Identification of open cracks using wavelet analysis

Damage detection in flexural members by wavelet analysis involves certain important factors such as the choice of wavelet function, the effects of windowing and the effects of masking due to the presence of noise during measurement. A numerical study has been performed in this paper addressing these issues for a beam element with an open crack. The first natural modeshape of a beam with an open crack has been simulated. Gaussian white noise has been synthetically introduced to the simulated modeshape and the onset of masking has been studied. A wavelet based method of damage detection can be useful in the identification of damaged bridge structures and is applicable under the presence of measurement noise as well

Damage calibration of a beam using wavelet analysis and image processing

Efficient damage detection and calibration of structures have gained great importance in recent times in terms of health monitoring and maintenance programmes. Wavelet analysis based damage detection and calibration from the deflected shape of beams are theoretically known to be a simple and efficient way of assessing damage. However, the measurement of the static or dynamic deflected shape of a vibrating beam is often difficult. The use of sophisticated devices to measure such spatial characteristics suffer from the disadvantage of high cost of the instrument and its unavailability. This paper considers a simply supported aluminium beam with an open crack and presents a video camera based inexpensive laboratory study to assess the damage using wavelet analysis. The vibrating deflected shape recorded by the camera has been processed using image processing methods and an intelligent pattern recognition procedure for the quantification of such the dynamic deflected shape at a particular instant of time. Wavelet analysis was subsequently performed on the damaged deflected shape to successfully identify the location of the damage and estimate the degree of damage for different crack depth ratios. The image analysis based detection is found to be a novel, easy and an inexpensive technique and the method is seen to have a potential for unmanned online structural health monitoring process

Métodos de detecção de dano em pontes mediante a utilização de técnicas de monitorização dinâmica : avaliação e aplicação

Tese de doutoramentoIn this thesis, a detailed analysis of the most important vibration-based damage detection methods applied to bridge structures is addressed. Special attention is focused on those methods capable to detect damage only with information provided from a damage stage of the structure. For that purpose, methods based on wavelet analysis, curvature of the mode shapes and changes in the flexibility and stiffness matrices of the structure methods are selected. These methods are easy to implement to bridge structures for its on-line structural evaluation or for its evaluation at different damage stages. The selected damage detection methods are evaluated under three different cases: (1) damage scenarios are simulated on numerical methods for cracked beam structures; (2) experimental tests are carried out in the laboratory with metallic and concrete beams strengthened with CFRP laminates; (3) real-scale bridge structures are tested under different damage scenarios. To do an accurate simulation of the dynamic behaviour of cracked bridges, some of these methods are investigated and evaluated on beams with rectangular cross sections. Later, the methods are generalized to be applicable to more complex structures, like bridges, and to other cross sections, as in composite bridges. From the research done here, it is concluded that the performance of the damage detection methods depends of several factors, for example, the number of sensors located near the damage zones, level of noise present in the acquired dynamic response, location, extension and severity of the damage. Finally, it is recommended to do the process of damage identification in the bridge using the selected group of damage detection methods where successful damage detection is obtained when more than one method clearly indicates damage.Na presente dissertação é apresentada uma análise comparativa detalhada da eficácia de métodos de detecção de dano em pontes. Uma atenção especial é dada aos métodos baseados, exclusivamente, na resposta dinâmica da estrutura danificada. Para este efeito são escolhidos os métodos baseados na análise de “wavelets”, na curvatura das formas modais e na modificação da matriz de flexibilidade ou de rigidez da estrutura. Estes métodos são de fácil implementação em pontes, tanto nos cases em que ser requer uma monitorização contínua do comportamento da estrutura como nos que é suficiente a obtenção de valores em fases discretas da vida útil das mesmas. Os métodos utilizados são avaliados em três situações distintas: (1) a introdução de cenários de dano em modelos numéricos de estruturas fissuradas; (2) a realização de ensaios experimentais em laboratório, em vigas metálicas e em vigas de betão armado reforçadas com lâminas de material compósito (CFRP); (3) a realização de ensaios dinâmicos em pontes de betão e madeira, sob diferentes cenários de dano. Para uma simulação apropriada do comportamento dinâmico de pontes fissuradas, alguns dos métodos existentes são investigados e avaliados em vigas com secções transversais rectangulares. Posteriormente, estes métodos são generalizados para ser aplicáveis a estruturas com secções transversais mais complexas, nomeadamente pontes de secções mistas aço-betão. Dos estudos realizados concluiu-se que a eficácia de detecção de dano dos métodos estudados depende de vários factores, como por exemplo: o número de sensores próximo da zona danificada; o nível de ruído da resposta dinâmica utilizada; a localização, extensão e intensidade do dano. Finalmente, recomenda-se fazer o processo de identificação de dano na ponte usando o grupo escolhido de métodos de detecção de dano onde uma detecção bem sucedida é obtida quando mais de um método detecta claramente o dano.En esta tesis se realiza un análisis detallado de la eficacia de los más importantes métodos de detección de daño aplicados a la respuesta dinámica de puentes. Una atención especial es considerada a los métodos capaces de detectar daño con únicamente la información obtenida de la estructura dañada. Para el análisis de evaluación, son seleccionados los métodos basados en análisis de “wavelets”, en la curvatura de las formas modales y en el cambio de las matrices de flexibilidades y rigideces de la estructura. Estos métodos son elegidos debido a que pueden ser fácilmente implementados en puentes, ya se requiera una monitorización continua ó a través de fases discretas durante la vida útil de las mismas. Los métodos seleccionados son evaluados bajo tres diferentes casos: (1) la introducción de escenarios de daño en modelos numéricos de estructuras agrietadas; (2) la realización de ensayos experimentales en vigas metálicas y de concreto reforzadas con láminas de fibra de carbono (CFRP); (3) la realización de ensayos dinámicos en puentes ante diferentes escenarios de daño. Para una simulación más precisa del comportamiento dinámico de puentes agrietados, se investigan y evalúan algunos de estos métodos en vigas de sección transversal rectangular. Más adelante, estos métodos se generalizan para ser aplicables a estructuras más complejas como puentes y a otro tipo secciones transversales, como en puentes de sección compuesta. De estos estudios realizados, se concluye que la eficacia de los métodos de detección de daño evaluados depende de varios factores, por ejemplo: el número de sensores próximo de la zona dañada; el nivel de ruido de la respuesta dinámica adquirida; la localización, extensión e intensidad del daño. Finalmente, se recomienda hacer el proceso de identificación de daño del puente utilizando el grupo seleccionado de métodos de detección del daño donde una detección adecuada se obtiene cuando más de un método indica claramente el daño.Sustainable Bridges Project in the Sixth Framework ProgrammePortuguese Foundation of Science and Tecnology (FCT) - SRFH/BD/29317/200

