PSI - Issue 78

Leandro Pancottini et al. / Procedia Structural Integrity 78 (2026) 1103–1110

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greater stiffness compared to the BF models, resulting in an increase in base shear and a reduction in lateral displacement. The pushover analyses also included a step-by-step verification of ductile and brittle mechanisms. This verification, as prescribed by NTC2018, was limited to the columns, given the importance of shear failure in these elements on the global structural response.

Figure 3: Pushover curves of all building models. ◊ Shear Failure; □ θ LS Failure; ☆ θ NC Failure. The seismic performance assessment of existing structures utilizes Engineering Demand Parameters (EDPs) such as chord rotation for the Life Safety ( θ LS ) and Near Collapse ( θ NC ) limit states, which are useful for defining ductile mechanisms. Shear failure was verified by comparing demand and capacity. The results of pushover analyses (Figure 3) reveal a prevalence of brittle (shear) failures preceding ductile failures. In BF models, the first failures, whether brittle or ductile, systematically occur in the short columns of the staircases, not limited to the ground floor. This can be attributed to the design practices of the time, which involved tapering columns at each floor, promoting failures even at upper levels. Conversely, in IF models, the inclusion of infills markedly influences the sequence of column shear failures. In these scenarios, failures are exclusively concentrated on perimeter columns, excluding those affected by the staircase. To evaluate seismic response, Non-linear Time History Analyses (NHA) were conducted using the Multi-Stripe Analysis (MSA) approach, following methodologies proposed by Jalayer (2003) and Jalayer and Cornell (2009). This methodology involves performing NHA for ten incremental seismic action levels (IML), corresponding to the discretized points of Naples' seismic hazard curve. The choice of Naples is relevant given its seismic classification only began in 1981, implying that most existing structures were designed solely for gravity loads. Each IML was subjected to twenty pairs of accelerograms. These horizontally two-dimensional ground motion records were selected from a previous study by the "Progetto Rischio Implicito NTC" (Iervolino et al., 2017). The NHAs were performed with 2% modal damping for all modes (Terrenzi et al., 2024). 3.3. Non-Linear History Analyses (NHA)