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.
Cutting rebar is much easier than bending it, especially upwards and in a proper curve.
Also, those hooks immensely complicate the concrete framework. (If they were done during the initial pour)
So it's pretty unlikely that they are leftovers from construction.
Cold war paranoia is the likeliest reason.
I appreciate the input from a building perspective and I'll buy that, sure, I don't know shit about pouring concrete.
I still haven't had any rational reason for these to be for bombs. It's just much more effective to have bombs actually in the structure instead of just hanging on it. Imagine trying to blow a safe. Would you do it just by leaning an explosive on it and wishing for the best? Nah. You'd at least try to attach it to the lock somehow.
And every article I can find on bombing bridges in Finland talks about "charge pits", not "a line of hooks well hang explosives off of". So I just don't buy these being military in any way. Not convinced.