| Recently, the technique of reinforced concrete columns strengthened withwrapped the FRP sheets is becoming popular in the civil engineering, andconcrete-filled FRP tubes are expected to be used in new constructions ofcolumns. At the same time, studies on concrete confined with FRP have beenwildly carried out, but most models consider FRP under uniaxially loadedproviding confinement only in the hoop direction. The fact that the FRP tubesare usually bi-axially loaded will reduce the confinement modulus and tensilestrength in the hoop direction.In this thesis, stress-strain models of FRP-confined concrete under axialloading are summarized firstly, including nine models for concrete confinedwith FRP sheets and three models for concrete-filled FRP tubes.By studying the mechanical behavior of FRP tubes and core concreteunder axial compression, this thesis presents an analytic stress-strain modelwhich considers that FRP tube is subjected to both axial compression andhoop tension, and the axial strain-lateral strain relationship proposed byHuang is used in the model. The stress-strain relation is determined by using astep-by-step strain increment technique, and the failure theory of FRP isadopted in the model to determine the strength of the concrete-filled FRP tube.The proposed model is shown to compare well with test results conducted inthis thesis and other researchers.The experimental studies on the concrete-filled FRP tubes and concreteconfined with CFRP sheets have been carried out. The concrete filled in tubesof different thickness, different stacking angle and different load-carryingconditions are contrasted, and the concrete-filled in hybrid FRP tubes areanalyzed. The experimental results of the strength, the ultimate strain and thestress-strain curves of the concrete confined by CFRPS are compared with themodels, and the concrete confined by both stirrup and CFRPS are analyzed.By using the suggested model, the parametric study is presented. |
