In a meeting of the National Construction Safety Team (NCST) Advisory Committee, investigators from the National Institute of Standards and Technology (NIST) (Gaithersburg, Maryland, USA) shared details of their investigation into the partial collapse of the Champlain Towers South building in Surfside, Florida, USA.
As part of this meeting, investigators highlighted preliminary evaluations of the data collected on site conditions and additional deviations from design in the construction of the building’s pool deck.
Shortly after the June 24, 2021, partial collapse, NIST established a team to conduct a technical investigation into its cause. The NCST Act authorizes NIST to investigate building failures and recommend changes to building codes, standards, and practices, with the goal of improving building safety nationwide. NIST’s role under the act does not include determining whether there was a criminal act or violation, and NIST does not determine any associated culpability.
“Understanding exactly what caused this collapse is taking meticulous investigation and the collection of copious amounts of evidence and information,” says Joannie Chin, director of NIST’s engineering laboratory. “Our team members are dedicated to unraveling the complexities of this tragic event, and their rigorous research and analysis will not only help us understand the likely technical cause of the collapse but will improve the safety of our communities.”
The team studied subsurface conditions of the site to determine if sinkholes or excessive settling of the pile foundations might have contributed to the collapse. According to NIST, the preliminary evaluation of the data collected indicates that approximately 0.25 inches (6.4 mm) or less of settling occurred in the pile foundations supporting the pool deck structure and basement, which would have had minimal impact on the pool deck structure. The preliminary evaluation did not reveal evidence of sinkholes that could have created voids under the foundation.
The team’s preliminary evaluation of physical and historical evidence also revealed how the construction of the pool deck deviated from design requirements. Specifically, the team found that the number of slab reinforcing bars centered over vertical columns was inadequate and that the reinforcing bars in the top of the slab in the vicinity of the columns were spaced farther apart than the design required. These deviations weakened the slab-column connections and added to the facility’s low margins against failure.
“We have been making progress on a number of fronts,” says Glenn Bell, NIST’s associate lead for the Champlain Towers South investigation. “If we can continue on our current schedule, we expect our technical work to be substantially completed in late June of 2024 so that we can release our report with findings and recommendations in late June of 2025.”
In May 2023, a portion of the evidence was moved into a second warehouse that provided enough space to safely access the specimens. To date, the team has extracted more than 300 concrete cores and rebar samples and has begun materials testing.
So far, according to NIST, the average tested concrete strength for various types of structural elements—such as slabs and columns—exceeds the specified design strength for those elements. The team says it will continue to conduct strength tests and detailed statistical analysis before drawing general conclusions.
Based on testing the building’s structural elements, the team procured materials similar to those used in the original construction, according to NIST. These materials will be used to build and test structural component mock-ups over the coming months.
“We have also made significant progress on our computer models used to simulate the collapse initiation and progression,” Bell says. “We have extended the model to represent the entire Champlain Towers South building and are populating it with data from many investigative activities, representing the condition of the building at the time of collapse.”
The team is actively seeking additional photos or videos of the building during the collapse and encourages anyone with such images to submit them via the NIST Disaster Data Portal. Members of the public are always welcome to submit relevant information or comments via the portal, email (disaster@nist.gov) and mail, and to sign up to provide comments during meetings of the NCST Advisory Committee, which are announced in advance in the Federal Register.
NIST will continue to provide updates on the investigation’s progress at NCST Advisory Committee meetings and on the investigation website.
Source: NIST, www.nist.gov.