Effect of self-stressing on concrete-encased-steel filled circular CFRP tubes under axial compression

This paper presents the experimental results of concrete-encased-steel filled CFRP (carbon fiber reinforced polymer) tube (CSFCT) cylinders under monotonic axial compression. In this experiment, the prestress produced by the expansion agent was applied to the self-stressing concrete-encased-steel filled CFRP tube cylinders. The experimental parameters included the prestress, the layers of CFRP (1, 2, 3 layers) and the dimensions of section steel. It is aimed to investigate the influence of these parameters on the behavior of concrete-encased-steel filled CFRP tube cylinders under axial compression. Test results showed that compared with the non-prestressed test specimens, the application of prestress in self-stressing cylinders eliminates the stress lag of CFRP, makes the utilization ratio of CFRP higher, and improves the standard ultimate load, intercept load and inflection load. Meanwhile, the axial compression behavior of columns was improved with the increase of CFRP layers regardless of the prestress. The results also indicated that CFRP has more efficient confinement effect on small-cross sectional area section steel compared with large one. According to the test results, on the basis of the existing theoretical model, considering the influence of initial prestress and section steel, the calculation models of the inflection load and ultimate axial strain were modified. Finally, the stress-strain model of CSFCT cylinders with high accuracy was developed.