March 26, 2001

NC State Researchers Work to Improve Coastal Structures

When a hurricane strikes, lives are saved by evacuation from coastal areas, but the homes left behind are vulnerable to tremendous damage. For example, Hurricanes Fran and Floyd caused widespread damage to coastal homes in North Carolina in recent years. Designing homes to withstand hurricane-force winds has been an engineering challenge for many years.

Now researchers at North Carolina State University, working with the National Sea Grant program, are exploring the feasibility of using high-tech materials to make coastal homes safer and more resistant to storm damage. Soheil Saadat, doctoral student in mechanical and aerospace engineering and Sea Grant Fellow, and Dr. Mohammad N. Noori, professor and head of the Department of Mechanical and Aerospace Engineering, are carrying out research to explore solutions to two problems associated with coastal structures in hurricane-prone areas. First, much storm damage to homes results from loss of the roof to high winds. Second, assessing damage to foundations remaining after the storm is important for homeowners considering rebuilding.

Consequently, the first goal of the study is to develop new wall-to-roof-connection fastening devices that will withstand high winds better than currently used fasteners. To do this, Saadat and Noori want to use Shape Memory Alloys (SMAs), a class of materials that has been manipulated to exhibit a high damping – or dissipation of energy through motion – capacity. Such materials have the potential to withstand vibration much better than conventional materials. SMAs may be metal alloys, such as nickel-titanium, or ferrous alloys, ceramics or polymers. In this study, nickel-titanium alloys have shown the most promise to be used for fastening devices.

SMAs are created by cyclic heating and cooling of an alloy using electric currents. This manipulation changes the properties of the alloy, making it "remember" its original shape after a distortion event such as a hurricane. This characteristic, called pseudoelasticity, enables researchers to develop "smart" materials that can adapt to external stress.

Much work remains to be done before cost-effective SMAs can be used in new construction. Noori and colleagues have high hopes for the development of the new mechanisms. "This new generation of structural systems can think and adapt themselves to the environment; they can react and self-repair," said Noori. These autoadaptive materials have many potential applications; past research has focused on their use in earthquake-prone areas, but Saadat and Noori are excited about exploring this new application to hurricane-vulnerable structures.

The second aspect of this study, assessing foundation damage after the storm, involves developing monitoring systems that can help homeowners and building inspectors decide if a foundation is sturdy enough for rebuilding. Frequently, only the foundation of a coastal home survives a severe hurricane. Homeowners might like to reuse this foundation, but only if it’s safe.

According to Noori, underwater robots that can stick themselves to a pillar and use sound waves to send data back to a researcher have been in use for other marine applications, and they have potential for coastal structures application. The challenge is in the interpretation of the data using mathematical tools, which is the focus of the ongoing study.

Eventually, Saadat and Noori envision that in the not too distant future, an integrated system would be commercially available that could be permanently attached to structures. This monitoring device would use the same sensor technology that is presently available in automotive and other applications to collect data, which could be interfaced with Global Positioning System (GPS) technology for remote monitoring of the structures. These data could pinpoint the time, location and extent of damage and could, for instance, aid builders in their decisions about foundation retention following a hurricane.

For the future, Saadat and Noori have determined that this second aspect of the study is of critical importance, and development of remote sensing technology is an urgent need for hazard mitigation of coastal structures. Their research for the next few years will focus on this challenge, which eventually will result in safer and more cost-effective construction for hurricane-prone coastal regions.

-- rudd --

Technical Contact: Dr. Mohammad N. Noori, 919/515-2365 or mnoori@eos.ncsu.edu
Media Contact: Linda E. Rudd, 919/515-3848 or linda_rudd@ncsu.edu>

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