Experimental study on low-cycle fatigue behavior of welded I-section steel bracing members under constant amplitude reversed cyclic axial loading

Based on the low-cycle fatigue behavior tests of welded I-section ST12 steel bracing members with pinned connections under constant amplitude reversed cyclic axial loading, the low-cycle fatigue behavior of welded I-section Q235 steel bracing members with pinned connections was examined. The test results about the maximum lateral deformation and the maximum compressive strength of 47 bracing members made of Q235 and ST12 were studied and verified in comparison with the results calculated by the relevant literatures or codes. According to the assumption that the geometry properties, loading amplitude and steel yield strength are independent of each other for estimating the low-cycle fatigue life, some empirical formulas are presented. It is found that the low-cycle fatigue life increases with the decrease in the width-thickness ratio of the flanges, the increase in the brace slenderness ratio, and the decrease in the loading amplitude and yield strength of the bracing members. Because the displacement histories of the bracing members can not be predicted during an earthquake, in order to avoid early fractures of the bracing members, besides limiting the width-thickness ratio of the flanges, low yield strength steel should be adopted and the brace slenderness ratio limitation in some current codes should be relaxed. Finally, based on the energy index ratios for different damage stages, it is proposed that the low-cycle fatigue life of brace members can be safely predicted by the empirical formulas for stage I.