MedWorm.com provides a medical RSS filtering service. Over 6000 RSS medical sources are combined and output via different filters. This feed contains the latest items from the 'Structural Health Monitoring' source. Sun, 21 Mar 2010 15:21:51 +0100 http://www.medworm.com/index.php?rid=3274141&cid=s_22297_23_f&fid=22297&url=http%3A%2F%2Fshm.sagepub.com%2Fcgi%2Fcontent%2Fabstract%2F9%2F2%2F193%3Frss%3D1 Mickael Lallart, Daniel Guyomar, and Thomas Monnier. Energy efficient method for embedded in-situ structural health monitoring. Structural Health Monitoring: An International Journal first published on August 10, 2009 as doi:10.1177/1475921708341015. This version is no longer available. The version of record is published in Vol 9 No 1, as 10.1177/1475921709341015. (Source: Structural Health Monitoring) Structural Health Monitoring journals http://www.medworm.com/rss/comments.php?id=3274141 Tue, 16 Feb 2010 14:13:33 +0100 3274141 http://www.medworm.com/index.php?rid=3274140&cid=s_22297_23_f&fid=22297&url=http%3A%2F%2Fshm.sagepub.com%2Fcgi%2Fcontent%2Fabstract%2F9%2F2%2F173%3Frss%3D1 A reduced 3D continuum model of dynamic piezoelectricity in a thin-film surface-bonded to the substrate/host is presented in this article. While employing large area flexible thin piezoelectric films for novel applications in device/diagnostics, the feasibility of the proposed model in sensing the surface and/or sub-surface defects is demonstrated through simulations — which involve metallic beams with cracks and composite beam with delaminations of various sizes. We have introduced a set of electrical measures to capture the severity of the damage in the existing structures. Characteristics of these electrical measures in terms of the potential difference and its spatial gradients are illustrated in the time domain. Sensitivity studies of the proposed measures in terms of the defect... Structural Health Monitoring journals http://www.medworm.com/rss/comments.php?id=3274140 Tue, 16 Feb 2010 14:13:33 +0100 3274140 http://www.medworm.com/index.php?rid=3274139&cid=s_22297_23_f&fid=22297&url=http%3A%2F%2Fshm.sagepub.com%2Fcgi%2Fcontent%2Fabstract%2F9%2F2%2F159%3Frss%3D1 The analysis of strong and weak motion recordings in existing structures is critical for understanding both the damaging process during earthquakes and their structural behavior. The time—frequency representation is one of the existing methods to get information on the frequency variations in buildings, which may indicate either damage or degradation. In this article, we use standard time—frequency methods with amplitude normalization and reassignment method in order to observe smaller variations in earthquake recordings in buildings. The method used in this article is first validated on strong recordings from the R. Millikan Library (Pasadena, California) and later applied to weak earthquakes recorded in the Grenoble City Hall (France). This method detects torsion activation a... Structural Health Monitoring journals http://www.medworm.com/rss/comments.php?id=3274139 Tue, 16 Feb 2010 14:13:33 +0100 3274139 http://www.medworm.com/index.php?rid=3274138&cid=s_22297_23_f&fid=22297&url=http%3A%2F%2Fshm.sagepub.com%2Fcgi%2Fcontent%2Fabstract%2F9%2F2%2F145%3Frss%3D1 In this article, a technique is proposed to detect damage in structures from measurements taken under different environmental and operational conditions. The method is based on the regression analysis of the features extracted from the vibration measurement. Macro strain was chosen as the selected feature to be measured using the long-gage distributed fiber Bragg grating (FBG) sensors. Features extracted from the measurements on an intact structure were used to construct a reference model for damage identification. Damage was identified by comparing the slope of the regression line of the subsequent measurements to its counterpart of the reference model. Experimental results show that the extracted features were very consistent. The proposed method was demonstrated and validated using nois... Structural Health Monitoring journals http://www.medworm.com/rss/comments.php?id=3274138 Tue, 16 Feb 2010 14:13:33 +0100 3274138 http://www.medworm.com/index.php?rid=3274137&cid=s_22297_23_f&fid=22297&url=http%3A%2F%2Fshm.sagepub.com%2Fcgi%2Fcontent%2Fabstract%2F9%2F2%2F133%3Frss%3D1 An algorithm based on correlation analysis was adopted to estimate the probability of the presence of damage in aluminum plates using Lamb wave signals from an active sensor network. Both finite element analysis and experimental evaluations were presented. The Shannon entropy optimization criterion was applied to calibrate the optimal mother wavelet and the most appropriate continuous wavelet transform scale for signal processing. The correlation coefficients for individual sensing paths between the present state (with damage) and the reference state (without damage) were calculated, and the probability of the presence of damage in the monitoring area enclosed by the active sensor network was estimated to identify the damage. A concept of virtual sensing paths (VSPs) was proposed to enhanc... Structural Health Monitoring journals http://www.medworm.com/rss/comments.php?id=3274137 Tue, 16 Feb 2010 14:13:33 +0100 3274137 http://www.medworm.com/index.php?rid=3274136&cid=s_22297_23_f&fid=22297&url=http%3A%2F%2Fshm.sagepub.com%2Fcgi%2Fcontent%2Fabstract%2F9%2F2%2F121%3Frss%3D1 This article presents a combined prediction model involving the parallel of classification and regression trees (CART) model, namely p-CART, and a long-term direct prediction methodology of time series techniques to predict the future stages of the machine’s operating conditions. p-CART model consists of multiple CART models which are connected in parallel. Each sub-model in the p-CART is trained independently. Based on the observations, these sub-models are subsequently used to predict the future values of the machine’s operating conditions separately with the same embedding dimension but different observations’ indices. Finally, the predicted results of sub-models are combined to produce the final results of the predicting process. Real trending data acquired from condi... Structural Health Monitoring journals http://www.medworm.com/rss/comments.php?id=3274136 Tue, 16 Feb 2010 14:13:33 +0100 3274136 http://www.medworm.com/index.php?rid=3274135&cid=s_22297_23_f&fid=22297&url=http%3A%2F%2Fshm.sagepub.com%2Fcgi%2Fcontent%2Fabstract%2F9%2F2%2F105%3Frss%3D1 Important engineering constructions require geometrical monitoring to predict their structural health during their lifetime. Monitoring by geodetic devices, vibration-based techniques, wireless networks or with GPS technology is not always optimal; sometimes it is impossible as shown in this article. A method based on geodetic measurements automation applying local optical scanners for monitoring is proposed. Its originality and contribution is based on the novel method of precise measurement of plane spatial angles. It considers robust invariant AD-conversion angle-to-code for dynamic angle, signal energetic center search method, initial reference scale adjustment, and uncertainty decrease using mediant fractions formalism for result approximation. An algorithm of electromechanic parts in... Structural Health Monitoring journals http://www.medworm.com/rss/comments.php?id=3274135 Tue, 16 Feb 2010 14:13:33 +0100 3274135 http://www.medworm.com/index.php?rid=3150982&cid=s_22297_23_f&fid=22297&url=http%3A%2F%2Fshm.sagepub.com%2Fcgi%2Freprint%2F9%2F1%2F99%3Frss%3D1 (Source: Structural Health Monitoring) Structural Health Monitoring journals http://www.medworm.com/rss/comments.php?id=3150982 Thu, 07 Jan 2010 15:20:18 +0100 3150982 http://www.medworm.com/index.php?rid=3150981&cid=s_22297_23_f&fid=22297&url=http%3A%2F%2Fshm.sagepub.com%2Fcgi%2Fcontent%2Fabstract%2F9%2F1%2F87%3Frss%3D1 This article introduces the principles of an ultra low-cost scheme for in situ, embedded structural health monitoring. Based on the interactions of a Lamb wave with the structure, the proposed technique relies in comparing the time period where the sensed signature of the Lamb wave is greater than an user-defined threshold with a reference value. Compared to similar methods based on the monitoring of the structural state evolution, the proposed scheme is ultra low-cost, and therefore suitable for integrated systems that have a limited amount of available energy. (Source: Structural Health Monitoring) Structural Health Monitoring journals http://www.medworm.com/rss/comments.php?id=3150981 Thu, 07 Jan 2010 15:20:18 +0100 3150981 http://www.medworm.com/index.php?rid=3150980&cid=s_22297_23_f&fid=22297&url=http%3A%2F%2Fshm.sagepub.com%2Fcgi%2Fcontent%2Fabstract%2F9%2F1%2F75%3Frss%3D1 A robust signal processing technique using linear mapping for removing dispersion of Lamb waves is presented in this article. Based on the assumption that the dispersion relation characteristic can be adequately approximated by a finite polynomial in the region close to the high wave energy intensity, the dispersion effect begins to reveal in the second-order term of the polynomial. The linear mapping performed in the finite usable frequency domain is to transform the original in priori known dispersion relation into the linear dispersion relation, i.e., truncated the polynomial up to the linear term which is nondispersive. The linear mapping technique does not require the propagation-path lengths and can be applied to the signals consisting of multiple arrivals with the same wave mode or ... Structural Health Monitoring journals http://www.medworm.com/rss/comments.php?id=3150980 Thu, 07 Jan 2010 15:20:18 +0100 3150980 http://www.medworm.com/index.php?rid=3150979&cid=s_22297_23_f&fid=22297&url=http%3A%2F%2Fshm.sagepub.com%2Fcgi%2Fcontent%2Fabstract%2F9%2F1%2F59%3Frss%3D1 This article presents a new data reduction method for sensors used in structural health monitoring application. Our goal is to achieve an effective data reduction capability while maintaining adequate power for damage detection. We propose to establish an explicit measure of damage detection capability for the features in the response signals and use this measure to select the subset of the features that balance between the degree of data reduction and the damage detection capability. We also explore a computationally efficient procedure searching for the best subset of the features. This new method is tested on experimentally obtained Lamb wave signals for beam damage detection. Performance comparisons with respect to the existing methods demonstrate the strength of the proposed method. (... Structural Health Monitoring journals http://www.medworm.com/rss/comments.php?id=3150979 Thu, 07 Jan 2010 15:20:18 +0100 3150979 http://www.medworm.com/index.php?rid=3150978&cid=s_22297_23_f&fid=22297&url=http%3A%2F%2Fshm.sagepub.com%2Fcgi%2Fcontent%2Fabstract%2F9%2F1%2F41%3Frss%3D1 This article presents the application of monitoring and detection of structural damage techniques to a historic monument. Seville cathedral’s famous bell tower ‘La Giralda’ is 96 m tall and is crowned with a large 16th century sculpture known as ‘Giraldillo’. The sculpture is supported with an internal bar structure, which is fitted over the axis about which it rotates according to the wind direction, allowing it to function as a weathervane. Between 1999 and 2005 the Giraldillo was demounted and underwent an intensive restoration process, which included mechanical and structural repair work. As the sculpture is only accessible by means of complex and costly scaffolding systems, an instrumentation system consisting of different types of sensors was installed t... Structural Health Monitoring journals http://www.medworm.com/rss/comments.php?id=3150978 Thu, 07 Jan 2010 15:20:18 +0100 3150978 http://www.medworm.com/index.php?rid=3150977&cid=s_22297_23_f&fid=22297&url=http%3A%2F%2Fshm.sagepub.com%2Fcgi%2Fcontent%2Fabstract%2F9%2F1%2F25%3Frss%3D1 An investigation was performed to develop a sensor placement method to maximize the performance of a structural health monitoring (SHM) system with a minimal number of sensors for detection of impact in structures, particularly for structures made of fiber-reinforced composite materials. The performance of the SHM system is evaluated based on the probability of detection (POD). This optimization problem was formulated to maximize the POD through selection of optimal sensor locations for a given sensor network. A genetic algorithm was adopted and integrated with the SHM system to perform the optimization process. Numerical simulations on two composite panels showed that the selection of sensor network configuration is crucial for the performance of the SHM system. For a targeted POD, the pr... Structural Health Monitoring journals http://www.medworm.com/rss/comments.php?id=3150977 Thu, 07 Jan 2010 15:20:18 +0100 3150977 http://www.medworm.com/index.php?rid=3150976&cid=s_22297_23_f&fid=22297&url=http%3A%2F%2Fshm.sagepub.com%2Fcgi%2Fcontent%2Fabstract%2F9%2F1%2F13%3Frss%3D1 Wireless networks of smart sensors with computations distributed over multiple sensor packages have shown considerable promise in providing low-cost structural health monitoring. In these networks, microprocessors are typically embedded in individual smart sensor packages. The efficiency of embedded computational algorithms is of critical importance because the size, cost, and power requirements of the sensor arrays are central concerns. Here, very efficient methodologies are presented to compute statistical moments of a measured response time-history. These moments: the mean, standard deviation, skewness, and kurtosis are often used to characterize a measured irregular response. Two alternative approaches are presented, each of which can save substantial computer memory requirements and C... Structural Health Monitoring journals http://www.medworm.com/rss/comments.php?id=3150976 Thu, 07 Jan 2010 15:20:18 +0100 3150976 http://www.medworm.com/index.php?rid=3150975&cid=s_22297_23_f&fid=22297&url=http%3A%2F%2Fshm.sagepub.com%2Fcgi%2Fcontent%2Fabstract%2F9%2F1%2F5%3Frss%3D1 This study presents an experimental verification of a structural damage recognition technique based on a fiber Bragg grating array and a back propagation neural network. A flat plate was designed and fabricated for these experiments. The plate structure was loaded using a lever and a weight, and damage was introduced by putting a hole in the plate. Data was collected for the healthy and damaged cases when the load was applied at different positions on the plate. The neural network was able to identify damage to the plate. This approach for damage detection is useful when a static load can be applied at multiple points on a structure. (Source: Structural Health Monitoring) Structural Health Monitoring journals http://www.medworm.com/rss/comments.php?id=3150975 Thu, 07 Jan 2010 15:20:18 +0100 3150975 http://www.medworm.com/index.php?rid=2884463&cid=s_22297_23_f&fid=22297&url=http%3A%2F%2Fshm.sagepub.com%2Fcgi%2Freprint%2F8%2F6%2F574-e%3Frss%3D1 (Source: Structural Health Monitoring) Structural Health Monitoring journals http://www.medworm.com/rss/comments.php?id=2884463 Tue, 13 Oct 2009 09:29:51 +0100 2884463 http://www.medworm.com/index.php?rid=2884462&cid=s_22297_23_f&fid=22297&url=http%3A%2F%2Fshm.sagepub.com%2Fcgi%2Freprint%2F8%2F6%2F574-d%3Frss%3D1 (Source: Structural Health Monitoring) Structural Health Monitoring journals http://www.medworm.com/rss/comments.php?id=2884462 Tue, 13 Oct 2009 09:29:51 +0100 2884462 http://www.medworm.com/index.php?rid=2884461&cid=s_22297_23_f&fid=22297&url=http%3A%2F%2Fshm.sagepub.com%2Fcgi%2Freprint%2F8%2F6%2F574-c%3Frss%3D1 (Source: Structural Health Monitoring) Structural Health Monitoring journals http://www.medworm.com/rss/comments.php?id=2884461 Tue, 13 Oct 2009 09:29:51 +0100 2884461 http://www.medworm.com/index.php?rid=2884460&cid=s_22297_23_f&fid=22297&url=http%3A%2F%2Fshm.sagepub.com%2Fcgi%2Freprint%2F8%2F6%2F574-b%3Frss%3D1 (Source: Structural Health Monitoring) Structural Health Monitoring journals http://www.medworm.com/rss/comments.php?id=2884460 Tue, 13 Oct 2009 09:29:51 +0100 2884460 http://www.medworm.com/index.php?rid=2884459&cid=s_22297_23_f&fid=22297&url=http%3A%2F%2Fshm.sagepub.com%2Fcgi%2Freprint%2F8%2F6%2F574-a%3Frss%3D1 (Source: Structural Health Monitoring) Structural Health Monitoring journals http://www.medworm.com/rss/comments.php?id=2884459 Tue, 13 Oct 2009 09:29:51 +0100 2884459 http://www.medworm.com/index.php?rid=2884458&cid=s_22297_23_f&fid=22297&url=http%3A%2F%2Fshm.sagepub.com%2Fcgi%2Freprint%2F8%2F6%2F574%3Frss%3D1 (Source: Structural Health Monitoring) Structural Health Monitoring journals http://www.medworm.com/rss/comments.php?id=2884458 Tue, 13 Oct 2009 09:29:51 +0100 2884458 http://www.medworm.com/index.php?rid=2884457&cid=s_22297_23_f&fid=22297&url=http%3A%2F%2Fshm.sagepub.com%2Fcgi%2Freprint%2F8%2F6%2F573-d%3Frss%3D1 (Source: Structural Health Monitoring) Structural Health Monitoring journals http://www.medworm.com/rss/comments.php?id=2884457 Tue, 13 Oct 2009 09:29:51 +0100 2884457 http://www.medworm.com/index.php?rid=2884456&cid=s_22297_23_f&fid=22297&url=http%3A%2F%2Fshm.sagepub.com%2Fcgi%2Freprint%2F8%2F6%2F573-c%3Frss%3D1 (Source: Structural Health Monitoring) Structural Health Monitoring journals http://www.medworm.com/rss/comments.php?id=2884456 Tue, 13 Oct 2009 09:29:51 +0100 2884456 http://www.medworm.com/index.php?rid=2884455&cid=s_22297_23_f&fid=22297&url=http%3A%2F%2Fshm.sagepub.com%2Fcgi%2Freprint%2F8%2F6%2F573-b%3Frss%3D1 (Source: Structural Health