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O r g a n i s i n g C o m m i t t e e J o h n C a r p e n t e r K e n C a r p e r C o s t a s G e o r g o p o u l o s T o b y Mottram Neil S a n d b e r g J o n a t h a n W o o d I n d e p e n d e n t C o n s u l t a n t ( C h a i r m a n ) A S C E , W a s h i n g t o n State U n i v e r s i t y K i n g s t o n & B r u n e i U n i v e r s i t i e s , U K U n i v e r s i t y of W a r w i c k S a n d b e r g S t r u c t u r a l S t u d i e s & D e s i g n L t d . T e c h n i c a l C o m m i t t e e S t u a r t A l e x a n d e r s c o s s L u k e B i s b y U n i v e r s i t y of E d i n b u r g h D a v i d B l o c k l e y U n i v e r s i t y of Bristol S e a n B r a d y B r a d y H e y w o o d Pty L t d . D e n y s B r e y s s e U n i v e r s i t y B o r d e a u x 1 E u g e n B r i i h w i l e r E c o l e P o l y t e c h n i q u e F e d e r a l e de L a u s a n n e M i c h a e l D r e r u p W a l t e r P M o o r e A h m e d E l g h a z o u l i S E C E D C h r i s Elliott Pitchill C o n s u l t i n g Ltd Mike F o r d e U n i v e r s i t y of E d i n b u r g h A m r i t G h o s e A E C O M B r u n o G o d a r t D é p a r t e m e n t S t r u c t u r e s et O u v r a g e s d'Art Haig G u l v a n e s s i a n Imperial C o l l e g e L o n d o n P e t e r Hartog B u i l d i n g D i a g n o s t i c s A s i a Pacific-^' R o b H e y w o o d H e y w o o d E n g i n e e r i n g S o l u t i o n s P e t e r Ho L o g i C a m m s Milan H o l i c k y K l o k n e r Institute, C T U J o h n L a n e R S S B W e i F . L e e N a t i o n a l T a i w a n U n i v e r s i t y of S c i e n c e a n d T e c h n o l o g y H a n - L o n g L i u C o l l e g e of Civil a n d T r a n s p o r t a t i o n E n g i n e e r i n g , H o h a i U n i v e r s i t y A l l a n M a n n J a c o b s S t u a r t M a r c h a n d W e n t w o r t h H o u s e P a r t n e r s h i p S t u a r t M a t t h e w s B R E P a u l Mlakar U S A r m y E n g i n e e r R e s e a r c h & D e v e l o p m e n t C e n t e r D e c l a n P h i l l i p s U n i v e r s i t y of L i m e r i c k A l a n P o w d e r h a m M o t t M a c D o n a l d G r o u p Ltd Neil S a n d b e r g S a n d b e r g S a r a h S t a l l e b r a s s C i t y U n i v e r s i t y L o n d o n R i c h a r d W i l l i a m s Mott M a c D o n a l d G r o u p Ltd I n s t i t u t i o n o f C i v i l E n g i n e e r s A l i c i a A l v a r e z G e m m a H o w e l lProject l\/lanager Operations Manager
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P R E S E N T E R
K a r e l T e r w e l
Lecturer and Researcher, Structural Design & Safety, T U Delft
C O - A U T H O R S W o u t e r Boot V o l k e r I n f r a D e s i g n M i r j a m Nelisse T N O vimr-eMTme A U T H O R B i o o R A i - ' H V K a r e l T e r w e l ( 1 9 7 5 ) s t u d i e d Civil E n g i n e e r i n g at Delft U n i v e r s i t y of T e c h n o l o g y ( D U T ) a n d g r a d u a t e d in 2 0 0 1 . F r o m 2 0 0 1 until 2 0 0 7 he w a s w o r k i n g as a s t r u c t u r a l d e s i g n e r / p r o j e c t l e a d e r at Z o n n e v e l d E n g i n e e r s o n c o m p l e x s t r u c t u r a l d e s i g n s like t w o t o w e r s (height: 1 4 6 m ) f o r t h e g o v e r n m e n t in T h e H a g u e . S i n c e 2 0 0 7 he is a lecturer on structural d e s i g n at D U T . In a d d i t i o n , he is w o r k i n g on a P h D - s t u d y o n structural s a f e t y of b u i l d i n g s in T h e N e t h e r l a n d s , w h e r e he is trying to d e t e r m i n e i n f l u e n c i n g f a c t o r s o n s t r u c t u r a l s a f e t y of b u i l d i n g s . T e r w e l is m e m b e r of the D u t c h P l a t f o r m o n S t r u c t u r a l S a f e t y a n d of l A B S E ' s W o r k i n g G r o u p 8 o n F o r e n s i c E n g i n e e r i n g . A B S T R A C T S t r u c t u r a l i n c i d e n t s in T h e N e t h e r l a n d s : a c o m p a r i s o n of t h r e e d a t a b a s e s A f t e r s e v e r a l m a j o r structural i n c i d e n t s in T h e N e t h e r l a n d s , v a r i o u s initiatives h a v e b e e n s t a r t e d to i m p r o v e s t r u c t u r a l safety. R e s e a r c h s t u d i e s w e r e initiated o n t h e c h a r a c t e r i s t i c s , c a u s e s a n d c o n s e q u e n c e s of s t r u c t u r a l i n c i d e n t s . In this p a p e r t h e results of t h r e e of t h e s e r e s e a r c h s t u d i e s a r e c o m p a r e d . E a c h s t u d y u s e s d i f f e r e n t data s o u r c e s : a