High strength expansive concrete-encased-steel filled carbon fiber reinforced polymer tubes under axial monotonic and cyclic load

Abstract

High-strength concrete-encased-steel filled CFRP (carbon fiber reinforced polymer) tube (HCSFC) takes advantages of high strength of concrete, steel and confinement of FRP, resulting in enhanced structural load carrying capacity and deformability. In this study, expansive high-strength concrete is filled between CFRP tube and sectional steel to study the mechanical properties of high-strength expansive concrete-encased-steel filled CFRP tube (HECSFC) under monotonic and cyclic axial compression. Twenty-four specimens were fabricated in this study. The variables included the number of CFRP layers (0, 1, 2 layers), cross-sectional shape (circular and square), self-stress level (with or without self-stress) and loading mode (monotonic and cyclic). Test results show that the peak load of HCSFC specimen is greater than their nominal load-carrying capacity, which indicates that CFRP plays a confinement role on the internal core concrete-encased-steel. As the number of layers increases, both the normalized peak load and the ultimate axial strain increase. For specimens under the same number of layers, cross sectional shape and loading mode, the ultimate axial strain and strain reduction factor of self-stressing specimens are higher than those of nonprestressed specimens. At the same time, it is found that the confinement efficiency of CFRP on circular specimen is higher than that of square specimen. Analytical results show that the modified existing stress-strain models of CFRP confined concrete predict well with the experimental results.