destroy building with girders in the walls

[tycera]

I have a building I'd like to destroy. I've modelled the walls and a framework of girders inside the walls, pillars etc. What I would like to do is have a different Voronoi on the walls and girders, so that when the building collapses some of the girders are poking out of the concrete. Any ideas? I have two problems .. 1) how do I get a different fracture on the two elements .. and 2) how can I get each girder particle to follow the nearest wall particle?

Thanks.