Experimental and numerical study on cyclic behavior of steel-plate composite (SC) member-to-RC member L-joint with novel strengthening methods

The steel-plate composite (SC) member-to-reinforced concrete (RC) member L-joints are pivotal connections in the subsequent modular nuclear power plants of Hualong Pressurized Reactor (HPR1000). However, despite the inherent shear weakness, limited research focuses on the shear failure mechanism of SC-RC L-joints, necessitating the development of shear-strengthening methods. This study investigates the cyclic behavior of SC-RC L-joints through experiments and numerical simulation. Based on the proposed four shear-strengthening methods, including X-shape tie-bar, #-shaped tie-bar, UHPC, and a combination of UHPC with X-shape tie-bar, cyclic loading tests were conducted on five large-scale SC-RC L-joint specimens. The test results showed that the unstrengthened specimen suffered joint shear failure, while the other four specimens underwent shear failure of RC member. Moreover, the developed finite element model accurately simulated the failure modes and load-deformation curves of test specimens. Parametric studies further revealed that both the steel ratio of tie bars and the strength of UHPC significantly influence the joint shear strength, proving the effectiveness of four strengthening methods. Additionally, comparison results indicated that existing design codes significantly overestimated the joint shear strength of SC-RC L-joint. Finally, design recommendations for joint shear-strengthening are proposed.