Condition assessment of existing concrete bridge pier caps using the general shear provisions of the AASHTO LRFD Bridge Design Specification has caused the Georgia Department of Transportation (GDOT) to post a large number of bridges in the State of Georgia. Posting of bridges disrupts the free flow of goods within the region served by the bridge and has a negative economic impact. To prevent structural deterioration, diagonal cracking or failure of concrete pier caps in shear, the GDOT employs an in-situ strengthening technique that utilizes an external vertical post-tensioning system. However, the fundamental mechanics of this system and its effectiveness under service load have not been examined previously. This research examines the behavior of reinforced concrete pier caps that utilize the above strengthening system in a combined analytical and experimental program. In the experimental part of the study, two groups of full-scale reinforced concrete deep beam specimens were tested. The first group consisted of six deep beams with shear span/depth ratios of approximately 1.0, which is typical of bridge pier caps; of these six, two included the external post-tensioning system. In the second group, nine deep beam specimens that included a segment of the column representing the pier were tested; four of those tests included the external post-tensioning system. The tests revealed that the shear capacity computed using the AASHTO LRFD Bridge Design Specifications provided a conservative estimate of the specimen capacity in all but one case when compared to the experimental results. However, the AASHTO strut and tie provisions were found to provide a much closer assessment of the load carrying mechanism in the pier cap than the general shear provisions, in that they were able to predict the load at which yielding of the tension reinforcement occurred as well as the angle of the compression strut. The presence of the column segment in the second group had a significant impact on the failure mechanism developed in the specimen near ultimate load. The stress concentration at the reentrant corner between the pier cap and column interface served as an attractor for the formation of diagonal shear cracks, a mechanism not observed in previous deep beam tests in shear. The research has led to recommendations for improving the design of pier caps and the external post-tensioning system, where required, based on mechanics which are consistent with the results of the experimental program.

Fiber reinforced composite materials are widely used in aerospace, mechanical, civil and other industries because of their high strength-to-weight and stiffness-to-weight ratios. However, composite structures are highly prone to impact damage. Possible types of defect or damage in composite include matrix cracking, fiber breakage, and delamination between plies. In addition, delamination in a laminated composite is usually invisible. It is very diffcult to detect it while the component is in service and this will eventually lead to catastrophic failure of the structure. Such damages may be caused by dropped tools and ground handling equipments. Damage in a composite structure normally starts as a tiny speckle and gradually grows with the increase in load to some degree. However, when such damage reaches a threshold level, serious accident can occur. Hence, it is important to have up-to-date information on the integrity of the structure to ensure the safety and reliability of composite components, which require frequent inspections to identify and quantify damage that might have occurred even during manufacturing, transportation or storage. How to identify a damage using the obtained information from a damaged composite structure is one of the most pivotal research objectives. Various forms of structural damage cause variations in structural mechanical characteristics, and this property is extensively employed for damage detection. Existing traditional non-destructive inspection techniques utilize a variety of methods such as acoustic emission, C-scan, thermography, shearography and Moir interferometry etc. Each of these techniques is limited in accuracy and applicability. Most of these methods require access to the structure.They also require a significant amount of equipment and expertise to perform inspection. The inspections are typically based on a schedule rather than based on the condition of the structure. Furthermore, the cost associated with these traditional non-destructive techniques can be rather prohibitive. Therefore, there is a need to develop a cost-effective, in-service, diagnostic system for monitoring structural integrity in composite structures. Structural health monitoring techniques based on dynamic response is being used for several years. Changes in lower natural frequencies and mode shapes with their special derivatives or stiffness/ exibility calculation from the measured displacement mode shapes are the most common parameters used in identification of damage. But the sensitivity of these parameters for incipient damage is not satisfactory. On the other hand, for in service structural health monitoring, direct use of structural response histories are more suitable. However, they are very few works reported in the literature on these aspects, especially for composite structures, where higher order modes are the ones that get normally excited due to the presence of flaws. Due to the absence of suitable direct procedure, damage identification from response