Damage identification from power spectrum density transmissibility

Damage identification under real operating conditions of the structure during its daily use would be suitable and attractive to civil engineers due to the difficulty and problems of carrying out controlled forced excitation tests on this kind of structures. In this case, output-only response measurements would be available, and an output-only damage identification procedure should be implemented. Transmissibility, defined on an output-to-output relationship, is getting increased attention in damage detection applications because of its dependence with output-only data and its sensitivity to local structural changes. In this paper, a method based on the power spectrum density transmissibility (PSDT) is proposed to detect structural damage

Application of an instrumental and computational approach for improving the vibration behavior of structural panels using a lightweight multilayer composite

Producción CientíficaThis work presents a hybrid (experimental-computational) application for improving the vibration behavior of structural components using a lightweight multilayer composite. The vibration behavior of a flat steel plate has been improved by the gluing of a lightweight composite formed by a core of polyurethane foam and two paper mats placed on its faces. This composite enables the natural frequencies to be increased and the modal density of the plate to be reduced, moving about the natural frequencies of the plate out of excitation range, thereby improving the vibration behavior of the plate. A specific experimental model for measuring the Operating Deflection Shape (ODS) has been developed, which enables an evaluation of the goodness of the natural frequencies obtained with the computational model simulated by the finite element method (FEM). The model of composite + flat steel plate determined by FEM was used to conduct parametric study, and the most influential factors for 1st, 2nd and 3rd mode were identified using a multifactor analysis of variance (Multifactor-ANOVA). The presented results can be easily particularized for other cases, as it may be used in cycles of continuous improvement as well as in the product development at the material, piece, and complete-system levels

Experimental Study on the Effect of Excitation Type on the Output-Only Modal Analysis Results

Output-only Modal Analysis (OMA) has found extensive use in the identification of dynamic properties of structures. This study aims to investigate the effect of excitation force on the accuracy of modal parameters. For this purpose, the modal parameters of a simply supported beam are obtained through the Experimental Modal Analysis (EMA) and the OMA method using three different types of artificial and natural excitations, namely a shaker, acoustic waves, and environmental noise. Frequency Domain Decomposition (FDD) technique is used to identify dynamic characteristics. Finally, these results are compared with those obtained by the analytical method and the EMA method. The results demonstrated the following: 1) Acoustic excitation presents the natural frequencies with the smallest errors in comparison with the analytical results. 2) Inaccuracy is observed at certain natural frequencies during the excitation with a shaker with respect to the connecting point between the shaker and the beam. 3) Modal Assurance Criterion (MAC) showed that the mode shapes extracted by the acoustic excitations are more similar to the analytical results

Modal identification of train passenger seats based on dynamic tests and output-only techniques

Railways are one of the most efficient and widely used mass transportation systems for mid-range distances, also being pointed out as the best strategy to reach European Union decarbonisation goals. However, to increase railways attractiveness, it is necessary to improve the quality of the ride, namely its comfort, by decreasing the vibration at the passenger level. This article describes the experimental vibration modal identification of train seats based on a dedicated set of dynamic tests performed on Alfa Pendular and Intercity trains. This work uses two output-only modal identification techniques: the transmissibility functions and the Enhanced Frequency Domain Decomposition (EFDD) method. The last method allows us to clearly distinguish the seat structural movements, particularly the ones related to torsion and bending of the seat frame, from the local vertical foam vibrations. The natural frequencies and mode shapes are validated by matching the results derived from the transmissibility functions and EFDD method. The identified modal parameters are particularly relevant to characterise the vibration transmissibility provided by the foams (local transmissibility) and the vibration transmissibility derived from the metallic seat frame (global transmissibility).This research was funded by Fundação para a Ciência e Tecnologia grant number PD/BD/143161/2019. The authors also acknowledge the financial support from the Base Funding-UIDB/04708/2020 and Programmatic Funding-UIDP/04708/2020 of the CONSTRUCT—Instituto de Estruturas e Construções, funded by national funds through the FCT/MCTES (PIDDAC).This work is a result of project “FERROVIA 4.0”, with reference POCI-01-0247-FEDER-046111, co-funded by the European Regional Development Fund (ERDF), through the Operational Programme for Competitiveness and Internationalization (COMPETE 2020) and the Lisbon Regional Operational Programme (LISBOA 2020), under the PORTUGAL 2020 Partnership Agreement. The first author thanks Fundação para a Ciência e Tecnologia (FCT) for a PhD scholarship under the project iRail (PD/BD/143161/2019). The authors would like to acknowledge the support of the projects FCT LAETA–UIDB/50022/2020, and UIDB/04077/2020. Finally, the authors express their gratitude to Nuno Pinto, from the LESE-FEUP laboratory, for his great assistance during the preparation of the experimental tests

