PSI - Issue 81

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ScienceDirect

Procedia Structural Integrity 81 (2026) 486–492

© 2026 The Authors. Copy from the contract: 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 DMDP 2025 organizers Keywords: natural frequencies; finite element modeling; reinforced concrete frame; dynamic behavior; structural stiffness. 1. Introduction The dynamic analysis of multi-storey reinforced concrete frame buildings remains a key topic in structural engineering, especially in relation to the influence of geometric irregularities on modal behaviour and seismic performance. Classical studies established that structural asymmetry — whether due to irregular mass distribution, openings, setbacks, or asymmetric extensions — significantly affects stiffness distribution and consequently modifies natural vibration modes. Chopra (2017) highlighted that even minor plan irregularities may lead to torsional amplification, increased modal coupling, and reduced structural safety under lateral dynamic loads. Contemporary research places strong emphasis on numerical modelling through the finite element method (FEM), as it enables detailed representation of stiffness characteristics, connection behaviour, and mode shapes. Works by Paz and Kim (2019) and Clough & Penzien (1995) underline the critical role of accurate discretisation and realistic material modelling in Abstract This paper presents the results of a numerical modal analysis of a multi-storey frame building with an asymmetric layout. This analysis was performed using the LIRA software. The aim of this study was to investigate the effect of geometric symmetry violations, including openings in the floors and asymmetrically located balconies, on the natural frequency spectrum and modal behavior of the structure. Reinforced concrete of class C20/25 was chosen as the material for the load-bearing elements. Three alternative models were considered. The first one had a modified floor plan with one opening, the second included two openings on each floor, and the third had asymmetrically located balconies. The analysis showed that the basic symmetrical model exhibits the lowest frequency spectrum, ranging from 1.3 Hz to 4.5 Hz. Conversely, the models with openings or balconies exhibited frequencies reaching 12.8 Hz, indicating a pronounced increase in stiffness. The results indicate a consistent increase in frequencies in the modified models without unexpected oscillations. This finding suggests that the presence of openings in the floors or the asymmetrical placement of balconies lead to predictable, coordinated structural behavior. The study confirms that asymmetrical planning and local changes in floor configuration can slightly change the dynamic characteristics of the building, but the consequences remain understandable and manageable. VIII International Conference “In - service Damage of Materials: Diagnostics and Prediction“ (DMDP 2025) Finite element modelling of natural vibrations of a frame building with an asymmetric plan Mykhailo Hud* Ternopil Ivan Puluj National Technical University,Ternopil,46000, Ukraine

* Corresponding author. Tel.: +3-098-061-97-16. E-mail address: mishagud77@gmail.com

2452-3216 © 2026 The Authors. Copy from the contract: 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 DMDP 2025 organizers 10.1016/j.prostr.2026.03.083