“At this time, the extent of the damage appears to be concentrated in the south position of the building involving the four floor slabs supported on the east exterior and interior load-bearing walls,” said Jack Tosta, chief building official. “The cause of the damage is unknown as the building is still under construction with work taking place as recently as last Friday afternoon.”
I'd bet it will be attributed to lack of final lateral bracing. Probably off site constructed wall panels that would end up requiring finicky site work to full connect all the lateral systems together to be competent. Those finicky things hadn't been completed yet, and likely not called for a structural inspection yet so they could get flagged as deficient. Or maybe they were currently sitting on the contractor's deficiency list, but "There's no time to get all of that done right now, my crane needs to get off site."
I wonder if it was loss of diaphragm continuity across the transverse direction of the hollowcore planks? Is there typically any sort of rebar placed in the topping? If there were hot-rolled steel framing in lieu of CFS bearing walls it would seem that those beams would tie the perimeter beams into the interior of the building. But the CFS bearing walls were probably not connected to the exterior/perimeter beams to prevent them from moving outward?! In this case it would seem that the only continuity would be provided by the bottom CFS track fastened to the top of the hollowcore planks or even just the topping - yikes!
In the pic below you can see the columns in the affected area seem to be leaning towards the exterior of the building. The vertical lines are all parallel.
Also, I wonder if the slanted shoring (clouded in green) may have had some influence on pulling/pushing the bottom floor perimeter beams (and edge of diahpragm) away from the building?
The lateral system appears to be cold form flat strap bracing in the direction transverse to the hollowcore spans, and hot-rolled diagonal bracing in the long direction.
The bottom level diagonal shores appear to be supporting all of the shores above. You can see that the shore between the red and green clouds is bowing outward.
Also, check out these cantilevers for the balcony. They seem to be moment-connected to the columns but there is no backspan beam on the other side of the column! Double yikes. It seems that would also cause the columns to want to lean away from the building, no? They are shored currently, but was this to be the final framing configuration?
The shoring suggests that the backspan for those cantilevers may have been in the form of rebar developed back into the topping slab. Just speculating… not sure what was going on with that. But those cantilevers sure do look dubious from the photos.
