Macro-modeling on cyclic behavior of concrete-encased steel short columns under shear failure

Abstract

Concrete-encased steel (CES) structural members, in which a steel shape is encased in a reinforced concrete (RC) section, are widely applied in high-rise buildings as the primary lateral resistance systems. Because the brittle shear failure is usually observed in CES short columns under seismic excitation, it is essential to accurately evaluate the cyclic behavior of these CES short columns to ensure structural safety. In order to account for the contribution of shear action to the entire cyclic response of CES short columns, a new macro-modeling strategy implemented in OpenSees is proposed in this paper. In the proposed numerical model, the cyclic behavior of CES short columns is simulated by traditional fiber sections and a novel nonlinear shear spring in series. Therefore, the applied fiber sections can evaluate the flexural action and the effect of bar slip, and the shear action, including shear deformation and shear capacity, can be formulated by the nonlinear shear spring. After the detailed parameters (shear strength, shear stiffness, post-peak behavior, hysteretic laws, and failure criteria) of the nonlinear shear spring are defined, available pseudo-static test results are employed to validate the proposed model. The comparison between the numerical and test results indicated that the proposed model could reasonably capture the peak load, ultimate load, peak displacement, and energy dissipation of the tested CES short columns, and the existing elements in Opensees (fiber element and flexure-shear interaction element) are inappropriate to apply for modeling the cyclic behavior of CES short columns.