DESIGN OF MASONRY STRUCTURES Part 1 ppt

DESIGN OFMASONRY STRUCTURES Third edition of Load Bearing Brickwork Design A.W.Hendry, B.Sc., Ph.D., D.Sc, F.I.C.E., F.I... First edition 1997 © 1997 A.W.Hendry, B.P.Sinha and S.R.Davies

DESIGN OF

MASONRY STRUCTURES

Third edition of Load Bearing Brickwork Design

A.W.Hendry, B.Sc., Ph.D., D.Sc, F.I.C.E., F.I Struct.E., F.R.S.E

B.P.Sinha, B.Sc., Ph.D., F.I Struct.E., F.I.C.E., C Eng

and

S.R.Davies, B.Sc., Ph.D., M.I.C.E., C.Eng

Department of Civil Engineering

University of Edinburgh, UK

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This edition published in the Taylor & Francis e-Library, 2004.

First edition 1997

© 1997 A.W.Hendry, B.P.Sinha and S.R.Davies

First published as Load Bearing Brickwork Design

(First edition 1981 Second edition 1986)

ISBN 0-203-36240-3 Master e-book ISBN

ISBN 0-203-37498-3 (Adobe eReader Format)

ISBN 0 419 21560 3 (Print Edition)

Apart from any fair dealing for the purposes of research or private study,

or criticism or review, as permitted under the UK Copyright Designs and Patents Act, 1988, this publication may not be reproduced, stored, or transmitted, in any form or by any means, without the prior permission in writing of the publishers, or in the case of reprographic reproduction only in accordance with the terms of the licences issued by the Copyright Licensing Agency in the UK, or in accordance with the terms of licences issued by the appropriate Reproduction Rights Organization outside the UK Enquiries concerning reproduction outside the terms stated here should be sent to the publishers at the London address printed on this page.

The publisher makes no representation, express or implied, with regard to the accuracy of the information contained in this book and cannot accept any legal responsibility or liability for any errors or omissions that may be made.

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

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Preface to the third edition

Preface to the second edition

Preface to the first edition

Acknowledgements

1 Loadbearing masonry buildings

1.1 Advantages and development of loadbearing masonry

1.2 Basic design considerations

1.3 Structural safety: limit state design

1.4 Foundations

1.5 Reinforced and prestressed masonry

2 Bricks, blocks and mortars

2.10 Proportioning and strength

2.11 Choice of unit and mortar

2.12 Wall ties

2.13 Concrete infill and grout

2.14 Reinforcing and prestressing steel

3.4 The tensile strength of masonry

3.5 Stress-strain properties of masonry

3.6 Effects of workmanship on masonry strength

4 Codes of practice for structural masonry

4.1 Codes of practice: general

4.2 The basis and structure of BS 5628: Part 1

4.3 BS 5628: Part 2—reinforced

and prestressed masonry

4.4 Description of Eurocode 6 Part 1–1

(ENV 1996–1–1:1995)

5 Design for compressive loading

5.1 Introduction

5.2 Wall and column behaviour under axial load

5.3 Wall and column behaviour under eccentric load 5.4 Slenderness ratio

6.3 Theoretical methods for wind load analysis

6.4 Load distribution between unsymmetrically

arranged shear walls

7 Lateral load analysis of masonry panels

7.1 General

7.2 Analysis of panels with precompression

7.3 Approximate theory for lateral load analysis of walls subjected to precompression with and without returns

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7.4 Effect of very high precompression

7.5 Lateral load design of panels without

precompression

8 Composite action between walls and other elements

8.1 Composite wall-beams

8.2 Interaction between wall panels and frames

9 Design for accidental damage

10.3 Shear strength of reinforced masonry

10.4 Deflection of reinforced masonry beams

10.5 Reinforced masonry columns, using BS 5628: Part 2 10.6 Reinforced masonry columns, using ENV 1996–1–1

12.2 Basis of design: loadings

12.3 Quality control: partial safety factors

12.4 Calculation of vertical loading on walls

12.10 Appendix: a typical design calculation for interior-span solid slab

13 Movements in masonry buildings

13.1 General

13.2 Causes of movement in buildings 13.3 Horizontal movements in masonry walls 13.4 Vertical movements in masonry walls

Notation

BS 5628

EC6 (where different from BS 5628)

Definition of terms used in masonry

References and further reading

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Preface to the third edition

