The bar that is susceptible of buckling is initially in contact with the concrete core, but once buckling starts lateral confinement is reduced facilitating the expansion of the concrete inside the buckled length of the bar, so that, contact between reinforcement and concrete can be maintained. Thus, the forces are transmitted from the stirrups to the concrete core, as well as to internal stresses in the longitudinal bar. In order to introduce the force in the stirrups, initially, an intermediate stage would be considered, where for an axial imposed strain, e, the bar does not buckle, Fig. 6b, and strains in the stirrups are only due to the lateral expansion of the concrete core, ect, considered identical for all stirrups. Under these conditions, the stirrups forces only due to the concrete expansion, Fhj , are transmitted completely to the concrete core.