Structural engineers are honing in on the lowest part of the building for reasons why Champlain Towers South collapsed last week in Surfside, Florida, killing at least 16. 

The big picture: While experts doubt that failures with the pool deck slab alone could have caused the fall of the building, "it may be one of the factors that contributed to the collapse," Jason Borden, a Fort Lauderdale-based structural engineer, told The Washington Post.

• A 2018 report found "major structural damage" in the building's pool deck area, caused by a concrete slab under the deck not sloped to drain properly, per the report's author.

Between the lines: Some experts say a failure at the base of the building may have triggered a "structural avalanche," per the New York Times.

• Video footage shows the center of the building maintaining its integrity as the rest of the building begins to fall.
• Most experts interviewed by WashPost said that the collapse appeared to involve a failure at the lowest levels of the building or in the building's parking garage.

Among the theories cited by engineers:

• “[T]hat part of the pool [area] came down first and then dragged the middle of the building with it, and that made that collapse," Allyn Kilsheimer told The Post.
• “You can see the failure came from the bottom,” said veteran structural engineer and the chairman of the California seismic safety commission Kit Miyamoto.
• "Vertically imploding," suggesting that columns at the bottom were "compromised," per The Post.
• "A foundation-related matter — potentially corrosion or other damage at a lower level,” is suggested by video footage, Donald Dusenberry told The Times.
• "You certainly can’t rule out a design or construction error that has survived for 40 years," Dusenberry added.
• "Punching shear failure," when slabs of concrete that make up a building's floors detach from the structure's vertical support columns, per The Post.
• "Axial failure," which would mean columns suffered excessive stress from compression.

The bottom line: At present, “there is no smoking gun,”Troy Morgan, an adjunct professor of engineering at New York University, told The Post.