Interim lessons learned from the Champlain Towers South Condo Building Collapse

On March 7, 2024, the National Institute of Standards and Technology (NIST) team presented an update on its investigation of the collapse of the Champlain Tower South condo tower in Surfside, FL, on June 24, 2021. NIST was directed to do the investigation to identify the root causes of the building collapse as a result of 2002 federal legislation called the National Construction Safety Team Act.

This is a link to the videos from the March 7, 2024, public meeting reports, which are interim findings and updates.

https://www.nist.gov/disaster-failure-studies/champlain-towers-south-collapse-ncst-investigation/public-meeting-videos#March24

The investigators do not draw definitive conclusions about what happened and why, because the investigation will not be complete until later next year, but they identify probable root causes and rank the potential causes of the collapse in terms of higher and lower probabilities.

They consider the underlying soil conditions and uneven building "settling" to be lower probability root causes. They also believe that the design and construction of the columns above the first floor to be of lower probability in terms of their contribution to the result.

They zero in on the pool deck slab and its connection to the columns that come through it and the lower levels of the building columns. These are some of the deficiencies they identified that could have contributed to the rapid collapse of the tower:

• The concrete on the pool deck and in the lower level columns intersecting the deck was of inadequate strength. The way concrete is mixed affects its demand-capacity ratio, that is, the capacity of a concrete slab or column to withstand all the stresses placed on it, including loads, wind, objects banging against it, and, in earthquake-prone areas, seismic stresses. The demand-capacity ratio for the Champlain Towers concrete was too high, meaning that the stresses placed on the concrete were moderately in excess of the concrete's capacity in certain spots, severely in other spots.
• The reinforcing bars (popularly called "rebars") in the slab and the column were improperly spaced within the concrete and, as a result, they both weakened the concrete and created a greater risk of water and chlorine leakage into the concrete, which caused the reinforcing bar to rust and further weaken the structure. Rebar works only when it is optimally spaced and placed relative to the concrete around it.
• Twice as many heavy planters were placed on the pool deck as originally specified in the design, which further weakened the pool deck.
• Drainage was inadequate, which meant that the water and excess chlorine from the pool remained on the pool deck and seeped into the cracks in the concrete.

They are doing further testing and simulation, which is why they do not have definitive conclusions today. But several things are unnerving for someone leading a condo association or running a business in which a building is being constructed, or, for that matter, someone getting a home built or rebuilt:

• The deficiencies in material and labor would not be obvious during construction. Experienced construction company leaders who are watching work being done might spot divergences from good standard practices in concrete mixing or rebar placements, but it would take a highly trained individual to catch something at the time.
• After a building is built, the inspections now required by Florida laws enacted in 2022 and 2023 require an exceptionally high level of structural engineering skill unless problems are obvious. Many problems remain hidden, although premature cracks in concrete are a telltale sign that further investigation and testing are needed. Florida has an inadequate supply of structural engineers to meet the requirements of these laws within the time frames spelled out in the legislation.
• Water seepage is a big issue, because it weakens both concrete and rebar. Our condo association discovered an issue with the rebar on the south wall of our garage, which also serves as the north wall of the swimming pool deck only because we saw water seepage and rusting of the rebar when we retiled the wall. We replaced the rebar and installed new concrete. The firm that installed a fence on the top of the garage deck decades ago had failed to seal the connection between the fence spindles and the deck, which meant that water seeped in from above a little at a time. We are installing a new fence on the deck because the City of Naples has determined that our 42 inch high fence is not high enough, a misguided position, but, nevertheless, an opportunity to do a better job in sealing around the fence spindles when we install the new fence.
• The excessive placement of heavy planters weakened the concrete slabs at Champlain Towers South. Many condo associations love planters because they make a space more attractive. If small trees are planted in them, they also can absorb CO2. But the pots in which the plantings are done are generally very heavy and they put incremental strain on concrete slabs. The Champlain Towers South pool deck went far overboard in installing planters, far beyond what the designers specified.
• The drainage holes were inadequate, and, probably, inadequately cleared to be as effective as possible. Draining cleaning is not a job that property maintenance people like to do, but it is essential to prevent standing water from corroding concrete and rebar, especially if the water is mixed with the chlorine from a swimming pool.
• Preventive maintenance and repairs are essential, but they are often neglected because they add maintenance costs to a homeowners or condo owners association. Condo associations want to keep maintenance costs low, but the new Florida laws will be appropriately harsh in making sure that maintenance and repair get done on strict schedules dictated by structural engineers and get pre-funded based on studies of HOA and condo association reserves.

Over 100 innocent people died because of the Champlain Towers South building collapse. But the NIST investigation recommendations, if implemented and incorporated into building code modifications, might prevent future deaths.

Regrettably, we all want more affordable housing, but we also have to recognize that we want safe, properly constructed housing that will withstand the rigors of weather, heavy objects, and other stresses on load-bearing surfaces. Innovation will produce stronger and more affordable lighter-weight materials, but there will always be a temptation to cut corners to make housing ownership, rental and maintenance more affordable. We have to make sure that housing remains safe.