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. Wed, 08 Feb 2012 19:15:02 +0100 http://www.medworm.com/index.php?rid=5599204&cid=s_22297_23_f&fid=22297&url=http%3A%2F%2Fshm.sagepub.com%2Fcgi%2Fcontent%2Fabstract%2F11%2F1%2F109%3Frss%3D1 This article presents a systematic investigation of power and energy transduction in piezoelectric wafer-active sensors (PWAS) for structural health monitoring (SHM). After a literature review of the state-of-the-art, we developed a predictive modeling of the multi-physics power and energy transduction between structurally guided waves and PWAS in closed-form analytical expressions. The model assumptions include: (a) one-dimensional axial and flexural wave propagations; (b) ideal bonding (pin-force) connection between PWAS and structure; and (c) ideal excitation source at the transmitter PWAS and fully resistive external load at the receiver PWAS. Both wave propagation method for an infinite beam and normal mode expansion method for a finite beam were considered. Frequency response functio... Structural Health Monitoring journals http://www.medworm.com/rss/comments.php?id=5599204 Mon, 09 Jan 2012 05:00:00 +0100 5599204 http://www.medworm.com/index.php?rid=5599203&cid=s_22297_23_f&fid=22297&url=http%3A%2F%2Fshm.sagepub.com%2Fcgi%2Fcontent%2Fabstract%2F11%2F1%2F95%3Frss%3D1 The objective of this article is to explore the relationship between the sensor signal amplitude and crack size through experiments and simulation for estimating the size. Cracks are machined into an aluminum plate and measurements are carried out with ultrasound excitation using piezoelectric transducer arrays that alternate their role as actuators or sensors. Initially, a hole of 2.5 mm diameter is drilled in the plate, and it is gradually machined to a crack with a size up to 50 mm. Signal amplitude is measured from the sensor arrays. The migration technique is used to image the crack and to find the crack location. The maximum received signal amplitude is found to vary linearly with size from simulation and this agrees with measurements with crack size up to 30 mm. The deviation betwee... Structural Health Monitoring journals http://www.medworm.com/rss/comments.php?id=5599203 Mon, 09 Jan 2012 05:00:00 +0100 5599203 http://www.medworm.com/index.php?rid=5599202&cid=s_22297_23_f&fid=22297&url=http%3A%2F%2Fshm.sagepub.com%2Fcgi%2Fcontent%2Fabstract%2F11%2F1%2F83%3Frss%3D1 A time–frequency analysis-based signal processing study for detecting active corrosion in aluminum plate-like structure utilizing the broadband piezoelectric wafer active sensors is presented in this article. Tests were conducted on an aluminum plate with a network of sensors installed on one side of the plate for Lamb wave generation and reception. The corrosion was emulated as material loss of an area of 50 x 38 mm2 on the opposite side of the plate. The corroded area resulted in a thickness loss on the plate and a change in wave propagation as well. The experimental data were first evaluated by a statistical damage index (DI) based on root mean square values and then the Cohen’s class motivated cross-time–frequency analysis. The cross-time–frequency analysis was ... Structural Health Monitoring journals http://www.medworm.com/rss/comments.php?id=5599202 Mon, 09 Jan 2012 05:00:00 +0100 5599202 http://www.medworm.com/index.php?rid=5599201&cid=s_22297_23_f&fid=22297&url=http%3A%2F%2Fshm.sagepub.com%2Fcgi%2Fcontent%2Fabstract%2F11%2F1%2F69%3Frss%3D1 This article presents the results and analysis of Acoustic Emission (AE) as recorded in a reinforced concrete (RC) slab supported by four steel columns and subjected to earthquake-type dynamic loading on a shake table. Fifteen seismic simulations were conducted using an accelerogram registered during the Campano-Lucano earthquake (Italy, 1980). The peak acceleration applied to the shake table was increased until the slab reinforcement was on the brink of yielding and slippage of the bars within the concrete occurred. This limit state is commonly associated with low-to-moderate intensity earthquakes in earthquake-prone regions. The evolution of damage to the slab was monitored in terms of AE energy and the history of plastic strain energy was calculated from the acceleration and displacemen... Structural Health Monitoring journals http://www.medworm.com/rss/comments.php?id=5599201 Mon, 09 Jan 2012 05:00:00 +0100 5599201 http://www.medworm.com/index.php?rid=5599200&cid=s_22297_23_f&fid=22297&url=http%3A%2F%2Fshm.sagepub.com%2Fcgi%2Fcontent%2Fabstract%2F11%2F1%2F51%3Frss%3D1 This article shows that the interpretation of data from a long-term static monitoring can be very helpful for the comprehension of the structural behavior under complex interaction structure–environment. The discussion aims at underlining that a scheduled and unique procedure is very hard to define depending on the great variety of structures and applications and on the right identification of the parameters able to explain structural degradation evolutions or sudden changes. In these cases, a multi-step algorithm with different signal processing techniques applied in cascade seems to be the only reliable approach. The proposed procedure will be carried out using available data from the long-term monitoring of a quay wall in the Port of Genoa, in Italy, but it can be generalized to s... Structural Health Monitoring journals http://www.medworm.com/rss/comments.php?id=5599200 Mon, 09 Jan 2012 05:00:00 +0100 5599200 http://www.medworm.com/index.php?rid=5599199&cid=s_22297_23_f&fid=22297&url=http%3A%2F%2Fshm.sagepub.com%2Fcgi%2Fcontent%2Fabstract%2F11%2F1%2F43%3Frss%3D1 This article presents an in situ imaging method able to detect in real-time the impact source location in reverberant complex composite structures using only one passive sensor. This technique is based on the time reversal acoustic method applied to a number of waveforms stored in a database containing the impulse response (Green’s function) of the structure. The proposed method allows achieving the optimal focalization of the acoustic emission source in the time and spatial domain as it overcomes the drawbacks of other ultrasonic techniques. This is mainly due to the dispersive nature of guided Lamb waves as well as the presence of multiple scattering and mode conversion that can degrade the quality of the focusing, causing poor localization. Conversely, using the benefits of a diff... Structural Health Monitoring journals http://www.medworm.com/rss/comments.php?id=5599199 Mon, 09 Jan 2012 05:00:00 +0100 5599199 http://www.medworm.com/index.php?rid=5599198&cid=s_22297_23_f&fid=22297&url=http%3A%2F%2Fshm.sagepub.com%2Fcgi%2Fcontent%2Fabstract%2F11%2F1%2F27%3Frss%3D1 A novel and effective approach for nondestructive in situ structural health monitoring of a hard-to-inspect location is presented in this article. Laser vibrometry is used to confirm that Lamb waves, generated by low-profile surface bonded piezoceramic transducers, are able to create circumferential creeping waves on the free surface of cylindrical cavities. The behavior of the propagating ultrasonic stress waves around the cavity and their interaction with simulated fatigue damage emanating from the top of the cavity is visualized. The transformation to a cylindrical co-ordinate system is found to be useful in visualizing wave scattering due to the presence of an open notch. Nondestructive evaluation of the structure is shown to be viable with the strength of the scattered spiralling cree... Structural Health Monitoring journals http://www.medworm.com/rss/comments.php?id=5599198 Mon, 09 Jan 2012 05:00:00 +0100 5599198 http://www.medworm.com/index.php?rid=5599197&cid=s_22297_23_f&fid=22297&url=http%3A%2F%2Fshm.sagepub.com%2Fcgi%2Fcontent%2Fabstract%2F11%2F1%2F13%3Frss%3D1 In this study, the Dempster–Shafer (D–S) evidence theory-based approach for structural damage detection is presented. First, the damage basic probability assignment (BPA) function of substructures using each data set measured from the monitored structure is calculated. Then, the D–S evidence theory is employed to combine the individual damage BPAs in order to reach the final damage detection results. To reduce the computational cost of this method when used in complex structures, the preliminary damage range is first localized by modal strain energy method. An experimental investigation on a 20-bay rigid truss structure is carried out to illustrate the identified ability of the proposed approach with considering the uncertainty of model and measurement noise. The results ... Structural Health Monitoring journals http://www.medworm.com/rss/comments.php?id=5599197 Mon, 09 Jan 2012 05:00:00 +0100 5599197 http://www.medworm.com/index.php?rid=5599196&cid=s_22297_23_f&fid=22297&url=http%3A%2F%2Fshm.sagepub.com%2Fcgi%2Fcontent%2Fabstract%2F11%2F1%2F3%3Frss%3D1 Health monitoring is highly dependent on sensor systems that are capable of performing in various engine environmental conditions and able to transmit a signal upon a predetermined crack length, while acting in a neutral form upon the overall performance of the engine system. Efforts are under way at NASA Glenn Research Center through support of the Intelligent Vehicle Health Management Project (IVHM) to develop and implement such sensor technology for a wide variety of applications. These efforts are focused on developing high temperature, wireless, low cost, and durable products. In an effort to address technical issues concerning health monitoring, this article considers data collected from an experimental study using high frequency capacitive sensor technology to capture blade tip clea... Structural Health Monitoring journals http://www.medworm.com/rss/comments.php?id=5599196 Mon, 09 Jan 2012 05:00:00 +0100 5599196 http://www.medworm.com/index.php?rid=5389619&cid=s_22297_23_f&fid=22297&url=http%3A%2F%2Fshm.sagepub.com%2Fcgi%2Fcontent%2Fabstract%2F10%2F6%2F659%3Frss%3D1 The structural health monitoring (SHM) of structures is acquiring a key role in the present time. An in situ system able to assess the health state of bolted joints would save money and maintenance time, by allowing quick assessment of residual life and degradation state of structures. In the last decades, SHM systems based on linear acoustic/ultrasound methods have been investigated extensively. The scope of this study was to develop a reliable index able to assess the loosening/tightening health