The fiery collapse of the World Trade Center towers in 2001 offered dramatic proof that even steel structures can fail at high temperatures. With information from Amit Varma, the towers of tomorrow may be able to better withstand the threat of missile or airplane impacts, earthquakes and fires.
Associate Professor of Civil Engineering
Varma's research focuses on the effects of fire on buildings and bridges. The findings will be used to potentially update design codes for steel structures, ultimately making them better and safer. His team also has demonstrated the safety of an emerging type of nuclear power plant design and shown that it is flexible and strong enough to withstand powerful earthquake forces. The new design may reduce the cost of building nuclear power plants by speeding construction time significantly, he says.
"This approach might dominate the future design of nuclear power plants because of its construction and structural efficiency," he says.
LAB SPACE OFFERS
At least 10 doctoral students have been involved in the projects, based at
Purdue's Robert L. and Terry L. Bowen Laboratory for Large-Scale Civil Engineering Research, a place where bigger is better. It's one of a handful of facilities around the world where testing can be performed on full-scale structures instead of smaller specimens that yield less-accurate data. The lab is equipped with heavy-duty hydraulic testing equipment and powerful overhead cranes.
Fires in buildings may reach temperatures of 1,000 degrees Celsius, or more than 1,800 degrees Fahrenheit. The strength of steel structures drops by about 40 percent when exposed to temperatures of 500 to 600 degrees Celsius.
Steel components in buildings are typically covered with fireproofing materials to resist the effects of extreme heating.
"So the air could be 1,000 degrees in a fire, but the insulated steel might be 500 degrees," Varma says. "Even with the fireproofing, it can get too hot for steel. Once you get beyond 600 degrees, steel structures can have real problems. They lose their stiffness and strength, just like cooked spaghetti."
Varma's research team is quantifying exactly what happens to steel buildings in fire, precise knowledge that will allow engineers to develop computational models that others can use to design buildings that have the best possible resistance to fire.
In one research area, Varma and his team designed a system made up of heating panels to simulate the effects of fire on steel structures. The panels have electrical coils, like giant toaster ovens, and are placed close to the surface of the specimens. As the system simulates the effects of fire, test structures are subjected to forces with hydraulic equipment to mimic the loads experienced in buildings.
"The research in our lab is directed toward helping industry by validating that the designs are safe, and producing design codes that others can use to build structures," Varma says. "I never imagined as a graduate student that my work would have such important impacts in society."
NUCLEAR PLANT DESIGN
In addition to the research into steel structures, Varma also has led extensive testing of the new design for nuclear power plants. Westinghouse Electric Co.'s innovative AP1000 nuclear power plant design features a "steel-concrete-composite" construction. Instead of using more conventional reinforced concrete, which is strengthened with steel bars, the steel-concrete approach is a sandwich of steel plates filled with concrete.
One advantage to the steel-concrete approach is that it enables engineers to sidestep a major impediment to conventional construction methods.
"With a nuclear power plant there is so much concrete involved that the construction schedule can be years," Varma says. "If you could cut just one year out of the construction timetable, the system would pay for itself, because selling electricity is far better than building the plant to generate it."
The researchers are creating models that could be used to test designs for seismic safety. Findings have shown the steel and concrete design can withstand the seismic forces that would result from strong earthquakes. The same data can be used to benchmark models for shielding against missile or aircraft impacts.
This form of steel and concrete construction was first used more than a century ago and is likely to dominate future nuclear plant design, Varma says, but no codes or standards yet exist. As vice chair of an industry committee, he is leading efforts to create a new standard.