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Update Provides New Surfside Collapse Insight
The National Institute of Standards and Technology recently shared new details of the investigation into the partial collapse of the Champlain Towers South building in Surfside, Florida.
At a meeting of the National Construction Safety Team Advisory Committee, they highlighted preliminary evaluations of the data collected on site conditions and additional deviations from design in the construction of the building’s pool deck.
“Understanding exactly what caused this collapse is taking meticulous investigation and the collection of copious amounts of evidence and information,” said 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.”
Tower, Collapse Background
The complex was built in 1981 by late developer Nathan Reiber and Nattel Construction, which is listed as inactive in state records. Since the collapse, media outlets and the City of Surfside have uncovered documents surrounding the structure’s condition. According to a 2018 inspection report from Morabito Consultants, the condominium had “major structural damage” to its concrete structural slab below the pool deck that needed “extensive repairs.”
These damages included descriptions of abundant cracking and spalling throughout the columns and walls, in addition to exposed and deteriorating rebar. The report was generated in preparation for the building’s 40-year recertification.
Update on the investigation into the 2021 building collapse in Surfside, FL:
— National Institute of Standards and Technology (@NIST) September 7, 2023
?? No evidence of sinkholes
?? Additional pool deck construction deviations from design requirements
Get the full details: https://t.co/DlSZYtXKc6 pic.twitter.com/bmEzC06f04
At the time of the collapse, consultants acknowledged that the building was in the early stages of a three-year renovation plan, which had started with roof work about six weeks prior.
Around 1:30 a.m. on June 24, 2021, part of the Champlain Towers South condominium in Surfside, Florida was reported to have collapsed. Made up of three buildings, the towers were each 12 stories tall and contained 342 units. In later reports, it was determined that the partial collapse had resulted in the death of 98 people.
In August that year, the U.S. Department of Commerce’s NIST announced its selection of a team of technical experts to investigate the partial collapse of the Champlain Towers South.
In early investigations of the collapse, the Miami Herald brought to light that the 12-story condominium tower had had multiple, extensive structural flaws present since the beginning of the building’s life—about 40 years.
Reportedly, the plans that came from a firm that no longer exists specified structural columns that were too narrow to accommodate the necessary amount of rebar to support the building. This meant that contractors had to choose between inadequately attaching floor slabs to supports or putting extra steel into columns that were too small.
Most experts weighing in on the matter chose the latter, which is a recipe for air pockets that accelerate corrosion.
In June last year, members of the NIST team investigating the partial collapse of the Champlain Towers South gave an update on their progress during a National Construction Safety Team Advisory Committee meeting.
Although the team has reportedly developed roughly two-dozen hypotheses—both publicly highlighted and others—regarding the deadly collapse, the associate lead investigator said that they have not yet determined a clear initiating event.
At the time, investigators noted that the team would begin invasive testing and preparation of physical evidence collected from the collapse site. This process will involve manipulating evidence, core drilling and cutting of specimens to collect samples, which cannot be fully accomplished in the tight confines of the NIST warehouse where it was previously stored.
Then, at the end of May this year, the Miami-Dade Police Department and National Construction Safety Team reportedly finished moving the evidence into a second warehouse, providing the team with the space necessary to extract samples of concrete and reinforcing steel from the specimens.
According to the release, the “challenging” move of the more than 300 building specimens was managed by MDPD contractors and subcontractors and overseen by NIST staff. The institute also reported that no specimens were damaged and the team followed a strict chain of custody process with extensive documentation.
Then, in June, investigators provided an update, indicating that the swimming pool deck had failed to comply with building codes and led to severe strength deficiency. The NIST team reportedly found that signs of corrosion, misplaced reinforcement and the placement of heavier and additional plant containers on the deck than those in the original plans, alongside design understrength, led to “critically low margins against failure.”
The concrete was allegedly cast in a way that left it permeable to water, consequently corroding much of the steel reinforcement. Investigators also say they found that the rebar was placed improperly into the cast concrete slabs of the pool deck, leaving those sections weaker than required.
Heavy items such as large planters containing palm trees were also placed on vulnerable sections of the pool deck. Structural engineers who work with concrete refer to this as a “punching shear” failure.
Latest Update
According to the NIST release, the team has been studying subsurface conditions of the site to determine if sinkholes or excessive settling of the pile foundations might have contributed to the collapse.
The preliminary evaluation of the data collected reportedly indicates that approximately one quarter of an inch 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. This data did not reveal evidence of sinkholes that could have created voids under the foundation.
Additionally, the team’s preliminary evaluation of physical and historical evidence also revealed how the construction of the pool deck deviated from design requirements, adding to the June speculation.
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, weakening the slab-column connections.
“We have been making progress on a number of fronts,” said 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.”
Average tested concrete strength for various types of structural elements, such as slabs and columns, reportedly continue to exceed the specified design strength during testing. The investigators plan to continue conducting strength tests and detailed statistical analysis before drawing general conclusions.
Based on testing of the building’s structural elements, the team has been able to procure materials similar to those used in the original construction, the NIST reports. 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,” said Bell. “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.”
