PSI - Issue 78

Caterina Carbone et al. / Procedia Structural Integrity 78 (2026) 1175–1182

1176

1. Introduction In Italy RC buildings became the prevailing construction system since the second half of 20th century; masonry panels constitute the predominant infills/partitions typology in such structures. The seismic vulnerability of RC buildings with ordinary masonry infills and lacking seismic detailing is well known in the literature (e.g. Calvi and Bolognini 2001; Ricci et al. 2011; De Luca et al. 2014; Morandi et al., 2025). In-plane damage, out-of-plane overturning or collapse has been frequently observed, particularly in brittle and low thickness masonry infills. Several authors (Dolce and Goretti 2015; Del Gaudio et al. 2016) recognised the strong impact of masonry infill/partitions on damage estimation, resulting in social and economic losses and affecting the usability outcome. However, the seismic performance of modern RC buildings with robust masonry infills and designed according to contemporary seismic codes has not been extensively explored, despite some existing examples (e.g. Morandi et al., 2018; Hak et al., 2018; da Porto et al., 2020). Therefore, this work aims to investigate the seismic vulnerability of different classes of Italian RC buildings by comparing fragility curves, that represent the probability of reaching or exceeding defined damage levels, as a function of seismic intensity. Fragility curves were empirically derived from post-earthquake damage data, collected during the reconnaissance campaigns following three recent and intense seismic events: the 2009 L’Aquila earthquake, the 2012 Emilia seismic sequence and the 2016-2017 Central Italy seismic sequence. The areas affected by seismic action host a representative building stock of RC buildings and post-earthquake damage data represent a great source of information, providing direct evidence of buildings’ performance under sei smic action. First, Italian seismic design regulations were briefly reviewed, to identify the main design characteristics of buildings of different ages, affected by seismic events. Post-earthquake damage databases were critically analysed to maintain only the necessary elements for statistical processing. A global damage level was assigned to each inspected building, based on damage reported by both structural elements and infills/partitions. Seismic shaking was characterized by PGA, locally estimated from INGV shakemaps. To account for the negative evidence of damage, the damage databases were merged with exposure data corresponding to undamaged buildings, properly filtered based on experienced ground motion. Consistently with the classification of exposure data, different macro-categories of buildings were identified based on the age of construction and the number of storeys. Buildings of every macro-category were categorized according to sustained damage and experimented seismic action. Finally, fragility curves were derived by applying the MLE procedure to observational data points. 2. Review of seismic design codes Most of the municipalities affected by the 2009 L’Aquila earthquake had already been classified as seismic zones since 1915. Regarding the Central Italy seismic events, the majority of municipalities in Abruzzo and Lazio impacted by the earthquakes were classified as seismic areas prior to 1980 (some of them since 1915), whereas most municipalities in Umbria and Marche were designated as seismic zones in the early 1980s. Finally, the municipalities affected by the 2012 Emilia earthquake were first classified as seismic zones in 2003, with the mandatory adoption by the Region occurred in 2005. It is reasonable to assume that buildings realized before seismic classification were designed only for gravity loads. Seismic design regulations in force in the seismic zones from the 1920s until before the 1990s (e.g., R.D. 13/03/1927 n. 431; R.D.L. 25/03/1935, n. 640; L. 25/11/1962, n. 1684; L. 02/02/1974 n. 64; D.M. 03/03/1975; D.M. 19/06/1984) mandated, basically, the application of an equivalent static horizontal force in the design and required structural verification using allowable stress method. Inter-story drift verifications were not required and no limitations for in-plane horizontal displacements were prescribed. Maximum heights of the buildings were defined as a function of the structural system, seismic categories and road width. Regarding infills/partitions, general guidelines were provided for construction practices and connections based on geometrical characteristics, but no in-plane or out-of plane verifications were required. Interaction between frames and partitions was not considered. The D.M. 16/01/1996 and its accompanying Circular No. 65 of April 10, 1997, introduced new requirements for regularity in plan and elevation, geometric and reinforcement limitations for structural elements; in addition, they permitted structural verifications using the semi-probabilistic limit states method. In-plane displacement verifications