Parameter identification of three hysteretic models for the simulation of the response of CFT columns to cyclic loading

A computational study is conducted to investigate the nonlinear response of square concrete-filled steel tubes (CFT) subjected to constant axial load and cyclically varying flexural loading. An accurate nonlinear finite element model is created with the ATENA software which includes all the important factors affecting the response of CFT members, such as, cyclic local buckling of steel tube, nonlinear behavior of confined concrete into tension and compression, cyclic softening and the interface action between steel tube and in-filled concrete. The validity of this finite element model is established by comparing its results with those of existing experiments. Using this finite element model, an extensive parametric study is conducted to determine expressions, providing the necessary parameters in three hysteretic models including strength and stiffness degradation. These hysteretic models are: (a) the Bouc-Wen model, (b) the Ramberg-Osgood model, and (c) the Al-Bermani model. The parametric study involves sixty-four CFT columns with different width to thickness ratios, steel tube strength and concrete strength under a recognized cyclic load protocol with variable intensity. Using these calibrated hysteretic models in the framework of the RUAUMOKO program, comparisons with experimental and numerical results are made for further model adjustments. As a result, one can directly use the aforementioned hysteretic models for the simulation of CFT columns alone or as members of composite MRFs frames to determine their response to cyclic loading.