Axial behavior of circular CFST encased seawater sea-sand concrete filled PVC/GFRP tube columns

In order to directly apply seawater and sea sand in construction without desalination, a new type of circular concrete-filled steel tube (CFST) encased prefabricated seawater sea-sand concrete filled Polyvinyl Chloride (PVC)/Glass Fiber Reinforced Polymer (GFRP) tube column was proposed. 24 short columns were tested under uniaxial loads and the test parameters included types of inner tubes, seawater sea-sand concrete replacement ratios, concrete strength, the wrapping area of Carbon Fiber Reinforced Polymer (CFRP) strips and the thickness of inner tube. Moreover, the effects of the parameters on bearing capacity, ductility, stiffness, and strain re-sponses were discussed. The results indicate that the bearing capacity and the strength index of specimens with PVC tube wrapped with CFRP strips and GFRP tube as the inner tube was significantly improved, and the improvement level increased as the wrapping area of CFRP strips or the thickness of GFRP tube increased. The increase in the concrete strength can also improve the bearing capacity and stiffness. In addition, an analytical model was proposed for the composite column with PVC tube wrapped with CFRP strips or GFRP tube as the inner tube.