De la Concorde overpass collapse
Contents |
[edit] Introduction
On 30th September 2006 the central ‘drop-in’ span of the de la Concorde highway over-bridge in Laval, Canada, suddenly collapsed onto the road below causing five fatalities and six injuries. This shocked both the public and the professional community. A commission of inquiry was quickly established and reported in October 2007.
The Commission concluded that the collapse was due to a number of factors, none of which was sufficient in itself to cause failure, but which came together on that day. They reflected both technical shortcomings and human failings: the latter amounted to negligence in respect of the construction, and serious lapses in the management of the structure throughout its life.
The de la Concorde overpass structure was built in the 1960s as part of Canada’s post-war infrastructure expansion. The structure was innovative for its time in the manner in which the central span was designed – allowing a single span over the roadway. The in-situ side spans had raking columns. A short cantilever, ending in a half-joint, picked- up the central ‘drop-in span’ of precast prestressed concrete boxes placed side by side. The structure failed at the half joint.
The Commission gave early warning to the authorities of shortcomings they had discovered in the design standards for thick slabs without shear reinforcement in the presence of concrete deterioration. As a consequence, the maintenance inspection standards, and associated quality controls for highway bridges, have been reviewed throughout Canada.
This type of half-joint is no longer an accepted detail: it is vulnerable to deterioration and very difficult, if not impossible, to inspect and maintain. The joint relies on accurate reinforcement placement and good quality concrete. Neither was achieved in this case.
[edit] Lessons for the UK
The Commission of Inquiry concluded that the fate of the structure was found to be determined by:
- Poor design (although in accordance with contemporary codes);
- Failure on the part of the designers to look beyond the design code;
- Poor quality control and supervision during construction;
- Deterioration over its life as a consequence of poor quality materials, salt contaminated water and freeze-thaw cycles;
- Poor maintenance and repair procedures;
- Inaccessibility of critical elements, and
- Failure by the maintaining authorities to act decisively.
Although the UK’s procedures differ from those of Canada, the conclusions drawn by the Commission should be carefully considered, namely:
- Failure of parties to discharge their contractual responsibilities in respect of quality control and supervision during construction;
- Failure of the maintaining authority to relate the maintenance regime to the needs of the structure and its risk profile; inspections were not allocated sufficient time and lacked proper consideration, and
- No one shortcoming was dominant in the cause of the collapse: it resulted from an accumulation of shortcomings over time.
The Commission recommended various measures designed to ensure engaged consultants and contractors are competent, have appropriate staff and identify sub-contracted work. It was also recommended that the performance of engaged organisations be recorded and that appointments take account of these wider issues. However, the inference is that once satisfied, cost determines the successful appointee.
[edit] Commentary
The need to undertake an assessment of highway structure proposals from a holistic perspective stands out from this incident. Good design does not just stem from the application of design codes. It requires consideration of aspects beyond many codes: buildability, required supervision levels, ease of maintenance and whole-life costings.
The UK has developed good practice both within HA and at national level (for example the new HA Bridge Inspection Manual and the CSS Code of Practice for Management of Highway Structures).
Forward-looking authorities are using these guides to manage infrastructure effectively with regard to relative risks. However, the standard at which it is applied does appear to vary (along with appropriate funding). Some authorities are no longer able to provide dedicated bridge engineers to manage infrastructure, nor do they engage consultants to undertake the management function. Occasional engagement of consultants is sometimes based on lowest cost rather than a mix of cost and quality.
The competency of those undertaking inspections is a subject which is attracting the attention of some of the major clients. There is a strong argument for a recognised training regime and NVQ or similar qualification.
The pressures on maintenance budgets will lead to a temptation to delay any remedial work if the safety of the structure can be justified (sweating the asset); although more sophisticated analysis can sometimes support this approach, it requires careful thought by those with suitable competency, and an appreciation of the long-term consequences.
This topic paper was issued by SCOSS in 2008. You can view the original here.
[edit] Related articles on Designing Buildings Wiki
Featured articles and news
Deputy editor of AT, Tim Fraser, discusses the newly formed society with its current chair, Chris Halligan MCIAT.
Barratt Lo-E passivhaus standard homes planned enmasse
With an initial 728 Lo-E homes across two sites and many more planned for the future.
Government urged to uphold Warm Homes commitment
ECA and industry bodies write to Government concerning its 13.2 billion Warm Homes manifesto commitment.
Places of Worship in Britain and Ireland, 1929-1990. Book review.
The emancipation of women in art.
CIOB Construction Manager of the Year 2025
Just one of the winners at the CIOB Awards 2025.
Call for independent National Grenfell oversight mechanism
MHCLG share findings of Building Safety Inquiry in letter to Secretary of State and Minister for Building Safety.
The Architectural Technology Awards
AT Awards now open for this the sixth decade of CIAT.
50th Golden anniversary ECA Edmundson awards
Deadline for submissions Friday 30 May 2025.
The benefits of precast, off-site foundation systems
Top ten benefits of this notable innovation.
Encouraging individuals to take action saving water at home, work, and in their communities.
Takes a community to support mental health and wellbeing
The why of becoming a Mental Health Instructor explained.
Mental health awareness week 13-18 May
The theme is communities, they can provide a sense of belonging, safety, support in hard times, and a sense purpose.
Mental health support on the rise but workers still struggling
CIOB Understanding Mental Health in the Built Environment 2025 shows.
Design and construction material libraries
Material, sample, product or detail libraries a key component of any architectural design practice.
Construction Products Reform Green Paper and Consultation
Still time to respond as consultation closes on 21 May 2025.
Resilient façade systems for smog reduction in Shanghai
A technical approach using computer simulation and analysis of solar radiation, wind patterns, and ventilation.