Experimental Study On Interface Bond Strength Of Rectangular Concrete Filled Steel Tube At Low Temperature

The stress transmission between the interface of steel tube and concrete is the precondition for excellent performance of Concrete Filled Steel Tubes(CFST).Due to the engineering application of CFST structure,especially in the severe cold area,the study on the interfacial bond behavior of CFST structure is becoming more and more urgent.The paper explores the relationship between the interfacial bond behavior of CFST structure and the change of temperature by simulating low temperature environment.Try to improve the steel-concrete bonding effect by changing the structure of steel pipe(mainly stiffening rib)at the same time,and provide reference for the application of concrete-filled steel tube in severe cold area.In the paper,there are three forms,a total of 16 pieces of CFST short columns have been tested through push-out test.In order to explore the relevant mechanism,the relationship between temperature and strain of CFST was testedThe main research results are as follows:(1)The damage morphology and the average bond strength of three forms CFST(no stiffener,with stiffener and PBL stiffener)are compared with each other.The result shows that the longitudinal stiffening ribs significantly improve the interfacial bonding strength of steel and concrete.The average bond strength of specimen with stiffener is 50% higher than ordinary specimen.The average bond strength of the PBL specimen is 60% higher than that of the conventional stiffener.(2)Conducted push-out test of CFST short column by simulating low temperature environment,and the load-slip relationship curve is obtained.The result shows that the relationship between average bond strength and temperature is linear,and the bond strength increases gradually with the decrease of temperature.(3)The wall strain of ordinary concrete filled steel tube under low temperature was analyzed.The result shows that the deformation degree of the specimens at the same temperature is basically the same.Comparing the circumferential and longitudinal strains during different temperature,and it is found that the growth rate of hoop strain decreases gradually with the decrease of temperature,while the longitudinal strain has no obvious change.In other words,the hoop restraint of the steel tube to the core concrete is enhanced,and the specific reasons need further study.