c o n f i d e n t i a l r e p o r t i n g s y s t e m called A B C r e g i s t r a t i o n , D u t c h arbitration a w a r d s on ' s t r u c t u r a l ' failures a n d a n e w s p a p e r c a l l e d C o b o u w . It a p p e a r s t h a t the reliability of t h e r e s e a r c h s t u d i e s v a r i e s d u e to t h e q u a l i t y of both s o u r c e a n d a n a l y s i s . In a d d i t i o n , a c o m p a r i s o n of the results s h o w s v a r i a t i o n s d u e to t h e t y p e of s o u r c e s u s e d . H o w e v e r , g e n e r a l p a t t e r n s h a v e b e e n d e r i v e d f r o m t h e t h r e e d a t a b a s e s . F r o m this s t u d y it c a n be c o n c l u d e d t h a t c o n t r a s t i n g a n d c o m b i n i n g r e s u l t s of d i f f e r e n t s o u r c e s h a s i m p r o v e d t h e o v e r v i e w of s t r u c t u r a l i n c i d e n t s a n d h a s p r o v i d e d an insight into t r e n d s .
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Structural incidents in The Netherlands:
a comparison of three databases
Karel Terwel TU Delft, Delft, The Netherlands
Wouter Boot Volker InfraDesign, Woerden, The Netherlands Mirjam Nelisse TNO, Delft, The Netherlands
Abstract
After several major structural incidents in The Netherlands, various initiatives have been started to improve structural safety. Research studies were initiated on the characteristics, causes and consequences of structural incidents. In this paper the results of three of these research studies are compared. Each study uses different data sources: a confidential reporting system called ABC registration, Dutch arbitration awards on ‘structural’ failures and a
newspaper called Cobouw. It appears that the reliability of the research studies varies due to the quality of both source and analysis. In addition, a comparison of the results shows
variations due to the type of sources used. However, general patterns have been derived from the three databases. From this study it can be concluded that contrasting and combining
results of different sources has improved the overview of structural incidents and has provided an insight into trends.
Introduction
In the last decade some major structural incidents have occurred in The Netherlands. In 2003 five balconies of a residential building in Maastricht collapsed a few months after completion causing two fatalities (Mans 2010). In 2010 a temporary structure in Rotterdam failed during the casting of concrete resulting in five injuries (Joustra 2012) and in 2011 the roof of a new extension of the FC Twente stadium collapsed during construction resulting in two fatalities and nine injuries (Konijn 2012). These failures, amongst others, drew much media attention and necessitated a response from the Dutch building industry.
The building industry has tried to find answers to questions like: ‘To what extent is a lack of structural safety an issue?’ ‘How can we avoid repetition of similar failures in the future?’ Finding answers to these questions starts with the investigations of structural incidents. Usually this kind of research focuses on single incidents or on comparing incidents from a single source. The research question to be answered in this paper is: ‘What patterns can be
detected from the comparison of various sources of data on structural failures and near misses in the Netherlands?’
Data sources
Various possible data sources of structural incidents are mentioned in literature such as insurance company files, forensic engineering firm files, newspaper articles, reporting
systems of incidents and arbitration awards (Terwel and Waarts 2010). However, only the last three sources could be used for research, as they were publicly available. Most other sources require collaboration with companies that are reticent because of liability issues, bad customer
relationship and fear for loss of corporate image. In the present study a comparative analysis is performed on the results of the three available studies.
A Cobouw database was set up in around 2004 by TNO (Dutch Organization for Applied Scientific Research) based on 230 structural failures that were reported in the Cobouw (Dieteren and Waarts 2009), a leading newspaper for the Dutch building industry. TU Delft developed this into a more extensive database which elaborated the format used by TNO. It currently includes 401 incidents based on Cobouw articles between 1993-2009. The results of this database have only recently been made available.
