Occurrence Of Structural Damage Research Articles

On the analysis of antiresonance frequencies for structural damage localization

During the service life of long-lasting constructions, structural changes occur that can lead to damage or failure. For reasons of economic and ecological sustainability, it is of great importance to detect these changes as early as possible to ensure safe operation and to be able to initiate maintenance measures if necessary. To detect and localize emerging damages, structural health monitoring systems can be employed. The realization of such systems requires methods that can derive information about the condition of the monitored object from measurement data. To develop a better understanding of how damage affects structural integrity, simulation models of generic structures can be used. In most cases, structural damage can be generalized as some type of local stiffness reduction, causing changes in the dynamic properties of the structure. From a numerical perspective, this means that the dynamic stiffness matrix of the system changes, which can lead to shifts in resonance and antiresonance frequencies. Since resonance frequencies are global characteristics of the structure, they may contain information about the occurrence of structural damage, but not about its location. Therefore, this paper investigates whether and how the observation of the antiresonance frequencies can be used to both detect and localize damages.

Neutrophil–lymphocyte ratio as a reliable marker to predict pre-clinical retinopathy among type 2 diabetic patients

BackgroundDiabetic retinopathy is now recognized as a neurovascular in lieu of a microvascular complication. Visual evoked potentials (VEPs) are greatly valuable in detecting early diabetic retinal functional changes before the occurrence of structural damage. Low-grade inflammation plays a fundamental part in the development and progression of retinopathy in diabetics. Detecting diabetic patients with early retinopathy before the occurrence of clinical symptoms provides a window of opportunity to ensure the best prognosis for these eyes. Neutrophil–lymphocyte ratio (NLR) has recently been introduced as a novel marker of inflammation in various diseases. Indeed, the presence of a cheap, available, and reliable marker of inflammation that is capable to detect pre-clinical diabetic retinopathy (P-DR) is crucial for early intervention to retard the progression of ocular damage. As far as we know no previous studies investigated the role of NLR in the detection of P-DR. The aim of this study was to investigate the quality of prediction of NLR in detecting pre-clinical retinopathy in type 2 diabetic patients.ResultsIn this case–control study, VEPs results showed a significant delay in P100 latencies of the patients’ group compared to the control group. According to the VEPs results, the patient group was further subdivided into two: diabetic with VEPs changes (a group with P-DR) and diabetic without VEPs changes. NLR was significantly elevated in patients with P-DR (p < 0.001). NLR cut-off point ≥ 1.97 is able to predict P-DR with 89.29% sensitivity and 84.37% specificity. Linear regression model revealed that NLR is the only independent factor that predicts P-DR. (odds ratio 3.312; 95% confidence interval 1.262–8.696, p = 0.015*.ConclusionsVisual evoked potentials have an important role to evaluate the visual pathway in diabetics and to diagnose pre-clinical diabetic retinopathy before the occurrence of structural damage. Neutrophil–lymphocyte ratio is a reliable marker for the detection of pre-clinical diabetic retinopathy with good sensitivity (89.29%) and specificity (84.37%). Finding a reliable available laboratory test to predict P-DR could be of help to save diabetic patients from serious ocular complications.

Inherent uncertainty in the extraction of frequencies from time-domain signals

One structural health monitoring method used to detect the occurrence of structural damage is the tracking of a structure’s natural frequencies. However, for bridges, this is complicated by the changing environmental and operational conditions, which also have an effect on the natural frequencies. Consequently, much of the research effort has been on trying to develop data-modelling approaches that correct for, or remove, environmental effects so that changes in structural behaviour can be revealed. However, the fact that the process of extracting frequencies from bridge response data sets has in itself some inherent uncertainties that have been largely ignored forms the major interest of this study. In this paper, various methods for extracting frequency data from time-domain signals are reviewed, and their suitability for use in automated approaches is discussed. A selection of these methods was then used to obtain frequencies from continuous acceleration data from a bridge over a 20 d period. Comparisons were then made between the obtained frequencies, and any observed differences are highlighted between the methods.

Application and preliminary validation of the hip inflammation MRI scoring system (HIMRISS) in spondyloarthritis.

