Study of Failure Mode and Ultimate Bearing Capacity for Self-Centering SMA Connection

An innovative self-centering shape memory alloy (SMA) connection that is used in a steel frame beam-column joint was developed to improve the energy dissipative capacity and self-centering capacity, and reduce the residual deformation. Five self-centering SMA connections with the effect of SMA fracture, bolt bending, and bolt pretension, were designed and analyzed, so the deformation modes, failure modes, hysteresis curves, and skeleton curves of the specimens can be obtained. Then, the validated finite element analysis method was used to simulate the analysis models, considering the influences of SMA areas, angle thicknesses, and slip bolt strength. The test results show that the hysteretic curves of the SMA connection can be idealized as a flag-shape, and the bearing capacity, energy dissipative capacity, and self-centering capacity will be effectively improved by enlarging the SMA areas. The SMA wires in the connection may be fractured while the strain of the SMA wires reaches 15%, so the displacement of the SMA connection should be restricted with a strain value of 8% for safety. The effect of asymmetry for the SMA connection may cause the bolt to bend and reduce the bending capacity. In addition, the yield force of each plate is suggested to be higher than the ultimate bearing capacity of the SMA connection. Finally, based on the test and finite element analysis results, the design method of the self-centering SMA connection is proposed to avoid the unexpected failure modes and achieve the expected mechanical properties.