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ARCPRESS AJ handbook of building structure - Part 3 - Structural safety 4 of 12 | Strength Of Materials | Beam (Structure)
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AJ Handbook of Building Structure
The Architectural Press, London
AJ Handbook of Building Structure Introduction
Scope There are two underlying themes in this new handbook on building structure. First, the architect and engineer have complementary roles which cannot bo separated. A main object of this handbook is to allow the architect to talk intelligently to his engineer, to appreciate his skills and to understand the reasons for his decisions. Second, the building must always be seen as a whole, where the successful conclusion is the result of optimised decisions. A balance of planning, structure or services, decisions may not necessarily provide the cheapest or best solution from any of these separate standpoints, but the whole building should provide the right solution within both the client's brief and his budget. The handbook provides a review of the whole structural field. It includes sections on movement in buildings, fire protection, and structural legislation, where philosophy of design is discusssed from the firm base of practical experience. Foundations and specific structural materials are also covered, while sufficient guidance on analysis and design is given for the architect to deal with simple structures himself. Arrangement The handbook deals with its subject in two broad parts. The first deals with building structure generally, the second with the main structural materials individually. The history of the structural designer and a general survey of his field today is followed by a section on basic structural analysis. The general part of the handbook concludes with sections on structural safetyincluding deformation, fire and legislationand on the sub-structure: foundations and retaining structures. Having discussed the overall structure, the sections in the second part of the handbook discuss concrete, steelwork, timber and masonry in much greater detail. Finally there are sections on composite structures and on new and innovatory forms of structure. Presentation Information is presented in three kinds of format: technical studies, information sheets and a design guide. The technical studies are intended to give background understanding. They summarise general principles and include information that is too general for direct application. Information sheets are intended to give specific data that can be applied directly by the designer. Keywords are used for identifying and numbering technical studies and information sheets: thus, technical study STRUCTURE 1, information sheet FOUNDATIONS 3, and so on. The design guide is intended to remind designers of the proper sequence in which decisions required in the design process should be taken. It contains concise advice and references to detailed information at each stage. This might seem the normal starting point, but the guide is published at the end of the handbook as it can be employed only when the designer fully understands what has been discussed earlier. The general pattern of use, then, is first to read the relevant technical studies, to understand the design aims, the problems involved and the range of available solutions. The information sheets then may be used as a design aid, a source of data and design information. The design guide, acting also as a check list, ensures that decisions are taken in the Tight sequence and that nothing is loft out.
Allan Hodgkinson Consultant editor and authors The consultant editor for the Handbook is Allan Hodgkinson MEng, FICE, FIStructE, MConSE, Principal of Allan Hodgkinson & Associates, consulting civil and structural engineers. Allan Hodgkinson has been the AJ consultant for structural design since 1951; he is a frequent AJ contributor and is the author of various sections of this handbook. The authors of each section will be credited at the start of the section of the Handbook in which their material appears. The original Architects' Journal articles were edited by Esmond Reid, BArch, and John McKean, BArch, MA, ARIBA, ACIA, ARIAS. The frontispiece illustration shows one, of the most magnificent building structures from the era of the Eiffel Tower, the Forth Bridge and the great railway stations. The Palais des Machines for the Paris Exhibition of 1889 (Contamin, Pierron & Charton, engineers) was a pioneer example of three hinged arches. Preface to the second edition There have been considerable changes in some British Standards, Codes of Practice, and Building Regulations since 1974; and unlike the reprints of 1976 and 1977, this is a substantially revised and updated re-issue of the now well-established AJ Handbook of Building Structure. The principal changes are in the sections on Masonry (rewritten to take account of the 1976 Building Regulations, and the new BS 5628 'limit state' code of practice); and on Timber (substantially revised to take account of the new timber gradings). Steel handbooks have been replaced for all types of structural sections; and technical study Steel 3 has therefore been revised accordingly. In general, the new 'limit state' approach to design is discussed (eg in the section on Masonry); but in view of the rejection of the limit state Codes and draft Codes in their present form, by the majority of practical designers, it has been thought prudent to retain the allowable stress methods of design as the basis of the handbook. Finally, it should be mentioned that the opportunity has been taken to bring all references in this Handbook up to date; and to correct a number of misprints of the first edition. ISBN 0 85139 273 3 (paperbound) First published in book form in 1974 by The Architectural Press Limited: London Reprinted 1976, 1977 Second edition 1980, 1982, 1983 Printed in Great Britain by Mackays of Chatham Ltd
Three aspects of structural safety are brought together in this section of the handbook. Building legislation and attitudes towards the analysis of building safety are discussed in the first technical study. The second study considers the movement of a structure either under changing environment or loading. Without discussing details of jointing techniques and sealants, it examines possible sources of movement which must be considered in any structural design. The third topic is fire protection of structures. This problem is discussed generally and by looking at each structural material separately. The study is supplemented by four information sheets which provide tables of deemed to satisfy situations for structural members in concrete, steal, timber and masonry. Much of this information has never been published before and, as far as the AJ can tell, gives the most up to date information available. The tables on concrete protection have been provided by the Code Servicing Panel of the Institution of Structural Engineers. These tables have since been published in CP 110 (the Unified Code of Practice for concrete). The AJ is grateful to officers of TRADA for general advice and the table on stud partitions, and to H. L. Malhotra of the Fire Research Station (BRE) for general advice and the tables on masonry. It is understood that these masonry tables will also become the basis of a Code of Practice.
Allan Hodgkinson, consultant editor to the handbook, has written the studies in this section. The help of the Institute of Structural Engineers, TRADA and the Fire Research Station in the preparation of the fire protection tables is acknowledged above.
The illustration on page 71 is can engraving of the 1666 fire of London from Thorntons History of London and Westminster (1743)
Building legislation and structural safety
The aim of ALLAN HODGKINSON'S technical study is to provoke thought on the approach to design safety. He also examines both the traditional and the recent CIRIA 'limit state' approaches, comparing them in a worked example
1.01 Legislation with regard to structure resides directly in Building Regulations and also indirectly in the Codes of Practice in that the latter are named as a deemed to satisfy condition of the regulations. Outside London, regulations are administered by local authorities of the UK, and evidence of compliance must be submitted to the local authoritys engineer in the form of calculations and working drawings. The engineer may check these in his own office or employ the services of a consulting engineer. Calculations must be clear, concise, indexed, related to drawings and referenced to bibliography where special formulae have been taken from textbooks; otherwise considerable waste of time and manpower will occur all round. The local authority building inspector examines the quality of work during construction. 1.02 The London Building Act is administered by the district surveyors, who are each responsible for a particular area of inner London (old LCC area). They check the calculations and drawings and inspect the work on site. The Constructional Bylaws (1972) were published in a new format early 1973 and rely largely on the Codes of Practice, as do the Building Regulations. While the comments below may refer particularly to the Building Regulations, they are also a reasonable statement, of the present state of legislation for London and Scotland.
2 Structural regulations
2.01 The Building Regulations up to April 1970 were comparatively simple, as the fundamental requirements were contained in two clauses D3 and D8.
D3 The foundations of a building shall a safely sustain and transmit to the ground the combined dead load and imposed load in such a manner as not to cause any settlement or other movement which would impair the stability of, or cause damage to, the whole or any part of the building or of any adjoining building or works; and b be taken down to such a depth, or to be so constructed, as to safeguard the building against damage by swelling. shrinking orfreezing ofthe subsoil; and c be capable of adequately resisting any attack by sulphates or any other deleterious matter present in the subsoil. D8 The structure of a building above the foundations shall safely sustain and transmit to the foundations the combined dead load and imposed load without such deflection or deformation as will impair the stability of, or cause damage to, the whole or any part of the building.
expounded in a new Regulation, D19 (incorporated within the Building Regulations 1972) which has been bitterly attacked by both individuals and representative engineering opinion. 2.03 This Regulation requires that in a building of five or more storeys, it should be possible to remove any one particular member from the structure with only restricted consequent collapse. Alternatively the member must be capable of supporting a load of 5 psi (34.5 kN/m2) from any direction (including load transmitted to that member from adjacent elements of structure similarly loaded) in addition to its normal loading, but at enhanced allowable stresses. 2.04 The intention is to avoid progressive collapse of the building, although the damage so sustained may mean rebuilding at a later date. Although the new Regulation arises from an explosion in a special use of structure in industrialised building with large concrete panels, the Regulation must be applied to all forms of structure indiscriminately. Continued efforts by the engineering institutions have secured some relaxation of the requirements in the case of structural steelwork and reinforced concrete frames, and testing work by the British Ceramic Research Association has shown that 178 mm and 229 mm brick internal walls can satisfy the requirements provided a specific vertical load is applied to the walls. 2.05 However, it should be appreciated that there is not the slightest guarantee that the added requirement of D19 produces a structure which would contain a gas explosion, only a structure with a variety of alternative paths of support could hope to have such resistance. It should also be appreciated that a block of dwellings of four storeys could collapse progressively along its length, causing equivalent damage to that of a five-storey structure collapsing progressively vertically.
