<p>Structural walls in existing buildings designed to pre 1970s codes may have deficient shear reinforcement and lap splice detailing. Lap splices at the bottom of the walls were designed in compression with anchorage length of 24-bar diameter. When the structural wall is subjected to lateral loads during a major seismic event, the lap splice is in the zone of maximum moment and shear and may be subjected to tension. Such design may cause nonductile behaviour and sudden failure of the wall due to shear or bond slip of the lap splice reinforcing bars. The effect of shear and ductility rehabilitation on the behaviour of reinforced concrete structural walls, without lap splice, have shown improvement in the structural wall shear resistance and ductility and hence overall structural ductility and seismic loads resistance. Research on rehabilitation of reinforced concrete (RC) structural walls with both deficient shear reinforcement and lap splice detailing is still needed. </p> <p> The principal objectives of this study were to evaluate the seismic behaviour of non-ductile reinforced concrete structural walls before and after rehabilitation using carbon fibre reinforced polymers (CFRP). These objectives were achieved through experimental and analytical investigations.</p> <p> The experimental phase of this research involved testing large scale models of RC structural walls with deficient shear strength and lap splice detailing to reproduce failure modes observed following major seismic events and to evaluate the rehabilitation schemes. Ten RC structural walls were built and tested under cyclic loading. Three control walls were tested as-built with non-ductile detailing and seven walls were rehabilitated before testing. The purpose of the rehabilitation techniques was to prevent brittle failure in shear or bond slip and to improve the ductility and energy dissipation of RC structural walls.</p> <p> The analytical phase of this study involved evaluation of the inelastic dynamic response of RC residential building with nonductile structural walls as well as retrofitted walls. An efficient macroscopic model to represent the behaviour of RC structural walls when subjected to pushover, cyclic and dynamic seismic loads was developed. The proposed model was intended to adequately describe the hysteretic behaviour of walls and to be capable of accurately predicting both flexural and shear components of inelastic deformation. The model predictions were compared with the experimental results. The comparisons showed that the developed analytical model predicted the inelastic walls response with a good accuracy. The analytical model was capable to evaluate the nonlinear dynamic behaviour of an existing building under seismic excitation before and after rehabilitation.</p> / Thesis / Doctor of Philosophy (PhD)

Σεισμικά γεγονότα τα οποία προέρχονται από σεισμικές πηγές των οποίων η απόσταση μεταξύ τους είναι πολύ μικρότερη από την απόσταση μέχρι τον κοντινότερο σταθμό καταγραφής, είναι γνωστά στη βιβλιογραφία σαν όμοια σεισμικά γεγονότα και αποτελούν αντικείμενο έρευνας εδώ και μια εικοσαετία. Η διαδικασία επαναπροσδιορισμού των υποκεντρικών παραμέτρων ή επανεντοπισμού όμοιων σεισμικών γεγονότων οδηγεί σε εκτιμήσεις των παραμέτρων που είναι συνήθως μεταξύ μίας και δύο τάξεων μεγέθους μικρότερου σφάλματος από τις αντίστοιχες των συνηθισμένων διαδικασιών εντοπισμού και επομένως, μπορεί εν δυνάμει να παράξει μια λεπτομερέστερη εικόνα της σεισμικότητας μιας περιοχής, από την οποία μπορεί στη συνέχεια να προκύψει η ακριβής χαρτογράφηση των ενεργών ρηγμάτων της. Πρόκειται για μια σύνθετη διαδικασία που μπορεί να αναλυθεί στα παρακάτω τρία βασικά βήματα: 1. Αναγνώριση ομάδων όμοιων σεισμικών γεγονότων. 2. Υπολογισμός διαφορών χρόνων άφιξης μεταξύ όμοιων σεισμικών γεγονότων. 