Last Wednesday, a high-rise apartment house at 205 Alexander Avenue in the Bronx, part of the New York City Housing Authority’s Mitchell Houses, had a catastrophic partial collapse. Fortunately, there were no injuries, but the building had to be vacated, and as of this blog post being written on Sunday, it was still partially vacated.
Like almost everyone else, I’m waiting for the results of the forensic investigation of the collapse to know what the exact causes were. The preliminary discussion is focussed on an explosion that might have started in a boiler located in the cellar and travelled up a shaft at the corner of the building. The two exterior walls of that shaft are what has visibly collapsed – although, again, I only have the publicly-released information about what happened. Here’s the building in 2021, with the shaft visible on the far left, at the rear corner of the building:
Both links above have pictures of the collapsed shaft.
Given that I don’t know anything beyond what’s in the news, it’s premature for me to discuss the incident at length, but I’ve heard two theories that appear to be based on misunderstanding of the situation, and I want to discuss why. First, a high-rise apartment house losing a corner to collapse immediately triggered a bunch of “this is just like Ronan Point” comments. The Ronan Point building was constructed of precast concrete elements, assembled in the field. That form of construction needs better-than-average quality control to be sure that the field connections have sufficient capacity, and it turned out in the post-collapse investigation that Ronan Point’s connections were badly built. Most buildings from the 1960s – including Ronan Point and the Mitchell Houses – are less resilient than modern construction would be, but the buildings at Mitchell Houses have cast-in-place concrete frames that are generally better for continuity and resilience than precast assemblages. In addition, the damage was so severe at Ronan Point because of progressive collapse, where each floor slab that fell overloaded the floor below, turning a gas explosion caused by an oven on the 18th floor into all of the apartments at entire corner collapsing to some degree. The collapse at Mitchell Houses was in an empty shaft, without floors, and the adjacent occupied spaces, so far, have not been reported to have structural damage.
Second, I’ve heard a number of comments along the lines “this shows that FISP1 is useless.” If the collapse is the result of gas explosion, or something similar, then the state of the shaft’s facade would not seem to be the cause of the trouble.
I expect to be returning to this topic whenever the Department of Buildings releases its investigation report.
- New York City’s facade-inspection regulation for buildings seven stories and taller. ↩︎
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