Axial compressive behavior of FRP spiral reinforced seawater sea‐sand concrete‐filled FRP tube stub columns

To investigate the composite confinement effect of pure FRP spiral stirrups and FRP tubes on seawater sea‐sand concrete (SSC), axial compression tests were conducted on GFRP spiral (without longitudinal GFRP bars) reinforced seawater sea‐sand concrete‐filled GFRP tube stub columns (GSCFGTs). The failure modes, stress–strain behaviors, ultimate compressive strength, and deformation capacity of the GSCFGTs were systematically analyzed with respect to key parameters, including the strength of seawater sea‐sand concrete, the GFRP spiral pitch, and the thickness of GFRP tube. For comparison, axial compressive tests were also conducted on GFRP spiral‐confined seawater sea‐sand concrete stub columns (GSCCs) and seawater sea‐sand concrete filled GFRP tube stub columns (CFGTs). The experimental results show that the ultimate compressive strength of GSCFGTs increases with increasing GFRP tube thickness and concrete strength, while the deformation capacity decreases as concrete strength increases. Compared with CFGTs, the incorporation of GFRP spiral stirrups significantly improves the failure characteristics of GSCFGTs. Both the ultimate compressive strength and ductility of GSCFGTs increase as the spacing of GFRP spiral stirrup decreases, with the effect of spiral spacing on deformation capacity being more pronounced than its influence on compressive strength. Besides, the decrease of the spacing of GFRP spiral stirrups would change the failure modes of the GSCFGTs. Finally, a design model was developed to predict the ultimate compressive strength of GSCFGTs. By comparing with the existing studies, the proposed model in this paper is demonstrated to have a reasonable level of predictive accuracy.