I wonder what's so special about this bridge for Québec. Europe is full of them and they do not appear to be problematic. On the other hand Seattle has a major problem with a box girder bridge which isn't very old (1984).

Evidently they plan to add a cable-stayed bridge-like construction to this bridge.

They also did this with a box girder bridge in the Netherlands. This bridge was built in 1970 and reinforced in 2010 with a cable-stayed addition. However it carries a vastly different traffic volume than the one in Québec (184,000 vehicles per day).

This bridge was built in 1978, and is problematic since the beginning. Shortly after its opening to traffic, about a hundred sensors were installed to monitor the bridge 24/7, and some load tests were done every now and then. It's after some of those tests, done in November 2021, and monitoring reports showing that the bridge deteriorates faster than expected, that the MTQ decided to close the bridge until the repair to be completed, expected by the end of 2022.
Meanwhile, building of the replacement bridge, a bit downstream from the actual one, and planned since June 2020, will start with some tree cutting this year, and the construction of the bridge itself is figured to start on spring of 2023, in order to be completed in 2025.
Here’s an update on the pont des Piles bridge, on A-55, in Shawinigan, QC, as of April 28th, 2022,
dixit MTQ (original in French).
• The works are going great, so the MTQ can announce the reopening of the bridge as soon as fall 2022.
• Building of the towers begun in mid-April, and the acquisition of the cables are going on smoothly, so they can expect a delivery for the next summer.
• Quebec Transport minister, François Bonnardel, said « Since the beginning of the works, our priority is to reopen the bridge as soon as possible, and we do the best to make it happen. Our teams are giving all they can to assure that the structure will be safe to use ASAP. »
• Laviolette—Saint-Maurice MNA*, Marie-Louise Tardif, said « It’s always interesting to call good news, and this is a good one. The reopening of the pont des Piles sooner than expected is a very positive news. Let’s hope that everything will continue to be good, and thank you for your patience. »
To sum up,…
• Pont des Piles bridge was closed preventively last February.
• Two detour routes were put in place; a first one for local trafic (A-55, routes 153 and 157, 125th Street, rang St-Mathieu, then routes 359 and 153), and a second one for transit and heavy vehicles (routes 153 and 359, then A-40).
• Reinforcement works are actually done in order to take a part of the deck loads by transforming the actual beam bridge to a cable-stayed one.
• Tree-cutting works will be done in 2022 in order to prepare the construction of the new bridge.
• Every effort in order to begin building of the new bridge in 2023 will be done.
* MNA stands for "Member of National Assembly".