USAeng:
Well..., at least you know who to blame, and who to sue when things start going south. I would think that most of that damage can be fixed with a little engineering imagination, judgement and experience. It will take a little structural analysis and understanding of how the various members function in the structure, and under what loads, etc., but since it is being repurposed, in house, most of that should already have been done. Some gentle straightening with a hammer, a come-along or a hydraulic jack, maybe a little heat would certainly be in order. Examine the member, welds and joints for ripping which could grow or reduce cap’y. If they are tension members you don’t want to have reduced the net area or allowed a nick/ripped area which can rupture under a tensile loading. If they are compression members the primary concern is slenderness, stiffness and the potential of column type buckling. In both cases a reinforcing angle added over the existing angle would normally be enough. Grind the corners so you get good fit-up and weld the two together. If the material is HDG you would have some welding problems, and the people doing the work should know what they are doing and do quality work, not just be able to melt welding rods. You might want to talk with your local fabricator who could supply the material, and send the right equipment and a qualified crew out for a day or so.