineers in the development of shear wall systems within the schemes they are charged with, illustrating the choices available both in design and construction from in situ slip form, precast hybrid twin wall and timber variants. In particular, this Guide is intended for structural engineers working for the consulting engineer, at all levels of the industry, to act as both an industry guide and the latest technical recommendation for shear walls. It intends to be a reliable source of reference during their projects. The Guide commences with an introduction to place the shear wall in context of stability provisions for a building, followed by a chapter on the aspects to be taken into account when considering a shear wall. A chapter on requirements of walls provides advice on the location, influence of cores and construction sequencing. A chapter on the elastic theory of thinwalled sections seeks to lay out simple understandable design advice ahead of a chapter on modelling and analysis to ensure realistic theory provides practical design. Chapters follow on monolithic reinforced concrete shear wall construction and non-monolithic shear wall construction, concluding with shear infill panels to seek to encapsulate the variations offered and used in’ine industry today. The Guide is illustrated throughout by clear structural philosophy sketches, current case histories and valuable references for those who wish to broaden their knowledge on the subject. As with Parts 1 and 2, the Institution believes this will be useful to those attempting the Institution’s Membership exam as well as to those practicing engineers wishing to complete a concept design report. Again, I would like to offer thanks to the consultees who have assisted in the development of this guidance in context with the previous Parts 1 and 2, and Dr Gareth Evans, Chairman of the Technical vi
The Institution of Structural Engineers Stability of buildings Part 3
Publications Panel, for managing the draft through its peer review.
Paul Perry Chairman of the Reviewing Panel
