re: #109 Nerdy Fish

Pretty much this. Bridges are designed to put support for the majority of the span in a few key places, namely, where they are anchored to the shore or to the riverbed. You impact one of those places, there’s a whole cascade of failures that occurs as the other anchoring points suddenly take on more load than they were designed to take and fail.

The video of the collapse is a perfect illustration of that failure cascade.