Empirical modelling of the cyclic response of reinforced concrete columns with deformed bars

In this paper, the results of the cyclic experimental tests performed on ductile rectangular reinforced concrete columns with deformed bars are processed to define characteristic points of the lateral base moment - chord rotation response envelope. Four characteristic points are determined: yielding, maximum, conventional ultimate, and collapse. The value of base moment corresponding to these points can be determined based on mechanical principles or is intrinsic to the definition itself of the characteristic points of the response. On the other hand, based on the processed experimental data, empirical equations are derived for calculating chord rotation values corresponding to the four characteristic points. The proposed cyclic response envelope can be implemented in OpenSees by adopting Pinching4 Material model, which also allows modeling the cyclic degradation of unloading stiffness, reloading stiffness, and the pinching effect. Based on the processed experimental data, the hysteretic parameters that should be adopted to model these phenomena are calibrated. The proposed model can be adopted for nonlinear static and dynamic analyses for the seismic assessment of new and existing buildings.