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Konstruktionsteknik, LTH1

Why do structural failures occur?

Sven Thelandersson,Lund University

Sweden

Konstruktionsteknik, LTH

Outline

• Some examples from practice• Investigation of failures in timber buildings• Why gross errors occur?• What can we do about it?

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Example 1: Structural collapse in Kista (Stockholm) 2008

• Sudden collapse of heavy concrete elements during construction of building extension for shopping centre, July 2008.

• One person died and two severely injured• A young structural engineer was sentenced (conditional + fines)• Her company was fined due to lack of control system• All other actors were acquitted!!!!

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The cause of the collapse?

Far too weak!

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The Kista collapse!

• The steel beam was described in one of 800 manufacturing drawings produced by a small consulting company in Sweden

• Drawings were produced in a software system (TEKLA)• Steel elements were manufactured in Finland and delivered to

building site in Stockholm • Control of documentation was only performed by the (sentenced)

structural engineer. • Nobody in the chain detected the error • The publicly appointed quality official was not even mentioned by

the court

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Example 2: Collapse of 3 storey building, Ystad, 2012

• Extensive collapse of three storey building, Ystad, May 2012• Occurred in the night, thus nobody injured• A few hours earlier shoring posts were demounted by construction

workers ignorant about the risk they suffered• Legal issues and conflicts not yet settled. Public prosecutor did not

press charges since nobody was injured or killed.• A report was published Jan. 2014 by the Swedish Accident

Investigation Authority (the first related to building construction)

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After the collapse


Cause of collapse Ystad

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•Steel columns in ground floor too weak (30 % of required capacity)

•Copy-paste in CAD-program from one-storey part of building

•Revision of dimensions was forgotten

•Nobody in the chain detected the error before the collapse

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Steel columns after the collapse(Typical stability failure)


From control plan(Ystad)

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Design/planning Document Remark OfficialStructural issues•Foundation and stability Certificate from

structural engineerSelf control K XX

•Prefab structural system Certificate from structural engineer

Self control K YY XX

Other observations

•Six different companies were involved in design and/or construction of the load bearing system. All had quality control systems corresponding to ISO 9001. •In the investigation after the collapse dozens of errors in the structural system were detected, e.g. •Ties between prefab concrete elements required by the code did not work as it should

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Collapse during construction of railway bridge, Botniabanan (Älandsfjärden)

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•The formwork collapsed during casting of bridge deck•Two construction workers died•Three were severely injured•Significant fines for three companies in the first court sentence•All were acquitted after appeal to higher court


What happened?

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Drawing automatically printed from computer program for trussed rafters conditional on bracing of timber elements in compression. These conditions were not shown in the drawing.

The formwork was therefore constructed with insufficient lateral bracing and collapsed during the first casting operation.

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Several hundred roof collapses during the snowy winters 2009/10 and 2010/11*

• Primarily gross errors in design/execution revealed by high snow load

• Snow loads were still generally below values in the building code. • In a few cases snow drift not covered by the code can have

influenced the situation• Flat roofs were particularly prone to damage. • Typical causes for failure are- Insufficent or lacking lateral bracing- Trapezoidal sheet steel roof plates with insufficient capacity and/or wit

incorrect joints/fastenings• Progressive collapse occurs quite often

* Source: Boverket. Erfarenheter från takras i Sverige13


Survey of failures in wood structures-Joint project Sweden-Finland 2005-2007

• survey– literature (L)– own investigations (I)

• partners number of cases– Limträteknik AB, Falun (I) 12– LTH (L) 67– SP (I) 18– VTT (I,L) 30

total of 127 cases

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Classification of error types causing failure

1. wood material performance2. manufacturing errors in factory3. poor manufacturing principles

4. on-site alterations5. poor principles during erection

6. poor design / lack of design with respect to mechanical loading

7. poor design / lack of design with respect to environmental actions

8. overload in relation to building regulations

9. other / unknown reasons

Materials & products

Construction work

Design/planning

Codes


failure cause – one or more categories (multiple failure causes)

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failure cause (127 cases)

design53%

building process27%

overloading4%

unknown / other5% material

11%

Construction


Example:Siemens Arena, Denmark

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Siemens Arena – the fish shape

72 m(double: center to center 10 m)

5 m

about 6.5 m

No diagonals!

R=175 m

R=380 m


Failure Jan 3, 2003Early morning – no fatalities

No load at failure2 out of 12 trusses failed

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Failure initiationDesign error: Capacity 30% of what it should be


Example: Jyväskylä Exhibition hall, Finland Primary structural element

55 m(center to center 9 m)

4.8 m

Double trusses

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The failure: 2500 m2 of the roof collapsed


Failure initiation

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Only 7 out of 33 dowels were correctly installed

Error in construction


General conclusion from this investigation and other similar published surveys*

*Kaminetzky D. Design and Construction failures – lessons from forensic investigations. McGraw-Hill, NY, 1991.

Failures are predominantly caused by gross human errors.

• Ignorance: Errors of knowledge (inadequate training in relation to tasks)

• Carelessness: Errors of performance (non-professionalactions)

• Greed: Errors of intent (consciously takingshort-cuts and risks to save time/money)

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Typical characteristics for these events i.e. why such errors occur?

• Many different actors are involved in the building process (also for the structural system)

• Not clear who has the overall system responsibility • An integrated documentation of stability and load-bearing capacity,

allowing third part control, is often not made.• Modern computer based tools lead to less possibilities for

independent checking of design.• Time pressure acceptance very low for time-consuming

questioning and criticism in the process • No formal requirements for third party control of design and no

sanctions if adequate control is neglected• This liberal attitude has been introduced in Sweden, in the (futile)

hope that building costs may be reduced

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Experience from 20-25 year of de-regulation of the building sector in Sweden!

• Over-confidence that the market will fix quality assurance by itself• Building costs still increase much more than consumer prices in

general • Sweden is quite unique in omitting requirements for independent

review for important aspects in the building process• The purpose has been to stimulate innovation, not to jeopardise

human safety• My opinion is that we need a much stricter exercise of public

authority at least for issues related to life and limb. • Sharper legal demands might add incentives to increase productivity

and quality in construction

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What should be done?

• Load capacity and stability in buildings must be documented so that qualified independent control is possible. (Result: Involved parties will identify most of the gross errors by themselves)

• Independent technical checking must be performed by qualified third party focussing on eliminating gross errors(Result: personnel with more adequate competence will be involved in the project)

• This evaluation should be organised by public authority• Failures and serious damage events should always be investigated

by experts with high integrity • Experience from such events should be disseminated in a

transparent manner to professionals active in the sector and not be swept under the carpet

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