Axial Compressive Behavior Of Square Ice-filled Thin-Walled Steel Tubular Stub Columns And Comparative Study On Three Kinds Of FRP-Concrete Shear Property Test Methods

In cold regions the temperature is lower than 0 ℃ all the year round,which leads to great difficulties in the preparation and transportation of concrete.Therefore,it is necessary to find a kind of building material that can replace concrete in this region.Considering that there are a lot of ice resources in cold regions,it is a feasible choice to replace concrete with ice.Considering that the damage of pure ice is brittle,which is not conducive to the safety design of the structure,this paper proposes a composite component of steel tube and pure ice,and improves the mechanical properties of the specimen by adding sawdust into pure ice.It is one of the basic works to study the mechanical properties of square ice-filled thin-walled steel tubular stub columns under axial compression.On the other hand,because of its light weight,high strength and corrosion resistance,fiber-reinforced polymer(FRP)is often used for flexural strengthening of concrete beams.However,the debonding failure of FRP sheet caused by intermediate crack of FRP strengthened concrete beams can not be avoided by anchoring measures,so it is of great significance to conduct in-depth research on it.Considering that shear stress mainly exists in the bond interface between FRP and concrete,beam test,single shear test and double shear test are commonly used to study the shear performance of FRP-concrete.The loading mode of beam test is the closest to the engineering condition,but it is more complex,and the operation of single shear test and double shear test is relatively simple.Therefore,the results of single shear or double shear tests are often used to predict the debonding failure of FRP strengthened concrete beams,but there is a lack of research on the relationship between the specific parameters of beam test,single shear test and double shear test.Based on this,this paper carries out experimental research on the axial compression mechanical properties of square ice-filled thin-walled steel tubular stub columns,and systematically carries out beam test,single shear test and double shear test to study the relationship between the specific parameters.The specific research contents are as follows:(1)The axial compressive mechanical properties of three plain ice columns,three sawdust-reinforced ice columns,nine square ice-filled thin-walled steel tubular stub columns,nine square sawdust-reinforced ice-filled thin-walled steel tubular stub columns and six hollow steel tubes were studied.The experimental variables were the width thickness ratio of steel tubes and the type of core ice.The test results show that with the decrease of confinement factor,the failure mode of composite column transforms from waist drum failure to shear failure.The elastic modulus and compressive strength of composite columns decrease with the increase of width thickness ratio.When the width thickness ratio is the same,the elastic modulus of square ice-filled thin-walled steel tubular stub columns is greater than that of square sawdust-reinforced ice-filled thin-walled steel tubular stub columns,but its compressive strength is less than that of square sawdust-reinforced ice-filled thin-walled steel tubular stub columns.(2)The whole stress-strain curve of square ice-filled thin-walled steel tubular stub columns is analyzed systematically.Based on the test data,the formulas for calculating the elastic limit stress and elastic limit strain of square ice-filled thin-walled steel tubular stub columns are proposed,which can predict the test results well.The formula of axial compression bearing capacity of square ice-filled thin-walled steel tubular stub columns is proposed.The formula can predict the bearing capacity of square ice-filled thin-walled steel tubular stub columns and square sawdust-reinforced ice-filled thin-walled steel tubular stub columns with small width thickness ratio,but it is conservative for square sawdust-reinforced ice-filled thin-walled steel tubular stub columns with 100 width thickness ratio.(3)12 beam specimens,12 single shear specimens and 12 double shear specimens are tested.The test variables are the type of test and the type of FRP sheet.The test results show that the failure mode of the beam specimen is different from that of the single shear specimen and the double shear specimen,which is the coexistence of the debonding failure of the adhesive layer and the concrete and the debonding failure caused by the concrete cracking.The main reason for the formation of the mixed failure mode is the relative vertical dislocation of the concrete on both sides of the intermediate crack during the loading process.The distribution of strain and shear stress of beam specimens,single shear specimens and double shear specimens bonded with different types of FRP sheets are similar,and the force transfer area of the interface is gradually developing from the loading end to the free end.(4)The results show that the impact of FRP sheet on the peak shear stress and fracture energy can be ignored because the failure occurs in the concrete.The peak shear stress and fracture energy are beam specimens,single shear specimens and double shear specimens from small to large.The debonding capacity formula,bond slip constitutive model and interface fracture energy formula based on in-plane shear test are compared with the test results of beam specimens,and the results show that the model based on in-plane shear test is not completely suitable for beam specimens.Considering that the relevant models based on inplane shear test can predict the development trend of test variables of beam specimen well,and considering the differences between single shear test and double shear test,the existing relevant models based on in-plane shear test are modified,so that they can predict the test results of beam test,single shear test and double shear test well.