I posted my theory in the Fraggle Rock thread, but it really belongs here:
I think the condo collapse is related to corrosion. No proof, but my gut tells me. No sinkholes in Miami (not a recharge area). I doubt it’s from settlement. Not a lot of clay in this area of florida and any settlement from sand would have occurred soon after construction in 1981. Clay is where you get most long term settlement. What decays after 40 years? Steel exposed to chlorides can and this thing sat right next to the Atlantic Ocean. Perhaps the rebar was not designed with thick enough sacrificial steel.
Now I’m also hearing there was work being done on the roof. However, unless they dropped a crane on that roof, I doubt some small equipment should have led to any collapse.