Experimental and Theoretical Studies on Plastic Torsional Buckling of Steel Buckling-restrained Braces

摘要

A type of partly-welded BRB was proposed in this paper to mitigate the unfavourable effect of the welds on the low-cycle fatigue property of BRBs. Three partly-welded BRB specimens under different strain amplitudes were tested and the plastic torsional buckling of the end portion was observed in two specimens. According to the experimental results, the strain amplitude is an important factor for the torsional buckling of the end portion. The critical stress declines with the increase of the strain amplitude, while the maximum compressive stress increases with the growth of the strain amplitude. Even though the hysteretic behaviour of specimens under large strain amplitudes met the requirement by seismic provisions (AISC 2010), torsional buckling is an undesired failure mode for BRBs, which leads to great torsional deformation of BRBs. Based on the principle of minimum potential energy, a theoretical formula of the critical stress was provided in this paper, which gave a good prediction to the failure mode. Moreover, a recommendation value of the calculated length based on the theoretical equation was given for the design to avoid torsional buckling in the unrestrained part of the BRB's yielding segment.