Abstract: This paper presents a nonlinear 3-D finite element (FE) study on the seismic behaviour of concrete-encased concrete-filled steel tubular column to steel beam joints with RC slabs. The FE model considers material and geometric nonlinearity, the cumulative damage of concrete and the interaction between concrete and steel. The proposed finite element model is verified by previous experimental results. The failure mechanism of such composite joints is analyzed using this model. It is found that a compression strut is formed in the concrete panel zone to resist the shear force together with the steel tube and reinforcement cage in the panel zone.