Pacific Standard: How Exactly Does a Bridge Collapse?

Ask a kid, if you can't figure it out. "Fall down, go boom." That's generally the way. If the engineering was solid, obviously a component was not made to spec or unplanned-for stresses overloaded the structure.

I've talked about 'Plastic Steel' having been used to build out attachments on prestressed concrete items in previous posts. You can imagine what goes on with lowest-bidder construction these days.