Florida Construction News staff writer
Evidence collected from the partial collapse of the Champlain Towers South condominiums in Surfside has been transferred to the Miami-Dade Police Dept., according to federal investigators.
The National Institute of Standards and Technology (NIST) announced the milestone, saying the transfer became possible once it had completed its extensive review, measurement and testing of critical building evidence extracted from the collapse site. Investigation work is still ongoing, with a projected release date of 2026 for the draft report.
“Our team members were in Surfside within 48 hours of the partial collapse of Champlain Towers South, working in collaboration with the Miami-Dade Police Department and others to help ensure the identification and preservation of potential evidence that could explain the collapse,” said investigative lead Judith Mitrani-Reiser. “Since then, we have conducted extensive testing of concrete slabs, columns and reinforcing steel so that we could understand the condition of the building and the forces acting on it at the time of the tragedy.”
NIST staff members arrived in Surfside on June 25, 2021, and five days later NIST announced it would conduct an investigation under the National Construction Safety Team (NCST) Act, which gives NIST the authority to investigate building failures. The goals of these investigations are to establish the likely technical cause or causes of a building failure; recommend specific improvements to building standards, codes and practices and recommend any research and other appropriate actions needed to improve the structural safety of buildings.
“The collaboration, coordination and cooperation with everyone on site was key to ensuring we would have the evidence needed to understand what caused this tragedy,” said investigation associate lead Glenn Bell. “We were able to obtain over 600 pieces from the site that have provided valuable insight into Champlain Towers South.”
By the end of July 2021, all of the evidence was moved to secure locations, where it was carefully cataloged so that it could be tracked throughout the investigation. In March 2023, a portion of the evidence was moved to a second warehouse so that NIST, MDPD and their contractors could efficiently work with all the pieces as needed to support their investigations.
Finding additional space to securely and safely store the evidence took several months, as the facilities had to meet certain criteria for security, scale and accessibility. The process of preparing the materials for the move and then securing them in their new location took several weeks. This included having a board-certified industrial hygienist conduct air sampling for asbestos fibers to ensure the safety of those accessing the materials.
The additional space gave team members room to extract concrete cores and reinforcing steel from the evidence and allowed them to begin the next phase of evidence analysis. After completing this phase, the physical evidence was condensed, and organized by type, into a single warehouse. MDPD contractors managed the move, which was overseen by NIST staff.
Concrete testing included compression and tension tests that revealed how well the samples would hold up to pushing and pulling forces. Researchers carefully studied the cement and aggregate making up the concrete, and how it had aged. They also measured how water moves through the concrete. This movement depends on how the cement was formulated and impacts the potential corrosion of the reinforcing steel within it. Tension tests of the steel reinforcing bars helped determine the strength and deformability properties of the bars, and the impacts of corrosion.
Despite extensive searching and inquiries, NIST has not been able to locate as-built drawings for Champlain Towers South. The team has therefore relied on the physical evidence to provide insight into how the building was constructed.
An added challenge that has made the physical evidence so important is the lack of video showing exactly what happened. Champlain Towers South had approximately 24 functional security cameras at the time of the collapse that were recording to a digital video recorder (DVR) within the building.
By carefully examining reinforcing steel in the Champlain Towers South evidence, NIST’s experts were able to document the type, degree and variability of its corrosion. This has provided critical information about potential degradation and strength of the overall structure at the time of collapse.
The team was able to “reverse engineer” the materials and concrete mixture used in the original construction by conducting microscopic and chemical analyses of concrete samples extracted from the evidence. This allowed team members to quantify the degree of aging and deterioration in the concrete samples. These analyses also made it possible for them to closely recreate the concrete from Champlain Towers South and use it to build large-scale replicas that are representative of critical structural members and connections from different parts of the building that were likely involved with the collapse initiation or its progression. These replicas are being tested to failure in structures laboratories at the University of Washington and the University of Minnesota. Data from these tests will be used to inform computer simulations that will play a key role in determining the probable initiation and progression of the partial collapse and its technical causes.
The recovered evidence also revealed various ways in which the building’s materials had changed or been changed over time. This included cracking and spalling (cracking or chipping) of concrete, corrosion of steel reinforcement, prior attempts to repair cracks and spalls in the concrete, the addition of new materials and finishes to the building (including concrete planters and landscaping vegetation on the pool deck), and mineral deposits indicative of water leakage through the structural elements.
Videos of NCST presentations to the NCST Advisory Committee provide overviews of the investigation’s progress and preliminary findings.
The investigation team began its work with about two dozen hypotheses of how the collapse may have initiated. Team members systematically considered all the hypotheses so that they could eventually rule out the most unlikely causes and fully understand the most probable.
“To be confident we have determined the most likely cause or causes of this terrible tragedy amongst the many possibilities, we are collecting and analyzing all the evidence we can for and against each hypothesis,” said Glenn Bell. “We are leaving no stone unturned.”
The investigation’s six project teams expect to complete technical work in 2025.
