Axial compressive behavior and model assessment of FRP-confined seawater sea-sand concrete-filled stainless steel tubular stub columns

Concrete-filled steel tubular (CFST) columns have corrosion issues in coastal/offshore constructions. Thus, a FRP-confined seawater sea-sand concrete (SSC)-filled stainless steel tubular (SST) column (FRP-SSCFSST) is proposed to mitigate corrosion problems. Meanwhile, the use of SSC can relieve the over-exploitation of river-sands. In the present study, the axial compressive behavior of FRP-SSCFSST columns was investigated through testing 12 pairs of stub columns (two duplicates in a pair) including 6 pairs of FRP-SSCFSST specimens, 4 pairs of SSCFSST specimens, and 2 pairs of unconfined concrete specimens. FRP thickness, wall thickness of stainless steel tubes, and concrete strength are the influencing parameters examined in this study. The experimental results showed that the FRP-SSCFSST specimens exhibited a strain-hardening response with the full activation segment as a second ascending line. The SST confinement was less significant, as doubling the wall thickness of SST only led to a small difference in strength index. However, both strength index and strain enhancement ratio increased almost linearly with the increase of FRP thickness. An increase in the concrete strength could result in a reduction in both strength index and axial strain enhancement ratio due to the brittleness of high strength concrete. In addition, the performances of seven load-capacity prediction models and two ultimate axial strain estimation equations were evaluated by using the test results. With minor modifications, Lam and Teng’s model had the best performance in predicting the load carrying capacities of the specimens with an average absolute error at only 3.9%.