EEMD-MUSIC-Based Analysis for Natural Frequencies Identification of Structures Using Artificial and Natural Excitations

This paper presents a new EEMD-MUSIC- (ensemble empirical mode decomposition-multiple signal classification-) based methodology to identify modal frequencies in structures ranging from free and ambient vibration signals produced by artificial and natural excitations and also considering several factors as nonstationary effects, close modal frequencies, and noisy environments, which are common situations where several techniques reported in literature fail. The EEMD and MUSIC methods are used to decompose the vibration signal into a set of IMFs (intrinsic mode functions) and to identify the natural frequencies of a structure, respectively. The effectiveness of the proposed methodology has been validated and tested with synthetic signals and under real operating conditions. The experiments are focused on extracting the natural frequencies of a truss-type scaled structure and of a bridge used for both highway traffic and pedestrians. Results show the proposed methodology as a suitable solution for natural frequencies identification of structures from free and ambient vibration signals

Time-frequency techniques for modal parameters identification of civil structures from acquired dynamic signals

A major trust of modal parameters identification (MPI) research in recent years has been based on using artificial and natural vibrations sources because vibration measurements can reflect the true dynamic behavior of a structure while analytical prediction methods, such as finite element models, are less accurate due to the numerous structural idealizations and uncertainties involved in the simulations. This paper presents a state-of-the-art review of the time-frequency techniques for modal parameters identification of civil structures from acquired dynamic signals as well as the factors that affect the estimation accuracy. Further, the latest signal processing techniques proposed since 2012 are also reviewed. These algorithms are worth being researched for MPI of large real-life structures because they provide good time-frequency resolution and noise-immunity

Fukunaga-Koontz feature transformation for statistical structural damage detection and hierarchical neuro-fuzzy damage localisation

Piotr Omenzetter and Simon Hoell’s work on this paper within the Lloyd’s Register Foundation Centre for Safety and Reliability Engineering at the University of Aberdeen was supported by Lloyd’s Register Foundation. The Foundation helps to protect life and property by supporting engineering-related education, public engagement and the application of research.Peer reviewedPostprin

Artificial Intelligence in Civil Infrastructure Health Monitoring—historical Perspectives, Current Trends, and Future Visions

Over the past 2 decades, the use of artificial intelligence (AI) has exponentially increased toward complete automation of structural inspection and assessment tasks. This trend will continue to rise in image processing as unmanned aerial systems (UAS) and the internet of things (IoT) markets are expected to expand at a compound annual growth rate of 57.5% and 26%, respectively, from 2021 to 2028. This paper aims to catalog the milestone development work, summarize the current research trends, and envision a few future research directions in the innovative application of AI in civil infrastructure health monitoring. A blow-by-blow account of the major technology progression in this research field is provided in a chronological order. Detailed applications, key contributions, and performance measures of each milestone publication are presented. Representative technologies are detailed to demonstrate current research trends. A road map for future research is outlined to address contemporary issues such as explainable and physics-informed AI. This paper will provide readers with a lucid memoir of the historical progress, a good sense of the current trends, and a clear vision for future research

Numerical and experimental investigation of spectral domain vibration based indicators for structural health monitoring

