I think this is a sta,ndard term used in construction — though I'm still worried about the 'bar', and exactly how the term is being used in the context.

For example, is this perhaps referring to the type of material used to make I-beams — I wouldn't have called that 'bar' myself, but who knows, without adequate context? It might be necessary to add something like 'profilé' to convey the same idea...

Je crois que "bar" a ici le sens de "armature".