1988 nor'easter structural collapses (New Jersey/Pennsylvania)

"300-year storm" Pennsylvania snowstorm collapsed mall/shopping-center roofs supported by mini-mill bar joists. Mini-mills had competed by varying truss member thickness using mid-1980s PCs (128K RAM, 20MB disk) — but the computer models assumed symmetric concurrence at joints, while as-built joints had small offsets producing shear loading. Steel sheared just like Hyatt Regency. Tom got two years of forensic work from this storm.

I've seen the same thing on roof collapses in buildings. In Pennsylvania, we had a snowstorm in the 1980s — the 300-year storm. Go to the weather channel, they have stories about this storm. I had work for the next two years on roof collapses. In that particular case, this was before computers got quite as sophisticated, and you're going to learn about safety factors tomorrow, but the building safety factor is 1.67. The 1.67 came about historically — people found that was good enough that we didn't have lots of buildings falling down.