An interesting letter to the editor from a structural engineer who claims the bridge design is at fault and not the bolts…
If the issue is in the design and not just a flaw in the bolts , then fixing it just got more expensive.
Engineer explains why bridge failed
There is a design flaw in the Nipigon River Bridge. There are no tie down cables. I designed the first cable stayed post tensioned steel structure in the world in 1974 in suburban Chicago.
The Nipigon River Bridge has no tie downs. A 100 degree F temperature change causes the longest cable to contract up to 3 inches. That cable alone requires 600,000 pounds of force to extend it 3 inches. Thus the bridge curled up. – Chronicle Journal
read full article here