Study On The Eccentric Compression Behavior Of Concrete Column Reinforced With BFRP Bars Service In Chloride Corrosion Environment

So far,the most widely used construction engineering in most areas of China,including coastal areas,is still reinforced concrete structure.However,the reinforced concrete structure in long-term service is often in the state of working with cracks.The corrosion solution mainly caused by chloride corrosion in coastal areas enters into the structure through cracks,resulting in the corrosion of steel bars and the premature failure of the structure.Fiber reinforced polymer(FRP)has the characteristics of light weight,high strength and good corrosion resistance.FRP can be used in concrete structure in the area of chloride erosion,which can improve the durability of concrete structureIn this paper,basalt fiber reinforced polymer(BFRP)is used to replace ordinary steel bars to form BFRP reinforced concrete columns.The specimens are divided into two groups,one group is corroded by pure chloride solution,the other group is subjected to continuous load of different stress levels,and then placed in chloride corrosion solution pool to form the coupling effect of load and chloride corrosion,so as to simulate the chloride corrosion service environment of coastal areas and marine concrete structures.After the erosion period,the specimens were taken out in batches and subjected to eccentric compression test,and the test results were analyzed.Taking the erosion duration and load level as variables,the effects of erosion duration and load level on the bearing capacity,failure mode,lateral displacement,cracks,concrete and longitudinal strain of BFRP reinforced concrete columns are studied by combining experimental data with theoretical analysis,and compared with HRB400 reinforced concrete columns with the same reinforcement ratio and erosion environment.The main research results are as follows(1)The ultimate bearing capacity of BFRP reinforced concrete column and ordinary reinforced concrete column in pure chloride and chloride corrosion service environment decreases with the increase of corrosion time and load level.The ultimate bearing capacity of reinforced concrete column in the same corrosion environment decreases more obviously than that of BFRP reinforced concrete column.The ultimate bearing capacity of BFRP reinforced concrete column decreased by 5.08%and reinforced concrete column decreased by 9.74%after 180 days of corrosion by pure chlorine salt;the ultimate bearing capacity of BFRP reinforced concrete column decreased by 8.47%and reinforced concrete column decreased by 12.82%after 180 days of corrosion by 45%stress(2)With the increase of erosion days and load level,the lateral displacement of specimens increases and the resistance to deformation decreases.Under the same conditions,the lateral displacement of BFRP reinforced concrete columns is larger than that of reinforced concrete columns.The results of short-term stiffness calculation also show that the short-term stiffness decreases with the increase of erosion days and load level,and the calculation results are consistent with the experimental phenomena.The strain of longitudinal bars in tension is less than that of BFRP bars,but the strain of longitudinal bars in compression is similar.The corroded concrete columns with BFRP bars are subjected to eccentric load,and the strain of longitudinal bars in tension is greater than that of longitudinal bars in compression.With the increase of erosion time,the tensile strain decreases and the compressive strain increases.With the increase of erosion days,the compressive strain of concrete in BFRP reinforced concrete column increases under the same load at the later stage of loading,and the compressive strain of concrete in reinforced concrete column under the same condition is smaller than that of BFRP reinforced concrete column.When the load level exceeds 30%,the compressive strain of concrete will be reduced and the utilization rate of compressive performance of concrete will be reduced due to the plastic deformation of the component in the process of load erosion.(3)The influence of load holding level on crack width is reflected in the early stage of loading,the larger the load holding level is,the larger the initial crack width is;the influence of erosion duration on crack width is reflected in the late stage of loading,the longer the erosion duration is,the larger the crack width is when the component is damaged,When the load level exceeds 30%,the transverse cracks perpendicular to the longitudinal reinforcement almost all appear,and the load level and erosion duration have no obvious effect on the total number and spacing of cracks.(4)According to the ultimate tensile strain of BFRP reinforcement,the ultimate tensile strain of BFRP reinforcement when the concrete in the compression zone is crushed is taken as the ultimate failure mode,and the expression of the height of the limit relative to the compression zone is derived.The stress level of BFRP bars far away from the axial force is 0,which is taken as the judgment basis of partial section compression failure and full section compression failure,and the expression of critical eccentricity is obtained.Based on the constitutive model and basic assumption of materials,considering the influence of second-order effect on eccentric compression members,the bearing capacity of two kinds of normal section of BFRP reinforced concrete column under compression and the limited reinforcement ratio of compression failure between tensile failure are deduced.The calculated value is compared with the measured value.The results show that the theoretical calculation value is safe and can reflect the real ultimate bearing capacity of the specimen very well(5)The Nu-Mu correlation equations of full section compression failure and partial section compression failure are derived,and they are combined into a complete Nu-Mu curve of compression failure.The measured data are compared with Nu-Mu curve,and it is found that the measured data are located outside the curve.With the increase of erosion duration and load holding level,the measured points close to the curve.According to the calculation formula of maximum crack width under long-term load and short-term stiffness of flexural members in "technical code for infrastructure application of FRP composites",considering the difference between flexural members and eccentrically compressed members,the formula is changed,and the average crack spacing,maximum crack width and short-term stiffness of BFRP reinforced concrete columns under eccentric compression are given.The accuracy of the formula is verified by comparing the calculated results with the experimental data and phenomena.