Structural Design for Architecture 1997 PDF

STRUCTURAL DESIGN FOR ARCHITECTURE ANGUS J MACDONALD Structural Design for Architecture Angus J. Macdonald Architectural Press Architectural Press 225 Wildwood Avenue, Woburn, MA 01801-204 An imprint of Butterworth-Heinemann Linacre House, Jordan Hill, O...

STRUCTURAL DESIGN FOR ARCHITECTURE ANGUS J MACDONALD Structural Design for Architecture Angus J. Macdonald Architectural Press Architectural Press 225 Wildwood Avenue, Woburn, MA 01801-204 An imprint of Butterworth-Heinemann Linacre House, Jordan Hill, Oxford 0X2 8DP A division of Reed Educational and Professional Publishing Ltd A member of the Reed Elsevier plc group OXFORD BOSTON JOHANNESBURG MELBOURNE NEW DELHI SINGAPORE First published 1997 Reprinted 1998 © Reed Educational and Professional Publishing Ltd 1997 All rights reserved. No part of this publication may be reproduced in any material form (including photocopying or storing in any medium by electronic means and whether or not transiently or incidentally to some other use of this publication) without the written permission of the copyright holder except in accordance with the provisions of the Copyright, Designs and Patents Act 1988 or under the terms of a licence issued by the Copyright Licensing Agency Ltd, 90 Tottenham Court Road, London, England W1P 9HE. Applications for the copyright holder's written permission to reproduce any part of this publication should be addressed to the publishers. British Library Cataloguing in Publication Data Macdonald, Angus J. Structural design for architecture 1. Architectural design 2. Structural design 1.Title 721 ISBN 0 7506 3090 6 Library of Congress Cataloguing in Publication Data Macdonald, Angus, 1945- Structural design for architecture/Angus J. Macdonald. p. cm. Includes bibliographical references and index. ISBN 0 7506 3090 6 1. Buildings. 2. Structural Design. 3. Architectural design. 1. Title. TH846.M33 97-27237 624. 1'771-dc21 CIP Composition by Scribe Design, Gillingham, Kent Printed and bound in Great Britain  Contents Foreword vii 4.3 A brief introduction to concrete Preface ix technology 118 4.4 Structural forms for reinforced concrete Acknowledgements xi 130 1 Structure and architecture 1 5 Masonry structures 147 1.1 The role of structure in architecture 1 5.1 Introduction 147 1.2 Structural requirements 4 5.2 The architecture of masonry - factors 1.3 Structure types 5 which affect the decision to use 1.4 Structural materials 11 masonry as a structural material 147 1.5 Structural design 17 5.3 The basic forms of masonry structures 164 2 Structural design for architecture 22 2.1 Introduction 22 6 Timber structures 179 2.2 The relationship between structural 6.1 Introduction 179 design and architectural design 24 6.2 Timber and architecture 180 2.3 Selection of the generic type of 6.3 The material, its properties and structure 34 characteristics 190 2.4 Selection of the structural material 40 6.4 Properties of timber 192 2.5 Determination of the form of the 6.5 Grading of timber 196 structure 41 6.6 Timber components 198 2.6 Conclusion 47 6.7 Structural forms for timber 215 3 Steel structures 49 Selected bibliography 233 3.1 Introduction 49 3.2 The architecture of steel - the factors Appendix 1: The relationship between which affect the decision to select steel structural form and structural as a structural material 49 efficiency 235 3.3 The properties and composition of steel 61 Appendix 2: Approximate methods for 3.4 Structural steel products 63 allocating sizes to structural elements 239 3.5 Performance of steel in fire 72 A2.1 Introduction 239 3.6 Structural forms 73 A2.2 Structural analysis 239 A2.3 Element-sizing calculations 249 4 Reinforced concrete structures 99 A2.4 Steel structures 258 4.1 Introduction 99 A2.5 Reinforced concrete structures 262 4.2 The architecture of reinforced concrete - A2.6 Masonry structures 263 the factors which affect the decision to A2.7 Timber structures 263 select reinforced concrete as a structural material 100 Index 265 V  Foreword Angus Macdonald states that this book is symbolised and high tech (i.e. celebrated or primarily for architects. In my view it is also an expressionist) is apt but contentious and could extremely good reference book on architectural result in some lively discussion between structures for students and practising architect and engineer, structural engineers. The book then divides into sections on the He stresses that buildings are designed as a major structural materials - steel, concrete, collaborative task between architects and masonry and timber. Each of these sections engineers and that the earlier in the design follows a similar pattern and includes process this happens, the better the result. properties, advantages and disadvantages, Current teaching ideas in many universities common structural forms, etc. are, at last, acknowledging the benefits of joint Structural Design for Architecture is a student working and it has certainly been my comprehensive and up-to-date work on the experience that close working produces the relationship of structure to architecture and will best product. form an extremely useful reference work for both The early part of the book covers the history, students and practitioners of architecture and technology and structural philosophy of engineering. I highly recommend it and look numerous buildings and building types and forward to having a copy in our office library, has a very comprehensive review of structural systems with excellent examples of seminal buildings and their structures. It also covers Professor Tony Hunt the history of structural'material development. Chairman The section on structure in relation to Anthony Hunt Associates architecture: structure ignored, accepted, June 1997 Previous page vii is blank  Preface The architect who considers him or herself to mine the maximum sizes of the internal spaces be an artist, dealing through the medium of and its type affects the extent to which the built form with the philosophical preoccupa- sizes and shapes of the spaces can be varied tions of the age in which he or she lives, is both within an individual storey and between surely engaged in a titanic struggle. One storeys. aspect of that struggle is the need to deter- The relationship between structure and mine building forms which are structurally architecture is therefore a fundamental aspect viable. All artists must acquire mastery of the of the art of building. It sets up conflicts technology of their chosen medium but few between the technical and aesthetic agendas face difficulties which are as formidable as which the architect must resolve. The manner those who choose buildings as their means of in which the resolution is carried out is one of expression. The sculptor has to contend with the most testing criteria of the success of a similar structural problems but his or her diffi- work of architecture. culties are trivial by comparison with those of This book is concerned with structural the architect. The difference is one of scale - design for architecture. It complements my the size of a building, compared to that of a previous volume, Structure and Architecture, and work of sculpture, means that the technical discusses the selection of structure type, the hurdle which must be surmounted by the selection of structural material and the deter- architect is of a different order of magnitude to mination of structural form. It deals primarily those which are faced by most other artists. with the development of the idea of the struc- The structure of a building is the armature ture for a building - that first stage in the which preserves its integrity in response to structural design process which is concerned load. It is a bulky object which is difficult to with the determination of the elementary form conceal and which must somehow be incorp- and arrangement of the structure, before any orated into the aesthetic programme. It must structural design calculations are made. It is therefore be given a form, by the building's intended primarily for architects and it is designer, which is compatible with other hoped that it will enable students and aspects of the building's design. Several funda- members of the profession to gain a better mental issues connected with the appearance understanding of the relationship between of a building including its overall form, the structural design and architectural design. The pattern of its fenestration, the general articula- basic structural layouts and approximate tion of solid and void within it and even, pos- element sizes which are given in Chapters 3 to sibly, the range and juxtaposition of the 6 should, however, also allow building design- textures of its visible surfaces are affected by ers to use the