Undamaged Structures Research Articles

Neuron-glial contacts formed in the cerebellum during electrical stimulation in the presence of an NO-generating compound

The molecular layer of the cerebellum of the frog Rana temporaria was studied by light and electron microscopy after electrical stimulation in the presence of an NO-generating compound. In these conditions, there was severe swelling of granule cell axon terminals (boutons) and astrocyte processes (AP), with loss of cytoplasmic elements. However, along with damaged structures, there were also undamaged structures: boutons with synaptic vesicles and AP with glycogen granules. It is suggested that these persisting viable AP may form 1) glial "wrappings" around damaged synapses or boutons and 2) neuron-glial contacts, which form when synaptic vesicles cross damaged bouton membranes to AP containing glycogen granules. It is also suggested that the presence of glycogen in AP in conditions of oxygen and glucose deficiency may provide a source of high-energy substrates such as glucose and ATP, thus providing conditions for neuron survival in pathological states (ischemia/hypoxia).

Nondestructive Evaluation of Rayleigh Pitch-Catch Contact Ultrasound Waves on Impacted-Damaged Composites

In particular, CFRP (carbon fiber reinforced plastics) composite materials have found wide applicability because of their inherent design flexibility and improved material properties. CFRP composites were manufactured from uni-direction prepreg sheet in this paper. However, impacted composite structures have 50-75% less strength than undamaged structures. It is desirable to perform nondestructive evaluation to assess material properties and part defect in order to ensure product quality and structural integrity of CFRP. In this work, a CFRP composite material was nondestructively characterized and a pitch-catch technique was developed to measure impacteddamaged area using an automated-data acquisition system. Also one-sided mode was performed to scan defect both manual contact measurement and an immersion tank. It is found a pitch-catch signal was found to be more sensitive than normal incidence backwall echo of longitudinal wave to subtle flaw conditions in the composite, including fiber orientation, low level porosity, ply waviness, and cracks. The paper describes the depth of the sampling volume with the head-to-head miniature Rayleigh probes and also ultrasonic C-scan images are acquired experimentally using one-sided measurement and a conventional scanner.

Two-stage damage diagnosis approach for steel braced space frame structures

In order to diagnose the location and extent of damage in steel braced space frame structures, a two-stage damage diagnosis approach is proposed. This approach is comprised of the damage locating vectors method and eigensensitivity analysis. By deriving formulas used to calculate characterizing stresses in space frame members, and by defining characterizing stresses in connections, the damage locating vectors method is extended to locate damage in space frame members and connections. In addition, the simplified calculation of modal mass-normalization constants for damaged structures is improved. The first- and second-order sensitivities of the modal parameter discrepancies with respect to the structural model parameters and the stiffness matrix of beam elements with one damaged end are utilized. To verify the effectiveness of the proposed approach, numerical simulation analysis and experimental testing of a steel braced space frame model are performed. Ten and seven damage patterns are simulated in the numerical example and experimental testing, respectively. Modal parameters of the undamaged and damaged structures are extracted from the acceleration data using the natural excitation technique (NExT) and the eigensystem realization algorithm (ERA). The extended damage locating vectors method is utilized to determine potentially damaged elements. Based on the identified modal information, the extent of damage of the potentially damaged elements is estimated using the second-order eigensensitivity analysis. It is demonstrated that the two-stage damage diagnosis approach is effective when the damage of the members or connections in steel braced space frame structures reaches a certain level.

