Seismic performance of steel-reinforced concrete hybrid structures considering vertical stiffness variations

Abstract

The load-carrying capacity and stiffness variation method of transfer connections significantly influence the dynamic response of steel-reinforced concrete vertical hybrid structures. This study proposes a new transfer connection characterized by short steel beams and U-shaped stirrups welded to the bottom of the steel tube to enhance the interaction between the steel tube and the concrete. Additionally, introducing concrete and steel angles inside the steel tube to form a concrete-filled steel tube (CFST) column facilitates smoother stiffness variation along the vertical direction. Five 0.5-scale specimens were designed and fabricated for physical tests. The tests were conducted by applying combined pre-axial loads and lateral cyclic loading to evaluate the seismic performance of the proposed transfer connections. The results demonstrate that incorporating concrete and steel angles inside the steel tube substantially improves the transfer connection's load-carrying capacity, stiffness, and energy dissipation capacity. A larger volume of concrete can enhance stiffness and energy dissipation; however, its effect on load-carrying capacity varies depending on whether steel angles are present inside the tube. Compared with standard EC3, the proposed transfer connection achieves a rigid connection between the structure's steel/CFST and reinforced concrete (RC) parts. Furthermore, a comparison with standards GB 50986, GB 50017, EC4, EC3, and AISC 360 shows that the load-carrying capacity of the proposed connection exceeds that of the steel/CFST column, thereby adhering to the design philosophy of strong connections and weak members.