Axial compressive behavior of FRP nonuniformly wrapped seawater sea-sand concrete in square columns

To facilitate the practical application of fiber-reinforced polymer (FRP) strengthened seawater sea-sand concrete (SSC) structures in marine infrastructures and alleviate the brittleness of abrupt failure of FRP confined SSC columns, the mechanical performance of carbon fiber-reinforced polymer (CFRP) nonuniformly wrapped square SSC columns under axial compression was explored. Test results show that the failure pattern of nonuniformly CFRP confined square SSC columns exhibits less brittle since the rupture of thinner CFRP band between two adjacent strips can provide a warning sign due to the inequivalent number of CFRP layers at different locations along the height of the specimens. Compared to the specimens uniformly wrapped with CFRP sheets and strips under the same volumetric ratio of CFRP, CFRP nonuniformly wrapped SSC columns possess superior mechanical properties, especially for the specimens with a smaller clear spacing. Besides, with the decrease of clear spacing ratio and the increment of the thickness of external CFRP strips, the ultimate strengths and strains of confined specimens increase obviously. In specific, the enhancement of ultimate strengths ranges from 5.4%-18.5% as the decreasing of clear spacing ratio. Moreover, under the same clear spacing ratio, the maximum ultimate strength improvement and strain improvement are equal to 15.8% and 21.8% respectively when the thickness of external CFRP strips doubles. Finally, several representative stress-strain models were selected to examine their validity in predicting the ultimate conditions of FRP nonuniformly wrapped concrete and the accuracy and reliability of each model were also assessed.