Converting an old three-bent (two bay) post and beam carriage barn to a work shop, and looking to install a second floor. Existing structure is three 20' bents on 15' spacings, so to keep joist span reasonable, they will be running parallel to the ridge as two 15 foot spans, riding on three girders perpendicular to the ridge. Photos and sketches for reference: Sketches of existing structure: So, plan is a load-bearing framed wall on each end, supporting a new 2 x 10 rim joist, and a girder down the center, to carry the new floor joists, as sketched: Total span of center girder is roughly 19 feet, minus whatever new jack posts are placed under the ends. The big question and/or goal, is eliminating the need for a lally column in the middle of the shop. Floor width is 28 feet by my figuring, as two joist spans of 14 feet each. Standard residential girder tables (interior 2308.9.6) put the max span of four 2 x 10's at 8' - 9" with a 28' floor width, meaning I'd need a lally column mid-span. I know of no tables calling out a solid lumber girder which will span anywhere near 19 feet. Truthfully, I could easily cut the span down to 17 feet, by moving the jack posts (end columns) in 1 foot each (gives better room for the supporting piers, anyway), but even that seems to be off the standard tables. Are there any structural guys out there? What span might four 2 x 12's get me on a 28 foot building width (single floor interior)? My father was a structural engineer, and I had some exposure to it, but I'm in over my head here. Adding to the mix is that there's already a 6" x 6" DF beam in the location of that girder. Seems a 6 x 6 doug fir exceeds two 2 x 10's in Vr and Mr (a little short on E, though), so I'm hoping to keep it there, and sister the new members on either side. Thanks!