Bridge Building & Destruction

I have built a bridge using simple primitives and now want to damage it. I plan on dropping bombs onto the bridge and showing the corresponding holes in the bridge. My idea is to somehow create a sphere that I can put at different points that “eats” or erases the bridge wherever it touches it. Thus before the bridge is displayed to the user, invisible spheres could be placed at various locations and make it look like the bridge had been hit.

So far I have tried using stencils with 1’s and 0’s, but I don’t get the results I want.

Any ideas?

This is referred to as Constructive Solid Geometry (CSG). I bet a google search will give you some nice websites which discuss this topic.