Behaviour of CFRP confined square concrete-filled stainless steel tubular columns under uni-axial compression

To study the behaviour of the carbon fibre-reinforced polymer (CFRP) confined square concrete-filled stainless steel tubular (CFSST) stub column, three square CFSST stub columns and nine CFRP confined square CFSST stub columns were tested under axial compression. The test parameters included the number of CFRP sheet layers and the thickness of the stainless steel tube. The test results showed that failure modes of all CFRP confined square CFSST stub columns were the fracture of CFRP sheets and the outward local buckling of the stainless steel tube at the chamfering. The typical load-displacement curves of the tested columns exhibited four stages, i.e., elastic stage, elastoplastic stage, descending stage and residual stage. CFRP sheets could restrain the local buckling of CFSST, and improve the ultimate bearing capacity and the ductility index of the columns. With the increase in the number of CFRP sheet layers and the wall thickness of the stainless steel tube, the bearing capacity of the column increased linearly. Based on the twin-shear unified strength theory, a calculation method of the ultimate bearing capacity of the square CFSST stub column was proposed. Besides, through the superposition method and regression analysis, two simplified methods to predict the ultimate bearing capacity of CFRP confined square CFSST stub column under axial compression were obtained.

Automated summary

This study examined the behavior of CFRP-confined square CFSST stub columns by conducting tests on three square CFSST columns and nine CFRP-confined square CFSST columns under axial compression. Test parameters included the number of CFRP sheet layers and the thickness of the stainless steel tube. Results showed that all CFRP-confined columns exhibited fracture of CFRP sheets and local buckling of the stainless steel tube at the chamfering. The tested columns followed a typical load-displacement curve with four stages. CFRP sheets effectively restrained the local buckling of CFSST, enhanced the ultimate bearing capacity and ductility index, and increasing the number of CFRP sheet layers and tube thickness resulted in a linear increase in column capacity. A calculation method for the ultimate bearing capacity of square CFSST stub columns was proposed based on the twin-shear unified strength theory, and two simplified methods for predicting the ultimate bearing capacity of CFRP-confined square CFSST stub columns were obtained using the superposition method and regression analysis.