Seismic assessment of complex assets through nonlinear static analyses: The fortress in San Felice sul Panaro hit by the 2012 earthquake in Italy

This paper proposes a procedure for the seismic assessment of unreinforced ma--sonry complex structures together with a first application to the case of fortresses. The proposal of such procedure arises from different reasons: firstly, Standards suggest proce--dures mainly addressed to ordinary structures; furthermore, even those Recommendations, which are more specifically addressed to monumental assets, state only general principles, without specifying operational targeted-‐procedure for their seismic assessment. The dam-age occurred after past earthquakes, and in particular the one hit the Emilia region in Italy, highlighted that fortresses are characterized by an aggregation of bodies with an own seismic behavior which, however, is strongly affected by their dynamic interaction due to the mutual boundary conditions. Hence, the adoption of a numerical three-‐dimensional model of the whole structure is necessary to take into account explicitly the effect of such interactions. The proposed procedure requires the execution of a modal analysis of the whole structure in order to define the modes involving the dynamic response of each units and their modal shapes. Then, fitting the modal shapes, proper load patterns are defined to pass to the execution of pushover analyses. In particular, one load pattern is applied for each unit but considering the whole numerical model. The pushover curve of each unit is then converted in the capacity curve to finalize the seismic assessment and verification. The proposed procedure is applied in the paper to the case-‐study of San Felice sul Panaro fortress, significantly hit by the Emilia earthquake, 2012 allowing the comparison between the occurred damage and the one simulated by the nonlinear static analyses and to vali--date the procedure. The potentialities of the proposed procedure seem relevant in order to provide a reliable seismic assessment also of other typology of complex structures.