Seawater sea-sand concrete columns using durable and ductile steel-FRP composite bars and FRP ties: A promising hybrid scheme for marine engineering

To overcome corrosion of steel bar and scarcity of freshwater and river sand, durable and ductile steel-FRP composite bar (SFCB) provides a promising longitudinal reinforcement alternative in seawater sea-sand concrete (SWSSC) columns for marine infrastructures. The unique mechanical properties and lower compressive strength of SFCB inevitably influence axial compressive performance of column. However, very few studies on axial compressive performance of hybrid longitudinal SFCBs and FRP ties reinforced concrete (hybrid-RC) columns lead to a lack of valuable experimental observations and failure mechanisms. Here, an experimental investigation of axial compressive performance for hybrid-RC columns is conducted. Results indicate that SFCB has a bilinear stress–strain characteristic with high elastic modulus under compression and can maintain its integrity until concrete crushing. Using SFCB as longitudinal reinforcement leads to satisfactory axial compressive behavior including high strength and great ductility for columns. Nevertheless, FRP ties show low confinement efficiency since the worse mechanical properties of bent portion and the slipping of lap splice. With the experimental and theoretical analysis for hybrid-RC columns, the prediction model of axial load capacity is developed and validated preliminarily, showing great accuracy. These findings provide a meaningful experimental basis and safe design tactics for this hybrid reinforcement scheme of SWSSC.