ABC registration was initiated in 2008 by the Platform on Structural Safety. It is a
confidential reporting system of mistakes in structural design, execution, use/maintenance and demolition, which was set up by TNO (Terwel, Nelisse et al. 2012). The essence of this system is similar to CROSS in the UK. Anyone in the building industry can report mistakes through a website. These mistakes are analysed by structural experts, who publish their results in periodic reports and newsletters. Although the last report dates from July 2011,
consideration is being given to further reports.
The Arbitration database was developed in 2010 in a master’s thesis containing 151 ‘structural’ failures extracted from arbitration awards of Dutch arbitration institutes for construction disputes from 1992-2009 (Boot 2011). Arbitration is a common means of construction dispute resolution in the Netherlands.
The choice of boundary conditions, for instance the definition of failure, varied for the three studies, making a direct comparison of their outcomes somewhat challenging. However, after thorough analysis and minor adjustments of some categories, useful results were obtained. Unfortunately, not all categories could be compared as each source provided different types of data about failures.
Results from incident investigations
Table 1 presents an overview of the process of data gathering and analysis and of the outcomes of the three database studies on incidents.
Table 1: Summary of Main Results
Cobouw ABC registration Dutch arbitration
awards
Gathering process of data
Source of data (Near) failures collected by using search terms in a digital archive of newspaper Cobouw
Voluntary reports of building participants. Over 80% from local building control officers and structural engineers
Arbitration awards found by using search terms in an online database with arbitration awards
Definition failure case
Every case where the (probability of) failure of a (temporary) structure (potentially) endangers persons
Near misses without damage and failures with damage. A building mistake is defined as an error in design, execution, asset management or maintenance threatening structural safety
Cases with insufficient functional or structural performance. Usually damage has occurred.
Indication of reliability of data
Cobouw ABC registration Dutch arbitration awards
Analysis of data
How? Analysis as part of a PhD
project
Analysis by professionals from TNO
Analysis as part of a master’s thesis
Who? Researchers from TU Delft TNO MSc student from TU
Delft
Control by? Approx. 50% was checked
by another person than the one performing the analysis. Comparison was made with results from an earlier database of Cobouw-failures from TNO
TNO. Controlling person was different from analyzing person. Review by steering committee of the Platform on Structural Safety
Review by graduation committee
Publication analysis Report on preliminary outcomes TNO database
Periodic reports and newsletters. Professional evaluation report. Peer reviewed conference paper
Master’s thesis, article in magazine and peer reviewed journal paper
Indication of reliability of analysis
Medium High Medium
Indication of reliability of outcomes
Low Medium Medium
Outcomes
Number of incidents 401 189 151
Years of detection failure
<1990-2009 2000-2011 <1990-2009
Type of structures 72% buildings, 8 cases unknown
97% buildings 91% buildings, 2 cases unknown
Function of buildings
38% residential, 2 cases unknown
40% residential 43% residential, 26 cases unknown Material 28% concrete, 31% steel/metal, 62 cases unknown 24% concrete, 38% reinforcement 26% concrete, over 26% steel/metal, 32 cases unknown Construction elements 24% facades, 15% floors, 1 case unknown
(only buildings regarded)
23% foundations, 21% floors
19% foundations, 19% roofs, 2 cases unknown
Type of damage 51% (partial) collapse, 29% structural damage, 2 cases other
84% no damage 27% (partial) collapse, 33% structural damage, 33% insufficient
functionality, 1 case other
Time of discovery 21% construction, 67% use, 2 cases unknown
27% design, 50% construction
25% construction, 67% use, 9 cases unknown
Phase of main cause 15% design phase, 30% construction phase, 23% use phase, 17% combination, 120 cases unknown 61% design phase, 31% construction phase 26% design phase, 30% construction phase, 19% combination, 16 cases unknown
Type of error 16% design error, 43%
construction error, 16% combination, 128 cases unknown 65% design error, 35% construction error 34% design error, 33% construction error, 23% combination, 15 cases unknown
Discussion of results
Reliability of the incident investigations
The reliability of the incident investigations depends on the reliability of the data source and of the analysis of the data. Often the researchers had to deal with human errors, for which it is usually very difficult to find truthful answers. Especially in an arbitration parties try to avoid liability.
In addition, usually there are several mistakes needed to cause an incident. If a source identifies only one error as the cause, probably not all errors have been identified.
Furthermore, from intensive studies of several major failures, it has been learned that experts can disagree on the main cause of the failure.