histories needs inverse mapping; like artificial neural network. But, the main diffculty in such mapping using whole response histories is its high dimensionality. Different general purpose dimension reduction procedures; like principle component analysis or indepen- dent component analysis are available in the literature. As these dimensionally reduced spaces may loose the output uniqueness, which is an essential requirement for neural network mapping, suitable algorithms for extraction of damage signature from these re- sponse histories are not available. Alternatively, fusion of trained networks for different partitioning of the damage space or different number of dimension reduction technique, can overcome this issue efficiently. In addition, coordination of different networks trained with different partitioning for training and testing samples, training algorithms, initial conditions, learning and momentum rates, architectures and sequence of training etc., are some of the factors that improves the mapping efficiency of the networks. The applications of smart materials have drawn much attention in aerospace, civil, mechanical and even bioengineering. The emerging field of smart composite structures offers the promise of truly integrated health and usage monitoring, where a structure can sense and adapt to their environment, loading conditions and operational requirements, and materials can self-repair when damaged. The concept of structural health monitoring using smart materials relies on a network of sensors and actuators integrated with the structure. This area shows great promise as it will be possible to monitor the structural condition of a structure, throughout its service lifetime. Integrating intelligence into the structures using such networks is an interesting field of research in recent years. Some materials that are being used for this purpose include piezoelectric, magnetostrictive and fiber-optic sensors. Structural health monitoring using, piezoelectric or fiber-optic sensors are available in the literature. However, very few works have been reported in the literature on the use of magnetostrictive materials, especially for composite structures. Non contact sensing and actuation with high coupling factor, along with other prop- erties such as large bandwidth and less voltage requirement, make magnetostrictive materials increasingly popular as potential candidates for sensors and actuators in structural health monitoring. Constitutive relationships of magnetostrictive material are represented through two equations, one for actuation and other for sensing, both of which are coupled through magneto-mechanical coefficient. In existing finite element formulation, both the equations are decoupled assuming magnetic field as proportional to the applied current. This assumption neglects the stiffness contribution coming from the coupling between mechanical and magnetic domains, which can cause the response to deviate from the time response. In addition, due to different fabrication and curing difficulties, the actual properties of this material such as magneto-mechanical coupling coefficient or elastic modulus, may differ from results measured at laboratory conditions. Hence, identification of the material properties of these embedded sensor and actuator are essential at their in-situ condition. Although, finite element method still remains most versatile, accurate and generally applicable technique for numerical analysis, the method is computationally expensive for wave propagation analysis of large structures. This is because for accurate prediction, the finite element size should be of the order of the wavelength, which is very small due to high frequency loading. Even in health monitoring studies, when the flaw sizes are very small (of the order of few hundred microns), only higher order modes will get affected. This essentially leads to wave propagation problem. The requirement of cost-effective computation of wave propagation brings us to the necessity of spectral finite element method, which is suitable for the study of wave propagation problems. By virtue of its domain transfer formulation, it bypasses the large system size of finite element method. Further, inverse problem such as force identification problem can be performed most conveniently and efficiently, compared to any other existing methods. In addition, spectral element approach helps us to perform force identification directly from the response histories measured in the sensor. The spectral finite element is used widely for both elementary and higher order one or two dimensional waveguides. Higher order waveguides, normally gives a behavior, where a damping mode (evanescent) will start propagating beyond a certain frequency called the cut-off frequency. Hence, when the loading frequencies are much beyond their corresponding cut-off frequencies, higher order mo des start propagating along the structure and should be considered in the analysis of wave propagations. Based on these considerations, three main goals are identified to be pursued in this thesis. The first is to develop the constitutive relationship for magnetostrictive sensor and actuator suitable for structural analysis. The second is the development of different numerical tools for the modelling the damages. The third is the application of these developed elements towards solving inverse problems such as, material property identification, impact force identification, detection and identification of delamination in