Seismic behavior of ring beam joints between concrete-filled twin steel tubes columns and reinforced concrete beams

This paper introduces a new type of connections—ring beam joints with a discontinuous outer tube between the concrete-filled twin steel tubes (CFTSTs) columns and reinforced concrete (RC) beams. In this connection, the outer steel tube is interrupted so the longitudinal reinforcement of the RC beams can be continuous in the joint zone. The transferring of moments and shear forces is ensured by the continuous rebars, and the reduced stiffness of the composite column due to the interruption of the outer steel tube is compensated by the confinement of the steel cage anchored inside the joint zone and the improvement on the compression area of the octagonal ring beam located outside the column. Four beam-column assemblage specimens were tested subjected to cyclic loads, and the seismic behavior of the joints was studied including the load-deflection performance, typical failure modes, stress and strain distributions, and energy dissipation capacity. The test results showed that the joints with good aseismatic behavior can easily achieve the anti-seismic design principles, namely “strong column-weak beam” and “strong joint-weak member”. Finite element modeling was also implemented to conduct some parametric analyses.