Engineers model effects of hurricane force winds on structures
As the rains from the downgraded Hurricane Frances move northward while the eastern U.S. continues to watch Hurricane Ivans approach, the destruction from the heavy winds and rains is mounting into the billions of dollars.
In Florida alone, initial estimates for losses caused by Frances were between $2 and 4 billion following the projected $7.4 billion in insured damages from Hurricane Charley, according to Reuters News Service.
In most cases, low-rise buildings, including residential, institutional, and commercial structures are the most vulnerable and carry the brunt of the damage and losses from extreme wind.
"Engineers have the ability to theoretically understand and simulate how a storm will impact a structure," said Muhammad Hajj, professor of engineering science and mechanics at Virginia Tech. "This ability, however, needs to be complemented with computational power such as the supercomputing system developed at Virginia Tech to obtain reliable values for wind loads," he said.
Hajj and his Virginia Tech colleagues, Professors Henry Tieleman and Saab Ragab in Engineering Science and Mechanics, and Finley Charney in Civil and Environmental Engineering, are a part of the Hurricane Loss Reduction Consortium: Wind and Structural Engineering Initiative. The consortium members are Virginia Tech, Clemson University, University of Florida and the Johns Hopkins University. The National Institute of Standards and Technology (NIST) funded this consortium.
Although the American Society of Civil Engineers (ASCE) maintains minimum building codes, and builders follow these codes "as a first basis," Hajj said, "there is still a wide fluctuation in the standards used." Hajj also notes that complex terrains of mountainous areas (as in the Carolinas, Virginia and some of the Caribbean Islands) create excessive turbulence that may cause increased wind loads."
In addition to differences in terrain, existing codes do not address how other factors contribute to damage to low-rise buildings. "As wind impacts a structure, different parameters such as duration of extreme loads, connector types, missing connectors, shoddy workmanship, and below-standard materials will determine the extent of damage," Hajj said. He and his colleagues are working on modeling these effects as well.
The researchers of the Hurricane Loss Reduction Consortium have instrumented homes along the Florida coast that were subjected to the winds of various storms such as Tropical Storm Isodore and Hurricanes Bonnie, Dennis and Floyd. They have analyzed these results and made preliminary comparisons to wind tunnel results. "The wind tunnel simulations are indeed capable of reproducing average values of wind loads, but appreciable differences may arise when considering local values," the team members from Virginia Tech explained in a progress report to NIST.
As the consortium continues its work, its long-term objective is to provide a full computational platform to calculate wind loads and structural capacities of low-rise buildings and to incorporate the findings into regional and national codes. Ultimately, the hope is to appreciably reduce damage and increase safety.
At Virginia Tech, the efforts are also a part of the recently established Center of Extreme Load Effects on Structures under Virginia Techs Institute for Critical Technology and Applied Science initiative.
Lynn Nystrom | EurekAlert!