state of a bolted structure based on linear and nonlinear acoustic/ultrasound parameters. In particular, for the linear acoustic/ultrasound method, a tightening/loosening state index based on the first-order acoustic moment was developed. This method is based on the assumption that a change of si... Structural Health Monitoring journals http://www.medworm.com/rss/comments.php?id=5389619 Mon, 07 Nov 2011 05:00:00 +0100 5389619 http://www.medworm.com/index.php?rid=5389618&cid=s_22297_23_f&fid=22297&url=http%3A%2F%2Fshm.sagepub.com%2Fcgi%2Fcontent%2Fabstract%2F10%2F6%2F643%3Frss%3D1 This article presents and evaluates the underlying technical elements for the development of an integrated inspection software tool that is based on the use of inexpensive digital cameras. For this purpose, digital cameras are appropriately mounted on a structure (e.g., a bridge) and can zoom or rotate in three directions (similar to traffic cameras). They are remotely controlled by an inspector, which allows the visual assessment of the structure's condition by looking at images captured by the cameras. By not having to travel to the structure's site, other issues related to safety considerations and traffic detouring are consequently bypassed. The proposed system gives an inspector the ability to compare the current (visual) situation of a structure with its former condition. If an inspe... Structural Health Monitoring journals http://www.medworm.com/rss/comments.php?id=5389618 Mon, 07 Nov 2011 05:00:00 +0100 5389618 http://www.medworm.com/index.php?rid=5389617&cid=s_22297_23_f&fid=22297&url=http%3A%2F%2Fshm.sagepub.com%2Fcgi%2Fcontent%2Fabstract%2F10%2F6%2F631%3Frss%3D1 This article introduces a hybrid signal processing technique for spindle health monitoring and diagnosis, through the integration of wavelet packet transform and principal feature analysis. Vibration signals measured from a spindle test system with different defect conditions are first decomposed into multiple sub-frequency bands by means of the wavelet packet transform. Statistical parameters such as energy and Kurtosis of these sub-frequency bands are then calculated. Subsequently, Principal Feature Analysis, which is an extension of the Principal Component Analysis, is performed on the statistical parameters to aid in the selection of the most representative features, which can be distinctively separated from each other, as inputs to a diagnostic classifier. Experimental analysis of sen... Structural Health Monitoring journals http://www.medworm.com/rss/comments.php?id=5389617 Mon, 07 Nov 2011 05:00:00 +0100 5389617 http://www.medworm.com/index.php?rid=5389616&cid=s_22297_23_f&fid=22297&url=http%3A%2F%2Fshm.sagepub.com%2Fcgi%2Fcontent%2Fabstract%2F10%2F6%2F617%3Frss%3D1 This article investigates the use of ultrasonic nonlinearity as a means to determine the level of load applied to the strands. Since an axial load on a multi-wire strand generates proportional contact stresses between adjacent wires, ultrasonic nonlinearity from the inter-wire contact must be related to the level of axial load. This article shows that the higher harmonic generation of ultrasonic guided waves propagating in individual wires of the strand indeed changes monotonically with the applied load, with smaller higher harmonic amplitudes with increasing load levels. This trend is consistent with known studies on higher harmonic generation from ultrasonic plane waves incident on a contact interface under a changing contact pressure. The article presents experimental studies on free st... Structural Health Monitoring journals http://www.medworm.com/rss/comments.php?id=5389616 Mon, 07 Nov 2011 05:00:00 +0100 5389616 http://www.medworm.com/index.php?rid=5389615&cid=s_22297_23_f&fid=22297&url=http%3A%2F%2Fshm.sagepub.com%2Fcgi%2Fcontent%2Fabstract%2F10%2F6%2F603%3Frss%3D1 This article improved the global projection denoising algorithm via calculating the optimal time delay and embedding dimension m, which can be regarded as an extension of the global phase space reconstruction. The de-noising effects of Lorenz signal and the experiment cases illustrated the optimal global projection method is very effective and reliable in reducing the noise and reconstructing the signals. Consequently, it is heavily recommended for use in fault diagnosis of large rotating machinery as well as in the other kinds of machinery. (Source: Structural Health Monitoring) Structural Health Monitoring journals http://www.medworm.com/rss/comments.php?id=5389615 Mon, 07 Nov 2011 05:00:00 +0100 5389615 http://www.medworm.com/index.php?rid=5389614&cid=s_22297_23_f&fid=22297&url=http%3A%2F%2Fshm.sagepub.com%2Fcgi%2Fcontent%2Fabstract%2F10%2F6%2F587%3Frss%3D1 The objective of this article is to develop methods for extracting trends from long-term structural health monitoring data and try to set an early warning threshold level based on the results of analyses. The long-term monitoring data in this study is the continuous monitoring of the dam static deformation. Two different approaches were applied to extract features of the long-term structural health monitoring data of the static deformation of the Fei-Tsui Arch Dam (Taiwan). The methods include the singular spectrum analysis with auto regressive model (SSA-AR) and the nonlinear principal component analysis (NPCA) using auto-associative neural network method (AANN). The singular spectrum analysis is a novel nonparametric technique based on principles of multi-variance statistics. An AR model... Structural Health Monitoring journals http://www.medworm.com/rss/comments.php?id=5389614 Mon, 07 Nov 2011 05:00:00 +0100 5389614 http://www.medworm.com/index.php?rid=5389613&cid=s_22297_23_f&fid=22297&url=http%3A%2F%2Fshm.sagepub.com%2Fcgi%2Fcontent%2Fabstract%2F10%2F6%2F573%3Frss%3D1 In the recent years, the piezoelectric wafer active sensors (PWASs) are increasing as a measurement tool in structural health monitoring techniques. In impedance-based structural health monitoring (ISHM) method, the electrical impedance of a PWAS bonded to the structure is measured and served as a defect detection index of the structure. The principle of this method is based on the electromechanical coupling effect of PWAS materials. As any change in the structure will lead to a change in mechanical impedance of structure, the electrical impedance of PWAS could sense this change by the electromechanical coupling effect of PWAS. Since the physical and mechanical properties of PWAS materials are temperature-dependent, so the electrical impedance of PWAS will change with varying temperature. ... Structural Health Monitoring journals http://www.medworm.com/rss/comments.php?id=5389613 Mon, 07 Nov 2011 05:00:00 +0100 5389613 http://www.medworm.com/index.php?rid=5389612&cid=s_22297_23_f&fid=22297&url=http%3A%2F%2Fshm.sagepub.com%2Fcgi%2Fcontent%2Fabstract%2F10%2F6%2F559%3Frss%3D1 The goal of this article is to detect structural damage in the presence of operational and environmental variations using vibration-based damage identification procedures. For this purpose, four machine learning algorithms are applied based on the auto-associative neural network, factor analysis, Mahalanobis distance, and singular value decomposition. A base-excited three-story frame structure was tested in laboratory environment to obtain time-series data from an array of accelerometers under several structural state conditions. Tests were performed with varying stiffness and mass conditions with the assumption that these sources of variability are representative of changing operational and environmental conditions. Damage is simulated through nonlinear effects introduced by a bumper mech... Structural Health Monitoring journals http://www.medworm.com/rss/comments.php?id=5389612 Mon, 07 Nov 2011 05:00:00 +0100 5389612 http://www.medworm.com/index.php?rid=5389611&cid=s_22297_23_f&fid=22297&url=http%3A%2F%2Fshm.sagepub.com%2Fcgi%2Freprint%2F10%2F6%2F557%3Frss%3D1 (Source: Structural Health Monitoring) Structural Health Monitoring journals http://www.medworm.com/rss/comments.php?id=5389611 Mon, 07 Nov 2011 05:00:00 +0100 5389611 http://www.medworm.com/index.php?rid=5164305&cid=s_22297_23_f&fid=22297&url=http%3A%2F%2Fshm.sagepub.com%2Fcgi%2Fcontent%2Fabstract%2F10%2F5%2F539%3Frss%3D1 This article explores the use of principal component analysis (PCA) and T2 and Q-statistic measures to detect and distinguish damages in structures. For this study, two structures are used for experimental assessment: a steel sheet and a turbine blade of an aircraft. The analysis has been performed in two ways: (i) by exciting the structure with low-frequency vibrations using a shaker and using several piezoelectric (PZT) sensors attached on the surface, and (ii) by exciting at high-frequency vibrations using a single PZT as actuator and several PZTs as sensors. A known vibration signal is applied and the dynamical responses are analyzed. A PCA model is built using data from the undamaged structure as a reference base line. The defects in the turbine blade are simulated by attaching a mass... Structural Health Monitoring journals http://www.medworm.com/rss/comments.php?id=5164305 Thu, 25 Aug 2011 23:00:00 +0100 5164305 http://www.medworm.com/index.php?rid=5164304&cid=s_22297_23_f&fid=22297&url=http%3A%2F%2Fshm.sagepub.com%2Fcgi%2Fcontent%2Fabstract%2F10%2F5%2F523%3Frss%3D1 This article presents these findings in a thorough manner, and in doing so conveys the ability of a HMS to provide realistic examples of thermal behavior, to estimate conditions at locations free of measurement devices, and to suggest areas of concern for future manual inspections. Furthermore, it provides evidence that a HMS is not only helpful for bridge design and management, but also for the development of itself. (Source: Structural Health Monitoring) Structural Health Monitoring journals http://www.medworm.com/rss/comments.php?id=5164304 Thu, 25 Aug 2011 23:00:00 +0100 5164304 http://www.medworm.com/index.php?rid=5164303&cid=s_22297_23_f&fid=22297&url=http%3A%2F%2Fshm.sagepub.com%2Fcgi%2Fcontent%2Fabstract%2F10%2F5%2F511%3Frss%3D1 Operational modal analysis is currently applied in structural dynamic monitoring studies using conventional wired-based sensors and data acquisition platforms. However, this approach becomes inadequate in cases in which aesthetic concerns arise (e.g., in cultural heritage buildings) or in which the use of wires greatly impacts the monitoring