Monitoring) Structural Health Monitoring journals http://www.medworm.com/rss/comments.php?id=2884455 Tue, 13 Oct 2009 09:29:51 +0100 2884455 http://www.medworm.com/index.php?rid=2884454&cid=s_22297_23_f&fid=22297&url=http%3A%2F%2Fshm.sagepub.com%2Fcgi%2Freprint%2F8%2F6%2F573-a%3Frss%3D1 (Source: Structural Health Monitoring) Structural Health Monitoring journals http://www.medworm.com/rss/comments.php?id=2884454 Tue, 13 Oct 2009 09:29:51 +0100 2884454 http://www.medworm.com/index.php?rid=2884453&cid=s_22297_23_f&fid=22297&url=http%3A%2F%2Fshm.sagepub.com%2Fcgi%2Freprint%2F8%2F6%2F573%3Frss%3D1 (Source: Structural Health Monitoring) Structural Health Monitoring journals http://www.medworm.com/rss/comments.php?id=2884453 Tue, 13 Oct 2009 09:29:51 +0100 2884453 http://www.medworm.com/index.php?rid=2884452&cid=s_22297_23_f&fid=22297&url=http%3A%2F%2Fshm.sagepub.com%2Fcgi%2Fcontent%2Fabstract%2F8%2F6%2F555%3Frss%3D1 Although vibration-based structural damage detection methods have demonstrated various degrees of success, the damage detection of civil structures still remains as a challenging task. The main obstacles include the insensitivity to local damage and the high sensitivity to measurement noise. A new structural damage detection method based on the statistical moments of dynamic responses of a structure has been recently proposed by the authors, and the numerical study manifested that the proposed method is sensitive to local structural damage but insensitive to measurement noise. The experimental investigation on this method is presented in this article. Three shear building models with and without damage were built and subjected to ground motions generated by a shaking table. The displacemen... Structural Health Monitoring journals http://www.medworm.com/rss/comments.php?id=2884452 Tue, 13 Oct 2009 09:29:51 +0100 2884452 http://www.medworm.com/index.php?rid=2884451&cid=s_22297_23_f&fid=22297&url=http%3A%2F%2Fshm.sagepub.com%2Fcgi%2Fcontent%2Fabstract%2F8%2F6%2F537%3Frss%3D1 A structural health monitoring system for assessing thermal damage in a metallic sandwich panel was developed in this article. The method of virtual forces was utilized to detect, locate, and quantify damage. The method assumes that a damaged structural response is a summation of the undamaged response and the response from an effective forcing function, which represents the effects of the material damage. The effective forcing function, or virtual force, is an estimate of the forces that the damage mechanism exerts on the undamaged structure. Virtual forces were shown to detect changes in the mass, stiffness, and damping matrices in a lumped parameter dynamic model. A finite element model of a mechanically attached sandwich metallic panel was used to detect a stiffness loss at different l... Structural Health Monitoring journals http://www.medworm.com/rss/comments.php?id=2884451 Tue, 13 Oct 2009 09:29:51 +0100 2884451 http://www.medworm.com/index.php?rid=2884450&cid=s_22297_23_f&fid=22297&url=http%3A%2F%2Fshm.sagepub.com%2Fcgi%2Fcontent%2Fabstract%2F8%2F6%2F523%3Frss%3D1 This article is an experimental study of the effects of multi-site damage on the vibration response of a composite beam damaged by low-energy impact. The variation of the modal parameters with different levels of impact energy and density of impact is studied. Specimens are impacted symmetrically in order to induce a global rate of damage. A damage detection tool Damage Index is introduced in order to verify the estimation of damping ratios. Design of Experiments is used to establish the sensitivity of both energy of impact and density of damage. The DOE analysis results (using natural frequency only) indicate that impact energy for 2nd, 3rd, and 4th bending modes is the most significant factor contributing to the changes in the modal parameters for this kind of symmetrical dynamic test. (... Structural Health Monitoring journals http://www.medworm.com/rss/comments.php?id=2884450 Tue, 13 Oct 2009 09:29:51 +0100 2884450 http://www.medworm.com/index.php?rid=2884449&cid=s_22297_23_f&fid=22297&url=http%3A%2F%2Fshm.sagepub.com%2Fcgi%2Fcontent%2Fabstract%2F8%2F6%2F509%3Frss%3D1 This article describes the development of an RSM scheme, developed at SERC, Chennai. The article outlines the laboratory and field investigations carried out to validate the developed scheme. Brief information about the observations and modifications made during these trials are also presented. A part of the work carried out for synthesizing online data using Auto Regressive Moving Average model is also presented. (Source: Structural Health Monitoring) Structural Health Monitoring journals http://www.medworm.com/rss/comments.php?id=2884449 Tue, 13 Oct 2009 09:29:51 +0100 2884449 http://www.medworm.com/index.php?rid=2884448&cid=s_22297_23_f&fid=22297&url=http%3A%2F%2Fshm.sagepub.com%2Fcgi%2Fcontent%2Fabstract%2F8%2F6%2F493%3Frss%3D1 This article presents the efforts to estimate the effects of these stress/strain concentrations induced by the integration of rectangular-shape sensors within unidirectional fiber-glass composites. The micro-crack initiation sites and the failure load are predicted using finite-element simulations. Good agreement has been found between the numerical results and the experimental findings presented in an accompanying paper. (Source: Structural Health Monitoring) Structural Health Monitoring journals http://www.medworm.com/rss/comments.php?id=2884448 Tue, 13 Oct 2009 09:29:51 +0100 2884448 http://www.medworm.com/index.php?rid=2884447&cid=s_22297_23_f&fid=22297&url=http%3A%2F%2Fshm.sagepub.com%2Fcgi%2Fcontent%2Fabstract%2F8%2F6%2F477%3Frss%3D1 This article presents the results of experiments conducted in order to identify and locate the failure initiation in glass fiber/epoxy laminates with integrated structural health monitoring sensors (SHM) and electronics. Recent advances in health monitoring technologies have resulted in the development of micro-dimensional devices that can be embedded into composite laminates. Notwithstanding their small size, such inclusions may affect the response of the composite. Damage induced by the peak values of stress concentration around the embedded inclusion is, in fact, one of the main concerns in smart structures technology. To address this specific issue, unidirectional S2 glass fiber/epoxy laminated composites are fabricated with embedded small implants that mimic potential sensors and micr... Structural Health Monitoring journals http://www.medworm.com/rss/comments.php?id=2884447 Tue, 13 Oct 2009 09:29:51 +0100 2884447 http://www.medworm.com/index.php?rid=2884446&cid=s_22297_23_f&fid=22297&url=http%3A%2F%2Fshm.sagepub.com%2Fcgi%2Fcontent%2Fabstract%2F8%2F6%2F463%3Frss%3D1 This study introduces the development of an automatic scour monitoring system using time domain reflectometry (TDR) principle. It presents the principles and system design of the TDR sediment scour monitoring system. An analyses algorithm for scour signals has been developed. It was found to be robust and can be implemented to automate scour signal interpretation. Simulated experiments were conducted to validate the performance of the scour monitoring system prototype. The results showed that this TDR technology can accurately measure the scour depth. Besides, the properties of the sediments, such as the porosity and density can be estimated with reasonable accuracy. At the end of the paper, a few important issues associated with field deployments of TDR scour monitoring system are discuss... Structural Health Monitoring journals http://www.medworm.com/rss/comments.php?id=2884446 Tue, 13 Oct 2009 09:29:51 +0100 2884446 http://www.medworm.com/index.php?rid=2884445&cid=s_22297_23_f&fid=22297&url=http%3A%2F%2Fshm.sagepub.com%2Fcgi%2Fcontent%2Fabstract%2F8%2F6%2F443%3Frss%3D1 This article, through computer simulation and experimental investigation of a simply supported beam, comparatively evaluates the performance of these techniques for practical civil SHM by using displacement modes from accelerometers and long-gage distributed strain measurements. Most of all the techniques proved unreliable for damage identification using noisy measurements from accelerometers, while successful with distributed strain measurements. The findings reveal that long-gage distributed strain measurements are much more efficient choice over the traditional measurement techniques for reliable civil SHM. It may therefore be concluded that the performance of some algorithms might be improved for application to civil infrastructure by using distributed strain fiber optic sensing measur... Structural Health Monitoring journals http://www.medworm.com/rss/comments.php?id=2884445 Tue, 13 Oct 2009 09:29:51 +0100 2884445 http://www.medworm.com/index.php?rid=2884444&cid=s_22297_23_f&fid=22297&url=http%3A%2F%2Fshm.sagepub.com%2Fcgi%2Fcontent%2Fabstract%2F8%2F6%2F425%3Frss%3D1 This paper presents and evaluates in detail a harmonics tracking method (HTM) for tracking the instantaneous frequency and amplitude of a vibration signal by processing only three most recent data points. Teager—Kaiser algorithm (TKA) is a popular four-point method for online frequency tracking, but its accuracy is easily destroyed by measurement noise due to the use of finite difference. Moreover, because a signal is assumed to be a pure harmonic in TKA, any moving average in the signal can destroy the accuracy of TKA. On the other hand, HTM uses a constant and a pair of harmonics to fit three recent data points and estimate the instantaneous frequency and amplitude, and it dramatically reduces the influence of any moving average. Moreover, noise filtering is an implicit capability ... Structural Health Monitoring journals http://www.medworm.com/rss/comments.php?id=2884444 Tue, 13 Oct 2009 09:29:50 +0100 2884444 http://www.medworm.com/index.php?rid=2884443&cid=s_22297_23_f&fid=22297&url=http%3A%2F%2Fshm.sagepub.com%2Fcgi%2Fcontent%2Fabstract%2F8%2F6%2F415%3Frss%3D1 In our recent study, a structural health monitoring strategy based on distributed fiber optic sensing techniques has been proposed to utilize the strain responses throughout the full or some partial areas of structures to detect the arbitrary and unforeseen damage. However, to perform this strategy more effectively, there is an increasing demand for improving the ability of such sensors to measure small structural responses, especially for the cases such as damage identification based on ambient vibration tests, fatigue crack monitoring of steel structures and crack detection of reinforced concrete structures. This work puts forward a novel packaging design for long-gage fiber Bragg grating (FBG) sensors to enhance the measurement sensitivity of strain responses. The basic idea is to utili... Structural Health Monitoring journals http://www.medworm.com/rss/comments.php?id=2884443 Tue, 13 Oct 2009 09:29:50 +0100 2884443 http://www.medworm.com/index.php?rid=2739496&cid=s_22297_23_f&fid=22297&url=http%3A%2F%2Fshm.sagepub.com%2Fcgi%2Fcontent%2Fabstract%2F8%2F5%2F397%3Frss%3D1 For structural health monitoring it is impractical to identify a large structure with complete measurement due to limited number of sensors and difficulty in field instrumentation. Furthermore, it is not desirable to identify a large number of unknown parameters in a full system because of numerical difficulty in convergence. A novel substructural strategy was presented for identification of stiffness matrices and damage assessment with incomplete measurement. The substructural approach was employed to identify large systems in a divide-and-conquer manner. In addition, the concept of model condensation was invoked to avoid the need for complete measurement, and the recovery process to obtain the full set of parameters was formulated. The efficiency of the proposed method is demonstrated nu... Structural Health Monitoring journals http://www.medworm.com/rss/comments.php?id=2739496 Wed, 26 Aug 2009 23:00:00 +0100 2739496 http://www.medworm.com/index.php?rid=2739495&cid=s_22297_23_f&fid=22297&url=http%3A%2F%2Fshm.sagepub.com%2Fcgi%2Fcontent%2Fabstract%2F8%2F5%2F381%3Frss%3D1 Ultrasonic guided waves offer the possibility of inspecting large areas of structures from a small number of sensor positions. However, inspection of complex structures is difficult as the reflections from different features overlap. Estimating the number and amplitude of the wave packets in ultrasonic time traces is crucial for the development of a guided wave inspection system, in order to detect and locate damage. Deconvolution has been extensively used in geophysical applications to resolve overlapping echoes in the recorded signals. The main objective of this work was to evaluate the applicability of the deconvolution approach for enhancing the resolution of ultrasonic time traces in structural health monitoring (SHM). Numerical simulations on strongly overlapping signals were carried... Structural Health Monitoring journals http://www.medworm.com/rss/comments.php?id=2739495 Wed, 26 Aug 2009 23:00:00 +0100 2739495 http://www.medworm.com/index.php?rid=2739494&cid=s_22297_23_f&fid=22297&url=http%3A%2F%2Fshm.sagepub.com%2Fcgi%2Fcontent%2Fabstract%2F8%2F5%2F369%3Frss%3D1 Modeling of an ultrasonic wave field inside a layered half-space is carried out by using the mesh-free semi-analytical Distributed Point Source Method (DPSM). The complete field is computed in a layered half-space in presence and absence of defects. The layered structure is excited by a bounded ultrasonic beam generated by a finite-sized transducer. It is important to have theoretical models to predict the ultrasonic fields in damaged and damage-free structures for its nondestructive evaluation. Numerical exercises can be carried out aided by these theoretical models to determine the area of the most distorted ultrasonic field in presence of an internal anomaly. Several numerical examples are provided for an aluminum half-space attached to layers made of two different materials. The struct... Structural Health Monitoring journals http://www.medworm.com/rss/comments.php?id=2739494 Wed, 26 Aug 2009 23:00:00 +0100 2739494 http://www.medworm.com/index.php?rid=2739493&cid=s_22297_23_f&fid=22297&url=http%3A%2F%2Fshm.sagepub.com%2Fcgi%2Fcontent%2Fabstract%2F8%2F5%2F357%3Frss%3D1 As part of Structural Health Monitoring (SHM), the history of a structure has become a crucial element to take into account. This has been shown, for example, by the spectacular accident of the flight Aloha 243 near Hawaï, when a whole part of the fuselage of a Boeing 737 had been torn off. Thus, monitoring impacts has become particularly interesting to give a comprehensive view of the occurrence of structural damage. Typical impact location estimation techniques use structural frequency drifts of a structure. Thus, such methods need an external excitation of the structure, which is unrealistic in most of the cases. As well, huge and possibly long computations, as genetic algorithms or artificial neural networks, are required for such techniques in order to retrieve the impact locatio... Structural Health Monitoring journals http://www.medworm.com/rss/comments.php?id=2739493 Wed, 26 Aug 2009 23:00:00 +0100 2739493 http://www.medworm.com/index.php?rid=2739492&cid=s_22297_23_f&fid=22297&url=http%3A%2F%2Fshm.sagepub.com%2Fcgi%2Fcontent%2Fabstract%2F8%2F5%2F345%3Frss%3D1 Headed shear studs are commonly used to resist longitudinal shear forces in composite railway bridges. Due to the growth of traffic and increase in train speed, these studs are subjected to high-cycle fatigue loading which may lead to damage, thus affecting the integrity between the steel girder and the concrete slab. Therefore, it is necessary to find a corresponding nondestructive damage detection method. Within the frame of this paper, the occurrence of damage in shear studs is studied by numerical analysis. In the numerical model of a real composite bridge, headed shear studs are represented by spring elements. A damage indicator based on the local modal curvature and the wavelet transform modulus maxima is proposed for stud damage identification. The efficiency of the damage indicator... Structural Health Monitoring journals http://www.medworm.com/rss/comments.php?id=2739492 Wed, 26 Aug 2009 23:00:00 +0100 2739492 http://www.medworm.com/index.php?rid=2491803&cid=s_22297_23_f&fid=22297&url=http%3A%2F%2Fshm.sagepub.com%2Fcgi%2Fcontent%2Fabstract%2F8%2F4%2F331%3Frss%3D1 Oil analysis is the main condition monitoring technique for reciprocating machinery maintenance and fault diagnosis. The object of this research was to choose and to investigate the best oil for Dump Truck HD325-5, used for transportation of minerals, by oil condition monitoring. This was achieved by analysing different oil samples after use in Dump Truck HD325-5. The oil analyses were initially carried out at regular intervals during life. A series of tests were then conducted during the operating hours of the machine. Oil samples were regularly collected. Numerical data produced by oil analyses were compared with those from another sample in order to quantify the effectiveness of the results of oil condition monitoring technique. The results from this article have enhanced understanding ... Structural Health Monitoring journals http://www.medworm.com/rss/comments.php?id=2491803 Thu, 18 Jun 2009 23:00:00 +0100 2491803 http://www.medworm.com/index.php?rid=2491802&cid=s_22297_23_f&fid=22297&url=http%3A%2F%2Fshm.sagepub.com%2Fcgi%2Fcontent%2Fabstract%2F8%2F4%2F313%3Frss%3D1 Traditional structural health monitoring techniques based