The first edition of this book was published in 1981 as Load Bearing

Brickwork Design, and dealt with the design of unreinforced structural

brickwork in accordance with BS 5628: Part 1 Following publication ofPart 2 of this Code in 1985, the text was revised and extended to coverreinforced and prestressed brickwork, and the second edition published

Edinburgh, June 1996

Preface to the second edition

Part 2 of BS 5628 was published in 1985 and relates to reinforced andprestressed masonry which is now finding wider application in practice.Coverage of the second edition of this book has therefore been extended

to include consideration of the principles and application of this form ofconstruction

Edinburgh, April 1987

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Preface to the first edition

The structural use of brick masonry has to some extent been hampered

by its long history as a craft based material and some years ago itsdisappearance as a structural material was being predicted The fact thatthis has not happened is a result of the inherent advantages of brickworkand the design of brick masonry structures has shown steadydevelopment, based on the results of continuing research in manycountries Nevertheless, structural brickwork is not used as widely as itcould be and one reason for this lies in the fact that design in thismedium is not taught in many engineering schools alongside steel andconcrete To help to improve this situation, the authors have written thisbook especially for students in university and polytechnic courses instructural engineering and for young graduates preparing forprofessional examination in structural design

The text attempts to explain the basic principles of brickwork design,the essential properties of the materials used, the design of various structuralelements and the procedure in carrying out the design of a completebuilding In practice, the basic data and methodology for structural design

in a given material is contained in a code of practice and in illustratingdesign procedures it is necessary to relate these to a particular document

of this kind In the present case the standard referred to, and discussed insome detail, is the British BS 5628 Part 1, which was first published in 1978.This code is based on limit state principles which have been familiar tomany designers through their application to reinforced concrete designbut which are summarised in the text

No attempt has been made in this introductory book to give extensivelists of references but a short list of material for further study is includedwhich will permit the reader to follow up any particular topic in greaterdepth

Preparation of this book has been based on a study of the work of alarge number of research workers and practising engineers to whom the

authors acknowledge their indebtedness In particular, they wish toexpress their thanks to the following for permission to reproducematerial from their publications, as identified in the text: BritishStandards Institution; Institution of Civil Engineers; the BuildingResearch Establishment; Structural Clay Products Ltd.

B.P.SinhaS.R.Davies

©2004 Taylor & Francis

Preparation of this book has been based on a study of the work of a largenumber of research workers and practising engineers, to whom theauthors acknowledge their indebtedness In particular, they wish toexpress thanks to the British Standards Institution, the Institution of CivilEngineers, the Building Research Establishment and Structural ClayProducts Ltd for their permission to reproduce material from theirpublications, as identified in the text They are also indebted to the BrickDevelopment Association for permission to use the illustration of CavernWalks, Liverpool, for the front cover

Extracts from DD ENV 1996–1–1:1995 are reproduced with thepermission of BSI Complete copies can be obtained by post from BSICustomer Services, 389 Chiswick High Road, London W4 4AL Usersshould be aware that DD ENV 1996–1–1:1995 is a prestandard; additionalinformation may be available in the national foreword in due course

Loadbearing masonry buildings

MASONRY

The basic advantage of masonry construction is that it is possible to usethe same element to perform a variety of functions, which in asteelframed building, for example, have to be provided for separately,with consequent complication in detailed construction Thus masonrymay, simultaneously, provide structure, subdivision of space, thermaland acoustic insulation as well as fire and weather protection As amaterial, it is relatively cheap but durable and produces external wallfinishes of very acceptable appearance Masonry construction is flexible

in terms of building layout and can be constructed without very largecapital expenditure on the part of the builder

In the first half of the present century brick construction for storey buildings was very largely displaced by steel- andreinforcedconcrete-framed structures, although these were very oftenclad in brick One of the main reasons for this was that until around 1950loadbearing walls were proportioned by purely empirical rules, whichled to excessively thick walls that were wasteful of space and materialand took a great deal of time to build The situation changed in a number

multi-of countries after 1950 with the introduction multi-of structural codes multi-ofpractice which made it possible to calculate the necessary wall thicknessand masonry strengths on a more rational basis These codes of practicewere based on research programmes and building experience, and,although initially limited in scope, provided a sufficient basis for thedesign of buildings of up to thirty storeys A considerable amount ofresearch and practical experience over the past 20 years has led to theimprovement and refinement of the various structural codes As a result,the structural design of masonry buildings is approaching a level similar

to that applying to steel and concrete

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1.2 BASIC DESIGN CONSIDERATIONS

