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Originally Posted by HobieMarty
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I’m not sure that that guy is an engineer, as he seems to imply, but he’s pull together some interesting photos that I haven’t seen elsewhere, so the video is worth watching for that alone.
You’ve heard some engineers say in the past few days that they don’t think that this building collapse reflects a systemic problem with all buildings on that chunk of land but that it’s related to peculiarities of this particular building. The only thing that I can think of that might be what they are referring to is one of the things brought up in the video, the design of the ground level parking deck and the waterproofing related to it. Basically, the short version is that that level of the structure was poured flat, so that water tended to not drain from it properly. The assumption is that the waterproofing failed at some point and water pooled underneath it in certain areas for extended periods of time and caused deterioration of the rebar in the slab. I’m of the opinion that there was some differential settlement in the building and that the middle of the building settled more than other areas, which caused most of the deterioration to be in that area.
It’s clear that the ground level slab failed first and that might’ve had two effects on the columns. There would have been some parked cars in the lower level and so the collapse of the slab would have been onto the tops of those cars, which might have given rise to areas of the slab that fell further than others and came to rest in a sloping orientation. That might’ve put some lateral loads on the columns. Also, when the slab fell, it removed some lateral support for the columns, effectively making their unsupported length longer. On some of the smaller diameter columns, perhaps that exceeded their resistance to buckling. It’s also likely that there were some damaged columns, as I saw pictures of columns that had concrete spalled off of them, exposing the rebar inside. All of that, coupled with loads that were not as designed as a result of the differential settlement might be why this thing came down.