PSI - Issue 78

Paolo Petrella et al. / Procedia Structural Integrity 78 (2026) 2062–2069

2065

In 1706 a violent earthquake struck the city of Sulmona, seriously damaging the building heritage. The dramatic effects of the earthquake on the city can certainly be traced back more to the materials than to the construction techniques used, given that the very thick walls were made of a conglomerate of sand, lime and river pebbles with a rounded shape, therefore easily crumbling following seismic stress. Work on the new church had not yet begun when the earthquake destroyed, at least in part, the Jesuit College and the pre-existing adjacent church. In July 1709 the college and the church had already been rebuilt. The Jesuit college then underwent changes in 1812, becoming a boarding school, and in 1862, becoming the Ovidio College. The College, also home to educational institutions, closed definitively following the damage suffered in the 1915 earthquake and the bombings of the First World War. Subsequently, around the years 1925 1930, the building underwent a significant and radical renovation to be used as a classical high school, reaching its current appearance. 3. Improvement of the seismic safety 3.1. Design criteria From the assessments carried out for the current state, it appears that the greatest criticality in the seismic resistance of the building is determined by the insufficient mechanical characteristics of the original materials in place. Other criticalities also contribute to the seismic inadequacy of the building, such as the total or partial lack of diaphragm behavior of the floors and the absence or insufficiency of the connections between the masonry piers and between the floors and the piers themselves. These conditions compromise the optimal box-like behavior of the building and also determine torsional effects in the dynamic response of the building, with a reduction in the full collaboration of all the structural elements in the seismic-resistant capacity, which is therefore further reduced. On the basis of these observations, the design strategy must be based primarily on increasing the mechanical characteristics of the masonry. In this regard, the interventions to reduce seismic vulnerability were preliminarily assessed in the general framework of the conservation of the building, with the fundamental objective of the conservation of the materials and of the structural functioning itself, considering that this, although presenting shortcomings with respect to the reference regulatory performance standards, has in reality shown satisfactory behaviour during the seismic attacks suffered. The design strategy therefore excluded the generalized interventions of widespread cladding of the walls with reinforced plaster foreseen in the definitive project based on the tender, focusing instead on interventions, such as injections of lime-based mortar and repointing with connection of the facings, which restore and improve the characteristics of the affected walls, eliminating their intrinsic critical issues, in compliance with the indications of the Cultural Heritage Directive (2011) and the recommendations put forward by the Superintendency on the definitive project based on the tender. It is noted that the increase in resistance of the masonry in question, obtainable with reinforcement interventions, is limited (also by law) to a factor between 3.0 and 3.5. With increases in material resistance of this order of magnitude, the increase in the overall capacity of the construction that can be achieved is of the order of approximately 2 times. Since the capacity index in the current state is equal to 0.30-0.35, it appears that interventions on the masonry can bring this index to 0.60-0.70. The further increase, necessary to comply with the objectives of the tender (index > 0.66), can be fundamentally achieved thanks to the introduction of additional seismic-resistant elements, or limited new wall partitions, or in the replacement of thin partitions with load-bearing walls. Furthermore, it is necessary to re-establish an effective box-like behaviour that the building in its current state does not possess with interventions of chaining and bracing of the floor horizontal elements and with stitching and connections of the walls with the other walls and with the floors. 3.2. Numerical model The information acquired from the original project and confirmed through sample checks, allowed to build a complete and detailed finite elements model of the building. The load-bearing structure in elevation is made of masonry, modelled with wall-equivalent frame elements, with a limited number of reinforced concrete elements,