Detection of anomalous structural behaviour using wavelet analysis

Author's manuscript version. The version of record is available from the publisher via: doi:10.1006/mssp.2001.1449 Copyright © 2002 Elsevier Science Ltd. All rights reserved.Structural health monitoring (SHM) can be defined as the continuous monitoring of a bridge’s state properties, such as static and dynamic response, in order to diagnose the onset of anomalous structural behaviour. This involves measuring and evaluating the state properties and relating these to defined performance parameters. The process of measuring state properties, either continuously or periodically, produces large quantities of data and by careful analysis of these data, sudden and gradual changes in the bridge’s behaviour can be identified and characterised. The ability of wavelet transforms to detect abrupt changes, gradual change beginnings and ends of events make them well suited for the analysis of bridge health monitoring data. This paper presents the application of wavelet analysis to identify events and changes in structural state in a bridge during and after its construction

Smart FRP Composite Sandwich Bridge Decks in Cold Regions

INE/AUTC 12.0

A Novel Method to Estimate the Damage Severity Using Spatial Wavelets and Local Regularity Algorithm

 In the process of structural damage detection using continuous wavelet transform (CWT), the perturbation or damage is located by identifying the defects locally in the input signal data.  In this work the damage identification procedure using continuous wavelet transform is developed. This method is studied numerically using a simple beam model. The influence of reduced spatial sampling using fundamental mode shape is investigated in detail. The method is also investigated to ascertain the smallest level of damage identified using strain energy mode shape data

Comparison of shearography to scanning laser vibrometry as methods for local stiffness identification of beams

Local stiffness of Euler–Bernoulli beams can be identified by dividing the bending moment of a deformed beam by the local curvature. Curvature and moment distributions can be derived from the modal shape of a beam vibrating at resonance. In this article, the modal shape of test beams is measured by both scanning laser vibrometry (SLV) and shearography. Shearography is an interferometric optical method that produces full-field displacement gradients of the inspected surface. Curvature can be obtained by two steps of derivation of the modal amplitude (in the case of SLV) or one step of derivation of the modal shape slope (in the case of shearography). Three specially prepared aluminium beams with a known stiffness distribution are used for the validation of both techniques. The uncertainty of the identified stiffness distributions with both techniques is compared and related to their signal-to-noise ratios. A strength and weakness overview at the end of the article reveals that the shearography is the technique that shows the most advantages

Damage localization by wavelet analysis of uniform load surface

This paper presents a new technique for identifying damages in beam-type structures based on wavelet analysis of uniform load surface (ULS). Having come into focus in the field of damage detection, wavelet analysis revealed itself as a practical and state-of-the-art signal processing method for discerning abnormalities of mode shapes of structures, where the irregularities are considered as the indications of cracks. ULS is beneficial in terms of participating lower mode shapes and better immunity to noise. Continuous wavelet transform (CWT) is employed to analyze the ULS in order to find the damage site. The proposed method does not require any prior knowledge of the structure and combines the synergistic advantages of ULS technique and CWT to provide more accurate results in the face of high signal to noise ratio. A numerical study is conducted and three kinds of wavelets are utilized to evaluate the technique, namely symmetrical 4, Gaussian 4 and bior 6.8. The procedure is also experimentally investigated using a free-free beam structure

Earthquake Accelerogram Selection and Scaling Procedures for Estimating the Distribution of Drift Response

The problem of selecting a suite of earthquake accelerograms for time-domain analyses is of particular practical and academic interest. Research in this field has led to numerous approaches for compiling suites of accelerograms that may be used to robustly estimate the median structural response. However, many applications in earthquake engineering require the estimation of the full distribution of a structural response parameter for a particular predefined scenario. This article presents an efficient procedure whereby the distributions of interstory or roof drifts may be well approximated. The procedure makes use of three-point approximations to continuous distributions and the strong correlation that exists between the spectral acceleration at the initial fundamental period of the structure and the drift response. The distributions obtained under the proposed approach are compared with a reference distribution assumed to represent the true underlying distribution of drift response. The reference distribution is defined through a regression analysis conducted on the results of time-domain analyses of a six-story reinforced-concrete frame building subjected to 1,666 unsealed natural accelerograms. The results indicate that robust estimates of the first and second moments of the distribution of logarithmic drift may be obtained by subjecting the structure to several accelerograms scaled to match three target spectra over a range of periods. The target spectra are defined by the numbers of standard deviations above or below the median 5%-damped spectral acceleration and correspond to the roots of a third-order Hermite polynomial. The results demonstrate that consideration of fifth-order Hermite polynomials does not lead to a significantly improved performance of the approac