Structural health monitoring has been defined as the acquisition, validation and analysis of technical data to facilitate life- cycle management decisions. It is the result of a convergent path from many previous existing disciplines the two most influential being condition monitoring for rotary machinery and non-destructive testing. Vibration based testing presents the greatest stage of maturity of all non-destructive techniques applied to structural health monitoring. Although modal domain use is convention, spectral domain data is by nature more complete in information and requires less manipulation. The use of spectral-domain measurements brings the need to develop new damage detection indicators, as much of the literature existing is focused on modal derived damage indicators. In this work, an integrated methodology for the evaluation of some spectral domain vibration based indicators for structural health monitoring is proposed. These indicators, namely the CFDAC and SCIs, are based on the correlation between covariance matrices of frequency response functions obtained from experimental modal analysis. An extensive numerical campaign is performed on a simple structure (consisting on a 1-edge clamped square aluminium plate) over multiple structural alteration scenarios to assess the sensibility and stability of the proposed indexes in front of common acquisition parameters. The ability of the proposed indicators to assess structural alteration progression is also evaluated. This numerical analysis is used as well to observe the relationship between proposed indicators and the residual stiffness of the simple structure evaluated in terms of relative shift from the pristine condition. Finally, the numerical methodology proposed is applied to a different and more complex typology of structure, a 3d latticed and downscaled power transmission tower to investigate the validity of the methodology for other structural configurations. Some of the cases studied in the numeric campaign are later reproduced in experimental scenarios using two specimens of aluminium plates and a downscaled prototype of a power transmission tower. Stability analysis on the indicators are reproduced and confirmed. For the aluminium plates, the relationship between indicators and residual stiffness is also obtained, showing close agreement with numerical data. Sensibility of the indicators to detect different damage typologies is found to be very similar to the one obtained in the initial numerical analysis. Results for the downscaled prototype model tower shown more dispersion than the results observed in the numerical investigation due to the influence of the boundary conditions in the model. The research finally applies the structural damage alteration indexes studied to the detection of degradation in a real scale structure in an operational environment. An installation consisting of 3 full-scale medium-voltage power transmission towers is constructed. An experimental modal analysis campaign is performed on the central tower of the installation by introducing a series of intentionally made structural alterations on the structure. Spectral indicators developed are applied to the detection of those structural modifications with noticeable success. Cases involving changes in the structural components of the tower are successfully detected. Changes in the interface between power lines and their supports of the tower are hardly noticeable using this methodology. Results of this investigation show that spectral domain damage indicators present some advantages over modal domain and temporal domain based indicators such as convenient condensing procedures without loss of information through the Fourier transform, added post-process simplicity and enhanced sensitivity to degradation that state of the art indexes.Es coneix com monitorització de la salut estructural a l'adquisició, validació i anàlisis de dades tècniques que faciliten la presa de decisions al llarg del cicle de vida d'un sistema. Aquesta tecnologia és resultat de la convergència tecnològica d'altres disciplines, com la monitorització operacional per màquines rotatòries i les tècniques d'assaig no destructiu. Els mètodes d'assaig basats en vibracions presenten el major grau de maduresa d'entre totes elles. Malgrat que la pràctica industrial sovint usa informació condensada en el domini modal, les dades en domini espectral son per naturalesa més completes i requereixen de menys post-procés. La utilització del domini espectral requereix desenvolupar nous indicadors d'alteració ja que la major part de la literatura existent se centra en indicadors basats en el domini modal. Es proposa una metodologia integrada per a la avaluació d'alguns indicadors d'alteració estructural en domini modal basats en vibració i aplicats a la monitorització de la salut estructural. Aquests indicadors, referits com a CFDAC i SCIs, estan basats en la correlació entre les matrius de covariància generades a partir de les funcions de resposta en freqüència obtingudes mitjançant anàlisi modal experimental. Es realitza una extensa campanya numèrica en una estructura senzilla (una placa d'alumini quadrada i encastada) a través d'una multitud d'estats estructuralment alterats per avaluar la sensibilitat i l'estabilitat dels indicadors enfront els paràmetres d?adquisició més comuns. En segon lloc, també s?avalua la capacitat dels indicadors per avaluar l'alteració estructural introduïda en cada cas. L'anàlisi numèrica s'utilitza a continuació per observar una possible relació entre els indicadors proposats i la rigidesa residual avaluada com a variació relativa respecte el seu valor intacte. Finalment, la metodologia numèric proposada s'aplica a una tipologia estructural diferent i més complexa, una estructura reticulada 3d que reprodueix una torre de transmissió d'energia elèctrica a escala per investigar la validesa de la metodologia en altres configuracions estructurals. Alguns dels casos estudiats a la campanya numèrica es reprodueixen experimentalment en un parell d?espècimens de placa d'alumini i en un prototip a escala de torre de transmissió elèctrica. Els anàlisis d'estabilitat numèrics sobre els indicadors es reprodueixen experimentalment, tot confirmant els resultats obtinguts. Per les plaques d'alumini, s'estudia la relació entre els indicadors i la rigidesa residual mostrant una correlació molt propera amb els resultats numèrics. La sensibilitat dels indicadors en la detecció de diferents tipologies de dany també s'observa molt similar als casos numèrics. Pere altra banda, els resultats experimentals sobre el prototip de torre a escala presenten més dispersió respecte a la corresponent campanya numèrica degut a la variabilitat en les condicions de contorn. Els indicadors proposats s'apliquen finalment en la detecció d'alteracions estructurals en una torre a escala real en condicions operacionals. Es construeix una línia que consisteix en tres torres de mitja tensió i s'executen anàlisis modals experimentals en la torre central de la mencionada instal·lació tot introduint una sèrie d'alteracions estructurals intencionals. Els indicadors espectrals presentats s'apliquen a la detecció de dites alteracions amb un èxit apreciable. Els casos que incorporen canvis en els membres de l'estructura son detectats amb èxit, mentre que la detecció en els casos que incorporen modificacions sobre les interfícies cable-estructura son més difusament detectables. Els resultats de la investigació mostren que els indicadors estructurals espectrals estudiats presenten algunes avantatges sobre els indicadors basats en domini com ara un procés de condensació més senzill sense pèrdua d'informació vibratòria (...

