Cyclic behavior and flexural-shear deformation mechanism of sea-sand concrete shear walls reinforced with steel-GFRP composite bars

Sea-sand concrete is attractive for coastal and marine engineering, but chloride salts in sea sand may induce corrosion of conventional steel bars, compromising the durability and safety of shear wall structures. Although FRP bars provide excellent corrosion resistance, their limited ductility and energy dissipation capacity restrict their seismic application. To address this issue, steel-GFRP composite bars (SGFCBs) were used as longitudinal bars in sea-sand concrete shear walls. Four SGFCB-reinforced sea-sand concrete shear wall (SFSW) specimens and one conventional steel-reinforced concrete shear wall (SSW) specimen were tested under quasi-static cyclic loading. The investigated parameters were axial compression ratio, steel–fiber ratio, and GFRP stirrup ratio in the boundary confinement region. Compared with SSW, the SFSW specimens exhibited similar flexural-shear failure, slightly lower lateral load-carrying capacity, and larger ultimate drift ratios. Cyclic response analysis showed that the SFSW specimens had higher ductility and more stable stiffness and strength degradation, but slightly lower energy dissipation capacity. Lateral deformation decomposition showed that flexural deformation contributed 72–84% of the ultimate lateral displacement when the reference shape factor 0.8 was adopted and remained dominant in the sensitivity analysis, which indicates that SGFCB bars did not change the flexure-dominated deformation mechanism. Parameter analysis showed that increasing the steel-fiber ratio improved overall cyclic performance, increasing the axial compression ratio enhanced load-carrying capacity but reduced deformation capacity, and increasing the GFRP stirrup ratio in the boundary confinement region mainly improved deformation capacity. Overall, the proposed SFSW system exhibited satisfactory cyclic behavior, providing experimental evidence for durable and ductile shear wall structures in coastal and marine environments.