on the vibration response of bridge structures are limited because of several factors — including a poorly formed aggregate system model, very low SNR, and unrealistic boundary conditions. Many times, these methods rely on global parameters to describe the dynamic behavior of local structural elements. In this paper, we proposed a novel efficient SHM technique that employs the use of compactly supported sub-band space/ frequency and time/frequency analysis using local vibration characteristics. To overcome the problem of the low-error sensitivity of features extracted from vibration signals, a near-field adaptive beamforming approach was used. This technique allows the sensor array to `scan' local portions of the structure, re... Structural Health Monitoring journals http://www.medworm.com/rss/comments.php?id=2491802 Thu, 18 Jun 2009 23:00:00 +0100 2491802 http://www.medworm.com/index.php?rid=2491801&cid=s_22297_23_f&fid=22297&url=http%3A%2F%2Fshm.sagepub.com%2Fcgi%2Fcontent%2Fabstract%2F8%2F4%2F303%3Frss%3D1 Structural health monitoring has been a research interest for its great potential for life safety and economic benefits for decades. Structural vibration impedance by way of piezoceramic patch excitation and sensoring offers a local damage detection technique and has caused a wide research interest. The commonly used damage index in this method is the rate of change of the real part of the measured electromechanical impedance. This paper studied several damage indices constructed by the real and imaginary parts or magnitude and phase. It theoretically deducted and concluded that the damage index in terms of changes in real part is in fact not a properly defined index and is physically obscure; on the other hand, indices in terms of the change in magnitude and phase were shown to be physica... Structural Health Monitoring journals http://www.medworm.com/rss/comments.php?id=2491801 Thu, 18 Jun 2009 23:00:00 +0100 2491801 http://www.medworm.com/index.php?rid=2491800&cid=s_22297_23_f&fid=22297&url=http%3A%2F%2Fshm.sagepub.com%2Fcgi%2Fcontent%2Fabstract%2F8%2F4%2F291%3Frss%3D1 This study aimed at the development of vibration-based health monitoring methodology for thin circular plates. The possibility of using the first several natural frequencies of a circular plate for damage detection purposes was investigated first. The study then suggested a damage detection method, which considered a vibrating plate as a dynamic system and used its time-domain response represented in a new phase (state) space to extract damage sensitive characteristics. The paper introduced the idea of using large amplitude vibrations and nonlinear time series analysis for damage detection purposes. The suggested damage detection approach explored the possibility to use certain characteristics of the distribution of phase space points on the attractor of the system. It studied the histogra... Structural Health Monitoring journals http://www.medworm.com/rss/comments.php?id=2491800 Thu, 18 Jun 2009 23:00:00 +0100 2491800 http://www.medworm.com/index.php?rid=2491799&cid=s_22297_23_f&fid=22297&url=http%3A%2F%2Fshm.sagepub.com%2Fcgi%2Fcontent%2Fabstract%2F8%2F4%2F283%3Frss%3D1 A 2.4 mm diameter piezoelectric ceramic disc was used to construct a spring-loaded pin-type transducer for intelligent monitoring of systems. Two types of lead-free KNN-based ceramics (0.95K0.5Na0.5 (Nb0.94Sb0.06)O 3 — 0.05LiTaO3 + 1.25 mol% BaO and K0.5Na 0.5NbO3 -0.75 mol% K5.4Cu1.3Ta 10O29) were selected as a sensing element of the pin. The piezoelectric spring-loaded pins were mounted on the corners of the aluminum plate for the performance evaluation using a laser ultrasonic technique. The signals detected by transducers with different sensing elements including lead-based ceramics have been compared. The capability of impact detection of the lead-free transducers was shown to be comparable to that of the lead-based one. It is envisaged that lead-free piezoelectrics will become ... Structural Health Monitoring journals http://www.medworm.com/rss/comments.php?id=2491799 Thu, 18 Jun 2009 23:00:00 +0100 2491799 http://www.medworm.com/index.php?rid=2491798&cid=s_22297_23_f&fid=22297&url=http%3A%2F%2Fshm.sagepub.com%2Fcgi%2Fcontent%2Fabstract%2F8%2F4%2F267%3Frss%3D1 A fuzzy logic system (FLS) with a new sliding window defuzzifier is proposed for structural damage detection using modal curvatures. Changes in the modal curvatures due to damage are fuzzified using Gaussian fuzzy sets and mapped to damage location and size using the FLS. The first four modal vectors obtained from finite element simulations of a cantilever beam are used for identifying the location and size of damage. Parametric studies show that modal curvatures can be used to accurately locate the damage; however, quantifying the size of damage is difficult. Tests with noisy simulated data show that the method detects damage very accurately at different noise levels and when some modal data are missing. (Source: Structural Health Monitoring) Structural Health Monitoring journals http://www.medworm.com/rss/comments.php?id=2491798 Thu, 18 Jun 2009 23:00:00 +0100 2491798 http://www.medworm.com/index.php?rid=2334943&cid=s_22297_23_f&fid=22297&url=http%3A%2F%2Fshm.sagepub.com%2Fcgi%2Fcontent%2Fabstract%2F8%2F3%2F251%3Frss%3D1 A crack detection technique based on nonlinear acoustics is investigated in this study. Acoustic waves at a chosen frequency are generated using an actuating lead zirconate titanate (PZT) transducer, and they travel through the target structure before being received by a sensing PZT wafer. Unlike an undamaged medium, a cracked medium exhibits high acoustic nonlinearity which is manifested as harmonics in the power spectrum of the received signal. Experimental results also indicate that the harmonic components increase nonlinearly in magnitude with increasing amplitude of the input signal. The proposed technique identifies the presence of cracks by looking at the two aforementioned features: harmonics and their nonlinear relationship to the input amplitude. The effectiveness of the techniqu... Structural Health Monitoring journals http://www.medworm.com/rss/comments.php?id=2334943 Tue, 14 Apr 2009 04:00:00 +0100 2334943 http://www.medworm.com/index.php?rid=2334942&cid=s_22297_23_f&fid=22297&url=http%3A%2F%2Fshm.sagepub.com%2Fcgi%2Fcontent%2Fabstract%2F8%2F3%2F243%3Frss%3D1 Bridge managers all over the world are always looking for simple ways to measure bridge vertical displacements for structural health monitoring. However, traditional methods to obtain such data are either tedious or expensive. There is a need to develop a simple, inexpensive, and yet practical method to measure bridge vertical displacements. This paper proposes two methods using either optical fiber (FBG) sensors or a charge-coupled-device (CCD) camera, respectively, for vertical displacement measurements of bridges. The FBG sensor method is based on the measured horizontal strains together with the identified curvature functions obtained by a self-developed FBG Tilt sensor. CCD cameras use a large number of pixels to form an image. The CCD camera method utilizes image processing technique... Structural Health Monitoring journals http://www.medworm.com/rss/comments.php?id=2334942 Tue, 14 Apr 2009 04:00:00 +0100 2334942 http://www.medworm.com/index.php?rid=2334941&cid=s_22297_23_f&fid=22297&url=http%3A%2F%2Fshm.sagepub.com%2Fcgi%2Fcontent%2Fabstract%2F8%2F3%2F223%3Frss%3D1 Conclusions drawn from this study have given an indication on how to select a better, if not the most optimal, data fusion scheme for structural damage evaluation. (Source: Structural Health Monitoring) Structural Health Monitoring journals http://www.medworm.com/rss/comments.php?id=2334941 Tue, 14 Apr 2009 04:00:00 +0100 2334941 http://www.medworm.com/index.php?rid=2334940&cid=s_22297_23_f&fid=22297&url=http%3A%2F%2Fshm.sagepub.com%2Fcgi%2Fcontent%2Fabstract%2F8%2F3%2F207%3Frss%3D1 In this paper, the distance measures of autoregressive (AR) models are used as damage indicators. Two distance measures are discussed: one is the Itakura distance, and the other is the cepstral distance. The distance measures of AR model have been successfully applied in image, speech, and neurological signal processing applications. This research explores new applications of two distance measures for damage detection in civil engineering. A five-storey building model is used for performance verification. Verification simulations show efficiencies of both distance-based damage indicators when the excitations are mutually uncorrelated. However, the ability of damage indicators for damage localization is deteriorated when the multiple excitations are mutually correlated as there are strong c... Structural Health Monitoring journals http://www.medworm.com/rss/comments.php?id=2334940 Tue, 14 Apr 2009 04:00:00 +0100 2334940 http://www.medworm.com/index.php?rid=2334939&cid=s_22297_23_f&fid=22297&url=http%3A%2F%2Fshm.sagepub.com%2Fcgi%2Fcontent%2Fabstract%2F8%2F3%2F195%3Frss%3D1 In this paper, an experimental test performed on a hybrid steel plate girder was subjected to concentrated loads at the end of an unstiffened panel is presented. This load was intended to produce a typical reaction of the piers while launching steel girders in bridges. In this test, strain measurements were taken with conventional pre-wired gauges as well as with newly developed wirelessly connected strain-measuring system. Both measurements were carefully compared and the accuracy of the developed system was demonstrated. Results were also compared with numerical simulations deployed with FE models and on such a basis; the reliability of the developed wireless system was proven. Finally, suggestions of potential research trends in this area are provided. (Source: Structural Health Monitor... Structural Health Monitoring journals http://www.medworm.com/rss/comments.php?id=2334939 Tue, 14 Apr 2009 04:00:00 +0100 2334939 http://www.medworm.com/index.php?rid=2252254&cid=s_22297_23_f&fid=22297&url=http%3A%2F%2Fshm.sagepub.com%2Fcgi%2Fcontent%2Fabstract%2F8%2F2%2F175%3Frss%3D1 This paper ascertains that Acoustic Emission (AE) monitoring is very effective for assessing the damage of reinforced concrete wide beam-column connections subjected to earthquake-type loadings. A cyclic test is conducted on an exterior connection until its failure. The experimental results show a strong correlation between the hysteretic strain energy and the AE energy histories. For this reason, a tentative formula is proposed, to predict the level of damage and the closeness to failure of the connection on the basis of the AE recorded by one piezoelectric sensor located near the critical zone (i.e., the beam-end and beam-column joint). (Source: Structural Health Monitoring) Structural Health Monitoring journals http://www.medworm.com/rss/comments.php?id=2252254 Wed, 11 Mar 2009 04:00:00 +0100 2252254 http://www.medworm.com/index.php?rid=2252253&cid=s_22297_23_f&fid=22297&url=http%3A%2F%2Fshm.sagepub.com%2Fcgi%2Fcontent%2Fabstract%2F8%2F2%2F149%3Frss%3D1 In this paper it is shown that natural frequency and antiresonant frequency shifts induced by a structural damage in an axially vibrating rod contain information on certain generalized Fourier coefficients of the stiffness variation caused by the degradation. This property is used to define a reconstruction procedure based on iterative updating of the undamaged configuration. The results of numerical simulations on rods with localized or diffuse damages are in good agreement with the theory, provided that average frequency and antiresonant frequency shifts due to degradation are bigger than the shifts due to modeling/measurement errors. Experimental results obtained on cracked steel rods showed that, in the inverse problem solution, noise and modeling errors on antiresonances are usually a... Structural Health Monitoring journals http://www.medworm.com/rss/comments.php?id=2252253 Wed, 11 Mar 2009 04:00:00 +0100 2252253 http://www.medworm.com/index.php?rid=2252252&cid=s_22297_23_f&fid=22297&url=http%3A%2F%2Fshm.sagepub.com%2Fcgi%2Fcontent%2Fabstract%2F8%2F2%2F137%3Frss%3D1 A monolithic interdigitated PVDF transducer (PVDF IDT) was built in this study. This PVDF IDT is capable of generating and receiving Lamb waves for structural health monitoring. Unlike most existing laminate-structured interdigitated PVDF transducers, this PVDF IDT features a monolithic structure, which eliminates sensor delamination as a potential problem. The flexible nature of PVDF promises the ability for the sensor to be attached to different structural surfaces. Other advantages of this PVDF IDT include low unit cost, easy installation, low power consumption, and the ability for wireless operation or remote interrogation. The fabrication of this sensor was accomplished by using etch-back photolithography technology. The interpretation of the complex Lamb wave signals was realized by ... Structural Health Monitoring journals http://www.medworm.com/rss/comments.php?id=2252252 Wed, 11 Mar 2009 04:00:00 +0100 2252252 http://www.medworm.com/index.php?rid=2252251&cid=s_22297_23_f&fid=22297&url=http%3A%2F%2Fshm.sagepub.com%2Fcgi%2Fcontent%2Fabstract%2F8%2F2%2F125%3Frss%3D1 Before the advent of computers, scientists used time domain periodogram analysis (TDPA) for analysis of phenomena described by time-dependent parameters. Famous examples of this approach include investigations of periodicities in Sun activity, analysis of annual rings of trees and deposits of clays in large lakes, both of which are indicators of climate variations. These periodicities found by TDPA were later confirmed using modern Fourier transform-based methods. Since the advent of the computer era and the fast Fourier transform, TDPA has been almost completely abandoned. In this work, we develop a computer-based TDPA algorithm and demonstrate its' utility for determining the existence (Level 1) of structural damage. First, the TDPA is compared to a frequency domain periodogram analysis ... Structural Health Monitoring journals http://www.medworm.com/rss/comments.php?id=2252251 Wed, 11 Mar 2009 04:00:00 +0100 2252251 http://www.medworm.com/index.php?rid=2252250&cid=s_22297_23_f&fid=22297&url=http%3A%2F%2Fshm.sagepub.com%2Fcgi%2Fcontent%2Fabstract%2F8%2F2%2F113%3Frss%3D1 This study is devoted to characterizing such performance of wireless sensors on a rotating lathe spindle and further examining the efficacy of a commonly adopted automatic repeat request (ARQ)-based reliable transmission method. The experimental measurements have shown that the transmission error rates were proportional to rotation speeds at certain receiver locations, while a minor change in the receiver location could significantly alter such dependency. It was found that the ARQ approach effectively assured a reliable data transmission during rotation with little retransmission overheads, and the reliable transmission throughput varied with different packet sizes and packet generation intervals. (Source: Structural Health Monitoring) Structural Health Monitoring journals http://www.medworm.com/rss/comments.php?id=2252250 Wed, 11 Mar 2009 04:00:00 +0100 2252250 http://www.medworm.com/index.php?rid=2252249&cid=s_22297_23_f&fid=22297&url=http%3A%2F%2Fshm.sagepub.com%2Fcgi%2Fcontent%2Fabstract%2F8%2F2%2F101%3Frss%3D1 Structural damage identification is an important objective of health monitoring for civil infrastructures. Frequently, damage to a structure may be reflected by a change of some system parameters, such as a degradation of the stiffness. In this paper, an auxiliary particle filtering (APF) method is applied to track a dynamic system with sudden parameter changes. In the APF, the importance density is proposed as a mixture density that depends upon the past state and the most recent observations, and hence which has a good time-tracking ability that is more suitable for tracking the nonstationary system than the conventional particle filters. Simulation results for tracking the sudden parameter changes of nonlinear hysteretic structures are presented to demonstrate the application and effect... Structural Health Monitoring journals http://www.medworm.com/rss/comments.php?id=2252249 Wed, 11 Mar 2009 04:00:00 +0100 2252249 http://www.medworm.com/index.php?rid=2109040&cid=s_22297_23_f&fid=22297&url=http%3A%2F%2Fshm.sagepub.com%2Fcgi%2Fcontent%2Fabstract%2F8%2F1%2F83%3Frss%3D1 A new condition-based preventive maintenance model for a system, subject to deterioration-failures and to random failures with increasing intensity, is presented. Deterioration is modeled as discrete stages. After an inspection, based on the degree of deterioration, a minimal maintenance or a major maintenance is performed, or no action is taken. Deterioration failures are restored by complete replacements; Random failures are restored by minimal repair. Major maintenance restores the system to `' deterioration stages younger ( > 1), while minimal maintenance restores the system one stage. The proposed model considers an accumulated deterioration based increasing intensity for the random failures. A continuously increasing failure rate (for example Weibull) is converted into a stepwise ... Structural Health Monitoring journals http://www.medworm.com/rss/comments.php?id=2109040 Fri, 16 Jan 2009 05:00:00 +0100 2109040 http://www.medworm.com/index.php?rid=2109039&cid=s_22297_23_f&fid=22297&url=http%3A%2F%2Fshm.sagepub.com%2Fcgi%2Fcontent%2Fabstract%2F8%2F1%2F71%3Frss%3D1 The active sensing methods using piezoelectric materials have been extensively investigated