STRUCTURAL DAMAGE QUANTIFICATION BY SYSTEM IDENTIFICATION

After a disaster such as an earthquake has struck, the damage assessment of the affected buildings, bridges and other forms of structures is often urgently required for follow-up action. Research in using system identification for damage assessment in a quantifiable and non-destructive way has rapidly increased in recent years, due to advances in computing power and sensing technology. Though considerable progress has been made, many challenges still remain in achieving robust and effective identification of large structural systems using incomplete and noisy measurement signals. In this paper a novel strategy to tackle this problem is presented. A modified genetic algorithm (GA) strategy incorporating a search space reduction method, progressively and adaptively reduces the search space for each unknown parameter. By concurrent evolution of multiple species, it provides an excellent balance between exploration of the search space and exploitation of good solutions. The modified GA is incorporated into a damage detection strategy that works by comparing identified parameters for the undamaged and damaged structures and quantifies damage as a relative change in the stiffness of a member or a group of members. The additional information obtained from the analysis of the undamaged structure is used to greatly improve speed and accuracy in the identification of the damaged structure. Numerical studies on 10 and 20 degree-of-freedom (DOF) systems and an experimental study of a 7-storey small-scale steel frame are presented to illustrate the applicability of the method in accurately identifying even small amounts of damage.

Damage diagnosis of a two-storey spatial steel braced-frame model

To verify the effectiveness of the damage diagnosis methods, an experimental study of a two-storey spatial steel braced-frame structure model was carried out. The test model had plan dimensions of 1.50 m × 1.50 m and a height of 2.82 m. Four known damage patterns, including single damage, symmetric damage, asymmetric damage and multi-storey damage, were simulated by removing different braces. Modal parameters of undamaged and damaged structures were obtained by employing the natural excitation technique (NExT) in conjunction with the eigensystem realization algorithm (ERA) from acceleration responses induced by hammer impacts and simulated ambient excitation. Finite element analysis using SAP2000 was performed to validate the identified modal parameters of the test model. The damage index method and the damage locating vectors (DLVs) method were utilized to locate damaged elements, respectively. Based on the identified modal information the damage extent (the stiffness loss) was estimated by using the second-order eigensensitivity approximation method. It is demonstrated that the above vibration-based methods are effective for damage diagnosis. Copyright © 2006 John Wiley & Sons, Ltd.

구조물의 결함 규명을 위한 위상최적설계 기법의 적용가능성 연구

A feasibility of using the topology optimization method for structural damage identification is investigated for the first time. The frequency response functions (FRFs) are assumed to be constructed by the finite element models of damaged and undamaged structures. In addition to commonly used resonances, antiresonances are employed as the damage identifying modal parameters. For the topology optimization formulation, the modal parameters of the undamaged structure are made to approach those of the damaged structure by means of the constraint equations, while the objective function is an explicit penalty function requiring clear black-and-white images. The developed formulation is especially suitable for damage identification problems dealing with many modal parameters. Although relatively simple numerical problems were considered in this investigation, the possibility of using the topology optimization method for structural damage identification is suggested through this research.

A Wavelet-based, Distortion Energy Approach to Structural Health Monitoring

A method for quantifying damage-induced distortions to the vibrational response of an experimental plate is presented. By examining a wavelet representation of the difference in strain response between the damaged and the undamaged structures, the distortion energy may be computed on multiple timescales. This feature is tested in its ability to detect both the presence and the location of degradation of the plate. In addition, the effects of competing excitation mechanisms, including the outputs of Lorenz and Rossler systems, as well as a 0-225 Hz Gaussian noise are studied. The results indicate that the distortion energies, statistically speaking, are significantly higher under damaged conditions compared to those extracted under undamaged conditions, implying that the new distortion energy approach will yield adequate features for detecting the presence as well as possibly the location of damage in a structure.

A Conceptual Structural Health Monitoring System based on Vibration and Wave Propagation

Development of efficient methodologies to determine the presence, location, and severity of hidden damage in critical structural components is an important task in the design and construction of structural health monitoring systems in aging as well as new structures. In this article, a methodology for automatic damage identification and localization is presented. The structure is assumed to be instrumented with an array of actuators and sensors to excite and record its dynamic response, including vibration and wave propagation effects. In the vibrational approach, the data consist of the modal response of the structure produced by the actuators while in the wave propagation approach, they are the broadband signals due to ultrasonic waves propagating in the structures. Both types of signals are affected by the presence of defects. The approximate location and severity of an unknown defect is determined using a damage correlation index calculated from the frequency response function (FRF) of the structure. The damage index is a relative measure whose value depends on the differences in the dynamical properties of the undamaged (baseline) and damaged structures. The method is applied to simple structural components involving aluminum beams and plates with reduced local stiffness and a composite plate with impact damage. The potential application of the technique to practical health monitoring problems is discussed.