Spondyloarthritis (SpA) is an inflammatory rheumatic disease and hip involvement often results in severe deformities and functional impairment. Magnetic resonance imaging (MRI) is a powerful imaging tool for detecting early hip lesions in SpA. The aims of this study are to apply the hip inflammation MRI scoring system (HIMRISS) in SpA patients and to evaluate its reproducibility and validity. Four readers new to HIMRISS (two radiologists and two rheumatologists) scored the MRI scans obtained from a total of 55 SpA patients with hip lesions in two separate exercises (33 patients in exercise 1 and 22 patients in exercise 2). After the training and review process for exercise 1, these well-trained readers with expertise in the HIMRISS method scored the scans obtained from 22 patients and evaluated the association between HIMRISS and clinical activity of SpA, including Ankylosing Spondylitis Disease Activity Score (ASDAS), laboratory features, Bath Ankylosing Spondylitis Disease Activity Index and Harris hip scores. HIMRISS is a reliable MRI scoring method for bone merrow lesions (BML) and synovitis in SpA. After 2 training exercises, the reliability improved from 0.67 to 0.90. The reliability for detecting femoral BML, acetabular BML, and synovitis effusion was very good after the 2 exercises (overall intraclass correlation coefficient=0.73, 0.84 and 0.88, respectively). The clinical correlations between HIMRISS and ASDAS were most significant, and the correlations were closer to summed bilateral HIMRISS scores than just the worse side. HIMRISS was found to be an excellent tool for the early diagnosis of inflammation before the occurrence of structural damage, which was not significantly reflected in the systemic diagnosis. HIMRISS offers a reliable MRI scoring method for hip joint in SpA, and it is beneficial for early detection and fast quantification in disease activity assessment.

Experimental Investigation of Residual Ultimate Strength of Damaged Metallic Pipelines

The ultimate strength of metallic pipelines will be inevitably affected when they have suffered from structural damage after mechanical interference. The present experiments aim to investigate the residual ultimate bending strength of metallic pipes with structural damage based on large-scale pipe tests. Artificial damage, such as a dent, metal loss, a crack, and combinations thereof, is introduced to the pipe surface in advance. Four-point bending tests are performed to investigate the structural behavior of metallic pipes in terms of bending moment–curvature diagrams, failure modes, bending capacity, and critical bending curvatures. Test results show that the occurrence of structural damage on the pipe compression side reduces the bending capacity significantly. Only a slight effect has been observed for pipes with damage on the tensile side as long as no fracture failure appears. The possible causes that have introduced experimental errors are presented and discussed. The test data obtained in this paper can be used to further quantify damage effects on bending capacity of seamless pipes with similar D/t ratios. The comparison results in this paper can facilitate the structural integrity design as well as the maintenance of damaged pipes when mechanical interference happens during the service life of pipelines.

Lower Ipsilateral Hippocampal Integrity after Ischemic Stroke in Young Adults: A Long-Term Follow-Up Study.

Background and purposeMemory impairment after stroke is poorly understood as stroke rarely occurs in the hippocampus. Previous studies have observed smaller ipsilateral hippocampal volumes after stroke compared with controls. Possibly, these findings on macroscopic level are not the first occurrence of structural damage and are preceded by microscopic changes that may already be associated with a worse memory function. We therefore examined the relationship between hippocampal integrity, volume, and memory performance long after first-ever ischemic stroke in young adults.MethodsWe included all consecutive first-ever ischemic stroke patients, without hippocampal strokes or recurrent stroke/TIA, aged 18–50 years, admitted to our academic hospital between 1980 and 2010. One hundred and forty-six patients underwent T1 MPRAGE, DTI scanning and completed the Rey Auditory Verbal Learning Test and were compared with 84 stroke-free controls. After manual correction of hippocampal automatic segmentation, we calculated mean hippocampal fractional anisotropy (FA) and diffusivity (MD).ResultsOn average 10 years after ischemic stroke, lesion volume was associated with lower ipsilateral hippocampal integrity (p<0.05), independent of hippocampal volume. In patients with a normal ipsilateral hippocampal volume (volume is less than or equal to 1.5 SD below the mean volume of controls) significant differences in ipsilateral hippocampal MD were observed (p<0.0001). However, patients with a normal hippocampal volume and high hippocampal MD did not show a worse memory performance compared with patients with a normal volume and low hippocampal MD (p>0.05).ConclusionsPatients with average ipsilateral hippocampal volume could already have lower ipsilateral hippocampal integrity, although at present with no attendant worse memory performance compared with patients with high hippocampal integrity. Longitudinal studies are needed to investigate whether a low hippocampal integrity after stroke might lead to exacerbated memory decline with increasing age.

