PSI - Issue 78

Available online at www.sciencedirect.com

ScienceDirect

Procedia Structural Integrity 78 (2026) 1103–1110

© 2025 The Authors. Published by ELSEVIER B.V. This is an open access article under the CC BY-NC-ND license (https://creativecommons.org/licenses/by-nc-nd/4.0) Peer-review under responsibility of XX ANIDIS Conference organizers Keywords: Reinforced Concrete; Staricases; Masonry Infills, Nonlinear static anlyses, Nonlinear time-history analyses, EDP, Fragility curves; 1. Introduction Assessing the seismic performance of existing reinforced concrete (RC) buildings is of paramount importance, particularly concerning staircases. They are crucial structural elements for evacuation and are often vulnerable to seismic events (Li et al., 2013). Despite their relevance, stairs and infill walls are typically neglected in professional numerical modeling. However, research emphasizes their importance, including them in models for new constructions (Ricci et al., 2018) and existing buildings (De Risi et al., 2023; Di Domenico et al., 2023). The primary effects of modeling staircases include: increased stiffness (Belletti et al., 2024), altered stiffness distribution (Hoseini and Jafarnejad, 2015), altered in internal force distribution (Alizerai et al., 2014). Abstract This paper investigates the seismic impact of modeling knee-beam staircases in an existing six-story reinforced concrete (RC) building designed for gravity loads based on 1970s Italian code. Nonlinear dynamic analyses are used to generate fragility curves for different configurations of the case study building, including bare frames and frames with centrally or corner-located staircases, with and without infills. Distributed plasticity models with fiber sections are used for the RC elements and equivalent strut-and-tie models are used for the infills. The results show that neglecting the knee-beam staircases may significantly affect the predicted seismic response and vulnerability, emphasizing the importance of their inclusion in seismic performance assessments. XX ANIDIS Conference Staircase modeling effects on the seismic assessment of RC gravity buildings Leandro Pancottini a *, Marco Terrenzi a , Enrico Spacone a a University of Chieti-Pescara, Viale Pindaro 42, Pescara, 65127, Italy

* Corresponding author. E-mail address: leandropancottini98@gmail.com

2452-3216 © 2025 The Authors. Published by ELSEVIER B.V. This is an open access article under the CC BY-NC-ND license (https://creativecommons.org/licenses/by-nc-nd/4.0) Peer-review under responsibility of XX ANIDIS Conference organizers 10.1016/j.prostr.2025.12.141