Load carrying capacity of masonry bridges: Numerical evaluation of the influence of fill and Spandrels

Filling materials directly laid on vaults are a common building technique that generally increases the load carrying capacity. This increase can be much larger than the stabilizing effect of a dead load on the vault and it is due to the mechanical interaction between vault and fill that activates the strength resources of the fill. This phenomenon was clearly shown to be effective in masonry bridges [1], on which this work is focused. A twodimensional model (Cavicchi and Gambarotta [12,13,14] is here used to analyse the effects of arch-fill interaction on collapse behavior. Arches and piers are described as beams made of no tensile resistant ductile in compression material, while fill is idealized as a no tensile resistant frictional-cohesive continuum. The principles of Limit Analysis are applied and upper and lower bounds on the true collapse load of the model are obtained. The effectiveness of the model is shown by simulating an experimental collapse test. Parametric analyses are carried out by varying the values of the constitutive parameters. Moreover, the effects of the out-of-plane boundary conditions of the fill on the collapse behavior are analysed.