for the efficient use in structural health monitoring (SHM) applications. Relying on high frequency structural excitations, the methods showed the extreme sensitivity to minor defects in a structure. Recently, a sensor self-diagnostic procedure that performs in situ monitoring of the operational status of piezoelectric (PZT) active sensors and actuators in SHM applications has been proposed. In this investigation, previously developed impedance models were revisited in order to investigate the effects of sensor and/or bonding defects on the admittance measurement. New parameters for sensor quality assessment of a PZT and coupling degradation effects between a PZT and bonding layer were incorporated ... Structural Health Monitoring journals http://www.medworm.com/rss/comments.php?id=2109039 Fri, 16 Jan 2009 05:00:00 +0100 2109039 http://www.medworm.com/index.php?rid=2109038&cid=s_22297_23_f&fid=22297&url=http%3A%2F%2Fshm.sagepub.com%2Fcgi%2Fcontent%2Fabstract%2F8%2F1%2F59%3Frss%3D1 This paper presents a study to the problem of features selection for accurate recognition of crack signals in raining conditions, using a multilayer perceptron and a radial basis function neural network. The features extraction process is accomplished for two time frames: in the first time frame the presence of the signal reflection is minimal; in the later a wider window include signal reflections at the specimen edges. An extensive set of 90 features (41 of them are novel), 67 in the time domain and 23 in the frequency domain, are extracted from the normalized signals and are sorted according to Fisher ratio (F-ratio). The signals database consists of over than 20,000 simulated cracks and drops signals. The NNs classification accuracy of a single crack signal in rain conditions using the... Structural Health Monitoring journals http://www.medworm.com/rss/comments.php?id=2109038 Fri, 16 Jan 2009 05:00:00 +0100 2109038 http://www.medworm.com/index.php?rid=2109037&cid=s_22297_23_f&fid=22297&url=http%3A%2F%2Fshm.sagepub.com%2Fcgi%2Fcontent%2Fabstract%2F8%2F1%2F47%3Frss%3D1 This paper presents an approach to use strain data from a multi-girder, composite steel bridge for long-term Structural Health Monitoring (SHM). The bridge being studied is part of a research project at the University of Connecticut in which long-term SHM systems are being installed on a series of bridges throughout the State of Connecticut. Strain data is collected from normal truck traffic to determine live load stresses, load distribution factors, and the location of the neutral axis in each girder. Known weight trucks were used along with a finite element analysis for verification of the behavior. The long-term monitoring approach is based on determining the live load distribution factors, peak strains, and the neutral axis locations. The goal is to use existing, readily applied techno... Structural Health Monitoring journals http://www.medworm.com/rss/comments.php?id=2109037 Fri, 16 Jan 2009 05:00:00 +0100 2109037 http://www.medworm.com/index.php?rid=2109036&cid=s_22297_23_f&fid=22297&url=http%3A%2F%2Fshm.sagepub.com%2Fcgi%2Fcontent%2Fabstract%2F8%2F1%2F29%3Frss%3D1 The applicability of guided waves as a structural health monitoring (SHM) tool to predict the point of impact and detect delamination in a thermal protection system (TPS) is studied. A model TPS was designed by bonding ceramic porous tiles to a 2.2 mm thick 2124-T351 aluminum alloy plate. The delamination defect may be caused by the impact phenomenon or due to other reasons such as manufacturing defect, thermal, or mechanical fatigue, etc. Impact phenomenon is simulated by dropping a ping pong ball on the tiled structure. The delamination at the interface between the ceramic tile and the aluminum plate is simulated by removing the adhesive bond at the selected interface regions during the specimen fabrication process. The conventional triangulation technique cannot predict the point of imp... Structural Health Monitoring journals http://www.medworm.com/rss/comments.php?id=2109036 Fri, 16 Jan 2009 05:00:00 +0100 2109036 http://www.medworm.com/index.php?rid=2109035&cid=s_22297_23_f&fid=22297&url=http%3A%2F%2Fshm.sagepub.com%2Fcgi%2Fcontent%2Fabstract%2F8%2F1%2F17%3Frss%3D1 A physics-based first principles approach is adopted in this study to simulate vibration signatures from an idealized gear such as a thin spur gear under plane dynamic stresses induced by an impulsive rotation. The governing equations of velocity—stress are solved using a finite-difference formulation in generalized curvilinear coordinates and a fully characteristic set of boundary conditions based on the theory of hyperbolic systems. The vibration signatures are thus directly obtained in the time domain. A second-order accurate in time and space, time-staggered leapfrog scheme, is used to integrate the time-dependent partial differential equations. Normal as well as damage signatures are obtained and compared; normal signatures correspond to uniform material properties of the gear, ... Structural Health Monitoring journals http://www.medworm.com/rss/comments.php?id=2109035 Fri, 16 Jan 2009 05:00:00 +0100 2109035 http://www.medworm.com/index.php?rid=2109034&cid=s_22297_23_f&fid=22297&url=http%3A%2F%2Fshm.sagepub.com%2Fcgi%2Fcontent%2Fabstract%2F8%2F1%2F5%3Frss%3D1 A method for damage localization based on the phased array idea has been developed. Four arrays of transducers are used to perform a beam-forming procedure. Each array consists of nine transducers placed along a line, which are able to excite and register elastic waves. The A0 Lamb wave mode has been chosen for the localization method. The arrays are placed in such a way that the angular difference between them is 45° and the rotation point is the middle transducer, which is common for all the arrays. The idea has been tested on a square aluminium plate modeled by the Spectral Element Method. Two types of damage were considered, namely distributed damage, which was modeled as stiffness reduction, and cracks, modeled as separation of nodes between selected spectral elements. The plate i... Structural Health Monitoring journals http://www.medworm.com/rss/comments.php?id=2109034 Fri, 16 Jan 2009 05:00:00 +0100 2109034 http://www.medworm.com/index.php?rid=1982676&cid=s_22297_23_f&fid=22297&url=http%3A%2F%2Fshm.sagepub.com%2Fcgi%2Fcontent%2Fabstract%2F7%2F4%2F347%3Frss%3D1 Recently, damage detection capability has been demonstrated successfully using state-space based algorithms. These methods are advantageous because they rely on data-driven techniques that do not conform to models or assumptions like linearity. State-space-based features traditionally involve comparisons between measurements taken at the same location but at different times to determine if a change has taken place. However, if features such as state-space cross-prediction error and generalized interdependence are formulated such that they instead employ comparisons between simultaneous measurements at different locations, a fuller assessment of structural damage is possible. In addition to the presence of damage, other characteristics such as the extent, location, and type of damage can be... Structural Health Monitoring journals http://www.medworm.com/rss/comments.php?id=1982676 Mon, 24 Nov 2008 05:00:00 +0100 1982676 http://www.medworm.com/index.php?rid=1982675&cid=s_22297_23_f&fid=22297&url=http%3A%2F%2Fshm.sagepub.com%2Fcgi%2Fcontent%2Fabstract%2F7%2F4%2F329%3Frss%3D1 The practical application of Acoustic emission (AE) testing in the Structural Health Monitoring (SHM) of vintage steel reinforced concrete highway bridges has been recently investigated by the Oregon Department of Transportation (ODOT) and Oregon State University (OSU). A large number of full scale laboratory test beams designed to simulate a particular class of highway bridge structure and a particular type of structural damage were tested with AE. The results of the AE test data analyzed using the Felicity and Calm ratios are presented and related to physically observed structural damage. New thresholds on the Felicity and Calm ratios specific to this class of structure and loading are suggested (based on the test results) to be used in both the damage assessment diagrams developed in th... Structural Health Monitoring journals http://www.medworm.com/rss/comments.php?id=1982675 Mon, 24 Nov 2008 05:00:00 +0100 1982675 http://www.medworm.com/index.php?rid=1982674&cid=s_22297_23_f&fid=22297&url=http%3A%2F%2Fshm.sagepub.com%2Fcgi%2Fcontent%2Fabstract%2F7%2F4%2F309%3Frss%3D1 Damage detection and structural health monitoring techniques based on vibration data have seen increased attention in recent years. Among the different vibration-based methods, the ones based on random vibrations are of particularly interest, especially when they do not require measurement of the input(s). In this work, several frequency and time domain signal processing techniques are explored in their respective abilities to detect damage in a bolted composite structure. First, a joint loosening model is developed and used to simulate the dynamic response to a stationary Gaussian excitation. Informed by the model, two signal processing techniques are used to assess the connection strength. The first method relies on basic statistical properties of the measured strains and their time deri... Structural Health Monitoring journals http://www.medworm.com/rss/comments.php?id=1982674 Mon, 24 Nov 2008 05:00:00 +0100 1982674 http://www.medworm.com/index.php?rid=1982673&cid=s_22297_23_f&fid=22297&url=http%3A%2F%2Fshm.sagepub.com%2Fcgi%2Fcontent%2Fabstract%2F7%2F4%2F293%3Frss%3D1 On-board sensors that can detect and size a crack in a structural component are being developed and will be deployed to enhance structural health monitoring and prognosis. This research examines the simulation of recurring automated inspections resulting from simulated on-board `crack' sensors, and their potential effect on reducing the probability-of-fracture of structural components. The concept of a probability-of-detection (POD) curve is used to characterize the performance of the sensor, as done for traditional inspections. However, we assert that, unlike the simulation of traditional infrequent inspections, recurring inspections for an automated system should be modeled as dependent with respect to the first inspection due to the largely repeatable aspects of the sensor and data coll... Structural Health Monitoring journals http://www.medworm.com/rss/comments.php?id=1982673 Mon, 24 Nov 2008 05:00:00 +0100 1982673 http://www.medworm.com/index.php?rid=1982672&cid=s_22297_23_f&fid=22297&url=http%3A%2F%2Fshm.sagepub.com%2Fcgi%2Freprint%2F7%2F4%2F291%3Frss%3D1 (Source: Structural Health Monitoring) Structural Health Monitoring journals http://www.medworm.com/rss/comments.php?id=1982672 Mon, 24 Nov 2008 05:00:00 +0100 1982672 http://www.medworm.com/index.php?rid=1784744&cid=s_22297_23_f&fid=22297&url=http%3A%2F%2Fshm.sagepub.com%2Fcgi%2Fcontent%2Fabstract%2F7%2F3%2F271%3Frss%3D1 A Lamb wave-based technique was developed for detecting damages in metallic structures, such as cracks and holes in metallic beams and plates. For metallic structures with transverse cracks and holes, A0 mode of Lamb waves was employed due to its shorter wave length compared with S0 mode, which leads to high sensitivity to small damages. Two kinds of excitation techniques for generating comparatively pure A0 mode using piezoelectric lead zirconate titanate (PZT) actuators were realized experimentally. In one technique, two PZT actuators with applied out-of-phase voltages were attached on both sides of the structures. While in the other technique, a kind of grease lubricant was used between the bottom surface of one PZT... Structural Health Monitoring journals http://www.medworm.com/rss/comments.php?id=1784744 Thu, 11 Sep 2008 04:00:00 +0100 1784744 http://www.medworm.com/index.php?rid=1784743&cid=s_22297_23_f&fid=22297&url=http%3A%2F%2Fshm.sagepub.com%2Fcgi%2Fcontent%2Fabstract%2F7%2F3%2F265%3Frss%3D1 Military and commercial aerospace organizations are exploring structural health monitoring (SHM) systems to reduce maintenance costs and to verify the integrity of structural components exposed to harsh conditions. This technical note considers the use of Lamb waves to monitor plate and shell components of aerospace structures. For fielded applications, SHM systems will need to operate across a variety of environmental conditions, including large temperature ranges. Therefore, it is critical to understand the effects of temperature on Lamb wave propagation. The focus of this study is the effect of temperature on Lamb wave propagation in a constant-thickness metallic plate under isothermal conditions. Experimental measurements and analytical predictions are made over temperatures ranging fr... Structural Health Monitoring journals http://www.medworm.com/rss/comments.php?id=1784743 Thu, 11 Sep 2008 04:00:00 +0100 1784743 http://www.medworm.com/index.php?rid=1784742&cid=s_22297_23_f&fid=22297&url=http%3A%2F%2Fshm.sagepub.com%2Fcgi%2Fcontent%2Fabstract%2F7%2F3%2F245%3Frss%3D1 This article presents an accurate survey of two on-piles quays with tie-rods during the building stage and the two first years of their opening. These first years after building are characterized by a very fair exploitation of both quays. The influence of the building conditions on the loads in the tie-rods of the two quays has been identified from measured data. On these two quays, identically designed, an original instrumentation strategy has been achieved: it aims to follow the behavior of the quays during the next 5 years including their building in view to set up models for the prediction of the loadings evolutions and to base the maintenance policy or exploitation during extreme events (storms) on a better understanding of the in-service behavior. This aim has been achieved by monito... Structural Health Monitoring journals http://www.medworm.com/rss/comments.php?id=1784742 Thu, 11 Sep 2008 04:00:00 +0100 1784742 http://www.medworm.com/index.php?rid=1784741&cid=s_22297_23_f&fid=22297&url=http%3A%2F%2Fshm.sagepub.com%2Fcgi%2Fcontent%2Fabstract%2F7%2F3%2F231%3Frss%3D1 This paper describes the application of a structural health monitoring technique based on electrical measurements obtained by piezoceramics (PZT) patches bonded in lightweight structures. The goal is to detect and locate imminent structural change occurrence with statistical confidence through a nondestructive evaluation test. Though the major focus in damage detection is given by monitoring electrical impedance in frequency-domain, the current research work applies a novel approach based on time-series. In such case, auto-regressive moving average with exogenous input (ARMAX) system identification models and statistical process control (SPC) charts are used for linear prediction to detect and locate damages. In order to compare the results, the classical damage metric chart obtained by fr... Structural Health Monitoring journals http://www.medworm.com/rss/comments.php?id=1784741 Thu, 11 Sep 2008 04:00:00 +0100 1784741 http://www.medworm.com/index.php?rid=1784740&cid=s_22297_23_f&fid=22297&url=http%3A%2F%2Fshm.sagepub.com%2Fcgi%2Fcontent%2Fabstract%2F7%2F3%2F215%3Frss%3D1 A hybrid reasoning methodology is applied to a complex aerospace structure, and its effectiveness is assessed in identifying and locating the position of impacts. Part of a commercial aircraft wing flap is impacted and time-varying strain response data from the structure are sensed using passive piezoceramic sensors. This structure can be regarded as a small scale version of part of a wing span with the corresponding features being a leading edge and trailing edge. The trailing edge is composed of aluminium skins with an aluminium honeycomb core, the leading edge of composite skins with a light weight honeycomb core, and the central section of thin composite material. Nine sensors, to detect time-varying strain response data, are distributed over the surface of the flap; two on the leading... Structural Health Monitoring journals http://www.medworm.com/rss/comments.php?id=1784740 Thu, 11 Sep 2008 04:00:00 +0100 1784740 http://www.medworm.com/index.php?rid=1784739&cid=s_22297_23_f&fid=22297&url=http%3A%2F%2Fshm.sagepub.com%2Fcgi%2Fcontent%2Fabstract%2F7%2F3%2F203%3Frss%3D1 This article discusses the research study conducted, which resulted in the development of a Structural Health Monitoring (SHM) system for a 2D polymeric composite T-joint, used in maritime structures. The SHM system was found to be capable of not only detecting the presence of multiple delaminations in a composite structure, but also capable of determining the location and extent of all the delaminations present in the T-joint structure, regardless of the load (angle and magnitude) acting on the structure. The system developed relies on the examination of the strain distribution of the structure under operational loading. (Source: Structural Health Monitoring) Structural Health Monitoring journals http://www.medworm.com/rss/comments.php?id=1784739 Thu, 11 Sep 2008 04:00:00 +0100 1784739 http://www.medworm.com/index.php?rid=1784738&cid=s_22297_23_f&fid=22297&url=http%3A%2F%2Fshm.sagepub.com%2Fcgi%2Fcontent%2Fabstract%2F7%2F3%2F189%3Frss%3D1 Assessment is made for welded joints in orthotropic steel decks based on monitored field data from the Runyang Bridge by making use of the Palmgren–Miner rule and S–N curves. In contrast to previous strategies, interactive behavior of fatigue damage, ambient temperature, and traffic