Time-Dependent Buckling of Steel Columns Exposed to Elevated Temperatures due to Fire

Sponsor: National Science Foundation
Principal Investigators: Michael Engelhardt, and Todd Helwig
Research Assistants: Mohammed A. Morovat, Eric Taleff

two photos of machine with column, right shows column buckling

The ability of steel columns to carry their design loads is greatly affected by time- and temperature-dependent mechanical properties of steel at high temperatures due to fire. It is well known that structural steel loses its strength and stiffness with temperature, especially at temperatures above 400 °C. Further, the reductions in strength of steel are also dependent on the duration of exposure to elevated temperatures. The time-dependent response or creep of steel plays a particularly important role in predicting the collapse load of steel columns subjected to fire temperatures. Specifically, creep of steel leads to the creep buckling phenomenon, where the critical buckling load for a steel column depends not only on slenderness and temperature, but also on duration of applied load.

To investigate the effect of time-dependent material behavior or creep on buckling of steel columns subjected to fire, material characterization tests are performed at temperatures up to 1000 °C to evaluate tensile and creep properties of ASTM A992 steel at elevated temperatures.

In addition, buckling tests on W4×13 wide flange columns under pin-end conditions are conducted to characterize short-time and creep buckling loads at elevated temperatures. The column test results are further used to verify analytical and computational tools developed in this project to model the time-dependent buckling of steel columns at elevated temperatures. Test results are also compared against code-based predictions from Eurocode 3 and the AISC Specification.

 4 photos, first 3 show machinery, last shows diagram