book as an aid to the basic the nature of its structure. The structure can planning of structural forms. also influence programmatic aspects of a build- ing's design because the capability of the struc- Angus Macdonald ture determines the pattern of internal spaces Edinburgh which is possible. Its span potential will deter- July 1997 Previous page ix is blank  Acknowledgements 1 would like to thank the many people who are due to all those who supplied illustrations have assisted me in the making of this book. and especially to the Ove Arup Partnership, These are too numerous for all to be George Balcombe, Sir Norman Foster and mentioned individually, but special thanks are Partners, Paul H. Gleye, Pat Hunt, Tony Hunt, due to the following: Stephen Gibson for his the late Alastair Hunter, Jill Hunter, Denys excellent line drawings, the staff of Lasdun Peter Softley and Associates, Ewan and Architectural Press for their hard work in Fiona McLachlan, Dr Rowland J. Mainstone and producing the book, particularly Neil Warnock- the Maritime Trust. I am also grateful to the Smith, Zoë Youd and Sarah Leatherbarrow. I British Standards Institution for permission to would also like to thank the staff and students reproduce tables, of the Department of Architecture at the Finally, I should like to thank my wife University of Edinburgh for the many helpful Patricia Macdonald for her encouragement and discussions which I have had with them on the support and for her valuable contributions to topics covered in this book. the preparation of the manuscript and Illustrations, other than those illustrations, commissioned especially for the book, are individually credited in their captions. Thanks Angus Macdonald Previous page xi is blank  Chapter 1 Structure and architecture 1.1 The role of structure in particular, with the question of the structural architecture support which must be provided for a building in order that it can maintain its shape and The final form which is adopted for a work of integrity in the physical world. The role of the architecture is influenced by many factors building as an aesthetic object, often imbued ranging from the ideological to the severely with symbolic meaning, is, however, also practical. This book is concerned principally central to the argument of the book; one with the building as a physical object and, in strand of this argument considers that the Fig. 1.1 Offices, Dufour's Place, London, England, 1984. Erith and Terry, archi- tects. As well as having a space-enclosing function the external walls of this build- ing are the loadbearing elements which carry the weights of the floors and roof. [Photo: E. & F. McLachlan] Structural Design for Architecture Fig. 1.2 Crown Hall, 1IT, Chicago, USA, 1952-56. Ludwig basic carcass of the building - the armature to Mies van der Rohe, architect. This building has a steel- frame structure. The glass walls are entirely non-structural. which all non-structural elements are attached. The visual treatment of structure can be subject to much variation. The structural contribution of the structure to the achieve- system of a building can be given great prom- ment of higher architectural objectives is inence and be made to form an important part always crucial. Technical issues are accordingly of the architectural vocabulary (Fig. 1.3). At the considered here within a wider agenda which other extreme, its presence can be visually encompasses considerations other than those played down with the structural elements of practicality. contributing little to the appearance of the The relationship between the structural and building (Fig. 1.4). Between these extremes lies the non-structural parts of a building may vary an infinite variety of possibilities (see Section widely. In some buildings the space-enclosing 2.2). In all cases, however, the structure, by elements - the walls, floors and roof - are also virtue of the significant volume which it structural elements, capable of resisting and occupies in a building, affects its visual charac- conducting load (Fig. 1.1). In others, such as ter to some extent and it does so even if it is buildings with large areas of glazing on the not directly visible. No matter how the struc- exterior walls, the structure can be entirely ture is treated visually, however, the need for separate from the space-enclosing elements technical requirements to be satisfied must (Fig. 1.2). In all cases the structure forms the always be acknowledged. Structural constraints  Structure and architecture Fig. 1.3 HongkongBank Headquarters, Hong Kong, 1979-84. Foster Associates, architects. The structure of this building is expressed prominently both on the exterior and in the interior. It contributes directly as well as indirectly to the appearance of the building. [Photo: Ian Lambot. Copyright: Foster & Partners ] Fig. 1.4 Staatsgalerie, Stuttgart, Germany, 1980-83, lames Stirling, architect. This building has a reinforced concrete struc- ture and non-structural cladding. Although the structure plays a vital role in the creation of the complex overall form it is not a significant element in the visual vocabulary. [Photo: P. Macdonald] Structural Design for Architecture therefore exert a significant influence, overt or hidden, on the final planning of buildings. This book is concerned with the program- matic aspects of the relationship between architecture and structure. Chapter 2, in par- ticular, deals with the process by which the form and general arrangement of structures for buildings are determined - with the design of architectural structures, in other words. Fig. 1.5 The first of the frameworks here is capable of achieving equilibrium under the loading shown but is Information on basic forms of structure - the unstable. The insertion of the diagonal element in the range of structural possibilities - is essential second framework renders it capable of achieving stable to the success of this process; this is provided equilibrium. in subsequent chapters which deal separately with the four principal structural materials of steel, reinforced concrete, masonry and timber. state of static equilibrium but is not stable and More general aspects of the topic are reviewed will collapse if subjected to a small lateral briefly here. displacement. The insertion of a diagonal bracing element in the second framework prevents this and renders the system stable. 1.2 Structural requirements Most structural arrangements require bracing for stability and the devising of bracing The principal forms of loading to which build- systems is an important aspect of structural ings are subjected are gravitational loads, wind design. pressure loads and inertial loads caused by As the simple diagrammatic structure in Fig. seismic activity. Gravitational loads, which are 1.6 illustrates, the structural elements of a caused by the weight of the building itself and building provide the link between the applied of its contents, act vertically downwards; wind loads and the foundation reactions in order and seismic loads have significant horizontal that equilibrium can be achieved. To be effec- components but can also act vertically. To tive the elements must be of adequate perform satisfactorily a structure must be strength. The strength of an element depends capable of achieving a stable state of static on the strength of the constituent material and equilibrium in response to all of these loads - the area and shape of its cross-section. The to load from any direction, in other words. This stronger the material and the larger the cross- is the primary requirement; the form and section the stronger will be the element. It is general arrangement of a structure must be possible to produce a strong element even such as to make this possible. though the constituent material is weak by The distinction between the requirements specifying a very large cross-section. for stability and equilibrium is an important In the case of a particular structure, once the one and the basic principles are illustrated in requirements for stability and equilibrium have Fig. 1.5. Equilibrium occurs when the reactions been met, the provision of elements with at the foundations of a structure exactly adequate strength is a matter firstly of deter- balance and counteract the applied load; if it mining the magnitudes of the internal forces were not in equilibrium the structure would which will occur in the elements when the peak change its position in response to the load. load is applied to the structure. Secondly, a Stability is concerned with the ability of a structural material of known strength must be structural arrangement which is in equilibrium selected and thirdly, the sizes and shapes of to accommodate small disturbances without cross-sections