Detecting and Evaluating Defects in Beams by Correlation Coefficients
TL;DR: In this article, the authors proposed a correlation coefficient for detecting and evaluating defects in beams, which brings about a positive outcome in terms of accuracy and efficiency, which surpasses other parameters such as natural frequency and damping coefficient, thanks to its sensitivity to structural changes.
Abstract: This research proposes a correlation coefficient for detecting and evaluating defects in beams, which brings about a positive outcome in terms of accuracy and efficiency. This parameter surpasses other parameters, such as natural frequency and damping coefficient, thanks to its sensitivity to structural changes. Our results show that although the damping coefficient had more variation than the natural frequency value in the same experiment, its changes were insufficient and unstable at different levels of defects. In addition, the proposed correlation coefficient parameter has a linear characteristic and always changes significantly according to increasing levels of defects. The results outweigh damping coefficient and natural frequency values. Furthermore, this value is always sensitive to measurement channels, which could be an important factor in locating defects in beams. The testing index is statistically evaluated by a normal distribution of the amplitude value of vibration measurement signals. Changes and shifts in this distribution are the basis for evaluating beam defects. Thus, the suggested parameter is a reliable alternative for assessing the defects of a structure.
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01 Dec 2003
TL;DR: The analytical results show that the modified model is practical for reliable evaluation of the service life of existing bridges under random traffic loading.
Abstract: This paper covers reliability assessment of the fatigue life of a bridge-deck section based on the statistical analysis of the strain-time histories measured by the structural health monitoring system permanently installed on the long-span steel bridge under study. Through statistical analysis of online strain responses in the frequency domain using multiple linear regression, a representative block of daily cycles of strain history is obtained. It is further assumed that all cycles of online strain response during bridge service are repetitions of the representative block. The rain-flow counting method is then used to determine the stress spectrum of the representative block of daily cycles. The primary assessment of fatigue life at a given value of failure probability is undertaken for the sample component in a bridge-deck section by using the classification of details for welded bridge components and the associated statistical fatigue model provided by the British Standard BS5400. In order to evaluate bridge fatigue at any value of failure probability, a modified probability model is proposed based on BS5400. The fatigue life of the considered component in the bridge-deck section is then evaluated for some other values of probability of failure which are not included in BS5400 by use of the modified probability model. The analytical results show that the modified model is practical for reliable evaluation of the service life of existing bridges under random traffic loading.
38 citations
TL;DR: This research investigates changes in the mechanical properties of complex structures using a combination of the discrete model, Fast Fourier Transform (FFT) analysis and deep learning, and applies deep learning in the noise reduction process for the original data.
Abstract: In this paper, we investigate changes in the mechanical properties of complex structures using a combination of the discrete model, Fast Fourier Transform (FFT) analysis and deep learning. The first idea from this research utilizes the discrete model from a perspective that is different from the finite element method (FEM) of previous works. As the method in this paper only models the mechanical properties of structures with finite degrees of freedom instead of dividing them into smaller elements, it reduces error in evaluation and produces more realistic results compared to the FEM model. Another advantage is how it allows the research to survey both parameters that affect the mechanical properties of structures—the overall stiffness (K) and the damping coefficient (c)—during vibration, while previous researches focus only on one of these two parameters. The second idea is to use FFT analysis to increase the sensitivity of the signal received during vibration. FFT analysis simplifies calculations, thereby reducing the effect of noise or errors. The sensitivity achieved in FFT analysis increases by 25% compared to traditional Fourier Transform (FT) analysis; moreover, the error in FFT analysis compared to experimental results is quite small, less than 2%. This shows that FFT is a suitable method to identify sensitive characteristics in evaluating changes in the mechanical properties. When FFT is combined with the discrete model, results are much better than those of several existing approaches. For the last idea, the manuscript applies deep learning (FFT-deep learning) in the noise reduction process for the original data. This makes the results much more accurate than in previous studies. The results of this research are shown through the monitoring of spans of the Saigon Bridge—the biggest and most important bridge in Ho Chi Minh City, Vietnam—during the past 11 years. The correspondence between the theoretically obtained result and the experimental one at the Saigon Bridge suggests a new area for development in evaluating and forecasting structural changes in the future.
12 citations
TL;DR: In this paper , the authors proposed a new indicator based on change in a vibration signal's probability spectrum center to assess structural change, which relies on the change of a central position of the probability spectrum (C-PSD).
4 citations
TL;DR: This study improves the model of Hooke’s traditional linear mechanical change using a nonlinear model to truly express the nature of structures in reality and adds to the current framework regarding changes in the mechanical properties of a material according to the Kelvin-Voigt model.
4 citations
TL;DR: In this paper, the authors investigated changes in the power spectral density caused by beam damage and proposed a parameter to monitor a structure's deteriorating conditions based on the shape of the damaged beam.
