External post-tensioning of composite bridges by a rating equation considering the increment of a tendon force due to live loads

Abstract

Strengthening by external post-tensioning is an effective technique to restore the load-carrying capacity of many types of bridge superstructures. In this paper, external tendons are used for strengthening steel-concrete composite bridges. Analytic expressions for the increment of the initial tendon force are derived by the principle of virtual work for configurations of straight and draped tendons under design loads. A new rating equation for bridges is then introduced considering the initial tendon force and its increment. A systematic procedure is illustrated to determine the number of strands in external tendons and the initial tendon force using the proposed rating equation. It is demonstrated with an example bridge that the proposed method is suitable for the strengthening of existing bridges with an external post-tensioning technique.