Flexural behavior of circular concrete filled steel tubular members strengthened by CFRP sheets

Abstract

The flexural behavior of CFRP-strengthened circular concrete filled steel tubular (CFRP-C-CFST) members was investigated experimentally and theoretically. A total of nine specimens were tested through four-point bending method, including a comparative CFST specimen without CFRP strengthening (C-CFST), and eight CFRP-C-CFST specimens. Based on experimental results, the effects of different CFRP wrapping length, number of CFRP layers and wrapping schemes on the flexural behavior of the CFRP-C-CFST specimens are analyzed. Two failure modes, including CFRP debonding and CFRP fracture, are observed from the tested CFRP-C-CFST specimens. Increasing the length of CFRP delays debonding, while increasing the number of CFRP layers causes debonding to occur earlier. The flexural capacity of CFRP-C-CFST specimens with two-four CFRP layers is increased by about 20%-70% compared to the C-CFST specimens. A theoretical model based on fiber element method is proposed. This model considers the bi-directional stress state of the steel tube and the effect of bending moment on the confinement factor. A representative test result is selected to calibrate the distribution law of the confinement factor, and all the test results are predicted based on the calibrated parameters. The comparison between the predicted and the test results shows that the fiber element model can simulate the bending moment-deflection curves of C-CFST and CFRP-C-CFST members, and hence it can predict the flexural capacity, stiffness and ductility accurately.