Circular RC sections confined with FRP: Modeling and design

In this paper, a design procedure is presented to determine the optimal thickness of FRP jackets, for enhancing the ductility of existing reinforced concrete bridge piers, having circular cross-section. The procedure stems from the definition of an upgrading index, given as the ratio of the target-to-available ductility at the pier base section, to be attained through FRP jacketing. The available ductility is that identified through the usual assessment procedures on the r.c. member to upgrade, while the target ductility is evaluated based on the expected actions on the bridge. A parametric study on old-code-designed bridge piers sections, upgraded with either glass or carbon fiber jackets, is performed, based on a fiber-section model, equipped with a recently proposed FRP-confined concrete model. The results of the parametric study has been used to developed a design equation that allows to design the optimal thickness of FRP jackets in terms of: the desired upgrading index, the mechanical characteristics of the selected composite material, and the quantities defining the initial state of the pier section.