Many Civil Engineering structures exhibit excessive vibration issues caused by dynamic actions with periodic or transient characteristics. Examples of such structures include bridges, viaducts, slender buildings, towers, and transmission lines. When excited, these structures are subject to fatigue failures, amplification of forces, and the phenomenon of resonance, which occurs when the excitation frequency approaches the natural frequency of the structure. This study aims to investigate the use of computational experimental modal analysis techniques for identifying the modal parameters of a portal frame excited by Gaussian white noise. The modal parameters reflect the behavior of the structure when excited, measuring its natural frequencies, damping factors, and mode shapes. A three dimensional portal frame was modeled in the SAP2000 software and computationally excited using a white noise signal. The simulated structural identification was based on the Frequency Response Function (FRF) in conjunction with the Least Squares Complex Exponential (LSCE) method. The modal parameters (frequency and damping) of the structure were determined using the stability diagram. Finally, to evaluate the influence of noise presence in the measured signals used for modal parameter estimation, noise levels of 5%, 10%, 15%, 20%, 25%, and 30% of the maximum amplitude of each acquisition were applied.
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