Stability and Ductility of Thin-Walled Circular Steel Columns under Cyclic Bidirectional Loading

Abstract

A cyclic bidirectional loading experiment is carried out to examine the ultimate seismic behavior of thin-walled circular steel columns by using an accurate three-dimensional (3D) experimental system recently developed by the writers. This experimental system is characterized by its unique 3D hinge and 3D transducer that are employed to apply accurate 3D force components to the top of columns by considering geometrical nonlinearity precisely. Cyclic circular loads are adopted as virtually the severest bidirectional horizontal loads for circular columns. From the experimental results, it is observed that the strength and ductility of the columns decrease considerably under the cyclic circular loads, compared with those under the conventional cyclic unidirectional loads. The experimental results are also used to confirm the validity of the nonlinear finite element method (FEM) shell analysis where a three-surface cyclic plasticity constitutive model is implemented after modifying the original three-surface model to consider the behavior under large plastic strain. With the extensive numerical results obtained from the nonlinear FEM analysis, empirical prediction equations are derived to evaluate the strength and ductility of thin-walled circular steel columns under the cyclic circular load with one loading cycle.