composite structure. The thesis consists of four parts spread over six chapters. In the first part, linear, nonlinear, coupled and uncoupled constitutive relationships of magnetostrictive materials are studied and the elastic modulus and magnetostrictive constant are evaluated from the experimental results reported in the literature. In uncoupled model, magnetic field for actuator is considered as coil constant times coil current. The coupled model is studied without assuming any explicit direct relationship with magnetic field. In linear coupled model, the elastic modulus, the permeability and magnetostrictive coupling are assumed as constant. In nonlinear-coupled model, the nonlinearity is decoupled and solved separately for the magnetic domain and mechanical domain using two nonlinear curves,’ namely the stress vs. strain curve and magnetic flux density vs. magnetic field curve. This is done by two different methods. In the first, the magnetic flux density is computed iteratively, while in the second, artificial neural network is used, where a trained network gives the necessary strain and magnetic flux density for a given magnetic field and stress level. In the second part, different finite element formulations for composite structures with embedded magnetostrictive patches, which can act both as sensors and actuators, is studied. Both mechanical and magnetic degrees of freedoms are considered in the formulation. One, two and three-dimensional finite element formulations for both coupled and uncoupled analysis is developed. These developed elements are then used to identify the errors in the overall response of the structure due to uncoupled assumption of the magnetostrictive patches and shown that this error is comparable with the sensitivity of the response due to different damage scenarios. These studies clearly bring out the requirement of coupled analysis for structural health monitoring when magnetostrictive sensor and actuator are used. For the specific cases of beam elements, super convergent finite element formulation for composite beam with embedded magnetostrictive patches is introduced for their specific advantages in having superior convergence and in addition, these elements are free from shear locking. A refined 2-node beam element is derived based on classical and first order shear deformation theory for axial-flexural-shear coupled deformation in asymmetrically stacked laminated composite beams with magnetostrictive patches. The element has an exact shape function matrix, which is derived by exactly solving the static part of the governing equations of motion, where a general ply stacking is considered. This makes the element super convergent for static analysis. The formulated consistent mass matrix, however, is approximate. Since the stiffness is exactly represented, the formulated element predicts natural frequency to greater level of accuracy with smaller discretization compared to other conventional finite elements. Finally, these elements are used for material property identification in conjunction with artificial neural network. In the third part, frequency domain analysis is performed using spectrally formulated beam elements. The formulated elements consider deformation due to both shear and lateral contraction, and numerical experiments are performed to highlight the higher order effects, especially at high frequencies. Spectral element is developed for modelling wave propagation in composite laminate in the presence of magnetostrictive patches. The element, by virtue of its frequency domain formulation, can analyze very large domain with nominal cost of computation and is suitable for studying wave propagation through composite materials. Further more, identification of impact force is performed form the magnetostrictive sensor response histories using these spectral elements. In the last part, different numerical examples for structural health monitoring are directed towards studying the responses due to the presence of the delamination in the structure; and the identification of the delamination from these responses using artificial neural network. Neural network is applied to get structural damage status from the finite element response using its mapping feature, which requires output uniqueness. To overcome the loss of output uniqueness due to the dimension reduction, damage space is divided into different overlapped zones and then different networks are trained for these zones. Committee machine is used to co ordinate among these networks. Next, a five-stage hierarchy of networks is used to consider partitioning of damage space, where different dimension reduction algorithms and different partitioning between training and testing samples are used for better mapping fro the identification procedure. The results of delamination detection for composite laminate show that the method developed in this thesis can be applied to structural damage detection and health monitoring for various industrial structures. This thesis collectively addresses all aspects pertaining to the solution of inverse problem and specially the health monitoring of composite structures using magnetostric tive sensor and actuator. In addition, the thesis discusses the necessity of higher order theory in the high frequency analysis of wavw propagation. The thesis ends with brief summary of the tasks accomplished, significant contribution made to the literature and the future applications where the proposed methods addressed in this thesis can be applied.