Numerical and experimental investigation of spectral domain vibration based indicators for structural health monitoring

Structural health monitoring has been defined as the acquisition, validation and analysis of technical data to facilitate life- cycle management decisions. It is the result of a convergent path from many previous existing disciplines the two most influential being condition monitoring for rotary machinery and non-destructive testing. Vibration based testing presents the greatest stage of maturity of all non-destructive techniques applied to structural health monitoring. Although modal domain use is convention, spectral domain data is by nature more complete in information and requires less manipulation. The use of spectral-domain measurements brings the need to develop new damage detection indicators, as much of the literature existing is focused on modal derived damage indicators. In this work, an integrated methodology for the evaluation of some spectral domain vibration based indicators for structural health monitoring is proposed. These indicators, namely the CFDAC and SCIs, are based on the correlation between covariance matrices of frequency response functions obtained from experimental modal analysis. An extensive numerical campaign is performed on a simple structure (consisting on a 1-edge clamped square aluminium plate) over multiple structural alteration scenarios to assess the sensibility and stability of the proposed indexes in front of common acquisition parameters. The ability of the proposed indicators to assess structural alteration progression is also evaluated. This numerical analysis is used as well to observe the relationship between proposed indicators and the residual stiffness of the simple structure evaluated in terms of relative shift from the pristine condition. Finally, the numerical methodology proposed is applied to a different and more complex typology of structure, a 3d latticed and downscaled power transmission tower to investigate the validity of the methodology for other structural configurations. Some of the cases studied in the numeric campaign are later reproduced in experimental scenarios using two specimens of aluminium plates and a downscaled prototype of a power transmission tower. Stability analysis on the indicators are reproduced and confirmed. For the aluminium plates, the relationship between indicators and residual stiffness is also obtained, showing close agreement with numerical data. Sensibility of the indicators to detect different damage typologies is found to be very similar to the one obtained in the initial numerical analysis. Results for the downscaled prototype model tower shown more dispersion than the results observed in the numerical investigation due to the influence of the boundary conditions in the model. The research finally applies the structural damage alteration indexes studied to the detection of degradation in a real scale structure in an operational environment. An installation consisting of 3 full-scale medium-voltage power transmission towers is constructed. An experimental modal analysis campaign is performed on the central tower of the installation by introducing a series of intentionally made structural alterations on the structure. Spectral indicators developed are applied to the detection of those structural modifications with noticeable success. Cases involving changes in the structural components of the tower are successfully detected. Changes in the interface between power lines and their supports of the tower are hardly noticeable using this methodology. Results of this investigation show that spectral domain damage indicators present some advantages over modal domain and temporal domain based indicators such as convenient condensing procedures without loss of information through the Fourier transform, added post-process simplicity and enhanced sensitivity to degradation that state of the art indexes.Es coneix com