W86

Building Pathology

BUILDING PATHOLOGY A STATE-OF-THE-ART REPORT

CIB Report

June 1993

0 CIB 1993

Publication 155

Preface 1

CIB Working Commission W86 - Building Pathology. comprising about 45 experts from several countries, is essentially concerned with the methodology of investiga- tion of defects and failures of buildings. Its tasks are: to produce and exchange infor- mation, to consider technical aspects of defects and failures. and to promulgate im-

proved practices. Building pathology has many Merent aspects. all of which could merit being subjects of study on their own. This Report was W e d with the aim of giving state-of- the-art information concerning those aspects, including their interrelationships. It

is hoped that experts involved with the investigation and prevention of building

defects will profit from the views, opinions and methods described.

The Report is the joint effort of W86s Members. Special thanks are due to the follo- wing Members who contributed by delivering substantial Information and/or by drafting parts of the Report: Mr. Brotherson, Mr. Castrillo Canda. Mr. Groce, Mr.

Gross, Mr. Henshell, Mr. Moroni, Ms. Pinterr. Mr. Tolstoy and Mr. Wintz. Assistance in the final editing, from W86's former Coordinator. Mr. I.L. Freeman, is gratefully

acknowledged.

At the date of issuing the Report W86 consisted of the following Members:

Australia: RF. Warner Belgium: J. Ratht; Canada: M. Lincourt, M.Z. Rousseau; Flnlpnd: T. Sne& France: F. Derrien; Hungary: J. Pint& Ireland K. Spencer; Italy: S. Groce. F. Lembo. M. Moroni, G. Tortorid, G. TurchM; Mozambique: J. Almeida Fernandes; New Zealand G. Robertson; Netherlands: A van den Beukel, P.Chr. €?aab;

Portugal: A. Canha da Piedade, J. Ferry Borges, A Ravara; Romania: L. Groll; Singapore: C. B s e t t ; South Africa: J.A.P. Laurie; Spain: A. Castrillo Canda, F.

Hostalet Alba; Sweden: N. Tolstoy; United Kingdom: D. Bishop, G.K. Cook, H. Gow. K.H. Murta, W.G. Sparksman. P. Trotman; US& D.E. Brotherson. C.G. Cash. C.T. Grimm, J.G. Gross. J. Henshell. S.D. Kaplan, J. LQSS. T. Nadel, J.A. Wintz; USSR: B A Kosicin.

June 1993

Delft. The Netherlands A van den Beukel Coordinator W86

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Building pathology is defined as the systematic treatment of building defects, its causes, its consequences and its remedies. Elements and notions of the building pa- thology 'domain' are reviewed firstly in Chapter l: 'Introduction'. A systematic approach to cause determination is the focal point in Chapter 2: 'Methodology of Investigation'. Such an approach is important in minimising the risk that Merent investjgators into some given defect arrive at different conclusions. Special attention is paid to the kind of information on causes of defects. Information should not just cover technical or liability aspects, but also aspects that can be used for the improve- ment of quality management systems. Furthermore. the concept of risk is dealt with along the three lines of a mathematical concept, a management tool and a psychologi- cal concept. The advantages and disadvantages of databanks on building defects are discussed jn Chapter 3: 'Databanks'. They are mostly seen as necessary to get a grip on the preven- tion of building defects. But certain conditions, as for instance, a sound financial basis and a clear vlew on input, processing and output of defect information have to be met in order to make a database successful. It is questioned, nevertheless. whether useful infoxmation produced on building defects really reaches those people who may 'build in' a defect Chapter 4: 'Costs' describes cost categories related to building defects. 'Quality costs'. 'costs of defects' and other types of costs are presented as an interrelated framework. Also, some data on costs arc given. They indicate that roughly 2% to 5% of total buil-

