Evidence of structural damage before the collapse emerges as search-and-rescue operations enter a sixth day.
Video released by a team of United States federal investigators shows more evidence of extensive corrosion and overcrowded concrete reinforcement in a Miami-area condominium that collapsed in June, killing 98 people.
The National Institute of Standards and Technology also announced Wednesday that it will conduct a five-pronged investigation into the Champlain Towers South collapse, which will be led by Judith Mitrani-Reiser.
“We are going into this with an open mind and will examine all hypotheses that might explain what caused this collapse,” Mitrani-Reiser said.
“Having a team with experience across a variety of disciplines, including structural and geotechnical engineering, materials, evidence collection, modeling and more, will ensure a thorough investigation.”
The video shows densely packed steel reinforcement in various sections of the building, along with extensive corrosion where one column met the building’s foundation.
Firefighters officially ended their month-long search for bodies in the debris of the collapsed Surfside, Florida condo building on July 23.
Early on, investigators probing the cause of the condo building collapse found evidence of water damage and structural corrosion so severe the building’s owner association had estimated it would cost $15m to repair.
“The corrosion on the bottom of that column is astronomical,” Dawn Lehman, a professor of structural engineering at the University of Washington, told the Miami Herald.
She said that amount of corrosion should have been obvious and documented as part of the 40-year inspection that was ongoing when the building collapsed on June 24.
“If there’s that amount of corrosion, this should have been fixed,” she said.
The images show beams, walls and columns that appear to be overcrowded with steel reinforcement, which suggests potential weaknesses, she explained.
“There is no reason there should be that kind of bar congestion,” Lehman said.
The risk posed by “congested” vertical rebar in columns would have been even worse in spots where the rebar overlapped, which is known as “lap splice” regions, Abieyuwa Aghayere, a Drexel University engineering researcher who also reviewed the video, told the newspaper.
While it’s already congested with rebar, at the splice regions, it would have been “even further congested”, Aghayere told the Miami Herald.
He said he was struck by how “powdery” and white the concrete in columns appeared in the newly released video. Stone-like aggregates used to strengthen concrete during construction typically remain visible, but they were not in the images from the collapse site.
“The white color just stuns me,” Aghayere told the newspaper. He added that instead of seeing aggregate material mixed into the concrete, “it’s just homogenous,” which is a likely indication of saltwater damage.
He said it is impossible to tell from just the images whether the concrete used in the original construction was weaker than the designs called for, or whether the apparent weakness was due to damage over time.
“It doesn’t look like normal concrete to me,” Aghayere said. “What’s going on?”