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Hurricane hardware

By: Melissa Schneider / Published: Jul 26,  2009

Scientists are developing new device to make homes safer during storms

 

Catastrophic losses due to hurricanes are the largest and most pervasive risk faced by Gulf of Mexico coastal communities. Because residential structures are a predominant casualty of hurricanes, the four Gulf of Mexico Sea Grant college programs are funding a project to improve home construction techniques so homes can withstand Category 4 hurricane conditions.

The project strengthens the connections between a building’s roofs, walls and foundations. Arindam Chowdhury, assistant professor of civil and environmental engineering at Florida International University, is leading the research project, assisted by Emil Simiu and Amir Mirmiran, also of Florida International University, and Steve Cai of Louisiana State University.

“Residential buildings often fail under hurricane stress due to weak or inadequate connections that prevent the load from being spread across the structure, leading to disintegration,” said Chowdhury.

In their quest to develop a novel residential connection device, the researchers constructed a unique, full-scale testing facility capable of producing winds of up to 140 miles per hour, called the Wall of Wind (WoW).

Using a series of fans, diffusers and grids to simulate wind-driven rain, the WoW facility mimics real hurricane conditions, meeting one of the main objectives of the research.

The other main objective of the research is developing a non-intrusive residential connection system able to withstand hurricane conditions. According to hurricane damage reports by the Federal Emergency Management Agency and the National Institute of Standards and Technology, poor performance of residential buildings has been observed when structures did not respond as a units due to discontinuous load paths. Chowdhury and his associates are designing a connection system that will distribute the windforce along a continuous path using connections between the roof, walls and foundations.

Small-scale component testing of a Fiber Reinforced Polymer (FRP) connection system has shown promise regarding its effectiveness. Fiber composite connections, once used only in aerospace engineering, have considerable civil engineering application in coastal areas due to their strength, light weight, non-corrosiveness and long-term durability. After determining the most suitable connection design using the small-scale tests, the next step will be to test the connections at full-scale under simulated hurricane conditions in the WoW.

If the connection system performs as well in the full-scale tests, the application of this system to existing residential structures could be a significant step toward increasing the resilience of coastal communities. According to Chowdhury, although Sheetrock repairs would be necessary, retrofitting an existing home with FRP requires much less strain to the structure compared to retrofitting with traditional hurricane clips and toe nails which require penetration of the structural members.

“In older homes, the biggest advantage of the FRP connection system is that the already weakened wood members from earlier nail/screw penetration do not have to be weakened further by more nails, but can be retrofitted by the FRP and epoxy,” said Chowdhury. The preliminary cost analysis indicates that retrofitting with FRP is approximately equal to retrofitting with existing hurricane hardware.

Potential users in the construction and insurance industries have been brought into the planning, funding and execution of the project.

Carl Schneider, of Schneider Insurance Agency, Inc. in Mobile, Ala., said that science and engineering is the answer to reducing loss exposure on the coast. In fact, Alabama just passed legislation that requires insurance carriers to offer discounts for fortified or mitigated structures. As a result, the industry will be very interested to see and discuss the outcome of the final testing of this innovative connection system.

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