Huffing and puffing to blow a house down

Blasting homes with 120 mph winds
Nicholas P. Jones, dean of the Whiting School of Engineering at Johns Hopkins University in Baltimore, said he wouldn’t have considered the progressive failure of the roof’s leeward side as a surprise, given that pressure there can be strongly negative in a storm. A weak link exposed by the wind, he said, can lead to a domino effect of failures. Every time a truss’s connection is compromised, for example, its neighbors are forced to shoulder higher loads and the likelihood increases that they, too, will fail.

Nevertheless, Jones said, “there is still a lot to be learned about the interactions of airflow in the lower part of the atmospheric boundary layer, where buildings are located.”

To that end, he views the University of Western Ontario’s unique facility as a good complement to other efforts like the Wind Science and Engineering Research Center at Texas Tech University in Lubbock, where members of the Hurricane Research Team also chase major storms to collect real-time data. At the University of Florida in Gainesville, scientists have used a cannon to blast storm shutters with ceramic roof tiles to simulate the power of hurricane-force winds and deployed the world’s largest portable hurricane wind and rain simulator to blast test homes with wind speeds up to 120 miles per hour.

In the town of Southern Shores on North Carolina’s Outer Banks, Jones helped outfit a two-story community center dubbed the “Hurricane House” with a suite of sensors to remotely monitor its response to hurricane-force winds. Although a lack of funding prematurely killed the project after six years, Jones said a few passing tropical storms and hurricanes provided some useful data on how the house — built to showcase a new wind-resistant design — handled wind speeds in the 50 to 60 mph range.

Ultimately, he said, a collaborative effort that adopts multiple approaches — including full-scale wind measurements and simulations with wind tunnels, pressure hoses and computational fluid dynamics — may have the best chance of successfully filling in the knowledge gaps. As president-elect of the American Association for Wind Engineering, Jones said he plans to use his tenure to push for exactly that.

As for Kopp, one next step is to use embedded sensors to measure the force exerted on the nails at each truss connection. Beyond those tests, he said, his team may start adding on some hurricane mitigation measures while removing other parts of the structure that don’t face relevant pressure loads.

Though current tests have focused entirely on the roof, the institute has previously analyzed the role of windows and glass in maintaining a home’s integrity during a storm. A window shattered by flying debris can act like a funnel for high winds, quickly increasing the pressure within a house by up to 70 percent, Kopp said. With that pressure pushing upward on the roof, in addition to the exterior pressure buffeting it from the side, the roof can fail at far lower wind speeds, sometimes explosively.

An effective deterrent is to install storm shutters or at least board up all windows with plywood — one fairly simple lesson that Kopp said could make all the difference.

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