Automated modal tracking and fatigue assessment of a wind turbine based on continuous dynamic monitoring

The paper describes the implementation of a dynamic monitoring system at a 2.0 MW onshore wind turbine. The system is composed by two components aiming at the structural integrity and fatigue assessment. The first component enables the continuous tracking of modal characteristics of the wind turbine (natural frequency values, modal damping ratios and mode shapes) in order to detect abnormal deviations of these properties, which may be caused by the occurrence of structural damage. On the other hand, the second component allows the estimation of the remaining fatigue lifetime of the structure based on the analysis of the measured cycles of structural vibration.

Gradual Bilinear Method를 이용한 사장교의 케이블 손상응답 해석

Cable-stayed bridge, which is one of the representative long-spanned bridge, needs prompt maintenances when a stay cable is damaged because it may cause structural failure of the entire bridge. Many researches are being conducted to develop abnormal behavior detection algorithms for the purpose of shortening the reaction time after the occurrence of structural damage. To improve the accuracy of the damage detection algorithm, ample observation data from various kinds of damage responses is needed. However, it is difficult to measure an abnormal response by damaging an existing bridge, numerical simulation can be an effective alternative. In most previous studies, which simulate the damage responses of a cable-stayed bridge, the damages has been considered as a load variation without regard to its stiffness variation. The analyses of using these simplification could not calculate exact responses of damaged structure, though it may reserve a sufficient accuracy for the purpose of bridge design. This study suggests Gradual Bilinear Method (GBM) which simulate the damage responses of cable-stayed bridge considering the stiffness and mass variation, and develops an analysis program. The developed program is verified from the responses of a simple model. The responses of a existing cable-stayed bridge model are analyzed with respect to the fracture delay time and damage ratio. The results of this study can be used to develop and verify the highly accurate abnormal behavior detection algorithm for safety management of architecture/large structures.

Experimental damage identification using modified mode shape difference

An experimental program was undertaken to test the feasibility to detect the occurrence of structural damage using a modified mode shape difference technique. The vibration response of a steel beam fixed at one end and hinged at the other was obtained for the intact and damage conditions. Modal analysis was performed to extract the frequencies and mode shapes. The method shows a good potential in detection of occurrence and location of damage.

Experimental tests on full‐scale RC unretrofitted frame and retrofitted with buckling‐restrained braces

SUMMARYThe results of experimental tests carried out on reinforced concrete (RC) full‐scale 2‐storey 2‐bays framed buildings are presented. The unretrofitted frame was designed for gravity loads only and without seismic details; such frame was assumed as a benchmark system in this study. A similar RC frame was retrofitted with buckling‐restrained braces (BRBs). The earthquake structural performance of both prototypes was investigated experimentally using displacement‐controlled pushover static and cyclic lateral loads. Modal response properties of the prototypes were also determined before and after the occurrence of structural damage. The results of the dynamic response analyses were utilized to assess the existing design rules for the estimation of the elastic and inelastic period of vibrations. Similarly, the values of equivalent damping were compared with code‐base relationships. It was found that the existing formulations need major revisions when they are used to predict the structural response of as‐built RC framed buildings. The equivalent damping ratio ξeq was augmented by more than 50% when the BRBs was employed as bracing system. For the retrofitted frame, the overstrength Ω and the ductility µ are 1.6 and 4.1, respectively; the estimated R‐factor is 6.5. The use of BRBs is thus a viable means to enhance efficiently the lateral stiffness and strength, the energy absorption and dissipation capacity of the existing RC substandard frame buildings. The foundation systems and the existing members of the superstructure are generally not overstressed as the seismic demand imposed on them can be controlled by the axial stiffness and the yielding force of the BRBs. Copyright © 2011 John Wiley &amp; Sons, Ltd.

