Buckling of a Normal Strength, Concentrically Loaded RC Bearing Wall under Fire Exposure

This project, funded by the National Science Foundation, has been investigating the effect of fire on the behavior of reinforced concrete bearing wall systems. Reinforced concrete bearing walls are one of the most common primary load-resisting components in building structures such as hospitals, hotels, offices, and condominiums. The walls carry much of the self-weight and other gravity loads on the building; and thus, their stability during and after a fire contributes significantly to the ability of the building to prevent catastrophic collapse. Maintaining the integrity of the walls until burn-out is also critical in developing fire-protected stairwell systems for sustainable building emergency egress and access activities.
Due to their large size, strength, stiffness, and thermal mass, reinforced concrete walls are generally considered as being very robust structures that have the capacity to withstand uncontrolled building fires until burnout. However, explosive spalling of concrete and degradation of steel and concrete strength due to elevated temperatures can induce out-of-plane instability. This effect can be especially severe under "compartment" fire events that affect the wall only from one side.
There is currently extremely limited information on the behavior of these structures under fire. This lack of information is largely due to sheer size of reinforced concrete bearing walls, limiting physical testing in the laboratory. The application of appropriate boundary conditions, response monitoring techniques, and appropriate magnitude of gravity loads are also extremely challenging under the presence of high temperatures. This is because most fire testing is conducted by enclosing and subjecting the structure to elevated temperatures inside a fire furnace chamber. Through this NSF research, we employed a different technique where a portable furnace was developed and brought next to the specimen to simulate a compartment style fire. This allowed full scale walls to be tested under fire and simultaneous large gravity loads, while also applying appropriate boundary conditions and unprecedented response monitoring techniques. The response monitoring of the test specimens was conducted in collaboration with researchers from the University of Texas at Tyler. We were able to show for the first time that buckling of reinforced concrete walls can occur under fire durations that are much shorter than currently allowed by U.S. building design codes. The research also revealed important wall design changes that must be adopted by the current codes to improve the behavior of these structures under fire.