This would have been perfect situation for some destructive testing.

During night time block all traffic. Then drive radio controlled, overloaded trucks over the bridge every six months.

If the bridge fails, you just saved human lives. If it doesn't, the cost of that project is relatively small compared to pre-emptive repairs. The likelihood of regular load destroying the bridge in the meantime could be managed to be negligible.

It's already used with pressure vessels, because hydraulic testing of them is very safe. Now you would no longer need suicidal truck drivers to do it on bridges.