Behavior of circular concrete-filled steel tabular columns under monotonic and cyclic torsions

Abstract

This paper studied the behavior of circular concrete-filled steel tabular (CFST) columns under monotonic and cyclic torsional loading. Experiments were performed on 16 CFST columns, followed by analyses. Each column was axially loaded by a constant axial load with ratios of 0–0.7 and monotonically or cyclically twisted until failure. Experimental results showed that the failure modes of CFSTs under monotonic and cyclic loading were similar and torsional buckling of steel tubes was absent due to the mutually beneficial interaction between the steel tube and concrete. An axial load ratio ≥ 0.5 resulted in the descending branch, reducing the ductility by up to 17.8%. The axial load ratio marginally affected the yield torsional moment capacity of CFSTs but considerably affected the elastic rotational stiffness. The yield rotational stiffness increased and the yield rotation decreased as the ratio of the axial load increased to ∼0.3. Further increase in the axial load ratio had an inverse effect. Cyclic loading reduced the yield and ultimate torsional moments by 6.4% and 11.1%, respectively; however, it did not induce a stiffness degradation. Further, it reduced the yield and ultimate rotations by 10% and 30.7%, respectively. A model to predict the torsional yield moment capacity was proposed based on the concept of decoupling the resistances resulting from cyclic loading. The proposed model is simple and accurate, and will be useful for engineers in practice.