New Flexible Loading Beam for Bidirectional Real-Time Hybrid Simulation of Reinforced Concrete Columns

This study presents a novel flexible loading beam (FLB) designed to address the challenges of applying axial force in real time during bidirectional real-time hybrid simulations (RTHSs) of reinforced concrete (RC) columns. The FLB is highly effective for applying axial forces to axially stiff members. However, existing FLBs face challenges in controlling axial force when out-of-plane rotations occur during bidirectional (i.e., two horizontal directions) RTHSs. To address this issue, a new FLB was developed by incorporating a spherical bearing at its central bottom. This design ensures stable force application by allowing free rotation at the column's top while maintaining parallel alignment of the FLB with the ground. Experimental validation was conducted using a multiactuator setup with an RC column subjected to bidirectional horizontal earthquake loads. The results demonstrated the exceptional performance of the new FLB in maintaining precise axial force control, even under significant bidirectional lateral displacements.