Novel filler-free buckling-restrained steel energy dissipation devices: Cyclic behavior and failure mechanism

The concept of self-centering structures has emerged in recent years to enhance seismic resilience under strong earthquakes. In self-centering structural systems, seismic damage is typically designed to be concentrated on energy dissipation (ED) devices that can be easily repaired or replaced after an earthquake. Among various ED devices, buckling-restrained steel bar-type dissipaters have received widespread attention due to their excellent hysteresis behavior. Traditionally, these types of dissipaters are designed with a reduced section (i.e., fuse part) surrounded by a steel confining tube, and the gap between them is filled with grout or epoxy to prevent global buckling of the steel bar under tension-compression cyclic loading. However, there is no doubt that such design concept faces several challenges in practical applications, including grouting difficulties, low material utilization, and laborious machining due to the reduced section in the fuse part. To address these issues, this paper presents a novel type of filler-free buckling-restrained ED device to overcome the abovementioned limitations of conventional steel bar-type dissipaters. The design concept of the proposed ED devices was illustrated first. Subsequently, cyclic behavior and failure mechanism of the proposed ED devices were investigated experimentally under quasi-static cyclic loading. Test results show that all specimens exhibit satisfactory hysteresis loops with stable ED capability under different loading conditions. The failure modes of all specimens concentrate in the fuse parts, and there is no out-of-plane bending instability failure due to the constraint provided by the additional restrained sleeves. Moreover, a practical evaluation method was proposed to prevent the out-of-plane bending instability of the proposed devices in seismic applications.