I say the rail road bridge is repairable and can be repaired very quickly my estimation is at most 2-3 day even less
only a little fire damage , just fix the guards , throw the burned wagon in water and pull the rest to the shore and fix the rails . its done the fire was on the bridge and the worst part of it was not in actual contact with bridge , and more importantly it was open fire and wind moved the heat away .
but about the road bridge that fall in the water , it clearly show some engineering defect otherwise why they must fall with the wave of the explosion
that is the road bridge and depend on how they want to fix it , they can always make a temporary metal bridge fix until the real fix become ready . but what is important is rail road bridge that seems to have received minimal damage
b the way just look at it it literally fall of from the explosion shock waves , you really wonder about the quality of Russian engineering these days , there is no visible damage to the bridge , who is gonna bet there are lots of pocket that get a lot fatten on building this bridge, oh and your photo showed one interesting matter , only half the road bridge fallen , they probably can use the other half in 5-6 day after properly inspecting it and strengthen if there is some structurally weakened areas