system cost and creates difficulties in the maintenance and deployment of the data acquisition platforms. In these cases, the use of a WSN and MEMS would clearly benefit the applications. This work illustrates an attempt to apply the wireless technology for the structural health monitoring of historical masonry constructions in the context of operational modal analysis. The article presents the state of the art of the wireless monitoring systems making... Structural Health Monitoring journals http://www.medworm.com/rss/comments.php?id=5164303 Thu, 25 Aug 2011 23:00:00 +0100 5164303 http://www.medworm.com/index.php?rid=5164302&cid=s_22297_23_f&fid=22297&url=http%3A%2F%2Fshm.sagepub.com%2Fcgi%2Fcontent%2Fabstract%2F10%2F5%2F503%3Frss%3D1 This study presents a new source localization methodology to identify the spatial location of active flaws on spaced structures using the acoustic emission (AE) method. The methodology uses the geometric boundaries and the local coordinate system to find the shortest direct paths from the acoustic source to the AE sensors. The structural elements are modeled as 1D so that the source location is determined using linear equations in the local coordinate system. The local source location is converted into the global coordinate system to determine the source location in space. The approach has been successfully demonstrated using computer and laboratory simulations. The use of linear equations to solve the spatial location of the acoustic source in multi-dimensional space reduces the computati... Structural Health Monitoring journals http://www.medworm.com/rss/comments.php?id=5164302 Thu, 25 Aug 2011 23:00:00 +0100 5164302 http://www.medworm.com/index.php?rid=5164301&cid=s_22297_23_f&fid=22297&url=http%3A%2F%2Fshm.sagepub.com%2Fcgi%2Fcontent%2Fabstract%2F10%2F5%2F491%3Frss%3D1 This article proposes an evolutionary algorithm that is able to identify both global and local minima. This is accomplished by including two new operators to a traditional steady-state genetic algorithm. The proposed algorithm uses a single population in contrast to other evolutionary algorithms available in the literature. The algorithm is used to update a model of a structural system and provide the analyst with different plausible solutions for the updated models. Model updating techniques are used to enhance the behavior of numerical models of existing structures based on experimental data. Although the optimal updated model corresponds to the global minimum of the objective function, the model with the best physical representation of the structure could be a local minimum because of m... Structural Health Monitoring journals http://www.medworm.com/rss/comments.php?id=5164301 Thu, 25 Aug 2011 23:00:00 +0100 5164301 http://www.medworm.com/index.php?rid=5164300&cid=s_22297_23_f&fid=22297&url=http%3A%2F%2Fshm.sagepub.com%2Fcgi%2Fcontent%2Fabstract%2F10%2F5%2F481%3Frss%3D1 This article presents an approach to structural health monitoring (SHM) using adaptive filters. The experimental signals from different structural conditions provided by piezoelectric actuators/sensors bonded in the test structure are modeled by a discrete-time recursive least square (RLS) filter. The biggest advantage of using a RLS filter is the clear possibility to perform an online SHM procedure because the identification is also valid for nonstationary linear systems. An online damage-sensitive index feature is computed based on portions of the autoregressive coefficients normalized by the square root of the sum of the squares. The proposed method is then used in a laboratory test involving an aeronautical panel coupled with piezoelectric sensors/actuators (PZTs) in different position... Structural Health Monitoring journals http://www.medworm.com/rss/comments.php?id=5164300 Thu, 25 Aug 2011 23:00:00 +0100 5164300 http://www.medworm.com/index.php?rid=5164299&cid=s_22297_23_f&fid=22297&url=http%3A%2F%2Fshm.sagepub.com%2Fcgi%2Fcontent%2Fabstract%2F10%2F5%2F467%3Frss%3D1 Uniform circular arrays (UCAs) with 360° azimuthal coverage are very useful for structural health monitoring (SHM) of large planar structures. Difficulties encountered when working with Lamb waves include their dispersive and multi-modal nature. In this article three different methods for estimating the direction-of-arrival (DOA) of incoming Lamb waves are compared and verified using simulated and experimental data. The previously proposed phase-mode excitation-based beamformer is compared with two high-resolution spectral estimation techniques, the Capon method and the multiple signal classification method. Design consideration and guidelines for UCAs are presented. To experimentally evaluate the performance of the considered DOA methods a prototype array consisting of 16 separate pin... Structural Health Monitoring journals http://www.medworm.com/rss/comments.php?id=5164299 Thu, 25 Aug 2011 23:00:00 +0100 5164299 http://www.medworm.com/index.php?rid=5164298&cid=s_22297_23_f&fid=22297&url=http%3A%2F%2Fshm.sagepub.com%2Fcgi%2Fcontent%2Fabstract%2F10%2F5%2F449%3Frss%3D1 This study describes the field testing and finite element modeling of an in situ, full-scale, five-girder bridge that is subjected to controlled levels of known damage. The focus of the study is finite element (FE) model calibration to enable the study of damage scenarios including those not imposed during the field tests. Modal parameters are extracted from triaxial vibration records obtained over a relatively dense measurement grid using inexpensive geophones and are used to calibrate a three-dimensional FE model of the bridge. The calibration process and considerations that should be made during field tests for proper model calibration are discussed. Various vibration-based damage detection techniques are evaluated based on their ability to locate the simulated damage. Results show that... Structural Health Monitoring journals http://www.medworm.com/rss/comments.php?id=5164298 Thu, 25 Aug 2011 23:00:00 +0100 5164298 http://www.medworm.com/index.php?rid=5000412&cid=s_22297_23_f&fid=22297&url=http%3A%2F%2Fshm.sagepub.com%2Fcgi%2Freprint%2F10%2F4%2F445%3Frss%3D1 (Source: Structural Health Monitoring) Structural Health Monitoring journals http://www.medworm.com/rss/comments.php?id=5000412 Tue, 05 Jul 2011 23:00:00 +0100 5000412 http://www.medworm.com/index.php?rid=5000411&cid=s_22297_23_f&fid=22297&url=http%3A%2F%2Fshm.sagepub.com%2Fcgi%2Fcontent%2Fabstract%2F10%2F4%2F429%3Frss%3D1 This study presents a modified LMS-based SHM method and a novel two-step structural identification technique using a baseline nonlinear Bouc—Wen structural model to directly identify changes in stiffness due to damage as well as plastic or permanent deflections. The algorithm is designed to be computationally efficient; therefore it can work in real-time. An in silico single-degree-of-freedom (SDOF) nonlinear shear-type structure is used to prove the concept. The efficiency of the proposed SHM algorithm in identifying stiffness changes and plastic/permanent deflections is assessed under different ground motions using a suite of 20 different ground acceleration records. The results show that in a realistic scenario with fixed filter tuning parameters, the proposed LMS-based SHM algori... Structural Health Monitoring journals http://www.medworm.com/rss/comments.php?id=5000411 Tue, 05 Jul 2011 23:00:00 +0100 5000411 http://www.medworm.com/index.php?rid=5000410&cid=s_22297_23_f&fid=22297&url=http%3A%2F%2Fshm.sagepub.com%2Fcgi%2Fcontent%2Fabstract%2F10%2F4%2F417%3Frss%3D1 The degradation process of structural systems is usually due to a combination of reasons such as design or constructive problems, unexpected loading or even natural causes. Such deterioration process results in damaged regions whose main characteristics are localized stiffness decreases in the structure. In this article, the efficiency of a damage detection technique is analyzed through experimental tests and numerical simulations performed in a cantilever beam involving several damage scenarios. The methodology consists of two stages: (i) damage location — determined by means of the strain energy deviation between damaged and undamaged structural vibration modes; and (ii) damage quantification — developed through the analysis of measured natural frequencies of a damaged struct... Structural Health Monitoring journals http://www.medworm.com/rss/comments.php?id=5000410 Tue, 05 Jul 2011 23:00:00 +0100 5000410 http://www.medworm.com/index.php?rid=5000409&cid=s_22297_23_f&fid=22297&url=http%3A%2F%2Fshm.sagepub.com%2Fcgi%2Fcontent%2Fabstract%2F10%2F4%2F403%3Frss%3D1 This article suggests a new technique to deconvolve narrowband and nonstationary ultrasonic signals by means of a time-varying inverse filter. This filter is realized through the application of the matching pursuit decomposition algorithm. The properties of this methodology are quantitatively compared with several onset-time estimation approaches and evaluated with experimental pitch-catch and differential signals between the pristine and the damaged structure. (Source: Structural Health Monitoring) Structural Health Monitoring journals http://www.medworm.com/rss/comments.php?id=5000409 Tue, 05 Jul 2011 23:00:00 +0100 5000409 http://www.medworm.com/index.php?rid=5000408&cid=s_22297_23_f&fid=22297&url=http%3A%2F%2Fshm.sagepub.com%2Fcgi%2Fcontent%2Fabstract%2F10%2F4%2F391%3Frss%3D1 The electromechanical impedance (EMI) method has been regarded as a promising tool for structural health monitoring (SHM) in real time. Usually, massive, high-cost, single-channel impedance analyzers are used to process the time domain data, aiming at obtaining the complex, frequency-dependent, EMI functions, from which features related to the presence, position, and extent of damage can be extracted. However, for large structures, it is desirable to deploy an array of piezoelectric transducers over the area to be monitored and interrogate these transducers successively so as to increase the probability of successful detection of damage in an early phase. In this context, a miniaturized, low-cost, highly expandable SHM architecture for monitoring an array of multiplexed piezoelectric trans... Structural Health Monitoring journals http://www.medworm.com/rss/comments.php?id=5000408 Tue, 05 Jul 2011 23:00:00 +0100 5000408 http://www.medworm.com/index.php?rid=5000407&cid=s_22297_23_f&fid=22297&url=http%3A%2F%2Fshm.sagepub.com%2Fcgi%2Fcontent%2Fabstract%2F10%2F4%2F381%3Frss%3D1 