Surfside collapse: How safe are our coastal buildings?

Surfside collapse: How safe are our coastal buildings?
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The tragic collapse of the ocean-front Champlain Towers in Surfside, north of Miami, has captured the attention of high-rise dwellers around the world. In Florida, people are understandably worried about the safety of their own buildings, with questions asked about the role of sea-level rise, salt-water intrusion, coastal subsidence and other potential contributing factors. It will take months for investigators and structural engineers to determine the root causes, but here are some answers to commonly asked questions — along with a few recommendations.

1. Should we worry about subsidence?

Probably not. While subsidence contributes to coastal flooding, it usually is only a problem on reclaimed land. In the past, some cities allowed reclamation projects in their coastal wetlands, backfilling areas with dredged material to create land where there was once only marsh. These areas can undergo compaction and surface lowering over time (subsidence), eventually contributing to flood susceptibility. The original dredging also destroyed sensitive coastal habitats including fringing mangroves, important habitat for many aquatic species and good protection against storm surge.

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However, the integrity of high-rise structures shouldn't be affected, since they are usually anchored on deep foundations designed to withstand the load of the building. The weak reclaimed material only makes up the upper few feet, while the building foundations typically extend much deeper.

The great majority of Florida's coast is quite stable, but the possible role of subsidence (in particular, differential subsidence, which can lead to tilting and stress build-up) is something investigators will look into.

2. Is sea-level rise a problem?

In the long run, sea-level rise is something all Florida residents should worry about, but it's not likely to be a major factor in this tragedy. Since the Champlain Towers building was constructed in the early 1980s, global average sea level has risen by about 4.5 inches. Locally, this value could be higher due to changing ocean currents but is still not significant compared to the vertical dimensions of the foundation, which are normally designed for saltwater conditions. While it might be appealing to point the finger at sea-level rise, it is likely not the cause of this sudden collapse. But there are some longer-term issues.

3. What about saltwater intrusion?

Similar answer here. Saltwater intrusion refers to the tendency of saltwater to replace fresh ground water in coastal aquifers as sea level rises, possibly exacerbated by excessive ground water pumping, but again it is unlikely to be the major cause of this tragedy. In the long run, it's something we should worry about: It accelerates corrosion of underground infrastructure such as water works, and of course affects our freshwater supply.

4. Is corrosion a factor?

This is certainly an area the structural engineers will be taking a look at. Long-time Florida residents who live near the ocean are well aware of the enhanced corrosion that comes with the territory, with humidity, salt air and the occasional tropical storm or hurricane contributing to the problem.

Whenever steel-reinforced concrete is used as a structural element, the steel reinforcement needs to be protected against oxidation (rusting), which can cause expansion and cracking of surrounding concrete, leading to further oxidation in a bad feedback cycle. Engineers work hard to minimize the process, but after many decades, corrosion barriers can break down. Regular inspection and preventive maintenance are key.

While sea-level rise and saltwater intrusion can exacerbate corrosion, steel reinforcing would need to be exposed to a wet, salty environment for a relatively long period of time before corrosion sets in, implying that regular inspection and maintenance can be effective. As investigators seek answers, they will surely be on the lookout for signs of corrosion.

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5. Do regulations need to be tightened?

Several Florida counties already mandate inspection of high-rise or civic buildings after 40 years to insure structural, electrical and fire safety. As we learn more about the causes of this incident, state and local regulators will undoubtedly be taking a hard look to see if these regulations need to be tightened. 

With the benefit of hindsight, 40 years is probably too long for properties in harsh marine climates. Condo owners should insist on structural inspections every 10 years followed by appropriate maintenance. Maintenance costs are like taxes — no one likes them, but we all need to pay them.

6. What about the long term?

While sea-level rise was probably not a significant factor in this tragedy, there are still lessons. Living on the coast carries rewards, risks and costs. As sea level rises, the cost of living in beautiful but dynamic environments like Florida’s coast will increase.

Eventually, some structures and activities will retreat from the coast because they are not economic. Maintenance and insurance costs will increasingly be factored into decisions about where people choose to live, work and invest.

Our hearts go out to the families who lost loved ones in the Surfside tragedy. We need to learn from it and make our built environment safer. While some of the environmental issues noted above are unique to Florida, the overarching issue of maintaining older buildings and other infrastructure is a national concern. A lot of our infrastructure was constructed in the post-war boom of the 1950s to 1970s including high-rise condos. As they approach or exceed their 50-year birthdays, it seems appropriate to consider the expected life spans of our infrastructure and begin the challenging job of maintenance or replacement.

Timothy H. Dixon is a professor in the School of Geosciences, University of South Florida, Tampa. He is the author of "Curbing Catastrophe," published by Cambridge University Press.