A method of online damage identification for structures based on ambient vibration

A method of damage identification for engineering structures based on ambient vibration is put forward, in which output data are used only. Firstly, it was identification of the statistic parameters to associate with the exterior excitation for undamaged structures. Then it was detection and location of the structural damages for damaged structures. The ambient identification method includes a theoretical model and numerical method. The numerical experiment results show the method is precise and effective. This method may be used in health monitoring for bridges and architectures.

Probabilistic method for the analysis of widespread fatigue damage in structures

A probabilistic method was developed to model structural failure associated with widespread damage as a stochastic chain of crack initiation and growth, linkup, and final failure. The major feature of this method is that multiple sites (fastener holes) have individual crack-initiation and crack-growth characteristics. These individual characteristics are established by Monte Carlo simulation. Stress analysis of undamaged and cracked structures is performed incrementally using a finite element method incrementally and the crack length increment is determined at a given time increment by using an equation for crack growth. Consequent application of the Monte Carlo simulation results in empirical distributions for (a) life to crack initiation, (b) residual life and (c) total life of the structure. A worst-case scenario of multiple cracks is introduced by assigning equal cracks growing simultaneously with highest speed at all sites. This case establishes the threshold of residual life of a structure. Utilizing the threshold, Monte Carlo simulations are conducted in conjunction with a three-parameter lognormal probability distribution for the residual life of a structure. Numerical studies were performed for panels with rows of holes and for a panel stiffened by stringers. The proposed method makes it possible to assess the probability of occurrence of a structure's failure associated with widespread damage as a function of time.

Paper #137 Minimally invasive treatment of medial compartment osteoarthritis of the knee using a polyurethane spacer: a new technique

Unicondylar arthroplasty (UKA), an almost forgotten option for the arthritic knee, has experienced a resurgence of interest with the Introduction of minimally invasive surgery (ENGH 2002). SCULCO (1994) described UKA as treatment of choice in unicompartmental arthritis of the knee, when arthroplasty is indicated. Advantages over total knee arthroplasty (TKA) are preservation of cruciate ligaments as well as other undamaged structures along with possible restoration of knee function to nearly normal. Patellar dislocation is not necessary as part of the procedure, and hospitalisation can be avoided. We report an extension of UKA using an even less invasive surgical technique to insert a spacer between the femur and tibia for treatment of medial compartment osteoarthritis.

Non-destructive evaluation of smart materials by using extrinsic Fabry–Perot interferometric and fiber Bragg grating sensors

The real-time non-destructive evaluation (NDE) technologies of engineering structures are very important to assess the performance of in-service structures. It is very difficult to carry out the on-line structural integrity monitoring by using classical NDE methods. Fiber optic sensors in smart structures provide a unique opportunity to real-time monitor the structural health status by using embedded sensors. This paper examines the possibility of extrinsic Fabry–Perot interferometric (EFPI) and fiber Bragg grating (FBG) sensors for NDE of composite and aluminum structures. The experiments of 3-point bending measurement of composite laminates and aluminum plates with and without damages by using the EFPI and FBG sensors are performed, respectively. The experimental results show that the flexural strain of damaged structures is much higher when compared with relevant undamaged structures under same bending load by using both EFPI and FBG sensors. Furthermore, an excellent accordance was found between the results of the 3-point bending tests by using surface-mounted EFPI and FBG sensors

Damage identification of laminated composite structures based on dynamic residual forces

This paper shows a damage identification method based on dynamic residual forces which can be evaluated using an analytical model of undamaged structures and measured vibration data of damaged structures. The method consists of a two-step damage detection procedure. In the first step, a rough damage region is identified from the dynamic residual forces. In the next step, error vectors of the residual forces are minimized to identify the accurate location and extent of structural damage. Effect of measurement points and measurement errors on the identification results is examined through numerical examples on symmetric laminated plates.