must be chosen such that each suffering a major change of shape. The first of element can safely carry the internal force 4 the beam/column frameworks in Fig. 1.5 is in a which the load will generate. Calculations are  Structure and architecture Fig. 1.6 Force system in a building's structure. The gravi- tational load on the roof is conducted, via the roof truss and the walls, to the founda- tions where it is balanced by reactions from the substrata. The same is true of loads imposed on the floors which are transmitted by the floor structural elements and walls to the foundations. The roof truss, wall and floor elements must be strong enough to carry the internal forces gener- Non-loadbearing ated by the load. partition wall an essential aspect of this process and are tectural shopping list of 'firmness', 'commod- required both to determine the magnitudes of ity' and 'delight') are the ability to achieve the forces in the individual elements - an equilibrium under all possible load conditions, activity known as structural analysis - and then geometric stability, adequate strength and to calculate the required sizes of the element adequate rigidity. Equilibrium requires that the cross-sections. structural elements be properly configured, A fourth property which a structure must stability is ensured by the provision of a possess, in addition to the requirements of bracing system; and adequate strength and equilibrium, stability, and strength, is rigidity are provided by the specification of adequate rigidity. All structural materials structural elements which are of sufficient size, deform in response to load and it is necessary given the strengths of the constituent that the overall deflection of a structure should materials. not be excessive. As with strength, the rigidity of the structure depends on the properties of the material and the sizes of the cross- 1.3 Structure types sections, which must be large enough to ensure that excessive deflection does not 1.3.1 Post-and-beam structures occur. Like strength, rigidity is checked and Most architectural structures are of the post- controlled through the medium of calculations. and-beam type and consist of horizontal To summarise, the basic requirements of the spanning elements supported on vertical structure (the firmness element of the archi- columns or walls. A characteristic of this type 5 Structural Design for Architecture Fig. 1.7 Steel skeleton framework. In this arrange- ment, which is typical of a multi-storey steel-frame structure, concrete floor slabs are supported by a grid of steel beams which is in turn supported by slender steel columns. These elements form the structural carcass of the building. External walls and internal partitions are non-structural and can be arranged to suit planning and aesthetic require- ments. of structure is that the horizontal elements are cladding is attached (Fig. 1.7). The configur- subjected to bending-type internal forces ation of the beam-and-column grid which is under the action of gravitational load adopted in a particular case depends on the (normally the primary load on an architectural overall form of the building concerned, on the structure). This has two consequences. Firstly, internal planning requirements and on the it requires that the structural material be properties of the particular structural material capable of resisting both tension and compres- which has been chosen - see Chapters 3 to 6. sion (e.g. steel, reinforced concrete, timber). In this type of arrangement the structure Secondly, it is an inefficient type of structure occupies a relatively small volume and this is (larger volumes of material are required to in fact one of its principal advantages. support a given load than are necessary with Considerable freedom is available to the build- other types of structure).1 The post-and-beam ing designer in the matter of internal planning structure has the great advantage that it is because both the internal partition walls and simple and therefore cheap to construct. This the exterior walls are non-loadbearing. Large group of structures can be subdivided into the wall-free spaces can therefore be created in the two categories of 'skeleton-frame' structures interiors and different plan-forms adopted at and 'panel' structures. The latter are also different levels in multi-storey buildings. The loadbearing-wall structures. choice of external treatment is wide. Relatively Skeleton-frame structures consist of a fragile materials such as glass can be used and network of beams and columns which support little restriction is placed on the locations of floor slabs and roof cladding and to which wall doors and windows (Fig. 1.8). A consequence of the small structural volume of the skeleton frame is that structural loads are concentrated into slender columns 6 1 See Appendix 1 for an explanation of this. and beams and these elements must therefore  Structure and architecture Fig. 1.8 Nenfeldweg Housing, Graz, Austria, 1984-88. Gunther Domenig, architect. The structure of this building is a reinforced concrete framework. Its adoption has allowed greater freedom to be exercised in the internal planning and external treat- ment than would have been possible with a loadbear- ing-wall structure. [Photo: E. & F. McLachlan] be constructed in strong materials such as levels of internal force. Structural materials of steel or reinforced concrete. low or moderate strength, such as masonry or Panel structures are arrangements of struc- timber, are therefore particularly suited to this tural walls and horizontal panels (Fig. 1.9). The form of construction (Fig. 1.10). walls may be of masonry, concrete or timber - Panel structures impose greater constraints the last of these being composed of closely on planning freedom than skeleton-frame spaced vertical elements - and the floors and equivalents because structural considerations roof of reinforced concrete or timber - again as well as space-planning requirements must the configuration with timber is one of closely be taken into account when the locations of spaced elements, in this case floor joists or walls are determined. The creation of large trussed rafters (Fig. 6.39). interior spaces is problematic as is the vari- Many different combinations of elements ation of plans between different levels in and materials are possible. In all cases the multi-storey arrangements. The advantage of volume of the structure is large in relation to the panel form of structure is that it is simpler skeleton-frame equivalents with the result that to construct than most skeleton frames and the structural elements are subjected to lower considerably less expensive. 7 Structural Design for Architecture Fig. 1.9 Multi-storey loadbearing-wall structure. In this arrangement the floors and roof of the build- ing are carried by the walls. The structural sections give an indication of the action of the walls in response to gravitational and wind loading. The plan arrange- ment of the walls must be such as to provide good structural performance and the plan-form must be maintained through all levels. These are constraints which must be accepted during the internal planning of this type of building. Fig. 1.10 Housing, Gogarloch Syke, Edinburgh, Scotland, 1996. E. & F. McLachlan, architects. These houses are good examples of panel structures in loadbear- ing masonry. | Photo: Keith Hunter; copyright: E. & F. McLachlan | 8  Structure and architecture 1.3.2 Vaults and domes Fig. 1.11 TGV Station, Lyon-Satolas, France 1989-94, Santiago Calatrava, architect/engineer. A vaulted structure Vaults and domes are structure types in which in reinforced concrete is used here to achieve a relatively the dominant feature is an upwards curvature long span. [Photo: E. & F. McLachlan] towards the dominant, downward-acting gravi- tational load (Fig. 1.11). They belong to a class of structure in which the internal forces are large horizontal spans to be achieved with predominantly axial rather than of the bending materials, such as masonry or unreinforced type,2 and, in the case of vaults and domes, concrete, which have little tensile strength (Fig. this internal force is compressive. They are 5.4): large-span interiors can be created in therefore normally constructed in materials masonry only by the use of domed or vaulted which perform well in compression, such as structures. This was the principal reason for masonry or concrete. the use of this type of arrangement prior to the The axial-compressive-stress-only condition invention of modern materials such as steel which is associated with vaults and domes has and reinforced concrete which allow large two important consequences. First, it allows spans to be achieved with post-and-beam forms due to their ability to resist