Time-Dependent Buckling of Steel Columns Exposed to Fire
Mohammed A. Morovat, Michael D. Engelhardt, Todd A. Helwig and Eric M. Taleff The University of Texas at Austin, Austin, TX
Sponsored by National Science Foundation
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 col-lapse load of steel columns subjected to fire temperatures.
Along with the main goal of developing a fundamental understanding of the phenomenon of creep buckling, this project has shown that time-dependent effects are significant in response of steel columns in fire. Now that the buckling tests on W4×13 columns have ended, the methodology devel-oped to account for the effect of material creep on the buckling of steel columns in fire can be further verified. An example of such veri-fications is shown where analytical and computational creep buckling predictions are compared against test results for W4×13 columns with KL/r of 51 at 600 °C. Analyt-ical solutions are based on the concept of time-dependent tan-gent modulus. Computational creep buckling analyses are per-formed in Abaqus®. A material creep model developed in this study for ASTM A992 steel is utilized in analytical and compu-tational buckling analyses. Con-sidering all the uncertainties in material creep models and buck-ling prediction methods, reasona-bly well agreements can be seen.