During the preliminary design of stiffened panels, the stability behaviour is critical and both buckling modes, global and local, have to be considered in order to avoid panel configurations in which the minimum stiffness of the stringers is not achieved. In the present work, a new simple computational model is presented that computes the critical column buckling load of an omega-stringer-stiffened panel with periodic boundary conditions. This is achieved by obtaining the effective stiffness properties for an equivalent composite column. The model is able to predict column buckling conservatively as numerical studies show and can easily be used, e.g. as a constraint for optimization studies.