The behaviour of a free-standing thin film differs from that of a film surface-bonded or embedded due to the boundary constraints. A general dearth of analytical models, in regard to prediction of the operational competence of a constrained Piezoelectric thin film, prevails. In conventional design of miniaturized thin film devices, several non classical effects, for instance the effect of boundary constraints, are not considered. To warrant the design and performance optimisation of thin film sensors, such effect must be taken into account in a forethoughtful manner. This thesis is an attempt to achieve such optimisation through modeling of thin films. The coupled problem of a film on a substrate is solved semi-analytically in theoretical cases; and by finite element analysis in realistic cases for damage identification in the host structure. We first propose a two-dimensional analytical model of a constrained Piezoelectric thin film embedded in a host. Analytical expressions of capacitance and voltage across the electrodes are obtained by assuming first order shear deformation across the film thickness. The bonding layer between the film and the substrate, which is assumed to be an equivalent single layer including electrodes, insulation layer, adhesive layer etc., is modeled by taking into account its viscoelastic property. Residual stress is incorporated in the constitutive model through equivalent residual strain. Simulations on 10 m thick PVDF and 100 mPZT films are conducted. They illustrate the dependence of voltage response and capacitance on the applied stress, as well as on the residual stress. A maximum percentage variation in capacitance, as compared to the conventional estimate, is about 2% in a PVDF film and +75% to-65% in a PZT film for various combinations of tensile stresses applied at the ends of the film. Effect of residual stress is also exemplified via comparative response of a 1 m PZT film deposited on Pt/Ti/Si(0 0 1), with and without residual stress. For this case, an almost +50% increase in the voltage and an equivalent drop in the capacitance is observed. Next, we look into the voltage response profile of this model by employing it as a sensor to identify a finite mode I and mode II sub-surface cracks in a finite size host. To model the embedded crack, additional perturbation functions in the displacement field due to linear elastic crack tips in an infinite solid under plane strain condition are introduced to accommodate the stress free conditions at its surfaces. The film model requires the interfacial displacement and traction conditions, which are obtained from the analysis of the host. The combined analysis of the film and crack models brings forth the voltage gradient along the film span as a direct indicator of the location of crack in the axial direction, whereas the voltage magnitude represents the size of the crack. Following this analysis, a quasi three-dimensional(3-D) model of a Piezoelectric thin film surface-bonded to the host structure is proposed. With due consideration of restriction on the thickness of the film, here the model is based on a reduced 3-D continuum mechanics approach. The displacement field in the film is assumed to vary according to the third-order shear deformation theory; and the electrical and mechanical boundary conditions on the surfaces of the film are accommodated in a consistent manner. The formulation yields a governing inhomogeneous system of second-order Partial Differential Equations(PDEs), which is dependent on the displacement field at the film-host interface through force terms. Semi-analytical expressions of potential difference and capacitance are obtained. This system is solved numerically for two unknown rotations about X and Y axes of the film by finite element method. A maximum variation of about 2.5% is obtained in the capacitance of a 10 m PVDF film, as compared to its conventional estimate. The operational performance of this model is assessed in terms of its voltage response over the film area for various displacement fields. Conformation of this response to the input displacement field attests to its mathematical integrity. Next, we ascertain the versatility of this model in its role as a sensor for Structural Health Monitoring. To deal with cracks in the host plate, finite size rectangular surfaces are introduced as crack faces. The film domain and the host domain are discretized with an a posteriori h-refinement strategy and compatible interfacial nodes at the film-host interface via finite element interpolation. The resulting coupled problem is solved by static finite element analysis. The nature of the voltage pattern over the film surface is peculiar to the mode of crack, and is a qualitative portrayal of its presence. To correlate the electric potential(voltage) –a distributed parameter – to the geometry and orientation of the crack, as well as to quantify it, electrostatic measures in terms of integrated potential difference and its spatial gradients on the film surface are proffered. The numerical implications of these measures are elicited through simulation results of various crack sizes in damaged and healthy hosts under identical conditions of stress and boundary. The pattern of these measures in a damaged host becomes oscillatory as compared to straight lines observed in a healthy host. Furthermore, the reduced 3-D model is extended to perform dynamic analysis with the inclusion of inertial terms in the governing equilibrium equations. Subsequently, the acceleration terms appear in the governing inhomogeneous system of PDEs in the force terms. Finite element analyses of this extended film model on an isotropic beam with surface and sub-surface cracks, and on a composite plate with delamination, are then performed in the time domain. In all cases, an excellent conformation of the voltage profile at any point in the film domain to the velocity profile at the corresponding point in the film-host interface is observed. Again, to quantify the extent of damage in the host, we proffer electrical measures based on the Lpnorm, of second order, of the voltage and its directional derivatives. We exemplify the numerical implications of these measures in the time domain through sensitivity analysis in regard to the defected areas, and their region of occurrence relative to the film sensor. The response of the film model educes that the relatively flat curves after the first incident pulse in a healthy structure shoots off to a monotonic pattern in damaged hosts. The measures depict high degree of sensitivity in regard to the variation in the area of damage of any nature. An apposition of the static and dynamic analyses is elaborated towards the end of this dissertation. It proves to be very insightful in the damage assessment of the host structure, for it shows the utility of the dynamic model to sense the location of the damage occurrence, whereas a more in-depth assessment on its nature and mode of the crack would demand a static analysis in its proximal regions. To sum up, in light of these models and the proposed measures, this thesis establishes salient justifications pertaining to their pragmatic significance. We believe that these results represent an important contribution towards the ongoing research on understanding the role of boundary constraints in mechanically thin Piezoelectric films.

