Not 100% sure correct forum but here goes.
Am renovating the kitchen and an old oak beam is being replaced by a steel I beam, 2 x pfc bolted together.
It is an old 16c property been messed about with and the joists to the first floor shall we say are not exactly uniform.
Two of the joists actually touch the steel beam whereas the rest miss it by varying degrees from around 2mm to over 20mm. I thought of packing out the joist using steel shims up to around 5mm , and fopr bigger gaps using plywood. Would this seem to be a reasonable approach. Attached is a drawing of the layout.