monitorització de la salut estructural a l'adquisició, validació i anàlisis de dades tècniques que faciliten la presa de decisions al llarg del cicle de vida d'un sistema. Aquesta tecnologia és resultat de la convergència tecnològica d'altres disciplines, com la monitorització operacional per màquines rotatòries i les tècniques d'assaig no destructiu. Els mètodes d'assaig basats en vibracions presenten el major grau de maduresa d'entre totes elles. Malgrat que la pràctica industrial sovint usa informació condensada en el domini modal, les dades en domini espectral son per naturalesa més completes i requereixen de menys post-procés. La utilització del domini espectral requereix desenvolupar nous indicadors d'alteració ja que la major part de la literatura existent se centra en indicadors basats en el domini modal. Es proposa una metodologia integrada per a la avaluació d'alguns indicadors d'alteració estructural en domini modal basats en vibració i aplicats a la monitorització de la salut estructural. Aquests indicadors, referits com a CFDAC i SCIs, estan basats en la correlació entre les matrius de covariància generades a partir de les funcions de resposta en freqüència obtingudes mitjançant anàlisi modal experimental. Es realitza una extensa campanya numèrica en una estructura senzilla (una placa d'alumini quadrada i encastada) a través d'una multitud d'estats estructuralment alterats per avaluar la sensibilitat i l'estabilitat dels indicadors enfront els paràmetres d?adquisició més comuns. En segon lloc, també s?avalua la capacitat dels indicadors per avaluar l'alteració estructural introduïda en cada cas. L'anàlisi numèrica s'utilitza a continuació per observar una possible relació entre els indicadors proposats i la rigidesa residual avaluada com a variació relativa respecte el seu valor intacte. Finalment, la metodologia numèric proposada s'aplica a una tipologia estructural diferent i més complexa, una estructura reticulada 3d que reprodueix una torre de transmissió d'energia elèctrica a escala per investigar la validesa de la metodologia en altres configuracions estructurals. Alguns dels casos estudiats a la campanya numèrica es reprodueixen experimentalment en un parell d?espècimens de placa d'alumini i en un prototip a escala de torre de transmissió elèctrica. Els anàlisis d'estabilitat numèrics sobre els indicadors es reprodueixen experimentalment, tot confirmant els resultats obtinguts. Per les plaques d'alumini, s'estudia la relació entre els indicadors i la rigidesa residual mostrant una correlació molt propera amb els resultats numèrics. La sensibilitat dels indicadors en la detecció de diferents tipologies de dany també s'observa molt similar als casos numèrics. Pere altra banda, els resultats experimentals sobre el prototip de torre a escala presenten més dispersió respecte a la corresponent campanya numèrica degut a la variabilitat en les condicions de contorn. Els indicadors proposats s'apliquen finalment en la detecció d'alteracions estructurals en una torre a escala real en condicions operacionals. Es construeix una línia que consisteix en tres torres de mitja tensió i s'executen anàlisis modals experimentals en la torre central de la mencionada instal·lació tot introduint una sèrie d'alteracions estructurals intencionals. Els indicadors espectrals presentats s'apliquen a la detecció de dites alteracions amb un èxit apreciable. Els casos que incorporen canvis en els membres de l'estructura son detectats amb èxit, mentre que la detecció en els casos que incorporen modificacions sobre les interfícies cable-estructura son més difusament detectables. Els resultats de la investigació mostren que els indicadors estructurals espectrals estudiats presenten algunes avantatges sobre els indicadors basats en domini com ara un procés de condensació més senzill sense pèrdua d'informació vibratòria (...)Postprint (published version

Detekcija i lokalizacija oštećenja pri monitoringu stanja građevinskih konstrukcija

