# Han, Yao, and Tao 2007

This paper represents an attempt to study the torsional behaviors of concrete-filled thin-walled steel tubes. ABAQUS software is used in this paper or the finite element analysis of CFT subjected to pure torsion. The FEA modeling was used to investigate the influence of important parameters that determine the ultimate torsional strength of the composite sections. The parametric studies provide information for the development of formulae to calculate the ultimate torsional strength as well as the torsional moment versus torsional strain curves of the composite sections.

## Experimental Study, Results, and Discussion

A finite element model of circular and square section CFT is developed and utilized to test the effect several parameters have on CFT members under pure torsion. It was found that there is a significant difference between failure modes of CFT and hollow steel sections. For hollow steel sections subjected to pure torsion, outward buckling occurs. CFT specimen showed good plastic and steady behavior and no obvious buckling occurred. The change in failure mode of the steel tube had significant effect on the ultimate torsional strength of the specimen. Steel to concrete interaction stress was compared to torsional angle. For members with circular sections, interaction stresses in symmetrical positions of the sections have comparable values. For square sections, the interaction stress mainly concentrates at the corners of the section. The influence of steel yield strength on the members with circular and square sections was found to be very similar. Steel yield strength had only a moderate influence on the rigidity in the elastic stage of torsion moment versus shear strain curves. Torsional strength of members increased as steel yield strength increased. The influence of concrete strength was found to be similar in both circular and square section CFT members. The concrete strength had a moderate influence on torsional strength of members but the elastic rigidity of torsion moment versus shear strain curves had a moderate increase with concrete strength increase. Similar results were found for the influence of steel ratio. Steel yield strength, concrete strength, and steel ratio only had influence on the numerical value of torsion moment versus shear strain curves; the shape of the curves was not affected. Within the parameter limitations of the analysis, torsion moment versus shear strain curves of CFT subjected to pure torsion had no falling stage.

## References

Han, L.-H., Yao, G.-H., and Tao, Z. (2007). "Performance of concrete-filled thin-walled steel tubes under pure torsion," Thin-Walled Structures, 45 (1), pp. 24-36. doi: 10.1016/j.tws.2007.01.008