Woof...it was a composite beam design done by students at UMO. As I see it, could be one of four mistakes or a combination:
1) Poor design by someone
2) Poor quality control during manufacturing of the composite beams
3) Incorrect concrete placement procedure during the deck pour.
4) Lack of proper girder bracing which could have caused the girders to twist, then fail during the deck placement
Why are we even trying to use composite beams in the first place? This will be a real black eye for someone. In any event, this speculating is way more fun than talking about hawkey.