Structural Health Monitoring Using Statistical Process Control

This paper poses the process of structural health monitoring in the context of a statistical pattern recognition paradigm. This paper particularly focuses on applying a statistical process control (SPC) technique known as an “X-bar control chart” to vibration-based damage diagnosis. A control chart provides a statistical framework for monitoring future measurements and for identifying new data that are inconsistent with past data. First, an autoregressive (AR) model is fit to the measured time histories from an undamaged structure. Coefficients of the AR model are selected as the damage-sensitive features for the subsequent control chart analysis. Next, control limits of the X-bar control chart are constructed based on the features obtained from the initial structure. Finally, the AR coefficients of the models fit to subsequent new data are monitored relative to the control limits. A statistically significant number of features outside the control limits indicate a system transition from a healthy state to a damage state. A unique aspect of this study is the coupling of various projection techniques such as principal component analysis and linear and quadratic discriminant operators with the SPC in an effort to enhance the discrimination between features from the undamaged and damaged structures. This combined statistical procedure is applied to vibration test data acquired from a concrete bridge column as the column is progressively damaged. The coupled approach captures a clearer distinction between undamaged and damaged vibration responses than by applying an SPC alone.

Long-term changes of GABAergic function in the sensorimotor cortex of amputees. A combined magnetic stimulation and 11C-flumazenil PET study.

Primary sensory and motor areas of the cerebral cortex contain organised maps of the body. These maps appear to reorganise after damage to the peripheral parts of the sensory or motor systems, so that the cortical representation of undamaged structures expands at the expense of the damaged parts. Several studies in animals have suggested that decreased activity of the inhibitory GABAergic neurones is responsible for driving these changes. However, whether similar mechanisms sustain the effects in the longer term in humans is unknown. The present study addressed this question by examining reorganisation of sensorimotor areas of cortex in six unilateral upper limb amputees several years after the initial injury. We measured two independent indices of GABAergic function. Volumes of distribution of GABA(A) receptors were determined from 11C-flumazenil binding measured with positron emission tomography (PET). The strength of inhibition in the motor cortex was measured with paired-pulse transcranial magnetic stimulation. In the six amputees taken as a whole and compared with 24 normal subjects, there was a highly significant increase in 11C-flumazenil binding in the upper limb region of primary sensorimotor cortex bilaterally and in medial frontal cortex of the hemisphere contralateral to the amputation. Surprisingly, however, there was no change in the time course or strength of intra-cortical inhibition in the motor cortex of the amputees compared with matched control subjects. The increased 11C-flumazenil binding may reflect up-regulation of GABA(A) receptors to compensate for a decrease in the GABA content or activity of inhibitory neurones. Up-regulation of GABA(A) receptors may also indicate that long-term changes require stabilisation of cortical organisation.

Use of modal testing to identify damage on steel members

There is a need to construct a structural monitoring system for assessment of current health condition of deteriorating structures and the prediction of their response under load. In this paper, basic experimental tests and numerical analysis are performed to investigate the feasibility of using modal testing techniques as a tool for structural health monitoring and damage detection. The objective of this study is to investigate the change of modal parameters due to imposed damage, and to verify the most sensitive modal parameters for identifying and locating the damage. Rectangular tudes, twelve feet in length, were tested for this purpose. They have either one or two spans and each of three cases has its own damage scenario. The modal parameters considered are modal frequency, displacement mode shape (DMS) and strain mode shape (SMS). The coordinate modal assurance criterion (CoMAC), and the modal vector error (MVE) are used to quantify the change of mode shape between the undamaged and damaged structures. The change of frequency can be measured rather precisely in this experimental test, but the location of damage could not be detected by use of DMS change with CoMAC. It is suggested that the DMS or preferably the SMS be used in collaboration with MVE as a more effective method of locating damage.

