Load carruing capacity of mansory arch bridges and collapse mechanisms

This paper presents some aspects of the approach to the assessment of masonry arch bridges developed by the Italian National Railway Authority (RFI) and the University of Genoa. Being the non linear response of masonry a crucial issue in the evaluation of the load carrying capacity of a bridge, a No Tensile Resistance approach, with limited inelastic compressive strains (controlled ductility), has been formulated to allow an incremental non linear analysis of the bridge up to collapse in the frame of a simplified 2-D geometry. 3-D FEM models give a general overview of the structural response, provide detailed information on the stress state but need simplified non linear constitutive models for masonry and are not able of giving a synthetic description of the bridge response. For this reason, 3-D analyses assuming either elastic material models, meaningful if the tensile stresses are limited, and non linear perfectly brittle ones are used in the procedure as a comparison with 2-D estimates of the limit load