Two Failed Garage Columns Began the Collapse That Killed 98 in Surfside

The building had already started to die three weeks before anyone noticed. Somewhere in the gloom of the parking garage beneath Champlain Towers South, in early June 2021, two connections gave way where columns met the slab of the pool deck. No alarm sounded. The tower above carried on as if nothing had changed, its residents sleeping, parking, swimming, while underneath them cracks crept outward and the weight that those two columns had been carrying went looking for somewhere else to go.

That, in essence, is what the National Institute of Standards and Technology now says happened in the slow prelude to one of the deadliest structural failures in American history. On 24 June 2021, the Surfside, Florida tower partially collapsed, killing 98 people.

NIST’s National Construction Safety Team has spent nearly five years working out why. The answer they released this week is not a single dramatic trigger but a redistribution of load, a structure passing its burden from one inadequate connection to the next until there was nowhere left to pass it. When the first two columns failed, their loads transferred to adjacent slab-column connections that were not strong enough to support them. Cracks grew. The deck sagged. And the failure waited.

It’s a peculiarly unsettling way for a building to fall. Forty years it had stood.

The team, co-led by Judith Mitrani-Reiser and Glenn Bell, examined two dozen possible scenarios for where and how things began, then worked through them one by one. They tested concrete, ran geotechnical studies, built physical mockups of the building’s components, interviewed survivors and people who had known the structure intimately, and fed everything into computer models of the collapse. What emerged was less a whodunit than a question of margins.

“When building structures are designed and built to required codes and standards, they have margins against failure, meaning they should be able to support much more load than they are expected to bear,” says Mitrani-Reiser. The trouble at Champlain Towers South was that those margins, she adds, “were too narrow from the start.”

A Building Born Close to the Edge

Where did the slack go? Bell lays the blame primarily at two doors. “The low margins against failure were primarily caused by two factors,” he says: first, “severe and widespread deviations in the building’s original structural design from the codes and standards of the day,” compounded by limitations in those codes themselves; and second, deviations in how the building was actually constructed compared with the design drawings. In other words the tower was already living closer to the edge than its blueprints promised, and the blueprints were not generous to begin with. Decades of added load, including modifications to the pool deck flagged in an earlier investigation update, and the steady corrosion that salt air visits on coastal concrete, whittled what little margin remained.

From those first two failed columns, NIST’s most likely scenario reads almost like a sequence of dominoes set in concrete. The failure spread across the pool deck and the street-level parking structure, eventually unseating the southern edge of the pool deck slab from the wall meant to support it. The slab sagged, then tore away at its northern edge from the face of the tower’s Middle section, damaging two connections there as it went. The collapse then ran through the Middle part of the building, and after it, the East.

Just as telling is the long list of things the team ruled out. Not the vibrations from nearby construction. Not a sinkhole, settling or some hidden foundation failure. Not the hurricane and storm surge that Florida towers are built to weather, nor an explosion, nor a load dropped from a crane, nor the rooftop project underway on the day itself. The villains people reached for in the immediate aftermath were, one by one, shown the door.

Getting the Concrete Right

Some of the hardest work was the least visible. Ken Hover, co-lead of the investigation’s materials science project, has spoken about the difficulty of recreating concrete to match what went into the original 1981 building, a deceptively fiddly task when the answers you draw from it have to bear the weight of a federal finding. Get the recipe wrong and every test downstream is suspect. This is forensic engineering at its most patient: rebuild the dead building, piece by piece, until it tells you how it died. The team now turns to its final report, which will carry all the evidence, testing and modelling behind this week’s findings, along with recommendations for changes to codes, standards and practice.

None of which brings anyone back, and the investigators know it. “We appreciate everyone who has helped with this work, including the survivors and the families of those who were lost,” says Bell. The hope, he adds, is that their input will help make other buildings safer and “help prevent tragedies like this from happening again” in the towers still to be built. Somewhere in the codes that govern the next tower on the next coastline, those two column failures in a Florida garage may yet leave their mark, which is perhaps the only kind of memorial structural engineering can offer.

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