Out-of-Plane Deformation Effects on the Seismic Performance of Friction Plastic-Hinge-Supported Walls: Experimental and Analytical Study

Abstract

The concentration of damage in the plastic hinge region of conventional reinforced concrete (RC) shear walls poses significant challenges to post-earthquake functional recovery. To address this, the Friction Plastic-hinge-Supported Wall (FPSW) was proposed as a resilient alternative. This system integrates a physical hinge at the base with replaceable friction dampers, isolating inelastic deformation while protecting the upper wall. Although out-of-plane actions severely impair conventional RC walls, their impact on FPSWs requires investigation. This study investigates the multi-axial seismic performance of FPSWs through subassemblage-level quasi-static testing under bidirectional loading. The experimental program evaluated out-of-plane deformation effects, damper connection details (pin-connected vs. cross-plate welded), and construction methods (cast-in-place vs. precast). Results demonstrate robust spatial stability; in-plane strength reduction due to projection efficiency loss remained below 10% even under a significant out-of-plane drift of 1/50 rad. Furthermore, cross-plate welded connections effectively eliminated mechanical slack, thereby enhancing initial stiffness and energy dissipation compared to pin connections. The tests also validated the reliability of the connection between the precast wall and the FPSW base. Finally, an analytical model accounting for out-of-plane interaction was developed. The proposed equations for predicting stiffness and strength agree with test results within a 15% margin, establishing a practical basis for local capacity-design workflows.