flow are considered. The results indicate that for long-span suspension bridge that is sensitive to temperature changes, fatigue damage accumulation is influenced by the ambient temperature in addition to the traffic growth. According to the fatigue equivalent index and statistical processing of traffic flow, the contribution of traffic growth to fatigue damage can be determined and then it is excluded from the total damage, so ... Structural Health Monitoring journals http://www.medworm.com/rss/comments.php?id=1784738 Thu, 11 Sep 2008 04:00:00 +0100 1784738 http://www.medworm.com/index.php?rid=1461882&cid=s_22297_23_f&fid=22297&url=http%3A%2F%2Fshm.sagepub.com%2Fcgi%2Fcontent%2Fabstract%2F7%2F2%2F175%3Frss%3D1 This paper presents a reliability-based methodology for health monitoring of aging bridges. Initially, critical failure criteria are proposed depending on the type of bridge. Safety margins are then defined based on these criteria. It is assumed that quantities in the failure criteria are random variables that are normally distributed. Based on this assumption, elementary reliability indices and thereby elementary failure probabilities are estimated for each critical failure mode. Having found the elementary failure probability values, system failure probability of the bridge is calculated for the period under consideration. Finally, the system failure probability is used to obtain a system reliability index of the bridge. The... Structural Health Monitoring journals http://www.medworm.com/rss/comments.php?id=1461882 Thu, 22 May 2008 04:00:00 +0100 1461882 http://www.medworm.com/index.php?rid=1461881&cid=s_22297_23_f&fid=22297&url=http%3A%2F%2Fshm.sagepub.com%2Fcgi%2Fcontent%2Fabstract%2F7%2F2%2F157%3Frss%3D1 Structural Health Monitoring (SHM) of a wind turbine blade using a Structural Neural System (SNS) is described in this paper. Wind turbine blades are composite structures with complex geometry and sections that are built of different materials. The 3D structure, large size, anisotropic material properties, and the potential for damage to occur anywhere on the blade makes damage detection a significant challenge. A SNS based on acoustic emission (AE) monitoring (passive listening) was developed for practical low cost SHM of large composite structures such as wind turbine blades. The SNS was tested to detect damage initiation and propagation on a 9 m long wind turbine blade during a quasi-static proof test to failure at the ... Structural Health Monitoring journals http://www.medworm.com/rss/comments.php?id=1461881 Thu, 22 May 2008 04:00:00 +0100 1461881 http://www.medworm.com/index.php?rid=1461880&cid=s_22297_23_f&fid=22297&url=http%3A%2F%2Fshm.sagepub.com%2Fcgi%2Fcontent%2Fabstract%2F7%2F2%2F143%3Frss%3D1 In this paper, the measurement behavior of BOTDR (Brillouin Optical Time Domain Reflectometry) in different sensing lengths and different strain levels is investigated theoretically and validated by experiments. Moreover, the relationship between measured strain distribution and actual strain distribution is derived in theory and validated by experiment. Based on these investigations, a standard method for evaluating the measurement performance of distributed or long gauge fiber optic sensors for monitoring cracks is proposed. The performance evaluation of BOTDR-based distributed fiber optic sensors are then performed based on the proposed method, and applicable conditions of different fiber optic installation methods for moni... Structural Health Monitoring journals http://www.medworm.com/rss/comments.php?id=1461880 Thu, 22 May 2008 04:00:00 +0100 1461880 http://www.medworm.com/index.php?rid=1461879&cid=s_22297_23_f&fid=22297&url=http%3A%2F%2Fshm.sagepub.com%2Fcgi%2Fcontent%2Fabstract%2F7%2F2%2F129%3Frss%3D1 The ambient temperature effect may result in limitations of vibration-based SHM approaches for civil engineering structures. This paper addresses the issue of discriminating changes in modal parameters due to damages and changes in modal parameters due to temperature effects. A nonparametric damage detection algorithm is proposed, which only assumes that several data sets are recorded on the safe structure at different and unknown temperatures, and smoothes out the temperature effect using an averaging operation. (Source: Structural Health Monitoring) Structural Health Monitoring journals http://www.medworm.com/rss/comments.php?id=1461879 Thu, 22 May 2008 04:00:00 +0100 1461879 http://www.medworm.com/index.php?rid=1461878&cid=s_22297_23_f&fid=22297&url=http%3A%2F%2Fshm.sagepub.com%2Fcgi%2Fcontent%2Fabstract%2F7%2F2%2F103%3Frss%3D1 This paper presents a method for extracting system nonlinearities and time-localized transient response to impulsive loading by processing stationary/transient responses using the Hilbert—Huang transform (HHT) and a sliding-window fitting (SWF) technique. Time-dependent dynamic characteristics of nonlinear systems are derived using perturbation analysis. The SWF is introduced mainly to show the mathematical implications of HHT and the differences between HHT and the discrete Fourier transform. Similar to the wavelet transform the SWF uses windowed predetermined regular harmonics and function orthogonality to extract local harmonic components. It simultaneously decomposes a signal into just a few regular/distorted ... Structural Health Monitoring journals http://www.medworm.com/rss/comments.php?id=1461878 Thu, 22 May 2008 04:00:00 +0100 1461878 http://www.medworm.com/index.php?rid=1461877&cid=s_22297_23_f&fid=22297&url=http%3A%2F%2Fshm.sagepub.com%2Fcgi%2Fcontent%2Fabstract%2F7%2F2%2F91%3Frss%3D1 An open source software-based solution for Finite Element Model Updating is presented. The calculation technique has been carried out by developing VCUPDATE, a Scilab (MATLAB-like software) code performing the iterative updating algorithm interfaced with OpenSees executing the Finite Element analysis. The code has been verified by many different applications on stay cables. The dynamic test results from real structures are applied if available. Otherwise, the investigated structures are numerically generated by OpenSees. (Source: Structural Health Monitoring) Structural Health Monitoring journals http://www.medworm.com/rss/comments.php?id=1461877 Thu, 22 May 2008 04:00:00 +0100 1461877 http://www.medworm.com/index.php?rid=1461876&cid=s_22297_23_f&fid=22297&url=http%3A%2F%2Fshm.sagepub.com%2Fcgi%2Freprint%2F7%2F2%2F89%3Frss%3D1 (Source: Structural Health Monitoring) Structural Health Monitoring journals http://www.medworm.com/rss/comments.php?id=1461876 Thu, 22 May 2008 04:00:00 +0100 1461876 http://www.medworm.com/index.php?rid=1240427&cid=s_22297_23_f&fid=22297&url=http%3A%2F%2Fshm.sagepub.com%2Fcgi%2Fcontent%2Fabstract%2F7%2F1%2F65%3Frss%3D1 A prototype structural neural system (SNS) is tested for the first time and damage detection results are presented in this study. The SNS is a passive online structural health monitoring (SHM) system that mimics the synaptic parallel computation networks present in the human biological neural system. Piezoelectric ceramic sensors and analog electronics are used to form neurons that measure strain waves generated by damage. The sensing of strain waves is similar to the proven nondestructive evaluation (NDE) technique of acoustic emission (AE) monitoring. Fatigue testing of a composite specimen on a four-point bending fiXture is performed, and the SNS is used to monitor the specimen for damage in real time. The prototype SNS used four sensors as inputs, but the number of inputs can be in the... Structural Health Monitoring journals http://www.medworm.com/rss/comments.php?id=1240427 Tue, 19 Feb 2008 05:00:00 +0100 1240427 http://www.medworm.com/index.php?rid=1240426&cid=s_22297_23_f&fid=22297&url=http%3A%2F%2Fshm.sagepub.com%2Fcgi%2Fcontent%2Fabstract%2F7%2F1%2F51%3Frss%3D1 This study describes a new optical fiber monitoring system to measure structural displacements. The underlying concept is based on a square fiberglass `Smart Rod' containing grooves in each face, glued into which are optical fibers containing fiber Bragg gratings (FBGs) at a succession of points along their length. The Smart Rod is rigidly fiXed at discrete points to the structure being assessed and the strain at each FBG is determined optically. The strain is thereafter converted to structural displacements. This study describes a series of `bench test' laboratory eXperiments designed to eXplore the challenges of installing the monitoring system and interpreting the results. The results from the tests are presented and discussed in the conteXt of the accuracy achievable with the proposed ... Structural Health Monitoring journals http://www.medworm.com/rss/comments.php?id=1240426 Tue, 19 Feb 2008 05:00:00 +0100 1240426 http://www.medworm.com/index.php?rid=1240425&cid=s_22297_23_f&fid=22297&url=http%3A%2F%2Fshm.sagepub.com%2Fcgi%2Fcontent%2Fabstract%2F7%2F1%2F37%3Frss%3D1 A conceptual structural health monitoring (SHM) system to monitor fatigue damage is discussed in this study. The first part of the study is concerned with damage prognosis. A methodology to use the data from a pre-crack damage monitoring system to predict the number of cycles to macrocrack-initiation in a probabilistic sense, is presented. Issues related to quantifying damage, a damage evolution law, and numerical evaluation of the probability of macrocrack initiation are discussed. The second part of the study deals with quantifying the effects of imperfect inspections during the growth of a macrocrack. The probability that there eXists an undetected critical crack is the quantity of interest. An analytical eXpression for this quantity is derived for the case of a two-dimensional crack. A... Structural Health Monitoring journals http://www.medworm.com/rss/comments.php?id=1240425 Tue, 19 Feb 2008 05:00:00 +0100 1240425 http://www.medworm.com/index.php?rid=1240424&cid=s_22297_23_f&fid=22297&url=http%3A%2F%2Fshm.sagepub.com%2Fcgi%2Fcontent%2Fabstract%2F7%2F1%2F21%3Frss%3D1 An online identification of variation of stiffness in structural systems has been presented in this study. The proposed technique is based on wavelet analysis. The time-frequency characteristics of the wavelets have been used in the formulation of online identification. The basis function used is a modified version of the Littlewood—Paley wavelet. The bases generated from this wavelet at different scales have the advantage of non-overlapping frequency bands which has been utilized in the frequency tracking algorithm. Further, an algorithm for detection of variation in modes shapes in time-varying linear multi-degree-of-freedom (MDOF) systems has been developed. Several types of changes in stiffness, such as a sudden jump, a ramp (gradual) change, or a sudden change with subsequent re... Structural Health Monitoring journals http://www.medworm.com/rss/comments.php?id=1240424 Tue, 19 Feb 2008 05:00:00 +0100 1240424 http://www.medworm.com/index.php?rid=1240423&cid=s_22297_23_f&fid=22297&url=http%3A%2F%2Fshm.sagepub.com%2Fcgi%2Fcontent%2Fabstract%2F7%2F1%2F5%3Frss%3D1 This study presents active sensing methods in structural health monitoring, for detecting cracks and debonds in metallic and composite structures, which can be potentially implemented into airframe structures. First, a pitch-catch method using a pair of piezoelectric actuator and sensor is introduced to generate a damage indeX which can be used to characterize damage at a known location. Tests on airbus fuselage panels are conducted to verify the method and damage indeX. The damage indeX relates changes in the energy content of a specific Lamb wave mode selected by group velocity analysis to the eXtent of damage. Second, an imaging method based on multiple pitch-catch information, a network of piezoelectric actuator/sensors, is presented for characterizing damage (location and size) withou... Structural Health Monitoring journals http://www.medworm.com/rss/comments.php?id=1240423 Tue, 19 Feb 2008 05:00:00 +0100 1240423 http://www.medworm.com/index.php?rid=1051531&cid=s_22297_23_f&fid=22297&url=http%3A%2F%2Fshm.sagepub.com%2Fcgi%2Fcontent%2Fabstract%2F6%2F4%2F325%3Frss%3D1 Higher order spectra (HOS) are the tools in signal processing for the identification of the presence of higher harmonics in a signal which is a typical case of a non-linear dynamic behavior in mechanical systems. The breathing of a crack during shaft rotation also exhibits a non-linear behavior. The crack is known to generate 2X (twice the machine RPM) and higher harmonics in addition to 1X component in the shaft response during its rotation. Misaligned shaft also shows such feature as a crack in a shaft. The HOS have now been applied on a small rotating rig to observe its features. Results are found to be encouraging to distinguish these two faults based on a few experiments conducted on a small rig, which are presented here. The presented results though limited suggest the potential of t... Structural Health Monitoring journals http://www.medworm.com/rss/comments.php?id=1051531 Tue, 27 Nov 2007 05:00:00 +0100 1051531 http://www.medworm.com/index.php?rid=1051530&cid=s_22297_23_f&fid=22297&url=http%3A%2F%2Fshm.sagepub.com%2Fcgi%2Fcontent%2Fabstract%2F6%2F4%2F309%3Frss%3D1 The authors focus on the construction of a structural health monitoring (SHM) system with an advanced grid structure (AGS) made of carbon-fiber reinforced plastic (CFRP). AGS is often applied to aerospace structures because the ribs carry only axial forces in the carbon fiber direction, making AGS structurally effective and lightweight, and because the repetition of many ribs in the AGS composition results in damage tolerance. The failure of a single rib hardly affects the fracture of the whole structure, making AGS a fail-safe structure. In this research, the authors have embedded multiplexed-fiber Bragg grating (FBG) sensors into an AGS rib in the longitudinal direction to measure mechanical strains of all ribs in order to detect the existence and regions of AGS rib fractures. Monitoring... Structural Health Monitoring journals http://www.medworm.com/rss/comments.php?id=1051530 Tue, 27 Nov 2007 05:00:00 +0100 1051530 http://www.medworm.com/index.php?rid=1051529&cid=s_22297_23_f&fid=22297&url=http%3A%2F%2Fshm.sagepub.com%2Fcgi%2Fcontent%2Fabstract%2F6%2F4%2F299%3Frss%3D1 The objective of the system is to detect and locate damage in structures such as those found in aerospace applications. The damage identification system involves Bragg gratings for sensing ultrasound by detecting the linear strain component produced by Lamb waves. A tuneable laser is used for the interrogation of the Bragg gratings to achieve high sensitivity detection of ultrasound. The interaction of Lamb waves with damage, e.g., the reflection of the waves at defects, allows the detection of damage in structures by monitoring the Lamb wave propagation characteristics. As the reflected waves produce additional components within the original signal, most of the information about the damage can be found in the differential signal of the reference and the damage signal. Making use of the di... Structural Health Monitoring journals http://www.medworm.com/rss/comments.php?id=1051529 Tue, 27 Nov 2007 05:00:00 +0100 1051529 http://www.medworm.com/index.php?rid=1051528&cid=s_22297_23_f&fid=22297&url=http%3A%2F%2Fshm.sagepub.com%2Fcgi%2Fcontent%2Fabstract%2F6%2F4%2F281%3Frss%3D1 A vibration-based approach to detect crack damage for large structural systems by using the Hilbert—Huang transform (HHT) has been proposed. The proposed method has been numerically implemented on a composite wingbox. In the implementation process, the following steps have been identified as being important: (a) An optimization procedure is developed by genetic algorithm (GA) in order to determine the location of piezoelectric sensor for damage detection in a composite wingbox; (b) To solve the end effect problem of empirical mode decomposition (EMD), axis-symmetry signal extension method is introduced; (c) Finally, a damage detection method by using HHT is developed. Furthermore, the effect of noise is considered. Examination of the results confirms that the identification method is... Structural Health Monitoring journals http://www.medworm.com/rss/comments.php?id=1051528 Tue, 27 Nov 2007 05:00:00 +0100 1051528 http://www.medworm.com/index.php?rid=1051527&cid=s_22297_23_f&fid=22297&url=http%3A%2F%2Fshm.sagepub.com%2Fcgi%2Fcontent%2Fabstract%2F6%2F4%2F265%3Frss%3D1 In this study, Gaussian chirplet is shown to be complete enough to match the characteristics of transient rotor vibration signals during speed varying processes. In order to avoid the amplitude distortion found in adaptive chirplet spectrograms, the Wigner—Ville distribution of normalized optimal chirplets is employed as a time—frequency window to filter the time—frequency distribution. The improved adaptive chirplet spectrogram possesses the best time—frequency resolution, and is free of cross term interference and amplitude distortion. Using this decomposition, the characteristic frequency components and their time evolution of main shaft vibration signals during the shut-down process ... Structural Health Monitoring journals http://www.medworm.com/rss/comments.php?id=1051527 Tue, 27 Nov 2007 05:00:00 +0100 1051527 http://www.medworm.com/index.php?rid=828689&cid=s_22297_23_f&fid=22297&url=http%3A%2F%2Fshm.sagepub.com%2Fcgi%2Fcontent%2Fabstract%2F6%2F3%2F245%3Frss%3D1 This study provides an overview of the computational intelligence methods developed for the corrosion damage assessment of aerospace