Experimental study and analytical model of full-scale concrete columns with hybrid steel-FRP reinforcements under axial compression and cyclic lateral loading

The susceptibility of steel to corrosion in marine infrastructures has driven the rapid development of corrosion-resistant fiber reinforced polymer (FRP) bars as promising alternative reinforcements, particularly for use in seawater sea-sand concrete structures. However, the brittle nature and poor compressive behavior of FRP bars limit their application in columns, particularly in high-risk seismic regions. To overcome these limitations, we developed a corrosion-resistant and ductile hybrid steel-FRP reinforcing system for columns. Quasi-static tests on full-scale hybrid-RC columns were conducted to reveal their seismic failure mechanism and the impact of reinforcement configuration. Results demonstrated that hybrid-RC columns with longitudinal bars of comparable axial stiffness exhibited comparable seismic performance to steel-RC columns in terms of stiffness, load capacity, ductility, and energy dissipation ability. The outer FRP layer in longitudinal bars enhanced post-damage repairability of columns, reducing residual displacement by 18.8 %. We recommend limiting stirrup spacing to 6 times the diameter of the smallest longitudinal reinforcement to achieve desirable seismic behavior. Moreover, a fiber model incorporating bar slip was established to accurately predict the skeleton curves of hybrid-RC columns, effectively calculating load capacity and deformation. This study offers experimental validation and practical design guidelines for the hybrid reinforcing system.