Seismic performance of prefabricated connections for partially encased composite beam to CFST column

Partially encased composite (PEC) beam and concrete-filled steel tube (CFST) column may take advantages of both steel and concrete for high-rise and long-span applications. However, understanding on the seismic performance of such PEC beam-to-CFST column joints is still quite limited, leading to a lack of relevant moment resistance design methods. Two experimental scenarios and nine finite element (FE) models subjected to cyclic loading were developed in this study to understand their moment-rotation responses. The main results showed that the initial rotational stiffness, plastic moment, and ultimate moment generally decreased with the reduction in bolt diameter and end-plate thickness. The middle rows of bolts had a minimal impact on the initial rotational stiffness and bearing capacity of the connections, while the edge rows of bolts and the stiffeners presented more significant effects. Based on the experimental and FE results, a design method was developed to estimate the moment resistance of the PEC beam-to-CFST column joints. The resulting moment resistance was compared with the plastic moments from the experiments and FE analyses, with 97 % in average and 0.06 in deviation.