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Montreal bridge collapse: design and inspection criticised

Report exposes maintenance failures and calls for £252M a year repair spend.
The official report into the fatal motorway bridge collapse in Montreal last year has revealed a catalogue of sub-standard
design, construction, inspection and maintenance.

The conclusions have sent shock waves through Canada's engineering community.

The report, written by former Quebec Premier Pierre Marc Johnson and a panel of engineers, highlights serious errors of engineering judgement throughout the concrete structure's 36-year life.

It makes 17 recommendations to tighten current design and maintenance procedures.

It also recommends that £252M be immediately set aside by the State of Quebec every year for the next 10 years for repairs to ensure the safety of existing structures.

Five people died and six were injured when the Concorde highway overpass at Laval, near Montreal, collapsed without warning on 30 September 2006 (NCE 5 October 2006).

Cars passing underneath were crushed by the concrete slab structure.

Former president of the Canadian Society for Civil Engineering, Professor Saeed Mirza of Montreal's McGill University welcomed the report.
But he said that it highlighted the lack of practical teaching for engineers on the whole life of structures.

"The deficiencies in inspections show a lack of attention to detail that comes from the education system. There is nothing in the education system – it is design, build and forget," he said.

"We must teach students to design for the entire life of the structure, so you can tell the owner that you may have to rehabilitate in 30 or 40 years," he added.

The 40m span reinforced concrete cast insitu bridge was built in 1970. Investigations showed that it collapsed due to a shear failure of the south-east cantilever just 36 years into its 70-year design life.

The report describes inspections carried out on the bridge deck in 1992 and again in 2004 as a "missed opportunity to understand and repair the structure". It added that Quebec Department of Transportation did not keep a coherent maintenance file or documentation for the overpass.

It lists deficiencies in the design and then positioning of reinforcement during construction, and crucially – substandard concrete which did not contain enough tiny air bubbles to prevent freeze-thaw action.

It added that inspection and repairs in 1992 were of "dubious quality" and were in fact likely to have accelerated deterioration.
The report names a number of engineers who were involved with the structure.

These include Gilbert Bossé, who carried out later inspections, even though, the report says, he "does not have any specialised academic training in structures".

It added that Bossé carried out routine inspections in 1997, 1998, 2000, 2001, 2003 and 2004, and general inspections in 1995, 1999 and 2002, after which he reduced the overpass rating down from "good" to "acceptable'.

A more detailed inspection in 2004 by another engineer Christian Mercier also failed to spot that the bridge was about to collapse.

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