Have you tried using a good old fashioned bomb? Hardliners prefer the IED...
To make a BOMB: Place an empty object in your mission at the base of the bridge you plan to destroy. Name the object TARGET.
Then create an trigger and choose how you want to activated it, for example we'll use Radio Alpha.
In the the trigger's Activation Field put the following:
BOMB = "Bo_GBU12_LGB" createVehicle getpos TARGET;
Start your mission, activate radio alpha and watch it light up the bridge
To make a your BOMB an IED: Follow the above instructions and save your mission.
Then access the mission.sqs file in the mission's folder and use the Ctrl+F feature to find the object named TARGET.
Once you've located your object, change the object vehicle name to bomb.
Then save and reload the mission and your bomb now looks like a pretty IED
id=0;
side="EMPTY";
vehicle="bomb";
leader=1;
skill=0.600000;
text="TARGET";
(Another serving suggestion is to name your player TARGETÂ
)
The above is proberly the hardest way to achieve your objective Ben, but it does work.
Hope it helps.