PSI - Issue 78

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ScienceDirect

Procedia Structural Integrity 78 (2026) 568–575

XX ANIDIS Conference Stiffness evaluation of floor diaphragms Alessandro Pisapia a, *, Francesco Fabbrocino a , Vincenzo Piluso b a Pegaso University, Centro Direzionale, Naples 80143, Italy b University of Salerno, Via Giovanni Paolo II, Fisciano 84084, Italy

© 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: floor diaphragm, seismic actions, seismic-resisting frames, in-plane flexural stiffness, shear deformability, Eurocode 8 1. Introduction In both seismic codes and structural engineering practice, considerable attention is traditionally devoted to the vertical structural elements that constitute the main components of the seismic-resisting system. These include frames, shear walls, and core walls, which are commonly treated as the primary contributors to global lateral resistance. Abstract The in-plane deformability of diaphragms plays a key role in the seismic response of structures, particularly affecting the distribution of horizontal forces and the overall behaviour of the lateral load-resisting system. This study proposes a new theoretical approach to evaluate diaphragm deformability, based on a simplified yet rigorous mechanical model. The proposed method allows for a direct estimation of the diaphragm stiffness, accounting for the geometric configuration and mechanical properties of its structural components. In particular, two simple cases have been analysed: one regular single-storey building with three seismic resisting frames and another one with four seismic resisting frames. In order to evaluate the accuracy of the model, theoretical predictions have been compared with results obtained from a numerical model developed in SAP 2000 and by means of a simple linear analysis, showing good agreement and confirming the reliability of the approach for preliminary design assessments or rapid evaluation purposes. Finally, for the examined cases, the threshold values of the non-dimensional diaphragm stiffness have been derived according to the deformability limits prescribed by Eurocode 8. The proposed methodology offers valuable insights, especially into the seismic design and assessment of both new and existing buildings.

* Corresponding author. Tel.: +0-000-000-0000 ; fax: +0-000-000-0000 . E-mail address: alessandro.pisapia@unipegaso.it

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.2025.12.073