Study on Stability of Equal-Leg Angle-Steel Members in Transmission Towers at Uniform Elevated Temperature

Equal-leg angle-steel members are widely used as main load-bearing and bracing members in transmission towers. Under elevated-temperature environments such as mountain fires and forest fires, the elastic modulus and strength of steel degrade significantly, which may reduce the overall stability capacity of compression members and even lead to instability failure. To investigate the stability performance of equal-leg angle-steel members made of Q420 steel at uniform elevated temperatures, a shell-element finite-element model was established in Abaqus by considering temperature-dependent material properties of steel. Parametric analyses were carried out under constant compressional loading and uniform heating for the cases of pinned–pinned, fixed–fixed and eccentric–pinned conditions. The effects of slenderness ratio, stability load ratio, section dimension, and initial imperfection amplitude on the critical temperature were systematically analyzed. The results show that the critical temperature decreases significantly with increasing stability load ratio. The eccentric–pinned condition leads to a higher critical temperature than the other two conditions. The initial geometric imperfection will reduce the fire resistance of members. Based on the critical temperature method, design curves of the critical temperature for three boundary conditions were developed using the finite-element results, which are demonstrated to be more accurate than the existing Chinese and European codes.