October 24, 2002

Safe, Affordable Housing a Focus for NC State Researcher

A sample wall made using unbonded post tensioning is ready to be tested at the Constructed Facilities Laboratory at NC State University.		During testing, which is intended to simulate the effects of an earthquake, the sample wall shows minor damage at the base but is otherwise intact and will return to its original configuration with minimal repairs.

Materials scientists and mechanical engineers have been busy in recent years developing a whole range of new materials that can make buildings safer and more able to withstand the stress of damaging events such as earthquakes and hurricanes. As wonderful as these new materials are, they tend to be expensive and could make the cost of building a home from them prohibitive.

Dr. Mervyn J. Kowalsky, assistant professor of civil engineering at NC State University, is trying to find ways to make damage-resistant buildings by applying conventional techniques and materials in new ways. He hopes the result will be homes that are more durable, easier to construct and more affordable than current construction.

Durability, reduced maintenance and affordability are inherent characteristics of masonry construction, so Kowalsky wanted to find a way to use precast masonry to make damage-resistant buildings. Using a technique called unbonded post tensioning, Kowalsky has constructed and tested walls designed to withstand shaking events.

Post tensioning is typically used in bridge construction; however, about eight years ago, Dr. Nigel Priestley, professor emeritus at the University of California, San Diego, proposed the use of the system for the seismic-resistant design of concrete buildings. At NC State, Kowalsky has applied this technique to masonry wall construction by replacing conventional cross-hatch rebar with two or three high-strength reinforcing bars placed vertically in the wall. The resulting wall can self-correct to the original configuration after a damaging event. According to Kowalsky, "The wall's inherent correctability comes from the force within the bars and the fact that they are not bonded to the surrounding masonry. The walls will rock back and forth during an earthquake or high wind, but then they will return to the original position."

For his research Kowalsky is identifying different types of configurations for the reinforcing bars to find the one with the best performance. The resulting walls are being tested at the Constructed Facilities Laboratory (CFL) on NC State's Centennial Campus. “The configuration that was the simplest to construct and gave us the best performance is a masonry wall containing high-strength rebars plus a set of galvanized steel plates that are placed in the mortar joints,” said Kowalsky. “The use of steel plates in masonry aims to mimic the effect of conventional reinforcement in concrete structures.”

The next step in Kowalsky’s research is to test the wall’s durability if holes for windows and doors are cut and to figure out how to attach roofs and floors to the walls. Kowalsky envisions a pilot project someday in which walls could be fabricated and tested in a controlled environment and then transported to a building site for homes.

Kowalsky’s work is just one facet of a National Science Foundation (NSF)-funded cooperative agreement with the Partnership for Advancing Technology in Housing (PATH). Begun during the Clinton administration, this organization has the goal of identifying mechanisms by which durable and affordable housing can be constructed. PATH is made up of government and industry groups, including homebuilders, federal agencies, researchers, developers and building industry professionals.

— rudd —

Media Contacts:

Dr. Mervyn J. Kowalsky, 919/515-7261, kowalsky@eos.ncsu.edu

Linda E. Rudd, 919/515-3848, linda_rudd@ncsu.edu

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