Endothelin‐1 and the Metalloproteases ECE and NEP in DOCA‐Salt Hypertensive Rats

Endothelin‐1 (ET‐1) is thought to be a key player in DOCA‐salt induced hypertension. We hypothesized that the bioavailability of ET‐1 is controlled by tissue specific expression of the metalloproteases endothelin converting enzyme (ECE) and neutral endopeptidase (NEP). To test this hypothesis we measured ECE and NEP protein content in kidneys and hearts of DOCA‐salt treated rats 3 and 6 weeks after implantation of a 100 mg DOCA pellet combined with high salt drinking water. In addition, ET‐1 content was determined in these organs by RIA. During DOCA‐salt treatment, blood pressure was significantly elevated in association with increased kidney and heart weight. Despite the occurrence of structural damage in these organs (verified by histology), ECE, NEP, and ET‐1 content were not significantly altered 3 and 6 weeks after DOCA treatment (n=6/organ/group). These data indicate that both ET‐1 and metalloprotease content in the heart and kidneys do not contribute to the maintenance of hypertension in the DOCA‐salt rat model.This research was performed within the framework of project T2‐108 of the Dutch Top Institute Pharma.

Structural Damage Warning of a Long-Span Cable-Stayed Bridge Using Novelty Detection Technique Based on Wavelet Packet Analysis

This paper describes the development of a multi-stage scheme for structural damage warning of the Runyang Cable-stayed Bridge using the measured dynamic responses from an on-line instrumentation system. In the first stage, the wavelet packet energy spectrum (WPES) is extracted using wavelet packet analysis from the measured dynamic responses caused by ambient excitations, thus providing parameters warning of occurrence of structural damage. The second stage is to formulate correlation models describing the seasonal relationship between WPES and temperature and the third stage is to classify the measured changes of WPES, whether due to environmental temperature or to structural damage, using a novelty detection technique based on statistical process control. The usefulness of the approach is examined on the Runyang Cable-stayed Bridge using 236 days of health monitoring data. The results reveal that the seasonal change of environmental temperature accounts for variation in the measured WPES, which averaged a 200% variance, and that the approach is able to eliminate the temperature effects and provides a good capability for detecting the damage-induced 10% variance.

Optimization of Wavelet Packets Analysis for Damage Detection in Composite Materials

A method based on entropy-based criteria is present to choose the optimal decomposition of Wavelet Packets Analysis (WPA) for damage detection in composite materials. The structural damage indexes constructed based on energy spectrum variation of the structural vibration responses decomposed using WPA before and after the occurrence of structural damage usually generate a complete binary tree to calculate its elements. Date mining is carried out in this paper by adoption entropy as the criteria to choose the optimal decomposition tree. In the decomposition process, only the sub-signals which contain main information of the original signal are decomposed to generate next level sub-signals. New damage index is constructed based on the optimal decomposition. Then the dimension of the damage index is reduced while still keeping its sensitive to damage. Whether Artificial Neural Network (ANN) or genetic algorithm (GA) is used in the further process of telling structural damage status from damage index, this reduction will make remarkable time saving.

Experimental validation of vibration-based damage detection for static laminated composite shells partially filled with fluid

A vibration-based damage detection method for a static laminated composite shell partially filled with fluid (LCSFF) is presented and validated by experiment. The crack damage is simulated using advanced composite damage mechanics in a dynamic finite element model, in which the interaction between the fluid and the composite shell is considered. The accuracy of FE model is first validated by comparing the computed and measured structural frequency response function. Structural damage indexes are constructed and calculated based on energy variation of the structural vibration responses decomposed using wavelet package before and after the occurrence of structural damage. An artificial neural network (ANN) is trained using numerically simulated structural damage index to establish the mapping relationship between the structural damage index and damage status. The test specimen used in experiment contains a cut in its surface made by laser cutting system. Response signals of both intact and damaged specimen are measured and used to construct the corresponding damage indices. The damage status is successfully identified using ANN, indicating that the method adopted in this paper can be applied to online structural damage detection and health monitoring for static LCSFF.

Vibration-based damage detection for composite structures using wavelet transform and neural network identification

This paper presents an integrated method for damage detection of composite structures using their vibration responses, wavelet transform and artificial neural networks (ANN) identification. Structural damage feature proxy vectors are constructed and calculated based on energy variation of the structural vibration responses decomposed using wavelet package before and after the occurrence of structural damage. The ANN are applied to establish the mapping relationship between structural damage feature proxy and damage status (location and severity). The results of crack damage detection for PVC sandwich plates show that the method developed in this paper can be applied to online structural damage detection and health monitoring for various industrial structures.