Identifying and modeling ductile RC columns with deformed bars

In this paper, empirical equations are proposed to calculate the moment-chord rotation response envelope of ductile rectangular reinforced concrete columns with deformed bars. The proposed envelope accounts for cyclic strength degradation and is defined by four characteristic points: yielding, maximum, conventional ultimate, and collapse. Also, the proposed envelope is implemented by adopting Pinching4 Material model in OpenSees and, based on the experimental data, the hysteretic parameters governing unloading and reloading stiffness degradation, as well as pinching effect, are calibrated. The proposed model is applied at the element level, thus showing the potential advantages and limitations of its use, also in comparison with other analogous proposals presented in the literature. The proposed model has two main advantages with respect to proposals existing in the literature: (i) the response envelope already includes cyclic degradation of force capacity, thus fulfilling the requests of current standards regarding the need of accounting for members’ mechanical softening within nonlinear static procedures; (ii) the hysteretic parameters governing unloading and reloading stiffness degradation, and pinching, allow a more accurate reproduction of members’ and structures’ seismic response within nonlinear dynamic procedures.