ding costs can be considered as building defect costs. Extreme losses due to collapses or structural failures are not taken into account. Financial losses due to imperfect control ofthe building process amount to roughly the same percentages. Some diagnostic tools are dealt with in Chapter 5: 'Diagnostic Aids'. Diagnostic charts and matrices may link anomalies (signs or symptoms). causes, defects and tests in a structural way. The fault tree - known from reliabilily analysis of structural systems - may be useful as a diagrammauc outline of possible errors aEecting the performance of a building element. The diagnostic tree is presented as a guide to the process of diag-

nosis. The basics of expert systems, which are attracttng more and more attention in

the building field, arc discussed but without going into details of expert system tech- nology. Next Chapter 6: 'Cases of Failures' presents a few cases to illustrate the systematics in

handling a building defect. Finally, Chapter 7: 'Information Dissemination' contains a selected bibliography. Only those boob and a ~ W e s which W86 Members thought to be useful are listed.

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Contents

PREFACE

SUMMARY

1 INTRODUCTION

2 METHODOLOGY OF INVESTIGATION 2 . 1 Investigation process 2 . 2 Cause determination 2 . 3 Origins of causes 2 . 4 The decay process and maintenance 2 . 5 Risk 2 . 6 Terminology

3 DATABANKS 3 . 1 Introductory 3 . 2 Advantages and disadvantage 3 . 3 Experiences 3 . 4 Conditions

4 COSTS 4 . 1 Introductory 4 . 2 Cost categories 4 . 3 Data on quality costs 4 .4 Data on costs of defects 4 . 5 What can be learned from data on costs?

5 DIAGNOSTIC AIDS 5 . 1 General 5 . 2 Diagostic charts and matrices 5 . 3 Fault trees 5 . 4 Diagnostic trees 5 . 5 Expert systems

6 CASES OF FAILURES 6 . 1 Introductory 6 . 2 Defects Information Sheets 6 . 3 Review of failures and defects

1

2

5

9 9

1 3 14 1 5 1 6 2 1

2 3 2 3 2 3 2 4 2 4

27 27 27 29 30 3 1

33 33 33 36 39 41

47 47 4 8 6 1

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Contents (Cont . ' d)

7 INFORMATION DISSEMINATION 7.1 Bibliography - Books 7.2 Journals, proceedings, technical notes, etc.

REFERENCES

71 71 73

77

APPENDIX A. Example of a check list 79 APPENDIX B. Building defects result from procedural inadequacies 81 APPENDIX C . Quality cost categories and types of costs 83 APPENDIX D. Causes of defects in Hungarian buildings 85 APPENDIX E. Building defects in The Netherlands 87 APPENDIX F. Building pathology related terms 89

WHAT'S A DEFECT ?

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1 Introduction

Though 'building pathology' may sound new, the treatment of building defects is surely not a new phenomenon. As early as the year 2200 BC, Hammurabi's Building Code testifies to rather rigorous punishment in case of building failures (Figure 1). This illustrates that building pathology is not only related to defects, but also to matters of liability.

A I f a builder build a house for a man and do not make its construction firm and the house he has built collapse and cause the death of the owner of the house - that builder shall be put to death.

B If it cause the death of the son of the owner of the house - they shall put to death a son of that builder.

C If it cause the the death of a slave of the owner of the house - he shall give to the owner of the house a slave of equal value.

D I f it destroy property, he shall restore whatever it destroyed, and because he did not make the house which he built firm and and it collapsed, he shall rebuild the house which collapsed at his own expens.

E I f a builder build a house for a man and do not make its construction meet the requirements and a wall fall in, that builder shall strengthen the wall at his own expense.

Translated by R.F . Harper 88Code of Hamnurabi81 p.83-seq.

Jacob Feld 1922

Figure 1. Laws of Hammurabi (from the book Vonstruction Failure" by Jacob Feld, publ. J. Uiley & Sons Inc.. New York)

Today's defect investigation is more complicated due to the increasing complexity of buildings, materials and systems and to an increasing rate of developments in our societies. Furthermore, there is a growing need for more effective handling, more ready access to available knowledge and more feedback.

Some major definitions have to be given firstly:

- Building Pathology ( ' B P ' ) = the systematic treatment of building d e f e c t s , t h e i r causes , t h e i r consequences and t h e i r remedies.

