Study On Fiber-concrete Smart Composite Columns

The durability damage of bridge is one of the most concerned problems in allover the world. It is a great threat to the safety and life of bridge. Fiber reinforced polymer (FRP) is a new material, and the composite structure composed by the FRP and concrete can effectively solve the long term durability of bridge. In this thesis, the concrete-filled FRP tube (CFFT) was studied, and the concrete-filled FRP-steel composite tube (CFST) was presented firstly. The compressive properties, durability and earthquake-resistance were studies. The FBG strain sensors were firstly pre-embedded in the FRP tube or the interface of the FRP-steel composite tube. It makes the structure have the ability of self-sensing. Then, the monitoring based damage assessment was presented.The main research in this thesis includes:First, the axial compressive properties of the CFFT were studied experimentally, including the winding mode of fibers and locally-strengthened FRP tube. To improve the axial ductility of CFFT, the concrete-filled FRP-steel composite tube (CFST) was presented firstly. The axial compressive properties of the CFST were studied experimentally. The axial ductility coefficients of the CFFT and CFST were presented, and the ductility of CFFT and CFST was analyzed. The descending coefficient of the compressive stress-strain relationship of the core concrete was analyzed in regression through a large of existing research results. A finite element model of CFFT and CFST was established and the compressive properties of the CFFT were modeled well through the model.Second, the durability of the CFFT and CFST was studied. 56 freeze-thaw cycles were conducted on those specimens. At the same time, the residual mechanical properties of the specimens after the freeze-thaw cycles, the relative dynamic modulus of elasticity of the core concrete with the freeze-thaw cycles, and the infrared thermography analysis on the pores and flaws on the surfaces of the specimens after the freeze-thaw cycles were studied. The damage mechanism of CFFT and CFST during the freeze-thaw cycles was analyzed. The diffusing of solution in the FRP tube was analyzed based on the Fick's law. The icing pressures in the FRP tube were calculated. The spalling of fiber reinforced concrete was tested, and the assessment and repair of CFFT after fire was presented. Third, the self-sensing of the CFFT and CFST was studied. The preparation of the CFFT and CFST having the self-sensing was introduced. The self-sensing in mechanical properties and durability was studied. Based on the monitoring information, the damage assessment methods on mechanical properties and durability were presented respectively.At last, the earthquake resistance of the CFFT and CFST was studied experimentally, and then compared with the RC structure. The ABAQUS finite element model applicable to earthquake resistance analysis was established on the CFFT and CFST. In using the model, the earthquake resistance of the CFFT and CFST was modeled respectively.