Development and performance of filler-free buckling-restrained shape memory alloy devices for self-centering seismic applications

This study proposes a novel filler-free buckling-restrained SMA device for self-centering seismic applications. The proposed device consists of an SMA core bar, a confining tube, two swaged sleeves, two restraining sleeves, and two connection parts. The SMA bar includes a fuse part and two swaged parts, functioning similarly to the fuse mechanism of conventional dog-bone shaped SMA bars. This design eliminates the time-consuming machining of the reduced section required for conventional dog-bone shaped SMA bars and the grout-filling process for buckling-restrained devices, thereby simplifying fabrication and improving material utilization. The design concept of the buckling-restrained SMA bars was first introduced, followed by an experimental investigation into the tension–compression behavior and failure modes under cyclic loading. A three-dimensional finite element model was then developed to further explore the device's cyclic characteristics. Experimental results show that all specimens exhibit stable and satisfactory flag-shaped hysteresis loops with excellent self-centering capability under cyclic tension–compression loading. Failure consistently occurred in the fuse part, and no pull-out failure of the SMA bar from the swaged sleeves was observed. Furthermore, the buckling behavior of the SMA bar, the contact interactions between the bar and the confining tube, and the restraining effects of the additional sleeves were numerically analyzed. The results demonstrate that the incorporation of restraining sleeves plays a critical role in suppressing out-of-plane instability of the unrestrained fuse part.