Pure torsion behaviors of concrete filled double-skin (CHS inner and SHS outer) steel tubes

When concrete filled double-skin steel tubular(CFDST) columns are used as viaduct piers,power transmission towers,wind power stents and so on,their torsion properties are very important.A study on pure torsion is the foundation for compression torsion,bending-torsion and compression bending torsion,and is necessary for investigation of the pure torsion behavior of concrete filled double-skin steel tubular(CFDST) columns.A total of four concrete filled double-skin steel tubes and one concrete filled steel tube were designed and tested.The tubes were fabricated with circular hollow section(CHS) and square hollow section(SHS) as inner and outer skins,respectively.The parameters that vary in the tests were the nominal steel ratio and hollow section ratio.Torque-angle curves of the pure torsion were calculated by the finite element software,ABAQUS.The following conclusions can be drawn from the study: firstly,all the specimens have good ductility and post-bearing capacity;secondly,the greater the nominal steel ratio is,the greater the bearing capacity is;thirdly,when the hollow section ratio is 0.4,the concrete filled double-skin steel tubes with square hollow sections have the similar mechanical properties with the concrete filled steel tubes with square hollow sections;thirdly,the calculated results and the experimental results are basically equal.The finite element method can simulate the torsion behavior of concrete filled double-skin steel tubes and concrete filled steel tubes.