3 Codes of practice
3.01 The Regulations avoid any direct rules for application to structures of aluminium, steel, reinforced concrete, prestressed concrete, timber and masonry but state that D8 shall be deemed to be satisfied if there is compliance with the Code of Practice or British Standard appropriate to the material. At first sight this appears to be a logical approach. The codes are technical documents containing guidelines and parameters for design. They provide norms on which the structural design can be assessed, and without which the agreement to calculations by an appraising authority might prove impossible. 3.02 However, the procedure does have two unfortunate aspects. First, Codes of Practice are intended to be a general recommendation of good practice and to be implemented by a qualified engineer. The slavish following of rules is not
2.02 In April 1970 an amendment (5th Amendment) was issued as a precaution against the collapse of buildings due to accidental damage. This arose directly from the collapse of part of an industrialised building and loss of life as the result of a town gas explosion. The incident received such adverse national publicity that logic was replaced by emotion in the ensuing considerations. The action taken was
Technical study Safety 1 para 3.02 to 5.06
74 tions of the above-mentioned items. Thus, over the last 20 years there has evolved first the concept of load factors, and more recently the statistical assessment of characteristic stresses and characteristic loads. 5.02 A CIRIA report2 represents seven years of thinking about the problem, with the object of suggesting an optimum balance between level of safety and overall economy of structural design. Its authors consider that their recommendations can be incorporated in the various Codes of Practice in the next five to 10 years. The new Unified Code of Practice for Concrete, BS CP 110, is the first to appear of the new series. 5.03 The attitude and method recommended by the CIRIA report is nowhere better summarised than in the reports appendix quoted below:
Limit state of collapse The limit load factor to be adopted in design is to be evaluated in terms of three partial factors as follows: y1 = to cover unusual and unforeseen deviations of loading from the characteristicloads, and unusual combinations of such loads y2 = to cover unusual and unforeseen deviations of strength from thecharacteristic strengths of the structure as built y3 = to cover the seriousness of the effects of collapse whether general or partial, sudden or gradual, including danger to personnel and associated economiclosses. Of these partial factors, yl. the load variability factor, should for established forms of construction be chosen in the range from 1.2 to 1.8; y2, the strength variability factor, in the range 1.1 to 1.6; and y3, the economic factor, in the range 0.9 to 1.4. Having chosen values for these partial factors, the load factor for collapse to be used in design is given by the product Y1 x Y2 x Y3. Limit state for local damage The limit load factor to be adopted in design is to be evaluated in terms of two partialfactors,asfollows: y4 = to cover the nature of the loads in service, whether static or dynamic and of rare or frequent occurrence y2 = to cover the nature and extent of the damage likely to arise in service. Ofthese partial factors, which areto be applied to characteristic loads,y4should, for established forms of construction, be chosen in the range 1.0 to 1.2, and y5 in the range of 1.0 to 1.4. Having chosen values for these partial factors. the load factor for local damage to be used in design is given by the product y4 x y5. Limit state of excessive deflection The limit load factor to be adopted in design is to be evaluated in terms of two partial factors, as follows: y6 = to cover the nature of the loads in service, their duration and fluctuation during the life of the structure y7 = to cover the nature and extent of the deflections likely to arise in service. Ofthese partialfactors, which areto be applied to characteristic loads, y4 should, for established forms of construction, be chosen in the range 0.2 to 1.0. and y7 from 1.0 to 1.2. Having chosen values for these partial factors, the load factor for excessive deflection to be used in design is given by the product y6 x y7.
in itself an assurance of a satisfactory whole structure. Secondly, in competitive design there is a tendency just to satisfy the code by using its letter rather than its intent, as there is then the opportunity of sheltering behind its apparent statutory respectability when liability is demanded for failure.
4.01 Generally, safety has been referred to already under the heading of legislation, but how safe is safe? How is safety measured, and is the engineers definition of safety the same as that of the public who use their structures? The Ronan Point aftermath in 1968 gave the impression that the public considers safe to mean impregnable and it was clearly not understood that total safety from all damage incidence cannot be achieved whatever the cost, though with increasing cost an increasing measure of safety can be provided. 4.02 Until recently, the method of ensuring a measure of safe construction in a particular material was to define safe working stresses in the appropriate Code of Practice or British Standard and then proportion each element of the structure so that the safe working stresses were not exceeded. The relationship of Yield Stress or its equivalent to the safe working stress was the- factor of safety. 4.03 In terms of the few failures which occurred in practice, it may be said that this method achieved a considerable record of success, despite constant narrowing of the safety factor as detailed knowledge and testing and control of the materials improved. Nevertheless, the method was not logical, for it treated all structure types as equal, all conditions of loading and quality of construction as equal, and all consequential failure effects as equal. 4.04 A committee of the Institution of Structural Engineers was set up in the mid-1950s to consider safety in structures. Out of the work of this committee has grown the modern statistical approach to all aspects of structural design introduced into a code of practice for the first time in November 1972. 4.05 When considering safety the following aspects require examination: 1 Loading-how accurate is the determination of loading used in analysis, what is risk of overload? 2 Materials-what is the risk that materials of construction do not comply with specification? 3 Design skill-what is the risk of a failure of the design in its basic conception or mistakes in calculation? (This is partly covered by the checking procedure referred to earlier) 4 Inadequate fabrication or construction-what is the risk of a weld in a steel structure being understrength, or the risk of concrete as mixed being understrength and inadequately compacted or reinforcing steel being fixed wrongly? (this is partly covered by the inspection process) 5 Seriousness of failure-what is the risk to life, to continued use of an industrial process, and further consequences of a failure? 6 What is failure? Failure can be collapse, excessive deflection or excessive cracking, all of which in appropriate circumstances can mean extensive repair or rebuilding of the structure.
5.04 In limit states, the actual loads in service are to be represented by systems of characteristic loads' relating to the particular limit states. The loads will eventually be specified in the codes with the aim of approximating to the most severe conditions to be expected in service during the life of the structure concerned. Eventually they will be determined statistically from experience, but initially loads will be based on those currently quoted in BS CP3 chapter v3 or on greater loads known to the designer. 5.06 Strengths of materials used in the structure are to be represented by characteristic strengths specified in the codes. These will be based on tests and specified with the aim of approximating to the smallest strength* that is likely to be incorporated in the structure. 5.06 The proposed CIRIA partial factors for steelwork and reinforced concrete building structures are shown in table I.
5 The CIRIA approach
5.01 Obviously the old concept of the safety factor of working stress related to yield stress cannot give either logical or factual discrimination between various combina-
*strength with not more than 5 per cent probability, ie the strength below which not more than 5 per cent of the test results would fail.
Technical study Safety 1 para 6.01 to 6.06
Proposed CIRIA partial factors for reinforced concrete and steelwork compared
Limit state Collapse 1.25 permanent 1.5 imposed 1.25 wind 1.4 t o 1.7 concret e 1.15 steel 0 . 9 - 1 - 1* 1.0 all loads 1.3 concrete 1.0 steel 1.0 all permanent loads 0.8 short-term imposed and wind together 1.0 short-term imposed and wind separately 0.25 t o 1 . 0 long-term loads 1.0 concrete 1.0 steel 1.2 permanent 1.5 imposed 1.25 wind 1.1 continuous frames 1.2 structural elements and non-continuous frames 0.9* collapse by plastic bending 1.1 to 1.2* collapse by buckling or fracture 1.0 all loads
7 Steelwork 1-
d2 3 4
1.0 all permanent loads 0.8 short-term imposed and wind together 1.0 short-term imposed and wind separately 0.25 to 1.0 long-term loads
*Factor 8, depends on probable nature of failure, and frequency or duration of occupation by people and valuable commodities Depending on the use of the structure and the likelihood of the characteristic loads acting for long periods
6 The two methods
6.01 Summarising the two approaches to design safety, in the traditional method the unfactored loads are applied to the chosen structure and an analysis determines certain stresses which can be compared with the 'allowable stresses' as set out in the Codes of Practice. The measure of safety is the relationship of the 'allowable stress' to the 'yield stress' or equivalent yield stress of the material in question. 6.02 In the new method, factored characteristic loads are applied in an analysis (which may use either plastic or elastic theories) and the strengths of the chosen structural members are compared with the 'characteristic strengths' attributed to the material in question. The applied factors are then the measure of safety. 6.03 Plastic analysis is perhaps best known to architects at present for calculation of steel frames, and the following examples will illustrate the way in which a simple portal frame can be designed by both methods for safety against collapse. 6.04 A 15 m span warehouse portal is to be designed with a spread load 8 8 kN/m run of portal beam of which 4 4 kN/m is live load 1. Ignore wind and deflection for this example and assume that a similar steel section will be employed for both beam and stanchion. The calculation of this portal by elastic analysis (BS 449) and plastic analysis (CIRIA recommendation) are compared on the next page.
1 Portal frame example 6.05 The difference between elastic design (with the allowable working stress approach) and plastic design (in the limit state of collapse) will be carried a stage further in section 6 of the handbook: STEEL. In the problem described, it is shown that the latter method results in a reduced section member representing an economy but giving a greater deflection. Had the portal beam been of reinforced concrete, it would also have been necessary to check for the size of cracks in tension areas if there was the possibility of deterioration of the reinforcing steel. Hence the three checks for collapse, deflection and local damage. 6.06 This leads to a critical assessment of the CIRIA recommendations in practice. Assuming that sufficient evidence is eventually obtained to make the 'characteristic' values meaningful, can the whole process be handled in the design office? The Code CP 110 has certainly brought considerable doubt on this point from practising engineers and time alone will tell whether it will be workable. In any case, it is presumed that Codes CP 111, 112, 114 and 115 will be preserved in their existing form for several years.
