Experimental and analytical studies on elastic-plastic local buckling behavior of steel material under complex cyclic loading paths

Under the action of complex earthquake loads, the elastic-plastic local buckling of a concrete-filled steel tubular column will most likely occur in the steel tube, which is difficult to be simulated using the traditional fiber beam-column finite element model. In this paper, 30 steel specimens with two strength grades, Q235 and LYP160, were prepared and tested considering various cyclic loading paths to obtain the hysteretic stress-strain relations and the elastic-plastic buckling behavior of steel material, aiming to develop an effective uniaxial constitutive model of steel material considering elastic-plastic buckling. Based on the available Légeron Model, Gomes and Appleton Model (GA Model), and Dhakal and Maekawa Model (DM Model) for determining the stress-strain relation of steel material considering the elastic-plastic buckling behavior, a comparison analysis was made between the test results and the predicted results. It is found that the buckling behavior of the steel in compression after yielding cannot be simulated well by Légeron Model; the compressive buckling stress and compressive strength of the steel with buckling behavior predicted by GA Model agrees well with the test results; and the unloading stiffness of the steel in tension and compression can be well predicted by DM Model.