...Immediately before the collapse, one of the residents saw a hole of sorts opening near the pool.
Michael Stratton said his wife, Cassie Stratton, who is missing, was on the phone with him and was looking out through the window of her fourth-floor unit when, she told him, the hole appeared. After that, the call cut off.
I did not see the back falling separate from the others in the surveillance video and had to look twice at the Times’ enhanced version to see it.
The investigation into what may be the deadliest accidental building collapse in American history has just begun, but experts who have examined video footage of the disaster outside Miami are focusing on a spot in the lowest part of the condominium complex — possibly in or below the underground parking garage — where an initial failure could have set off a structural avalanche.
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Structural engineers were shocked that a building that had stood for decades would abruptly crumble on an otherwise unremarkable summer night.
But three years before the deadly collapse, a consultant found alarming evidence of “major structural damage” to the concrete slab below the pool deck and “abundant” cracking and crumbling of the columns, beams and walls of the parking garage under the building.
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From what can be seen in the video, part of the structure first slumped, seemingly falling vertically in one giant piece, as if the columns had failed beneath the southern edge of the center of the building, not far from the pool. Like a nightmarish avalanche, the failure quickly spread and brought down the entire center of the building. Seconds later, a large section to the east also toppled.
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[Donald O.] Dusenberry, a consulting engineer who has investigated many structural collapses...whose impressions matched those of several other structural engineers who examined the video, said such a failure “would suggest a foundation-related matter — potentially corrosion or other damage at a lower level.” But he said it was not certain that corrosion was the culprit, and added that “you certainly can’t rule out a design or construction error that has survived for 40 years.”
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One other clue that a problem started at the bottom of the building: Immediately before the collapse, one of the residents saw a hole of sorts opening near the pool.
Michael Stratton said his wife, Cassie Stratton, who is missing, was on the phone with him and was looking out through the window of her fourth-floor unit when, she told him, the hole appeared. After that, the call cut off.
...
Explanations for an initial failure at the bottom of the building could include a problem with the deep, reinforced concrete pilings on which the building sits — perhaps set off by an unknown void or a sinkhole below — which then compromised the lower columns. Or the steel reinforcing the columns in the parking garage or first few floors could have been so corroded that they somehow gave way on their own. Or the building itself could have been poorly designed, built with substandard concrete or steel — or simply with insufficient steel at critical points.
Whoa, whoa, whoa. The Times is missing a step. In vertically-ascending order it's, 1) the reinforced "concrete structural slab", singular, below the pool and driving entrance. That is the "foundation", it "supports the design load," that is, it is what the entire building sits on. It is to that foundation that Morabito Consultants found "major structural damage". And if a sinkhole developed beneath that then the foundation would buckle or give way all at once and that would bring down the entire structure all at once. 2) the reinforced concrete pilings which are set vertically in the horizontal concrete structural slab. It is these pilings that the Times has first. 3) the ground-level surfacing of the parking lot and pool.4) The reinforced concrete columns driven vertically into the parking lot surfacing. 5) vertical reinforced concrete columns that are the superstructure of the building and to which each of the twelve floors of the building, and the individidual unit floors are anchored.
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Evan Bentz, a professor of structural engineering at the University of Toronto, said that the best evidence so far had come from the video and some simple reasoning — pointing a finger of suspicion at the supporting columns in the underground parking garage.
“The primary purpose of all the columns in the basement is to hold the structure up in the air,” he said. “Because the structure stopped being held up in the air, the simplest explanation is that the columns in the basement ceased to function.”
😂I love Prof. Bentz.
“The primary purpose of all the columns in the basement is to hold the structure up in the air,” he said. “Because the structure stopped being held up in the air, the simplest explanation is that the columns in the basement ceased to function.”
😂I love Prof. Bentz.
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The structural fiber of the building was largely reinforced concrete. That means the floor slabs upon which apartments sat were made of concrete that was poured around horizontal lengths of rebar, or stout steel rods, that provided critical strength when the concrete dried. Likewise, the columns that held up the slabs were created by pouring concrete around vertical stretches of rebar.
The corrosion of the rebar in the slabs, as revealed in the 2018 report, was probably significant only if it occurred in places where the slabs joined with the columns, Mr. Dusenberry said. Corrosion there could have weakened the connection to the columns, potentially leading to a failure, he said.
Respectfully, but I realize arrogantly, the Times is confused. "The structural fiber of the building "was largely reinforced concrete." But the apartment "floor slabs", like the floor of the condo unit that my chair is sitting on which I am sitting in as I type this, has got nothing to do with this collapse. The Times is mixing their slabs. It is the foundational concrete structural slab that Morabito found had "major structural damage," not the goddamned floor slabs of the apartments!
The same idea holds for the reinforced concrete pilings — deeply buried, vertical supports on which the entire building sat…
Omg Quasis. What do the "deeply buried" "vertical" "pilings" sit on that "the entire building" sits on, sand? You know better than that you just stick sticks of pilings into sand to support a twelve story structure, no, the pilings sit on the concrete structural slab. Come on now, pull yourselves together.
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Danger would emerge only if there had been something like a void or a sinkhole that had caused one or several piles to settle downward and left the others unchanged. That could have threatened the structure that sat atop those piles: columns in the underground parking garage.
...No. a "void" or "sinkhole" would cause the CONCRETE STRUCTURAL SLAB to buckle and crater and the pilings which rest on that would then "settle downward", with extreme prejudice.
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Another possibility is improperly installed piles, [Dusenberry] said.
😂 Alright Quasis.