The threaded fasteners are one of the most versatile methods for assembly of structural components. For example, in bridges large bolts are used to fix base columns and small bolts are used to support access ladders. Naturally not all bolts are critical for the operation of the structure. Fasteners loaded with small forces and present in large quantities do not receive the same treatment as the critical bolts. Typical maintenance operations such tension measurements, internal stress checking or monitoring of crack development are not practical due to cost and time constrains. Although failure of a single non-critical fastener is not a significant threat to the structure's stability, massive malfunction may cause structural problem such as insufficient stiffness or excessive vibrations. The health of bolted joints is defined by a single parameter: the clamping force (CF). The CF is the force that holds the elements of the joint together. If the CF is too low, separation and bolt fatigue may occur. On the other hand, excessive CF may produce damages in the structural members such as excessive distortion or breakage. The CF is generated by the superposition of the individual tension of the bolts. The bolt tension, also referred as bolt preload, is the actual force that is stretching the bolt body. Maintaining the appropriate tension in bolts ensures a proper CF and hence a good health of the joint. In this thesis, a novel methodology for estimating the tension in bolts using surface acoustic waves (SAWs) is investigated. The tension is estimated by using the reflection of SAWs created by the bolt head interference. Increments in the bolt tension raise the points of interaction between the waves and the bolt head (real area of contact), and hence the position of the reflective boundaries. The variations are estimated using the "conventional linear synthetic array" imaging technique. A singular transducer is actuated from predefined positions to produce an array of signals that are subsequently arranged and added to construct an acoustic image. Three sets of experiment are presented in this research for validating the proposed concept: tension estimation of a ¼ inch stainless steel bolt, a ½ inch stainless steel bolt and ¼ inch grade 8 bolt. Acoustic images of the surface of the clamped plate illustrate a clear trend in the position of the reflective boundary when torque is changed. In all cases, the torque increments increase the real area of contact and therefore the position of the reflective boundary. As expected, the real area of contact grew from the bolt head center to the perimeter, which causes an effect of apparent movement of the boundary. This research proves the potential of the ultrasonic imaging methodology to measure applied tension. The result showed that the system can be used to successfully inspect tension in bolts of ½ and ¼ inches. The methodology investigated in this thesis is the first steps towards the development of bolt tension sensor based on surface acoustic waves.

The work in this dissertation comprises aeroservoelastic simulation development, two modal filter design case studies and theoretical improvement of the modal filter. The modal filter is made robust to sensor bias. Studies have shown that the states estimated by the modal filter can be integrated into active structural control. The integration of modal filters into aircraft structural control systems is explored. Modal filters require distributed sensing to achieve accurate modal coordinate estimates. Distributed sensing technology has progressed to the point, where it is being tested on aircraft such as Ikhana and the upcoming X-56A. Previously, the modal filter was criticized for requiring too many sensors. It was never assessed for its potential benefits in aircraft control. Therefore it is of practical interest to reinvestigate the modal filter. The first case study shows that under conditions of sensor normality, the modal filter is a Gaussian efficient estimator in an aeroservoelastic environment. This is a fundamental experiment considering the fact that the modal filter has never been tested in the airflow. To perform this case study a linear aeroservoelastic code capable of modeling distributed sensing is developed and experimentally validated. From this code, a computational wing model is fitted with distributed sensing. A modal filtering design methodology is developed and applied. With distributed sensing and modal filtering feedback control is achieved. This is also compared and contrasted with a controller using state-of-the-art accelerometers. In addition, new methods of active shape control are introduced for warping an aeroelastic structure utilizing the modal filter and control surfaces. The next case study takes place in a realistic setting for an aircraft. Flexible aircraft bring challenges to the active control community. Increased gust loads, possibility of flutter, and off-design drag may detrimentally affect performance and safety. Aeroservoelastic tailoring, gust load alleviation (GLA) and active flutter suppression (AFS) may be required on future flexible air vehicles. It is found that modal filters can theoretically support these systems. The aircraft case study identifies additional steps required in the modal filtering design methodology. Distributed sensing, the modal filter and modal reference shape control are demonstrated on the X-56A flutter-unstable simulation model. It is shown that control of deformations at potentially millions of points on an aircraft vehicle can be achieved through control of a few modal coordinates. Finally modal filter robustness is theoretically improved and computationally verified. State-of-the-art modal filters have high bias sensitivity. In fact, this is so critical that state-of-the-art modal filters may never be certified for aircraft implementation. This is especially true within a flight critical control system. The solution to this problem is found through derivation of the robust modal filter. The filter combines good properties of concentration algorithms with robust re-descending M-estimation. A new trim criterion specific to the strain based modal sensing system is derived making the filter robust to asymmetric or leverage point outliers. Robust starts are introduced to improve convergence of the modal estimation system to the globally optimal solution in the presence of 100s of biased fiber optic sensors.