VIBRATION-BASED MODEL-DEPENDENT DAMAGE (DELAMINATION) IDENTIFICATION AND HEALTH MONITORING FOR COMPOSITE STRUCTURES — A REVIEW

There are strong needs and requirements for on-line damage (delamination) detection and health-monitoring techniques on composite structures. Vibration-based model-dependent methods with piezoelectric sensor and actuator incorporated into composite structures offer a promising option to fulfil such requirements and needs. These methods utilize finite element analysis techniques, together with experimental results, to detect damage. They locate and estimate damage events by comparing dynamic responses between damaged and undamaged structures. According to the dynamic response parameters analyzed, these methods can be subdivided into modal analysis, frequency domain, time domain and impedance domain. Model-dependent methods are able to provide global and local damage information. They are cost-effective and are relatively easy to operate. However, there are still many challenges and obstacles before these methods can be implemented in practice.

動的残差力に基づく積層板の損傷同定

In this paper, we propose a damage identification method of laminated composite structures based on dynamic residual forces. Dynamic residual forces are evaluated using an analytical model of undamaged structures and measured vibration data of damaged structures. In the first step, a rough damage region is identified from the dynamic residual forces. Then, error vectors of the residual forces are minimized to identify the accurate location and extent of structural damage. Effect of measurement points and measurement errors on the identification results is examined through numerical examples on symmetric laminated plates.

Embedded Self-Sensing Piezoelectric for Damage Detection

A method for damage detection based on self-sensing piezoelectrics is presented. When a piezoelectric actuator is electronically excited, it causes stress in the structure to which it is attached. As the structure deformation is influenced by the presence of damage, so will be the response of the sensor. The goal of the method is to use the same piezoelectric element as both actuator and sensor, by analyzing the electromechanical response of the system in the frequency domain. In this way, damaged and undamaged structures can be distinguished and the extent of damage estimated. The distinction between the excitation and the response signals is achieved by an electronic bridge circuit. A comparison between this self-sensing method and the more common cross-talk method is performed, showing the similarity of the two methods and the validity of our technique. A method to differentiate among the spectrum changes due to actual damage and those due to temperature shifts is also presented. As the temperature rises, the PZT characteristics change and the resonance frequencies of the spectrum shift. However, the acquired signal can be processed to compensate for the temperature changes.

Groundwater rise and hydrocollapse: technical and political implications of ‘Special Geologic Report Zones’ in Riverside County, California, USA : R. J. Shlemon, in: Land subsidence. Proc. international symposium, The Hague, 1995, ed F.B.J. Barends & others, (IAHS; Publication, 234), 1995, pp 481–486

Rapid urbanization in the semi-arid southwestern part of Riverside County, California is made possible only by the large-scale importation of water for domestic use. The resulting irrigation run-off and infiltration has caused groundwater levels to rise over 20 m within the past few years, particularly in former, alluvium-filled channels. Soil hydrocollapse, differential settlement and ground fissures are now occurring, causing extensive damage to houses, schools and related infrastructure. Alleged property damages exceed 50 million (US) dollars, and litigation has ensued. For public safety, the County of Riverside established two Special Geologic Report Zones, each about 500 ha, deemed CaliforniaOaks and Silverhawk, respectively. Inretrospect: the formation of the zones has proven to be administratively time- consuming and expensive; the litigation between home-owners, builders, geotechnical firms and reviewing agencies is divisive; home values, even for undamaged structures, have been reduced owing to disclosure laws; and the geotechnical community now recognizes, from sad experience, that rapid urbanization and related water level rise accelerates the potential for soil hydrocollapse and extensive property damage.