Analytical and experimental investigation on axial compression capacity of carbon fiber-reinforced plastic-confined concrete-filled double-skin steel tube stub columns

Concrete-filled double-skin steel tubes (CFDSTs) are widely used in civil engineering. During the service life of CFDSTs, their bearing capacity can be easily weakened by the corrosion of outer steel tubes. This study investigated the interaction mechanism and reinforcement effects of carbon fiber-reinforced plastic (CFRP)-confined CFDSTs under axial compression. Typical failure modes, axial load-shortening curves, and axial load-strain behaviors of CFDST and CFRP-confined CFDST (CFRP-CFDST) specimens were obtained. The test results showed that the ultimate bearing capacity of stub columns with concrete strength of C40 and C60 increased by 19.78% and 15.12%, respectively, when wrapped with two layers of CFRP sheets, and by 41.60% and 37.99%, respectively, when wrapped with four layers of CFRP sheets. In addition, the FE modeling of CFRP-CFDSTs was established and validated by experimental results. On this basis, the parametric analysis was conducted. To avoid local buckling and yield failure of the inner steel tubes before the outer steel tubes, a calculation formula was proposed for predicting the minimum wall thickness of the inner tube. Furthermore, the prediction formulas for the bearing capacity of CFDSTs and CFRP-CFDSTs were proposed.