Experimental Study On The Effect Of Multiple Low-velocity Impacts On The Mechanical Properties Of GFRP Reinforced Concrete Square Columns

Glass fiber composite(GFRP)steel bars have been gradually replaced by carbon steel bars in bridge engineering to solve the problem of steel corrosion in corrosive environment because of its excellent corrosion resistance and tensile properties.However,considering the anisotropy and brittleness characteristics of GFRP material itself,the mechanical behavior of GFRP reinforced concrete structures under impact is significantly different from that of reinforced concrete structures,which may be much lower than that of traditional RC structures under multiple low-speed impacts.The GFRP reinforced concrete structure began to show serious damage,resulting in its bearing capacity greatly decreased,resulting in serious safety accidents.At present,the research on the mechanical properties of GFRP reinforced concrete structures under multiple low-speed impact is still very rare.Based on this,this paper takes GFRP reinforced concrete square column as the object,a total of 4 specimens were studied.In order to quantify the dynamic stress response and impact damage of GFRP reinforced concrete square columns under multiple impacts,a drop hammer impact test device with horizontal load holding subsystem independently developed by our research group was used to carry out multiple lateral low-speed impact tests.Furthermore,static axial compression tests are carried out on GFRP reinforced concrete square columns subjected to multiple impacts to determine the degree of impact damage on the residual compression capacity of GFRP reinforced concrete square columns.In multiple low-speed impact tests,three GFRP bar concrete square column specimens of the same structure were subjected to the same initial kinetic energy impact twice,four times and six times,respectively,and the time history curves of impact force,acceleration,support reaction,and strain of GFRP bar and concrete key points during the impact process were obtained.The test results show that the bending damage and punching damage of GFRP reinforced concrete square column increase with the increase of impact times.At the same time,the fluctuation frequency of the impact force time history curve decreases,and the peak impact force increases first and then decreases.The time history curve of the support reaction lags obviously,and the specimen shows good energy absorption.In the static axial compression test,the influence mechanism of initial impact damage on the axial compression failure process of concrete square columns with GFRP bars under different impact times was determined,and the axial load-displacement curve and the development curve of the strain at the key point of GFRP bars and concrete with load were obtained.The test results show that the damage accumulation of GFRP reinforced concrete square column is significant,but the effect on the residual bearing capacity is not a simple linear relationship.Under different impact times,the initial impact damage on the residual bearing capacity of GFRP reinforced concrete square columns has two stages: sudden drop and gentle decrease.At the same time,in the case of initial impact damage,the longitudinal reinforcement and stirrup of GFRP in the column under axial compression load have obvious stress redistribution phenomenon.