3. Επίλυση προβλήματος αντιστροφής. Το πρώτο από τα παραπάνω βήματα είναι η αναγνώριση των λεγόμενων σεισμικών οικογενειών που υπάρχουν στον διαθέσιμο κατάλογο και έχει ξεχωριστή σημασία για την ολική επιτυχία της διαδικασίας. Μόνο εάν εξασφαλιστεί η ορθότητα της επίλυσης αυτού του προβλήματος τίθενται σε ισχύ οι προϋποθέσεις για την εφαρμογή της διαδικασίας και άρα έχει νόημα η γεωλογική ανάλυση που ακολουθεί. Είναι επίσης ένα πρόβλημα που απαντάται και σε άλλες γεωλογικές εφαρμογές, όπως είναι για παράδειγμα ο αυτόματος εντοπισμός του ρήγματος γένεσης ενός άγνωστου σεισμικού γεγονότος μέσω της σύγκρισής του με διαθέσιμες αντιπροσωπευτικές οικογένειες. Το πρόβλημα της αναγνώρισης είναι στην ουσία ένα πρόβλημα ταξινόμησης και ως εκ τούτου προϋποθέτει την επίλυση δύο σημαντικών επιμέρους υποπροβλημάτων. Συγκεκριμένα, αυτό της αντιστοίχισης των σεισμικών κυματομορφών (matching problem) και αυτό της κατηγοριοποίησής τους (clustering problem). Το πρώτο έχει να κάνει με τη σύγκριση όλων των δυνατών ζευγών σεισμογραμμάτων του καταλόγου ώστε να εντοπισθούν όλα τα όμοια ζεύγη, ενώ το δεύτερο αφορά την ομαδοποίηση των ομοίων σεισμογραμμάτων ώστε να προκύψουν οι σεισμικές οικογένειες. Στα πλαίσια αυτής της εργασίας, λαμβάνοντας υπόψη τις ιδιομορφίες που υπεισέρχονται στο παραπάνω πρόβλημα ταξινόμησης από τις ιδιαιτερότητες των σεισμογραμμάτων αλλά και την ιδιαίτερη φύση της εφαρμογής, προτείνουμε μια μέθοδο σύγκρισης που βασίζεται σε μια γενικευμένη μορφή του συντελεστή συσχέτισης και μια μέθοδο κατηγοριοποίησης βασισμένη σε γράφους, με στόχο την αποτελεσματική αλλά και αποδοτική επίλυσή του. / Seismic events that occur in a confined region, meaning that the distance separating the sources is very small compared to the distance between the sources and the recording station, are known in the literature as similar seismic events and have been under study for the past two decades. The re-estimation of the hypocenter parameters or the relocation of similar events gives an estimation error that is between one and two orders of magnitude lower that the one produced by the conventional location procedures. As a result, the application of this approach creates a much more detailed image of the seismicity of the region under study, from which the exact mapping of the active faults of the region can occur. The relocation procedure is in fact a complex procedure, consisting of three basic steps: 1. Identification of groups of similar seismic events. 2. Estimation of the arrival time differences between events of the same group. 3. Solution of the inverse problem. The first of the above steps, namely the identification of the seismic families of the given catalog plays an important role in the total success of the procedure, since only the correct solution of this problem can ensure that the requirements for the application of the procedure are met and therefore the geological analysis that is based on its outcome is meaningful. The problem is also encountered in other geological applications, such as the automatic location of the fault mechanism of an unknown event by comparison with available representative families. The problem of the identification of the seismic families is a classification problem and as such, requires the solution of two subproblems, namely the matching problem and the clustering problem. The object of the first one is the comparison of all the possible event pairs of the catalog with the purpose of locating all the existing similar pairs, while the second one is concerned with the grouping of the similar pairs into seismic families. In this work, taking into consideration the particularities that supersede the classification problem described above due to the special nature of the seismograms and also the specific requirements of the application, we propose a comparing method which is based on a generalized form of the correlation coefficient and a graph – based clustering technique, as an effective solution of the problem at hand.

