"When it starts sagging, the question is, how do the connections perform? This has been a big question for the industry," Varma said.
The researchers analyzed critical joints after a floor system was subjected to extreme heat in a special oven at Michigan State University. Results will be used to help researchers create a model of the steel-concrete floor system.
"It is far more difficult to model a floor system than it is to model columns," Varma said. "But we will eventually be able to do that."
Another paper to be published in December in the American Institute of Steel Construction's Engineering Journal shows how to use the models to create design specifications for columns. The paper was written by Agrawal, who also is involved in modeling the steel columns and the collapse of entire building systems. The work is ongoing.
Varma also has led research to test a new type of design for nuclear power plants. The work focuses on testing structures like those to be used in the Westinghouse Electric Co. AP1000 standard nuclear power plant design. Engineers tested components of an "enhanced shield building" that will contain the plant's main system components.
The building consists of an inner steel-wall containment vessel and an outer radiation shield made using a technology called steel-concrete-composite construction. Instead of using more conventional reinforced concrete, which is strengthened with steel bars, the steel-concrete approach uses a sandwich of steel plates filled with concrete.
The new design may reduce the cost of building nuclear power plants by speeding construction time. The composite construction method was first used more than a century ago, but no codes or standards for its use in nuclear power plants yet exist, said Varma, who is vice chair of an industry committee writing a new specification for composite structures in nuclear power plants.
Findings have shown the design withstands the seismic forces that would result from strong earthquakes. Data also indicate the construction method, also called armored construction, could be used to create structures capable of withstanding aircraft or missile attacks.
"When you have steel plates on the inside and on the outside, it's a structure that would hold up against an aircraft impact or extreme weather events, such as tornados," Varma said. "Nothing can easily punch through that sort of structure."
The Bowen lab is one of a handful of facilities where testing can be performed on full-scale structures instead of smaller-scale specimens, yielding more accurate data. The 66,000-square-foot laboratory is equipped with special hydraulic testing equipment and powerful overhead cranes.