PSI - Issue 44

Roselena Sulla et al. / Procedia Structural Integrity 44 (2023) 998–1005 Sulla et al./ Structural Integrity Procedia 00 (2022) 000–000

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of knowledge and material availability. The structural behavior of these buildings is highly influenced by their geometry, material properties and construction details. The assessment of these buildings is also dependent on the numerical method chosen to calculate their response under seismic actions. In the literature there are many studies on the methods for the assessment of masonry buildings. Among the others, in (D'Amato, Gigliotti, & Laguardia, 2019) the results obtained from the comparison between the three levels of evaluation proposed in the Italian Directive for cultural heritage to assess churches seismic vulnerability are discussed. In (D'Amato & Sulla, 2021) the linear kinematic analysis is applied, allowing to consider a macro element failure mode in order to study the activation of some mechanisms on an existing brick masonry church. Very often, masonry structures are evaluated according to the equivalent frame model. For instance, in (Beyer & Mangalathu, 2013) an overview about the models developed for spandrels is presented, in (Celano, Argiento, Ceroni, & Casapulla, 2021) a critical review on the existing design formulations concerning masonry walls in-plane strength is reported, while in (D’Altri, Cannizzaro, Petracca, & Talledo, 2022) different numerical models using nonlinear static analysis are applied. This study is a preliminary investigation on the strength models of masonry elements according to (NTC, 2018) and (Circolare n. 7, 2019). It is investigated how the seismic performance changes as the specific masonry strength and the in-plane floor stiffness change. At this scope, the results concerning a parametric analysis on a reference ideal case study are presented and discussed. 2. Strength of main failure mechanisms According to (Circolare n. 7, 2019), the seismic response global analysis of masonry buildings having an individual structure (i.e., not included in an aggregate) can be carried out either through the individual masonry panels analysis or through a global model. The global response assessment of existing masonry buildings at the ultimate limit state can be performed through the linear or nonlinear analysis methods. In particular, the nonlinear analysis provides for the global assessment by comparing the displacement demand with the corresponding capacity. Masonry elements capacity models are influenced by their geometry, boundary conditions, structural function and masonry type. Frequently, there are two types of elements recognized in masonry structures: piers (with vertical axis) and spandrels (with horizontal axis). For these masonry elements (i.e., piers and spandrels), according to the nonlinear analysis, a bilinear shear-displacement or moment-rotation model can be applied. The strength is defined as the minimum among those of the different possible failure mechanisms. According to (Circolare n. 7, 2019), the masonry piers in-plane failure mechanisms are:  bending;  shear sliding;  shear with diagonal cracking. As regards spandrels, the in-plane failure mechanisms that may occur are:  bending;  shear with diagonal cracking. In the next paragraphs, the equations of (NTC, 2018) and (Circolare n. 7, 2019) are recalled, in order to be applied to a case study. 2.1. Pier bending According to (NTC, 2018), the ultimate resistant moment is calculated by assuming no tensile strength for the masonry:   =        1 −   .   (1) where:   is the moment corresponding to bending failure;  is the masonry pier total length;  is the thickness of the masonry pier compressed area;   = /  is the mean normal stress, referring to the section total area;  is the