The behavior of the longitudinal reinforcement under compression resulting in global buckling is studied in this work, based on a concentrated plasticity fiber model that considers four (4) plastic hinges. The model was originally validated for local buckling and here is extended to global buckling by introducing the effect of traversal reinforcement and expansion of the core concrete in the analysis. Modeling of the forces from the stirrups acting on the longitudinal bar assumes that part of the force is transferreddirectly to the expanding concrete core and the remaining force is balanced by internal stresses in thelongitudinal bar