[Alberta's Child]

That's not a bad theory.

With precast concrete, the sections are often subject to more rigorous loading during installation than after they're in place.

In this particular case, it looks like it could just be a simple (pathetic, in fact) matter of the bridge having insufficient support without the suspension tower completed. Who the hell thought this was a bright idea?

[Covenantor]

Looks like a fancy long span truss...there were what seem to be intermediate supports in this photo published by FIU four days age in a PR release.

Wonder where the initial point of failure occurred. Since that deck/truss span was prefabricated and swung into place it was capable of holding itself together while lifted...unless damage happened during hoist an drop. Somebody inspected that placement and signed off on it.