The reliability of the data from the arbitration awards is considered to be the highest of the three studies. An arbitration award usually provides detailed information about the structural failure. Arbitrators are impartial and independent structural experts. In contrast, ABC
registration is dependent on only one source, although by calling every reporting person confusion about information is reduced. Therefore it has the lowest number of unknowns per category (table 1). For Cobouw there is a large variation in the reliability of the individual cases. In general the reliability of these cases has to be considered low.
The reliability of the analysis is supposed to be the highest for the ABC registration. The analysis is done by a structural engineer, the checking is done by another engineer and a review is done by a steering committee of senior professionals. The reliability of the analysis for arbitration awards and Cobouw is considered to be medium, because the reviewing process seems to be less thorough.
The reliability of the incident investigations can be considered as the lesser of the reliability of the data and the reliability of the analysis process, because a perfect analysis can never
compensate for poor data. It appears that the reliability of the investigation of the ABC registration and Dutch arbitration awards are better than the reliability of the investigation of Cobouw cases.
Characteristics of cases
Number of incidents
In figure 1 incidents from all three studies are summarized. 54 of the arbitration awards are not depicted because the moment of occurrence of damage is not known.
Figure 1: Number of incidents of all sources, depicted for the year of occurrence of damage or, if no damage resulted, for the year of the unsafe act.
Most of the cases from ABC registration did not result in damage and this system was only active from 2007-2011. In contrast, most of the cases from Cobouw and Dutch arbitration awards did lead to damage and the periods covered are similar. Therefore, to detect possible trends in the number of failures only the cases from Cobouw and Dutch arbitration awards are shown in figure 2. The chosen time span is 1993 to 2004, assuming there is an average period of five years between the damage and an arbitration award.
Figure 2: Number of cases Cobouw and Dutch arbitration awards 1993-2004
Figure 2 indicates an increase in the number of failures. This rise in failures over the years might be explained by an increase in media attention after major failures and a growing litigiousness. However, the increase is in line with an estimated increase of failure costs (USP_Marketing_Consultancy 2008). It seems a decline is starting after 2002. However, from the number of Cobouw cases it can be seen that maximum values were reached in 2006 and 2007, after the period presented in figure 2.
Type and function of structures
Figure 3 shows that approximately 85% of all incidents in the databases are related to
buildings. In comparison, buildings count for approximately 74% of the yearly turnover in the construction sector (EIB 2012). This indicates that buildings seem slightly more vulnerable to failures than civil structures.
Figure 4 shows that approximately 40% of the cases have a residential function. About 55-60% of all buildings in The Netherlands are residential buildings. It is possible that, because there are many small houses, structural failures of individual houses are usually not
worthwhile mentioning in newspapers or the damage costs are too small to start an arbitration procedure. Nevertheless, it seems reasonable to draw the conclusion that residential buildings suffer less often from structural failures.
Figure 4: Function of buildings
Materials
Figure 5 shows that the frequency of failure cases with concrete and steel/metal is similar. It seems that steel structures are more prone to errors, because concrete structures are more common than steel structures in The Netherlands. However, reliable data on the exact number of steel and concrete structures is not available.
Unlike the other researches, the ABC registration recorded relatively more problems with reinforcement. It is possible that local building control, who reported nearly 70% of the cases, more often focuses on reinforcement deviations.
Construction elements
Figure 6 indicates that horizontal elements like floors and beams are more vulnerable to failures than vertical elements like columns. Failures of foundations are also common, which is to be expected because of soft soils and erratic soil profiles in The Netherlands.
Figure 6: Construction elements
Type of damage
Figure 7 shows that Cobouw more often reports cases with partial/full collapse than the other sources. This can be explained, because these incidents attract the most attention. On the contrary, ABC registration usually reports incidents without damage. This is a consequence of the large number of design error reports (see figure 9).
Time of discovery
Figure 8 depicts that incidents from ABC registration are discovered in an earlier phase than cases in Cobouw and Dutch arbitration awards. This follows from the nature of each database; there is little or no sense in media attention or arbitration of errors detected in the design phase, because no damage has occurred yet. Results from Cobouw and arbitration awards show a noticeable resemblance.
Figure 8: Time of discovery
Causes
Phase with main cause
A remarkably large range of outcomes can be observed in figure 9 between the three
researches, especially for the design and use phase. Because most of the mistakes within ABC registration are already discovered in the design phase, it is to be expected that the cause is more frequently found in the design phase.
