PSI - Issue 78

Sara Silvana Lucchini et al. / Procedia Structural Integrity 78 (2026) 1079–1086

1080

1. Introduction Un-Reinforced Masonry (URM) buildings represent a considerable portion of the existing building stock in Italy and exhibit significant structural vulnerabilities under seismic loading, particularly when constructed before the introduction of modern seismic design codes. The seismic upgrading of such buildings is a priority and requires compatible, effective, and minimally invasive solutions. In recent years, composite-based strengthening systems with inorganic matrices have gained increasing attention due to their promising performance. Among these, Textile Reinforced Mortar (TRM) (Garcia-Ramonda et al. 2022) and Composite Reinforced Mortar (CRM) (Gattesco et al. 2023) systems, have been extensively investigated and applied in masonry retrofit interventions. Within this framework, Steel Fiber Reinforced Mortar (SFRM) coatings represent a valid alternative (Piazzon et al. 2025). The inclusion of randomly distributed steel fibers within the mortar matrix enhances both strength and ductility of masonry walls, with advantages in terms of application simplicity, material compatibility, and long-term durability. Several experimental studies have confirmed the effectiveness of SFRM coatings applied only to the external façades in improving the global seismic capacity of masonry buildings (Lucchini et al. 2021). However, the analytical and numerical models available for the assessment and design of SFRM-retrofitted structures are still under development and are not yet codified in current design standards. This study presents a comparative evaluation of linear and nonlinear analysis approaches applied to a real case study consisting of a three-story residential masonry building with decreasing mechanical performance at upper levels. The structure is assessed in both the as-built condition and after retrofitting with SFRM. The aim is to evaluate the consistency between different modeling approaches and to identify their limitations and potentialities for practical implementation. 2. Case study A real case study consisting of a three-story residential masonry building constructed in the 1960s – 1970s and sited in Brescia, a city in Northern Italy, on a soil type C was analyzed in this research. As commonly observed in traditional construction practices, the building is made of masonry with mechanical properties that tend to decrease with increasing height. In particular, the ground floor (GF) is made of 120 (length) × 120 (height) × 250 (width) mm 3 clay blocks with randomly oriented holes and a void area ≤ 45% , whereas the first (1 st F) and second (2 nd F) floors are made of 250 (length) × 120 (height) × 250 (width) mm 3 hollow clay blocks with horizontal holes and a void area equal to 60% of the gross section area. In both cases, the head and bed joints have an average thickness of 15 mm and are filled with a M5-class mortar. To be on the safe side, the mechanical properties of blocks at the ground floor have been evaluated assuming all the holes were horizontal. The structure has plan dimensions of 20.3 × 10.3 m 2 (see Fig. 2a), a total height of about 10 m, one-way concrete slabs forming the three floors and a pitched roof. In particular, SAP technique and Varese technique were used to build the one-way concrete slabs forming first and second floors (25 cm thick) and third floor (30 cm thick), respectively. The building was retrofitted by the application of a 20 mm thick SFRM coating on the external surface, not connected to the building foundation by rebars. The global seismic resistance of the building, before and after retrofitting, was investigated through linear and nonlinear methods, as described in the following paragraphs. The analyses were carried out by considering the two principal directions (X and Y) separately, in both loading senses, without combining their effects. The results reported herein focus only on the most critical direction, i.e. the +Y direction. The torsional effects related to the eccentricity between the center of mass of the floor and the center of stiffness of the resisting system composed of the walls were included in structural verifications, while accidental eccentricity was neglected. The main mechanical properties of masonry and SFRM coating, used both in analytical and numerical models, are listed in Table 1. A Limited Knowledge Level (KL1) was assumed for existing materials, so, according with the Italian standard NTC (2018), the mean properties of masonry were divided by the Confidence Factor 1.35. Regarding SFRM coating, the mean value of all properties was adopted both in linear and nonlinear analyses.