- Defect - a s i t u a t i o n where one or more elements do not perform i t s / t h e i r intended func t ion ( s ) .

- Failure = the termination of the a b i l i t y o f an i tem t o perform a required f u n c t i o n .

- Anomaly = an indicat ion of a poss ib le d e f e c t .

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j MEASURESOF ! IMPROVEMENT

Though the definitions of 'defect' and 'failure' seem almost identical, they do not have the same meaning. The term defect implies a shortcoming in respect of some normative or even perceived standard. But the defect may lead - by some means - to a situation in which a specific required function cannot be fullfilled any longer. A crack in a partition wall can be considered as a defect. It depends on the functions of the wall and o n , for instance, crack-width whether the wall fails in performing its required functions.

REMEDIAL MEAS. PREVENTlAL MEAS.

The type of defect may vary widely; from a minor crack to a major collaps. Obviously, the latter implies a failure, i.e. the termination of required use. Also; BP is more than just a science that studies the influencing factors and the mechanisms of degradation processes in building materials and structures. Many aspects may be the subject of BP and several relations exist with other activities in the building field.

Normally, a manifested or supposed defect requires action from a 'building pathologist'. And, in fact, there are building pathologists who make a living out of defects. But on a more macro-economic scale, losses due to building defects are a matter for concern. From the point of view of interests - i.e. the building pathologist on one hand and society on the other hand - a distinction between the treatment of a single case (Figure 2) and the treatment of several types of defects (Figure 3 ) can be made. Figures 2 and 3 together represent the main elements of the 'BP domain'.

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DESCRIPTION OF j FAILURE

i I I I

! ! ! ! ! ! ! ! ! i

! ! ! ! ! !

1

Y Y SEARCH FOR METHODOLOGY DEFECT OF INVESTIGATION

METHODOLOGY CAUSE OF INVESTIGATION

outputto: -

( _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ * COSTS

Figure 2. Elements of the 'BP domain' for a single case

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For the sake of completeness, Figure 2 starts with a failure as the possible consequence of one or more defects. But as outlined before, defects may occur without leading to failure. Assuming that a defect is confirmed by objective signs, the next stage is to search for cause(s) and for measures that prevent or cure the defect. The way of handling may vary from a simple observation plus statement to a consultation of an expert system (if available), or to a more elaborate investigation. Whatever the way of handling may be, two matters are important. Firstly a clear and accurate description of the defect. Secondly a suitable method of investigation that leads to the most probable cause(s). A suitable methodology requires relevant expertise and a deducing mechanism. The methodology depends on the 'case'. The most simple mechanism could be a brief checklist; the most elaborated one could be the inference mechanism of an expert system. In between, the use of fault tree analysis can be mentioned.

Building pathology should not only offer information to direct involved parties - on some specific defect - but also information for matters like liability and insurance, costs of defects, quality assurance, regulations and the building community in general. This latest kind of information is generally given by way of publications, articles, information sheets, seminars, etc. But it is questionable whether such output is always effective in preventing defects.

!

! METHODOLOGY

! 3. ! I

REGISTRATION ! METHOD !

1 Figure 3. Elements of the 'BP domain for several types

of defects

i

It may be stated that a general need for more systematic feedback from experiences and knowledge exists. Such feedback should preferably be an

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element of a broader system that encounters several types of defects (Figure 3 ) . This leads to the necessity of collecting, recording and evaluating data, to cost/benefit analysis and to providing information to involved bodies like: regulations and code makers, designers, contractors, implementers of quality assurance systems, insurance companies, planners, etc. Such output can be quite different for different users of the information. It mainly comprises: number and/or frequency of several specific defects, actual causes, characteristics of the degradation process, losses or costs involved and appropriate remedial and/or preventive measures. The basis of such a system is formed by a databank. And in fact, several countries have one or more databanks which records cases of defects. But very often these banks have limitations with respect to accessability and the amount and types of recorded cases.