Three-dimensional hysteretic modeling of thin-walled circular steel columns

An empirical hysteretic model is presented to simulate the three-dimensional cyclic behavior of cantilever-type thin-walled circular steel columns subjected to seismic loading. This steel column is modeled into a rigid bar with multiple vertical springs at its base. Nonlinear hysteretic behavior of thin-walled columns is expressed by the springs. As the hysteretic model for the spring, we modify the Dafalias and Popov's bounding-line assumption in order to take into account the degradation caused by the local buckling. The material properties for the vertical spring are determined by using curve-fitting technique, based on the in-plane restoring force-displacement hysteretic relation at the top of the column obtained by FEM analysis. By properly increasing the number of springs, the homogeneity of thin-walled circular columns is maintained. Finally this model is used in three-dimensional earthquake response analysis.