Structural Behavior of RC Foundation Connections for Hybrid FRP-Concrete-Steel Double-Skin Tubular Columns under Constant Axial Compression and Lateral Cyclic Loading

During an earthquake, the casualties and economic loss due to infrastructure failure, such as bridges, are prohibitive. In addition, the deterioration in the steel reinforcements in bridges due to corrosion issues leads to significant structural damage and maintenance costs. As a novel form of composite structural member, hybrid fiber-reinforced polymer (FRP)-concrete-steel double-skin tubular columns (DSTCs), which consist of an inner steel tube, an outer FRP tube, and a sandwich concrete layer between the two tubes, with enhanced corrosion and seismic resistance, could be employed as bridge members (e.g., bridge piers) in harsh environments, seismic zones, or both, to enhance the seismic resistance, and extend the serviceable life of the bridges, achieve a lower maintenance cost, or both. This paper presents an experimental study on the behavior of DSTC-to-RC foundation connections that are subjected to a combination of axial compression and lateral cyclic loading, with the embedment depth of the column footing, axial load ratio of DSTCs, thickness of FRP tubes, and the additional anchoring measures within the foundation connections as the main parameters to be explored. Based on the test results, design suggestions, which include the critical embedment depth of the column footing and reliable structural measures, were proposed for DSTC-to-RC foundation connections.