The presented thesis studied proposed a novel procedures that was implemented to develop a Structural Health Monitoring (SHM) technique as non-destructive tests that can be applied to detect damage, localization and quantification of civil structures. This technique based on investigations of dynamic characteristics of the structures to detect the damages through their operational conditions of service life. The proposed procedure was built using Artificial Intelligence Technique (AIT) under concept of the methods of damage detection based on updating FE model using heuristic optimization methods. The proposed SHM procedure Using Simulated Annealing heuristic optimization methos was shortened to "SHMUSA-procedure". The SHMUSA-procedure was verified on four types of steel structural models; simply supported overhang beam; grid bridge, Verendeel bridge and Multi-storey building model to prove reliability, efficiency and robustness under various dynamic behaviours. The SHMUSA-procedure was adopted the changes in dynamic characteristics, natural frequency and normalized mode shape vector, which are extracted from experimental modal analysis and estimated from numerical modal analysis of the damage scenario for structural models. and their characteristics, location and severity,. The experimental testing is implemented using simulation of ambient vibration measurements by exciting the structural models by shaker device using generated vibration signal. The dynamic response, output only, of the structural models are recorded using 8- accelerometers and 8-channel acquisition device. Experimentally, the modal properties of the structural models are extracted by ARTeMIS extractor software using Frequency Domain Decomposition (FDD) technique by peak picking method. The numerical simulation of structural models are modeled in Finite Element Model (FEM) using ANSYS package software by ANSYS Parametric Design Language (APDL). Numerically, the modal properties of structural models are estimated by ANSYS software using block Lanczos method of dynamic modal analysis for isotropic elastic linear structural models type. The Finite Element Analysis (FEA) is performed using three element types in the FE models, Beam4, Shell63 and Mass21, to analyze the four structural models...Prikazani teza studije je predložio nove procedure koje se sprovode da razvije Strukturno Zdravlje monitoring (SHM) tehniku kao bez razaranja testova koje se mogu primeniti za detekciju oštećenja, lokalizaciju i kvantitativno državnih struktura. Ova tehnika zasniva na istraživanjima dinamičkih karakteristika objekata da otkriju štetu kroz njihove operativne stanja radnog veka. Predloženi SHM Postupak se utvrdi na četiri vrste čeličnih strukturnih modela; jednostavno podržali ispust zraka; rešetka most, Verendeel most i model višespratnica. Predloženi SHM postupak je usvojila izmene u dinamičkih karakteristika, prirodnog učestalosti i načina oblika, strukturnih modela, koji su izvađeni iz eksperimentalne modalne analize i procenjene od numeričke analize modalni. Eksperimentalno ispitivanje se sprovodi pomoću simulaciju ambijentalnih vibracija merenja od najuzbudljivijih strukturne modele šejker uređaja sa generiše vibracije signalom. Dinamički odgovor, samo izlaz, strukturnih modela su snimljeni korišćenjem 8- ubrzanja i 8-channle uređaj sticanje. Eksperimentalni modal osobine strukturnih modela su izdvojite pomoću Artemis odsisnog softvera pika metodom branje frekventnom domenu razlaganja (FDD) tehnikom. Numerička simulacija strukturnih modela su modelira konačnih elemenata Model (MKE) koristeći ANSIS paket Softvare bi ANSIS Parametric Design Jezik (APDL). Numeričke modal svojstva strukturnih modela se procenjuju pomoću ANSIS softver za blok algoritam metodom dinamičke analize modalne za izotropnoj elastične linearno tipa strukturni modeli. U analizi FE, dva tipa elementa se primenjuju na FEM da se analiziraju strukturne modele, Beam4 i Mass21 tip elementa. Predloženi SHM Postupak se vrši pomoću vještačka inteligencija tehnika (AIT), koji se primenjuje u ovoj studiji pomoću funkcije na tzv metodu heuristike optimizaciju za otkrivanje oštećenja i njihove karakteristike, lokacije i ozbiljnost, u strukturnim modelima. Predloženi SHM postupak usvaja heurističkog optimizaciju simuliranog kaljenja (SA) metoda u AIT. Predloženi SHM procedura se kreira pomoću višu stručnu računara jezik MATLAB softvera životne sredine za te svrhe. U ovoj studiji, modifikovani cilj funkcija je usvojen u SA metode optimizacije uključiti osetljive modalni parametri za promenu u savijanja krutosti strukturnog modela usled prisustva štete..

