Well, if you were that worried, you could upgrade your Mortar and open fire on the bridges, a lengthy process but it works.
Another similar way would be to us Commander's Arty, but the mortar would be a better way.
Honestly if I can't blow it up myself I do this:
X=Tank Trap
_=Wire
-=Sandbag
O=Mines(For Soviets, Mines are found on Tank Hunters and Mechanics, NOT Ingenery. A line of Mines represents 2, maybe 3 depending on the bridge)
My Side of the Bridge
----------------------------
_________________________
0000000000000000000000000
XXXXXXXXXXXXXXXXXXXXXX
_________________________
Enemies' Side
I usually put down Wire for the first layer because tank traps can be a long process, and wire can hold off any early scout vehicles like Motorbikes or Schwimmigans.
It's a VERY lengthy process to carry out that system, but it seems to work often.
The only occasion that it fails is when you have a Tiger or a Panther roll through it. But that's what the mines are for ;) The engines on the beast are actually very easy to break.
The sandbags are for any kinds of Mortars or Tank Hunters whom like to hide in heavy cover >: )
Wires keep out infantry, and tank traps + Mines cover Tanks.