The field of bridge monitoring is one of rapid development. Advances in sensor technologies, in data communication and processing algorithms all affect the possibilities of Structural Monitoring in Bridges. Bridges are a very critical part of a country’s infrastructure, they are expensive to build and maintain, and many uncertainties surround important factors determining their serviceability and deterioration state. As such, bridges are good candidates for monitoring. Monitoring can extend the service life and avoid or postpone replacement, repair or strengthening works. The amount of resources saved, both to the owner and the users, by reducing the amount of non-operational time can easily justify the extra investment in monitoring. This thesis consists of an extended summary and five appended papers. The thesis presents advances in sensor technology, damage identification algorithms, Bridge Weigh-In-Motion systems, and other techniques used in bridge monitoring. Four case studies are presented. In the first paper, a fully operational Bridge Weigh-In-Motion system is developed and deployed in a steel railway bridge. The gathered data was studied to obtain a characterization of the site specific traffic. In the second paper, the seasonal variability of a ballasted railway bridge is studied and characterized in its natural variability. In the third, the non-linear characteristic of a ballasted railway bridge is studied and described stochastically. In the fourth, a novel damage detection algorithm based in Bridge Weigh-In-Motion data and machine learning algorithms is presented and tested on a numerical experiment. In the fifth, a bridge and traffic monitoring system is implemented in a suspension bridge to study the cause of unexpected wear in the bridge bearings. Some of the major scientific contributions of this work are: 1) the development of a B-WIM for railway traffic capable of estimating the load on individual axles; 2) the characterization of in-situ measured railway traffic in Stockholm, with axle weights and train configuration; 3) the quantification of a hitherto unreported environmental behaviour in ballasted bridges and possible mechanisms for its explanation (this behaviour was shown to be of great importance for monitoring of bridges located in colder climate) 4) the statistical quantification of the nonlinearities of a railway bridge and its yearly variations and 5) the integration of B-WIM data into damage detection techniques. / <p>QC 20140910</p>

The development of structural monitoring systems is a critical research area because of the age and sustainment costs associated with many aircraft in use today. Specifically, integrated structural health monitoring (SHM) systems are advantageous because they allow for automated, near real-time assessment of the state of the structure, where the automation improves both the accuracy of the measurements and allows for more frequent system interrogation than possible with traditional nondestructive evaluation methods. Ultrasonic techniques are particularly well-suited for SHM systems because of their potential to detect and track damage well before structural failure using in situ sensors. The research problem considered in this thesis is detection and tracking of fatigue cracks emanating from fastener holes in metallic structural components. The sensing method utilizes attached ultrasonic transducers, and tracking of damage is achieved by employing a state estimation framework that incorporates a well-known empirical model for crack growth and a measurement model relating the ultrasonic response to crack size. The state estimation process is preceded by an automated crack detection algorithm, and can be followed by a prediction of remaining life assuming future usage. The state estimation framework provides a better estimate of crack size than either the ultrasonic measurement model or crack growth model alone. Although the example application is monitoring of fastener holes, the general approach is applicable to a variety of SHM problems.

