Researchers at Purdue University are studying the effects of fire on steel structures such as buildings and bridges using a one-of-a-kind heating system and a specialized laboratory for testing large beams and other components.
Building fires may reach temperatures of more than 1,800°F (1,000°C), notes Amit Varma, a Purdue associate professor of civil engineering who is leading the work. "At that temperature, exposed steel would take about 25 minutes to lose about 60 percent of its strength and stiffness," he says. "As you keep increasing the temperature of the steel, it becomes softer and weaker."
One project focuses on how a building's steel-and-concrete floor and its connections to the building behave in a fire. Another project concentrates on how fire affects steel columns and a building's frame.
Such testing is customarily conducted inside large furnaces. "However, in a furnace, it is very difficult to heat a specimen while simultaneously applying loads onto the structure to simulate the forces exerted during a building's everyday use," Varma says.
To overcome this limitation, Purdue researchers designed a system made up of heating panels to simulate fire. The panels have electrical coils - like giant toaster ovens - and are placed close to the surface of the specimens. As the system is used to simulate fire, test structures are subjected to forces with hydraulic equipment.
Though better at subjecting the test specimens to load, the setup is not perfect. Purdue researchers note that in practice, beams and other steel components in buildings are covered with fireproofing materials to resist the effects of extreme heating. So, researchers are conducting tests with and without fire protection.
The Test RigThe heating system being used to test full-scale steel columns - located at Purdue's Robert L. and Terry L. Bowen Laboratory for Large-Scale Civil Engineering Research -is believed to be the only such heating system in the world, Varma says.
Each panel is about 4' square, and the system contains 25 panels that cover 100 ft2. Having separate panels enables researchers to heat only certain portions of specimens, recreating "the heating and cooling path of a fire event," Varma says.
The Bowen Lab is one of a handful of facilities where testing can be performed on full-scale structures to yield more accurate data. The 66,000-ft2 laboratory is equipped with hydraulic testing equipment and overhead cranes.