A static-based detection method is proposed in this study to provide an insight to the location and extent of structural damage. The proposed method makes use of the new flexibility disassembly technique and approaches the damage location and extent problem in a decoupled fashion. First, a scheme is developed to determine the damage location by calculating a damage localization vector, which is derived from the static response equation. With location determined, the corresponding damage extent can be easily calculated only by simple arithmetic operations. For selecting the loading location, a simple approach is presented to determine the static load that can activate all parts of a structure to have deformations. The efficiency of the proposed method is demonstrated by three numerical exam... Structural Health Monitoring journals http://www.medworm.com/rss/comments.php?id=5000407 Tue, 05 Jul 2011 23:00:00 +0100 5000407 http://www.medworm.com/index.php?rid=5000406&cid=s_22297_23_f&fid=22297&url=http%3A%2F%2Fshm.sagepub.com%2Fcgi%2Fcontent%2Fabstract%2F10%2F4%2F361%3Frss%3D1 Current and future trends in naval craft design are leaning toward the development of high-speed and high-performance vessels. Lack of information on wave-induced loads for these vessels presents a challenge in ensuring their safety that is best tackled with monitoring operational loads and detecting damage via structural health monitoring (SHM) systems. These monitoring systems, however, require efficient statistical and probabilistic procedures that are able to effectively treat the uncertainties inherent in the massive volumes of collected data and provide interpretable information regarding the reliability and condition of the craft structure. In this article, an approach for using SHM data in the reliability analysis and damage detection in high-speed naval craft (HSNC) under uncertai... Structural Health Monitoring journals http://www.medworm.com/rss/comments.php?id=5000406 Tue, 05 Jul 2011 23:00:00 +0100 5000406 http://www.medworm.com/index.php?rid=5000405&cid=s_22297_23_f&fid=22297&url=http%3A%2F%2Fshm.sagepub.com%2Fcgi%2Fcontent%2Fabstract%2F10%2F4%2F351%3Frss%3D1 This work focuses on the progress of a new analysis technique to detect pipeline leaks and features based on analysis of a pressure transient. The measured time domain signals of these transients were obtained using a single pressure transducer. The instantaneous phase and frequency of the signals are analyzed using the Hilbert transform (HT) and the Hilbert—Huang transform (HHT). Both simulated and experimental pressure signals were used to evaluate the performance of these transforms. The analysis of simulated signals allowed features in the pipeline network such as leaks and pipe ends to be ascribed to features in the signals. Analysis of the experimental tests corroborates the simulated test results when the HT and the HHT analysis are used. (Source: Structural Health Monitoring) Structural Health Monitoring journals http://www.medworm.com/rss/comments.php?id=5000405 Tue, 05 Jul 2011 23:00:00 +0100 5000405 http://www.medworm.com/index.php?rid=5000404&cid=s_22297_23_f&fid=22297&url=http%3A%2F%2Fshm.sagepub.com%2Fcgi%2Fcontent%2Fabstract%2F10%2F4%2F335%3Frss%3D1 This study uses a spectral method to study wave scattering by the local defect in the structural waveguide. The force response is decomposed into some subproblems by combining with standard finite element method with lower computational cost. Dynamic reduction method is used for both the narrowband and wideband analyses of wave scattering by defects or some standard structural features. Numerical study of plate mode scattering by defects indicates that the mode conversions complicate the resultant signal, and a set of modes with different frequencies is necessary to properly estimate the defect type and severity. If the wideband wave modes are generated, some signal processing, such as time-frequency analysis, should be used for mode identification or defect localization. Numerical study c... Structural Health Monitoring journals http://www.medworm.com/rss/comments.php?id=5000404 Tue, 05 Jul 2011 23:00:00 +0100 5000404 http://www.medworm.com/index.php?rid=4776789&cid=s_22297_23_f&fid=22297&url=http%3A%2F%2Fshm.sagepub.com%2Fcgi%2Fcontent%2Fabstract%2F10%2F3%2F309%3Frss%3D1 Civil infrastructure systems experience damage, overloading, aging due to normal operations, severe environmental conditions, and extreme events. These effects change the structural behavior and performance. Novel structural health monitoring (SHM) strategies are increasingly becoming more important to objectively determine the actual condition and these changes. The main objective of this study is to demonstrate the integration of video images and sensor data as promising techniques for the safety of bridges in the context of SHM. The UCF 4-span bridge model is used to demonstrate the method. Image and sensing data are analyzed to obtain unit influence line (UIL) as an index for monitoring the bridge behavior under loading conditions identified using computer vision techniques. UILs are e... Structural Health Monitoring journals http://www.medworm.com/rss/comments.php?id=4776789 Mon, 02 May 2011 23:00:00 +0100 4776789 http://www.medworm.com/index.php?rid=4776788&cid=s_22297_23_f&fid=22297&url=http%3A%2F%2Fshm.sagepub.com%2Fcgi%2Fcontent%2Fabstract%2F10%2F3%2F291%3Frss%3D1 This article deals with some results of a research focused on the development of optimized structural health monitoring (SHM) technologies and data processing techniques for critical structures in seismically prone areas. Specific solutions are proposed to take advantage of seismic early warning systems (SEWSs), which are becoming very popular and effective worldwide. The most relevant aspects of seismic early warning (SEW) and SHM systems are herein reviewed and the main issues related to their integration are discussed in order to properly design the final system. Attention is mainly focused on dynamic behavior in operational conditions and on earthquake effects. Hardware and software solutions adopted for the characterization and monitoring of the dynamic response of a sample building a... Structural Health Monitoring journals http://www.medworm.com/rss/comments.php?id=4776788 Mon, 02 May 2011 23:00:00 +0100 4776788 http://www.medworm.com/index.php?rid=4776787&cid=s_22297_23_f&fid=22297&url=http%3A%2F%2Fshm.sagepub.com%2Fcgi%2Fcontent%2Fabstract%2F10%2F3%2F275%3Frss%3D1 In the field of structural health monitoring of concrete bridges, one of the most challenging problems is the crack identification. In our previous study, we proposed a crack-sensitive skin to monitor the crack initiation and development in a structure and to visualize them remotely using computer. However, the material used in the sensitive skin is not suitable for large-scale structural monitoring. In this article, magnetic wire smart film is proposed for crack monitoring of large-scale concrete structures. Fabrication of the smart film, the working principle of the film, and the application of the film on a real bridge will be presented and discussed. The results show that the smart film is a good technique for crack monitoring of large-scale concrete structures. (Source: Structural Hea... Structural Health Monitoring journals http://www.medworm.com/rss/comments.php?id=4776787 Mon, 02 May 2011 23:00:00 +0100 4776787 http://www.medworm.com/index.php?rid=4776786&cid=s_22297_23_f&fid=22297&url=http%3A%2F%2Fshm.sagepub.com%2Fcgi%2Fcontent%2Fabstract%2F10%2F3%2F261%3Frss%3D1 Damage detection of beam-type components, which are often vital elements in many structures, is crucial for the prevention of failure of the entire structure and potential catastrophic consequences. In this article, the effectiveness of a damage index, referred to as the EMD energy damage index, for damage detection of beams is demonstrated through a set of numerical and experimental investigations. The proposed damage index utilizes the empirical mode decomposition for health assessment of the system based on its vibrational data. In the numerical study, finite element simulation of a cantilevered steel beam with a transverse notch was analyzed and various notch sizes, located at different locations along the beam, were investigated. In the experimental investigation, which used the same ... Structural Health Monitoring journals http://www.medworm.com/rss/comments.php?id=4776786 Mon, 02 May 2011 23:00:00 +0100 4776786 http://www.medworm.com/index.php?rid=4776785&cid=s_22297_23_f&fid=22297&url=http%3A%2F%2Fshm.sagepub.com%2Fcgi%2Fcontent%2Fabstract%2F10%2F3%2F247%3Frss%3D1 Sparse-array structural health monitoring systems based on guided waves have been proposed by many authors, current signals being compared with a baseline obtained when the structure was known to be defect free. An image of the structure in the form of a ‘C-scan’ map showing likely defect locations can be produced by combining information from different sensor pairs in the array. It is generally recognized that temperature compensation is essential for the method to work and various compensation methods have been proposed with good results. However, artifacts are commonly seen in the images, making reliable defect location difficult. This is because, as well as the first reflection from the defect that maps to the correct defect location in the image, shadowing effects occur la... Structural Health Monitoring journals http://www.medworm.com/rss/comments.php?id=4776785 Mon, 02 May 2011 23:00:00 +0100 4776785 http://www.medworm.com/index.php?rid=4776784&cid=s_22297_23_f&fid=22297&url=http%3A%2F%2Fshm.sagepub.com%2Fcgi%2Fcontent%2Fabstract%2F10%2F3%2F235%3Frss%3D1 In structural health monitoring (SHM) of civil structures, data compression is often needed to reduce the cost of data transfer and storage, because of the large volumes of sensor data generated from the monitoring system. The traditional framework for data compression is to first sample the full signal and, then to compress it. Recently, a new data compression method named compressive sampling (CS) that can acquire the data directly in compressed form by using special sensors has been presented. In this article, the potential of CS for data compression of vibration data is investigated using simulation of the CS sensor algorithm. For reconstruction