Possible Failure Point Emerges in Miami-Area Building Collapse
JAMES GLANZ, ANJALI SINGHVI, MIKE BAKER
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.
Called “progressive collapse,” the gradual spread of failures could have occurred for a variety of reasons, including design flaws or the less robust construction allowed under the building codes of four decades ago, when the complex was built. But that progression could not have occurred without some critical first failure, and close inspections of a grainy surveillance video that emerged in the initial hours after the disaster have given the first hints of where that might have been.
“It does appear to start either at or very near the bottom of the structure,” said Donald O. Dusenberry, a consulting engineer who has investigated many structural collapses. “It’s not like there’s a failure high and it pancaked down.”
“它似乎从结构底部或非常接近底部开始，”曾调查过许多结构倒塌的咨询工程师唐纳德·O·杜森伯里(Donald O. Dusenberry)说。“并不像是高处出现问题然后逐渐压垮。”
The early examinations came as rescuers on Sunday spent a fourth day pushing through the enormous heap of debris created when half the 13-story building, Champlain Towers South, fell away early on Thursday. The death toll climbed to nine as additional remains were found, and more than 150 people remained unaccounted for.
While a number of bridges, overpasses and buildings under construction fail each year, the catastrophic collapse of an occupied building — absent a bomb or an earthquake — is rare, and investigators are struggling to understand how it could have come with so little urgent warning.
“It would be like a lightning strike happening,” said Charles W. Burkett, the mayor of Surfside, Fla., where the collapse occurred. “It’s not at all a common occurrence to have a building fall down in America,” he said. “There was something very, very wrong with this situation.”
“这就像发生了雷击，”发生坍塌的佛罗里达州瑟夫赛德市市长查尔斯·W·伯克特(Charles W. Burkett)说。“在美国，建筑物倒塌并不常见，”他说。“这种情况非常、非常有问题。”
The National Institute of Standards and Technology, a federal agency, was sending scientists and engineers to do a preliminary review, hoping to identify and preserve materials that might help understand the collapse. Officials said they expected a number of local, state and federal agencies also to be involved in the inquiry, though it was not clear which agency would lead the effort.
联邦机构美国国家标准与技术研究所(The National Institute of Standards and Technology)正在派遣科学家和工程师进行初步审查，希望能够识别和保存可能有助于查明坍塌原因的材料。官员们表示，他们预计一些地方、州和联邦机构也将参与调查，但尚不清楚哪个机构将领导这项工作。
The search for an explanation comes with a sense of urgency not only for sister buildings near the complex but also for a broad part of South Florida, where a necklace of high-rise condos, many of them decades old, sits on the edge of the Atlantic Ocean, enduring an ever-worsening barrage of hurricane winds, storm surge and sea salt.
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.
While no definitive conclusions could be drawn from the surveillance video, which was shot from a distance and reveals only one perspective of the disaster, some of the engineers reviewing it last week said it seemed to suggest that the failure began at a specific point near the bottom of the structure — perhaps as far down as the parking garage beneath the building, or on the first few floors.
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.
Mr. Dusenberry, 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.”
Rick De La Guardia, an engineer based in Miami with experience in forensic investigation of building component failures, said that the collapse could have also started higher than the foundation, possibly on the second floor, based on his cursory review of the columns in the floor plans and his review of the video.
迈阿密工程师里克·德·拉·瓜尔迪亚(Rick De La Guardia)在建筑部件故障的司法调查方面有着丰富的经验，他说，根据他对平面图中的支柱的粗略审视和对视频的审查，坍塌的起点也可能高于地基，可能在二楼。
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.
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.”