Most bridges here do, and often when one needs to be demolished and rebuilt, the military blows it up just for practice.
Edit: Source for the sceptics
The deep demolition, which became a central element in Finnish post-war demolition tactics, and especially the development of readiness to counter surprise attacks that emerged as a threat scenario in the 1960s, received significant support immediately after the wars. The decision concerning structural demolition preparations for bridges was made on January 15, 1946. These preparations meant building charge wells, charge chambers, charge pipes, and charge hooks. Authorities responsible for constructing bridges were required to include the aforementioned structures in their plans, which significantly improved the readiness to destroy the bridges.
If it was not possible to place the charge space inside the abutment or pier, charge hooks could be embedded in the supports during the casting phase, to which the charges could then be attached.
Yeah, it does. And it's also designed so that it takes 10 kilograms of pressure to detonate. Are you gonna rig up sideways launchers for each? Perhaps there already are remote detonators that you just replace the normal weight switch with.
But still. I don't buy it. First off why hang them so frequently, and do all the texts speak of charge PITS instead of "charge hooks"?
It just doesn't make sense to me and I just think OP has heard it from someone in real life and decided to believe it and is now spreading it here.
Unless someone can actually show these are for explosives, I just don't buy it.