The possibility of a major hurricane striking a large population center in the southeast United States during the next two decades of high activity is a near certainty. Structural mitigation, however, can significantly reduce hurricane damage. Recent research indicates that improving the resiliency of the building stock in hurricane prone regions can significantly reduce loss and damage. In the aftermath of Hurricane Charley in 2004, post-disaster assessments indicated that insured losses for structures built under the 2002 Florida Building Code were as much as 40-50% lower than equivalent homes built to the Standard Building Code.
According to the preliminary estimates from the Florida International University public hurricane loss model, funded by the Florida Office of Insurance Regulation, the reduction in ground-up loss can be as much as 70% for categories 1 to 3 hurricanes. Obviously, much more can and must be done to make hurricane prone areas resistant to storm impacts, which will greatly reduce the cost to homeowners, businesses and government.
To build better and stronger requires knowing how to build structures that are hurricane survivable. We can test building components, such as windows, doors, etc. with air canons, but we cannot determine how the whole structure will perform in hurricane conditions. While wind tunnel testing of models of houses has provided useful information, this approach has many limitations - gravity cannot be scaled nor can roof shingles be reduced to miniature size and provide any useful understanding of the wind dynamics and failure mode.
Buildings have been constructed without this basic understanding and knowledge, because we have not previously had the capability of using an holistic approach to testing structures.
Now, however, the wall of wind (WoW) developed by the International Hurricane Research Center (IHRC) in Florida, allows full scale, destructive testing of houses and low rise commercial buildings.
The phase I WoW consists of two 2.5m diameter fans with dual propellers, each driven by 500 horsepower Chevrolet hot rod engines. This two fan model can generate category 3 wind fields with water injection to simulate wind blown rain. Mounted on a trailer, the WoW can be deployed for on-site testing of new designs and retrofits to existing housing. It can be calibrated based on wind field measurements of land falling hurricanes to simulate storm conditions.
Successful testing with the two fan model, funded by the Florida Division of Emergency Management, has demonstrated proof of concept of full scale destructive testing. Our research includes the following elements:
- Assess relationship between roof edges and wind loads
- Determine the causes of water intrusion in buildings (even when roofs remain intact)
- Examine the production and behavior of windborne debris
- Perform impact assessments to identify deficiencies in building codes
The WoW facility will be used in partnership with the commercial sector and government agencies to test low rise buildings, especially houses, and develop new products, standards and building codes. The insurance and reinsurance industry has already recognised its potential. We are presently completing a six fan model funded by Bermuda based RenaissanceRe, one of the largest catastrophe reinsurers in the world. This more powerful, WoW can generate a 130 to 140mph (209 to 225kph) wind field. Ultimately, we plan to build the world class facility - an 18 fan wall of wind that can generate category 5 wind and rain conditions.
Vision
We have embarked on a mission to develop a national laboratory for full scale destructive testing of low rise residential and commercial buildings. Our vision (as depicted above) involves coupling academic goals and commercialisation and includes:
- Conducting fundamental and applied research to gain better understanding of hurricane wind and rain induced effects on the built environment
- Making strategic alliances with industry leaders that will result in new inventive technologies, products, trades and spin-off companies
- Enhancing building codes and standards
- Providing the highest quality graduate education in hurricane research
- Enhancing education at all levels, including in the building industry
We will be able to advance hurricane mitigation by using the wall of wind to
- Test new building designs and prototypes from manufacturers
- Research materials and procedures for retrofitting existing buildings
- Design solutions for structures and components
- Test building materials in situ
- Provide research that can be used to improve building codes and standards
- Expand the education and training of professionals who design, build or inspect residential construction
- Support available and affordable insurance through better building practices and the development of a culture of mitigation
Some examples
- Aerodynamic edge components can be developed to perform vortex suppression on abrupt and sharp edges and the corners of structures, which would lessen uplift pressures and attendant damage to roofs.
- We are also developing methods to reduce the water penetration of wall systems. The approach is to design new soffits that resist being blown out or redesign soffits so that they greatly reduce water infiltration when remaining intact.
- Dr. Stephen Leatherman is director of the International Hurricane Research Center at Florida International University, Miami.
Leatherm@fiu.edu
www.ihrc.fiu.edu
ORIGINS
The International Hurricane Research Center (IHRC) developed as a result of a public-private partnership between the We Will Rebuild Foundation, a private organisation set up to lead the rebuilding of Miami-Dade County after Hurricane Andrew in 1992, and Florida International University. IHRC is Florida's official hurricane research centre for 10 universities that comprise the state system. It is also designated as the formal liaison for NOAA's Tropical Prediction Center and National Hurricane Center.
IHRC research tries to answer fundamental questions in order to reduce the hurricane threat. Current studies involve such areas as storm surge hazard and vulnerability mapping, socioeconomic analysis of hurricane warnings and evacuation strategies, and catastrophe modelling.
Among IHRC successes have been a building code modification approved in 2003 by the State Building Code Commission to make the ring-shank nail the standard for roof sheathing in the high velocity hurricane zone in Florida. This new standard increased the resistance of roofs to hurricane wind uplift forces from a low category 3 hurricane up to a high category 4 hurricane (130% improvement) without raising the cost of construction. In 2005, the center's new high resolution storm surge model predicted 24 hours in advance the 30 foot (9.1m) surge from Hurricane Katrina that hit Waveland, Mississippi.
The IHRC board of trustees has grown from the original key members of the We Will Rebuild Foundation to include executives in the banking, insurance and building industries. The board composition directly reflects the IHRC mission to bridge the gap among stakeholders and provide objective information in order to make collective, informed decisions on hurricane mitigation. This national board of 12 people includes, among others:
- Robert Epling, IHRC board chair and president, Community Bank of Florida
- Ray Kothe, vice-present, National Association of Home Builders (NAHB)
- Steve Lyons, hurricane specialist, The Weather Channel
- Max Mayfield, director, National Hurricane Center (ex officio)
- Frank Nutter, president, Reinsurance Association of America (RAA)
- Bill Riker, president, Renaissance Re.
