Ponte alla Vergine. Structural Analysis of a Medieval Masonry Footbridge

The paper is concerned with the application of a numerical method, available to the analysis of voussoir arches and/or any type of masonry structure, in the structural investigation of the medieval masonry footbridge called Ponte alla Vergine, close Pistoia. The masonry structure is modelled as a discrete system of rigid blocks connected by unilateral elastic contact constraints. The contact device which links the blocks, through which both a mortar joint and a dry joint could be simulated, consists of a set of elastic links, orthogonal to the contact surface between two adjacent blocks, and an additional link, parallel to the interface, through which the shear forces can be transmitted. In accordance with the assumption of no tensile strength in the joint, only compressive forces can be transmitted from one element to another. Reasonable hypotheses can be assumed for the link parallel to the contact surface in order to calibrate both the shear behaviour and the influence of the friction between the blocks. Through the results of the numerical procedure it is possible both to define the cracking failure pattern, highlighting the actual reacting structure within the apparent one, and to evaluate the width of the cracks located in the mortar joints.