materials and structures. Specifically, cellular automata modeling of corrosion pit initiation and growth, wavelet based image processing methods for corrosion damage assessment, and artificial neural networks (ANNs) for material loss and residual strength predictions. In addition, ANN based prediction of life due to corrosion-fatigue conditions are considered and presented. Results obtained from selected computational intelligence methods are compared to the existing alternate solutions and experimental data. The results presented illustrate the feasibility of computational intelligence methods for modeling and assessing the corrosion health of aging aircraf... Structural Health Monitoring journals http://www.medworm.com/rss/comments.php?id=828689 Wed, 29 Aug 2007 04:00:00 +0100 828689 http://www.medworm.com/index.php?rid=828688&cid=s_22297_23_f&fid=22297&url=http%3A%2F%2Fshm.sagepub.com%2Fcgi%2Fcontent%2Fabstract%2F6%2F3%2F231%3Frss%3D1 This study presents an experimental verification of the IPV technique for structural system identification and damage detection. A scaled three-story, base-excited structure is designed and fabricated for these experiments. The structure is excited using a displacement-controlled shake table, and damage is introduced by triggering the release of cross-bracing tendons, i.e., inducing sudden changes in the restoring forces. Experimental results using harmonic and recorded earthquake excitation data clearly demonstrate the effectiveness of this IPV technique. (Source: Structural Health Monitoring) Structural Health Monitoring journals http://www.medworm.com/rss/comments.php?id=828688 Wed, 29 Aug 2007 04:00:00 +0100 828688 http://www.medworm.com/index.php?rid=828687&cid=s_22297_23_f&fid=22297&url=http%3A%2F%2Fshm.sagepub.com%2Fcgi%2Fcontent%2Fabstract%2F6%2F3%2F215%3Frss%3D1 This article carries out a comparative study of various classification algorithms for fault diagnosis of electric motors using different types of signals. The authors evaluate experimentally the relative performances of five classifiers using five types of steady-state signals based on three kinds of performance evaluation strategies: training-test, cross-validation, and similar measure. First, the raw signals are collected and features are extracted from the collected signals. Then, the extracted features are classified using the five classification algorithms. Next, an overall comparison of the five classifiers is described, and experiment results are discussed. Finally, conclusions are summarized and suggestions are offered. (Source: Structural Health Monitoring) Structural Health Monitoring journals http://www.medworm.com/rss/comments.php?id=828687 Wed, 29 Aug 2007 04:00:00 +0100 828687 http://www.medworm.com/index.php?rid=828686&cid=s_22297_23_f&fid=22297&url=http%3A%2F%2Fshm.sagepub.com%2Fcgi%2Fcontent%2Fabstract%2F6%2F3%2F199%3Frss%3D1 In order to localize and quantify the effects of externally bonded carbon fiber reinforced polymer (CFRP) composites on a deteriorating reinforced concrete (RC) bridge structure, a vibration based monitoring approach is implemented. Modal data, including mode shapes of the deck slab, are extracted under the output-only configuration using time domain decomposition (TDD) techniques from ambient vibration tests conducted prior to rehabilitation, and at periodic intervals over a period of about two years after rehabilitation. Damage indices and fractional stiffness changes are determined by bay to enable assessment of CFRP rehabilitation effectiveness and response changes as a function of time. (Source: Structural Health Monitoring) Structural Health Monitoring journals http://www.medworm.com/rss/comments.php?id=828686 Wed, 29 Aug 2007 04:00:00 +0100 828686 http://www.medworm.com/index.php?rid=828685&cid=s_22297_23_f&fid=22297&url=http%3A%2F%2Fshm.sagepub.com%2Fcgi%2Fcontent%2Fabstract%2F6%2F3%2F191%3Frss%3D1 Fiber Bragg grating (FBG) hybrid sensors and thermocouples measure strain and temperature simultaneously during and after cure of asymmetric cross-ply composite laminates. FBG strain sensor is used to measure strain; FBG temperature sensor and thermocouple are used to measure temperature. The characteristic matrix of the sensor is derived analytically and measurements can be done without sensor calibration experiments. A wavelength-swept fiber laser is used as the light source. Two FBG hybrid sensors and two K-type thermocouples are embedded in a carbon/epoxy asymmetric cross-ply composite laminate in different directions and different locations. The real-time measurement of fabrication strains and temperatures is performed at two points within the asymmetric composite laminate during the ... Structural Health Monitoring journals http://www.medworm.com/rss/comments.php?id=828685 Wed, 29 Aug 2007 04:00:00 +0100 828685 http://www.medworm.com/index.php?rid=828684&cid=s_22297_23_f&fid=22297&url=http%3A%2F%2Fshm.sagepub.com%2Fcgi%2Fcontent%2Fabstract%2F6%2F3%2F177%3Frss%3D1 In this study, the effects of change in environmental temperature on the frequencies and mode shape curvatures of a cable-stayed bridge are analyzed considering seasonal temperature difference (a uniform temperature difference) and sunshine temperature difference (an asymmetric temperature difference). Changes in dynamic characteristics due to temperature variation are compared to changes in dynamic characteristics due to damage of girders and cables in a cable-stayed bridge. Guidelines are presented in this study to explain how frequencies and mode shape curvatures change due to average and asymmetric temperature variations in the cable-stayed bridge. An important conclusion is that changes in dynamic characteristics of the bridge due to damage in girders or cables may be smaller than cha... Structural Health Monitoring journals http://www.medworm.com/rss/comments.php?id=828684 Wed, 29 Aug 2007 04:00:00 +0100 828684 http://www.medworm.com/index.php?rid=661104&cid=s_22297_23_f&fid=22297&url=http%3A%2F%2Fshm.sagepub.com%2Fcgi%2Fcontent%2Fabstract%2F6%2F2%2F145%3Frss%3D1 Error metrics based on nonlinear dynamical predictive models has been implemented earlier to determine discrepancies or nonstationarity in time series caused by external sources, such as noise or filtering. The structural health monitoring (SHM) field has adapted various forms of such prediction error metrics for damage detection. This process usually requires randomly selecting a number of fiducial points on a reconstructed attractor, tracking their time evolutions, and then comparing them to a corresponding set (in a general sense) of points on another attractor. Such an approach has been successful, but it is a process that is globally averaged over the whole data set. However, changes to dynamics resulting from processes such as damage may only noticeably affect small regions within st... Structural Health Monitoring journals http://www.medworm.com/rss/comments.php?id=661104 Thu, 07 Jun 2007 04:00:00 +0100 661104 http://www.medworm.com/index.php?rid=661103&cid=s_22297_23_f&fid=22297&url=http%3A%2F%2Fshm.sagepub.com%2Fcgi%2Fcontent%2Fabstract%2F6%2F2%2F133%3Frss%3D1 This article summarizes the packaging design and manufacture method of such long-gage FBG sensors and verifies the performance of the developed sensors and the distributed sensing system by using a series connection of long-gage FBG sensors. Combined with the practical application in steel and reinforced concrete (RC) structures, the efficiency and ascendancy of the proposed distributed fiber optic sensing system in SHM are elaborated. (Source: Structural Health Monitoring) Structural Health Monitoring journals http://www.medworm.com/rss/comments.php?id=661103 Thu, 07 Jun 2007 04:00:00 +0100 661103 http://www.medworm.com/index.php?rid=661102&cid=s_22297_23_f&fid=22297&url=http%3A%2F%2Fshm.sagepub.com%2Fcgi%2Fcontent%2Fabstract%2F6%2F2%2F121%3Frss%3D1 This study presents two wavelet approaches to overcome the difficulties in the on-board monitoring and detection systems of rail wheel flats using vibration signals. Signal average techniques, wavelet local energy average concept, and wavelet decomposition are employed in this study. A Matlab-Simulink based dynamic simulation system capable of modeling the wheel flats and track irregularities is also developed for predicting the wheelset/bogie frame acceleration time series. An analysis of the numerical simulation results demonstrates that the methods proposed in this study are effective for the on-board monitoring of wheel flats of sizes smaller than the condemning limits. (Source: Structural Health Monitoring) Structural Health Monitoring journals http://www.medworm.com/rss/comments.php?id=661102 Thu, 07 Jun 2007 04:00:00 +0100 661102 http://www.medworm.com/index.php?rid=661101&cid=s_22297_23_f&fid=22297&url=http%3A%2F%2Fshm.sagepub.com%2Fcgi%2Fcontent%2Fabstract%2F6%2F2%2F111%3Frss%3D1 The process of performing nondestructive evaluation (NDE) on a structural system is a well developed and continuously growing field. One very prominent method of performing NDE on a structure is through the use of eddy currents. Eddy current NDE methods are commonly applied to aircraft during maintenance checks in order to identify the formation of cracks, corrosion, or degradation of rivets. Structural health monitoring (SHM) takes NDE a step further and is a process of periodically or continuously monitoring and assessing the performance and safety of a structural system based on data obtained from a sensing system integrated into the structure. Here a method of integrating an eddy current sensing system into the structure such that the structure can be remotely monitored in an automated... Structural Health Monitoring journals http://www.medworm.com/rss/comments.php?id=661101 Thu, 07 Jun 2007 04:00:00 +0100 661101 http://www.medworm.com/index.php?rid=661100&cid=s_22297_23_f&fid=22297&url=http%3A%2F%2Fshm.sagepub.com%2Fcgi%2Fcontent%2Fabstract%2F6%2F2%2F99%3Frss%3D1 A combined analytical and experimental study is conducted to develop efficient and effective damage detection techniques for beam-type structures. Unlike many other vibration-based damage detection methods, in which the mode shapes are often chosen to retrieve damage information, the uniform load surface (ULS) is employed in this study due to its less sensitivity to ambient noise. In combination with the ULS, two new damage detection algorithms, i.e., the generalized fractal dimension (GFD) and simplified gapped-smoothing (SGS) methods, are proposed. The GFD method is developed by modifying the conventional definition of fractal dimension. By using a moving window, the GFD of ULS can be obtained for each sampling point, and due to the irregularity of ULS introduced by the damage, a peak ex... Structural Health Monitoring journals http://www.medworm.com/rss/comments.php?id=661100 Thu, 07 Jun 2007 04:00:00 +0100 661100 http://www.medworm.com/index.php?rid=456993&cid=s_22297_23_f&fid=22297&url=http%3A%2F%2Fshm.sagepub.com%2Fcgi%2Fcontent%2Fabstract%2F6%2F1%2F81%3Frss%3D1 In this study, the spectral element method (SEM) is used in combination with electric circuit analysis for impedance modeling. SEM more accurately models higher frequency vibrations than finite element methods since the mass is modeled exactly and it incorporates higher order models more easily. Simulations of sensor multiplexing, high frequency response, and the inclusion of damage are presented. Experimental verification is also included. (Source: Structural Health Monitoring) Structural Health Monitoring journals http://www.medworm.com/rss/comments.php?id=456993 Wed, 28 Feb 2007 05:00:00 +0100 456993 http://www.medworm.com/index.php?rid=456992&cid=s_22297_23_f&fid=22297&url=http%3A%2F%2Fshm.sagepub.com%2Fcgi%2Fcontent%2Fabstract%2F6%2F1%2F67%3Frss%3D1 The harmonic displacement response of a beam is utilized as the input signal function in wavelet analysis. Sudden changes in the spatial variation of transformed response identify the location of damages and defects. The damage incurred causes a change in the stiffness or mass of the beam. This causes a localized singularity which can be identified by a wavelet analysis of the displacement response. In this article, it is shown that using harmonic response is superior to the static deflection response and this approach is more effective in the presence of noise and more sensitive to the versatility of the applied harmonic loads. (Source: Structural Health Monitoring) Structural Health Monitoring journals http://www.medworm.com/rss/comments.php?id=456992 Wed, 28 Feb 2007 05:00:00 +0100 456992 http://www.medworm.com/index.php?rid=456991&cid=s_22297_23_f&fid=22297&url=http%3A%2F%2Fshm.sagepub.com%2Fcgi%2Fcontent%2Fabstract%2F6%2F1%2F49%3Frss%3D1 This study presents some results from the field trials of the techniques developed in (Lee, M.L., Chiu, W.K. and Koss, L.L (2005). A numerical study into the reconstruction of impact forces on railway track-like structures. Structural Health Monitoring: An International Journal, 4(1), 19–45. Lee, M.L. and Chiu, W.K (2005). The reconstruction of dynamic impact forces on a railway track-like structure by using an inverse analysis technique. In: Proceedings of the 4th Australasian Congress of Applied Mechanics, pp. 605–610, Melbourne, Australia. Lee, M.L. and Chiu, W.K. (2005). A comparative study on impact force prediction on a railway track-like structure. Structural Health Monitoring: An International Journal, 4(4), 355–376.). A length of track carrying freight rail traff... Structural Health Monitoring journals http://www.medworm.com/rss/comments.php?id=456991 Wed, 28 Feb 2007 05:00:00 +0100 456991 http://www.medworm.com/index.php?rid=456990&cid=s_22297_23_f&fid=22297&url=http%3A%2F%2Fshm.sagepub.com%2Fcgi%2Fcontent%2Fabstract%2F6%2F1%2F39%3Frss%3D1 This article assesses quantitatively the future needs for bridge diagnostics of structurally deficient bridges through structural health monitoring. Logistic components of bridge diagnostics are also discussed. The detailed aspects are intended to help, plan, and manage financial resources and implementation practices for bridge evaluation. (Source: Structural Health Monitoring) Structural Health Monitoring journals http://www.medworm.com/rss/comments.php?id=456990 Wed, 28 Feb 2007 05:00:00 +0100 456990 http://www.medworm.com/index.php?rid=456989&cid=s_22297_23_f&fid=22297&url=http%3A%2F%2Fshm.sagepub.com%2Fcgi%2Fcontent%2Fabstract%2F6%2F1%2F25%3Frss%3D1 This study proposes the use of S-transformation techniques to identify the frequency–time domain characteristics and to reduce the noise of the signals at the receiver. Two time domain models, time delay–attenuation (DA) and time delay–attenuation–phase (DAP), are utilized to represent the propagation of Lamb waves in a compact and meaningful model. The parameters of the models are estimated by using genetic algorithm (GA) techniques. The results of the study show that the DA and DAP models work effectively on the simulated and experimental data. (Source: Structural Health Monitoring) Structural Health Monitoring journals http://www.medworm.com/rss/comments.php?id=456989 Wed, 28 Feb 2007 05:00:00 +0100 456989 http://www.medworm.com/index.php?rid=456988&cid=s_22297_23_f&fid=22297&url=http%3A%2F%2Fshm.sagepub.com%2Fcgi%2Fcontent%2Fabstract%2F6%2F1%2F5%3Frss%3D1 In this article, a new damage-sensitive parameter based on bending moment response power spectral density (MSD) is presented for damage identification in two-dimensional plate-like structures. The total energy or the average output power under the bending MSD graph quantified by the zero order moment of the response spectral density, known as mean square value (MSV), is implemented as a principal response parameter. Damage indices (DIs) derived from MSV, namely relative changes in MSV, mean square value curvature (MSVC), normalized damage index, and relative root mean square error (RRMSE) are then used to detect and localize structural damage. The effectiveness of this approach is illustrated by comparing the results with those obtained from existing and well-established techniques, namely... Structural Health Monitoring journals http://www.medworm.com/rss/comments.php?id=456988 Wed, 28 Feb 2007 05:00:00 +0100 456988 http://www.medworm.com/index.php?rid=299220&cid=s_22297_23_f&fid=22297&url=http%3A%2F%2Fshm.sagepub.com%2Fcgi%2Freprint%2F5%2F4%2F389%3Frss%3D1 (Source: Structural Health Monitoring) Structural Health Monitoring journals http://www.medworm.com/rss/comments.php?id=299220 Thu, 30 Nov 2006 07:00:00 +0100 299220 http://www.medworm.com/index.php?rid=299219&cid=s_22297_23_f&fid=22297&url=http%3A%2F%2Fshm.sagepub.com%2Fcgi%2Fcontent%2Fabstract%2F5%2F4%2F373%3Frss%3D1 A passive acoustic method is developed for material damage detection and location in homogeneous thin metallic sheets and sandwich panels using non-contact acoustic transmission measurements. Theoretical models of a flat sheet and sandwich panel are developed to describe the effects of global material damage due to density, modulus, or thickness changes on backplane radiated sound pressure level distributions. To describe the effects of local material damage, a two-dimensional, three-segment stepped beam model is developed. It is shown that increases in transmitted sound energy at high frequencies occur behind a damaged material component that exhibits changes in thickness or other geometric or material property. Experiments o... Structural Health Monitoring journals http://www.medworm.com/rss/comments.php?id=299219 Thu, 30 Nov 2006 07:00:00 +0100 299219 