of the signal, both wavelet and Fourier orthogonal bases are examined. The acceleration data collected from the SHM system of Shandong Binzhou... Structural Health Monitoring journals http://www.medworm.com/rss/comments.php?id=4776784 Mon, 02 May 2011 23:00:00 +0100 4776784 http://www.medworm.com/index.php?rid=4617715&cid=s_22297_23_f&fid=22297&url=http%3A%2F%2Fshm.sagepub.com%2Fcgi%2Fcontent%2Fabstract%2F10%2F2%2F231%3Frss%3D1 K. Liu and G. De Roeck. Damage detection of shear connectors in composite bridges - first published as an online first in March 2009 with doi: 10.1177/1475921708102087 and then into the September 2009 issue (8.5) of SHM. The same article was erroneously published with the incorrect doi: 10.1177/1475921709102087 in June 2009 as an online first. The publisher would like to apologize for this error. The correct DOI of the article is 10.1177/1475921708102087 and is available in September 2009 issue [http://shm.sagepub.com/content/8/5.toc] (Source: Structural Health Monitoring) Structural Health Monitoring journals http://www.medworm.com/rss/comments.php?id=4617715 Tue, 22 Mar 2011 00:00:00 +0100 4617715 http://www.medworm.com/index.php?rid=4617714&cid=s_22297_23_f&fid=22297&url=http%3A%2F%2Fshm.sagepub.com%2Fcgi%2Fcontent%2Fabstract%2F10%2F2%2F219%3Frss%3D1 Deterioration and degradation of aging structures is a major concern worldwide. It is often necessary to evaluate the integrity of such structural systems. Early detection and eventual quantification of damage are important for improved safety, to prevent potential catastrophic events, and to extend the service life by repairing/retrofitting the components of the structure. Different methodologies have been proposed in the literature for the identification and localization of damage based on optimization techniques and modal-based approaches. The main drawback in using the optimization approach based on evolutionary algorithms is that it requires the evaluation of the objective function for the total population in each generation. As this is computationally intensive, in this study, a mult... Structural Health Monitoring journals http://www.medworm.com/rss/comments.php?id=4617714 Tue, 22 Mar 2011 00:00:00 +0100 4617714 http://www.medworm.com/index.php?rid=4617713&cid=s_22297_23_f&fid=22297&url=http%3A%2F%2Fshm.sagepub.com%2Fcgi%2Fcontent%2Fabstract%2F10%2F2%2F199%3Frss%3D1 This article presents a basic experimental technique and simplified finite element (FE)-based models for the detection, localization, and quantification of impact damage in composite beams around the barely visible impact damage level. Detection of damage is carried out by shift in modal parameters. Localization of damage is done by a topology optimization tool, which showed that correct damage locations can be found rather efficiently for low-level damage. The novelty of this article is that we develop an all in one package dedicated to impact identification by modal analysis. The damaged zones in the FE models are updated by reducing the most sensitive material property, in order to improve the experimental/ numerical correlation of the frequency response functions. These approximate dam... Structural Health Monitoring journals http://www.medworm.com/rss/comments.php?id=4617713 Tue, 22 Mar 2011 00:00:00 +0100 4617713 http://www.medworm.com/index.php?rid=4617712&cid=s_22297_23_f&fid=22297&url=http%3A%2F%2Fshm.sagepub.com%2Fcgi%2Fcontent%2Fabstract%2F10%2F2%2F189%3Frss%3D1 This article presents a methodology for real-time monitoring of fatigue life in machinery components that utilizes the accumulation of entropy to assess the severity of degradation associated with fatigue. Using this concept, a prototype called the fatigue monitoring unit that automatically shuts down the machine prior to the onset of fatigue fracture based on a user-specified factor of safety is developed. The method is applicable to variable loading and does not require the specification of the loading history or loading sequence. The results of a series of laboratory fatigue tests pertaining to Al 6061-T6 and SS 304 specimens, which show the utility of the approach and its suitability for implementation in the field, are provided. (Source: Structural Health Monitoring) Structural Health Monitoring journals http://www.medworm.com/rss/comments.php?id=4617712 Tue, 22 Mar 2011 00:00:00 +0100 4617712 http://www.medworm.com/index.php?rid=4617711&cid=s_22297_23_f&fid=22297&url=http%3A%2F%2Fshm.sagepub.com%2Fcgi%2Fcontent%2Fabstract%2F10%2F2%2F173%3Frss%3D1 This article reports the determination of hot spot stresses in mining dragline booms, which are often ≥100 m in length, using strain gage measurements and finite element analysis (FEA) modeling as part of a structural health monitoring concept. Strain gages were installed on a typical A11 cluster for estimating hot spot stresses, as recommended in the existing fatigue design guidelines by the International Institute of Welding (IIW) and the International Committee for the Development and Study of Tubular Construction (CIDECT). The results from the experimental measurements and the FEA were found to be comparable to a large measure. It was concluded that while hot spot stresses were high enough at the weld toes to cause cracking, they could not explain the cracking that occurs at the wel... Structural Health Monitoring journals http://www.medworm.com/rss/comments.php?id=4617711 Tue, 22 Mar 2011 00:00:00 +0100 4617711 http://www.medworm.com/index.php?rid=4617710&cid=s_22297_23_f&fid=22297&url=http%3A%2F%2Fshm.sagepub.com%2Fcgi%2Fcontent%2Fabstract%2F10%2F2%2F157%3Frss%3D1 This article presents a solution that eliminates this drawback. The proposed method is tested first on a numerical example. Next, it is verified on the laboratory measurement data, and finally, it is applied to a real structure — a footbridge over a street in Krakow. (Source: Structural Health Monitoring) Structural Health Monitoring journals http://www.medworm.com/rss/comments.php?id=4617710 Tue, 22 Mar 2011 00:00:00 +0100 4617710 http://www.medworm.com/index.php?rid=4617709&cid=s_22297_23_f&fid=22297&url=http%3A%2F%2Fshm.sagepub.com%2Fcgi%2Fcontent%2Fabstract%2F10%2F2%2F147%3Frss%3D1 Structural health monitoring is an emerging area of strategic engineering with a great potential for extending the service life of civil infrastructures and reducing their maintenance costs. In spite of the deflection measurement being one of the main parameters for assessing the real state of a bridge, the measurement techniques and the existing deflection transducers often do not respond to the necessities of structural monitoring. Therefore, a novel displacement transducer to measure bridge deflections based on noncontact measurement technique supported by the liquid leveling method was developed. The measurement of bridge deflections is performed using a hydrostatic level position along the structure as an absolute reference and without any external physical reference to the ground. Fi... Structural Health Monitoring journals http://www.medworm.com/rss/comments.php?id=4617709 Tue, 22 Mar 2011 00:00:00 +0100 4617709 http://www.medworm.com/index.php?rid=4617708&cid=s_22297_23_f&fid=22297&url=http%3A%2F%2Fshm.sagepub.com%2Fcgi%2Fcontent%2Fabstract%2F10%2F2%2F131%3Frss%3D1 This study is applied to a cantilever beam subjected to dynamic loadings. Parametric studies are conducted to investigate the sensitivity of vibrational behavior to the crack angle, depth, and position. The accuracy of the results is validated through comparisons with results available from the literature. (Source: Structural Health Monitoring) Structural Health Monitoring journals http://www.medworm.com/rss/comments.php?id=4617708 Tue, 22 Mar 2011 00:00:00 +0100 4617708 http://www.medworm.com/index.php?rid=4617707&cid=s_22297_23_f&fid=22297&url=http%3A%2F%2Fshm.sagepub.com%2Fcgi%2Fcontent%2Fabstract%2F10%2F2%2F115%3Frss%3D1 This article addresses uncertainty effect on the health monitoring of a smart structure using control gain shifts as damage indicators. A finite element model of the smart composite plate with surface-bonded piezoelectric sensors and actuators is formulated using first-order shear deformation theory and a matrix crack model is integrated into the finite element model. A constant gain velocity/position feedback control algorithm is used to provide active damping to the structure. Numerical results show that the response of the structure is changed due to matrix cracks and this change can be compensated by actively tuning the feedback controller. This change in control gain can be used as a damage indicator for structural health monitoring. Monte Carlo simulation is conducted to study the ef... Structural Health Monitoring journals http://www.medworm.com/rss/comments.php?id=4617707 Tue, 22 Mar 2011 00:00:00 +0100 4617707 http://www.medworm.com/index.php?rid=4425788&cid=s_22297_23_f&fid=22297&url=http%3A%2F%2Fshm.sagepub.com%2Fcgi%2Fcontent%2Fabstract%2F10%2F1%2F83%3Frss%3D1 A comprehensive review on modal parameter-based damage identification methods for beam- or plate-type structures is presented, and the damage identification algorithms in terms of signal processing are particularly emphasized. Based on the vibration features, the damage identification methods are classified into four major categories: natural frequency-based methods, mode shape-based methods, curvature mode shape-based methods, and methods using both mode shapes and frequencies, and their merits and drawbacks are discussed. It is observed that most mode shape-based and curvature mode shape-based methods only focus on damage localization. In order to precisely locate the damage, the mode shape-based methods have to rely on optimization algorithms or signal processing techniques; while the c... Structural Health Monitoring journals http://www.medworm.com/rss/comments.php?id=4425788 Wed, 02 Feb 2011 00:00:00 +0100 4425788 http://www.medworm.com/index.php?rid=4425787&cid=s_22297_23_f&fid=22297&url=http%3A%2F%2Fshm.sagepub.com%2Fcgi%2Fcontent%2Fabstract%2F10%2F1%2F65%3Frss%3D1 The article presents techniques for localization and quantification of defects based on the evaluation of reflection, transmission, and conversion of Lamb wave modes and of the spatial evolution of their phase. Reflection, transmission, and conversion coefficients are estimated using mode separation and incident-wave removal procedures implemented in the