So I can't remember where it was posted but regarding the Crimean Bridge, there was implication that there was a possible drone in the water beneath the bridge.

The idea that the explosion originated from under the bridge is supported by someone by the name of Zahed Amanullah, who is either a civil engineer or is otherwise knowledgable on the subject. Zahed surmises that an explosion originating from the top of the bridge would have been largely dispersed by the road deck and supporting piers, while an explosion beneath the bridge would have disconnected the deck from the supports and resulted in a clean break in the piers.

So picture it something like this. You have several metal rods holding up a long, thin rectangular plane. These rods are very good at absorbing compressive force and, indeed, the compression forces actually serve to harden the material. An explosion occurs in the middle of the row of supporting rods, which lifts the road deck and causes a very sudden release of all that compression. Assuming this very sudden release of compression energy, the same kind that causes earthquakes, doesn't cause the piers to tear themselves apart, they'll likely still be crumbled by the concussive effects of the explosion, and the bridge will collapse along damaged and missing rods until its weight is sufficiently supported again.