Technical study Safety 1 para 7.01
Portalframe calculation: comparison of traditional and CIRIA recommended methods Elastic analysis: BS 449 Dead load 4. 4 kN/m Live load 4.4 kN/m Total 8.8 kN/m Portal span 1b = 15 m, moment of inertia = Ib Stanchion height 1s = 6 m, moment of inertia = Is It can be proved that the bending moment at the knee Plastic analysis: CIRIA recommendation Actual dead load 4.4 kN/m
Factored dead load = 1.2 x 1.1 x 0.9 x 4.4 = 5.21 kN/m
Factored live load = 1.5 x 1.1 x 0.9 x 4.4 = 6.51 kN/m
*Frame braced againstbuckling
= 328.0 kNm Hinges will form at collapse thus:
Bending moment diagram is therefore:
Therefore the bending moment at centre and knee will be 328= 164 kN/m 2 Bending moment diagram is therefore :
The allowable working stress = 165 N/mm2 from M = fz (see technical study ANALYSIS 1, AJ 25.4.71 for explanation of symbols) 130000 x 1000 Elastic z = = 789 000 mm3 or 789 cm3 165 Section from Handbook is 406 x 178 by 54 kg/m (z=922.8) The stanchion would have to be checked for the combination of the direct load and bending moment yield stress Notional safety factor = working stress 250 = 1.52 165
Characteristic stress (yield stress) = 250 N/mm2. From Mp = fzp 164 000 x 1000 Plastic Zp = = 656 000 mm3 or 656 cm3 250 Section from Handbook is 356 x 171 by 45 kg/m (Zp=771.7) Reduced plastic modulus for stanchion section (direct load with bending moment) = 7 13.0 Both OK NB the reduced section of the steel members will lead in this case to a larger deflection than the 'elastic design' portal Notional safety factor (from load factors) on dead load 1.2 x 1.1 x 0.9 = 1.19 on live load 1.5 x 1.1 x 0.9 = 1.48
7.01 In the event of failure attributable to design error, a client may sue the designer responsible to him for negligence. If the architect is tho only person under contract to the client, clearly he will be sued; this liability can only be transferred to the engineer when he too is appointed directly by the client. The architect can, of course, in turn sue for
negligence an engineer working to his direction who is not employed by the client. The surest way of minimising failure is for one person to be in charge of the structural design and at all times to appraise the superstructure and foundation as a whole. The practice of having elements of the building designed by various people (who may well be specialists in their own field) leaves the process open both to failures in communication between the parties and failure
77 in the overall achievement of the project conception. 7.02 If an architect considers a project beyond his own structural design capabilities he should appoint a structural engineer or preferably ask the client to make such an appointment. A chartered engineer in the modern contractors organisation can be as efficient as, and of equal integrity to, his counterpart in the office of the consulting engineer, but his employer, the contractor, may have a commercial axe to grind in the conception of a project. Equally it should be realised that the unlimited liability of a professional consultant is of no greater value than the substance of the consulting engineer: his personal wealth and professional indemnity insurance.
Technical study Safety 1 para 7.01 to 8.03
3 The Building Standards (Scotland) (Consolidation) Regulations 1971 SI 2052 (S218) HMSO 1.30; The Building Standards (Scotland) Amendment Regulations 1975 SI 404 (S51) 0.29p; The Building Standards (Scotland) Amendment Regulations 1973 SI 794 (S65) 0.21p [(A3j)] 4 Construction Industry Research and Information Association Report R30 CIRIA study committee on structural safety, London 1971 [(21) (K) (E2g)] o/p 5 BS CP 110: Parts 1-3 1972 The structural use of concrete 6 BS CP 111: Part 2 1970 Structural recommendations for load bearing walls 7 BS CP 112: Part 2 1971 The structural use of timber 8 BS CP 114: Part 2 1969 Structural use of reinforced concrete in buildings 9 BS CP 115: Part 2 1969 Structural use of prestressed concrete in buildings
8.01 As design processes tend to produce structures with minimum mass members and errors of fabrication become of greater potential hazard, supervision at all stages of construction should be an essential contribution to building with an adequate reserve of strength. Neither architect nor engineer can relieve the contractor of his responsibility to supervise the work under construction, although by a system of routine testing and inspection, they can cause a general level of quality to be established. The achievement of this level requires great determination on the part of the supervisor and the clients full support. 8.02 It is of no profit to the client to demand compliance with the programme and a high quality of workmanship if he has already accepted a price for the job which will not yield an adequate return to the contractor. Equally the client should be prepared to pay for the level of supervision required and not expect the architect to supplement the contractors staff free of charge. It is unfortunate that the various RIBA and ACE (Association of Consulting Engineers) agreements are not as clear as they might be on this matter. The future 8.03 Relationships between architect, engineer and contractor are changing as both design and fabrication of buildings become more involved. Unless the training of architects can keep pace with the refinements of analysis and the understanding of structural legislation there will be very little structure with which the architect can work without the services of a chartered engineer. This is a regrettable state of affairs as there are many simple structures where no Building Control Authority should even ask for calculations and many more where the simplest of codes of practice should give an adequate guide to a properly trained architect. In the search for more design refinement and in the application of more theory and laboratory testing, Code Committees have lost sight of the bread and butter structures of the building industry and have instead created a method of computation in the limit state codes which produces almost the same end result with at least twenty percent more effort. CP 110 has had several years of practical testing in design offices and has been found sadly wanting. It is to be hoped that a lesson has been learned and much simpler limit state guidance will be provided in future codes of practice. Bibliography 1 The Building Regulations 1976 SI 1676. HMSO 3.30; The Building (First Amendment) Regulations 1978 SI 723. HMSO 0.60p 2 The London Building (Constructional) Bylaws 1972 GLC [ (Ajn)]
Technical study Safety 2 para 1.01 to 3.02
Technical study Safety 2
Section 3 Structural safety
Movement in building
Possible sources of movement must be considered in any structural design. Movement of structure under changing environment and applied loading is discussed by ALLAN HODGKINSON in terms which do not obscure principles with details such as specific jointing techniques
1.01 The subject of this study, movement of structure under changing environment and under applied loading, is one which does usually receive appropriate consideration in large engineering structures. Buildings, however, have both the added complications of applied finishes, attached elements and services work, and the contradictions of architectural planning requirements and structural logic. When the problems associated with movement are considered, these conflicting requirements often lead to the replacement of considered common sense by optimism. 1.02 Buildings seldom fail by total collapse, but the adverse effects of movement and excessive deflection can lead to cracking and deformations, which involve repair and maintenance costs and perhaps consequential loss of use. The actual amount of movement is of importance, but differential movement between major portions of the building and building elements is the real problem and a decision has to be made either to prevent such movement or to allow it to take place by incorporating joints.
3 Major division of the structure
3.01 Major divisions of the structure may have to be made with regard to foundation considerations, overall length of the building and horizontal or vertical variations in building shape. The reasons for soil movement are considered in greater detail in section 4 of this handbook: FOUNDATIONS; here the effect on the building is discussed. 3.02 An isolated infinitely stiff building, loaded reasonably evenly, will settle bodily and if total settlement does not interfere with access or service connections this may not be of consequence. Buildings in Mexico City have settled in amounts ranging from several inches to a whole storey. There is a practical limitation to stiffness however and in the average building, unless founded on rock, there will be differential movements within the building and, in a large development, between different units of the development. Movement joints which were required in a large London development are shown in 1 and 2.
2 Sources of movement
2.01 Sources of movement can be summarised as shown in table I. All these sources can have either an overall or a differential resulting movement. Table I Sources of structural movement
Source Active loading Type Dead load Steady superimposed load Impact superimposed load Wind load Seismic load Prestress load Chemical expansion of soil or foundation Freezing expansion of soil Mining effects Vibration Short-term effect Long-term effect
Passive loading Soil deflection Soil settlement Mining effects Water movement Environment Materials (almost all building materials) Temperature Moisture Creep Shrinkage Moisture movement Insulation* Conductivity* Elasticity* Coefficient of expansion* *Controlling properties
(to lesser degree)
1 a Basement plan, Shell Centre, London; upstream building. Chain lines are joints in both basement and superstructure. Figures are net increases in pressure on soil (ie load of building minus weight of excavated material per unit area) in kN/m2; b superstructure plan; joints isolate stiff corner areas and stiff lift/stair complexes
2 Section through Shell Centre upstream building showing computed settlements
3.03 Differential movement may arise from uneven soil types; perhaps due to sloping strata, a localised peat layer or a large clay filling of a pocket in chalk. It may also arise from the use of different foundations in adjacent building units, for instance where one building is piled and the next on a pad foundation, or from simple pad foundations sized so as to produce differing ground pressures 3. A notable example is the Queens Tower of the former Imperial Institute in London, which had a thick raft foundation bearing on London clay at 644 kN/m2. The surrounding buildings were equally massive but were carried on thick strip footings with a bearing pressure of 215 kN/m2. The buildings achieved a differential settlement of 178 mm producing some very odd effects on the floor levels and in the surrounding buildings when they tried to resist this movement. Tilting can become a problem in high buildings when adjacent ground is loaded unevenly, as 4, or where the loading within the building is uneven. 3.04 In most cases a vertical separation joint of about 25 mm width between the buildings is desirable. Below ground this may produce problems in keeping out ground water, and above ground in keeping out rain, wind and snow. It may give the architect problems in modelling the elevation, and in the general appearance of the building. Alternatively the structure may be arranged so that during construction there is complete freedom between the high and low areas. On soils where settlement takes place quickly, the connections between the high and low areas can be made after the whole permanent load is in position or, and certainly in the case of long-term settlement, the connections can be designed with provision for articulation. 3.05 The positioning of major movement joints is so fundamental to both the architectural planning and the basic structural concept that decisions must be taken in the earliest stages of the project. The order of settlements can be assessed from the results of ground investigation tests; but both this type of movement and overall longitudinal movement produce different effects in different structural types and the final decision will derive largely from intuition and experience. 3.06 Some advice is given on distortion and settlement in a paper by Skempton and McDonald1. They refer to damage
3.07 For design purposes they suggest that a factor of safety of 1.25 to 1.50 should be applied. Using the latter figure, an angular distortion limited to 1 in 450 would be considered desirable. The bare frame distortion, ie without stiffening panels, could be double this amount, ie 1 in 225. Other investigators have suggested comparable figures of 1 in 750 and 1 in 150 respectively, indicating the lack of precision possible and therefore the desirability of erring on the safe side. 3.08 In the case of contraction or expansion joints in the length of a building, the object is to avoid damage resulting from the movement of sections which are restrained between stiffer sections. Irrespective of the length, a 150 mm thick concrete slab, if fully restrained, would develop a compressive force between the restraints of about 500 kN/m width of the slab, with a rise in temperature of 17C. The same slab, if cast in one pour between restraints would produce a tension force on shrinking of the same order. The distance between restraints determines the extent of potential temperature movement. In 30 m this might amount to 6 mm. Obviously the restraints and/or the slab will move or crack under such conditions. 3.09 Summarising the whole question of major movement and joint positioning, building or group of joined buildings will probably crack around certain points. By predetermining these expected cracks in the form of joints, the problems can be faced before the cracks occur. Some examples from experience are shown in 5-9.
