Out-of-plane simulation of masonry structures using novel finite element techniques

The out-of-plane response is a complex and at the same time key aspect of the seismic vulnerability of masonry structures. It depends on several factors, some of which are the material properties, the quality of the walls, the geometry of the structure, the connections between structural elements and the stiffness of the diaphragms. Despite its importance and due to the related difficulties, there is still lack of a robust and straightforward assessment technique. During the last years, a wide variety of numerical methods has been employed to the out-of-plane assessment of unreinforced masonry structures (URM). Among the most famous of them are finite element macro-modelling approaches as they allow the modelling of large structures at a reasonable computational cost. However, macro-modelling approaches may result in the non-realistic representation of localized cracks and dependency of the numerical solution on the used finite element mesh. As a remedy to this problem, the mixed strain/displacement finite elements have been recently proposed. Thanks to the independent interpolation of the strains and displacements, the proposed formulation is characterized by an enhanced accuracy in strain localization and crack propagation problems, being at the same time mesh bias independent. For these reasons, the mixed finite elements are employed in this thesis for the out-of-plane assessment of URM structures, being at the same time the first real-scale application. A full scale experimental campaign of two masonry structures, namely a stone and a brick, subjected to shaking-table test is chosen here as benchmark problem (Candeias et al, 2017), and different nonlinear static analyses are performed. In order to assess the efficiency of the proposed model, the results are compared firstly with the experimental results, secondly with the results obtained by the standard elements and finally, with a previous similar simulation attempt existing in the literature. Furthermore, physical and numerical input parameters, such as the effect of the lintels, the damage model or the stabilization parameter used, are also examined. As a general overview, the proposed model provides a good estimation in terms of collapse mechanism and PGA for both structures, while a sufficient estimation in terms of displacements is obtained only for the brick house. Several observed differences are attributed to shortcomings of the methodology adopted, related mainly to the homogenized nature of the model and the static monotonic loading applied. Moreover, the results of the mixed formulation do not appear to suffer by any mesh bias dependency, justifying their superiority, but arriving with an increased computational cost.La respuesta fuera del plano es un aspecto complejo y a la vez clave de la vulnerabilidad sísmica de las estructuras de mampostería. Depende de varios factores, algunos de los cuales son las propiedades del material, la calidad de las paredes, la geometría de la estructura, las conexiones entre los elementos estructurales y la rigidez de los diafragmas. A pesar de importancia del tema y debido a las dificultades asociadas a ella, todavía no existe una técnica de evaluación robusta y directa. Durante los últimos años, se ha utilizado una amplia variedad de métodos numéricos para la evaluación fuera del plano de las estructuras de mampostería no reforzada. Entre los más populares están los métodos de modelado macro de elementos finitos, ya que permiten el modelado de grandes estructuras a un costo computacional razonable. Sin embargo, los enfoques de macro-modelado pueden resultar en una representación poco realista de las fisuras localizadas y en la dependencia de la solución numérica respecto de la malla de elementos finitos usada. Como remedio a este problema, se han propuesto recientemente los elementos finitos mixtos deformación/desplazamiento. Gracias a la interpolación independiente de las deformaciones y desplazamientos, la formulación propuesta se caracteriza por una mayor precisión en los problemas de localización de las deformaciones y de propagación de fisuras, proporcionando al mismo tiempo resultados independientes de la malla. Por estas razones, los elementos finitos mixtos se emplean en esta tesis para la evaluación fuera de plano de estructuras de mampostería no reforzada, siendo al mismo tiempo la primera aplicación a escala real de esta técnica. Se elige aquí como estudio de caso una campaña experimental (Candeias et al., 2017) a escala completa de dos estructuras de albañilería, a saber, una de piedra y una de ladrillo, sometidas a ensayo de mesa vibratoria, y se realizan diferentes análisis estáticos no lineales. Para evaluar la eficiencia del modelo propuesto, los resultados se comparan en primer lugar con los resultados experimentales, en segundo lugar con los resultados obtenidos por los elementos estándar y, finalmente, con una simulación numérica previa. Además, también se examinan parámetros de la simulación físicos y numéricos, tales como el modelo de daño utilizado, la influencia de los dinteles o el parámetro de estabilización. Como resultado general, el modelo propuesto proporciona una buena estimación en términos de mecanismo de colapso y aceleración máxima del suelo para ambas estructuras, aunque sólo se obtiene una estimación satisfactoria en términos de desplazamientos para la casa de ladrillo. Varias de las diferencias observadas se atribuyen a las deficiencias de la metodología adoptada, relacionadas principalmente con la naturaleza homogeneizada del modelo y la carga monótona estática aplicada. Además, los resultados de la formulación mixta parecen no sufrir de ningún sesgo debido a la malla, justificando su superioridad, pero comportando un coste computacional incrementado

