NC State News ServicesCampus Box 7504 Raleigh, NC 27603[email protected]www.ncsu.edu/news
NEWS RELEASE
Media Contacts: Dr. Bo Kasal, 919/515-5726 or [email protected]Kevin Potter, NC State News Services, 919/515-3470 or [email protected]
Oct. 30, 2000
Engineer: Improved Building Standards in Hurricane Zones Needed
FOR IMMEDIATE RELEASE
As the 2000 tropical storm season comes to an official close, the United States appears to have dodged the hurricane bullet this year. A North Carolina State University structural engineer, however, believes few homes are built well enough to withstand the powerful winds of hurricanes destined to someday pound the U.S. Southeast.
Dr. Bo Kasal, NC State associate professor of wood engineering and mechanics, says current construction codes may not reflect state-of-the-art knowledge about the behavior of light-frame wood buildings under hurricane conditions. He predicts that four or five hours of hurricane-force winds could cause substantial damage to many such residences.
Current building codes, he explains, represent only "bare bones" minimum measures that builders must meet to protect wood-frame homes from powerful winds. Those standards, for example, were written for "box-type" homes, not the large and complicated residences that are now common on or near the coast. Low-rise residential structures built to these standards usually meet the minimum requirements, but rarely exceed them.
"It's assumed that these houses are safe, but past performances showed deficiencies in construction practices and code enforcement," Kasal says. "One can reduce these risks with updated building practices and state-of-the-art technology."
Kasal advocates giving homebuilders broad leeway in designing coastal homes based on "performance-based" building standards, rather than the current minimum "prescriptive" – or required – construction standards. Unlike most homes currently being built, however, their building plans would have to be approved by structural engineers.
"Our goal is to make the building perform better when buffeted by such natural forces as powerful sustained winds or ground motion caused by earthquakes," Kasal says.
Performance-based standards would encourage homebuilders to use construction strategies that add to the structural integrity of the building, including interior load-bearing walls and clearly established pathways to transfer load forces to the foundation. Performance-based design criteria would also encourage innovation and open the door to new materials and technologies, Kasal says.
Some people may express concerns that performance-based construction standards could add to the cost of a home. But Kasal doubts that would be the case, since the performance-based standards could reduce the amount of material used to build a home, as long as the building material is used more wisely.
Additionally, he says, an investment in developing and implementing such standards could save significant government resources, especially in the face of increased home construction in coastal areas at risk from strong storms. "The social impacts of hurricanes are not the same that they were 50 years ago when the population density along the coastline was much lower," Kasal explains. "It's only going to get worse, not better."
Windstorms can result in substantial loss of life and property, he says. In 1992, for example, Hurricane Andrew resulted in 61 fatalities and $26.5 billion in losses when it slammed into south Florida. Five years earlier, Hurricane Hugo killed 86 and caused $7 billion in damage.
The federal government currently spends only about $5 million per year to develop and encourage practices and policies that aim to reduce losses from wind-related disasters. That amount is inadequate, Kasal says.
"This is an opportunity for improving the safety of our citizens and mitigating the impact of natural disasters on society," he says. "The government usually mitigates after the disastrous damage has occurred. Why not spend a fraction of that amount up front and reduce the impact?"
Kasal is helping to lay the foundation for improved national building standards by designing a computer program that models how natural forces affect a structure's integrity. He's now refining the program based on tests he conducted this summer in Melbourne, Australia, on a specially designed building.
That L-framed house was fitted with instruments to measure how loads simulating natural forces, which were applied by hydraulic presses to different parts of the building, were distributed throughout the structure. The goal is to find out how the forces "travel" to the building's foundation, and how parts of the structure, such as load-bearing beams and connecting walls, hold up under the "lateral displacement" of the building caused by those forces. The four-year project will be finished next year.
Kasal hopes to next build an experimental house somewhere on the Eastern Seaboard, equipped with instruments that would allow him to directly measure how the structure performs under the force of high winds.
–potter–
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