PSI - Issue 78

Allegretti M. et al. / Procedia Structural Integrity 78 (2026) 852–858

855

Fig. 2. Tests for material characterization (1) Concrete core sampling (2) Double flat-jack test

As the level of knowledge increases, the masonry exhibits improved mechanical properties in terms of strength and an almost doubled sti ff ness when moving from LV0 to LV1, which results in a clear improvement of the safety factor, as will be discussed in Section 4.

3. Methods of analysis and numerical models

The seismic assessment of a masonry bridge can be carried out using di ff erent analytical approaches; among these, nonlinear analyses provide a more realistic representation of the seismic behavior of masonry structures compared to linear methods. Nonlinear dynamic analysis is considered the most accurate method to study the seismic response of such structures; however, it involves a high computational burden that cannot always be sustained. For this reason, nonlinear static analysis, also known as pushover analysis, represents an e ff ective compromise between accuracy and computational complexity, making it the preferred solution in professional practice for the seismic assessment of existing masonry bridges. The analyses were carried out using the 3D software Midas FEA NX MIDAS IT Co., Ltd. (2024), which enables macro-modeling of masonry, accounting for the overall e ff ect of the brick–mortar assembly. This behavior is mod eled through a nonlinear constitutive law known as the Smeared Crack Model (SCM) , which allows the evolution of cracking and failure to be tracked. In addition to the standard mechanical parameters (elastic modulus, Poisson’s ratio, density), this constitutive law is fully defined by assigning parameters that describe the nonlinear softening behav ior in tension, compression, and shear: in the present case, these are assumed to be linear, parabolic, and constant, respectively. In all analysis levels, the mechanical parameters of the masonry were defined according to the level of knowledge achieved. In the initial phase, reference was made to the values provided in Circular no. 7 of January 21, 2019, issued by the Consiglio Superiore dei Lavori Pubblici, containing the guidelines for the application of the “Technical Standards for Construction” (D.M. January 17, 2018). In a later phase, these parameters were updated based on the results obtained from the in-situ tests described above. The model developed in this way allows the identification of global “ductile” collapse mechanisms but does not capture potential “brittle” mechanisms. For this reason, at the reference step of the capacity curve, a shear check was performed to exclude the possibility of brittle failure in the critical sections.

4. Evaluation and Comparison of Seismic Response Analyses

As a first step, a modal analysis was performed in order to determine the main vibration modes of the structure and the corresponding mode shapes in the longitudinal and transverse directions (X and Y).