Numerical analysis and restoring force model of semi-prefabricated CFDST column-steel beam joint

Concrete-filled double-skin tubular (CFDST) structures demonstrate considerable potential in high-rise building applications and resilience against extreme disasters. However, traditional CFDST joint designs face challenges in engineering practice, such as high construction difficulty and complex on-site welding, which limit the widespread application of CFDST structures. This study developed a novel semi-prefabricated CFDST column-teel beam joint and conducted quasi-static tests on five joints. Subsequently, an accurate finite element model (FEM) was established and validated through comparison with the experimental results, including the failure modes, the hysteresis and skeleton curves, and the moment capacity. Building on the high accuracy of the model, 21 finite element simulations were conducted to analyze the effects of eleven parameters on the performance of the joint. The results revealed that increasing the thickness of the outer square steel tube by 4 mm and extending the ring plate length by 80 mm enhanced energy dissipation by 14.6 % and 95.3 %, respectively. Replacing a solid-core CFDST column with a hollow-core design not only reduced structural weight but also facilitated the inner circular steel tube to carry more load as the outer square tube reached its ultimate strength. Additionally, the joint exhibited excellent seismic performance even under a high axial compression ratio of 0.45. Finally, a trilinear skeleton curve model and hysteretic rules were established, and a simplified restoring force model was proposed. This model demonstrates high evaluation accuracy and can serve as a reference for the elasto-plastic seismic response analysis of such structures.