Condition assessment of bridge structures using statistical analysis of wavelets

La surveillance à distance des structures a émergé comme une préoccupation importante pour les ingénieurs afin de maintenir la sécurité et la fiabilité des infrastructures civiles pendant leur durée de vie. Les techniques de surveillance structurale (SHM) sont de plus en plus populaires pour fournir un diagnostic de "l'état" des structures en raison de leur vieillissement, de la dégradation des matériaux ou de défauts survenus pendant leur construction. Les limites de l'inspection visuelle et des techniques non destructives, qui sont couramment utilisées pour détecter des défauts extrêmes sur les parties accessibles des structures, ont conduit à la découverte de nouvelles technologies qui évaluent d’un seul tenant l'état global d'une structure surveillée. Les techniques de surveillance globale ont été largement utilisées pour la reconnaissance d'endommagement dans les grandes infrastructures civiles, telles que les ponts, sur la base d'une analyse modale de la réponse dynamique structurale. Cependant, en raison des caractéristiques complexes des structures oeuvrant sous des conditions environnementales variables et des incertitudes statistiques dans les paramètres modaux, les techniques de diagnostic actuelles n'ont pas été concluantes pour conduire à une méthodologie robuste et directe pour détecter les incréments de dommage avant qu'ils n'atteignent un stade critique. C’est ainsi que des techniques statistiques de reconnaissance de formes sont incorporées aux méthodes de détection d'endommagement basées sur les vibrations pour fournir une meilleure estimation de la probabilité de détection des dommages dans des applications in situ, ce qui est habituellement difficile compte tenu du rapport bruit à signal élevé. Néanmoins, cette partie du SHM est encore à son stade initial de développement et, par conséquent, d'autres tentatives sont nécessaires pour parvenir à une méthodologie fiable de détection de l'endommagement. Une stratégie de détection de dommages basée sur des aspects statistiques a été proposée pour détecter et localiser de faibles niveaux incrémentiels d'endommagement dans une poutre expérimentale pour laquelle tant le niveau d'endommagement que les conditions de retenue sont réglables (par exemple ancastrée-ancastrée et rotulée-rotulée). Premièrement, des expériences ont été effectuées dans des conditions de laboratoire contrôlées pour détecter de faibles niveaux d'endommagement induits (par exemple une fissure correspondant à 4% de la hauteur d’une section rectangulaire équivalente) simulant des scénarios d'endommagement de stade précoce pour des cas réels. Différents niveaux d'endommagement ont été simulés à deux endroits distincts le long de la poutre. Pour chaque série d'endommagement incrémentiel, des mesures répétées (~ 50 à 100) ont été effectuées pour tenir compte de l'incertitude et de la variabilité du premier mode de vibration de la structure en raison d'erreurs expérimentales et du bruit. Une technique d'analyse par ondelette basée sur les modes a été appliquée pour détecter les changements anormaux survenant dans les modes propres causées par le dommage. La réduction du bruit ainsi que les caractéristiques des agrégats ont été obtenues en mettant en œuvre l'analyse des composantes principales (PCA) pour l'ensemble des coefficients d'ondelettes calculés à des nœuds (ou positions) régulièrement espacés le long du mode propre. En rejetant les composantes qui contribuent le moins à la variance globale, les scores PCA correspondant aux premières composantes principales se sont révélés très corrélés avec de faibles niveaux d'endommagement incrémentiel. Des méthodes classiques d'essai d'hypothèses ont été effectuées sur les changements des paramètres de localisation des scores pour conclure objectivement et statistiquement, à un niveau de signification donné, sur la présence du dommage. Lorsqu'un dommage statistiquement significatif a été détecté, un nouvel algorithme basé sur les probabilités a été développé pour déterminer l'emplacement le plus probable de l'endommagement le long de la structure. Deuxièmement, se basant sur l'approche probabiliste, une série de tests a été effectuée dans une chambre environnementale à température contrôlée pour étudier les contributions relatives des effets de l’endommagement et de la température sur les propriétés dynamiques de la poutre afin d’estimer un facteur de correction pour l'ajustement des scores extraits. Il s'est avéré que la température avait un effet réversible sur la distribution des scores et que cet effet était plus grand lorsque le niveau d'endommagement était plus élevé. Les résultats obtenus pour les scores ajustés indiquent que la correction des effets réversibles de la température peut améliorer la probabilité de détection et minimiser les fausses alarmes. Les résultats expérimentaux indiquent que la contribution combinée des algorithmes utilisés dans cette étude était très efficace pour détecter de faibles niveaux d'endommagement incrémentiel à