I'm planning on building a 12' x 40' balcony or mezzanine in a commercial building. It needs to be rated at 100 psf. My plan is to bolt a double 2x12 to the exterior wall 40' across the back and 12' on the right side also supported by 6x6 wood post every 10'. A 12x26 steel I-beam across the front supported by steel columns on each ens and one in the middle. So my beam would span 20' from the center column to the outside columns. I would bolt double 2 x 12's to the web of the i-beam to support joist hangers for 2 x 12 joist on 12" centers. 1 1/4" tongue and groove plywood to finish. My questions: Would the 12x26 beam be sufficient to span 20' and what column size will I need to support the load?