[pt] A visualização volumétrica direta (volume rendering) aplicada a dados sísmicos é uma técnica ainda emergente. Apenas recentemente alguns software comerciais tornaram-se disponíveis para a indústria de petróleo. Comparado ao método tradicional de interpretação sobre seções bidimensionais, essa técnica representa uma alternativa interessante que possibilita investigar o volume de dados na sua totalidade, dessa forma permitindo um melhor entendimento da geologia estrutural e da estratigrafia da subsuperfície. Este trabalho analisa diversos aspectos da natureza dos dados sísmicos e da forma como eles afetam os resultados obtidos pelas técnicas de visualização volumétrica direta tradicionalmente empregadas. Três aspectos são discutidos em maior detalhe: quantização das amplitudes medidas para representação digital de 8-bit, segmentação do volume e modelos de iluminação. O impacto da quantização é analisado experimentalmente utilizando diferentes algoritmos de quantização de cor adaptados para tratar com amplitudes. A quantização uniforme é selecionada pela sua simplicidade e eficiência. A segmentação dos eventos sísmicos é analisada teoricamente e verificada experimentalmente. São discutidas diversas características dos dados sísmicos que restringem o sucesso da segmentação. A validade da aplicação aos dados sísmicos de modelos de iluminação local comumente empregados em visualização volumétrica é analisada teoricamente. A estimativa dos vetores normais diretamente a partir dos valores de amplitude representa uma alternativa inadequada. Por fim, é identificada uma série de requisitos aos quais um sistema deve atender para que a visualização volumétrica de dados sísmicos seja bem sucedida. / [en] Volume rendering is an emerging technique in the field of seismic data visualization. Only recently commercial software has been made available to the oil industry. Volume rendering is particulary useful for understanding structural and stratigrafhic features present in seismic data in a more natural way than using the tradicional method of interpreting over a set of 2D slices. This work adresses several topics related to the nature of seismic data and to how they interrelate with techniques commonly used in volume redering.Special attention is given to three topics: quantization of acquired seismic amplitudes to 8-bit representations, segmentattion techiniques to highlight seismic events and use of illumination models.The quantatization effects are analyzed by appying different color quantization algorithms adapted to handle seiosmic amplitudes. Uniform quantization is selected due to its simplicity and efficiency. The segmentation of seismic events is studie theorecally and verified experimentally.Several characteristics of seismic data that prevent segmentation frombeing successful are discussed. The significance of shading obtained by applying common illumination models is studie theoretically. The estimation of normal vectors directly from amplitude values is shown to be inadequate. Finally, several basic requisites to be fulfilled by seismic data volume visualization algorithms are identified. / [es] La visualización volumétrica directa (volumen rendering) aplicada a datos sísmicos es una técnica de incipiente desarrollo. A sido recientemente que algunos software comerciales han disponibilizado ésta técnica para la indústria de petróleo. En comparación con el método tradicional de interpretación sobre secciones bidimensionales, esta técnica resulta una alternativa interesante para investigar el volumen de datos en su totalidad, permitiendo así una mejor comprensión de la geología extructural y de la estratigrafía de la subsuperfície. Este trabajo analiza diversos aspectos de la naturaleza de los datos sísmicos; y de la forma como ellos afectan los resultados obtenidos por las técnicas de visualización volumétrica directa, empleadas tradicionalmente. Se discuten tres aspectos importantes: cuantización de las amplitudes medidas para representación digital de 8-bit, segmentación del volumen y modelos de iluminación. Se analiza experimentalmente el impacto de la cuantización, utilizando diferentes algoritmos de cuantización de color adaptados para amplitudes. Se selecciona la cuantización uniforme por su simplicidad y eficiencia. La segmentación de los eventos sísmicos se analiza teóricamente y se verifica experimentalmente. Se discuten diversas características de los actos sísmicos que limitan el éxito de la segmentación. Se analiza teóricamente la validez de la aplicación de los modelos de iluminación local a los datos sísmicos, que comúnmente se emplean em la visualización volumétrica. La estimación de los vectores normales a partir de los valores de amplitud representa una alternativa inadecuada. Finalmente, se identifican una serie de requisitos que un sistema debe tener para una exitosa visualización volumétrica de datos sísmicos.

