Criteria for identifying vulnerability classes for rocking masonry church façades via fragility curves

The activation of out-of-plane (OOP) mechanisms in the façade walls of masonry churches has been frequently observed during seismic events and therefore represents an important source of vulnerability for this kind of structure. Although there is a wealth of literature on the OOP behaviour of masonry elements, there is a lack of specific analytical studies on the OOP behaviour of masonry church façades and, in particular, on the possibility of identify homogeneous vulnerability classes. To fill this gap, this paper is focused on: i) assessing the influence of some geometrical parameters of church façades on their vulnerability to the OOP mechanism of simple rocking, ii) defining reliable criteria for assessing homogeneous vulnerability classes, iii) validating the proposed criteria on a large scale. For these purposes, façades are modelled under free and restraint rocking conditions, being the latter ones represented by their interlocking with the sidewalls and the presence of steel tie rods. A sample of 500 façades is generated thanks to a Monte Carlo simulation, starting from the actual data of the façades of 14 existing masonry churches. Non-linear static analyses are carried out for the rocking response of the façades under different restraint conditions, aimed at verifying the achievement of three limit states: the onset of rocking, a moderate and a severe rocking motion, as conventionally defined according to the indications provided by the Italian seismic code. By investigating the influence of some geometrical parameters for a generic façade on its vulnerability to simple rocking, different criteria for identifying homogeneous classes of seismic vulnerability (high, medium and low) are proposed for each investigated limit state. Finally, by using incremental static analysis, multiple stripe analysis and acceleration-displacement response spectra, fragility curves are developed for each limit state and under different restraint and seismic input conditions in order to validate the proposed criteria on a large scale too. • Influence of geometrical parameters on the vulnerability of masonry church facades to simple rocking. • Development of fragility curves for masonry church facades under rocking at different Limit States. • Assessment of homogeneous classes for rocking for masonry churches facades at different Limit States.