Changes in load characteristics, deterioration with age, environmental influences and random actions may cause local or global damage in structures, especially in bridges, which are designed for long life spans. Continuous health monitoring of structures will enable the early identification of distress and allow appropriate retrofitting in order to avoid failure or collapse of the structures. In recent times, structural health monitoring (SHM) has attracted much attention in both research and development. Local and global methods of damage assessment using the monitored information are an integral part of SHM techniques. In the local case, the assessment of the state of a structure is done either by direct visual inspection or using experimental techniques such as acoustic emission, ultrasonic, magnetic particle inspection, radiography and eddy current. A characteristic of all these techniques is that their application requires a prior localization of the damaged zones. The limitations of the local methodologies can be overcome by using vibration-based methods, which give a global damage assessment. The vibration-based damage detection methods use measured changes in dynamic characteristics to evaluate changes in physical properties that may indicate structural damage or degradation. The basic idea is that modal parameters (notably frequencies, mode shapes, and modal damping) are functions of the physical properties of the structure (mass, damping, and stiffness). Changes in the physical properties will therefore cause changes in the modal properties. Any reduction in structural stiffness and increase in damping in the structure may indicate structural damage. This research uses the variations in vibration parameters to develop a multi-criteria method for damage assessment. It incorporates the changes in natural frequencies, modal flexibility and modal strain energy to locate damage in the main load bearing elements in bridge structures such as beams, slabs and trusses and simple bridges involving these elements. Dynamic computer simulation techniques are used to develop and apply the multi-criteria procedure under different damage scenarios. The effectiveness of the procedure is demonstrated through numerical examples. Results show that the proposed method incorporating modal flexibility and modal strain energy changes is competent in damage assessment in the structures treated herein.

Submitted by Sanderson Manoel Da Conceição (enders83@yahoo.com.br) on 2018-08-24T00:09:53Z No. of bitstreams: 1 TeseDR_Sanderson.pdf: 5806318 bytes, checksum: 51410134afd7ae86d0783074d6012e88 (MD5) / Approved for entry into archive by Cristina Alexandra de Godoy null (cristina@adm.feis.unesp.br) on 2018-08-24T17:09:49Z (GMT) No. of bitstreams: 1 conceicao_sm_dr_ilha.pdf: 5957405 bytes, checksum: 16cab2d9c84f81cd3cd4ff0b9fa36219 (MD5) / Made available in DSpace on 2018-08-24T17:09:49Z (GMT). No. of bitstreams: 1 conceicao_sm_dr_ilha.pdf: 5957405 bytes, checksum: 16cab2d9c84f81cd3cd4ff0b9fa36219 (MD5) Previous issue date: 2016-12-20 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / A ideia central deste trabalho é utilizar o método dos Elementos Espectrais (SEM, do inglês Spectral Element Method) para aplicações de controle ativo de vibrações e monitoramento da integridade estrutural (SHM, do inglês Structural Health Monitoring). Diversos trabalhos têm abordado estes tópicos de forma independente. No entanto, para aplicações reais de engenharia, utilizar os mesmos atuadores, sensores e sistemas de aquisição de dados para controle e monitoramento pode reduzir investimentos e simplificar processos. Por esta motivação, este trabalho apresenta um estudo de modelos espectrais para estruturas do tipo viga considerando aplicações de controle de vibrações e monitoramento da integridade estrutural. Na modelagem são considerados os modelos de vigas de Euler-Bernoulli e Timoshenko, além de transdutores piezelétricos acoplados. A técnica de controle clássico PID (Proporcional, Integral, Derivativo) é explorada e uma nova modelagem é proposta para se considerar técnicas modernas de controle por realimentação de estados na formulação espectral. Em particular, discute-se o controlador LQR (do inglês, Linear Quadratic Regulator), no entanto, a metodologia permite se considerar outras técnicas de controle por realimentação baseada na representação no espaço de estados. Também, especificamente para monitoramento estrutural, no presente trabalho de tese apresenta-se uma discussão sobre índices de detecção de danos. Índices de detecção calculados a partir de sinais experimentais têm sido amplamente utilizados em trabalhos da literatura de SHM. No entanto, pouco tem sido esclarecido sobre seus comportamentos em função das características estruturais e dos danos. Neste sentido, o presente trabalho apresenta uma discussão do comportamento de índices baseados na norma H2, norma H∞ e no CCDM (Correlation coefficient deviation metric), para duas faixas de frequência, em função da severidade do dano e quantidade de amortecimento no sistema. Os resultados obtidos indicam que a formulação por Elementos Espectrais é adequada para viabilizar os projetos simultâneos de um controlador de vibrações e um sistema de monitoramento estrutural