Out-of-plane seismic response and failure mechanism of masonry structures using finite elements with enhanced strain accuracy

The out-of-plane response is a complex and at the same time key aspect of the seismic vulnerability of masonry structures. It depends on several factors, some of which are the material properties, the quality of the walls, the geometry of the structure, the connections between structural elements and the stiffness of the diaphragms. During the last years, a wide variety of numerical methods has been employed to assess the out-of-plane behaviour of unreinforced masonry structures. Finite element macro-modelling approaches are among the most famous as they allow modelling large structures at a reasonable computational cost. However, macro-modelling approaches may result in a non-realistic representation of localized cracks and a dependency of the numerical solution on the finite element mesh. Mixed strain/displacement finite elements have been recently proposed as a remedy to the above nu-merical pathologies. Due to the independent interpolation of strains and displacements these finite element formulations are characterized by an enhanced accuracy in strain localization and crack propagation problems, being at the same time practically mesh independent. For these reasons, mixed finite elements are employed in this work for the out-of-plane assessment of unreinforced masonry struc-tures, being at the same time their first real-scale application. A full-scale experimental campaign of two masonry structures, a stone and a brick one, subjected to shaking-table tests is chosen as reference benchmark. Their structural response under seismic actions is numerically assessed through nonlinear static analysis. The proposed approach is validated through the comparison of the numerical results with the experimental ones, as well as with the results obtained using standard irreducible finite ele-ments.Peer ReviewedPostprint (author's final draft

Out-of-plane seismic response and failure mechanism of masonry structures using finite elements with enhanced strain accuracy

The out-of-plane response is a complex and at the same time key aspect of the seismic vulnerability of masonry structures. It depends on several factors, some of which are the material properties, the quality of the walls, the geometry of the structure, the connections between structural elements and the stiffness of the diaphragms. During the last years, a wide variety of numerical methods has been employed to assess the out-ofplane behaviour of unreinforced masonry structures. Finite element macro-modelling approaches are among the most famous as they allow modelling large structures at a reasonable computational cost. However, macro-modelling approaches may result in a non-realistic representation of localized cracks and a dependency of the numerical solution on the finite element mesh. Mixed strain/displacement finite elements have been recently proposed as a remedy to the above numerical pathologies. Due to the independent interpolation of strains and displacements these finite element formulations are characterized by an enhanced accuracy in strain localization and crack propagation problems, being at the same time practically mesh independent. For these reasons, mixed finite elements are employed in this work for the out-of-plane assessment of unreinforced masonry structures, being at the same time their first real-scale application. A full-scale experimental campaign of two masonry structures, a stone and a brick one, subjected to shaking-table tests is chosen as reference benchmark. Their structural response under seismic actions is numerically assessed through nonlinear static analysis. The proposed approach is validated through the comparison of the numerical results with the experimental ones, as well as with the results obtained using standard irreducible finite elements

Energy loss mechanisms of rocking blocks: experimental observations

A variety of different structures experience rocking motion when subjected to dynamic actions, making rocking dynamics a fundamental problem of earthquake engineering. Rocking motion presents peculiar dynamic characteristics, such as negative stiffness during pivoting and non-smooth phenomena during impacts. Hence, modelling of the rocking problem faces significant challenges. One of the most significant is related to the energy losses that occur during impacts, commonly represented by the coefficient of restitution. Despite the numerous theoretical attempts to accurately estimate the coefficient of restitution, it is apparent that experimental observations are essential in providing a direct insight into the complex and non-smooth phenomena of rocking motion. To this end, the present work conducts an extended experimental campaign on the free-rocking motion of limestone blocks. More specifically, a total of 36 blocks are tested, corresponding to 12 different geometrical aspect ratios. The free-rocking motion is thoroughly analysed, while attention is also given to three-dimensional effects. Finally, the coefficient of restitution is experimentally quantified and compared with both previous theoretical and experimental results gathered from the literature.- (undefined