frequency/wavenumber domain. The practical implementation of the concept relies on the availability of spatially refined measurements, as provided for example by a Scanning Doppler Laser Vibrometer. The application to simulated and experimental data illustrate the effectiveness of the proposed procedures. Specifically, a finite element model of a 2D elastic domain in plane strain featuring a notch is used to estimate the reflection, transm... Structural Health Monitoring journals http://www.medworm.com/rss/comments.php?id=4425787 Wed, 02 Feb 2011 00:00:00 +0100 4425787 http://www.medworm.com/index.php?rid=4425786&cid=s_22297_23_f&fid=22297&url=http%3A%2F%2Fshm.sagepub.com%2Fcgi%2Fcontent%2Fabstract%2F10%2F1%2F49%3Frss%3D1 The displacement measurement in structural health monitoring (SHM), though important, was not popular due to inaccessibility of the civil infrastructures and high installation cost. The currently popular approaches use accelerometer, strain gauge, PZT, GPS, etc., most of which indirectly measure the displacement and require high cost to install and maintain. Thus the development of SHM system that directly measures the displacement of the structure using low-cost sensors is urgently needed. In this article, a multiple paired structured light (SL) system is proposed as a displacement measurement system for a massive structure. The proposed paired SL module which consists of cheap cameras and lasers is inexpensive to implement and can directly measure the accurate relative displacement betwe... Structural Health Monitoring journals http://www.medworm.com/rss/comments.php?id=4425786 Wed, 02 Feb 2011 00:00:00 +0100 4425786 http://www.medworm.com/index.php?rid=4425785&cid=s_22297_23_f&fid=22297&url=http%3A%2F%2Fshm.sagepub.com%2Fcgi%2Fcontent%2Fabstract%2F10%2F1%2F33%3Frss%3D1 This article presents the application of artificial neural networks (ANNs) for the structural damage detection to bending in the girders of a vehicular bridge. An analytical model of the bridge was developed to generate 12,800 damage scenarios, in which the flexural stiffness of the elements was modified to simulate the damage. Such rigidities were used as output data for the network, while the modal strain energy differences were used as input data. To verify the NNs generalization capability in presence of noise in the measurements, four levels of noise were analyzed (2.5%, 5.0%, 7.5%, and 10.0%). It was observed that the developed NNs model is able to predict with high accuracy the location and severity of the damage in the studied bridge. (Source: Structural Health Monitoring) Structural Health Monitoring journals http://www.medworm.com/rss/comments.php?id=4425785 Wed, 02 Feb 2011 00:00:00 +0100 4425785 http://www.medworm.com/index.php?rid=4425784&cid=s_22297_23_f&fid=22297&url=http%3A%2F%2Fshm.sagepub.com%2Fcgi%2Fcontent%2Fabstract%2F10%2F1%2F17%3Frss%3D1 Transportation agencies commonly have conventionally steel reinforced concrete deck girder (RCDG) bridges in their inventory that were built in the mid-twentieth century. These bridges have been in service beyond their intended design lives and tools are needed to permit freight mobility and maintain operational safety. The practical applicability of AE monitoring techniques were investigated to help estimate the condition of diagonally cracked RCDG bridges. Experiments on two full-scale girder specimens representative of Oregon’s RCDG bridges were built and tested under realistic service conditions. Overloading conditions were imposed to increase the level of deterioration. It was found that characterizing the current health condition of a monitored bridge component or element based... Structural Health Monitoring journals http://www.medworm.com/rss/comments.php?id=4425784 Wed, 02 Feb 2011 00:00:00 +0100 4425784 http://www.medworm.com/index.php?rid=4425783&cid=s_22297_23_f&fid=22297&url=http%3A%2F%2Fshm.sagepub.com%2Fcgi%2Fcontent%2Fabstract%2F10%2F1%2F5%3Frss%3D1 A passive structural health monitoring (SHM) system for locating foreign-object impact using a network of fiber Bragg grating (FBG) sensors that monitor high frequency dynamic strains is described. The FBG sensor signals are adaptively demodulated using a two-wave mixing (TWM) spectral demodulator. Strains applied on the FBG sensors are encoded as wavelength shifts of the light reflected by the FBG sensor which are then converted into phase shifts and demodulated by the TWM interferometer. The demodulator adaptively compensates for low frequency drifts caused by large quasi-static strain and temperature drift and allows only high frequency signals to pass through. The FBG sensor network is mounted on a plate, and the structure is subjected to artificial impacts generated by dropping small ... Structural Health Monitoring journals http://www.medworm.com/rss/comments.php?id=4425783 Wed, 02 Feb 2011 00:00:00 +0100 4425783 http://www.medworm.com/index.php?rid=4079292&cid=s_22297_23_f&fid=22297&url=http%3A%2F%2Fshm.sagepub.com%2Fcgi%2Fcontent%2Fabstract%2F9%2F6%2F555%3Frss%3D1 This article discusses a nonintrusive corrosion monitoring technique for early detection of damages in steel embedded in concrete. Corrosion manifests itself in debond and pitting steel bars. Guided ultrasonic waves offer a potentially attractive solution for this problem. But it is imperative to excite the right mode for detection of a particular type of corrosion. In the present work, longitudinal guided ultrasonic waves have been utilized to monitor notch and debond defects in steel bars in concrete simulating pitting and delamination phenomena caused by corrosion. Two ultrasonic techniques of pulse transmission and pulse echo were used to monitor the healthy and damaged specimens. The developed methodology is successfully applied for real time monitoring of RC beam specimens undergoing... Structural Health Monitoring journals http://www.medworm.com/rss/comments.php?id=4079292 Sun, 17 Oct 2010 23:00:00 +0100 4079292 http://www.medworm.com/index.php?rid=4079291&cid=s_22297_23_f&fid=22297&url=http%3A%2F%2Fshm.sagepub.com%2Fcgi%2Fcontent%2Fabstract%2F9%2F6%2F541%3Frss%3D1 The paper demonstrates the application of cross-modulation vibro-acoustic technique for impact-damage detection in composite laminates. A composite plate is monitored for damage resulting from a low-velocity impact. The plate is excited simultaneously with two harmonic signals: a slow amplitude-modulated vibration pumping wave and a constant amplitude-probing wave. The frequency of both the excitation signals coincides with the resonances of the plate. An electromagnetic shaker is used to introduce the pumping wave to the plate. Two surface-bonded, low-profile piezoceramic transducers are used for probing-wave excitation and measurement. The wave modulation is transferred from the pumping wave to the probing wave in the presence of impact damage. This effect is exhibited in a power spectru... Structural Health Monitoring journals http://www.medworm.com/rss/comments.php?id=4079291 Sun, 17 Oct 2010 23:00:00 +0100 4079291 http://www.medworm.com/index.php?rid=4079290&cid=s_22297_23_f&fid=22297&url=http%3A%2F%2Fshm.sagepub.com%2Fcgi%2Fcontent%2Fabstract%2F9%2F6%2F527%3Frss%3D1 Scattering of ultrasonic waves by an elliptical cavity is modeled. The ratio of the semimajor to semiminor axes is varied from 1 to model a cylindrical cavity with a circular cross section to a large value to approximately model a Griffith crack. The distributed point source method (DPSM), which is a Green’s function-based semi-analytical technique, is adapted in the present modeling. DPSM generated results for slit opening and elliptical cavity are compared. In the elliptical cavity model, the entire cavity surface is considered traction free, whereas in the slit model, two parallel crack surfaces are assumed traction free and no special consideration is given to the crack tips. Because a Griffith crack under tensile loads opens like an ellipse, the elliptical cavity with a large se... Structural Health Monitoring journals http://www.medworm.com/rss/comments.php?id=4079290 Sun, 17 Oct 2010 23:00:00 +0100 4079290 http://www.medworm.com/index.php?rid=4079289&cid=s_22297_23_f&fid=22297&url=http%3A%2F%2Fshm.sagepub.com%2Fcgi%2Fcontent%2Fabstract%2F9%2F6%2F513%3Frss%3D1 This article presents a preliminary study with the main purpose of identifying the possibility of developing PWAS transducers for high-temperature applications. After a brief review of the state of the art and of candidate high-temperature piezoelectric materials, the article focuses on the use of gallium orthophosphate (GaPO4) samples in pilot PWAS applications. The investigation started with a number of confidence-building tests that were conducted to verify GaPO4 piezoelectric properties at room temperature and at elevated temperatures in an oven. Electromechanical (E/M) impedance measurements and material characterization tests (scanning electron microscopy, X-ray diffraction, energy dispersive spectrometry) were performed before and after exposure of HT-PWAS to high temperature; it wa... Structural Health Monitoring journals http://www.medworm.com/rss/comments.php?id=4079289 Sun, 17 Oct 2010 23:00:00 +0100 4079289 http://www.medworm.com/index.php?rid=4079288&cid=s_22297_23_f&fid=22297&url=http%3A%2F%2Fshm.sagepub.com%2Fcgi%2Fcontent%2Fabstract%2F9%2F6%2F497%3Frss%3D1 This article presents the results of tests conducted with composite testboxes to study the effect of skin-stiffener separation on the strain profiles. Different types of testboxes were fabricated and tested to compare bolted, co-bonded, and co-cured configurations. Bending loads were applied on the boxes, and the strains were measured near and away from the debonds using both strain gages and fiber Bragg grating sensors. The difference in the strains between healthy and unhealthy boxes are indicative of the presence of the debonds in the structure. These strain differences could be used in conjunction with suitable pattern recognition tools such as neural networks for damage detection and health monitoring. (Source: Structural Health Monitoring) Structural Health Monitoring journals http://www.medworm.com/rss/comments.php?id=4079288 Sun, 17 Oct 2010 23:00:00 +0100 4079288 http://www.medworm.com/index.php?rid=4079287&cid=s_22297_23_f&fid=22297&url=http%3A%2F%2Fshm.sagepub.com%2Fcgi%2Fcontent%2Fabstract%2F9%2F6%2F481%3Frss%3D1 In this study, a real-coded parallel GA