It is still unclear exactly what caused the partial collapse of an oceanfront condo tower in Surfside, Florida, causing some units of the 12-story building to collapse.
Experts are still trying to determine the exact factors that led to the disaster. But from what investigators know, the building appears to have fallen into a “crepe collapse,” Miami-Dade Fire District Chief Jason Richard told CNN, although there was evidence of other types of collapse are also present.
Pancake collapses are dangerous and serious, and their damage can complicate search and rescue efforts. Here is how they happen.
About pancake collapses: Pancake collapses are so named for the way that collapsing floors land and pile up as they fall, said Gregg Favre, executive director of St. Louis Regional Response Systems, a former commander of the St. Louis department. St. Louis Fire and a senior member of the Special Rescue Team.
“Pancake collapses tend to ‘pile’ floors on themselves, bringing all of their almost square weight to the floor below,” Favre told CNN. “It continues downward, accumulating more weight and stress as the structure falls.”
A crepe collapse is a “progressive failure” that often begins at the bottom: a load-bearing element is damaged, usually in the lower floors or foundations of a building, which triggers the vertical collapse of the upper floors into the lower floors. said Necati Catbas, professor in the Department of Civil, Environmental and Construction Engineering at the University of Central Florida. “Once there is ‘no’ support for the lower floors or foundations, the upper floors start to hammer up and down in a gradual fashion,” Catbas said in an email to CNN.
Why they are dangerous: A crepe collapse is more dangerous than other collapses, Favre said, because there are often few voids, or pockets of space and air, in the rubble. “The tonnage of material (…) makes it very difficult for empty spaces to exist,” Favre said.
Pancake collapses also complicate search and rescue missions, he said, as the structures that remain near the collapse site are unstable and could fall when rescuers move through the rubble.
However, voids can still be present, especially when multiple types of collapses are present, such as the Surfside incident, said urban search and rescue expert Scott Goldstein.
Goldstein told CNN that there was evidence of four types of collapse in the Surfside incident. Aside from a crepe collapse, this includes a V-shaped collapse, where the center of the floor collapses and creates voids on either side; a shed collapse, when a floor collapses on one side while the other side is still attached to a wall; and cantilever collapse, when a wall supporting floors is damaged but the opposite wall is intact. Void spaces are more likely in V-shaped, lean-to and cantilever collapses.
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