On May 16, 2024, a powerful derecho swept through Houston, killing seven people and causing significant damage to several of the city’s towering skyscrapers. Those buildings were constructed to withstand much stronger hurricane-force winds up to 67 meters per second, as one would get with a Category 4 hurricane. The derecho’s winds peaked at 40 meters per second, well below that threshold. And when Hurricane Beryl hit Houston that July with roughly comparable wind speeds of 36 meters per second, the damage wasn’t nearly so severe. Why would that be the case?
Engineers at Florida International University (FIU) in Miami think they’ve found the answer, according to a new paper published in the journal Frontiers in Built Environment. “We show that a type of highly localized strong winds called ‘downbursts,’ which were generated during the May derecho, can significantly impact tall buildings and facades due to their unique characteristics in comparison to hurricanes,” said co-author Amal Elawady. This is particularly the case for skyscrapers that are close together, creating a “wind-channeling” interference effect that increases pressure on walls and windows.
One might assume that hurricanes and derechos are similar in that they both produce markedly intense winds, but the origin and characteristics of those winds are very different, per the authors. Hurricanes are vast tropical storms that form over warm ocean waters and affect large areas, usually lasting for several days, accompanied by heavy rains, storm surges, waves, and yes, high winds. By contrast, derechos and downbursts are much more localized convective systems, producing hurricane-force winds but over a much smaller area and shorter period of time.
There are more than 2,000 skyscrapers higher than 200 meters worldwide that are especially vulnerable to high winds, and understanding those differences is crucial to coming up with better mitigation strategies in the future. Hurricane impacts tend to be widespread and can cause a lot of damage to the glass and cladding of skyscrapers, such as the damage Hurricane Katrina inflicted on tall buildings in New Orleans in 2005. Damage from derechos and downbursts causes more severe, concentrated damage, such as the collapse of a 37-story building in Brazil in 2011.
“Bouncing” winds
Elawady decided to investigate why the Houston derecho’s structural damage was so much more extensive than one might expect. He and his colleagues analyzed the impact of the derecho on five of the city’s most notable buildings: The Chevron Building Auditorium, the CenterPoint Energy Plaza, the El Paso Energy Building, the RRI Energy Plaza, and the Wedge International Tower.
The Chevron Building Auditorium, for instance, suffered significant damage to its cladding and shattered glass windows, mostly on the side facing another skyscraper: the Chevron Corporation Tower. The CenterPoint Energy Plaza’s damage to its double-skin facade was concentrated on one corner that had two tall buildings facing it, as was the damage to two corners of the El Paso Energy building. This suggested a wind-channeling effect might have played a role in that damage.
Next Elawady et al. conducted wind tunnel experiments at the FIU Natural Hazards Engineering Research Infrastructure’s “Wall of Wind” facility to determine how the winds may have specifically caused the observed damage. They placed a revolving miniature tall building in the tunnel and blasted it with wind speeds of up to 70 meters per second while placing an identical mini-model at increasing distances from the first to mimic possible interference from nearby buildings.
The results confirmed the team’s working hypothesis. “When strong winds move through a city, they can bounce due to interference between tall buildings. This increases pressure on walls and windows, making damage more severe than if the buildings were isolated,” said co-author Omar Metwally, a graduate student at FIU. For example, in the case of the Chevron Building Auditorium, the channeling effects intensified the damage, particularly at higher elevations.
“On top of this, downbursts create intense, localized forces which can exceed typical design values for hurricanes, especially on the lower floors of tall buildings,” Metwally added. The problem is only likely to worsen because of accelerating climate change. Glass facades seem to be particularly vulnerable to this kind of wind damage, and the authors suggest current design and construction guidelines for such elements should be re-evaluated as a result of their findings.
Frontiers in Built Environment, 2025. DOI: 10.3389/fbuil.2024.1514523 (About DOIs).