Demolition of the remnants of the de la Concorde Blvd. overpass was called off suddenly yesterday to allow members of the newly appointed public inquiry to investigate the site.

Equipment contracted by the Surete du Quebec was about to begin tearing down the rest of the structure as part of its investigation into the collapse and the deaths of five people.

"Finally, after discussions with the different parties involved, it was decided to delay the demolition to allow the various parties to plan the collection of evidence," said SQ spokesperson Isabelle Gendron.

Motorists will have to wait a while longer before Highway 19 is reopened to traffic. It's not known how much time the extra investigation will take, Gendron said.

Former premier Pierre Marc Johnson was officially appointed by cabinet yesterday to head the public inquiry into the collapse.

Transport Department engineers took photographs and concrete samples from the overpass yesterday, which will be analyzed for clues of structural flaws.
At a news conference yesterday, Anne-Marie Leclerc, the Transport Department's assistant deputy minister in charge of infrastructure and technology, said: "All hypotheses are still on the table and still considered plausible."

Among those were published reports suggesting steel supports were missing from the concrete structure, causing its collapse.

Others have said that corrosion might have played a part, rust weakening the steel bars that run through concrete beams to support it.

The department, which is responsible for more than 5,000 bridges over major roads in Quebec, narrowed the list of structures similar to that of the de la Concorde overpass to 18, four of them in Montreal.

All have received full inspections, Leclerc said, and apart from an overpass on de Blois Blvd. in Laval, built by the same contractor and in the same year as the de la Concorde span, all are safe, she said.

Considered the twin of the doomed span, the de Blois overpass is being used as a guinea pig for more tests, with "windows" cut into the concrete to examine its interior.

Results of the tests are being analyzed by Transport Quebec experts. Five of the overpasses require extra examination, including two in Montreal, Leclerc said, but the follow-ups are routine.

The two in Montreal are at the junction of Highways 40 and 15 northbound. Esthetic plastic panels along the sides of the overpasses interfered with the full examination and had to be removed, slowing the investigation, she said.

Asked how tests could determine the safety of the spans, considering the faulty overpass passed safety checks a year before it collapsed, Leclerc replied that investigators were looking for signs of similar weaknesses in the 18 structures.

"As we've seen, it was an exceptional break, affecting a mass of concrete, whereas normally we would see problems along the joints. ... It's this type of problem that we're looking for."

Transport Quebec will not be doing extra investigations of all its bridges, deeming them not at risk. The structures are examined once a year by engineers.

Leclerc said she did not know at this point which companies were responsible for the construction of the overpass, or whether the Transport Department would be paying closer attention to any spans built by the same firm.