bending effectively. Secondly, and perhaps more importantly for the buildings of today, it allows loads to be 2 See Macdonald, Structure and Architecture, Chapter 4 for a classification of structure types. The principles are resisted with much greater structural efficiency summarised here in Appendix 1. than is possible where bending is the principal 9 Structural Design for Architecture Fig. 1.12 Building for IBM Europe travelling exhibition. fore, like their axial compressive equivalents, Renzo Piano, architect/engineer, Ove Arup and Partners, potentially highly efficient in resisting load.4 As structural engineers. A complex, highly efficient vaulted structure like this would not normally be used for a short- with domes and vaults they are used in situa- span enclosure. It was justified in this case due to a tions in which high structural efficiency is requirement for a lightweight structure for a portable desirable, such as for long spans or where a building. The choice of lightweight materials - timber and lightweight structure is required. plastic-was also sensible. [Photo: Ove Arup & Partners] 1.3.4 Combined-action structures 3 result of the application of load. In modern A fourth category of structure is one in which practice, vaults or domes are normally used to the load is resisted by a combination of achieve high levels of structural efficiency, bending and axial internal forces. The ubiqui- either because a very long span is required or tous portal frame (Fig. 1.14) is perhaps the because a special requirement must be satis- best-known example of this but any structure fied such as the need for a very lightweight which is neither purely 'form-active' nor purely structure (Fig. 1.12). 'non-form-active' will carry load through the combined effect of axial and bending action. 1.3.3 Tents and cable networks These structures have properties which are Tents and cable networks are tensile equiva- intermediate between those of the post-and- lents of domes and vaults (Fig. 1.13). The in- beam arrangement, which is inefficient but ternal forces which occur in these structures simple to construct, and the arch, vault or are those of axial tension and they are there- cable network, which are highly efficient but 10 3 See Macdonald, Structure and Architecture, Chapter 4. 4 See Appendix 1.  Structure and architecture complicated to construct. Combined-action Fig. 1.13 Olympic Stadium, Munich, Germany, 1968-72. structures are therefore used in situations in Behnisch & Partner, architects, with Frei Otto. The struc- ture of this canopy consists of a network of steel wires (the which intermediate levels of efficiency are very fine square mesh) supported on a system of masts required, for example in the medium-span and cables. The pattern of heavy rectangular lines results range. They are most often found in the form from the flexible joints between the cladding panels. of skeleton-frame arrangements. Highly efficient structure types such as this are required where long spans are involved. [Photo: A. Macdonald] 1.4 Structural materials manufacture which contribute to determining the structural forms for which it is most The form and general arrangement of architec- suitable. These issues are considered in detail tural structures are greatly influenced by the in the chapters on individual materials. Only properties of the materials from which they are the most general aspects are reviewed here. constructed. For this reason the basic structure The properties of materials which affect the types appropriate to the four principal materi- load-carrying performance of a structure are als of steel, reinforced concrete, masonry and strength, elasticity and, to a lesser extent, timber are described in separate chapters. specific gravity (which determines the self- Each material has its own individual charac- weight of structural elements). Other signifi- teristics in terms of physical properties and cant physical properties are durability (i.e. 11 Structural Design for Architecture Fig. 1.14 Palmerston Special School, Liverpool, England, elasticity are also significant because these 1973-76 (demolished 1989). Foster Associates, architects; determine the efficiency with which a material Anthony Hunt Associates, structural engineers. Semi-form- active portal frames of steel hollow-section are used here can be used. Of the four principal structural as the primary structural elements in a multi-bay arrange- materials, steel and reinforced concrete may ment with relatively short spans. The moderately high be thought of as high-strength materials and efficiency of this type of structure has permitted very timber and masonry as low-strength materials. slender elements to be adopted. |Photo: lohn Donat] Each of the four has a unique combination of properties which makes it perform best in susceptibility to both physical and chemical particular types of structural arrangement. deterioration) and performance in fire. Non- Another set of factors which influences the physical, but interrelated, properties which are types of structure for which a material is relevant are cost, availability and environmen- suitable are the conditions of its manufacture tal impact. The last of these is concerned with and finishing. These determine the type of the environmental issues (depletion of mater- product in which the material becomes avail- ial resources and energy sources, pollution, the able to the builder. Steel, for example, is avail- health of workers, etc.) which will arise from able in the form of manufactured elements the manufacture, installation and use of struc- which are straight and of constant cross- tural elements of a particular material. section. The construction of a steel structure is Of the purely physical properties, perhaps therefore a process of assembly of prefabri- the most important so far as structural per- cated components. Concrete, on the other formance is concerned is strength, although hand, normally arrives on a building site in 12 the ratios of strength to weight and strength to liquid form and the building is literally formed  Structure and architecture Fig. 1.15 The high strength of steel allows the creation of structures with very slender elements. In buildings which are supported by steel frameworks the volume occupied by the structure is low in relation to the total volume of the building. (Photo: A. Macdonald). Fig. 1.16 Multi-storey steel frameworks are typically a combination of l-section beams and H-section columns. (Photo: A. Macdonald). on the site by pouring the concrete into moulds. The strongest of the structural materials is steel, which is therefore used for the tallest buildings and the longest spans. It is a highly versatile material, however, and is also used over a very wide variety of building types and span sizes. Because it is very strong the struc- tural elements are slender and of low volume, so that steel is used almost exclusively in the form of skeleton-frame structures (Fig. 1.15). The majority of these are assembled from standard rolled sections; these are elements with I- and H-shaped cross-sections (Fig. 1.16) and longitudinal profiles which are straight 13 Structural Design for Architecture and parallel-sided, and which lend themselves to use in straight-sided frameworks. Most steel structures therefore have a regular, rectilinear geometry. The range of possible forms has been extended in recent years by the develop- ment of techniques for bending rolled sections into curved shapes and by the increased use of casting to produce structural steel elements. However, the fact that all steel structures are prefabricated tends to require that regular and repetitive structural geometries be adopted even though the individual components are of irregular or curvilinear shape. A typical steel-frame building thus has a relatively simple overall form and an interior which is open and unencumbered by structural walls. Great freedom is therefore available to the designer so far as the internal planning of such buildings is concerned: the interior volumes may be left large or they may be subdivided by non-structural partition walls; different arrangements of rooms may be adopted at different levels and a free choice is available in the treatment both of the external walls and of the internal partitions. An advantage of prefabrication is that steel structural elements are manufactured and pre- assembled in conditions of very high quality control. Great precision is possible and this, Fig. 1.17 Goetheanum, Eurhythmeum, 'Glashaus' studio, together with the slenderness which results Dornach, Switzerland, 1924-28. Rudolf Steiner, architect. from high strength, means that structures of The complexity of form which is possible with in situ reinforced concrete is