Experimental Research On Mechanical Properties Of Eccentrically Loaded Short Concrete Column Reinforced With BFRP Bars

Steel corrosion is the main cause of the deterioration of the durability of concrete structure,and the use of fiber reinforced plastics(FRP)bars instead of steel reinforcement is an effective method to solve the problem of reinforcement corrosion in concrete structure.Because of its marvelous advantages,such as high tensile strength,light weight,green environmental protection,good durability and low cost,the basalt fiber reinforced plastic(BFRP)bars deserve further research.At present,the research is mainly about the tensile properties of BFRP bars,the bonding performance of BFRP bars and concrete and BFRP bars reinforced concrete beams,and the researches on compressive properties of BFRP bars and BFRP bars reinforced concrete columns are relatively poor.In view of this,in order to promote the application of the new composite materials in practical engineering and give full play to its excellent mechanical properties,the BFRP bars tensile properties test,BFRP bars compressive performance test and mechanical properties test of BFRP reinforced concrete column under eccentric load was carried out in this paper,and based on the experimental results the design calculation method of FRP reinforced concrete column was given.The main contents and results are as follows:1.Experimental study on tensile properties of BFRP bars.Effects of the diameter change on the tensile properties of BFRP bars were studied,the failure modes were observed,and the tensile strength of BFRP bars,the tensile modulus and the tensile stress-strain curves were measured.The experimental results shows that:BFRP bars have two kinds of tensile failure modes,namely "burst type" and "incomplete split" failure;the stress-strain curves of BFRP bars are linear,BFRP bars is a typical brittle material without destruction warning;the effect of the diameter change on tensile strength has no obvious regularity,the tensile strength of BFRP bars should be the result of multiple factors;The tensile strength of BFRP bars is much higher than that of steel bars,but the tensile modulus of elasticity is very low.In practical application,it is necessary to consider the utilization ratio of BFRP bars,structural deformation and cracks.2.Experimental study on compressive properties of BFRP bars.Effects of the diameter and slenderness ratio on the compressive performance of BFRP bars were studied,failure modes were observed,and compressive strength of BFRP bars,compressive elastic modulus and compressive stress-strain curves were measured.The experimental results show that,BFRP bars compressive failure modes can be divided into four kinds,namely shear failure,splitting fracture failure,crushing failure and buckling failure;the ultimate compressive strength of BFRP bars is about55% of the ultimate tensile strength;the measured compressive elastic modulus of BFRP bars is between 44.5 and 51.8MPa,which is close to the tensile modulus of BFRP bars(45.07~49.34MPa);the compressive strength and ultimate compressive strain decrease with the increase of slenderness ratio,but the effect of slenderness ratio on elastic modulus is not obvious;when slenderness ratio is certain,compressive strength and ultimate compressive strain of the BFRP bars decreases with the increase of diameter;under the different slenderness ratios,the effect of the diameter on the compression elastic modulus of BFRP bars is not regular.3.BFRP reinforced concrete columns eccentric compression test.The effects of concrete strength,longitudinal reinforcement ratio and eccentricity on the cracking load,ultimate load,lateral deformation and crack width were investigated by mechanical properties test of 7 eccentrically compressed concrete columns reinforced with BFRP bars,in which the failure modes were analyzed,the strain distribution in the middle section of columns,the lateral deflection of columns,the strains of BFRP bars and concrete were all measured.The test results indicate that,the failure modes of BFRP reinforced concrete columns are all concrete crushing failure;strains in the middle section accord with the plane section assumption;the ultimate bearing capacity of columns decreases with the increase of eccentricity,and increases with the increase of reinforcement ratio;the increase of concrete strength can significantly improve the ultimate bearing capacity of columns.When the load is constant,the bigger the eccentricity,the bigger the lateral deformation of columns;the smaller the reinforcement ratio,the bigger the lateral deformation of columns;the bigger the strength of concrete,the smaller the lateral deformation of column;the effects ofeccentricity,reinforcement ratio and concrete strength on the strain of concrete and the strength utilization ratio of BFRP bars are also obvious.4.According to the theoretical bearing capacity calculation method of reinforced concrete column under eccentric compression,equilibrium equations and deformation coordination with the plane cross section assumption and based on the results of available researches,the calculation method of bearing capacity of BFRP reinforced concrete short columns is put forward in the paper,in which the effect of compressive BFRP bars is considered,and the calculation results agree well with the test results.