7 Two-storey car park, approximately 7.6 m square grid with beams running parallel to x axis, slabs spanning in Y direction. The columns, internal 610 mm x 229 mm, and external 610 mm x 305 mm parallel to Y axis (as a), were successful. But when external columns were turned through 90 for planning reasons (as b), these failed. Stiffness had been increased to four times its original value, and instead of flexing they attempted to act as buttresses
9 Effect of layout of stiff vertical supports. In typical multi-storey block, positioning of stiff stair and lift complexes as in a, although desirable planning, contradicts free movement of structure. Alternative solutioons which solve the structural problem either b allow movement outwards from the stiff complex, or c provide a flexible wall at the end to accept movement
4 Seismic and mining problems
4.01 Earthquakes are the surface vibration caused either by earth slip along fault lines or by volcanic explosions. Vibrations occur in both horizontal and vertical directions, the former being about five to 10 times the magnitude of the latter. Tremors are occasionally experienced in the UK but are not considered in design. In other parts of the world they present a serious design problem. 4.02 Joints are determined in accordance with the normal procedures outlined previously with the added isolation of building parts dissimilar in mass or rigidity. The joints in such conditions should be much wider than normal to prevent the sections of the building pounding each other during an earthquake. 4.03 Mining problems are found in some areas of the UK, and with increasing scarcity of building land, the use of sites hitherto ignored because of this condition is likely to increase. Two situations arise, one where the mining has already occurred and the other where it will occur after the building has been built. The former becomes a settlement problem of rather large magnitude and follows normal
settlement design and detailing procedure. The latter is more complex and requires the help of a mining expert to predict the pattern and order of movement. 4.04 Put in its simplest form, a wave movement occurs so that a part of the building is at one time on the crest, in the trough or riding up and down the slope. As the wave progresses across the site, the foundations will tend to be either torn apart from each other or compressed towards each other. On completion of the mining operation the long-term settlement effect will again occur, depending on the extent to which the mined volume is replaced by fill. 4.05 It is possible to articulate the building by a three-point foundation system, though this is very costly. The entire structure is carried on a triangular frame incorporating levelling jacks at the apexes. More usually the building is divided into small sections, and these are dealt with independently. A shallow raft with a granular underlayer will allow the building to slide over the wave. Where the size is such that normal pad foundations are essential, a high bearing pressure should be employed and the bases tied to each other. The more flexible the superstructure, the less repair will be necessary on completion of the movement. A detailed and useful description by F. W. L. Heathcote2 has explained both the problems and some methods of overcoming them.
modulus of elasticity (the relationship between stress and strain), which results in more deflection when these materials are used with improved structural efficiency. 6.03 The strength of concrete in reinforced concrete structures has risen from a cube strength of 2000 lb psi (13.790 N/mm2) to between 3000 and 6000 lb psi (20.685 and 41.470 N/mm2). The modulus of elasticity does not increase linearly with the strength, therefore the use of high strength concretes tends to produce greater deflection by virtue of the reduced section employed. BS CP 1143 recognises this by reducing the allowable span to depth ratios of beams and slabs for various combinations of concrete and steel reinforcement stress. 6.04 In prestressed concrete even higher concrete strengths are demanded, but tho deflection becomes a more complex condition. On the one hand the section may be made smaller, but the prestress can keep the whole concrete section uncracked so that the product of second moment of area and elastic modulus may be greater than that of a cracked reinforced concrete section of equal size, therefore having less deflection potential 11. On the other hand the prestressing force is an active one and will result in an axial shortening of the member and long-term deflections upwards or downwards resulting from further stress variations due to creep. This condition will be examined further on.
10 Floor is jointed around pile cap. Beam settles with poor in groove in pile cap face, thus stabilising pile cups while avoiding damage to settlingpoor slab 5.02 The heated floor of a boiler house can cause shrinkage if there is a cohesive soil underneath, while the cold effect from a cold store can cause expansion of the soil below the floor and therefore heave.
6 Differential movement of building elements
6.01 The obvious movements to be considered are the deflections of beams, floors, walls and columns due to self weight, service load and wind loads. Over the last 30 years a better knowledge of the performance of materials and control in manufacture has led to designed members becoming smaller in section to carry the same load. 6.02 Since the 1930s the allowable bending stress in structural steel has risen from 8 tons psi (123.5 N/mm2) to 10.5 tons psi (162.1 N/mm2) for mild steel, and to 13.5 tons psi (208.4 N/mm2) for high tensile steel. The allowable tensile stress in reinforcing steel has risen from 16 000 lb psi (110.3 N/mm2) to 20 000 lb psi (137.9 N/mm2) for mild steel, 33 000 lb psi (227.5 N/mm2) for medium high tensile steel and even 50 000 lb psi (344.75 N/mm2) for very high tensile steel. In all cases there has been little change in the
6.05 However, kept within normal limits, the movement of the structure is not harmful and it is only when it is considered relative to the other members which it supports that concern arises. Obviously a deflection large enough to give the impression that the building is about to collapse is undesirable, or a vibration produced by jumping on an over-flexible member can be disquieting. But the major problems arise with other building elements supported on the structure such as partitions, applied finishes, cladding panels and so on. Service conditions also may be unacceptable, such as drainage falls in a roof which become reversed by the deflections.
7.01 Despite the advice of BS CP 52346, partitions still remain a constant source of distress and are a frequent battleground of claims for professional negligence. This need not be so, for partitions can be designed to be compatible with the structure, or vice versa. Unfortunately old traditions die hard despite new materials and design concepts, and it is not unusual to find heavy rigid partitions with hard plaster faces being placed on flexible floors. 7.02 In the 1930s, columns in reinforced concrete invariably had a beam framing into the head on each face as a measure of stability. Relative economics of concrete, formwork and
Technical study Safety 2 para 7.02 to 8.02
steel indicated a deep beam solution and with this a considerable degree of rigidity. In the early 1950s there arrived the now commonplace concrete slab with 'beam strip' within its depth. Relative economics had changed and a flat slab requiring minimum finishing treatment led to minimum building height and minimum decoration costs. It also led to a more flexible, floor both from direct load and windloading effects, a property which is still largely unappreciated. Some indication of the cracking which can occur is shown in 12 and 13, while 14 illustrates the transfer of load from a beam to a non-loadbearing partition.
8 Other deflection problems arising from applied load
8.01 Cantilevers are often calculated as though they spring from an infinitely stiff structure and no consideration is given for the rotation at the support, which increases or decreases the end deflection 15. Even when the correct calculation is made, distress can still occur in supported elements 16, if allowance for the movement is not made. Continuous beams develop tension over the supports, and joints are needed in supported elements 17.
15 In a, dotted line is simple cantilever deflection. Rotation at support produces real deflection as shown in solid line. In b, dotted line shows cantilever lifting as load is applied to next span 16 If edge cladding is too stiff or too rigidly connected to the cantilevers it may be damaged, or even fall out. A wall built along cantilever may crack as shown.
concrete parapet
support preventing rotation
17 Cracks occur in parapets over column supports to bridge deck. In this case joints had to be sawn in parapet 8.02 Large panel construction or heavy precast beam erection requires the use of levelling bolts or shims. Unless the shim or bolt is released, or unless a packing capable of carrying the erection load and capable of settling uniformly with the finished structure is employed, 'stress raisers' will occur which will split the supported member 18. Cladding panels should not be supported in such a manner that they become a prop between floors unless specially designed to do so. It is preferable to have support on one member, and flexible attachment elsewhere 19. Changes of grid can be another source of cracking 20. A long span floor can be damaged by the intervention of an extra supporting system and this happens frequently at the ramps in multi-storey car park construction. Problems which arise with the rotation of simply supported beams at support points are shown in 21, 22 and 23.