Loadbearing construction is most appropriately used for buildings inwhich the floor area is subdivided into a relatively large number ofrooms of small to medium size and in which the floor plan is repeated oneach storey throughout the height of the building These considerationsgive ample opportunity for disposing loadbearing walls, which arecontinuous from foundation to roof level and, because of the moderatefloor spans, are not called upon to carry unduly heavy concentrations ofvertical load The types of buildings which are compatible with theserequirements include flats, hostels, hotels and other residentialbuildings

The form and wall layout for a particular building will evolve fromfunctional requirements and site conditions and will call forcollaboration between engineer and architect The arrangement chosenwill not usually be critical from the structural point of view providedthat a reasonable balance is allowed between walls oriented in theprincipal directions of the building so as to permit the development ofadequate resistance to lateral forces in both of these directions Veryunsymmetrical arrangements should be avoided as these will give rise totorsional effects under lateral loading which will be difficult to calculateand which may produce undesirable stress distributions

Stair wells, lift shafts and service ducts play an important part indeciding layout and are often of primary importance in providing lateralrigidity

The great variety of possible wall arrangements in a masonry buildingmakes it rather difficult to define distinct types of structure, but a roughclassification might be made as follows:

• Cellular wall systems

• Simple or double cross-wall systems

• Complex arrangements

A cellular arrangement is one in which both internal and external wallsare loadbearing and in which these walls form a cellular pattern in plan

Figure 1.1 (a) shows an example of such a wall layout

The second category includes simple cross-wall structures in whichthe main bearing walls are at right angles to the longitudinal axis of thebuilding The floor slabs span between the main cross-walls, andlongitudinal stability is achieved by means of corridor walls, as shown in

Fig 1.1(b) This type of structure is suitable for a hostel or hotel buildinghaving a large number of identical rooms The outer walls may be clad innon-loadbearing masonry or with other materials

It will be observed that there is a limit to the depth of building whichcan be constructed on the cross-wall principle if the rooms are to have

effective day-lighting If a deeper block with a service core is required, asomewhat more complex system of cross-walls set parallel to both majoraxes of the building may be used, as in Fig 1.1(c).

All kinds of hybrids between cellular and cross-wall arrangements arepossible, and these are included under the heading ‘complex’, a typicalexample being shown in Fig 1.1(d)

Considerable attention has been devoted in recent years to thenecessity for ensuring the ‘robustness’ of buildings This has arisen from

a number of building failures in which, although the individualmembers have been adequate in terms of resisting their normal serviceloads, the building as a whole has still suffered severe damage fromabnormal loading, resulting for example from a gas explosion or fromvehicle impact It is impossible to quantify loads of this kind, and what isrequired is to construct buildings in such a way that an incident of thiscategory does not result in catastrophic collapse, out of proportion to theinitial forces Meeting this requirement begins with the selection of walllayout since some arrangements are inherently more resistant toabnormal forces than others This point is illustrated in Fig 1.2: abuilding consisting only of floor slabs and cross-walls (Fig 1.2(a)) isobviously unstable and liable to collapse under the influence of smalllateral forces acting parallel to its longer axis This particular weaknesscould be removed by incorporating a lift shaft or stair well to provideresistance in the weak direction, as in Fig 1.2(b) However, the flank orgable walls are still vulnerable, for example to vehicle impact, andlimited damage to this wall on the lowermost storey would result in thecollapse of a large section of the building

A building having a wall layout as in Fig 1.2(c) on the other hand isclearly much more resistant to all kinds of disturbing forces, having ahigh degree of lateral stability, and is unlikely to suffer extensive damagefrom failure of any particular wall

Robustness is not, however, purely a matter of wall layout Thus afloor system consisting of unconnected precast planks will be much less

resistant to damage than one which has cast-in-situ concrete floors with

two-way reinforcement Similarly, the detailing of elements and theirconnections is of great importance For example, adequate bearing ofbeams and slabs on walls is essential in a gravity structure to preventpossible failure not only from local over-stressing but also from relativemovement between walls and other elements Such movement couldresult from foundation settlement, thermal or moisture movements Anextreme case occurs in seismic areas where positive tying together ofwalls and floors is essential

The above discussion relates to multi-storey, loadbearing masonrybuildings, but similar considerations apply to low-rise buildings wherethere is the same requirement for essentially robust construction

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