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5 results on '"Gkoktsi, Kyriaki"'

1. Effectiveness of Drive‐By Monitoring in Short‐Span Bridges: A Real‐Scale Experimental Evaluation.

Author

Gkoktsi, Kyriaki, Bono, Flavio, Tirelli, Daniel, and Del Grosso, Andrea

Subjects
*STRUCTURAL health monitoring, *MODAL analysis, *ENERGY transfer, *ACCELEROMETERS, *DETECTORS, *BRIDGES
Abstract

This paper experimentally assesses the efficacy of the indirect Structural Health Monitoring (iSHM) framework on a full‐scale short‐span bridge of nine meters long, using an instrumented vehicle with non‐negligible mass with respect to the mass of the bridge. Emphasis is given to the dynamic identification of the two mechanical systems through Experimental Modal Analysis (EMA) on both the vehicle and the bridge. The EMA vehicle testing is among the main contributions of this paper, as such data become available in experimental iSHM implementations for the first time in the literature. Thus, new insights are brought on the vehicle's dual role as a roving sensing unit and a vibrating mechanical system. A wireless sensor network is adopted that supports a dual monitoring system, i.e., an indirect system with accelerometers on the vehicle and a conventional system with fixed sensors on the bridge. Under a stationary vehicle's position on the bridge, it is shown that a strong dynamic coupling occurs between the two systems due to their high mass ratio and the vehicle's function as a Spring Mass Damper (SMD). In vehicle's moving state, it is demonstrated that transfer of energy occurs between the vehicle and the bridge, which both oscillate under multiple modes of vibration that change over time. It is identified that four main parameters influence the quality of the extracted bridge natural frequencies from the vehicle‐acquired data, i.e., (i) the filtering properties of the vehicle, (ii) the effective signals length in the presence of road discontinuities, (iii) the speed trade‐offs, and (iv) the level of vehicle‐induced bridge excitation and its transmissibility level. The careful consideration of those parameters determines the effectiveness of iSHM implementations in short‐span bridges. [ABSTRACT FROM AUTHOR]

Published
2024
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4. On the influence of frequency selectivity of wavelet bases for relative wavelet entropy-based structural damage localization

Author

Agathoklis Giaralis, Gkoktsi, Kyriaki, Rodellar, J, Guemes, A, and Pozo, F

Subjects
TA
Abstract

Wavelet analysis of vibration signals measured by sensors placed on dynamically excited linear structures has proved to be an effective tool for detection and localization of structural damage. Recently, it has been shown that the relative wavelet entropy (RWE) computed from signal energy-preserving wavelet coefficients of vibration signals from “healthy” (reference) and from “damage” structural states is a potent tool for structural damage assessment applications. Herein, the influence of the frequency domain (FD) properties of the adopted analysis wavelet basis on the efficiency and robustness of the RWE for structural damage localization is assessed. To this aim, simulated benchmark free vibration signals from different locations of a simply supported beam “damaged” at various different positions are discrete wavelet transformed by three different analyzing wavelet bases: Daubechies wavelets (non-compactly supported in the FD), Meyer wavelets (compactly supported in the FD with overlapping frequency bands among wavelet scales), and harmonic wavelets (compactly supported in the FD with non-overlapping frequency bands among wavelet scales) are utilized. A wavelet scale dependent RWE-related index plotted against the frequency axis along the length of the beam is utilized to compare the effectiveness of the wavelet bases considered for damage position inference. The reported numerical data demonstrate that compactness in the FD and frequency selectivity among wavelet scales offered by Meyer and harmonic wavelet bases enhances the damage localization potential of the RWE compared to the commonly considered in the literature Daubechies wavelet bases. Furthermore, it is shown that non-constant Q analysis readily achieved with harmonic wavelets is advantageous over the standard discrete wavelet transform constant Q analysis, Q being the ratio of central frequency over bandwidth at each wavelet scale, to discriminate RWE contributions at high frequencies. It is concluded that judicial construction of wavelet analysis bases or, equivalently, of discrete wavelet analysis filter banks, in the FD is an important aspect for effective damage localization of linear vibrating structures based on the concept of the RWE.

Published
2014

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