is implemented to detect structural damage. The objective function is based on operational modal data; it considers the initial errors in the numerical model. False damage detection is avoided by using damage penalization. The algorithm is verified with two experimental cases. First, a test structure of an airplane subjected to three increasing levels of damage. Second, a multiple cracked reinforced concrete beam that is subjected to a nonsymmetrical increasing static load to introduce cracks. In both cases, the detected damage has a good correspondence with the experimental damage. (Source: Structural Health Monitoring) Structural Health Monitoring journals http://www.medworm.com/rss/comments.php?id=4079287 Sun, 17 Oct 2010 23:00:00 +0100 4079287 http://www.medworm.com/index.php?rid=3905418&cid=s_22297_23_f&fid=22297&url=http%3A%2F%2Fshm.sagepub.com%2Fcgi%2Fcontent%2Fabstract%2F9%2F5%2F465%3Frss%3D1 Wireless sensor networks have attracted attention as a possible solution for applications of periodic and continuous structural health monitoring. Ensuring synchronous data acquisition across wireless nodes in large networks of sensors spatially distributed on a structure is of critical importance for many methods of structural health monitoring, especially those based on analysis of vibration. In this article we present a novel Wireless Intelligent Sensor and Actuator Network (WISAN) addressing the issue of scalability for applications of structural health monitoring. We also present a novel time synchronization algorithm that can keep the synchronization error between any number of globally distributed sensors nodes less than ±23 µs. We show proof of stability for the time s... Structural Health Monitoring journals http://www.medworm.com/rss/comments.php?id=3905418 Thu, 26 Aug 2010 10:33:44 +0100 3905418 http://www.medworm.com/index.php?rid=3905417&cid=s_22297_23_f&fid=22297&url=http%3A%2F%2Fshm.sagepub.com%2Fcgi%2Fcontent%2Fabstract%2F9%2F5%2F447%3Frss%3D1 This article presents a technique for the structural identification of hysteretic oscillators that are characterized by degradation in stiffness. The main assumption of the proposed procedure is that it is possible to replace the expression of the time derivative of the restoring force with a polynomial approximation, characterized by time-varying coefficients. The work aims at generalizing a method that the authors have proposed for hysteretic nondegrading systems: system parameters are evaluated from instantaneous estimates of the time-varying coefficients. The instantaneous estimation, based on optimization techniques, is made possible through the temporal localization of frequency components, i.e., the representation in the joint time—frequency domain. A numerical application con... Structural Health Monitoring journals http://www.medworm.com/rss/comments.php?id=3905417 Thu, 26 Aug 2010 10:33:44 +0100 3905417 http://www.medworm.com/index.php?rid=3905416&cid=s_22297_23_f&fid=22297&url=http%3A%2F%2Fshm.sagepub.com%2Fcgi%2Fcontent%2Fabstract%2F9%2F5%2F433%3Frss%3D1 Demand of composite fuel tank for space vehicles keeps increasing globally in the aerospace industry, and requires of a mean to detect the structural damage or predict its service life. As important and valid tools, in the past years, lots of nondestructive evaluation techniques have been developed, and they are carried out according to a regular time schedule. The structure has to be taken out of service during each inspection, causing serious financial implications for the user. That is why much research effort is now focused on real-time monitoring techniques. Optical grating fiber attracts more and more attention due to its excellent sensing and mechanical performances and ability of monitoring online. But it still can only measure the local deformation, but not the damage that is far ... Structural Health Monitoring journals http://www.medworm.com/rss/comments.php?id=3905416 Thu, 26 Aug 2010 10:33:44 +0100 3905416 http://www.medworm.com/index.php?rid=3905415&cid=s_22297_23_f&fid=22297&url=http%3A%2F%2Fshm.sagepub.com%2Fcgi%2Fcontent%2Fabstract%2F9%2F5%2F413%3Frss%3D1 First, the internal slippage between bare fiber and coating material of current commercial fiber optic sensors (FOSs) has been, experimentally, verified and investigated in this article. Second, two types of effective package methods are proposed to develop non-slippage optical fibers. Finally, the performance of developed nonslippage FOSs are examined and evaluated with a series of experiments, and the thermal expansion coefficient and creep property of the packaged optical fibers are also investigated. The experimental results indicate that the packaged fibers can be used as non-slippage sensors with high sensing performance both on actual and virtual spatial resolution. Especially, the creep property is much more stable than that of the current commercial fibers. (Source: Structural Hea... Structural Health Monitoring journals http://www.medworm.com/rss/comments.php?id=3905415 Thu, 26 Aug 2010 10:33:44 +0100 3905415 http://www.medworm.com/index.php?rid=3905414&cid=s_22297_23_f&fid=22297&url=http%3A%2F%2Fshm.sagepub.com%2Fcgi%2Fcontent%2Fabstract%2F9%2F5%2F401%3Frss%3D1 In this study, an effective method is developed to detect the position of nonlinear components in periodic structures. The detection procedure requires exciting the nonlinear systems only once by using a sinusoidal-like input which has two frequency components. The effectiveness of this method is demonstrated by numerical studies. As the position of a nonlinear component often corresponds to the location of defect in periodic structures, this new method is of great practical significance in fault diagnosis for mechanical and structural systems. (Source: Structural Health Monitoring) Structural Health Monitoring journals http://www.medworm.com/rss/comments.php?id=3905414 Thu, 26 Aug 2010 10:33:44 +0100 3905414 http://www.medworm.com/index.php?rid=3905413&cid=s_22297_23_f&fid=22297&url=http%3A%2F%2Fshm.sagepub.com%2Fcgi%2Fcontent%2Fabstract%2F9%2F5%2F385%3Frss%3D1 This study seeks to examine the effects that a typical data acquisition (DAQ) process has on the signal dimension by examining both simulated and experimental signals. It is concluded that the DAQ process does not substantially alter the embedded dimension of a chaotic signal as long as the digital resolution is at least 12-bits and that increased signal dimension results in decreased damage state resolution. (Source: Structural Health Monitoring) Structural Health Monitoring journals http://www.medworm.com/rss/comments.php?id=3905413 Thu, 26 Aug 2010 10:33:44 +0100 3905413 http://www.medworm.com/index.php?rid=3731628&cid=s_22297_23_f&fid=22297&url=http%3A%2F%2Fshm.sagepub.com%2Fcgi%2Freprint%2F9%2F4%2F379%3Frss%3D1 (Source: Structural Health Monitoring) Structural Health Monitoring journals http://www.medworm.com/rss/comments.php?id=3731628 Wed, 07 Jul 2010 15:05:02 +0100 3731628 http://www.medworm.com/index.php?rid=3731627&cid=s_22297_23_f&fid=22297&url=http%3A%2F%2Fshm.sagepub.com%2Fcgi%2Fcontent%2Fabstract%2F9%2F4%2F361%3Frss%3D1 Based on the distributed fiber optic sensing technique of pulse-prepump Brillouin Optical Time Domain Analysis, this paper proposes an improved conjugated beam method (ICBM) for distributed structural deformation monitoring. Because ICBM is suitable for the combined actions of loads, support settlements and temperature variations, it extends the application of the classical conjugated beam method. Other advantages include the linear and explicit relationship between structural deformation and strain and the fact that all calculation parameters can be easily determined free from random load or section stiffness distribution. Theoretical and experimental investigations are carried out to confirm that the accuracy of deformation monitoring with ICBM in one span of a continuous structure is re... Structural Health Monitoring journals http://www.medworm.com/rss/comments.php?id=3731627 Wed, 07 Jul 2010 15:05:02 +0100 3731627 http://www.medworm.com/index.php?rid=3731626&cid=s_22297_23_f&fid=22297&url=http%3A%2F%2Fshm.sagepub.com%2Fcgi%2Fcontent%2Fabstract%2F9%2F4%2F347%3Frss%3D1 Damage in structural members usually causes stiffness changes that could be linear or nonlinear. Opening and closing fatigue cracks are usually represented by a bilinear stiffness characteristic. This work describes damage identification approach that is based on the changes in statistical properties of randomdec signatures caused by the onset of nonlinearity. The approach is applied to acceleration data collected from a cracked beam. The results suggest that the method allows to detect the crack if excitation level is high enough. Practical difficulties encountered during implementation are also discussed. (Source: Structural Health Monitoring) Structural Health Monitoring journals http://www.medworm.com/rss/comments.php?id=3731626 Wed, 07 Jul 2010 15:05:02 +0100 3731626 http://www.medworm.com/index.php?rid=3731625&cid=s_22297_23_f&fid=22297&url=http%3A%2F%2Fshm.sagepub.com%2Fcgi%2Fcontent%2Fabstract%2F9%2F4%2F341%3Frss%3D1 Fiber Bragg grating (FBG) makes excellent optical strain gauge with high sensitivity and lead-in fiber insensitivity and Brillouin OTDR offers a distributed sensing method along a sensing fiber. Considering the mismatch in the thermal expansion coefficients between fiber and host structure, the optothermo-mechanical equations of FBG sensor and Brillouin tight buffered fiber are conducted. By using temperature-compensated grating and fiber, FBG, and Brillouin measurement systems provide two independent ways to demodulate strain and temperature. The cross-check of redundancy strain and temperature proves the validity of measurement. According to the exploration of Bai Ni-jing No.3 Tunnel by using seismic CT, 110 gratings are installed on 10 monitoring cross sections; additionally, the four d... Structural Health Monitoring journals http://www.medworm.com/rss/comments.php?id=3731625 Wed, 07 Jul 2010 15:05:02 +0100 3731625 http://www.medworm.com/index.php?rid=3731624&cid=s_22297_23_f&fid=22297&url=http%3A%2F%2Fshm.sagepub.com%2Fcgi%2Fcontent%2Fabstract%2F9%2F4%2F323%3Frss%3D1 The current fatigue life estimation methods of railway bridges are generally based on combinations of measured strain histories, Miner’s rule, and railway code provided fatigue curve. Even though the past