Tall buildings rarely just collapse. Could it happen near Tampa Bay?

As the dust cleared on the rubble from Thursday’s partial collapse of a condo building in Surfside, structural engineers and residents of high-rise towers both had a similar question.

What happened? And could it happen to my building?

At 40 years old, Champlain Towers South is hardly unique in Florida, where the coasts are dotted with decades-old condo towers. From Tampa’s Bayshore Boulevard to the beaches of Pinellas County, the specter of a sudden, deadly collapse suddenly felt a little more real.

Experts say the catastrophic and seemingly sudden collapse of buildings like Champlain Towers is extremely rare. While they said it’s too early to determine what caused this one, images from the scene suggest the condo building sustained what’s called a “progressive collapse,” said Nick Bradford, a structural engineer with the Structures Group in Tampa.

Progressive collapses happen when one floor of a building sustains enough localized damage that it can’t support the floors above it, and they all come pancaking down. That can be caused by a single incident, like a kitchen explosion, or a foundational weak spot. The effect is similar to that of a controlled demolition, or the 9/11 World Trade Center collapse.

Natural elements can also be a factor. Salt water can oxidize and weaken a building’s rebar, which could theoretically weaken its integrity, said Robert MacLeod, director of the University of South Florida’s School of Architecture and Community Design.

One Florida International University researcher who’d studied reclaimed wetlands in Surfside told USA Today the Champlain Towers building had sunk several millimeters since the early ‘90s. That may have weakened its foundation, the researcher said, though it might not necessarily have led to the collapse.

Either way, in a state where plenty of tall buildings stand on dredged land — including Harbour Island and Davis Islands in Tampa — it’s a consideration investigators won’t ignore.

“The more we intensely use and tax the infrastructure of the earth, the more potential problems we reach,” MacLeod said. “Rising waters are real, and they are certainly going to compromise buildings and cities for years to come. For the next 40 or 50 years, Florida’s going to have rough go of it.”

In Florida, developers of large buildings — at least three stories or 50 feet in height, or encompassing at least 5,000 square feet with a capacity of 500 people — must employ what’s called a threshold building inspector during construction, to ensure they meet certain structural standards.

Local municipalities can pass ordinances requiring more oversight. Miami-Dade and Broward counties are among the few that have, requiring every building at least 40 years old to undergo a structural evaluation every 10 years. Champlain Towers was due for its first such inspection this year. Many other local codes, including those for Pinellas County and the city of Tampa, just refer back to the statewide law.

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Thresholds for fortification aren’t universal. In Florida, tall buildings must be able to withstand hurricane-force winds; but not necessarily tornado-force winds, which can be much stronger; or damage from a powerful earthquake.

And while beams and other support elements — known as structural members — must meet certain capacity load requirements in the event of a progressive collapse, most projects aren’t engineered around that.

“The reason is cost,” said Bradford, the structural engineer. “It’s just more expensive to design a building where you have a bunch of members blown out and your building still stands. It’s like saying, ‘Why don’t we design for tornado loads?’ Because those are twice as strong as hurricane loads, and it would be much more expensive.”

While it could be a long time before we see another building collapse like this one — “Realistically, you probably stand a much better chance of being struck by lightning than having this happen to you at your building,” Bradford said — it might prompt lawmakers to start thinking about how to handle aging towers.

“There has to be a discussion of long-term safety of these kinds of buildings,” said MacLeod, the USF architecture school director. “If this collapse is not pinpointed to something that was a problem in this particular building, then it raises very large questions for the building community, the building inspection community and the engineering community. They’ll have to think twice about the engineering standards of 40, 50 years ago versus today. And I say that knowing that there are great buildings, very soundly engineered, that long ago.”

In some cases, deadly incidents have led to new building laws. After six people died in a balcony collapse in Berkeley, Calif. in 2015, the state passed a law requiring inspections of apartment balconies, decks and outdoor walkways.

The challenge, said Abi Aghayere, an engineering researcher at Drexel University, will be in figuring out what the new standards should be, and how to account for older buildings without them.

“People will probably say that there should be more inspections, the city should inspect the building more,” he said of Champlain Towers. “But this building has been standing for 40 years. We don’t know yet what caused it. Could be a gas explosion, could be a foundation failure. Could be any number of things. We don’t know yet. But it’s disheartening for a building that has withstood hurricanes all these years to just collapse.”

Times staff writer Gabe Stern contributed to this report.