well illustrated here. [Photo: E. & F. great elegance can be produced. Steel is there- McLachlan] fore frequently selected as much for its aesthetic qualities and for the stylistic treat- ment which it makes possible as for its struc- tural performance. element shape to be available. Continuity Reinforced concrete, the other 'strong' between elements is also easily achieved and material, is of lower strength than steel with the resulting statical indeterminacy5 facilitates the result that equivalent structural elements the production of structures of complicated are more bulky. It too is used principally in form. Irregular geometries in both plan and skeleton-frame structures of regular geometry cross-section, with cantilevering floor slabs, and therefore offers similar advantages to steel tapering elements and curvilinear forms may in respect of internal planning and exterior all be produced more easily in reinforced treatment. Concrete structures are normally manufac- tured on the building site by the pouring of liquid concrete into temporary formwork struc- 5 See Macdonald, Structure and Architecture, Appendix 3, for an explanation of the phenomenon of statical indeter- tures of timber or steel which are specially minacy and its relevance to the determination of struc- 14 made to receive it. This allows a wide choice of tural form.  Structure and architecture concrete than in steel (Figs 1.17 and 4.20). The Fig. 1.18 Casa Pfaffli, Lugano, Switzerland, 1980-81. shapes of the elements are usually, however, Mario Botta, architect. The structure of this building consists of loadbearing masonry walls supporting more crude at a detailed level. reinforced concrete horizontal structural elements. [Photo: Masonry is the term for a range of materials E. &F. McLachlan] which have the common characteristic that they consist of solid elements (bricks, stones, concrete blocks, clay tiles) which are bedded in only. They can be used as walls, piers, arches, mortar to form piers and walls. A range of vaults and domes but not as slab-type horizon- other materials with similar physical properties tally spanning elements. When used as walls, to masonry, such as various forms of dried or they must be supported laterally at regular baked earth, are suitable for the same types of intervals due to their inability to withstand structural configuration. out-of-plane bending loads such as might The principal physical properties of these occur due to the effect of wind pressure. materials are moderate compressive strength, Masonry is therefore used in the loadbear- relatively good physical and chemical durabil- ing-wall form of structure (Fig. 1.18) to produce ity and good performance in fire. Very signifi- multi-cellular buildings in which the principal cant properties are brittleness and low tensile walls are continuous through all levels, giving strength. The last of these, in particular, has a similar arrangements of spaces on every profound effect on the structural forms for storey. The horizontal elements in such build- which masonry is suitable. Lack of tensile ings are normally of timber or reinforced strength means that bending-type load of concrete but may be of steel. Structural con- significant magnitude cannot be resisted so tinuity between these elements and the that masonry structural elements must be supporting masonry walls is difficult to achieve subjected principally to axial compression and the internal forces in the structural 15 Structural Design for Architecture elements must be maintained at modest levels. Spans are therefore normally kept small and in modern practice loadbearing masonry buildings are usually fairly small in scale. (This is in contrast to the very large-scale masonry structures of previous ages which were achieved by the use of masonry vaults and domes as the horizontal spanning elements - see Section 5.2. and Fig. 5.1.) Although modest in scale, modern loadbear- ing masonry structures exhibit very good combinations of properties and produce build- ings which are durable and fireproof and which have walls which perform extremely well in respect of thermal and acoustic insulation. They are therefore ideal for all kinds of living accommodation. Timber is a structural material which has similar properties to steel and reinforced concrete in the sense that it can carry both tension and compression with almost equal facility. It is therefore capable of resisting bending-type load and may be used for all types of structural element. It is significantly less strong than either steel or reinforced concrete, however, with the result that larger cross-sections are required to carry equivalent amounts of load. In practice, large cross- Fig. 1.19 Timber loadbearing-wall structure. Everything sections are rarely practicable and timber here is structural. The wall and floor structures consist of elements must therefore normally be used in closely spaced timber elements. Temporary bracing situations where the internal forces in the elements, which provide stability until non-loadbearing cross-walls are inserted, are also visible. [Photo: A. structural elements are low, that is in buildings Macdonald] of small size, and, in particular, short spans. A significant advantage which timber has over other structural materials is that it is very light, due to its fibrous internal structure and tied together by horizontal timber elements at the low atomic weights of its constituent the base and top, and the panels are arranged chemical elements. This results in a high ratio in plan configurations which are similar to of strength to weight. Other advantageous those used in masonry construction. The properties are good durability and, despite grouping together of timber posts into panels being combustible, relatively good perform- ensures that the load which each carries is ance in fire. relatively small. Even so, such buildings rarely Timber is commonly used for the horizontal consist of more than two storeys. Timber floor and roof elements in loadbearing loadbearing-wall structures are simple to masonry structures (Fig. 6.39). Loadbearing- construct, using components which are light in wall 'panel' construction, in which the struc- weight and easily worked. The use of timber in ture of a building is made entirely of timber, is skeleton-frame configurations for multi-storey another common configuration (Fig. 1.19). Wall structures is relatively rare and normally 16 panels consist of closely spaced timber posts requires that columns be closely spaced to  Structure and architecture Fig. 1.20 Forth Railway Bridge, Scotland, 1882-90, Henry Fowler and Benjamin Baker, engineers. Two types of structure are visible here. Short-span viaducts, consisting of parallel-chord triangulated girders, are used at each end where the ground conditions allow closely-spaced foundations to be provided. The two deep river channels separated by the island are spanned by an arrangement of three pairs of balanced cantilevers. The configuration of the bridge was determined by a combination of site conditions, structural requirements and function. [Photo: P. & A. Macdonald] keep beam spans short. Very large single- as consisting of two broad categories of activ- storey structures have, however, been ity: first, the invention of the overall form and constructed (see Section 6.2). general arrangement of the structure and, secondly, the detailed specification of the precise geometry and dimensions of all of the 1.5 Structural design individual components of the structure and of the junctions between them. As with any other type of design, the evolution In the case of an architectural structure both of the form of a structure is a creative act of these activities, but especially the first, are which involves the making of a whole network closely related to the broader set of decisions of interrelated decisions. It may be thought of connected with the design of the building. The 17 Structural Design for Architecture overall form of the structure must obviously be compatible with, if not identical to, that of the building which it supports. The preliminary stage of the structural design is therefore virtu- ally inseparable from that of the building, taken as a whole. It is at this stage that architectural and structural design are most closely related and that the architect and engineer, be they different persons or different facets of the same individual, must work most closely together. The second stage of the design of the structure, which is principally concerned with the sizing of the elements and the finalising of details, such as the configuration of the joints, is principally the concern of the structural engineer. The different aspects of the structural design activity are most easily seen in relation