Performance of steel-reinforced circular concrete-filled steel tubular members under combined compression and torsion

Only limited investigations on mechanical behavior of circular steel-reinforced concrete-filled steel tube (SRCFST) under coupled compression and torsion have been reported in open literature. Therefore, eighteen circular SRCFST members were tested to study the torsional behavior. The effects of various parameters, i.e., sectional forms of steel reinforced, axial compression ratios, loading paths and slenderness ratios were considered, respectively. The failure modes, torsional moment-rotation angle curves and torsional moment-strain curves of SRCFST members derived from the loading tests were investigated and discussed, respectively. Test results show that the development of concrete crack is effectively restrained due to the embedded steel reinforced. When the ratio of steel reinforced is the same, the torsional bearing capacity of specimens with internal cross-shaped steel is very close to that of specimens with internal I-shaped steel. The axial compression ratios and the slenderness ratios showed significant impact on the torsional rigidity and ultimate torsional bearing capacity (Tue). In addition, a finite element model was developed and verified against the testing results, which can accurately predict the Tue, and finally the formulas for calculating the Tue of specimens with internal I-shaped steel and cross-shaped steel were proposed, respectively.