utilizando os mesmos equipamentos e simplificando análises ao se utilizar um único modelo dinâmico do sistema. / The main idea of this thesis is to use the Spectral Element Method (SEM), in applications of Active Vibration Control (AVC) and Structural Health Monitoring (SHM). These two topics have been approached in several works, but in an independent way. However, for real engineering applications, to use the same actuators, sensors and data acquisition systems to active control and structural monitoring can reduce the costs and simplify processes. For this reason, this thesis presents a study of spectral models for beam-like structures considering applications of vibration control and structural health monitoring. The Euler-Bernoulli and Timoshenko beam theories are used in the spectral modelling and the piezelectric transducers bonded in the structures are also considered. A classical control technique, PID (Proportional, Integral, Derivative) is explored and a new modelling approach to consider modern control methods of state feedback is proposed in spectral formulation. In particular, the Linear Quadratic Regulator (LQR) is discussed, however, this methodology allows for any other state feedback control techniques based in state space representation. Also, specifically for structural monitoring, is presented a discussion about damage detection indices. Detection indices computed from experimental data have been widely used in SHM studies. However, little has been clarified about their behaviours due to structural characteristics and damages. In this context, this work presents a discussion of the behaviour of indices based in the H2 norm, H∞ norm and CCDM (Correlation coefficient deviation metric), for two frequency ranges, depending on the severity of damage and amount of damping in the system. The obtained results indicate that the spectral element formulation is suited to enable the simultaneous design of a vibration controller and a structural monitoring system using the same data acquisition systems and simplifying analysis when using just one dynamic model of the system.

Orientador: Vicente Lopes Junior / Resumo: A ideia central deste trabalho é utilizar o método dos Elementos Espectrais (SEM, do inglês Spectral Element Method) para aplicações de controle ativo de vibrações e monitoramento da integridade estrutural (SHM, do inglês Structural Health Monitoring). Diversos trabalhos têm abordado estes tópicos de forma independente. No entanto, para aplicações reais de engenharia, utilizar os mesmos atuadores, sensores e sistemas de aquisição de dados para controle e monitoramento pode reduzir investimentos e simplificar processos. Por esta motivação, este trabalho apresenta um estudo de modelos espectrais para estruturas do tipo viga considerando aplicações de controle de vibrações e monitoramento da integridade estrutural. Na modelagem são considerados os modelos de vigas de Euler-Bernoulli e Timoshenko, além de transdutores piezelétricos acoplados. A técnica de controle clássico PID (Proporcional, Integral, Derivativo) é explorada e uma nova modelagem é proposta para se considerar técnicas modernas de controle por realimentação de estados na formulação espectral. Em particular, discute-se o controlador LQR (do inglês, Linear Quadratic Regulator), no entanto, a metodologia permite se considerar outras técnicas de controle por realimentação baseada na representação no espaço de estados. Também, especificamente para monitoramento estrutural, no presente trabalho de tese apresenta-se uma discussão sobre índices de detecção de danos. Índices de detecção calculados a partir de sinais experimen... (Resumo completo, clicar acesso eletrônico abaixo) / Abstract: The main idea of this thesis is to use the Spectral Element Method (SEM), in applications of Active Vibration Control (AVC) and Structural Health Monitoring (SHM). These two topics have been approached in several works, but in an independent way. However, for real engineering applications, to use the same actuators, sensors and data acquisition systems to active control and structural monitoring can reduce the costs and simplify processes. For this reason, this thesis presents a study of spectral models for beam-like structures considering applications of vibration control and structural health monitoring. The Euler-Bernoulli and Timoshenko beam theories are used in the spectral modelling and the piezelectric transducers bonded in the structures are also considered. A classical control technique, PID (Proportional, Integral, Derivative) is explored and a new modelling approach to consider modern control methods of state feedback is proposed in spectral formulation. In particular, the Linear Quadratic Regulator (LQR) is discussed, however, this methodology allows for any other state feedback control techniques based in state space representation. Also, specifically for structural monitoring, is presented a discussion about damage detection indices. Detection indices computed from experimental data have been widely used in SHM studies. However, little has been clarified about their behaviours due to structural characteristics and damages. In this context, this work presents a d... (Complete abstract click electronic access below) / Doutor