Seismic behaviour of a novel demountable joint connecting FTCES columns and RC beams

Abstract

Fiber-reinforced polymer (FRP) tube-concrete-encased steel (FTCES) column shows excellent strength, stiffness and ductility owing to composite action. However, its practical application is very limited because there is a lack of knowledge on the behaviour of the entire structural system, which includes the beam-column joint. Indeed, the design of the connection between FTCES columns and beams is the most challenging task, which governs the reliability and safety of the entire structural system. To fill up the research gap, a novel demountable beam-column joint was proposed to connect the FTCES columns and reinforced concrete (RC) frame beams using high-strength bolts. The joint consisted of two cover plates, two steel ring plates, two connecting beams (with end plates) and a hollow steel tube infilled with core concrete. A total of four specimens were designed to study the seismic behaviour of the proposed joint, considering the effect of the steel tube / plate (ring plate and flange of connecting beams) thickness and the axial load ratio. Test results showed that the proposed demountable joint could provide an effective and simple connection with favourable seismic performance. Besides, with thinner steel tube and steel plate, specimen failed due to steel fracture in the joint region and few minor cracks were observed on the RC beams. Under this circumstance, the material strength of RC beams was not fully utilized, leading to smaller peak load. For specimens with thicker steel tube and steel plate, the failure was due to serious concrete crushing on the RC beams and excellent seismic performance was achieved. Lastly, an analytical model was proposed to estimate the peak load of the joint and by comparison, it is concluded that the proposed model could give a very accurate prediction.