plusieurs endroits le long de la poutre tout en minimisant les effets indésirables du bruit et de la température dans les résultats. Les résultats de cette recherche démontrent que l'approche proposée est prometteuse pour la surveillance des structures. Cependant, une quantité importante de travail de validation est attendue avant sa mise en œuvre sur des structures réelles. Mots-clés : Détection et localisation des dommages, Poutre, Mode propre, Ondelette, Analyse des composantes principales, Rapport de probabilité, TempératureRemote monitoring of structures has emerged as an important concern for engineers to maintain safety and reliability of civil infrastructure during its service life. Structural Health Monitoring (SHM) techniques are increasingly becoming popular to provide ideas for diagnosis of the "state" of potential defects in structures due to aging, deterioration and fault during construction. The limitations of visual inspection and non-destructive techniques, which were commonly used to detect extreme defects on only accessible portions of structures, led to the discovery of new technologies which assess the "global state" of a monitored structure at once. Global monitoring techniques have been used extensively for the recognition of damage in large civil infrastructure, such as bridges, based on modal analysis of structural dynamic response. However, because of complicated features of real-life structures under varying environmental conditions and statistical uncertainties in modal parameters, current diagnosis techniques have not been conclusive in ascertaining a robust and straightforward methodology to detect damage increments before it reaches its critical stage. Statistical pattern recognition techniques are incorporated with vibration-based damage detection methods to provide a better estimate for the probability of the detection of damage in field applications, which is usually challenging given the high noise to signal ratio. Nevertheless, this part of SHM is still in its initial stage of development and, hence, further attempts are required to achieve a reliable damage detection methodology. A statistical-based damage detection strategy was proposed to detect and localize low levels of incremental damage in an experimental beam in which the level of damage and beam restraint conditions are adjustable (e.g. fixed-fixed and pinned-pinned). First, experiments were performed in controlled laboratory conditions to detect small levels of induced-damage (e.g. 4% crack height for an equivalent rectangular section) simulated for early stage damage scenarios in real cases. Various levels of damage were simulated at two distinct locations along the beam. For each sate of incremental damage, repeat measurements (~ 50 to 100) were performed to account for uncertainty and variability in the first vibration mode of the structure due to experimental errors and noise. A modal-based wavelet analysis technique was applied to detect abnormal changes occurring in the mode shapes caused by damage. Noise reduction as well as aggregate characteristics were obtained by implementing the Principal Component Analysis (PCA) into the set of wavelet coefficients computed at regularly spaced nodes along the mode shape. By discarding components that contribute least to the overall variance, the PCA scores corresponding to the first few PCs were found to be highly correlated with low levels of incremental damage. Classical hypothesis testing methods were performed on changes on the location parameters of the scores to conclude damage objectively and statistically at a given significance level. When a statistically significant damage was detected, a novel Likelihood-based algorithm was developed to determine the most likely location of damage along the structure. Secondly, given the likelihood approach, a series of tests were carried out in a climate-controlled room to investigate the relative contributions of damage and temperature effects on the dynamic properties of the beam and to estimate a correction factor for the adjustment of scores extracted. It was found that the temperature had a reversible effect on the distribution of scores and that the effect was larger when the damage level was higher. The resulted obtained for the adjusted scores indicated that the correction for reversible effects of temperature can improve the probability of detection and minimize false alarms. The experimental results indicate that the combined contribution of the algorithms used in this study were very efficient to detect small-scale levels of incremental damage at multiple locations along the beam, while minimizing undesired effects of noise and temperature in the results. The results of this research demonstrate that the proposed approach may be used as a promising tool for SHM of actual structures. However, a significant amount of challenging work is expected for implementing it on real structures. Key-words: Damage Detection and Localization, Beam, Mode Shape, Wavelet, Principal Component Analysis, Likelihood Ratio, Temperatur

