Calculation Method Of Compressive Properties And Bearing Capacity Of Damaged Reinforced Concrete Columns Reinforced By FRP Strip

Fiber Reinforced Polymer(FRP for short)-restricted reinforced concrete structures are research and application hotspots in structural strengthening and rehabilitation at home and abroad,which are particularly suitable for existing damaged concrete structures.However,damaged reinforced concrete structures still require long-term work during the subsequent service period after being strengthened by FRP materials and are subjected to various applied loads and environmental effects.The aggressive environment may also cause further corrosion of the steel bars and affect the restraint effect of FRP.Therefore,it is necessary to study the mechanical properties of FRP-confined damaged concrete structures under the erosive environment.In this paper,the experimental study and theoretical analysis of the compressive behavior of damaged reinforced concrete columns strengthened by FRP strip are carried out.The main contents are as follows:(1)Through the tensile test of 15 groups of FRP strips,the effects of the type of erosion environment and the mode of action,the type of FRP strips and the number of layers on the tensile properties of FRP strips were studied.The results show that the tensile stress-strain relationship of CFRP and GFRP strips is approximately linear under laboratory environment,freeze-thaw environment and dry-wet environment;the tensile strength,elastic modulus and elongation at room temperature are almost unaffected by the layers number of CFRP strips and GFRP strips.The freeze-thaw environment affects the GFRP strips more than the CFRP strips.When the freeze-thaw cycle is 75 times,the tensile strengths of CFRP and GFRP strips were 0.978 and 0.898 times that of the control specimens,respectively.With the increase of freeze-thaw cycles,the tensile strength of CFRP strips and GFRP strips gradually decreased.The wet-dry cycle has no obvious effect on the tensile properties of GFRP strips.Finally,a method for calculating the tensile strength of FRP strips in erosive environment was proposed.(2)Accelerated corrosion test was used to analyze the influence of the damage degree,type and number of FRP strips on the ultimate load,axial displacement,ring strain of FRP reinforced concrete cylinders.Based on the study and analysis of FRP strip restraint effect,the effect of damage degree on the concrete cross section and the mechanical properties of reinforced bars,a calculation model for the axial compression bearing capacity of FRP strips reinforced concrete columns was proposed.(3)Through the axial compression test of FRP strips reinforced concrete columns with corrosive damage under erosion environment,the influence of erosion environment on the strength,ultimate load,axial displacement and ring strain of concrete columns was analyzed.The results show that the strength of concrete is greatly affected by the erosive environment,and the axial ultimate load and load-axial displacement curves are related to the type of FRP strips and the number of times of the erosive environment.Based on the research and analysis of the restraint effect of FRP strips,the damage coefficient of concrete strength and the mechanical properties of steel bars in the corrosive environment,a calculation method for the axial compression bearing capacity of FRP strips reinforced concrete columns with corrosive damage under erosive environment was proposed.(4)Through the eccentric compression tests of FRP strip reinforced corrosion damage reinforced concrete cylinders,the effect of eccentricity,corrosion rate of steel bar and FRP strip type on the failure mode,bearing capacity,vertical strain and the height of the compression zone of the reinforced concrete column were analyzed,A continuous steel strip was used to replace the distributed steel bars and the circular section was equivalent to a rectangular section,then a numerical model for calculating the eccentric compression bearing capacity of FRP strips reinforced concrete columns was proposed,and a simplified calculation method for the eccentric compression bearing capacity of FRP strips reinforced concrete columns with corrosive damage under different compression states of steel strip was established.