At least 20 people are dead and 120 are missing after the Champlain Towers South condominium in Surfside, Florida abruptly collapsed last week. As rescuers continue to search for buried victims, investigators have started sifting through building records, videos, and physical wreckage to determine what, precisely, caused the structure to fall.
While it’s extremely uncommon for a building to collapse in the absence of a natural disaster like an earthquake or hurricane, there are a handful of reasons why it could happen, three structural engineers told Insider.
Some of the most likely causes include poor maintenance or overloading part of a structure with too much weight. Buildings are designed to hold up to twice as much load as is deemed necessary — but that strength decreases as a building ages and deteriorates over time.
“Very simply, structures collapse when the load that is placed upon them exceeds the strength of the structure,” Ronald Hamburger, a structural engineer with the national engineering firm Simpson, Gumpertz, & Heger, told Insider. (A member of that firm, not Hamburger, is helping investigate the Surfside condo disaster.)
Erosion under a building’s foundation, a corroded exterior, or a design flaw could also make a structure more vulnerable to collapse.
Here’s how five problems may contribute to building collapses like the one in Surfside, Florida.
The building isn’t properly maintained
Most often, a sudden collapse can be traced back to poor maintenance, experts said. That may include a lack of new paint, or a failure to shore up cracks in concrete and eliminate rust and stagnant water.
“You can have a perfectly designed building, and a perfectly constructed building per the engineer drawings, but if that building doesn’t receive proper maintenance, that is an issue,” Joel Figueroa-Vallines, a structural engineer from Orlando and member of the American Society of Civil Engineers, told Insider.
“Buildings are like anything else — the cars we drive, or even ourselves as human beings,” he added. “If we don’t maintain ourselves, we don’t age well.”
In Miami-Dade County, where Champlain Towers South is located, buildings are recertified 40 years after their construction. Builders finished the condo in 1981, and it was due for its 40-year inspection this year.
Some experts said that’s too long to wait.
“If maintenance or inspection happened every five years, think of how much safer that would be,” Kit Miyamoto, a structural engineer with Miyamoto International based in Sacramento, California, told Insider.
Part of the structure gets overloaded
A collapse can occur if there’s more weight on one part of a building than the structure is designed to handle — what’s known as overloading.
In 2015, six people died in Berkeley, California when an apartment balcony collapsed during a party. While part of the balcony had rotted, Miyamoto said, the excessive weight catalyzed the fall.
Overloading also contributed to a factory collapse in Dhaka, Bangladesh eight years ago.
Land underneath the foundation moves or erodes
Buildings “very rarely naturally fall,” Miyamoto said, adding, “maybe every five years or so you hear of an abrupt collapse worldwide.”
But sometimes, wind and running water can erode the soil underneath a building’s foundation, or cause the land to sink. When these events happen, “it creates a vacuum that would definitely cause an instability,” Miyamoto said.
In the case of the Surfside condo — which is built on top of reclaimed wetlands — it’s possible that a large amount of groundwater is flowing back and forth under the building, which could exacerbate erosion, Figueroa-Vallines said.
Steel and concrete deteriorates over time
All three engineers agreed that deterioration could play an outsized role in building collapses like the recent disaster in Surfside.
As building materials interact with chemicals in the air around them, those materials start to break down.
“Buildings and structures located in coastal environments where they are repeatedly exposed to salt-laden air experience more corrosion than structures located in central US,” Hamburger said.
After four or five decades, a concrete and steel structure is vulnerable to substantial rusting, he added.
That’s why continually repainting a seaside building is critical, because the coating protects it from damage.
“Salt essentially melts away the concrete,” Figueroa-Vallines said.
The building has a design flaw
Typically, buildings are designed with redundancies — if part of the structure fails or weakens to the point that it can’t support the building’s weight anymore, that load gets redistributed somewhere else. If the floor of an apartment building caves in, for example, it shouldn’t drop to the floor below it.
These local accidents can be caused by several factors — a fire, corrosion, or even a truck backing up into a weight-bearing column in the building’s basement, Hamburger said.
Normally, they shouldn’t cause a catastrophic failure like the one at Champlain Towers South, he added. But some older buildings lack redundancies that stop local accidents from cascading into bigger, building-wide problems.