Load-bearing capacity of Gerber saddles in existing bridge girders by different levels of numerical analysis

Abstract

This paper numerically investigates three typologies of Gerber saddle in existing ordinary and post-tensioned girder concrete bridges. The main goals of this work concern the evaluation of the effective load-bearing capacity of Gerber saddles, and the identification of weak points (i.e., lack of enough diagonal reinforcement, loss of pretension in tendons) of existing dapped-end connections, which lead to the re-entrant corner diagonal crack, typical of these kinds of structural elements. At this aim, two analytical approaches, with different level of approximations, are used. First, different strut-and-tie models are arranged for each typology of Gerber saddle considered, and the global safety factor is estimated for several cases. Second, using nonlinear finite-element method, the results obtained by strut-and-tie models are compared. In addition, several information about the condition of Gerber saddle at collapse are obtained (deformation and stress of concrete and steel rebar, crack patterns) also taking into account the corrosion-damage effects. Moreover, the results of analyses allow identifying the potential modes of crisis of the dapped-end connections and their critical aspects.