http://www.medworm.com/index.php?rid=299218&cid=s_22297_23_f&fid=22297&url=http%3A%2F%2Fshm.sagepub.com%2Fcgi%2Fcontent%2Fabstract%2F5%2F4%2F355%3Frss%3D1 This research proposes and experimentally implements a new method to identify the location and magnitude of a single impulsive excitation to body armor. The technique could easily be extended to other components that undergo rigid body dynamics. Impact loads are identified in two steps. First, the location of the impact force is determined from time domain acceleration responses by comparing them to attributes of either reference acceleration time histories or the responses generated by a proposed Newtonian analytical model. Then based on that location, appropriate reference frequency response functions are used to reconstruct the input force in the frequency domain through a least squares inverse problem. Both the analytical ... Structural Health Monitoring journals http://www.medworm.com/rss/comments.php?id=299218 Thu, 30 Nov 2006 07:00:00 +0100 299218 http://www.medworm.com/index.php?rid=299217&cid=s_22297_23_f&fid=22297&url=http%3A%2F%2Fshm.sagepub.com%2Fcgi%2Fcontent%2Fabstract%2F5%2F4%2F343%3Frss%3D1 The characteristics of a PZT ceramic element embedded in concrete are studied in this article. Based on the theory that the material coefficients of ceramic change their values under different stress levels, a method of measuring concrete stress by detecting the characteristics of the embedded ceramic element is proposed. The experiment uses a network analyzer to monitor some physical parameters of the piezoelectric element during the loading cycle in which the loads are applied on a concrete specimen with an embedded PZT ceramic. In order to describe the characteristic change from the aspect of energy losses, three dissipation factors are also obtained from the piezoelectric equations. The experimental results show th... Structural Health Monitoring journals http://www.medworm.com/rss/comments.php?id=299217 Thu, 30 Nov 2006 07:00:00 +0100 299217 http://www.medworm.com/index.php?rid=299216&cid=s_22297_23_f&fid=22297&url=http%3A%2F%2Fshm.sagepub.com%2Fcgi%2Fcontent%2Fabstract%2F5%2F4%2F333%3Frss%3D1 This study is concerned with the acoustic tomography method, using measurements of primary wave (P-wave) travel time. In the first step, the principle of the technique is described. Then, the ability of this technique to assess the quality of concrete dams is discussed through two field surveys. It is shown that the acoustic tomography technique enables the evaluation of a large volume of material compared to other conventional nondestructive testing technologies. The benefit of this technique is more evident in identifying the location of anomalous zones that require further investigation and/or restoration work. (Source: Structural Health Monitoring) Structural Health Monitoring journals http://www.medworm.com/rss/comments.php?id=299216 Thu, 30 Nov 2006 07:00:00 +0100 299216 http://www.medworm.com/index.php?rid=299215&cid=s_22297_23_f&fid=22297&url=http%3A%2F%2Fshm.sagepub.com%2Fcgi%2Fcontent%2Fabstract%2F5%2F4%2F325%3Frss%3D1 The centrifugal pump has a long history of frequent failure of anti-friction bearing since its commissioning in 1985. Vibration based conventional condition monitoring has regularly been used to identify the progressive nature of the bearing failure, but has failed to identify the root cause. Modal tests have been conducted on the pump assembly to understand the dynamics of the complete assembly. A typical case of the resonance of the bearing pedestals with 2X component (two times the pump RPM) of the response during pump operation mainly due to nonlinear interaction between the pump foundation and the concrete floor has been identified as the main source of the bearing failure. The results, observations, and the diagnosis to ... Structural Health Monitoring journals http://www.medworm.com/rss/comments.php?id=299215 Thu, 30 Nov 2006 07:00:00 +0100 299215 http://www.medworm.com/index.php?rid=299214&cid=s_22297_23_f&fid=22297&url=http%3A%2F%2Fshm.sagepub.com%2Fcgi%2Fcontent%2Fabstract%2F5%2F4%2F313%3Frss%3D1 An artificial neural network (ANN) based approach for the assessment of damage in prestressed concrete (PSC) beams using its present stiffness and natural frequency as the test inputs to the ANN has been proposed. The details of the extensive experimental programme designed and executed in this study to induce the known extent of damage in the PSC beams by a method that resembles natural damage processing techniques and to generate the training and test data for the ANN used to model damage levels have been presented. It has been demonstrated that it is possible to assess the damage with reasonable accuracy by the ANN learning by a back propagation algorithm and stiffness and natural frequency as test inputs. The effic... Structural Health Monitoring journals http://www.medworm.com/rss/comments.php?id=299214 Thu, 30 Nov 2006 07:00:00 +0100 299214 http://www.medworm.com/index.php?rid=148932&cid=s_22297_23_f&fid=22297&url=http%3A%2F%2Fshm.sagepub.com%2Fcgi%2Fcontent%2Fabstract%2F5%2F3%2F297%3Frss%3D1 This study improves the general guided-wave technique with magnetostrictive transducers for the detection and sizing of defects in strands. The improvement consists of extracting sensitive and robust features of the wave signals, and then using these features to construct a damage index (D.I.). The proposed D.I. is unaffected by accidental variations in the excitation power or by changes in the electromechanical coupling efficiency of the transducers. The specific defect under investigation is a notch cut at varying depths in a strand that is subjected to a typical operational load. Features extracted after discrete wavelet processing of the wave signals result in a D.I. that is robust against noise and is linearly rel... Structural Health Monitoring journals http://www.medworm.com/rss/comments.php?id=148932 Thu, 17 Aug 2006 06:00:00 +0100 148932 http://www.medworm.com/index.php?rid=148931&cid=s_22297_23_f&fid=22297&url=http%3A%2F%2Fshm.sagepub.com%2Fcgi%2Fcontent%2Fabstract%2F5%2F3%2F267%3Frss%3D1 This article presents a utilitarian view of WT and its technologies. By reviewing the state-of-the-art in WT for SHM, the article discusses specific needs of SHM addressed by WT, classifies WT for damage detection into various fields, and describes features unique to WT that lends itself to SHM. The ultimate intent of this article is to provide the readers with a background on the various aspects of WT that might appeal to their need and sector of interest in SHM. Additionally, the comprehensive literature review that comprises this study will provide the interested reader a focused search to investigate using wavelets in SHM. (Source: Structural Health Monitoring) Structural Health Monitoring journals http://www.medworm.com/rss/comments.php?id=148931 Thu, 17 Aug 2006 06:00:00 +0100 148931 http://www.medworm.com/index.php?rid=148930&cid=s_22297_23_f&fid=22297&url=http%3A%2F%2Fshm.sagepub.com%2Fcgi%2Fcontent%2Fabstract%2F5%2F3%2F255%3Frss%3D1 In the present work, the effect of delamination or debonding on the static and dynamic characteristics of laminated piezoelectric beams and plates is studied. A four-noded quadrilateral shear flexible plate element is developed to model the damages in composite substrate and in piezoelectric layers. The elastic stiffness and electro-elastic stiffness degradations are introduced at the elemental level through coupled constitutive relations. The undamaged structure is modeled as a single laminate while the delaminated region is modeled as sublaminates whose interface contains the desired delamination or debonding. The continuity of displacement is maintained across the delaminated edge by imposing the strain-based multip... Structural Health Monitoring journals http://www.medworm.com/rss/comments.php?id=148930 Thu, 17 Aug 2006 06:00:00 +0100 148930 http://www.medworm.com/index.php?rid=148929&cid=s_22297_23_f&fid=22297&url=http%3A%2F%2Fshm.sagepub.com%2Fcgi%2Fcontent%2Fabstract%2F5%2F3%2F243%3Frss%3D1 The feasibility of imaging low-velocity impact damage in thin multi-layered composite plates using Lamb wave tomography is explored. Low-velocity impact damages (6-20 J) are induced by the drop-weight method on graphite fiber epoxy matrix composite laminates of cross-ply and quasi-isotropic lay-up and the damage assessment is carried out by conventional C-scans and ultrasonic Lamb wave tomography. Lamb wave based tomography based on modified cross-hole sensor configuration is used to image the damage as a function of impact energy for graphite composite plates. The reconstructed tomograms are able to capture the lateral extent of the damage even for impact energies as low as 11 J in a 2 mm graphite epoxy quasi-isotropic lay-up... Structural Health Monitoring journals http://www.medworm.com/rss/comments.php?id=148929 Thu, 17 Aug 2006 06:00:00 +0100 148929 http://www.medworm.com/index.php?rid=148928&cid=s_22297_23_f&fid=22297&url=http%3A%2F%2Fshm.sagepub.com%2Fcgi%2Fcontent%2Fabstract%2F5%2F3%2F215%3Frss%3D1 This article presents a survey of some of the more commonly used algorithms and describes the conditions under which they may or may not work. The success of individual algorithms is measured through computer simulation studies. It may, however, be noted that additional practical difficulties that cannot entirely be reproduced through computer simulation exist, which makes vibration-based damage identification a challenging field with many unanswered questions. (Source: Structural Health Monitoring) Structural Health Monitoring journals http://www.medworm.com/rss/comments.php?id=148928 Thu, 17 Aug 2006 06:00:00 +0100 148928 http://www.medworm.com/index.php?rid=148927&cid=s_22297_23_f&fid=22297&url=http%3A%2F%2Fshm.sagepub.com%2Fcgi%2Fcontent%2Fabstract%2F5%2F3%2F205%3Frss%3D1 This article presents the real-time strain measurement of a composite liquid hydrogen (LH2) tank using fiber Bragg grating (FBG) sensors. The tank was composed of carbon fiber reinforced plastic (CFRP), and an aluminum liner was fabricated by the filament winding method and mounted on a reusable rocket. This rocket (vertical takeoff and landing) is called a reusable rocket vehicle test (RVT) and was developed by the Institute of Space and Astronautical Science of the Japan Aerospace Exploration Agency (ISAS/JAXA). Considering the high operational pressure and the iterative use of the tank, its structural integrity must be guaranteed. Thus, the authors have attempted a real-time strain measurement of the composite LH2 t... Structural Health Monitoring journals http://www.medworm.com/rss/comments.php?id=148927 Thu, 17 Aug 2006 06:00:00 +0100 148927 http://www.medworm.com/index.php?rid=5376&cid=s_22297_23_f&fid=22297&url=http%3A%2F%2Fshm.sagepub.com%2Fcgi%2Fcontent%2Fabstract%2F5%2F2%2F195%3Frss%3D1 The multistage helical transmission gearbox in the present study is driven by an induction motor and is coupled to a DC generator, which is connected to an electrical resistance bank for loading purposes. One and two teeth are artificially removed in one gear of the gearbox to simulate actual fault condition. When the gearbox is operated under several loads, the vibration signals are acquired from the tail-end bearing of the gearbox, and simultaneously the current drawn by the induction motor is acquired and monitored. For signal analysis, discrete wavelet transform is applied to the current and vibration signal. Subsequently, short-time Fourier transform (STFT) was applied to the level that contains information of the ... Structural Health Monitoring journals http://www.medworm.com/rss/comments.php?id=5376 Tue, 09 May 2006 06:00:00 +0100 5376 http://www.medworm.com/index.php?rid=5375&cid=s_22297_23_f&fid=22297&url=http%3A%2F%2Fshm.sagepub.com%2Fcgi%2Fcontent%2Fabstract%2F5%2F2%2F185%3Frss%3D1 This article presents the architecture of a multi-tier, complex remote diagnostics system by applying CORBA. Functionality for each tier of the architecture is elaborated. A remote diagnostic system is then implemented and applied to the diagnosis of mechanical equipment in a large-scale iron and steel corporation. The system can cross platforms, including heterogeneous hardware and software, operating systems, and network protocols. Some results of remote diagnosis in the large-scale iron and steel plant are presented. The advantages of remote diagnosis for the industrial system under consideration are discussed. (Source: Structural Health Monitoring) Structural Health Monitoring journals http://www.medworm.com/rss/comments.php?id=5375 Tue, 09 May 2006 06:00:00 +0100 5375 http://www.medworm.com/index.php?rid=5374&cid=s_22297_23_f&fid=22297&url=http%3A%2F%2Fshm.sagepub.com%2Fcgi%2Fcontent%2Fabstract%2F5%2F2%2F173%3Frss%3D1 This article discusses experimental and analytical efforts focused on estimating fastener damage in a square aluminum plate test article. Fastener condition is estimated using classifiers based on statistical pattern recognition methods. The classifiers utilize features from measured vibration data with the ability to discriminate between damage conditions. Finite element analyses are used to provide a physical understanding of the structural dynamics of the aluminum plate and an interpretation of the selected features used for the classifier. Techniques to detect, locate, and assess damage resulting due to fastener failure have been investigated. The classification systems presented perform reasonably well in detectin... Structural Health Monitoring journals http://www.medworm.com/rss/comments.php?id=5374 Tue, 09 May 2006 06:00:00 +0100 5374 http://www.medworm.com/index.php?rid=5373&cid=s_22297_23_f&fid=22297&url=http%3A%2F%2Fshm.sagepub.com%2Fcgi%2Fcontent%2Fabstract%2F5%2F2%2F155%3Frss%3D1 Although many algorithms have been developed in the last two decades to detect damage in civil structures using dynamic properties, few studies have considered the challenge imposed by the variability of these properties due to changing environmental conditions. To address this concern, a statistically based analysis is proposed herein to analyze the distribution of identified structural parameters over an unknown number of external conditions and to effectively reduce their influence on the localization of damage. The proposed SHM scheme can be divided into three main steps: (1) identification of modal properties using acceleration responses of the structure to ambient loads under the influence of environmental conditions; (2... Structural Health Monitoring journals http://www.medworm.com/rss/comments.php?id=5373 Tue, 09 May 2006 06:00:00 +0100 5373 http://www.medworm.com/index.php?rid=5372&cid=s_22297_23_f&fid=22297&url=http%3A%2F%2Fshm.sagepub.com%2Fcgi%2Fcontent%2Fabstract%2F5%2F2%2F143%3Frss%3D1 The instrumented long-term continuous health-monitoring system installed on the Tech 21 Bridge during its fabrication is used to evaluate the performance of the instrumentation system itself. The bridge has been continuously monitored for nearly four years to demonstrate its performance. Field monitored results are studied to evaluate the behavior and durability of the bridge structure, components, and material. This evaluation is also studied to determine the level of long-term performance of the instrumented monitoring system in the harsh infrastructure environment. The measured readings of the bridge include the hidden additive of the system’s performance. In addition to the structural behavior, results measur... Structural Health Monitoring journals http://www.medworm.com/rss/comments.php?id=5372 Tue, 09 May 2006 06:00:00 +0100 5372 http://www.medworm.com/index.php?rid=5371&cid=s_22297_23_f&fid=22297&url=http%3A%2F%2Fshm.sagepub.com%2Fcgi%2Fcontent%2Fabstract%2F5%2F2%2F125%3Frss%3D1 A new indicator is proposed to facilitate the detection of newly induced damage in reinforced concrete (RC) beams, based on the transient characteristics of nonlinear vibration. Two full-scale RC beams, one reinforced with externally bonded fiber-reinforced-polymer sheets, are tested to develop the proposed damage indicator. Both beams are statically and dynamically loaded to correlate the dynamic characteristics of the beams to the damage level. A phenomenological model is developed to simulate the general behavior of cracked concrete members with a softening Duffing oscillator. Numerical results and test data show that the indicator rapidly increases with the severity of damage and is very sensitive to cracking even ... Structural Health Monitoring journals http://www.medworm.com/rss/comments.php?id=5371 Tue, 09 May 2006 06:00:00 +0100 5371 http://www.medworm.com/index.php?rid=5370&cid=s_22297_23_f&fid=22297&url=http%3A%2F%2Fshm.sagepub.com%2Fcgi%2Fcontent%2Fabstract%2F5%2F2%2F99%3Frss%3D1 A spectral finite element model (SFEM) for a laminated composite beam with a transverse crack is developed and employed in wave-based diagnostic simulations. Although many simplified models of damage in beams for dynamic analysis have been reported in the literature, their utility in the context of damage severity estimation and related structural health monitoring (SHM) applications is not well addressed. The performance of the present simplified model is compared with detailed 2D finite element model (FEM). To estimate the damage severity, two quantities, namely the strain energy release rate (SERR) and a damage force indicator (DFI) are considered. SERR is a localized damage parameter, which can be employed to predict ... Structural Health Monitoring