Seismic Vulnerability Assessment of an Existing R.C. Building with One-Direction-Only Frames

Italy’s long architectural history has resulted in a vast stock of buildings constructed prior to the introduction of seismic provisions. These structures were designed to resist only gravitational loads, with no consideration for lateral forces induced by earthquakes. While the lateral capacity of reinforced concrete (RC) frames without seismic detailing has been extensively studied, the contribution of Hollow Clay Block Floor Systems (HCBFS) in the transverse direction remains largely overlooked and is often underestimated. This study presents a preliminary seismic vulnerability assessment (based on simplified analysis methods) of a real RC building located in the city of Turin, designed and built in mid-20th century without seismic detailing or provisions. Despite the relatively low seismic hazard of its location, the structural vulnerability is expected to be significant. To avoid underestimating the building’s lateral capacity and to better capture the hierarchy of failure, the contribution of both the infills and the HCBFS to the overall lateral load capacity will be considered. While several validated modelling approaches exist to represent the effect of infills, few methodologies are available to accurately assess the contribution of HCBFS. This research evaluates the Equivalent Beam Approach (EBA) proposed by Montuori et al. [2016], in which the joists within an effective slab strip are converted into an equivalent beam element. The outcomes of these evaluations aim to support the development of a standardized methodology for Arup Italia SRL to carry out Initial Seismic Analysis (ISA) of similar structures, specifically addressing the contribution of the HCBFS. Such a methodology would provide a more comprehensive understanding of vulnerabilities in RC buildings with one-direction-only frames, especially in regions of relatively low seismic hazard where assessments are often postponed due to their perceived lower urgency. The findings confirm that the combined action of infills and HCBFS can significantly enhance the lateral stiffness of RC buildings originally designed for gravity loads only. These insights support the development of more inclusive and representative modelling strategies, paving the way for improved assessment methodologies and retrofit solutions for Italy’s existing building stock.