Type of errors
Figure 10 highlights that the majority of failures are caused by a human error. Only a minority are due to material deficits or force majeure. Design errors might range from conceptual, modeling, calculation and drawing errors to conflicts between calculation and drawing or even the absence of a drawing or calculation. Construction errors might range from the choice of wrong materials or erroneous assemblage of elements to the application of an insufficient amount of material or erroneous sizing. Use errors usually have to do with overloading or sometimes with lack of inspection and maintenance.
The relative number of errors classified as design errors is similar to the number of cases originating in the design phase. Especially in the Cobouw database a larger number of construction/production errors are found than the number of cases originating in the
construction phase, because errors during rebuilding or demolition (category ‘other’) are more often construction/production errors than design errors. Failures originating in the use phase are relatively often ascribed to force majeure, for instance when the current traffic load is higher than could be expected during design of a bridge.
Figure 10: Type of errors
Other contributing factors
All three studies mention underlying factors, like the complexity of the design, number of building participants in a project, absence of warnings, role of changes, time pressure, lack of budget, underdeveloped safety culture, unclear responsibilities, insufficient communication, lack of coordination and control, inadequate codes, the quality of the engineers and workmen, and working conditions. However, comparison of these factors is difficult, because the
researches did not focus on the same aspects, and often insufficient information on these aspects was available.
Nevertheless, the authors would like to highlight some significant outcomes. First, from the Cobouw research it was concluded that only about 15% of the cases could be classified as an unusual design. From this it can be concluded that complexity of design is not an essential requirement for failure. Second, from Cobouw and arbitration award research it appeared that in various cases changes were made in design or construction phase. Without these changes, the failure would not have manifested itself. For 19% of the arbitration awards changes influenced the initiation of the failure. Third, from Cobouw and arbitration award research it is known that in many cases prior warnings were given by persons, after control or inspection,
or by the structure itself, resulting in cracks or exceptional deformations. In the Cobouw database at least 168 cases were found, where physical signs could be observed before damage or failure occurred to the full extent. Therefore, appropriate response to warnings needs more attention.
Conclusions
The type of source used for investigating structural failures can bias the results for one or more characteristics of that failure. Arbitration awards seem the least prone to this. ABC registration finds its strength in the thorough analysis. Therefore, it can be concluded that the outcomes of ABC registration and Dutch arbitration awards are considered more reliable than the outcomes of newspaper articles. However, because newspapers provide a significantly larger number of cases, they can be complementary and can give a valuable insight in trends. Despite these issues results show resemblances and therefore some general conclusions can be drawn. Buildings are involved in approximately 85% of all reported incidents. Horizontal construction elements are more vulnerable to failures than vertical ones. Steel structures tend to be more prone to errors than concrete structures, although this statement should be
supported by additional research. It appears that the cause of origin of structural failure is approximately 35% in the design phase, approximately 30% in the construction phase and less often in the use phase (approximately 8%). A reasonable number of cases have a combination of design and construction errors. Other remarkable outcomes include the influence of
changes in design or construction on failures and presence of warnings given by people or the structure itself. This indicates an opportunity to reduce failure risks by better procedures when there are changes and proper response to warning indications.
It has been shown that combining results of various sources of structural failures gives a more balanced view of the characteristics of structural incidents than a single source. This
comparison study has provided an insight into the causes of failures. Hopefully, this awareness will lead to a safer building industry in The Netherlands.
References
-Boot, W. F. (2011). "Constructieve schade - een analyse van oorzaken aan de hand van jurisprudentie." Tijdschrift voor Bouwrecht 2011/6.
-Dieteren, G. G. A. and P. H. Waarts (2009). Samenvatting analyse van schades. Delft, TNO Bouw en Ondergrond.
-EIB (2012). Verwachtingen bouwproductie en werkgelegenheid 2012. Amsterdam, Economisch Instituut voor de Bouw.
-Joustra, T. H. J. e. a. (2012). Instorting verdiepingsvloer B-tower Rotterdam. The Hague, Dutch Safety Board.
-Konijn, M. C. F. e. a. (2012). Instorten van het dak van de aanbouw van het stadion van FC Twente, te Enschede. The Hague, Dutch Safety Board.
-Mans, D. G. e. a. (2010). Falende constructies: Case-onderzoek naar structurele oorzaken van falen en maatregelen die dat tegengaan. Gouda, CURnet. 232.
-Terwel, K. C., R. M. L. Nelisse, et al. (2012). Confidential reporting of mistakes in structural design and execution. Global thinking in structural engineering: recent achievements. F. Saad. Sharm el Sheikh, IABSE.
-Terwel, K. C. and P. H. Waarts (2010). Measuring structural (un)safety in the Dutch building industry. 13th International symposium on Loss Prevention and safety promotion in the Process industries. G. Suter and E. d. Rademaeker. Brugge: 135-138.