Mining engineers are tasked with ensuring that underground mining operations be both safe and efficiently productive. Induced stress in deep mines has a significant role in the stability of the underground mines and hence the safety of the mining workplace because the behavior of the rock mass associated with mining-induced seismicity is poorly-understood. Passive seismic tomography is a tool with which the performance of a rock mass can be monitored in a timely manner. Using the tool of passive seismic tomography, the advance rate of operation and mining designs can be updated considering the induced stress level in the abutting rock. Most of our current understanding of rock mass behavior associated with mining-induced seismicity comes from numerical modeling and a limited set of case studies. Therefore, it is critical to continuously monitor the rock mass performance under induced stress. Underground stress changes directly influence the seismic wave velocity of the rock mass, which can be measured by passive seismic tomography. The precise rock mass seismicity can be modeled based on the data recorded by seismic sensors such as geophones of an in-mine microseismic system. The seismic velocity of rock mass, which refers to the propagated P-wave velocity, varies associated with the occurrence of major seismic events (defined as having a local moment magnitude between 2 to 4). Seismic velocity changes in affected areas can be measured before and after a major seismic event in order to determine the highly stressed zones. This study evaluates the seismic velocity trends associated with five major seismic events with moment magnitude of 1.4 at a deep narrow-vein mine in order to recognize reasonable patterns correlated to induced stress redistribution. This pattern may allow recognizing areas and times which are prone to occurrence of a major seismic event and helpful in taking appropriate actions in order to mitigate the risk such as evacuation of the area in abrupt cases and changing the aggressive mine plans in gradual cases. In other words, the high stress zones can be distinguished at their early stage and correspondingly optimizing the mining practices to prevent progression of high stress zones which can be ended to a rock failure. For this purpose a block cave mine was synthetically modeled and numerically analyzed in order to evaluate the capability of the passive seismic tomography in determining the induced stress changes through seismic velocity measurement in block cave mines. Next the same method is used for a narrow vein mine as a case study to determine the velocity patterns corresponding to each major seismic event. / Doctor of Philosophy / Mining activities unbalance the stress distribution underground, which is called mining induced stress. The stability of the underground mines is jeopardized due to accumulation of induced stress thus it is critical for the safety of the miners to prevent excessive induced stress accumulation. Hence it is important to continuously monitor the rock mass performance under the induced stress which can form cracks or slide along the existing discontinuities in rock mass. Cracking or sliding releases energy as the source of the seismic wave propagation in underground rocks, known as a seismic event. The velocity of seismic wave propagation can be recorded and monitored by installing seismic sensors such as geophones underground. The seismic events are similar to earthquakes but on a much smaller scale. The strength of seismic events is measured on a scale of moment magnitude. The strongest earthquakes in the world are around magnitude 9, most destructive earthquakes are magnitude 7 or higher, and earthquakes below magnitude 5 generally do not cause significant damage. The moment magnitude of mining induced seismic events is typically less than 3. In order to monitor mining induced stress variations, the propagated seismic wave velocity in rock mass is measured by a series of mathematical computations on recorded seismic waves called passive seismic tomography, which is similar to the medical CT-scan machine. Seismic wave velocity is like the velocity of the vibrating particles of rock due to the released energy from a seismic event. This study proposes to investigate trends of seismic velocity variations before and after each seismic event. The areas which are highly stressed have higher seismic velocities compared to the average seismic velocity of the entire area. Therefore, early recognition of highly stressed zones, based on the seismic velocity amount prior the occurrence of major seismic events, will be helpful to apply optimization of mining practices to prevent progression of high stress zones which can be ended to rock failures. For this purpose, time-dependent seismic velocity of a synthetic mine was compared to its stress numerically. Then, the seismic data of a narrow vein mine is evaluated to determine the seismic velocity trends prior to the occurrence of at least five major seismic events as the case study.

