What are the 2 bright flashes at the beginning of the collapse video? Maybe power cables being severed but looks too bright for that. Lightning strike? I've seen unbelievable structural damage from lightning. If there was roofing work being done, there are three common collapse occurrences: plugged roof drains causing water ponding (extreme weight), improper storage of new roofing materials/equipment causing localized stress, and fire from torches. Deterioration of concrete may in fact be the cause but a total collapse from that would be somewhat surprising to me. Roof (or other construction) work would be the first thing I'd need to rule in or out. -- retired forensic structural engineer.