12 Effect of deflection-prone floors on rigid partitions, with or without doors in them: a arching action of partitions as supporting floor deflects; b resultant cracking, downward movement and rotation of cracked areas
cracking pattern upper floor
load transferred from upper floor into partition
deflected pattern of lower floor deflected pattern of upper floor
13 Partition damage by load transfer from floor above. Here partition spans as deep beam, with load transferred from differential deflection between upper and lower floors
roof nylon or plastic washer
18 Nylon or plastic washer carries initial erection loads, but it deflects more than the concrete member when further load is applied
14 Partition damage by load transfer from beam over. Here partition is constructed too early in building programme, and pinned to roof beam. Roof beam deflects more than first floor beam and transfers load to partition
Technical study Safety 2 para 9.01 to 9.02
9 Movement resulting from change in environment
9.01 While all materials react to temperature change, concrete, masonry and timber react also to shrinkage and moisture migration. Despite the use of modern lightweight insulation materials of great efficiency, it is unlikely that all parts of a building will be at the same temperature. Where a structure can be contained entirely within the insulation, the best movement control is effected, but exposed columns and edge beams create transverse deformations which result in the cracking of internal walls or floors 24. Cladding members, inevitably outside the insulation barrier, should be given an adequate allowance for movement, depending on the size of the member, both in terms of gaps between members and the form of the fixings to the structure.
19 Cracking, caused by hard joints
20 Cracking caused by change of grid 24 Cracking effects of temperature difference on exposed columns and edge beams: a ,floors; b internal walls
21 Underground structure, with large span over a theatre or swimming pool. Change in slope in main girder will cause cracking in finishes at x, unless slip surface is introduced
9.02 Roof beams and slabs will tend to deflect upwards when subjected to heat; this can be a very sudden movement in sunshine where there is poor roof insulation. The roof as a whole can expand and damage the supporting structure, or itself if the supporting structure is stiff. Parapets can be pushed out of place and non-loadbearing partitions can be pulled over laterally or cracked along their length 25. The effect of direct sun heat on a large concrete panel is shown in 26.
22 Change in slope at end of heavy girders on brackets or bearings can break the edge. This can be avoided by raising beam on bearing with flexible pad such as neoprene
25 Dark faced aggregate concrete panel bowed 13 mm in sunshine between cross walls 5.5 m apart
23 Prestressed barns with high pressure under bearing can pull bracket away as creep occurs
84 9.03 BS CP 1115 proposes vertical joints in facing brickwork at intervals not exceeding 15 m and where an external face of a cavity wall exceeds 9 m in height; the wall should be supported from the internal structure to avoid disruption of the wall ties. Combination of brickwork panels in a concrete structure is complicated by the addition of shrinkage and moisture movement. An actual occurrence where rigid brick panels expanded within a frame which was contracting is illustrated in 27. This resulted in diagonal cracks in the corners of the floor slabs. Supporting nibs in gable walls of concrete have been sheared off by the moisture movement of the brickwork when a soft joint has not been left below the nib, as 28. 9.04 Shrinkage and creep in concrete will be considered in more detail later in the handbook (section 5: CONCRETE). One effect often encountered is where an extend concrete member has tiles, mosaics or precast cladding. Unless adequate horizontal joints are made, the cladding will be forced off as the concrete moves downwards under elastic compression, creep and shrinkage.
10.01 The purpose of this study has been to examine the general aspects of movement but not to solve the detail of movement joints. In normal circumstances these are costly; and even more costly if keeping out the weather. Fine judgment is therefore needed to balance the risk of cracking against the cost of the joints, and this is an area in which there should be full understanding between architect and engineer.
1 SKEMPTON, A. w. and MCDONALD, D. H. A comparison of calculated and observed settlements. Stress Conference: London, 1955, Institution of Civil Engineers [(2-) (L4)] p318 2 HEATHCOTE, F. w. L. The movement of articulated buildings on subsidence sites. ICE Journal, vol 30, 1965, February [(2-)(L4)] p347-368
3 BS CP 114: Part 2 1969 Structural use of reinforced concrete in buildings 4 BS CP 121: Part 3 1973 Brick and block masonry 5 BS CP 111: Part 2 1970 Structural recommendations for load bearing walls 6 BS 5234: Code of Practice for internal non-load bearing partitioning, 1975
Technical study Safety 3 para 1.01 to 2.03
Technical study Safety 3
ALLAN HODGKINSON's final technical study on safety discusses the effects of flame and heat on structural materials. He considers the general principles of protection. and in four information sheets which follow, adds tables of 'deemed to satisfy' conditions for protected structural members in concrete, steel, timber and masonry. This information is the most up to date available on the subject, now largely published for the first time. The technical study is concerned only with general aspects, and protection of structural members
1 The general problem
1.01 Various statutory regulations classify the use of buildings according to fire risk. They also define fire resistance of structural elements and the resistance of finishes to spread of flame; this is related to the purpose, size and degree of separation of buildings or parts of buildings. The main concern is safety of life but further fire resistance may be necessary for reasons of insurance premium. 1.02 A fire spreads because the radiation and convection from its flames and hot gases heat other combustible materials so that they also ignite. Burning doors and breaking windows may increase ventilation and so help to spread the fire. With smoke and toxic gases a hazard both to escaping occupants and firemen, it is important that this spread should be retarded. The structural material, or finishes applied to it, can help to prevent this spread. 1.03 The temperature may reach 1200C if a fire continues unchecked. Heat can then be transmitted through walls, floors or roofs, igniting other materials or causing structural members to crack or collapse If a very hot member is hosed by firemen, the sudden cooling may further impair its strength. 1.04 There are tests that make allowances for these effects and can be used to allot fire resistance gradings to the main structural elements. In addition many commercially sponsored tests on specific products have been carried out by the Joint Fire Research Organisation. The JFRO reports, published from time to time, give guidance on other forms or combinations of materials. From their experience, the officers of JFRO may be able to assess gradings of new structural elements and their advice is usually accepted as the basis of a successful waiver of Building Regulation. 1.05 BS 4761 defines fire resistance, incombustibility and non-inflammability of building materials and structures, and describes all the requirements for testing. The heating curve given in the standard represents a rapidly growing fire with a smooth temperature profile of maximum duration six hours and maximum temperature 1200C. Fire resistance is related to the 'standard fire' (as defined in BS 476). Building elements are tested in a furnace where
temperature is controlled so that particular temperatures are reached after periods ranging from hour to 6 hours. Then, for a particular time resistance required, relative to the severity of fire expected, a fire should not be more severe in its effect than the BS 476 test. 1.06 For many years there has been a movement towards basing fire requirements on the actual fire load, ie the calorific value of the buildings' contents. But this would require a special grading procedure and more basic design data. Two JFRO tests, one on multi-storey car parks and the other a two-storey steel-framed building forming part of a multi-storey block of flats, have provided valuable information. The second test established that the position of a stanchion inside the fire compartment has a marked effect on the temperature it reaches. It also showed that the size of the steel section in a casing affects the temperature it reaches and that the degree of protection needed can be calculated. Building Regulations now recognise the effect of the mass of the protected member by relating deemed to satisfy requirements to a minimum weight of steelwork.
2 Choice of structure
2.01 Structure provides support for floors (for habitation) and roofs (for cover). With medium or large spans, the roof is invariably of lightweight construction, but where there are suspended floors, the construction is often repeated at roof level. 2.02 Floors are usually made of reinforced concrete, timber or sheet steel screeded over, roofs have been built in almost every material. Fire hazards exist for all types of structure, and, for those materials lacking the in-built protection of concrete, a careful consideration of protection method is essential. 2.03 Long-span structureslike hangar roofsare traditionally built in steel or aluminium. But the extra costs of drencher systems, sprinklers and insurance premiums should be assessed before making a final choice. (An aircraft hangar has been built with prestressed precast space frame roof and industrial buildings have employed roof trusses of lightweight concrete.)
Technical study Safety 3 para 3.01 to 4.01
proposed that for beams and slabs, built into a structure with restraints to thermal expansion provided at opposite ends, the amount of protective cover to reinforcement may be reduced to that for the next lower period in tables of fire resistance requirements. 3.09 The surrounding structure can be assumed to provide thermal restraint if there are no gaps between it and the ends of floor or beam, no combustible materials used to fill these gaps, and if the surrounding structure can withstand thermal stresses induced by the heated floor or beam.
