I am deeply saddened by the tragic news of the fatal collapse of Champlain Towers South Condominium in Surfside, Florida early Thursday morning. My thoughts and prayers are with the victims and their families. I hope for the safety of my Urban Search and Rescue friends and their success in finding miracles in the debris of the building.
Structural Engineers take on incredible responsibility when they design and inspect buildings. Most young structural engineers go through sleepless nights when they first take on the responsibility for building designs. In fact, I have stated many times that someone is not truly a Structural Engineer until they have been through these sleepless nights. Throughout my adult life, I have been educated and trained to be a structural engineer to be able to design buildings, became an engineer designing and constructing buildings, and became a forensic engineer investigating problems in buildings. Since day one the fear of a nightmare scenario like this was always in my mind. Fortunately collapses like this are extremely rare. It is now the job of engineers like me to identify the causes of this failure so that future incidents can be prevented.
Tragic incidents have taught structural engineers in the past. The Northridge Earthquake taught about better seismic design. Hurricane Andrew taught about the importance of protecting a building from the effects of wind-blown debris impacts. Ronan Point Apartments, Alfred P. Murrah, and the World Trade Center taught us about Progressive Collapse.
The question I ask myself after a collapse is why did the structure pick this day and time to collapse? Like most catastrophic collapses the Champlain Towers South appears to be a progressive collapse. The failure of a relatively small element of a building causing a cascading collapse of all or a large part of a building. The earliest study of progressive or disproportionate collapse in my library (NBS Building Science Series;98 “Design Methods for Reducing the Risk of Progressive Collapse in Buildings” by Edgar V. Leyendecker and Bruce R. Ellingwood) was published in 1977. The earliest building code reference that I can find is in ASCE 7-02, published in 2002. Both were too late to impact the design and construction of this condominium building. But what was the trigger? Studies of progressive collapse generally address external extreme forces on buildings. These include the World Trade Center and the Alfred P. Murrah building in Oklahoma City. The triggers of these were clear but, the buildings were also not constructed to resist progressive collapse. News reports of the Champlain Towers tragedy seem to be suggesting deteriorating concrete resulting in a weakening of the building over time. It is way too early to determine that weakening was the cause. There is still the possibility of an extreme external force causing the condominium collapse.
I normally start an investigation like this by looking for external forces. I look at weather reports, local seismographs, and nearby construction. In my experience leaking water pipes and leaking steam lines have caused partial collapses. I have seen explosions, extreme winds, thermal effects, industrial accidents, earthquakes, landslides, snowdrifts, fires, and waves causing collapses. Those were all easy to determine the trigger. There are a few collapses in my experience that are more difficult. These have dealt with the undetected slow-moving parts of the building due to corrosion, creep, and changing loads.
The nightmare for Structural Engineers will continue until the causes of this horrific event are determined. Many of us will be asked to inspect similar buildings to determine if they are structurally sound. Without knowing the cause of this condominium collapse this will be a difficult task where we will need to rely on our engineering judgment. Buildings of this age will likely be very susceptible to progressive collapse due to the failure of a relatively small element of the buildings. Progressive collapse is a difficult design in new buildings as well. When you design for progressive collapse, you are always accepting some risk. The failure of the elements could be caused by many external factors including fire, vehicular impact, utility leak, sinkhole, explosion, and many more. The risk is small, but the impact is devastating. Structural Engineers recognize and live with this risk daily. Some will have sleepless nights thinking about the risk they are accepting.
God bless the souls lost, their families, the responders, the local officials, and anyone else impacted by this tragedy.