Overpass tests come up short

Overpass tests come up short
Published: 13 August 2007

Examinations being carried out on 135 overpasses in Quebec Province Canada can’t detect a flaw like the the one that caused the de la Concorde Blvd. overpass to collapse last September, a Transport Quebec director says.

As a result of findings from the Johnson commission investigating the Laval overpass collapse, the province identified a number of structures that needed to be examined by engineers, and have banned heavy trucks on those structures until the analysis is completed.

The cement in those spans will be tested by engineers during the next few weeks. But if the tests being carried out on the 135 structures had been done on the de la Concorde overpass in Laval, it still would have been impossible to detect the structural flaw that led to its collapse, said Jacques Gagnon, director of administration for Montreal and the western region of the province. "We believe that (with these tests) we would not have been able to detect the internal fracture because it was very deep in the structure," Gagnon said.

The type of tests being performed on the 135 overpasses are generally done only when officials believe a structure must be replaced, he said. Officials drill out small cylindrical slabs of concrete from the structures. These slabs - known as "carrots" - are sent to laboratories to be tested.

Inspectors apparently can often tell if a structure is solid even before the slabs go out for testing, Bodnariuc said. If the concrete isn’t discoloured and doesn’t crumble, then it’s usually a sign the structure is safe, he said.