Thanks. This has been a hot topic of discussion around the office and on our sites under construction. Not doubting that someone could have shorted the rebar, but that’s a lot less frequent than one might think on highrise construction. It’s not that there is more inspection (there is), but with a larger project, the amount of money that would yield is such a small percentage that there just isn’t much incentive.
The available photographs do show some corrosion in the bar and accompanying spalling in the concrete (the bar swells as it rusts and breaks the concrete cover), so that probably contributed.
The current favorite theory at work is that corrosion lead to a local failure at a column cap, and a punching shear failure on the pool deck. That lead to a progressive failure on the deck, and since that deck was tied in to the tower columns, those may have been pulled out of plumb, leading to the tower failure. That’s all conjecture from looking at the video and the plans, of course.
The good news is that NIST is on site. Those guys are serious nerds, and are not fully under control of the lawyers. They’ll figure out the things that lead to the failure, and put it in a very dense report with a lot of math. For sure this will lead to improvements in the next few code cycles, hopefully this terrible tragedy won’t be repeated.
Back in the 1980s during the construction boom, I spent a year living on Marco Island south of Naples. On many early mornings on the way to work, I stopped at the island's main convenience store for coffee and a donut. On weekdays, the place would be jammed with construction workers buying beer and drinking in a nearby vacant lot. More than a few began the work day getting hammered before going off to tie rebar and pour concrete, among other things.