All Intensive Purposes

Michael O'Hare, here, has the most interesting discussion of the engineering issues implicated by the bridge collapse that I've seen yet (although it's not like I've spent hours looking -- if there are other good ones, I'd appreciate a tip in the comments). Among many other things, he says:

I will make the conjecture that the bridge deck was calculated as a composite top chord of the trusses and failed in tension over the supports. If this is true, the deck repair may well have been a contributing cause of the failure.