measured strain histories are available for major bridges, most of the old bridges do not have past strain measurements. Furthermore, in case of existing railway bridges where the detailed loading history is known, Miner’s rule might provide incorrect results because of its omission of load sequence effect. These reasons hinder the usage of current methods to estimate the realistic remaining fatigue life of most of the existing railway bridges. Therefore, a new method is presented in this article to estimate remaining fatigue life of riveted railway bridges. The method mainly ... Structural Health Monitoring journals http://www.medworm.com/rss/comments.php?id=3731624 Wed, 07 Jul 2010 15:05:02 +0100 3731624 http://www.medworm.com/index.php?rid=3731623&cid=s_22297_23_f&fid=22297&url=http%3A%2F%2Fshm.sagepub.com%2Fcgi%2Fcontent%2Fabstract%2F9%2F4%2F309%3Frss%3D1 This article presents the application of two types of fiber optic sensors, which can be embedded in FRP materials to monitor the global and local behavior of the strengthened structure, respectively. The global sensor is designed to evaluate the overall condition of a structure based on the measured elongation of the FRP layer along the entire span of the structure. The success of this low-cost global sensor has been demonstrated using a full-scale prestressed concrete bridge girder that was loaded up to failure. The test results indicate that this type of sensor can be used to identify major changes in the overall behavior of the structure such as cracking of prestressed members or yielding of the internal reinforcement. The second sensor component consists of fiber Bragg grating sensors.... Structural Health Monitoring journals http://www.medworm.com/rss/comments.php?id=3731623 Wed, 07 Jul 2010 15:05:02 +0100 3731623 http://www.medworm.com/index.php?rid=3731622&cid=s_22297_23_f&fid=22297&url=http%3A%2F%2Fshm.sagepub.com%2Fcgi%2Fcontent%2Fabstract%2F9%2F4%2F297%3Frss%3D1 Resonance demodulation technique is widely employed to diagnose faults of rolling bearings. In order to reduce the energy leakage influence of the traditional demodulated resonance method, a new approach based on harmonic wavelet transform (HWT) is proposed to extract the fault characteristics of rolling bearing. From the results of the numerical simulation analysis, this method is proven to be efficient in detecting the impact signal clouded in noises. Moreover, this article proposes a resonance demodulation scheme, which can obtain the optimal HWT parameters automatically to construct the proper sub-frequency band filter by calculating the relative wavelet energy of the different sub-frequency band. It solves the shortcoming in which a resonance frequency band filter is chosen manually. ... Structural Health Monitoring journals http://www.medworm.com/rss/comments.php?id=3731622 Wed, 07 Jul 2010 15:05:02 +0100 3731622 http://www.medworm.com/index.php?rid=3731621&cid=s_22297_23_f&fid=22297&url=http%3A%2F%2Fshm.sagepub.com%2Fcgi%2Fcontent%2Fabstract%2F9%2F4%2F285%3Frss%3D1 This study presents a basis for a general model free damage assessment and structural health monitoring framework. The study presented is particularly useful in the context of continuous online bridge health monitoring, since the data necessary for analysis can be obtained from the operating condition of the bridge and the structure does not need be closed down. (Source: Structural Health Monitoring) Structural Health Monitoring journals http://www.medworm.com/rss/comments.php?id=3731621 Wed, 07 Jul 2010 15:05:01 +0100 3731621 http://www.medworm.com/index.php?rid=3488614&cid=s_22297_23_f&fid=22297&url=http%3A%2F%2Fshm.sagepub.com%2Fcgi%2Fcontent%2Fabstract%2F9%2F3%2F269%3Frss%3D1 In this article, we present experimental investigations using energy harvesting and wireless energy transmission to power wireless structural health monitoring sensor nodes. The goal of this study is to develop sensing systems that can be permanently embedded within a host structure without the need for an on-board power source. With this approach the required energy will be harvested from the ambient environment, or periodically delivered by a radio-frequency energy source to supplement conventional harvesting approaches. This approach combines several transducer types to harvest energy from multiple sources, providing a more robust solution that does not rely on a single energy source. Both piezoelectric and thermoelectric transducers are considered as energy harvesters to extract the am... Structural Health Monitoring journals http://www.medworm.com/rss/comments.php?id=3488614 Tue, 20 Apr 2010 16:15:28 +0100 3488614 http://www.medworm.com/index.php?rid=3488613&cid=s_22297_23_f&fid=22297&url=http%3A%2F%2Fshm.sagepub.com%2Fcgi%2Fcontent%2Fabstract%2F9%2F3%2F257%3Frss%3D1 One practical issue that must be addressed prior to the implementation of a vibration-based structural health monitoring system is the influence that variations in the structure’s environmental and boundary conditions can have on the vibration response of the structure. This issue is especially prominent in the structural health monitoring of aircraft, which operate in a wide variety of different environmental conditions and possess complex structural components connected through various boundary conditions. However, many types of damage introduce nonlinear stiffness and damping restoring forces, which may be used to detect damage even in the midst of these varying conditions. Vibro-acoustic modulation is a nondestructive evaluation technique that is highly sensitivity to the presenc... Structural Health Monitoring journals http://www.medworm.com/rss/comments.php?id=3488613 Tue, 20 Apr 2010 16:15:28 +0100 3488613 http://www.medworm.com/index.php?rid=3488612&cid=s_22297_23_f&fid=22297&url=http%3A%2F%2Fshm.sagepub.com%2Fcgi%2Fcontent%2Fabstract%2F9%2F3%2F247%3Frss%3D1 This study shows PESEA can reasonably simulate the adhesive layer effect at elevated temperatures and hence can be a useful tool for understanding the behavior of Lamb wave propagation generated by adhesively bonded PZTs on structures. (Source: Structural Health Monitoring) Structural Health Monitoring journals http://www.medworm.com/rss/comments.php?id=3488612 Tue, 20 Apr 2010 16:15:28 +0100 3488612 http://www.medworm.com/index.php?rid=3488611&cid=s_22297_23_f&fid=22297&url=http%3A%2F%2Fshm.sagepub.com%2Fcgi%2Fcontent%2Fabstract%2F9%2F3%2F233%3Frss%3D1 Obtaining the strain data all along the optical fiber, with adequate spatial resolution and strain accuracy, opens new possibilities for structural tests and for structural health monitoring. Formerly, only point sensors, as strain gages or fiber Bragg grating, were available, and information about the response to loads was restricted only to those points on which the sensors were bonded. Unless a sensor was located near the damage initiation point, details about the failure initiation and growth were lost. With a distributed system, the information is given as an array of data with the position in the optical fiber and the strain or temperature data at this point. In this article, the physical principles underlying the different techniques for distributed sensing are discussed, a classifi... Structural Health Monitoring journals http://www.medworm.com/rss/comments.php?id=3488611 Tue, 20 Apr 2010 16:15:28 +0100 3488611 http://www.medworm.com/index.php?rid=3488610&cid=s_22297_23_f&fid=22297&url=http%3A%2F%2Fshm.sagepub.com%2Fcgi%2Fcontent%2Fabstract%2F9%2F3%2F219%3Frss%3D1 Structural health monitoring (SHM) technology has been successfully applied to understand the loads, environment actions, and behaviors of a structure subjected to various actions through solving a reverse problem. The sensing technology is a critical part of SHM. In this article, the development of advanced sensing technology and sensors in mainland China in the past decade, such as optic fiber sensing technology, wave propagation-based piezoelectric ceramic (PZT) sensing technology, smart cement-based sensing technology, and corrosion detection technology, have been critically reviewed. In addition, the article also summarizes the application of SHM technologies in earthquake engineering, wind engineering and life-cycle performance evaluation and corresponding progress achieved in mainla... Structural Health Monitoring journals http://www.medworm.com/rss/comments.php?id=3488610 Tue, 20 Apr 2010 16:15:28 +0100 3488610 http://www.medworm.com/index.php?rid=3488609&cid=s_22297_23_f&fid=22297&url=http%3A%2F%2Fshm.sagepub.com%2Fcgi%2Fcontent%2Fabstract%2F9%2F3%2F209%3Frss%3D1 This article shows the way from a simple monitoring system to a state-of-the-art support system based on examples from the German Air Force (GAF). From a military aircraft manufacturer’s point of view, the pro and contra of these systems based on in-service experience of various aircraft types are listed. Referring to this experience the benefit of the modernization of SHM-System will be presented and the requirements on a modern SHM-System especially for the ground support system and the logistic and in addition for new monitoring areas will be worked out. The approach for hot spot monitoring for damage detection is explained. A special view will be given on the possible integration of modern damage detection methods in existing and new SHM-Systems. Furthermore the combination of da... Structural Health Monitoring journals http://www.medworm.com/rss/comments.php?id=3488609 Tue, 20 Apr 2010 16:15:28 +0100 3488609 http://www.medworm.com/index.php?rid=3488608&cid=s_22297_23_f&fid=22297&url=http%3A%2F%2Fshm.sagepub.com%2Fcgi%2Fcontent%2Fabstract%2F9%2F3%2F199%3Frss%3D1 This article will review some of the aspects that need to be addressed in order to make structural health monitoring (SHM) of military systems a reality in the near future. (Source: Structural Health Monitoring) Structural Health Monitoring journals http://www.medworm.com/rss/comments.php?id=3488608 Tue, 20 Apr 2010 16:15:28 +0100 3488608 http://www.medworm.com/index.php?rid=3488607&cid=s_22297_23_f&fid=22297&url=http%3A%2F%2Fshm.sagepub.com%2Fcgi%2Freprint%2F9%2F3%2F197%3Frss%3D1 (Source: Structural Health Monitoring) Structural Health Monitoring journals http://www.medworm.com/rss/comments.php?id=3488607 Tue, 20 Apr 2010 16:15:28 +0100 3488607 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=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