Extension to rectangular section of an analytical model for concrete confined by steel stirrups and/or FRP jackets

In this paper, an analytical model of confined concrete proposed for square sections is extended to the case of rectangular ones. The new and generalized formulation, based on the elasticity theory, is developed under the key assumption that the confinement arises in plane-strain conditions. The proposed model provides, through the analogy among the section core and internal cylinders, the confining pressure in polar coordinates to be applied for computing the actual concrete curve subjected to passive confinement. In this procedure, as for the square confined sections, any active confinement model derived from triaxial tests on cylindrical specimens may be involved. The extended model is also suitable for evaluating the confining pressure offered by additional external strengthenings in any material, such as for example FRP wraps and/or steel jackets. Comparisons among numerical simulations and experimental data demonstrate the accuracy of the new generalized analytical model in predicting the confined stress-strain relationship of concrete in the case of either newly designed or old existing concrete elements, also when multiple transverse reinforcements are applied.