Data from North Carolina Structure Could Help Future Homes
Stand Up to High Winds
When Hurricane Bonnie bore down on North Carolina's Outer Banks last summer, one gray two-story building was wired and ready to capture critical information about what happens when powerful winds pound a typical coastal home. Although Bonnie was downgraded to a tropical storm by the time it reached the test house, Johns Hopkins University engineers collected important data that could lead to more wind-resistant house designs in the future.
With a new hurricane season under way, the Johns Hopkins team, led by Nicholas P. Jones , a professor of civil engineering, and doctoral student Michelle Porterfield, has made certain the structure is ready again to gauge the impact of winds up to and including hurricane force. Although its exterior resembles that of a two-story tract house, this building, owned by the town of Southern Shores, actually operates as a community center. High-tech equipment inside and outside can record weather conditions, wind pressure on the building and movement of the structure itself. Data from these sensors is collected inside the house by a computer that can relay the information by modem to the university's Baltimore campus. As a result, the engineers do not need to be on the premises when a dangerous storm strikes. "This structure was built to demonstrate a wind-resistant construction design," says Jones. "I think the odds are better than even that it would survive a fairly severe blow, such as a hurricane, but not necessarily without damage."
The system was activated in October 1997. Since then, the Johns Hopkins team has collected more than 2,000 data sets, including readings from a "northeaster" storm in February 1998 and from Bonnie in August 1998. Jones and Porterfield presented a paper describing the project and providing preliminary data from Bonnie during the 10th International Conference on Wind Engineering, held recently in Copenhagen, Denmark.
Their research is important because hurricanes can deal a devastating blow to people and property. Even though the 1998 season was relatively mild, federal officials estimated that Bonnie and other storms caused about $6.5 billion in damage. Hurricane Andrew, which struck South Florida in 1992, killed dozens of people, destroyed more than 100,000 homes and caused about $25 billion in damage. Changes in construction methods and materials could help reduce the property loss in future storms. But builders and regulators need scientific data to help them determine how best to resist the power of hurricane-force winds. Readings from the "wired" house in Southern Shores could provide such clues.
The building, called the Kern P. Pitts Center, is located about a quarter-mile west of the Atlantic Ocean in a region that is commonly in the path of hurricanes and tropical storms. Its construction was initiated by the nonprofit Blue Sky Foundation to test how sections made of wood frame, steel beams and concrete would hold up in severe weather. During its construction in 1997, Johns Hopkins engineers were permitted to install 13 pressure gauges in the walls and roof, 20 strain gauges on the studs and rafters, an ultrasonic anemometer to measure wind speed in three directions and rooftop equipment to measure rainfall, temperature and barometric pressure.
Information collected by this equipment during harsh weather, including nearly 60 mph winds when Bonnie swept through, should help engineers determine whether building codes in hurricane zones need revision. Current codes are based mainly on data gathered in wind tunnels, using simple scale-model buildings. But some researchers question whether these lab tests accurately predict what will happen to a full-size structure in a real-life storm. Before the Johns Hopkins experiment was launched, very few field measurements had been made to find out how low-rise structures respond to severe wind. When the analysis is completed, the "hurricane house" findings could lead regulators to alter building codes. "The existing codes are not based on measurements of full-scale buildings," says Porterfield, a 26-year-old graduate student from Binghamton, N.Y. "That's one of the concerns we have. Are the codes adequate? We may be under-designing these structures, or we may be over-designing them."
Adds Jones, an internationally known expert on structural dynamics and on wind and earthquake engineering: "We may be over-designing buildings on average, but at one isolated location in the house, we may be under-designing. Yet that one weak spot may be what initiates a failure, causing the entire building to come apart."
To broaden the range of data it collects, the Johns Hopkins team is adding a few more pressure gauges and relocating some other sensors at the house. These modifications should be completed by the end of the summer. A National Science Foundation grant, along with support from the American Society of Civil Engineers and the town of Southern Shores, should allow the team to continue operating the hurricane test house at least through the end of the year 2000 storm season.
Photographs of the researchers and the test house available; contact Phil Sneiderman
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