Masonry arch bridges fragility assessment

Masonry arch bridges still represent a crucial element of the railway transportation network across Europe, but their exposition to seismic hazard has not been currently exploited as for the other bridge typologies. The paper deals with seismic vulnerability assessment of existing single-span masonry arch bridges following the principles of limit analysis. An iterative procedure is implemented to define the capacity curve through a non linear Kinematic analysis. The process involves the determination of the collapse mechanism depending on geometrical features, the hinges location, the collapse multiplier and the thrust line. Seismic fragility curves for generalized classes of railway masonry bridges are subsequently obtained considering the effective ranges of main geometric and material parameters affecting the arch bridge capacity. The intrinsic variability of the seismic action is incorporated through a set of ground motions compatible with EC8 spectra for different types of soil, with PGA varying in the range of 0.05-1.5g. The fragility curves obtained represent an useful tool to plan retrofit interventions on stock of existing masonry bridges.