Crews working on the troubled 102 Avenue Bridge in Edmonton will not be able to do concrete pours through the winter due to safety concerns.
"To pour concrete on the bridge, we would require sustained temperatures of at least 5C," said Laura McNabb with the city's Transportation Services. "At this time of year, that's no longer a reasonable expectation."
The contractor examined the possibility of erecting a tenting structure over the entire bridge in order to maintain the necessary temperatures, but a combination of the heat inside and freezing temperatures outside could result in ice build-up.
With Edmonton's freeze/thaw cycles there is a strong chance that ice would plummet to the road below and cause damage or collisions.
"A secondary worry was the fact that Groat Road runs through a valley, with the result that winds are amplified via a natural tunnel effect," she said. "Although the tenting structure could be built to withstand winds of up to 90 km/h, we have actually had winds exceed that speed through that corridor. This represents another risk to both workers and motorists should the tent structure collapse."
There was also concern on the part of the city that if it proceeded to pour and the temperature either dropped unexpectedly or something happened to the tenting structure during the pour itself, the contractor would have to remove the concrete and would add significantly to the already long delay.
"It is essential that the bridge be completed properly the first time so that we can open the bridge for good in the fall of 2016 and we can be sure that the structure will meet the 75 year lifespan for which it was engineered," McNabb said.
The project has already faced significant challenges after three massive steel girders buckled in March while being installed. According to the city, a preliminary investigation suggested the buckling was the result of the Supreme Group, a subcontractor responsible for installing the girders, misinterpreting the precise bracing requirements between the last four girders.
The spacing braces failed after the crane released the second to last girder, resulting in the buckling of three girders. For every day that passes after the original project deadline – Sept 30, 2015 – there is a penalty to the contractor for $11,500.