- While Acapulco’s oceanfront high-rises were built to withstand the region’s powerful earthquakes, they had a weakness.
- Since powerful hurricanes are rare in Acapulco, Mexico’s building codes didn’t require that their exterior materials be able to hold up to extreme winds.
- Otis’ powerful winds ripped off exterior cladding and shattered windows, exposing bedrooms and offices to the wind and rain.
I have worked on engineering strategies to enhance disaster resilience for over three decades and recently wrote a book, “The Blessings of Disaster,” about the gambles humans take with disaster risk and how to increase resilience. Otis provided a powerful example of one such gamble that exists when building codes rely on probabilities that certain hazards will occur based on recorded history, rather than considering the severe consequences of storms that can devastate entire cities.
The fatal flaw in building codes
- Building codes typically provide “probabilistic-based” maps that specify wind speeds that engineers must consider when designing buildings.
- Some models may include additional considerations, but these are still typically anchored in known experience.
- Return periods are a somewhat arbitrary assessment of what is a reasonable balance between minimizing risk and keeping building costs reasonable.
How probability left Acapulco exposed
- According to the Mexican building code, hotels, condos and other commercial and office buildings in Acapulco must be designed to resist 88 mph winds, corresponding to the strongest wind likely to occur on average once every 50 years there.
- A 200-year return period for wind is used for essential facilities, such as hospital and school buildings, corresponding to 118 mph winds.
- The probability wind maps for both return periods show Acapulco experiences lower average wind speeds than much of the 400 miles of Mexican coast north of the city.
- Yet, Acapulco is a major city, with a metropolitan population of over 1 million.
Florida faces similiar challenges
- For example, new buildings along most of Florida’s coast must be able to resist 140 mph winds or greater, but there are a few exceptions.
- A 2023 update to the Florida Building Code raised the minimum wind speed to approximately 140 mph in Mexico Beach, the Panhandle town that was devastated by Hurricane Michael in 2018.
Acapulco’s earthquake design weakness
- As a result, the lateral-load-resisting structural systems in tall buildings there are designed to resist seismic forces that are generally larger than hurricane forces.
- However, a drawback is that the larger the mass of a building, the larger the seismic forces the building must be designed to resist.
A ‘good engineering approach’ to hazards
- A better building code could go one step beyond “good science” probabilistic maps and adopt a “good engineering approach” by taking stock of the consequences of extreme events occurring, not just the odds that they will.
- Unfortunately, as I explain in “The Blessings of Disaster,” we will see more extreme disasters before society truly becomes disaster resilient.
Michel Bruneau does not work for, consult, own shares in or receive funding from any company or organization that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.