to purely engineering types of structure, such as bridges. It will be instructive here, before looking at the process as it takes place in the case of a building, to consider the design of a prominent example of this type. The Forth Railway Bridge in Scotland (Fig. 1.20), despite being now over 100 years old, provides a good illustration of the various stages in the evolu- tion of a structural design. The issues involved Fig. 1.21 Forth Railway Bridge, Scotland, 1882-90, Henry are broadly similar to those which occur in any Fowler and Benjamin Baker, engineers. The main part of engineering design project, including those of the structure consists of three pairs of balanced the present day. The same issues will be cantilevers. In this shot the central tower of one pair of considered again in Chapter 2, where they are cantilevers has been completed and the first elements of the cantilevers themselves have been added. The arrange- discussed in relation to architectural design. ment was adopted so that the uncompleted structure This preliminary review, in the context of could be self-supporting throughout the entire period of engineering, serves to identify the essential construction. [Photo: E. Carey; copyright: British Rail aspects of the structural design process. Board Record Office] As is normal in bridge design, the most significant sets of factors which influenced the design of the Forth Bridge were those connected with its function and with its edge of the water. At the other, the ground location. The ground level at each side of the rises steeply from the water's edge but a broad estuary of the River Forth, where the bridge is strip of shallow water occurs close to the shore. situated, slopes steeply up from the shore and Between these two flanking strips of relatively the railway therefore approaches from a level of level ground the estuary consists of two very approximately 50 m above water level at each deep channels separated by a rocky island. The end. This, together with the requirement that bridge was therefore broken down into three the busy shipping channels which the bridge parts and made to consist of two long approach crosses should not be blocked, dictated that viaducts, each with a sequence of girders the railtrack level should also be relatively high spanning relatively short distances between (50 m above sea level). At one shore a broad regularly spaced piers, and a massive central 18 strip of low lying ground occurs close to the structure spanning the two deep channels.  Structure and architecture (a) (b) (c) (d) (e) The structure which spans the central Fig. 1.22 Forth Railway Bridge, Scotland. 1882-90, channels consists of three sets of balanced Henry Fowler and Benjamin Baker, engineers. (a) A diagrammatic representation (not to scale) of the cantilevers - a configuration which was main elements of the bridge. The two river channels are adopted because it could be built without the crossed by three sets of balanced cantilevers. Viaducts need for temporary supporting structures. The consisting of short-span girders supported by closely arrangement was essential due to the near spaced piers provide the necessary link with the high impossibility of providing supporting struc- ground on the approaches to the bridge. tures in the deep channels and due to the (b) The bending moment diagram which results from the action of a uniformly distributed load across the entire need to maintain the shipping lanes free of structure gives an indication of the variation which occurs obstruction during the construction process.6 in the magnitudes of the internal forces across the span. The method of construction which was (c) The insertion of two extra hinges creates a cantilever- adopted was to build three towers first and and-suspended-span arrangement which alters the then extend pairs of cantilevers simultaneously bending moment diagram (d) and reduces the magnitude of the maximum bending moment. on each side of these (Fig. 1.21). The structure (e) The external profile which was finally adopted is closely was therefore self-supporting during the entire related to the bending moment diagram. The triangulation process of construction. of the internal geometry was necessary to achieve high The basic form of the structure is shown structural efficiency. diagrammatically in Fig. 1.22 together with the bending moment diagram7 which results from the peak load condition (a distributed load 6 The device of constructing the main elements of the 7 The bending moment is the internal force produced by bridge on the shore and floating these into the final the load on the structure in the type of arrangement position, which had been used earlier in the shown in Fig. 1.22. The bending moment diagram is a nineteenth century at Saltash (I. K. Brunei) and the graph which shows how the intensity of this internal Menai Straights (Robert Stephenson and William force varies across the span. For an explanation of Fairbairn) was impractical due to the very long spans bending moment see Macdonald, Structure and involved. Architecture, Chapter 2. 19 Structural Design for Architecture Fig. 1.23 Forth Railway Bridge, Scotland, 1882-90, Henry Fowler and Benjamin Baker, engineers. The railway track is carried on an internal viaduct which is supported at the junctions of the triangu- lated main structure. [Photo: A. Macdonald] across the entire span). This shows that the Figure 1.22c represents, in diagrammatic intensity of internal force is at its highest at form, the basic configuration which was finally the locations of the support towers and falls to adopted for the bridge. It was modified to give zero at the mid-span points, where the improved load-carrying efficiency by matching adjacent cantilevers are joined. The distribu- the longitudinal profile of the structure to the tion of internal force was modified by the pattern of internal forces so that the structural insertion of two hinge-type connections material was concentrated at the locations of between each set of cantilevers (Fig. 1.22c) highest internal force. It was further improved which had the effect of reducing the magnitude by the adoption of a triangulated internal of the maximum internal force at each support geometry. Yet another decision taken by the 20 tower. designers was to carry the railtrack on a  Structure and architecture viaduct (similar to the approach viaducts) size of each cross-section, thickness of metal, located within the primary structure and etc.). At this stage structural calculations were supported by it at regular intervals (Fig. 1.23). employed to determine the magnitudes of the The primary structure therefore provided internal forces which each element would carry regularly spaced supports for this internal and to check that sufficient thicknesses of viaduct rather in the manner of the equally metal were specified to maintain the stresses spaced piers which carry the approach within acceptable limits. The detailed viaducts. determination of the configuration of the joints Figure 1.22e shows diagrammatically the between the elements, which could only be final form of the bridge. It represents the done once the sizes of the elements were culmination of the first stage of the design known, was then carried out. process in which the form and general arrange- The description given above illustrates, in ment of the entire structure were determined. much abbreviated form, the typical sequence The sequence of decisions which led to this of decisions which is involved in the design of proposal illustrates, in a much abbreviated any major civil engineering structure and form,8 the key stages of the preliminary design allows the two key stages in this - the initial process and allows the nature of the process determination of form and the final realisa- which concerns us here to be appreciated. In tion of the form - to be appreciated. A particular, it shows that the basic form of this sequence of decision-making which is broadly purely engineering structure was determined similar to this is involved in the design of all by the designers from a consideration of the structures whether civil engineering or archi- function of the bridge, from the constraints of tectural. the site, from a knowledge of structural behav- In the case of an architectural structure, the iour and from an awareness of the vocabulary form and general arrangement must also be of structural possibilities which was available entirely compatible with that of the building to them. The design was an imaginative which it will support. The preliminary stage in response to these various influences. the design of an architectural structure is The second stage in the design process, the therefore inseparable from the design process realisation of the structure, led to the detailed of the building as a whole. Once the overall specification of the various structural elements form of a building has been determined, the from which the bridge was constructed. This choice of structural arrangement will normally involved decisions on the precise shape of the be fairly narrow. The act of architectural design individual elements (in longitudinal profile and is therefore also an act of structural design in cross-section) and on the precise amount of which the most fundamental decisions relating material which would be specified (the overall to the structure are taken. 