Le problème de la dimension stochastique élevée est récurrent dans les analyses probabilistes des structures. Il correspond à l’augmentation exponentielle du nombre d’évaluations du modèle mécanique lorsque le nombre de paramètres incertains est élevé. Afin de pallier cette difficulté, nous avons proposé dans cette thèse, une approche à deux étapes. La première consiste à déterminer la dimension stochastique efficace, en se basant sur une hiérarchisation des paramètres incertains en utilisant les méthodes de criblage. Une fois les paramètres prépondérants sur la variabilité de la réponse du modèle identifiés, ils sont modélisés par des variables aléatoires et le reste des paramètres est fixé à leurs valeurs moyennes respectives, dans le calcul stochastique proprement dit. Cette tâche fut la deuxième étape de l’approche proposée, dans laquelle la méthode de décomposition de la dimension est utilisée pour caractériser l’aléa de la réponse du modèle, par l’estimation des moments statistiques et la construction de la densité de probabilité. Cette approche permet d’économiser jusqu’à 90% du temps de calcul demandé par les méthodes de calcul stochastique classiques. Elle est ensuite utilisée dans l’évaluation de l’intégrité d’une toiture à ossature bois d’une habitation individuelle installée sur un site d’aléa sismique fort. Dans ce contexte, l’analyse du comportement de la structure est basée sur un modèle éléments finis, dans lequel les assemblages en bois sont modélisés par une loi anisotrope avec hystérésis et l’action sismique est représentée par huit accélérogrammes naturels fournis par le BRGM. Ces accélérogrammes permettent de représenter différents types de sols selon en se référant à la classification de l’Eurocode 8. La défaillance de la toiture est définie par l’atteinte de l’endommagement, enregistré dans les assemblages situés sur les éléments de contreventement et les éléments d’anti-flambement, d’un niveau critique fixé à l’aide des résultats des essais. Des analyses déterministes du modèle éléments finis ont montré que la toiture résiste à l’aléa sismique de la ville du Moule en Guadeloupe. Les analyses probabilistes ont montré que parmi les 134 variables aléatoires représentant l’aléa dans le comportement non linéaire des assemblages, 15 seulement contribuent effectivement à la variabilité de la réponse mécanique ce qui a permis de réduire la dimension stochastique dans le calcul des moments statistiques. En s’appuyant sur les estimations de la moyenne et de l’écart-type on a montré que la variabilité de l’endommagement dans les assemblages situés dans les éléments de contreventement est plus importante que celle de l’endommagement sur les assemblages situés sur les éléments d’anti-flambement. De plus, elle est plus significative pour les signaux les plus nocifs sur la structure. / The problem of the curse of dimensionality is frequently encountered in practical applications. It can be defined as the significant increase of the number of mechanical model calls with the number of uncertain parameters. To overcome this difficulty, a two-steps stochastic approach has been developed in this work. The first step of this approach consists in calculating the stochastic effective dimension by the means of Morris screening method. Once the most significant uncertain parameters on the variability of the mechanical responses are identified, they are modeled as random variables and the remaining parameters are fixed to their respective mean values. This allows us to reduce significantly the stochastic dimension of the problem in the second step of the approach where the decomposition method is used to estimate the statistical characteristics of the mechanical responses. The efficiency and the accuracy of this approach are evaluated through an academic problem dealing with the assessment of the integrity of a three-span five-story frame structure subjected to horizontal loads. We have demonstrate that we can reduce about 90% of the computation time required by the classical stochastic methods. Then, the proposed approach is used to the analysis of the integrity of timber roofs under seismic loading. The behaviour of this structure is described through a finite element model where the timber joints are modeled by anisotropic hysteresis law, and the seismic action is represented by eight real earthquake ground motion records. These accelerograms provided by the French institution involved in geosciences BRGM allow us to take into account different soil types according to the classification provided by the europeen design code dealing with seismic events Eurocode 8. The failure of timber roofs is reached when the damage levels in the timbers joints localized on the buckling and bracing members reach the critical value. It is shown, through a deterministic analysis, that the structure resists the seismic hazard representing the city of Le Moule in Guadeloupe. The stochastic analysis has shown that, among the 134 random variables representing the uncertainty in the nonlinear behaviour of the timber joints, only 15 have a significant effect on the variability of the structural response, which allow us to reduce the stochastic dimension in the computation of the statistical moments. According to the estimates of the mean and the standard deviation, we have shown that the variability of bracing members damage is greater than the variability of buckling members damage. Moreover, the variability of the bracing members damage is more significant for the earthquake ground motion records having the lowest collapse PGA.