There was another problem -- the beams were spec'd as box section, but what was on the shop drawings was 2 channel sections with the flanges welded together. (l

There was another problem -- the beams were spec'd as box section, but what was on the shop drawings was 2 channel sections with the flanges welded together. (like this: []). The attachment point that supported twice the design load was also compromised by the weld and less competent section. Whoever was checking the shop drawings didn't pick up on the importance of the change. IIRC, either change on it's own would have been marginally ok, the two together weren't. (by marginally, I mean probably wouldn't have killed people but wouldn't be to code) When I was going through civil engineering, there was a big push to use a statistical basis for loads and resistances, rather than using a blanket factor of safety. Loads vary, strengths vary, potentially normally, probably not. But they're described by statistics at any rate. Blunders of this sort aren't, at least on a per project basis.