8 Several alternative arrangements were in fact consid- ered by the designers before the chosen form was adopted. 21  Chapter 2 Structural design for architecture 2.1 Introduction The purely technical aspects of the design of a structure were reviewed at the end of the previ- ous chapter. The complex relationship between structural design and architectural design will now be considered. As was seen in Section 1.5 the process of structural design may be subdivided into two parts: there is a preliminary design stage, when the form and general arrangement of the struc- ture are devised, and a second stage in which structural calculations are performed and the dimensions of the various structural elements are determined. In the case of an architectural structure many of the decisions associated with the preliminary stage of the design of a structure are taken, consciously or uncon- Fig. 2.1 Rooftop Remodelling in Vienna, Austria, 1988. Coop Himmelblau, architects. This glazed, irregular form sciously, when the form of the building is required that a skeleton framework structure be adopted. determined. The general arrangement chosen [Photo: Gerald Zugmann] for a building will normally determine the type of structure which will have to be adopted to support it and will probably also dictate the The complex arrangements of the Rooftop selection of structural material. Office in Vienna by the Coop Himmelblau In the case of the Willis, Faber and Dumas group, to take another example (Fig. 2.1), building (Fig. 4.17), for example, where there would have been unrealisable with any other was a requirement for a large wall-free interior type of structure than a skeleton framework, and glass external walls, there was no alterna- which had to be of steel to ensure that the tive to the adoption of a frame-type structure. elements were sufficiently slender. The Hysolar The requirements for a curvilinear plan-form building of Behnisch (Fig. 2.2) is a similar type and for columns which were set back from the of building and could only have been realised perimeter, dictated that reinforced concrete with a skeleton framework of structural steel. rather than steel be employed as the structural The buildings of Richard Meier (Fig. 4.18) and material. The outcome in this case was a build- Frank Gehry (Fig. 4.20), on the other hand, ing in which architectural and structural required that reinforced concrete structures be requirements were satisfied in equal measure adopted. and the building stands up well to both archi- Thus, although some aspects of the design 22 tectural and technical criticism. of structures, such as the precise geometry of a  Structural design for achitecture Fig. 2.2 Solar Research Institute (Hysolar), Stuttgart, Germany, 1988-89. Gunther Behnisch & Partner, architects. The irregular geometry and large areas of glazing required that a skeleton framework structure be adopted to support this building. The choice of steel produced a particular aesthetic quality - the most notable aspects of this are the slenderness of the structural elements and the refined appearance of the exposed steelwork. [Photo: E. &F. McLachlan] beam or column grid or the dimensions of the void within it, therefore exerts a dominating elements, may remain undecided until a later influence on its subsequent structural make- stage in the design, many important structural up. The architect is thus, consciously or uncon- choices will be closed once the overall form of sciously, a structural designer. a building has been determined. The initial The design of the structure which will concept for a building, which determines its support a building is an identifiable and overall form and the disposition of solid and discrete part of the overall design process in 23 Structural Design for Architecture which four broad categories of decision-making It is quite possible to project whole forms may be identified. These are: first, the decision in the mind without any recourse to on the kind of relationship which will exist material,...' between the architectural design and the struc- More recently, Wolf Prix of Coop tural design; secondly, the selection of the Himmelblau expressed the view that: generic type of structure for the building; thirdly, the selection of the structural material;... we want to keep the design moment free and lastly, the determination of the detailed from all material constraints...2 form and layout of the structure. In a particular case these sets of decisions may not be taken It is possible to say therefore that at least in an ordered sequence and some - for some European architects have, since the example on the relationship which is to be Renaissance, considered it feasible to ignore adopted between structural and architectural structural considerations when they invent the design - may not even be taken consciously. form of a building, believing that a preoccupa- They are nevertheless decisions which are tion with technical matters inhibits the process taken by the designer of every building. of creative design. The second of the quota- tions above is a fairly explicit comment from a In the design of the majority of buildings, in contemporary architect whose work many which the relationship between architectural would regard as controversial but it neverthe- design and structural design is not one of less describes the reality of a very significant 'structure ignored' (see Section 2.2 for an proportion of present-day architectural design explanation of this term), the preliminary activity, including much of what might be structural decisions are taken consciously, thought of as belonging to the mainstream usually by a team of designers which includes rather than the fringe. Many architects, in fact, architects and structural engineers. The nature pay little attention to structural issues when of the decision-making sequence is explored in determining the form of a building. Few, this chapter. however, find it appropriate to make state- ments such as that quoted above. Just as it is possible virtually to ignore struc- 2.2 The relationship between tural issues when carrying out the preliminary structural design and architectural design of a building, it is also possible to design allocate the highest priority to the satisfaction of structural requirements. In such cases the 2.2.1 Introduction aesthetic and programmatic aspects of the The detailed design of a structure is normally design are accorded a lower priority than those carried out by a structural engineer (more connected with the structure and are not probably a team of engineers) but, as was allowed to compromise the quality of the noted above, the overall form of an architec- structural design. This approach can occur tural structure is determined by that of the through necessity, when the limits of what is building which it supports and therefore princi- feasible structurally are approached due, for pally by the architect (or architectural team). example, to the extreme height of a building or This raises the issue of the extent to which the architect should be preoccupied by structural considerations when determining the form and general arrangement of a building. There are several possible approaches to 1 L. B. Alberti, On the Art of Building in Ten Books, 1486, this. Leon Baptista Alberti, who in his treatise Trans. Rykwert, Leach and Tavernor, London, 1988. on architecture written in the fifteenth century 2 Quotation from 'On the Edge', the contribution of Wolf Prix of Coop Himmelblau to Architecture in Transition: more-or-less outlined the job description of Between Reconstruction and New Modernism, N o e v e r (ed.), 24 the modern architectural profession, stated: 1991.  Structural design for achitecture to the need for a very long span (e.g. Fig. 3.10). 