Seismic behavior and design method of a novel high-resilient CFST composite joint with SMA bars and low-yield angle fuses

Beam-column joints are critical force-transfer components in concrete-filled steel tubular (CFST) frame systems. However, conventional CFST joints often develop excessive residual deformation after earthquakes, hindering post-earthquake repair and functional recovery. To address this limitation, this study proposed a high-resilient CFST composite joint that couples a self-centering mechanism with a replaceable fuse concept. Shape memory alloy (SMA) bars provided a self-centering force, while low-yield (LY) steel angle fuses served as the primary energy-dissipating elements. Cyclic loading tests were conducted on three high-resilient specimens and one standard specimen to characterize failure evolution and seismic behavior. Under cyclic loading, the steel beam and CFST column of the high-resilient joints remained largely elastic, and plastic deformation was intentionally concentrated in the replaceable angle fuses. The proposed high-resilient joint exhibited stable flag-shaped hysteresis loops while demonstrating superior initial stiffness and peak load-bearing capacity. Compared with the standard specimen, their initial stiffness and peak load-bearing capacity increased by no less than 58.8% and 9.9%. Meanwhile, the study analyzed the effects of the test variables, including SMA bars, angle fuse thickness, and axial compression ratio. The results demonstrated that SMA bars effectively reduced residual deformation. Increasing the angle fuse thickness enhanced energy dissipation but compromised self-centering efficiency. Although a higher axial compression ratio increased the initial stiffness, it also accelerated stiffness degradation under conditions of large deformation. Further, a component-based analytical model was developed to predict the flexural capacity. The prediction error of this model was within ±5.9%, supporting its applicability for design-oriented assessment.