Cyclic loading behavior and restoring force model of disc-spring self-centering beam-column joints

This study theoretically investigated a new type of prefabricated Disc spring Self-centering Steel beam-column Joints (DsSCSJs). It incorporates the disc-spring device to produce restoring force and web friction cover plates to provide energy dissipation capacity, while confining plastic damage primarily to the upper flange cover plates at the splicing connection of the main beams. The spliced beam segment rotates about the center of the upper flange cover plates, reducing the adverse impact of the "beam elongation" effect in traditional self-centering frames. Based on the previous cyclic loading tests of the joints, this paper mainly investigates the working mechanism and hysteretic performance of the new joint by using the verified finite element analysis (FEA). The effects of key factors on the hysteretic behavior and self-centering ability were explored, including disc-spring stiffness, web plate friction, flange cover plate thickness, bolt slip, and connection detailing. Subsequently, a moment-rotation restoring force model of the joint was established from theoretical derivations, with detailing suggestions proposed. The results showed that the finite element model and analysis were in good agreement with the test results, revealing its working mechanism and performance. The proposed theoretical restoring force model can accurately simulate the cyclic loading behavior of joints. A pin connection in the self-centering device results in lower stress concentrations and better self-centering ability in the DsSCSJ. To attain complete self-centering, the pre-compression bending moment produced by the disc spring should be greater than the friction moment and the plastic resistance moment of the beam flange cover plates. The residual deformation of the joints is primarily caused by the bolt slippage and possible local yielding at the beam-column connection, and consequently the self-centering ability of the DsSCSJ can be effectively improved by diminishing bolt slip and preventing the beam-column connection yielding by proper design and construction detailing.