ABSTRACT
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. Differently from other bridge typologies, for which significant advances in seismic risk assessment were carried out in the development of tools as fragility curves for generalized classes of bridges (like in HAZUS method), no comparable results are currently available for masonry arch structures.
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 is based on the determination of the collapse mechanism depending on geometrical features, the hinges location, the collapse multiplier and the thrust line. The main step of the procedure involves the determination of the load factor α using the upper bound theorem. It employs an assumption that a masonry arch becomes a mechanism when at least four plastic hinges appear in the arch barrel (Heyman, 1982). In the nonlinear Kinematic analysis, this process is applied to a deformed shape of the structure. An iterative procedure has been implemented using to determine the capacity of the bridge, taking into account the finite strength of the material.
The seismic assessment is made with reference to two performance levels defined from the capacity curve and related to d0 * the displacement where the horizontal load multiplier becomes zero (Cattari et al., 2012).
Through the evaluation of the main geometric parameters which influence the collapse mechanism, fragility curves for single-span masonry arch bridges were obtained, considering the geometric characteristics related to the arch bridge typology, mechanical parameters of the masonry and infill, and the type of soil in which the structure is located. 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 0.05–1.5 g. The fragility curves obtained represent an useful tool to plan retrofit interventions on stock of existing masonry bridges. Capacity curve with the corresponding two limit states, DLS and ULS. https://s3-euw1-ap-pe-df-pch-content-public-p.s3.eu-west-1.amazonaws.com/9781315207681/cd556cd4-4dcf-4efe-8e29-56fc67b8bfbd/content/fig294_1.tif"/>