journals http://www.medworm.com/rss/comments.php?id=5370 Tue, 09 May 2006 06:00:00 +0100 5370 http://www.medworm.com/index.php?rid=5383&cid=s_22297_23_f&fid=22297&url=http%3A%2F%2Fshm.sagepub.com%2Fcgi%2Fcontent%2Fabstract%2F5%2F1%2F83%3Frss%3D1 This article outlines a statistical damage detection engine for the automated characterization of disbonds in bonded structural joints. Unlike other complex pattern recognition algorithms, the statistical technique described in this article is model-independent. This avoids the need to generate accurate numerical models of the structure which is time and resource intensive. Instead, the training data for the damage detection engine is derived from actual measurements of the virgin (undamaged) structure using embedded sensors. The sensor measurements are normalized to remove the effect of varying loads acting on the structure and desensitized to reduce the probability of false alarm before being used to train the statistical ... Structural Health Monitoring journals http://www.medworm.com/rss/comments.php?id=5383 Tue, 14 Feb 2006 07:00:00 +0100 5383 http://www.medworm.com/index.php?rid=5382&cid=s_22297_23_f&fid=22297&url=http%3A%2F%2Fshm.sagepub.com%2Fcgi%2Fcontent%2Fabstract%2F5%2F1%2F69%3Frss%3D1 Stress redistribution and stress drop often coincide with fracture processes. The two experiments that were chosen for our b-value analysis generate failure processes with the corresponding stress drops and stress redistributions. Using acoustic emission analysis, the acoustic waves emitted from the different fracture areas are recorded. The cumulative frequency-magnitude distribution, which leads to the b-value, was originally used in seismology to characterize earthquake populations. Concerning acoustic emissions, the b-value decreases with increasing stress levels. Therefore, it was possible to determine the start of the arise of macro-cracks over time using the b-value analysis. Furthermore, a possible application in a mon... Structural Health Monitoring journals http://www.medworm.com/rss/comments.php?id=5382 Tue, 14 Feb 2006 07:00:00 +0100 5382 http://www.medworm.com/index.php?rid=5381&cid=s_22297_23_f&fid=22297&url=http%3A%2F%2Fshm.sagepub.com%2Fcgi%2Fcontent%2Fabstract%2F5%2F1%2F59%3Frss%3D1 The study presents an application of two different optical measurement techniques for the detection of cracks at the surface of a realistically sized concrete beam subjected to flexural loading conditions. Both techniques provide displacement measurements in a discrete number of points on the surface. Based on these displacement fields, deformations are calculated by means of the Green-Lagrange strain expression. The study deals with the relationship between cracks and the concept of deformation and it examines which of the two methods presented appears to be the most suitable for crack prediction or detection. The study shows that it is possible to detect the appearance and evolution of cracks, even before the cracks ... Structural Health Monitoring journals http://www.medworm.com/rss/comments.php?id=5381 Tue, 14 Feb 2006 07:00:00 +0100 5381 http://www.medworm.com/index.php?rid=5380&cid=s_22297_23_f&fid=22297&url=http%3A%2F%2Fshm.sagepub.com%2Fcgi%2Fcontent%2Fabstract%2F5%2F1%2F45%3Frss%3D1 Distributed sensor networks are emerging as a critical technical driver in the application of structural health monitoring for large-scale structures as a result of their excellent abilities to enhance the reliability and robustness of monitoring systems. One of the key technical opportunities in the implementation of a distributed sensor network is the application of information fusion. Not only does this enable the integration of data from all sensors for the comprehensive assessment of structural conditions, but it also facilitates the combination of decisions or perceptions from multiple sources or different approaches. In this article, the feasibility of combining a distributed sensor network and several technique... Structural Health Monitoring journals http://www.medworm.com/rss/comments.php?id=5380 Tue, 14 Feb 2006 07:00:00 +0100 5380 http://www.medworm.com/index.php?rid=5379&cid=s_22297_23_f&fid=22297&url=http%3A%2F%2Fshm.sagepub.com%2Fcgi%2Fcontent%2Fabstract%2F5%2F1%2F29%3Frss%3D1 This article presents the research, development, and field testing of a computer-controlled integrated instrumentation and monitoring system for rapid-response infrastructure testing and evaluation. The system eliminates both stand-alone laboratory benchtop equipment sets and cable-based, hard-wired, on-site networking for individual sensors. A software-based virtual instrumentation program package is developed to replace conventional data acquisition and monitoring equipment and control all system components through a user-friendly graphical user interface. In addition, a multiple-channel wireless site network throughout the structure is developed to substitute cable networking and integrated in the modular system. Co... Structural Health Monitoring journals http://www.medworm.com/rss/comments.php?id=5379 Tue, 14 Feb 2006 07:00:00 +0100 5379 http://www.medworm.com/index.php?rid=5378&cid=s_22297_23_f&fid=22297&url=http%3A%2F%2Fshm.sagepub.com%2Fcgi%2Fcontent%2Fabstract%2F5%2F1%2F17%3Frss%3D1 An investigation to detect debond in steel-reinforced concrete (RC) using built-in piezoelectric elements has been conducted. Results of the experimental work are presented in Part I of the study. In Part II, numerical solutions using a finite element method are applied to simulate the test results. Parametric studies are performed to evaluate the behavior of the sensor response to the various types of RC structures with debonding damage. Based on the extensive parametric studies, a debond detection algorithm for RC structures is established. (Source: Structural Health Monitoring) Structural Health Monitoring journals http://www.medworm.com/rss/comments.php?id=5378 Tue, 14 Feb 2006 07:00:00 +0100 5378 http://www.medworm.com/index.php?rid=5377&cid=s_22297_23_f&fid=22297&url=http%3A%2F%2Fshm.sagepub.com%2Fcgi%2Fcontent%2Fabstract%2F5%2F1%2F5%3Frss%3D1 This study utilizes built-in piezoelectric discs as sensors and actuators in a pitch-catch mode to generate sensor data, which are sensitive to debond in reinforced concrete. A comparison of sensor measurements or signal changes before and after maintenance or inspection can be correlated to debonding. Both experimental and analytical works are performed during the study. Experimental study and test data are presented in this article. The test results clearly indicate that debond between concrete and rebar and yielding in rebar can be detected with built-in piezoelectric sensors and actuators in a pitch-catch mode. (Source: Structural Health Monitoring) Structural Health Monitoring journals http://www.medworm.com/rss/comments.php?id=5377 Tue, 14 Feb 2006 07:00:00 +0100 5377 http://www.medworm.com/index.php?rid=5390&cid=s_22297_23_f&fid=22297&url=http%3A%2F%2Fshm.sagepub.com%2Fcgi%2Freprint%2F4%2F4%2F393%3Frss%3D1 (No abstract is available for this citation) (Source: Structural Health Monitoring) Structural Health Monitoring journals http://www.medworm.com/rss/comments.php?id=5390 Fri, 11 Nov 2005 07:00:00 +0100 5390 http://www.medworm.com/index.php?rid=5389&cid=s_22297_23_f&fid=22297&url=http%3A%2F%2Fshm.sagepub.com%2Fcgi%2Fcontent%2Fabstract%2F4%2F4%2F377%3Frss%3D1 The aeroelastic characteristics of a cantilevered composite panel of large aspect ratio and with an edge crack are investigated. The panel consists of several fiber-reinforced composite plies, and is modeled with a one-dimensional beam vibrating in coupled bending and torsion. The fundamental mode shapes of the cracked cantilever are used to study the interaction between a crack and aerodynamic characteristics by employing Galerkin’s method. Variation of the divergence/flutter speed with respect to the crack ratio, its location as well as the fiber angle is investigated. The divergence/flutter speed is more sensitive to the bending-torsion coupling parameter than to the presence of the crack. The crack may or may... Structural Health Monitoring journals http://www.medworm.com/rss/comments.php?id=5389 Fri, 11 Nov 2005 07:00:00 +0100 5389 http://www.medworm.com/index.php?rid=5388&cid=s_22297_23_f&fid=22297&url=http%3A%2F%2Fshm.sagepub.com%2Fcgi%2Fcontent%2Fabstract%2F4%2F4%2F355%3Frss%3D1 This study compares impact force prediction on a railway track-like structure by a number of methods. One proposed technique utilized to estimate dynamic impacts on railway tracks involve correlating a root mean square (RMS) calculation of the track response over a selected frequency bandwidth with different impact force levels. Another technique involves the use of strain gauges configured into a full bridge circuit to reconstruct the time history of the impact force on the track structure. A third method utilizes a classical inverse analysis approach to reconstruct the force time history with a calibrated transfer function in the frequency domain. This article uses both finite element and experimental techniques to e... Structural Health Monitoring journals http://www.medworm.com/rss/comments.php?id=5388 Fri, 11 Nov 2005 07:00:00 +0100 5388 http://www.medworm.com/index.php?rid=5387&cid=s_22297_23_f&fid=22297&url=http%3A%2F%2Fshm.sagepub.com%2Fcgi%2Fcontent%2Fabstract%2F4%2F4%2F341%3Frss%3D1 This article presents the experimental results of adopting a geophysical migration technique to interpret the ultrasonic flexural wave signals for the purpose of realizing quantitative damage identification in structures. In this study, a homogeneous isotropic plate is examined with a surface-mounted linear array of piezoelectric ceramic (PZT) disk. The piezoelectric disks function as actuators to excite flexural waves and also as sensors to receive the waves scattered from the structural damage in the plate. A prestack reverse-time migration technique, which is an advanced technique in geophysics to reverse the reflection wavefield and to image the Earth’s interior, is then used to back-propagate the scattering ... Structural Health Monitoring journals http://www.medworm.com/rss/comments.php?id=5387 Fri, 11 Nov 2005 07:00:00 +0100 5387 http://www.medworm.com/index.php?rid=5386&cid=s_22297_23_f&fid=22297&url=http%3A%2F%2Fshm.sagepub.com%2Fcgi%2Fcontent%2Fabstract%2F4%2F4%2F319%3Frss%3D1 Presented in this article is a novel damage detection method based on best approximation of dead load stress redistribution due to damage. It is a simple, economical, fast, and passive method that requires no artificial means of loading. The measurement is made of strain readings due to dead load at different stages of the structure during its life cycle. The approach is by finding a ‘null plane’, which is a unique identity of each structural member, such that the measurement is closest to its orthogonal projection on this null plane. The detection procedure resembles the process of finding the shortest distance from a point to a plane in elementary geometry. Both theoretical proof with a flexibility formul... Structural Health Monitoring journals http://www.medworm.com/rss/comments.php?id=5386 Fri, 11 Nov 2005 07:00:00 +0100 5386 http://www.medworm.com/index.php?rid=5385&cid=s_22297_23_f&fid=22297&url=http%3A%2F%2Fshm.sagepub.com%2Fcgi%2Fcontent%2Fabstract%2F4%2F4%2F301%3Frss%3D1 This article discusses various less-emphasized critical aspects of multidisciplinary research experience on bridge structural health monitoring, to explore dependable evaluation methods, compile practical data on actual bridge monitoring for immediate implementation, and generate focused insight for the development of advanced, reliable, and practical research methods in the future. To reach a systematic conceptualization for a better methodology, various diagnostic components are criticized. The resulting discussions on the various bridge evaluation aspects are practical for transportation agencies, bridge officials, and researchers. The detailed aspects are intended to help select appropriate implementation practices... Structural Health Monitoring journals http://www.medworm.com/rss/comments.php?id=5385 Fri, 11 Nov 2005 07:00:00 +0100 5385 http://www.medworm.com/index.php?rid=5384&cid=s_22297_23_f&fid=22297&url=http%3A%2F%2Fshm.sagepub.com%2Fcgi%2Freprint%2F4%2F4%2F299%3Frss%3D1 (No abstract is available for this citation) (Source: Structural Health Monitoring) Structural Health Monitoring journals http://www.medworm.com/rss/comments.php?id=5384 Fri, 11 Nov 2005 07:00:00 +0100 5384 http://www.medworm.com/index.php?rid=5396&cid=s_22297_23_f&fid=22297&url=http%3A%2F%2Fshm.sagepub.com%2Fcgi%2Fcontent%2Fabstract%2F4%2F3%2F283%3Frss%3D1 Development of efficient methodologies to determine the presence, location, and severity of hidden damage in critical structural components is an important task in the design and construction of structural health monitoring systems in aging as well as new structures. In this article, a methodology for automatic damage identification and localization is presented. The structure is assumed to be instrumented with an array of actuators and sensors to excite and record its dynamic response, including vibration and wave propagation effects. In the vibrational approach, the data consist of the modal response of the structure produced by the actuators while in the wave propagation approach, they are the broadband signals due ... Structural Health Monitoring journals http://www.medworm.com/rss/comments.php?id=5396 Mon, 15 Aug 2005 06:00:00 +0100 5396 http://www.medworm.com/index.php?rid=5395&cid=s_22297_23_f&fid=22297&url=http%3A%2F%2Fshm.sagepub.com%2Fcgi%2Fcontent%2Fabstract%2F4%2F3%2F259%3Frss%3D1 This study investigates the nonlinear dynamic failure characteristics of a notched cantilever beam using numerical finite element models and experiments with various displacement loads at the root of the beam. Damage states of the beam are represented as quasi-static equilibrium points and, subsequently, all significant damage events are modeled as bifurcations (qualitative changes) in the set of stable equilibria for the structure-damage system using a set of low-order normal forms. When analytical models are used to interpret trends in data from the beam as it undergoes different routes to failure, the state-space relationship between estimated crack length and rate of change of crack length exhibits elastic-plastic ... Structural Health Monitoring journals http://www.medworm.com/rss/comments.php?id=5395 Mon, 15 Aug 2005 06:00:00 +0100 5395 http://www.medworm.com/index.php?rid=5394&cid=s_22297_23_f&fid=22297&url=http%3A%2F%2Fshm.sagepub.com%2Fcgi%2Fcontent%2Fabstract%2F4%2F3%2F247%3Frss%3D1 A method for quantifying damage-induced distortions to the vibrational response of an experimental plate is presented. By examining a wavelet representation of the difference in strain response between the damaged and the undamaged structures, the distortion energy may be computed on multiple timescales. This feature is tested in its ability to detect both the presence and the location of degradation of the plate. In addition, the effects of competing excitation mechanisms, including the outputs of Lorenz and Rossler systems, as well as a 0-225 Hz Gaussian noise are studied. The results indicate that the distortion energies, statistically speaking, are significantly higher under damaged conditions compared to those extracted u... Structural Health Monitoring journals http://www.medworm.com/rss/comments.php?id=5394 Mon, 15 Aug 2005 06:00:00 +0100 5394 http://www.medworm.com/index.php?rid=5393&cid=s_22297_23_f&fid=22297&url=http%3A%2F%2Fshm.sagepub.com%2Fcgi%2Fcontent%2Fabstract%2F4%2F3%2F229%3Frss%3D1 The artificial neural receptor system is a new approach that greatly simplifies data acquisition, and hence may enable practical Structural Health Monitoring for large structures. The benefits of the system involve reducing data acquisition channels while maintaining the ability to extract substantial structural response information. The approach presented uses an array of piezoelectric sensors wired to mimic the basic receptor connectivity of the biological nervous system. The method of solving for array outputs from individual sensor strains is demonstrated using a 3-by-3 sensor array. For an N-by-N array of sensors, the number of channels of data acquisition is reduced from N 2 in a conventional system to 2N in the ... Structural Health Monitoring journals http://www.medworm.com/rss/comments.php?id=5393 Mon, 15 Aug 2005 06:00:00 +0100 5393 http://www.medworm.com/index.php?rid=5392&cid=s_22297_23_f&fid=22297&url=http%3A%2F%2Fshm.sagepub.com%2Fcgi%2Fcontent%2Fabstract%2F4%2F3%2F213%3Frss%3D1 In this paper, algorithmic approaches to enhance model correlation and system health monitoring capability are developed in which direct frequency response function (FRF) data are utilized. The algorithmic approaches utilizes the concept of minimum rank perturbation theory. The use of direct FRFs, as opposed to measured modal parameters, is shown to be one method to address a part of the incomplete measurement problem common to model correlation and system health monitoring; namely the mismatch in the number of measured vibration modes in the measured frequency band in comparison to the number of modes included in the analytical finite element model. Key points made in the development are highlighted using numerical and ... Structural Health Monitoring journals http://www.medworm.com/rss/comments.php?id=5392 Mon, 15 Aug 2005 06:00:00 +0100 5392