Rectangular seawater sea-sand concrete columns using steel-FRP composite bars and closed-type winding FRP ties: Axial behavior and confinement model

Abstract

<p>Seawater sea-sand concrete (SWSSC) columns reinforced with steel-fiber reinforced polymer (FRP) composite bars (SFCBs) and closed-type winding FRP ties (CWFTs) are highly suitable for marine environments. However, due to limited research, the axial performance and confinement model of the columns have not been fully clarified. Therefore, axial compression tests of the columns in the study reveal that larger volumetric stirrup ratios and appropriate tie configurations can significantly enhance column ductility. Specifically, compared to columns with a 1.75% stirrup ratio, the strain ductility coefficients of columns with ratios of 3.44% and 4.55% increase by 54% and 195%, respectively. The coefficient of columns with B-configuration ties is 2.86 to 4.34 times that of columns with A-configuration ties. The impact of stirrups’ cross-sectional area and spacing on axial behavior is similar, and the effect of stirrups’ width-to-thickness ratio is minimal. Compared to steel-tie columns, CWFT columns with various tie configurations and volumetric stirrup ratios exhibit similar load-strain curves before the peak load and lower axial capacity. With the same stirrup ratio, steel-tie columns demonstrate better ductility than CWFT columns with A-configuration ties, but for B-configuration ties, the ductility coefficient of CWFT columns is 2.23 times that of steel-tie columns. Factors influencing the stress-strain curve of CWFT-confined concrete include the strength in the bent section, stirrup configuration, spacing, volumetric ratio, and elastic modulus of stirrups. Peak stress and strain are associated with the latter four factors, and the first four coefficients influence ultimate stress and strain. Formulas for calculating the axial capacity and confinement model have been derived and show good agreement with the experimental results. The bearing capacity, ductility and complete stress-strain curves of the columns under axial compression can be predicted, promoting the development of marine civil engineering.<br></p>