Structural, seismic and geotechnical analysis of the Sant' Agostino church in L'aquila (Italy)

Existing masonry buildings are often the result of constructions, changes and alterations that have developed over the centuries. Therefore, the adaptation and improvement of existing masonry buildings must be accompanied by an adequate level of knowledge of their history. The tragic consequences of the recent earthquakes, in Italy and abroad, have stimulated the belief that, sometimes, the cause of seismic damage might be just the wrong intervention of improvement or adaptation. In most cases, this is attributable to retrofit works which are carried out without any knowledge concerning the construction rules of the building. The case study presented here regards the seismic analysis of the Sant' Agostino Church in L'Aquila (seriously damaged by the earthquake occurred in April 2009), which takes into account the in-depth knowledge of the factory, respecting all three evaluation levels of seismic safety provided by the Italian seismic Guidelines for Cultural Heritage (Eurocode 8, 2003; NTC, 2008). In particular for LV1 (Evaluation Level 1), all the analyses requested to fill the annexes of the Directive of December 10th, 2007 were carried out, starting from Module A, which is the "identifier registry", passing through Module B, which concerns the study of "sensitivity factors", and ending with Module C, which considers the "morphology of the elements". From this examination, we concluded that the ground acceleration during the earthquake of April 6th, 2009 surpassed the acceleration value corresponding to the limit state of collapse. For LV2 (Evaluation Level 2), we especially focused on the verification of all macro-elements as a potential source of damage mechanisms. In particular, we found that these mechanisms concerned mostly the facade, the hall, the dome, the apse/presbytery, the roofing, the side chapels, the joints between horizontal and vertical alignment, and finally, the bell tower. Once we collected all data regarding the site, the geometry of construction, the characteristics of the materials, the structure, the soil, etc., we carried out a dynamic FEM modal analysis on the structure, valid for LV3 (Evaluation Level 3). Moreover, these dynamic tests are essential for the evaluation of seismic safety and they also present the clear advantage of being non-destructive. Finally, the analysis provided the most significant vibration modes and suggested the optimal structural interventions to remedy the existing damage and prevent the formation of these mechanisms under the action of future earthquakes.