Steel beam-column connections using shape memory alloys

This study evaluates the feasibility of a new class of partially restrained connections using shape memory alloys. In the martensitic form, shape memory alloys (SMAs) have the ability to recover large residual deformations by heating the alloy above its transformation temperature. The proposed connection consists of four large diameter NiTi SMA bars connecting the beam flange to the column flange and serve as the primary moment transfer mechanism. Two full-scale connections were tested using the SAC loading protocol. The connections exhibited a high level of energy dissipation, large ductility capacity, and no strength degradation after being subjected to cycles up to 4% drift. Following the initial testing series, the tendons were heated to recover the residual beam tip displacement. After initiating the shape memory effect within the tendons, the connections were retested, displaying repeatable and stable hysteretic behavior. An additional test was performed under dynamic loading to examine the strain rate effects on the performance of the connection. The dynamic tests showed similar behavior, except for a decrease in energy dissipation capacity when compared to the quasi-static tests.