3.01 Reinforced concrete has the best fire resistance of common structural materials and indeed concrete is used to protect other structures. It does not burn or give off sufficient inflammable vapour to ignite and so may be regarded as incombustible. 3.02 The fire resistance depends largely on the type of aggregate. Siliceous aggregates are the poorest; the class 2 reference of the Building Regulations couples flint-gravel, granite and all crushed natural stones other than limestone. Aggregates which have been subjected to heat during their beam attacked on 3 sides manufacture give a better performance; the class 1 reference couples foamed slag, pumice, blast furnace slag, pelleted fly ash, crushed brick and burnt clay products, well-burnt clinker and crushed limestone. This group contains the commercial lightweight aggregates. 3.03 Concrete fails in fires because of the differential expansion between exposed hot surface layers and inner cooler layers. The movement of cement, as it shrinks with loss of moisture, compared with the continued expansion of the aggregate as temperature increases, creates another differential and so a further stress. 3.04 Steel reinforcement, exposed by cracking, conducts the heat rapidly and increases the temperature differential. The concrete cracks and spalls and the reinforcement loses strength as its temperature rises. Ultimately the element fails. The insulation value of reinforced concrete, as a structural element or as a casing to steelwork is obviously important; from this point of view lightweight aggregate concretes offer the better value. 3.05 As concrete with sand, ballast, sandstone and lime- Concrete structures: 1 rib beams; 2 prestressed beams; stone aggregates (but not aggregates of igneous rocks) is 3a exposed column; 3b column in wall heated, the colour changes from pink or red at between 300C and 600C, to grey between 600C and 900C, and 4 Structural steelwork to buff at higher temperatures. These colour changes are permanent and so help to identify the extent of the damage. 4.01 Steelwork is incombustible. When heated it expands at Strength begins to fall rapidly at about 250 C and although a known rate and its strength decreases 4. Mild steel is not the structure may appear sound at 600 C, the strength will really affected until 300C but decreases rapidly in yield strength to about 50 per cent at 550C and to 10 per cent at have dropped to 40 per cent. 3.06 Repair of a damaged structure is often easy. The tem- 800C. On cooling it will recover about 90 per cent of its perature is unlikely to have exceeded 800C if less than one- initial strength; this is also true of alloy steel. Work-hardquarter of the steel surface is exposed by spalling. In the ened steels, usually cold-worked bars or prestressing wire, ease of mild steel, this represents a permanent loss of deteriorate more rapidly and equivalent yield strength drops strength of 20 per cent of yield strength and 15 per cent of to half at about 400C. On cooling, this steel reverts to the ultimate strength. Work-hardened steels are more seriously original unworked form. There is considerable permanent affected and it is essential that test pieces are cut from the loss of strength, and elongation characteristics are affected. bars, which is obviously more difficult with prestressing tendons. The steel may revert to its unworked condition, depending on the temperature attained. When the structure is under both superimposed load and fire attack, the critical temperature for ordinary reinforcing steel will be about 550C and for prestressing tendons about 400C. At these temperatures the steel retains about half its normal ambient temperature strength. 3.07 A given thickness of concrete protects the reinforcement for a specific time under the worst fire conditions; a total thickness of member controls the temperature rise on the unexposed face and reduces cracking. Different shapes react differently to fire. Variations are needed with different materials, eg less protection thickness for lightweight aggregate, more protection thickness for hard-drawn steel used in prestressed concrete. 3.08 Finishing materials such as plastics, renderings and suspended ceilings add to the protection. Recent investigations showed that end restraint against thermal expansion can substantially increase the fire resistance of a structural element. Until more research results are available, it is 4 Graph shows changing strength of steel with temperature
4.02 With a thermal conductivity of 42 W/m C, there is rapid heat transmission through the element. Hut there is a high heat capacity, so the temperature of the steel lags behind the environmental temperature. Unprotected members in standard fire tests have reached failure conditions in 10 to 15 minutes, showing that some protection is necessary for even the lowest fire grading. 4.03 The protection system chosen must provide overall value; relative costs of a number of treatments are shown in table I. These are costs of protection per foot of member, assuming conventional I-shaped sections. A protection that follows the profile of the steel should be cheaper with an RHS section.
quickly with aluminium but because it melts at 650C the section would melt before the end of a 30-minute fire test.
6.01 Unlike the other materials discussed, timber actually burns. But though combustible, the ease of ignition is related to the density and moisture content of the timber and the size of the member. 6.02 In a fire, moisture (which may be from 10 to 20 per cent of the dry weight) is driven from the surface layers of the timber. Little chemical change occurs until the temperature reaches 270 to 290C when exposed surface layers begin to decompose and the liberated gases can ignite. Flaming continues as long as there is a heat input; without this, heat radiated back towards the wood by the flames is not sufficient to maintain the decomposition process. 6.03 With continued flaming, a layer of charcoal is produced. This shields the inner timber from the effects of the fire. The charcoal is a better insulator than the natural timber, so strength is lost only from the outer layers which are consumed. This charcoal layer is inert up to temperatures of about 500C, glowing combustion then starts and the charcoal is gradually consumed. A state of steady combustion is achieved and the charring area advances into the unburnt timber at a steady rate 5.
4.04 The Building Regulations suggest a variety of protection methods for stanchions of minimum weight 44.64 kg/m, and beams of minimum weight 29-76 kg/m. These are illustrated in information sheet SAFETY 2. 4.05 The 44.64 kg/m limit excludes the three lowest-weight sections in the universal column range and the eight lowestweight sections in the universal beam range if the beams are employed as columns. The 29.76 kg/m limit excludes only the lowest-weight section in both the universal beam range and universal column range, and all the six joists in the
a circuit is formed. This can work as a radiator heating system in reverse when columns are subjected to heat. The heated water moves upwards and is replaced by cooler water, thus keeping the shell of the column at a lower temperature. A header tank can be used, as in a radiator system, to ensure that the system is kept full. 4.08 This might seem to have rather limited application because the bare steelwork is the structural member which is exposed to corrosion. But there are now weathering steels that develop their own protective oxide coating and which, in external situations or on unclad structures, may hot reach critical temperature in a fire because the heat is so rapidly dissipated.
6.04 Laboratory tests have established that for the majority of timber species this rate is 0.64 mm/min, with lowdensity woods charring quicker than high-density ones. The rate is scarcely influenced by the severity of the fire, and this makes reasonably accurate prediction of the fire resistance of timber members possible. Sacrificial timber 6.05 A timber member can be designed by the usual methods and then increased in size to allow for the loss of timber expected in a particular period of fire. For example a timber beam 6 bearing its design load, is exposed to fire for 30 minutes on the soffit and two sides. The resulting section for calculation purposes will be (D - 30 x 0.64) mm deep and (W - 2 x 30 x 0-64) mm wide. That is, the section is reduced on each exposed face by the product of the elapsed time (30 min) and the charring rate (0.64 mm/min).
5.01 Aluminium is not widely used in building structures. Table II compares three properties of steel and aluminium. In a fire, heat would be conducted away from a point more
6 Timber beams showing sacrificial material
6.06 For timber columns, heat can usually be applied on all sides; an arbitrary charring rate of 0.83 mm/min is used because of the more rapid temperature rise possible under such conditions. 6.07 Beams or columns laminated from smaller timbers using structural adhesives of the resorcinal or phenolresorcinol type, have charring and strength loss characteristics equal to those of the solid section. But this does not apply to mechanically fastened laminated members, unless the fixings remain within the undamaged timber at the end of the period of required fire resistance. Walls and floors can be calculated in the same way but are generally of such small sections that it would be more economical to consider the protective properties of an applied finish.
7.01 Masonry, in the form of solid brick, cellular brick, solid concrete blocks, hollow concrete blocks (with either heavy or lightweight aggregate) and aerated concrete blocks, provides considerable resistance to fire. 7.02 Bricks and concrete blocks with hollow cores not exceeding 25 per cent by volume can withstand the four-hour furnace test of about 1100C face temperature without fusion or spalling from the exposed face. Blocks with larger cavities can have thin internal webs; here the high thermal stresses across the section could lead to fracture. Aerated concrete blocks provide better insulation but as the material loses more strength than other blocks at high temperatures, extra thickness is required. 7.03 As temperature rises, the heated face not only loses strength but, in an axially-loaded wall, creates a condition of eccentricity and thus a further reduction in ultimate loadbearing capacity due to greater instability. 7.04 As the result of a large number of tests which have been carried out on loadbearing walls, the Building Regulations give good guidance in deemed to satisfy form. However the latest information will be published in the next revision of CP 1212. References 1 BS CP 476 Part 8: 1972 Test methods and criteria for the fire resistance of elements of building construction 5.60 2 BS CP 121: Part 1: 1973 Brick and block masonry (CP 121.201Masonrywalls: CP 121.202Masonry: rubblewalls)
Information sheet Safety 1
A Reinforced concrete walls
When using lightweight concrete a reduction of thickness is possible but this must be confirmed by a test Concrete cover to the reinforcement should not be less than 1 5 mm for fire resistance up to 1 h and not less than 25 mm for higher periods Walls containing less than one per cent vertical reinforcement are considered as plain concrete for fire purposes unless a test shows otherwise
