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Introduction
Published in Heung-Fai Lam, Jia-Hua Yang, Vibration Testing and Applications in System Identification of Civil Engineering Structures, 2023
Modal analysis, in general, is the technique used to calculate the modal parameters of a structural system by utilizing the measured dynamic data from vibration tests. If forced vibration tests are conducted (see Section 1.1.2), both the measured excitation and responses are available. Modal testing can be used to identify natural frequencies, mode shapes, and damping ratios of the system. However, both free and forced vibration tests are usually difficult to arrange for civil engineering structures, as discussed earlier. As a result, modal analysis for civil engineering structures is usually done with ambient vibration tests. As it is not necessary to apply external force or introduce disturbance to the target structure, the vibration test and the corresponding modal identification can be carried out under the operational condition of the structure, and therefore, this technique is called “operational modal analysis.” Operational modal analysis is convenient, as only structural responses (system output) are needed to be measured, and its implementation is cost-effective. As the vibration level under ambient excitation is usually very low, the identified modal parameters can only reflect the structural characteristic under low-level vibration. Furthermore, the accelerometer employed must be very sensitive due to the low vibration level. Without using the force information and the relatively low signal-to-noise ratio, the uncertainties associated with the operational modal analysis results are believed to be high.
Accuracy of instantaneous frequencies predicted by the Hilbert-Huang transform for a bridge subjected to a moving vehicle
Published in Hiroshi Yokota, Dan M. Frangopol, Bridge Maintenance, Safety, Management, Life-Cycle Sustainability and Innovations, 2021
M. Casero, A. González, E. Covián
The characterization of the dynamic properties of a bridge is of significant importance in the monitoring of structures. Changes in the natural frequencies and mode shapes (Kim et al. 2003) and damping ratios (Curadelli et al. 2008) of the structure are often used as damage detection methods. In order to obtain the mode shapes of a structure, it is necessary to place several sensors along the structure; however, one or two sensors are usually enough to capture the natural frequencies (Carden & Fanning 2004). Operational modal analysis aims to obtain the dynamic properties of the structures under its operational loading, i.e. when traffic is traversing a bridge.
On continuous health monitoring of bridges under serious environmental variability by an innovative multi-task unsupervised learning method
Published in Structure and Infrastructure Engineering, 2023
Alireza Entezami, Hassan Sarmadi, Bahareh Behkamal, Carlo De Michele
Feature extraction is intended to discover meaningful information from measured data called damage-sensitive features. Depending upon the type of vibration data, one can exploit advanced signal processing techniques for feature extraction (C. Zhang et al., 2022). Operational modal analysis is one of the effective and tried-and-tested techniques for extracting dynamic features called modal data; that is, modal frequency, mode shape, and modal damping (Magalhães & Cunha, 2011; Zeng & Hoon Kim, 2023). Among them, the modal frequency is related to the inherent structural properties (i.e. the mass and stiffness) that can be simply identifiable. For these reasons, it is a widely-used damage-sensitive feature for global SHM or early damage detection. Feature classification mainly aims at analyzing the extracted structural features and achieving a correct decision on the current state of the structure by leveraging various machine learning algorithms (Malekloo et al., 2022).
Structural Health Assessment of Historical Buildings via Ambient Vibrations: The SMAV Methodology for “Palazzo delle Laudi” at Sansepolcro (AR)
Published in International Journal of Architectural Heritage, 2021
Noemi Fiorini, Gianluca Acunzo, Daniele Spina, Giuseppe Falzone
The identification of natural frequencies, mode shapes and damping ratios is performed through the Operational Modal Analysis (OMA). Many different identification techniques are available in literature, some of them are also implemented in various commercial software. The authors used the LMS Test.Lab software by Siemens, which allows the user to perform a frequency-domain analysis using the Polymax algorithm (Peeters and Van der Auweraer 2005).