Análisis modal experimental en campo completo empleando Correlación Digital de Imágenes en alta velocidad/ Full-field experimental modal analysis using High Speed Digital Image Correlation

En esta tesis se explora la técnica HS DIC para su uso en análisis modales experimentales. Esta técnica ofrece mayor densidad espacial de medida de manera no invasiva frente a sensores tradicionales. Primeramente, se propone una metodología para la caracterización modal en ensayos por movimiento de la base. Esta metodología establece una conversión de la respuesta al movimiento de la base en su equivalente respuesta a una fuerza puntual. El método de ajuste del círculo es empleado por ser un eficiente método de identificación modal para medidas de HS DIC. Los modelos teóricos y numéricos validan los resultados de esta metodología para una viga en voladizo. Se explora también la medida en imágenes de movimiento magnificado. Esta metodología es validada en una viga en voladizo y aplicada en un complejo panel de material compuesto. Los resultados muestran notables mejoras en la medida tanto en 2D como en 3D.In this thesis HS DIC is explored to be used in experimental modal analyses. This technique provides higher spatial density and non-invasive measurements over traditional sensors. Firstly, a methodology for modal characterisation in base motion test is proposed. This methodology establish a converstion of the response to base excitation into its equivalent response to pointwise force excitation. The circle-fit method is employed since it is an efficient modal identification method for HS DIC measurements. The theroretical and numerical models validate the methodology results for a cantilever beam. Additionally, it is explored the measurements in magnified motion images. The methodology is validated in a cantiléver beam and applied to a complex composite panel. The results show notable improvements in the measurements both in 2D and 3D.Tesis Univ. Jaén. Departamento de Ingeniería Mecánica y Minera. Leída el 26 de abril de 2018

Damage Detection and Quantification Using Transmissibility Coherence Analysis

A new transmissibility-based damage detection and quantification approach is proposed. Based on the operational modal analysis, the transmissibility is extracted from system responses and transmissibility coherence is defined and analyzed. Afterwards, a sensitive-damage indicator is defined in order to detect and identify the severity of damage and compared with an indicator developed by other authors. The proposed approach is validated on data from a physics-based numerical model as well as experimental data from a three-story aluminum frame structure. For both numerical simulation and experiment the results of the new indicator reveal a better performance than coherence measure proposed in Rizos et al., 2008, Rizos et al., 2002, Fassois and Sakellariou, 2007, especially when nonlinearity occurs, which might be further used in real engineering. The main contribution of this study is the construction of the relation between transmissibility coherence and frequency response function coherence and the construction of an effective indicator based on the transmissibility modal assurance criteria for damage (especially for minor nonlinearity) detection as well as quantification

Framework of damage detection in vehicle-bridge coupled system and application to bridge scour monitoring

Most vibration-based damage identification methods make use of measurements directly from bridge structures with attached sensors. However, the vehicle moving on the bridge can serve as both an active actuator and a response receiver. This dissertation aimed to develop new methodologies to eventually detect bridge damages such as scour using the dynamic response of the vehicle. To reach the final objective, a framework of damage identification was developed first, which gave a guideline on the three crucial steps for damage detection. An optimization method was proposed that combines the Genetic Algorithm (GA) and the First Order (FO) method. It has the advantages of the global and local algorithms and converges faster than the traditional method using any initial values. Secondly, a new methodology using the transmissibility of vehicle and bridge responses was developed to detect bridge damages. The transmissibility of a simplified vehicle-bridge coupled (VBC) system was analyzed theoretically and numerically to study the feasibility of this method. To obtain the transmissibility, two methods were proposed using two “static” vehicles on the bridge. Then, a tractor-trailer test system was designed to obtain reliable responses and extract bridge modal properties from the dynamic response of moving vehicles. The test vehicle consists of a tractor and two following trailers. The residual responses of the two trailers were used, which successfully eliminated the roughness and vehicle driving effect and extracted the bridge modal properties. This methodology was applied on a field bridge and revealed a good performance. Most previous studies of bridge scour focus on the scour causes instead of its consequences. Finally, in this dissertation the developed methodologies were applied to detect scour damage from the response of bridge and/or vehicles. The scour effect on a single pile was studied and methods of scour damage detections were proposed. A monitoring system using fiber optic sensors was designed and tested in the laboratory and is being applied to a field bridge. Finally, the scour effect on the response of the entire bridge and the traveling vehicle was also investigated under the bridge-vehicle-wave interaction, which in turn was used to detect the bridge scour