This sheet consists of tables of 'deemed to satisfy' conditions for concrete walls, beams and floors
Table I Fire resistance of reinforced dense concrete walls exposed to fire on one side only
Description of applied finish none cement or gypsum plaster on one or both sides vermiculite/gypsum plaster* at least 15 mm thick on both sides Minimum thickness of concrete in mm to give fire resistance of 4 3 2 1 1 hours
180 150 100 100 75 75
The fire is assumed to attack the soffit and two sides of the beam When the reinforcement is used in more than one layer the value of the total protective concrete cover is the arithmetic mean of the nominal cover to the tensile reinforcement in each layer The value of the minimum cover to any bar should not be less than half the value shown in table II for different periods of fire resistance and never less than the value shown under the i hour period Alternatively the average concrete cover may be determined by summing the product of the cross sectional area of each bar or tendon and the distance from the nearest exposed face and dividing it by the total area of the steel provided to resist tensile stresses induced by the imposed loads Average concrete cover where AS 1 cross sectional area of the steel bar or tendon and c 1 its distance from the nearest exposed face
D Reinforced concrete columns
Table III Columns with all faces exposed
Dimension of concrete in mm to give fire resistance of 4 3 2 1 1 hours 450 400 300 250 200 150
Type of construction 1 dense concrete a without additional protection b with cement or gypsum plaster 15 mm thick on light mesh reinforcement
*Vermiculite/gypsum plaster should have a mix ratio in the range from 1 1 to 2 1 by volume Walls exposed to fire on more than one face should be regarded as columns
B Plain concrete walls
From the limited data available the fire resistance of plain concrete walls can be taken as 1 h for concrete 1 50 mm thick 1h for concrete 175 mm thick
c with vermiculite/gypsum plaster* 15 mm thick 275 d with supplementary reinforcement in concrete cover or limestone aggregate concrete 300 2 lightweight aggregate concrete 300
C Reinforced concrete beams
Table II Fire resistance of reinforced concrete beams
Description 1 dense concrete a concrete cover to mam reinforcement b beam width Dimension of concrete in mm to give a fire resistance of 4 3 2 1 1 hours
2CO 200
*Vermiculite/gypsum plaster should have a mix ratio in the range from 1 1 to 2 1 by volume Sprayed asbestos should conform to BS 3590 Note The minimum dimension of a column is a determining factor in the fire resistance it can provide The dimensions given in the table relate to columns which may be exposed to fire on all faces when subjected to characteristic loads The use of limestone or other calcareous aggregates or the use of supplementary reinforcement in the concrete cover would reduce spalling and allow a reduction in the size of the section The supplementary reinforcement should consist of steel fabric of not less than 2 mm diameter wire and of mesh not greater than 150 mm or an equivalent material and should be placed at mid cover not more than 20 mm from the face The concrete cover to the main bars should not exceed 40 mm without the use of supplementary reinforcement The data in table III are based on a rectangular or a circular cage reinforcement
65* 55* 45* 35 280 240 180 140
2 as 1 with cement or gypsum plaster 15 mm thick on light mesh reinforcement a concrete cover to mam reinforcement 50* 40 b beam width 250 210 3 as 1 with vermiculite/gypsum plaster or sprayed asbestos 15 mm thick a concrete cover to mam reinforcement 25 b beam width 170 4 lightweight aggregate concrete a concrete cover to mam reinforcement b beam width
30 20 170 110
15 15 85 70
Table iv Columns with only one face exposed
15 15 145 125 15 85 15 15 60 60
Type of construction dense concrete a without additional protection b with 15 mm vermiculite/gypsum plaster* on exposed face *As footnote to table III Note Columns with their full height built into fire resisting walls may be exposed to fire on one face only Data in table IV apply when the face of the column is flush with the wall or when that part of the column embedded in the wall is structurally adequate to support the load provided that any opening in the wall is not nearer to the column than the minimum dimension for the column specified in table IV Dimension of concrete in mm to give a fire resistance of 4 3 2 1 1 hours 180 125 150 100 100 75 100 75 75 65 75 65
*Supplementary reinforcement consisting of either a wire fabric not lighter than 0 5 kg/m 2 (2 mm diameter wires at not more than 100 mm centres) or a continuous arrangement of stirrups at not more than 200 mm centres must be incorporated in the concrete cover at a distance not exceeding 20 mm from the face Note Vermiculite/gypsum plaster should have a mix ratio in the range from 1 1 to 2 1 by volume Sprayed asbestos should conform to BS 3590
E Reinforced concrete floors
Table V is not exhaustive and the performance of types not shown can either be assessed by analogy or determined by testing
Table v Fire resistance of reinforced concrete floors
Floor type Dimension of concrete in mm to give fire resistance of 4 3 2 1 1 hours cover to reinforcement overall depth* cover to reinforcement thickness under cores overall depth*
1 solid slabs
2 cored slabs, area of cores less than 50 per cent of solid area, cores higher than width
50 190 25 50 230 25 125 190
40 175 25 40 205 25 100 175
40 160 20 40 180 20 90 160
30 140 20 30 155 20 80 140
25 110 15 25 130 15 70 110
20 100 15 20 105 15 50 100
3 hollow box sections with one or more cover to reinforcement thickness of bottom flange longitudinal cavities overall depth* 4 inverted T-section beams with hollow infill blocks of concrete or clay having not less than 50 per cent of solid material cover to reinforcement width of T-flange overall depth*
5 ribbed floor with hollow infill blocks cover to reinforcement of clay having less than 50 per cent width of T-flange of solid material and with a 15 mm overall depth* plaster coating on soffit 6 upright T-sections bottom cover to reinforcement side cover to reinforcement width of web depth of flange bottom cover to reinforcement side cover to reinforcement width of web depth or thickness at crown* bottom cover to reinforcement side cover to reinforcement width of web* depth or thickness at crown*
25 125 190
25 100 175
20 90 160
20 80 140
15 70 110
7 inverted channel sections, radius at intersection of soffits with top of leg not exceeding depth of section 8 inverted channel sections or U-sections, radius at intersection of soffits, top of leg exceeding depth of section * Non-combustible screeds and finishes may be included in these dimensions ** Additional reinforcement is necessary to hold the concrete cover in position
65** 55** 45** 35 40 30 25 20 75 70 60 45 150 150 125 125 65** 40 55** 30 45** 25 35 20
25 15 40 100 25 15
15 10 30 90 15 10
Note In estimating the thickness of concrete, non-combustible screeds or finishes can be taken into account. The effect of the ceiling finish is shown in table VI.
Table vi Effect of ceiling finish on fire resistance of structural suspended floors
Thickness of finish in mm to give an increase in fire resistance of 3 2 1 1 hours
F Prestressed concrete beams
Table vii Fire resistance of prestressed concrete beams
Description 1 dense concrete: a concrete cover to main reinforcement b beam width 2 as 1 with vermiculite concrete slabs, 15 mm thick, used as permanent shuttering: a concrete cover to main reinforcement b beam width 3 as 2 with 25 mm thick slabs: a concrete cover to main reinforcement b beam width 4 as 1 with 15 mm thick gypsum plaster with light mesh reinforcement: a concrete cover to main reinforcement b beam width 5 as 1 with vermiculite/gypsum plaster, or sprayed asbestos* 15 mm thick: a concrete cover to main reinforcement b beam width Dimension of concrete in mm to give a fire resistance of 4 3 2 1 1 hours
1 vermiculite/gypsum plaster* or sprayed asbestos applied to the soffit of floor types 1, 2 or 3 25 2 vermiculite/gypsum plaster* or sprayed asbestos on expanded metal as a suspended ceiling to floor types 4 or 5 3 gypsum/sand or cement/sand on expanded metal as a suspended ceiling to any floor type
100* 85 65* 50* 40 25 280 240 180 140 110 80
75* 60 45 35 210 170 125 100
25 15 70 70
*Vermiculite/gypsum plaster should have a mix ratio in the range of 1 i :1 to 2:1 by volume. Sprayed asbestos should conform to BS 3590
65 50 35 180 140 100
15 15 60 60
90* 75 250 210
30 15 85 70
75* 60 170 145
Information sheet Safety 1 Dimension of concrete in mm to give a fire resistance of 4 3 2 1 1 hours
Description 6 as 5 with 25 mm thick coating a concrete cover to mam reinforcement b beam width 7 lightweight aggregate concrete a concrete cover to main reinforcement b beam width
*Supplementary reinforcement consisting of either a wire fabric not lighter than 0 5 kg/m2 (2 mm diameter wires at not more than 100 mm centres) or a continuous arrangement of stirrups at not more than 200 mm centres must be incorporated in the concrete cover at a distance not exceeding 20 mm from the face
Vermiculite/gypsum plaster should have a mix ratio in the range from 1 1 to 2 1 by volume Sprayed asbestos should conform to BS 3590 The protective cover to the tendon for different periods of fire resistance should not be less than in table VII, in no case should the minimum cover to any tendon be less than half the value shown in the table for different periods of fire resistance it should never be less than the value shown under the i hour period When the prestressing tendons to resist tensile stresses due to imposed or working loads are provided in a number of layers, the value of the protective concrete cover is the arithmetic mean of the nominal cover for each layer I section beams with web thickness of half or less the lower flange breadth require web stirrups amounting to 0 15 per cent of the web area on plan
G Prestressed concrete floors
Table viii Fire resistance of prestressed concrete floors
Floor typesillustrated as Table V 1 solid slabs 2 cored slabs, area of cores less than 50 per cent of solid area, cores higher than width 3 hollow box sections with one or more longitudinal cavities 4 inverted T-section beam with hollow infill blocks of concrete or clay having not less than 50 per cent solid material 5 upright T-sections cover to reinforcement overall depth* cover to reinforcement thickness under cores overall depth* cover to reinforcement thickness of bottom flange overall depth* cover to reinforcement width of T-flange overall depth* bottom cover to reinforcement side cover to reinforcement width of web depth of T-flange* bottom cover to reinforcement side cover to reinforcement width of leg depth or thickness at crown* bottom cover to reinforcement side cover to reinforcement width of leg* depth or thickness at crown* Dimension of concrete in mm to give fire resistance of 4 3 2 1 1
65" 150 50" 150 40 125 30 125 25 100
65" 50 190
50** 40 175
40 40 160
30 30 140
25 25 110
65** 125 190 100** 100 250 150 100"
50** 100 175 85" 85 200 150 85"
40 90 160 65" 65 150 125 65**
30 80 140 50" 50 110 125 50**
25 70 110 40 40 90 100
15 50 100 25 25 60 90
