Abstract Part of a reinforced concrete column between two consecutive sets of transverse reinforcement bars, is simulated by a plane truss model with bars obeying nonlinear uniaxial stress-strain laws of concrete or steel The equilibrium and stiffness conditions are written with respect to the deformed structure, in order to account for structural instability phenomena. First, this part of the column is subject to a gradual monotonic compressive axial loading, and then a gradual monotonic compressive deformation, which produces strain gradient across the column section. In both cases, the loading continues until the appearance of a global structural instability of concrete. In the second case, a more ductile behavior of the RC column is observed, that is, the global instability is delayed and finally occurs for a larger value of peak compressive strain of concrete. This is found in satisfactory approximation with recently published experimental results. However, in the case of cyclic loading, the RC column does not exhibit a ductile behavior, which is also in agreement with recent experimental evidence. Keywords: Buckling, cracking, ductility, strain gradients, structural instability, truss model.