Abstract: Using the vibration signals of damaged beams under the act of a moving load, this article investigates changes in the power spectral density caused by beam damage. Based on the results, the authors have proposed a parameter to monitor a structure’s deteriorating conditions. Cracks were created in beams that changed the stiffness of the structure, and simulations of deterioration were conducted. The features proposed in this article are based on the changing shapes of power spectral density from which deterioration in a damaged beam structure can be detected. The experiment was designed to achieve the simulation that best corresponds to a realistic flow of traffic along bridges. Acceleration sensors installed along the beams received the vibration signals that were used to establish the power spectral density. The results of this article show that for a damaged beam, changes in the shapes of power spectral density are much more prominent than changes in the fundamental frequency value. In other words, when compared to using fundamental frequency changes, using shape changes in power spectral density will increase the likelihood of detecting damage for a variety of beam structures.
3 citations
References
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TL;DR: In this article, a minimal remeshing finite element method for crack growth is presented, where Discontinuous enrichment functions are added to the finite element approximation to account for the presence of the crack.
Abstract: A minimal remeshing finite element method for crack growth is presented. Discontinuous enrichment functions are added to the finite element approximation to account for the presence of the crack. This method allows the crack to be arbitrarily aligned within the mesh. For severely curved cracks, remeshing may be needed but only away from the crack tip where remeshing is much easier. Results are presented for a wide range of two-dimensional crack problems showing excellent accuracy. Copyright © 1999 John Wiley & Sons, Ltd.
4,185 citations
01 May 1996
TL;DR: A review of the technical literature concerning the detection, location, and characterization of structural damage via techniques that examine changes in measured structural vibration response is presented in this article, where the authors categorize the methods according to required measured data and analysis technique.
Abstract: This report contains a review of the technical literature concerning the detection, location, and characterization of structural damage via techniques that examine changes in measured structural vibration response. The report first categorizes the methods according to required measured data and analysis technique. The analysis categories include changes in modal frequencies, changes in measured mode shapes (and their derivatives), and changes in measured flexibility coefficients. Methods that use property (stiffness, mass, damping) matrix updating, detection of nonlinear response, and damage detection via neural networks are also summarized. The applications of the various methods to different types of engineering problems are categorized by type of structure and are summarized. The types of structures include beams, trusses, plates, shells, bridges, offshore platforms, other large civil structures, aerospace structures, and composite structures. The report describes the development of the damage-identification methods and applications and summarizes the current state-of-the-art of the technology. The critical issues for future research in the area of damage identification are also discussed.
2,916 citations
TL;DR: In this paper, the authors provide an overview of methods to detect, locate, and characterize damage in structural and mechanical systems by examining changes in measured vibration response, including frequency, mode shape, and modal damping.
Abstract: This paper provides an overview of methods to detect, locate, and characterize damage in structural and mechanical systems by examining changes in measured vibration response. Research in vibration-based damage identification has been rapidly expanding over the last few years. The basic idea behind this technology is that modal parameters (notably frequencies, mode shapes, and modal damping) are functions of the physical properties of the structure (mass, damping, and stiffness). Therefore, changes in the physical properties will cause detectable changes in the modal properties. The motivation for the development of this technology is presented. The methods are categorized according to various criteria such as the level of damage detection provided, model-based versus non-model-based methods, and linear versus nonlinear methods. The methods are also described in general terms including difficulties associated with their implementation and their fidelity. Past, current, and future-planned applications of this technology to actual engineering systems are summarized. The paper concludes with a discussion of critical issues for future research in the area of vibration-based damage identification.
2,715 citations
TL;DR: In this article, a method of non-destructively assessing the integrity of structures using measurements of the structural natural frequencies is described, where measurements made at a single point in the structure can be used to detect, locate and quantify damage.
Abstract: A method of non-destructively assessing the integrity of structures using measurements of the structural natural frequencies is described. It is shown how measurements made at a single point in the structure can be used to detect, locate and quantify damage. The scheme presented uses finite-element analysis, since this method may be used on any structure. The principle may, however, be used in conjunction with other mathematical techniques. Only one full analysis is required for each type of structure.Results are presented from tests on an aluminium plate and a cross-ply carbon-fibre-reinforced plastic plate. Excellent agreement is shown between the predicted and actual damage sites and a useful indication of the magnitude of the defect is obtained.
1,379 citations
TL;DR: A new approach for modelling discrete cracks in meshfree methods is described, in which the crack can be arbitrarily oriented, but its growth is represented discretely by activation of crack surfaces at individual particles, so no representation of the crack's topology is needed.
Abstract: A new approach for modelling discrete cracks in meshfree methods is described. In this method, the crack can be arbitrarily oriented, but its growth is represented discretely by activation of crack surfaces at individual particles, so no representation of the crack's topology is needed. The crack is modelled by a local enrichment of the test and trial functions with a sign function (a variant of the Heaviside step function), so that the discontinuities are along the direction of the crack. The discontinuity consists of cylindrical planes centred at the particles in three dimensions, lines centred at the particles in two dimensions. The model is applied to several 2D problems and compared to experimental data. Copyright © 2004 John Wiley & Sons, Ltd.
1,274 citations