Behavior and analysis of FRP and steel hybrid-reinforced concrete columns subjected to combined compression and bending

This paper presents the experimental results and analysis on fiber-reinforced polymer (FRP) and steel hybrid-reinforced concrete columns (hybrid-RCCs) subjected to combined compression and bending. The effects of axial load level, reinforcement ratio, and reinforcement type on the behavior of hybrid-RCCs under compression-bending were investigated. The test results revealed that the behavior of the hybrid-RCCs under compression-bending was gradually transformed from bending-dominated to axial compression-dominated as the axial load level increased, resulting in a shift in the failure mode of the hybrid-RCCs from tension to compression. the hybrid-RCCs experienced a significant improvement in bearing capacity and flexural stiffness, along with a reduction in deflection, crack width, crack number, and crack depth. When axial load level increased from 0 to 0.6, the cracking moment of the hybrid-RCCs increased nearly ten times and the ultimate bending moment increased almost three times. As the reinforcement ratio increased, the hybrid-RCCs displayed an enhancement in bearing capacity and flexural stiffness, while the extent of increase was restricted by the axial load level. The reinforcement ratio has little influence on the ultimate moments of the hybrid-RCCs under compression-bending with a large axial load. Moreover, the equations for the bearing capacity of hybrid-RCCs under compression-bending were proposed. Finally, a finite element (FE) model was established to analyze the compression-bending performance of hybrid-RCCs, and the axial force-ultimate moment interaction curves of the hybrid-RCCs under compression-bending were exhibited.