PSI - Issue 73

Lenka Koubova et al. / Procedia Structural Integrity 73 (2025) 66–72 Lenka Koubova / Structural Integrity Procedia 00 (2025) 000–000

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Secondly, the weight was increased by changing the cross-sectional area. In real structures, increasing the weight by increasing the cross-section of the load-bearing elements also leads to an increase in stiffness. In such a case, the increase in stiffness can be so significant that it exceeds the effect of the increased mass. The result is an increase in the natural frequency. We can say that a mere increase in mass leads to a decrease in the natural frequency. While an increase in mass associated with a significant increase in stiffness leads to an increase in the natural frequency. It is therefore always important to evaluate both factors simultaneously during design changes, especially when optimizing the frequency response of the structure. Finally, it is worth mentioning that the presented procedure allows us to determine the mode shapes of the structure for the corresponding natural frequency. Examples of mode shapes of the structure's oscillations in horizontal and vertical directions are presented. Acknowledgements Financial support from VSB-Technical University of Ostrava by means of the Czech Ministry of Education, Youth, and Sports through the institutional support for conceptual development of science, research, and innovations is gratefully acknowledged. References Bruneau, M. et al., 2011. Ductile Design of Steel Structures, McGraw-Hill Companies, Inc., pp. 347, ISBN 978-0-07-162395-7. Koubova, L., 2024. Numerical Solution of Natural Frequencies and Mode Shapes, Procedia Structural Integrity, Vol. 63, pp. 35-42. ISSN 24523216. https://doi.org/10.1016/j.prostr.2024.09.006. Landolfo, R., D’aniello, M., Safaei, S., Fiorino, L., Di Sarno, L. et al., 2025. Shake table test on a steel moment resisting frame with nonstructural elements, Engineering Structures, Vol. 333, ISSN 01410296, https://doi.org/10.1016/j.engstruct.2025.120191. Norouzi, A., Poursha, M., Amini, M. A., 2024. Seismic collapse fragility analysis of steel moment-resisting frames (MRFs) with stiffness and strength deterioration considering the spectral shape of ground motion records, Soil Dynamics and Earthquake Engineering, Vol. 183, ISSN 02677261, https://doi.org/10.1016/j.soildyn.2024.108781. Siddika, A., Awall, M. R., Mamun, Md. A. A., Mumyra, T., 2019. Study on Natural Frequency of Frame Structures, Computational Engineering and Physical Modeling, Vol. 2 (6), pp. 36-48, ISSN 2588-6959, https://doi.org/10.22115/CEPM.2019.183201.1062. Shi, G., Hou, L., Zhao, H., 2025. Numerical study on the seismic behaviour of high-strength steel moment-resisting frames: Multi-scale modelling and validation, Thin-Walled Structures, Vol. 20, ISSN 02638231, https://doi.org/10.1016/j.tws.2024.112807. Tao, H., Yang, H., Zhou, Z., Wu, Y., Ju, G. et al., 2025. Influence of slab composite effect on the seismic performance of a six-story timber-concrete composite moment-resisting frame, Journal of Building Engineering, Vol. 101, ISSN 23527102, https://doi.org/10.1016/j.jobe.2025.111815. Hud, M., Ihnatieva, V., Baran, D., 2024. Influence of mass distribution on natural vibrations of a reinforced concrete building frame, Procedia Structural Integrity, Vol. 59, pp. 692-696, ISSN 24523216, https://doi.org/10.1016/j.prostr.2024.04.098.