Lateral torsional buckling of steel W-beams subjected to localized fires

Abstract

Current design approaches to assess the lateral torsional buckling capacity of steel beams in fire are based on the assumption of uniform steel temperature. This paper investigates the effect of temperature gradients on the lateral torsional buckling behavior of steel wide flange (W) beams in fire conditions. The effects of localized fires and the temperature gradients they produce in steel beams were studied. Laterally unrestrained beams of various dimensions were subjected to a range of load ratios. The location of the localized fire was varied to provide different heating conditions. The standard ISO834 fire, and a uniform temperature condition in which the steel temperature was ramped linearly were used for comparison. The study shows that temperature gradients within a steel W-beam may have a detrimental effect on the lateral torsional buckling capacity of the beams in fire. The critical temperature, defined as the maximum temperature in a steel beam at which the beam undergoes lateral torsional buckling, in real fires may be hundreds of degrees lower than that in the standard ISO834 fire. The critical temperature in real fires may also be lower than that in the uniform heating condition. Design approaches based on the standard ISO834 fire or uniform steel temperature assumption may give unconservative results if the potential real fires are localized fires.