Tackling tornado alley
AMES – To anyone living in the Midwest, it’s hard to believe that the National Science Foundation has spent $100 million on earthquake engineering research, but only $1 million on wind engineering research, including tornadoes.
This funding trend persists, even though the U.S. insurance industry reports that tornadoes cause estimated losses of nearly $1 billion in America each year. That’s why ongoing research at Iowa State University’s unique tornado/microburst simulator remains so vital.
“We’re trying to reflect the real world,” said Dr. Partha Sarkar, an ISU structural engineer. “Present building codes are based on straight-line winds, but tornadoes create rapidly changing loads on buildings. We’re studying these air flows to find new ways to design buildings.”
Measuring 18 feet in diameter and 12 feet high, the simulator is affixed to a five-ton crane and glides horizontally above a large wooden ground plane, generating a “tornado” that moves across the landscape. The equipment, which was completed in 2004 with the help of dedicated ISU students and a miniscule budget, can emulate tornadoes from an F1 to an F5 rating.
The researchers have found that a tornado wind can meaning a tornado with 150 miles per hour winds will have a much different effect on buildings, than a hurricane with 150 mph winds. All this hit close to home when a number of tornadoes swept across central Iowa in 2005, including one that touched down in Ames. “People accused us of letting one go,” joked Sarkar, who narrowly escaped the violent storm.
While 90 percent of tornadoes rate less than F2, 113 to 157 miles per hour on the Fujita scale, scientists still haven’t been able to definitively answer why two storms can look exactly the same, but one will produce a tornado and one won’t.
Research suggests there are some small-scale features important to getting a tornado to the ground, and these are produced by the storm itself, said Dr. Bill Gallus, a professor of geological and atmospheric sciences at ISU.
“The main culprit appears to be a downdraft of air near the spinning part of a storm, and what its temperature is like. We have limited evidence that if it is relatively warm, a tornado happens, but if not, it usually does not. We need much better data from near the storms, and some should be collected this year.”
ISU scientists have focused on merging Gallus’ knowledge of the latest research on tornado formation with Sarkar’s expertise in wind tunnel design and testing to determine the effects of wind loads on buildings. As a result, their work with the tornado simulator has attracted worldwide attention, especially since the equipment has been featured in a variety of well-known media outlets, including the National Geographic Explorer television show.
The scientists have studied tornadoes’ effects on multistory buildings, hip-roof buildings, trailer houses, grain bins and two-story gable-end houses.
“Now we’re clustering buildings to study how this would impact a tornado in a typical downtown or a suburban block,” said Bill Rickard, an ISU laboratory mechanical technologist. “There’s an old saying that the city destroys the tornado and it turns out there’s some truth to this.”
ISU researchers are also using the latest technology to study tornadoes, including particle imaging velocimetry, which uses lasers and a camera to measure the size of a tornado’s vortex and provide a precise picture of the air flow around a building.
“As the instruments become more sophisticated, this allows us to better understand how air flows go over a building and predict which parts of the building will fail first,” Sarkar said.
If new buildings could be constructed to withstand an F 2 tornado, with 111-135 mph winds, these structures would also suffer less damage in the event of an F3, 136-165 mph, or an F4, 166-200 mph, tornado, Sarkar said. He envisions the day when an inexpensive black box-type device could be installed in every home to record tornado winds for better damage scale rating, in the event that the building is damaged in a tornado.
“Tornadoes might only hit a portion of a rural area or a small town, but their impact on Iowa’s ag economy can be dramatic,” Rickard added. “Studying tornadoes is always fascinating and the work never gets boring, because our goal is to minimize damage to people and property.”
Contact Darcy Dougherty Maulsby by e-mail at firstname.lastname@example.org.
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