Reseach On The Bond Slip Behavior Of Concrete Filled Square GFRP Columns

The bond slip performance between the GFRP pipe and the concrete interface is the performance of the GFRP pipe concrete column.The main subject of the research is that most of the previous research results are in the field of concrete filled steel tubes.Therefore,the bond slip behavior of GFRP pipe concrete was studied in this paper.In order to quantitatively and qualitatively understand the bond-slip behavior of concrete columns with square GFRP pipes under high temperature,this paper studies the bond-slip behavior of GFRP concrete columns with high temperature after the action.This test has a total of 117 specimens,including 108 tests.High-temperature,concrete columns and nine control samples without high-temperature treatment.The test is based on the wall thickness of the GFRP pipe(3.5mm,5mm,6mm),the concrete compression grade(C20,C30,C40),high temperature(150 ° C,200 ° C,250 ° C,300 ° C)and high temperature duration(60min,90 min,120min).The four parameters are design variables.Slip performance tests were performed on 117 specimens,and the surface of 9 specimens was subjected to strain tracking tests.This article first describes the test plan,the phenomenon of the specimen after high temperature,and then describes and discusses the load-slip curve and the load-strain curve.It mainly analyzes four variables(wall thickness,concrete compression level,high temperature and high temperature duration)on the influence of the sliding force of the specimen.Through the analysis of the experimental results,the bonding force of the test piece is mainly composed of three parts(chemical bonding force,mechanical engagement force and friction force).The load-slip curve of the test piece after high temperature can be roughly divided into three stages(straight rise Section,curve decreasing section and gentle section),as the wall thickness of the GFRP tube increases,the ultimate bonding force of the specimen gradually increases,and the strain of the GFRP tube is exponentially distributed along the embedding length during the loading stage,and is close to the member during the initial loading The strain at the end is very small,and the distribution is similar to a horizontal straight line.As the load increases,the strain values at the loading end and the free end increase,and the strain growth rate at the free end is faster.With the improvement of concrete strength grades,the average ultimate bond strength of specimens at room temperature has slightly improved overall.As the wall thickness of the GFRP tube increases,the average ultimate bonding force of the specimen gradually increases.The chemical bonding force between concrete components of GFRP pipe accounts for at least one-third of the total bonding force of the component;high temperature has a greater impact on the test piece.With the gradual increase of high temperature,the ultimate bonding force of the specimen gradually increases.The effect of temperature duration on the bonding force of the test piece is not uniform.The load-slip curves of specimens with different durations of high temperature are similar or even coincide.Through the experimental data,the calculation formula of the bond slip strength of the square GFRP pipe concrete column is obtained.By analyzing the width-thickness ratio and concrete strength of the square GFRP pipe,reasonable design suggestions are put forward.