6 inverted channel sections, radius at intersection of soffits, top of leg not exceeding depth of section 7 inverted channel or U-sections, radius at intersection of soffits, top of leg exceeding depth of section
100** 50 110 150
45 100 150
85** 45 90 150
35 75 125
65** 35 70 125
25 55 125
50" 25 50 125 40 20 45 100 25 15 30 90
Non-combustible screeds and finishes may be included in these dimensions "*Supplementary reinforcement is necessary as in table VII or consisting of equivalent expanded metal lath Notes The average cover at a section is assessed as the arithmetic mean of the nominal cover of each equal tendon of prestressing steel in the member below the neutral axis; but the minimum cover to any tendon should not be less than half the value shown under different periods of fire resistance and in no case should it be less than the value shown under the period of hour If the thickness of concrete cover for floor types 4 and 5 exceeds 40 mm, mesh reinforcement must be incorporated in the cover to retain the concrete in position This is not necessary when ceiling protection of the types shown in section E of this sheet (reinforced concrete floors) is used Similarly the fire resistance of a given form of construction can be improved by using an insulating finish on the soffit or by a suitable suspended ceilingas described for reinforced concrete floors
Information sheet Safety 2
A Fire resistance of protected steel columns
Table i Fire resistance of protected steel columns; stanchion weight per metre not less than 44-6 kg
Construction and materials Solid protection (unplastered) The casing is bedded close to the steel without intervening cavities and all joints in the casing made full and solid Minimum thickness (in mm) of protection for a fire resistance of 4 2 1 1 hours Concrete not leaner than 1 :2:4 mix with natural aggregates: a Concrete assumed not loadbearing reinforced* 50-8 b Concrete assumed to be loadbearing reinforced in accordance with BS 449 76-2
25-4 50-8
Solid bricks of clay, composition sand or sand lime Solid blocks of foamed slag or pumiced concrete reinforced* in every horizontal joint Sprayed asbestos 144 to 240 kg/m 3 Sprayed vermiculite cement
63-5 44-5
50-8 19-1 38-1
50-8 15-9 31-8
50-8 9-5 19-1
50-8 9-5 12-7
Solid bricks of clay, composition or sand lime reinforced in every horizontal joint unplastered 114-3 Solid blocks of foamed slag or pumice concrete reinforced** in every horizontal joint unplastered 76-2
50'8
Metal lath with gypsum or cement lime plaster of thickness Metal lath with vermiculite or perlite gypsum plaster of thickness Metal lath spaced 25 mm from flanges with vermiculite gypsum or perlite gypsum plaster of thickness Gypsum plasterboard with 16 swg binding at 100 mm pitch: a 9-5 mm plasterboard with gypsum plaster of thickness b 19 mm plasterboard with gypsum plaster of thickness:
38-1 19-1
25-4 15-9
19-1 12-7
12-7 6-4
Plasterboard with 16 swg binding at 100 mm pitch a 9 - 5 mm plasterboard with vermiculite gypsum plaster of thickness b 19 mm plasterboard with vermiculite gypsum plaster of thickness 31-8** Metal lath with sprayed asbestos of thickness
15-9 9-5
12-7 9-5
9-5 6-4
Construction and materials Vermiculite cement slabs of 4:1 mix reinforced with wire mesh finished with plaster skim Slabs of thickness Minimum thickness (in mm) of protection for a fire resistance of 4 2 1 1 hours
Asbestos insulating boards of density 513 to 881 kg/m3 (Screwed to 25 mm asbestos battens for hour and 1 hour periods)
*Reinforcement of steel binding wire 13 swg or a steel mesh weighing not less than 0-542 kg/m2. Minimum spacing in concrete not less than 150 mm **Light mesh reinforcement required 12 to 19 mm below surface unless special corner beads are used
B Fire resistance of protected steel beams
Table II Fire resistance of protected steel beams; joist weight per metre not less than 30 kg
Construction and materials Solid protection (unplastered) The casing is bedded close to the steel without intervening cavities and all joints with casing made full and solid Concrete not leaner than 1 -2:4 mix with natural aggregate: a Concrete not assumed to be loadbearing reinforced* b Concrete assumed to be loadbearing reinforced in accordance with BS 449 Minimum thickness (in mm) of protection for a fire resistance of 4 2 1 1 hours floor
concrete floor Sprayed asbestos 144 to 240 kg/m2 Sprayed vermiculite cement 44-5 19-1 38 1 15-9 31-8 9-5 19-1 9-5 12-7
metal lath void
Metal lathing: a with cement lime plaster of thickness b with gypsum plaster of thickness c with vermiculite gypsum or perlite gypsum plaster of thickness 31-8
38-1 22-2 12-7
25-4 19-1 12-7
19-1 15-9 12-7
12-7 12-7 12-7
floorplasterboard void
Gypsum plasterboard with 16 swg wire binding at 100 mm pitch: a 95 mm plasterboard with gypsum plaster of thickness b 19 mm plasterboard with gypsum plaster of thickness
Plasterboard with 16 swg wire binding at 100 mm pitch: a 9 - 5 mm plasterboard nailed to wooden saddles finished with gypsum plaster of thickness b 9 - 5 mm plasterboard with vermiculite gypsum plaster of thickness c 19 mm plasterboard with vermiculite gypsum plaster of thickness 38-1 d 19 mm plasterboard with gypsum plaster of thickness Metal lathing with sprayed asbestos 144 to 240 kg/m3 of thickness
15-9 9-5 12-7
4-8 6-4 6-4
Construction and materials Asbestos insulating boards of density 513 to 881 kg/m2 (screwed to 25 mm asbestos battens for hour and 1 hour periods) asbestos insulating board screw to battens asbestos battens
Minimum thickness (in mm) of protection for a fire resistance of 4 2 1 1 hours floor
Vermiculite cement slabs of 4 1 rise reinforced with wire mesh and finished with plaster skin slabs of thickness slabs reinforced with wire mesh vermiculite cement slabs plaster skim coat
Gypsum sand plaster 12 mm thick applied to heavy duty (type B) woodwool slabs of thickness
woodwool slobs gypsum sand plaster
'Reinforcement of steel binding wire 13 swg or a steel mesh weighing not less than 0 542 kg/m 2 Minimum spacing in concrete not less than 150 mm
Information sheet Safety 3
Fire resistance of timber structures
This sheet consists of two tables of deemed to satisfy conditions for timber floors and structural stud partitions
Information sheet Safety 4
Fire resistance of masonry walls
This sheet consists of two tables of 'deemed to satisfy' conditions for brick and block walls
A Single leaf walls
T a b l e I E i r e r e s i s t a n c e of s i n g l e leaf m a s o n r y w a l l s
* the number of cells in any cross-section through the wall thickness ** suitable for 75 m m brick-on-edge construction with a completely solid unit with plane faces
Note 1 Class I aggregates for concrete blocks can be limestone, aircooled blast furnace slag, foamed or expanded slag, crushed brick, well burnt clinker. expanded clay or shale, sintered pelleted flyash, pumice. Class II aggregates for concrete blocks include all gravels and crushed natural stone except limestone. 2 The finish shall be not less than 13 mm plaster or rendering on each face of a single s k i n wall and o n the exposed face of a cavity wall. sc = sand cement plaster with or without lime sg = sand gypsum plaster with or without lime sc/sg may be replaced by plaster board of equivalent thickness forfire resistance up to two hours. vg - vermiculite gypsum plaster in proportions 13 : 1 or 2:l by volume. (Purlite may be substituted in fired clay brickwork or other materials with similar surfaces). 3 Solid brickwork is of bricks without frogs orfrogs up to 20 per cent of the brick volume with no through holes or perforations. (This definition differs from BS 3921).
B Cavity walls
Table II Fire resistance of cavity walls
AJ Handbook of
edited by Allan Hodgkinson In its first edition, this Handbook became a standard reference for both students and practitioners. Recent changes to British Standards, Codes of Practice and Building Regulations have generated demand for a new, updated edition; and unlike the reprints of 1976 and 1977, this is a radically revised and updated version of the original 1974 Handbook. The principle changes are in the sections on Masonry (totally rewritten to take account of the 1976 Building Regulations) and on Timber (substantially revised to take account of new timber gradings). In addition to many minor improvements, the opportunity has also been taken to bring up to date all the references quoted. For the rest, this remains the widely acclaimed structural design handbook first published in 1974. Information is specific enough to be of practical value, yet presented in a way intelligible to users without engineering backgrounds. Some press comment on previous editions: "This admirable and useful volume deserves to be studied carefully by readers outside the architectural profession, as well as those within it. . . a well designed and thoroughly interesting book" Build International ''This handbook provides a review of the whole structural field" Building Technology and Management "All in all, a most useful and comprehensive textbook which no self-respecting architect can afford to be without" Architect's News
AJ Handbook of Building Enclosure edited by A J Elder and Maritz Vandenberg "With its many references and general high quality of presentation, the handbook will be of use and interest to anyone concerned with the built environment" IHVE Journal "A new and more integrated approach to construction techniques than the traditional textbook" Building Trades Journal "The information is generally of a very high Standard . . - great care has been taken by the various section authors" Building "For the student, the handbook ought to be a 'set book' to take him through many years of use . . . it deserves widespread circulation" The Architects' Journal Paper edition ISBN 0 85139 282 2
Guide to the 1976 (Seventh A J Elder
Building Edition)
This new 1982 edition of the Guide to the 1976 Building Regulations, coming on the heels of the Secretary of State's long-awaited Command Paper, incorporates two new appendixes: on the Proposed Second Amendment, and on The Future of Building Control in England and Wales. Some press comment on previous editions: "An invaluable source of guidance through the verbal jungle of the Regulations" Building Technology and Management "The book provides a comprehensive reference on matters of everyday practice for all members of the building team and students and should act as a companion to the 1972 Regulations themselves" Building Trades Journal "Should provide a valuable reference book for the architect and for the builder in ensuring that their work complies with the Regulations" Construction News ISBN 0 85139 850 2
New Metric Handbook edited by Patricia Tutt and David Adler With sales approaching 100 000 over the past 10 years, the original Metric Handbook is an established drawing board companion. But now that the metrication programme in the UK is virtually complete, the emphasis on conversion to metric which formed the basis of the old Metric Handbook is no longer appropriate. This radically revised and greatly expanded New Metric Handbook retains many of the features of the old, but concentrates much more strongly on planning and design data for all common building types. If ever there was a drawingboard bible, this is it. 480 A4 pages. ISBN 0 85139 468 X
ISBN 0 85139 273 3 The Architectural Press 9 Queen Anne's Gate, London SWlH 9BY
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