2.2.2 Structure ignored It can also occur through choice. It is possible, principally due to the existence Some architects hold the view that one of of structural materials such as steel and the marks of a well-designed building is that reinforced concrete, to invent architectural all potential conflicts between the architectural form without considering the structural impli- programme and its structural consequences cations of that form. The wide variety of forms have been resolved without either aspect into which steel is fashioned in the manufac- dominating the other. This represents yet ture of motor cars, ships, marine oil produc- another relationship between structure and tion platforms and consumer durables, for architecture and it is one with which most example (Fig. 2.3), all of which have shapes mainstream architects would openly, if which are determined principally from criteria perhaps somewhat hypocritically, concur. In other than those connected with structure, this scenario well-designed structure is illustrate the almost limitless possibilities regarded as a necessary precondition for good which are present in the matter of form when architecture. Such an approach requires that the structural make-up of a building be evolved in conjunction with all other aspects of its design and that structural issues be considered from an early stage in the design process and allowed to play as significant a part in the determination of the final form of a building as the aesthetic and space-planning programmes. In this approach the objective of design is to determine the form in which all requirements are satisfied equally. It is possible therefore for structure and architecture to be related in several different ways and one of the first decisions which has to be taken by a design team which has a full awareness of the activity in which it is engaged, is concerned with the nature of this relationship. Often the issue is allowed to remain unclear and some architects even deny that there can be more than one proper relationship between structure and architec- ture. It has been suggested however3 that the relationship can take a number of different forms and that the totality of possible relation- ships between structure and architecture may be summarised in the four categories of struc- ture ignored, structure accepted, structure symbolised and structural 'high tech'. The implications of these categories of relationship are now reviewed. Fig. 2.3 Steel can be fabricated into almost any shape as the structures which are built for the marine environment demonstrate. The construction of a ship requires techniques of fabrication which are significantly more complex and expensive than those which are normally used in the construction of buildings. There is, neverthe- less, no technical reason why such shapes should not be 3 See Macdonald, Structure and Architecture, Chapter 7. employed in architecture. [Photo: P. Macdonald] 25 Structural Design for Architecture Fig. 2.4 Sailing Yacht 'Gipsy Moth IV. In the construction of ships and yachts timber has been used to produce a wide variety of complex shapes. The material itself places little restriction on form but the production of geometries like that illus- trated is highly labour intensive and therefore expensive. [Photo: The Maritime Trust] the objects concerned are made from steel. A of steel and reinforced concrete, together with similar statement could be made of reinforced the fact that very effective structural joints can concrete but in this case the exemplars would be made between components of these mater- perhaps be grain silos or water towers. Timber ials, are additional factors which make possi- too is capable of being used in a very wide ble the creation of practically any form. range of shapes although, because timber is It may seem surprising therefore that, in the less strong than steel or reinforced concrete, period since these materials became widely these are of a smaller scale. Again, ships and available to the builder in the late nineteenth yachts serve as examples of the level of century, architects have availed themselves so complexity of form which is possible (Fig. 2.4). little of the potential for the free invention of In all of these examples a criterion other than form which they made possible. Instead, archi- structure, such as hydrodynamic performance tects have, for the most part, generally contin- or adherence to fashion, was the dominating ued to produce buildings with plane vertical influence on the form which was chosen. walls and horizontal or pitched roofs which are The structural factor which is common to the not significantly different in overall shape from three materials considered above (steel, the traditional architectural forms which were reinforced concrete and timber) and which evolved from the much more restrictive struc- allows them to be shaped into almost any tural technology of masonry. There have been form, is that they can all resist tension, several reasons for this, most of which were compression and bending.4 The high strength not technical. Perhaps the most significant reason for the apparent lack of basic (as opposed to superfi- cial) complexity in the architectural forms of They can therefore be used to make any type of struc- the twentieth century has been cultural. In the tural element: form-active, semi-form-active or non- period in which the freedom to experiment form-active. The same cannot be said of masonry, with form has been available it has not gener- which has very limited tensile strength and therefore ally been fashionable for buildings to be given also limited bending strength. As is shown in Chapter 5, the need to prevent significant tensile stress from irregular or curvilinear forms. For ideological developing imposes constraints on the structural forms reasons, modernity preferred to accept the 26 of masonry. vocabulary of orthogonality, which symbolised  Structural design for achitecture Fig. 2.5 East Pavilion, Groninger Museum, Groningen, Netherlands, 1990-94, Coop Himmelblau, architects. Parts of this build- ing were manufactured in a shipyard using shipbuilding techniques. It is a relatively rare example in architecture of the employment of a large-scale industrial process to create a complex form. [Photo: R. Talbot] rationality-, of regularity and repetition, which One of the reasons for the continuation, into symbolised the production line; and of straight the twentieth century, of the relatively simple lines and sharp edges, which symbolised structural geometries of architectural tradition manufacture by machine rather than by hand was the elementary one of convenience. crafting (e.g. Figs 1.2 and 4.6). Thus, at the very Arrangements of rectangular rooms with time when developments in structural horizontal floors and ceilings are more engineering could have released architects suitable, for most human purposes, than from the tyranny of the straight line and the enclosures made from curvilinear surfaces or right angle they voluntarily restricted wall and roof planes which intersect at acute or themselves to the use of little else. In recent oblique angles. There was no technical reason, years the mood has changed, however, and however, why buildings with complex forms, architects of the late modern Deconstruction with non-vertical walls, inclined roof planes school, in particular, are now availing and curvilinear enclosures could not have been themselves of the freedom which their prede- constructed once materials such as steel and cessors failed to exploit. reinforced concrete became available to the This may be seen in buildings such as designers of buildings in the late nineteenth those illustrated in Figs 2.1, 2.2 and 4.20. It is century. interesting to note that in the East Pavilion of Yet another factor, which is not strictly the Groninger Museum (Fig. 2.5), major technical but which may have inhibited the use elements of the steelwork were manufactured of irregular forms, is obviously that of cost. in a local shipyard using shipbuilding Complicated forms are difficult and therefore techniques. This allowed the use of shapes expensive to construct. This is why artefacts and configurations which, in the context of such as motor cars or aeroplanes are relatively building, were exciting and new. It is a matter more expensive than buildings, despite the of conjecture whether this can be taken economies of mass production which are seriously as a method by which buildings associated with their manufacture. The cost should be constructed but it does show that per tonne of steel used in a motor car is an architects are finally making use of the full order of magnitude greater than that of a struc- potential of the materials which industry has tural steel framework for a building. The same placed at their disposal. is true of timber used for yacht construction 27 Structural Design for Architecture compared to structural timber in buildings and forces are so high that, even with strong of the aluminium alloys used in aircraft materials such as steel or reinforced concrete, construction. The high