We haven’t learned enough to make enough of a difference to warrent changing out all of these bridges. If properly maintained they should last indefinately.
Advances in FEA and CAD are great if you want to reduce weight (FEA) or build to tighter tolerances. This is importantin autos and airplanes...Bridges are best left overbuilt and under engineerd. It’s cheaper and more durable that way.
As far as corrosion protection, sacrificial zinc is hard to beat. It would be interesting to see what is being used now. Probably nothing new.
If money as spent on maintenance instead of light rail (reflecting your frustration) then all of this infrustruction should last hundreds of years.
Thanks for the information. Most interesting. We have been slighting the things we should do here in MN