Possible failure point emerges in Miami building collapse

New York

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."

The early examinations came as rescuers on Sunday spent a fourth day pushing through the enormous heap of debris created when half the 13-storey building, Champlain Towers South, fell away early last Thursday.

The death toll climbed to nine as additional remains were found, and more than 150 people remained unaccounted for.

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.

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 centre of the building, not far from the pool.

Like a nightmarish avalanche, the failure quickly spread and brought down the entire centre 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". NYTIMES