InfrastructureSimulating hurricanes to test buildings' resilience

Creative destruction. Researchers later this year will attempt to reduce a house to rubble using a new hurricane simulator which mimics the powerful gusts of a category 5 hurricane. The tests should help researchers understand how buildings can be better designed to withstand hurricanes. The Three Little Pigs project at the University of Western Ontario, Canada, does not use fans or a wind tunnel. Instead a network of seventy special “pressure boxes” mounted on the building exert pressure at various points around the full-size two-story brick house. The blower boxes — a little like very powerful hand driers — are up to 2 by 2 metres in size and are placed over the entire surface of the building, including the roof. The blower boxes can apply both negative and positive pressure on the building by either blowing or sucking air, producing pressures between -15 and 5 kilopascals. The boxes can flip between those two extremes as frequently as 7 times per second. The rapid changes mimic the buffeting of winds from gusts exceeding 250 kilometers per hour, says Gary Kemp, of U.K. firm Cambridge Consultants, whose team developed the pressure boxes. “The building will be shaken around quite violently,” he told the New Scientist’s Phil McKenna. “It’s those rapid variations in pressure that cause the building to start to fall apart.”

To facilitate such rapid pressure changes, Kemp and colleagues developed valves, connected to continuously operating blowers, that can rapidly open and close. The company also worked out how to coordinate the boxes to recreate the kind of buffeting airflow that could be expected in a hurricane. A scale model of the house in a wind tunnel was used to map out the turbulence and eddies of wind that would occur when it was blasted with wind. The results were used to program the network of boxes and make the simulated hurricane more realistic. Note that researchers at Florida International University in Miami recently used a pair of powerful 2.5-meter fans to blast a one-storey wooden house with 190 kph winds, similar to those experienced in a category 3 hurricane.

The test, known as the “Wall of Wind,” has limitations in maximum wind speed and the ability to fluctuate in intensity, says Gregory Kopp, who heads the Three Little Pigs project. “There is a lot of gustiness to the wind [of a real hurricane], it’s very difficult to do that with very large fans,” Kopp says. Kopp adds that despite the one megawatt of power his project will draw, roughly equivalent to ten car engines, such pressure loading is significantly more energy efficient than wind testing. “We probably use one tenth the power of fans,” Kopp says. Richard Perdichizzi, of MIT, has successfully conducted hurricane tests of buildings inside the university’s wind tunnel with scale models less than a meter tall at significantly less expense and power. He says the new full-scale pressure box approach looks promising, but that it must still prove itself. “They are interested in gust conditions — that is something that is very difficult to do in a wind tunnel,” Perdichizzi says. “But you have to wait until they actually do it. It will be interesting to see how it stacks up against other types of testing methods.”