When Hurricane Laura came onshore Aug. 27 as a Category 4 hurricane with sustained winds of 150 mph, it shattered windows on nearly every level of the 22-story Capital One Tower in the Lake Charles, La., business district. The glass damage is perplexing to engineers who study wind dynamics and window performance.
It’s not unusual for a building’s lower-level windows to get knocked out by flying debris. But the fact the majority of the building’s windows were blown out — including dozens of windows on the upper levels — is remarkable, they say.
“When I looked at the pictures, I said this is not typical of how windows come out of a building,” says Anton Davies, wind engineering consultant and founding partner at RWDI Consulting Engineers and Scientists in Guelph, Ontario, Canada. The firm has conducted wind engineering for some of the world’s tallest buildings, including the 1,776-ft-tall One World Trade Center in New York City. The firm is not involved with the Capital One Tower.
Presuming the building was constructed to code, outside wind alone should not have been able to produce that much damage, Davies says. That means other forces may have been at play. “Wind is incredibly powerful, and there are some really cool things that happen that most people don’t understand,” he says. “So I can’t tell you whether this is missile damage or whether this was a failure due to inadequate design,” construction or maintenance.
The wind’s angles are another variable, and Davies explains that wind blowing around the edge of the building can create a tornado-like vortex that could cause the windows to fail.
Davies says it’s worth noting that the pile of glass seen at the foot of the low-rise structure next to the main tower could mean that wind-strewn debris struck the short face of this low-rise building. “This would have pressurized the large interior space – much like blowing up a balloon – which could have blown out the glass,” he says. “Once the glass was outside the low-rise structure, some (pieces) would have become missiles that impacted the front face of the tower, thus breaking more glass and so on.”
The 400,000-sq-ft building, constructed in the early 1980s, has an assessed value of $67.6 million, according to Calcasieu Parish records. The building sustained window damage during Hurricane Rita in 2005, though that storm knocked out only a few windows on the lower floors and damaged the atrium roof. In later upgrades unrelated to Rita, a layer of ballistic film was placed behind the windows of some offices.
Hertz Lake Charles One LLC, which owns Capital One Tower, could not be reached for comment.
Watching images of Capital One Tower on the news the night before Laura made landfall, Ashan Kareem, University of Notre Dame’s Natural Hazards Modeling Laboratory and professor of engineering, predicted the glass curtain wall building would be a prime target for significant damage.
Kareem’s suspicion was informed by years of studying window damage to high-rise buildings after other storms, including the Hyatt Regency after Hurricane Katrina in New Orleans.
Backed by a research grant, Kareem visited New Orleans to study the Hyatt immediately after Katrina. He determined that a major culprit of the hotel’s damage was the layer of loose, pea gravel several inches thick that covered the roofs of some neighboring buildings, including New Orleans City Hall. Bits of gravel became airborne and blasted out nearly every window on the hotel’s north face. Some of the falling glass damaged windows at lower levels, creating a domino effect of further damage.
Kareem was not able to visit Lake Charles after Laura but says a similar scenario could have played out at Capital One. Once windows are broken, high winds can get inside the building and create pressure that can push the glass out.“Either the pressure was higher than what they designed for, or wind debris and the pressure combined did it,” Kareem says.
Most likely, Kareem says, is that wind blowing inside the building created great pressure that caused the glass to blow outward. “If you are sucking a window from the outside, and then someone from the inside also pushes the window out, don’t you think it will be easier to push the window out?” Kareem says.
Regional restoration continues
Lake Charles and other parts of Louisiana and Texas are still reeling from the historic storm, which is estimated to have caused up to $12 billion in property damage in the two states, according to real estate and insurance data analytics firm CoreLogic.
In a major sign of progress following catastrophic damages to the region’s power grid, Entergy Corp. announced Sept. 22 that the utility had restored electricity to 910,000 customers, or about 99% of those who lost power in the storm. Entergy estimates total restoration costs could reach $1.7 billion.
Large segments of the region’s transmission system – the backbone of the electric grid – required nearly a complete rebuild. The damages included approximately 225 transmission lines, more than 300 substations and about 1,900 transmission structures that were damaged or destroyed.
In hard-hit southwest Louisiana, Entergy restoration workers have repaired or replaced 839 of 1,459 damaged transmission structures and 302 of 316 damaged substations.