Detekcija i lokalizacija oštećenja građevinskih konstrukcija na osnovu registrovanih ambijentalnih vibracija

Generally, damage detection of different types of steel structures is the main aspect that has been studied in the present work. Damage could be detected by different ways which depend on different procedures existed in literature. In the present work, the adopted concept of damage detection depends on the procedure of comparison between the updated modal parameters (natural frequencies and mode shapes) of the FE model with their corresponding experimental values. Hence, estimating of structural modal parameters experimentally and numerically are another aspects that are adopted in the present work. Based on ambient vibration measurements (AVM) that implemented upon different types of steel structures, experimental modal parameters are extracted using ARTeMIS software according to the frequency domain decomposition (FDD) technique. On the other hand, modal analysis by ANSYS software is implemented to compute the numerical values of modal parameters which required during the procedure of damage detection. The process of damage detection is executed with the aid of proposed Tabu Search (TS) optimization procedure to detect the location and severity of damage. This technique is relatively new and was not used before in the field of civil structure damage detection which satisfies the state of the art in the present work. The proposed procedures of TS optimization are written and performed in MATLAB environment. MATLAB has the ability of simultaneously handling the experimentally extracted modal parameters with their corresponding numerical values which are continuously updated by ANSYS software. The comparison between the estimated experimental and numerical modal parameters is executed according to values obtained by a certain proposed form called "objective function" which produces the value of error that used in the comparison. Minimum value of error reflects the optimum value that indicates the closest result to the target (actual) value. For the sake of damage detection, another important aspect had been adopted in the present work which is the calibration process by updating of FE model. Due to several reasons, mismatch between modal parameters of the experimental and numerical model is usually exist leading to erroneous results in the procedure of damage detection. Hence, calibration process is aimed to produce numerical (updated) values of structural modal parameters as close as possible to their corresponding experimental values. In this way, the convergence between the compared modal parameters is achieved which allows the procedure of damage detection to be implemented with more accurate results...Općenito, u radu je razmatrana detekcija oštećenja različitih tipova čeličnih konstrukcija. Oštećenje se moţe otkriti na različite načine, koji zavise od različitih postupaka navedenih u literaturi. Detekcija oštećenja zavisi od postupka poredjenja između aţuriranih modalnih parametara (prirodnih frekvencija i oblika) modela KE s odgovarajućim eksperimentalnim vrednostima. Procenjuju se modalni strukturni parametari, eksperimentalno i numerički. Na osnovu merenja ambijentalnih vibracija (MAV), na različitim vrstama čeličnih konstrukcija, eksperimentalni modalni parametri se određuju pomoću ARTeMIS softvera u skladu s tehnikom frekvencijskog razlaganja (FR). S druge strane, primenom ANSYS softvera, izračunavaju se numeričke vrednosti modalnih parametara potrebnih u postupku otkrivanja oštećenja. Detekcija oštećenja vrši se uz pomoć predloţene Tabu (TS) optimizacije za otkrivanje lokacije i ozbiljnost oštećenja. Tehnika TS optimizacije je relativno nova i nije ranije korišćena u detekciji oštećenja gradjevinskih konstrukcija. Predloţene procedure TS optimizacije su napisane i izvedene u MATLAB okruţenju. MATLAB ima sposobnost za istovremeno razmatranje eksperimentalno dobijenih parametara modela, i odgovarajućih numeričkih vrednosti koje se kontunualno aţuriraju uz pomoć ANSYS softvera. Poređenje između procenjenih eksperimentalnih i numeričkih parametara modela se vrši u skladu s vrednostima dobijenih predloţenom "objektivnom funkcijom" (treba "funkcija kriterijuma" ili "funkcija cilja") koja određuju vrednost greške. Minimalna vrednost greške odraţava optimalnu vrednost koja ukazuje na najbliţi rezultat ciljne (stvarne) vrednosti. U cilju detekcije oštećenja usvojen je još jedan vaţan korak, tj. kalibracija s aţuriranjem FE modela. Iz više razloga, neslaganje između modalnih parametara eksperimentalnog i numeričkog modela je obično dovodi do pogrešnih rezultata u postupku otkrivanja oštećenja. Stoga, proces kalibracije ima za cilj da proizvede (aţurira) numeričke vrednosti strukturnih parametara modela, što je moguće bliţe, odgovarajućim eksperimentalnim vrednostima. Na ovaj način je ostvarena konvergencija između odnosa modalnih parametara, što omogućava postupak detekcije oštećenja..