Experimental And Theoretical Study On Axial Compression Performance Of Circular High Strength Concrete-filled Double Skin Steel Tubular Members

Concrete-filled double skin steel tubular is a new type of composite component for pouring concrete between two concentric steel tubes.It not only has the advantages of traditional concrete-filled steel tube,such as high bearing capacity,good plasticity and toughness,convenient construction,but also has the characteristics of section development,large bending rigidity,light self weight,good fire performance and high economic benefits.Compared with the ordinary concrete-filled double skin steel tubular members,the high-strength concrete filled double skin steel tubular members can greatly enhance the bearing capacity of the members and further reduce the self weight of the members.In this paper,through the combination of experimental research,numerical simulation and theoretical analysis,the axial compression bearing capacity and failure mechanism of the high strength concrete-filled double skin steel tubular members are studied,and the calculation method of the axial compression bearing capacity and stiffness of the high strength concrete-filled double skin steel tubular members are put forward.The main research contents are as follows:(1)In this paper,six circular high strength concrete-filled double skin steel tubular members are tested.The bearing capacity and failure mode are studied,and the influence of concrete strength,section void ratio and section steel ratio on its performance is analyzed.The results show that there are two failure modes of "tympanic" and "shear" under the action of axial compression.The "tympanic" failure specimen has higher later bearing capacity and good ductility,while the "shear" failure specimen has lower ductility.With the increase of the concrete strength,the bearing capacity of the specimen increases;with the increase of the section void ratio,the bearing capacity of the specimen decreases;with the increase of the section steel ratio,the bearing capacity of the specimen decreases.(2)The finite element software ABAQUS 2017 is used to simulate the test specimen.The failure mode,ultimate bearing capacity and load displacement curve obtained from the finite element analysis and test are compared.The finite element results are in good agreement with the test results,which verifies the rationality and correctness of the finite element simulation.(3)The stress development process of the high strength concrete-filled double skin steel tubular members under the axial load is as follows: the internal and external steel tubes and sandwich concrete are stressed separately→the interaction between the external steel tube and sandwich concrete is increasing continuously,the concrete is in the threeway compression state→the bottom of the external steel tube is partially yielding→the internal and external steel tubes are yielding in large area→the test piece is damaged by buckling or shear.(4)The influences of concrete strength,void ratio of section,diameter thickness ratio of inner(outer)steel tube,strength of inner steel tube and length diameter ratio of components on the mechanical properties of circular high-strength concrete filled double skin steel tube under axial compression are studied.The results show that: With the increase of concrete strength grade,the bearing capacity and stiffness of the component increase;With the increase of void ratio,the ultimate bearing capacity of the specimen decreases,and the change of void ratio has little influence on the axial compression stiffness;With the increase of the diameter thickness ratio of the inner steel tube,the bearing capacity and stiffness of the component decrease;With the increase of the diameter thickness ratio of the outer steel tube,the bearing capacity and stiffness of the component decrease obviously;The increase of the strength of the inner steel tube has little effect on the bearing capacity of the component,but has no effect on the axial compression stiffness of the component;With the increase of the ratio of length to diameter,the ultimate bearing capacity of the component decreases,the component changes from strength failure to instability failure,and the change of the ratio of length to diameter has little effect on its axial compression stiffness.(5)Based on the test results and theoretical analysis,the calculation formula of the axial bearing capacity and stiffness of the high-strength concrete filled double skin steel tubular members is put forward.