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Netting being installed under 90-year-old College Street underpass to catch falling concrete

Underpass is safe, city engineer says, with major structural review is planned for later this year
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A contractor is going to spend the next four weeks installing netting under the 90-year-old College Street underpass to prevent flaking concrete from falling into the street.

The netting is being installed by Belanger Construction at a cost of around $60,000. 

Built in 1930, the underpass allows traffic to flow beneath the CP rail line running near downtown Sudbury.

And while installing netting to catch falling concrete might suggest the bridge is in a poor state of repair, Stephen Holmes, a city engineer, said structurally the bridge is sound.

“When concrete falls off the outside of a structure, it’s important to know that concrete isn’t actually providing strength, but cover for the rebar,” Holmes said. “It’s corrosion of that rebar that would be a cause for concern.”

From what he’s seen, Holmes said there’s little to no exposed rebar visible on the underside of the College Street underpass.

In 2017, the city contracted a bridge engineer to review the structure. That visual inspection recommended scaling work be done to remove loose, unsound concrete that was flaking off.

Holmes said the bridge is regularly inspected every two years as required by legislation, and more often if issues arise. For example, there have been occasions were a large truck has become wedged in the underpass. When this happens, the bridge is inspected after the truck is removed to ensure no structural damage was sustained.

An inspection near the end of 2018 suggested the installation of netting. Asked why it took more than a year for that netting to be installed, Holmes said he isn’t sure why it took so long.

The 2018 inspection, which was also a visual inspection like the one in 2017, estimated the bridge had around six years of life left in it.

Holmes said a structural analysis engineer is being retained this year to conduct a thorough structural review of the bridge. Based on the results of that review, the city will decide whether the College Street underpass can be rehabilitated or whether it must be replaced. 




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