the problem is the road bridge actually didn't get completely destroyed if you consider that section of the bridge at 6 section it only damaged section 1-3-5 that were in contact with each other it didn't destroyed section 2-4-6 that were alongside it but had no contact with it and those section were just 1m away .
now the rail-road bridge it was 40-50m away and as you distance yourself from explosion the amount of energy you receive reduced by the power of 3 it mean at 40m you receive 64 time less energy than what you receive at 10m and at 50m you receive 125 time less energy than 10m also remain the question of that the railroad bridge is a lot stronger than the car bridge
then my question why an explosion that could not dislodge a plate that was only 1m away from the section it was on could made serious damage to a more robust structure 50m away
It did NOT need to be completely destroy.......If that happen, it only mean it suffered worse, it does not mean it did not suffer failure now.
On the other hand, you quite obviously do not know how radius blast damage work. First of all, you don't even know where the origin of the explosion is, secondly, a blast that big, 40 -50 meters is not really a matter, again, I am suspecting a 2000lb bombs or equivalent, that have a blast damage of 600 meters, so no, it set 50 meters away would not have any different.
And finally, just because the rail bridge did not felt it does not mean it took no damage. As I explained before, the heat damage is added ON TOP of the blast damage, which mean whatever the rail bridge suffered is going to be more than that road bridge and I would say if that bring down the road bridge, it would have been catastrophic, now unless Russia build that road bridge with crap material and shit engineering and that rail bridge on best material and detailed engineer calculation, the damage would be applies to the same loading to BOTH bridge, and just because it did not collapse, now, that does not mean it is not damaged beyond repair.
Now, I will say that one final time, I DON'T KNOW HOW MUCH DAMAGE WERE DONE TO THE BRIDGE. As i said many times before, you have to see and inspect the bridge to know, but judging from the damages done to the other bridge and by a logical deduction, that bridge is gone, it will not be able to fix in just a few days. You can't lay a concrete or metal slab on top of it and call it fixed, I for one will not be willing to drive over that and bet my life on it if you know what I mean, I mean if you want to do that, that's up to you.