Resilient Slip-friction Joint (RSFJ) Secondary Fuse and Its Influence on Seismic Sequences

Abstract

The Resilient Slip-Friction Joint (RSFJ) is a friction damper designed to provide stable hysteresis and self-centering behavior in its primary stage of response. Under extreme loading, a secondary ‘fuse’ mechanism is activated by yielding the steel rods (used as bolts), enabling additional deformation capacity. While the secondary mechanism enhances ductility, it also elongates the rods permanently, allowing the disc springs to decompress, and therefore reduce the pre-stressing forces. These can potentially degrade the joint's damping and re-centering performance in subsequent loading cycles. This study investigates whether such hysteresis degradation increases the system's vulnerability to subsequent earthquakes like aftershocks. A numerical model was developed to simulate RSFJ behavior across both primary and secondary stages, capturing key nonlinear and degradation effects consistent with experimental observations. The model was applied in a single-degree-of-freedom system to simulate a tested RSFJ-braced frame and analyzed under mainshock-aftershock sequences. Results reveal that hysteresis degradation caused the aftershock responses to amplify in proportion to the mainshock response and to the aftershock intensity ratio (AR). To mitigate the risk of bolt rupture during strong aftershocks, i.e. AR > 0.8, pre-stressing losses from the initial mainshock must remain below 40–60 %. In contrast, for aftershocks with AR below 0.6–0.7, the system was generally capable of sustaining aftershocks without further deterioration regardless of the initial pre-stress loss. In sum, these findings reinforce current design practices which limit the activation of the RSFJ's secondary fuse only to strong and rare earthquakes, typically up to 1.5 times the design-level earthquake.