Learning from failure: Damage and failure of masonry structures, after the 2017 Lesvos earthquake (Greece)

On the 12th of June 2017 an earthquake of Mw = 6.3 struck SSE of Lesvos Island, causing one human fatality and severe damage to the built environment. The traditional settlement of Vrissa was the most affected area, having masonry structures as the majority of its building stock. The objective of the present study is two-fold: to present the structural damage and failure patterns induced by the Lesvos earthquake to masonry structures; to highlight the causes and weaknesses that led to damage, or the factors that prevented it. Particular attention is paid to traditional construction techniques and architectural features that contributed to the seismic response of the structures, either having beneficial or detrimental effect. To this end, a field reconnaissance has been conducted and meaningful technical conclusions are drawn by the observations. Structural systems of both unreinforced and timber-reinforced masonry are inspected. Besides the identification of frequent cases of local, out-of-plane and in-plane mechanisms, combined global mechanisms are also pointed out. Finally, insight into the performance of past interventions is also given, assisting the challenging task of engineering practice.This work was partly funded by project STAND4HERITAGE that has received funding from the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation programme (Grant agreement No. 833123), as an Advanced Grant

Treatment of hemangiomas in children using a Nd:YAG laser in conjunction with ice cooling of the epidermis: techniques and results

BACKGROUND: Hemangiomas are the most common type of congenital anomaly in childhood. Although many resolve spontaneously, intervention is required when their growth could damage vital adjacent structures. Various therapeutic approaches to childhood hemangiomas with different types of laser have been described previously. The objective of this study was to determine whether the cooling of the epidermis during irradiation of hemangiomas with a Nd:YAG laser prevents thermal damage and decreases the number of sessions required to treat these lesions. METHODS: Between 1993 and 2001, 110 patients aged 3 months to 4 years, with cutaneous hemangiomas were treated with a Nd:YAG laser. The lesion was cooled with ice prior to, during, and after the irradiation. During each session the laser beam passed through the pieces of ice. The laser power was between 35–45 W with a pulse length of 2–10 seconds. RESULTS: After 6 months of follow-up, from the first session of laser treatment, total resolution was obtained in 72 (65.5%) patients. A second or third session followed in 30 out of 38 patients in which, the initial results were good, moderate, or poor. The parents of the remaining eight children refused this second session and these patients excluded from the study Complications were seen in nine (8.8%) patients. One patient had postoperative bleeding which stopped spontaneously, while atrophic scars occurred in six (5.8%) patients, and hypertrophic scars in two (1.9%) patients. CONCLUSIONS: Nd:YAG laser irradiation in conjunction with ice protection of the epidermis produces good cosmetic results for the treatment of cutaneous hemangiomas in children, and decreases the number of sessions for treatment of these lesions

Η "φυσική" του Νικηφόρου Θεοτόκη σταθμός στην επιστημονική σκέψη τον 18ο αιώνα

This PhD thesis is placed in a more general trend in the studies of history of science in Greece, which has focused its interest on the treatment of the scientific evolution during the so-called "Greek enlightment" (1750-1821). The particular subject which is examined is the "Stichia Phisikis" (=Elements of Physics), a book written by one of the most famous Greek scholars of that period, Nikeforos Theotokis and published in Leipsia in 1766-1767. As it is demonstrated, this book is the first printed book, which imported and supported as a whole the Newtonian physics in the major geek area. The main sources used by Theotokis were books written by Peter van Musschenbroek and Abbe Nollet. There is a detailed analysis of "stichia phisikis" and an investigation of the social and educational conditions of the period is tried. At last a connection between what was taking place in Greece and what had prevailed in Europe is examined, just to find out the degree, if any, of the positive or negative influence on the Greek scholars.Αυτή η διατριβή εντάσσεται σε ένα γενικότερο πλαίσιο στις σπουδές της ιστορίας της επιστήμης στην Ελλάδα, που εντοπίζει το ενδιαφέρον των ερευνητών στη μελέτη της επιστημονικής εξέλιξης κατά τη διάρκεια του λεγόμενου "νεοελληνικού διαφωτισμού" (1750- 1821). Το ειδικό αυτό κείμενο που εξετάζεται είναι τα "Στοιχεία Φυσικής", ένα δίτομο έργο που γράφηκε από ένα από τους επιφανέστερους λόγιους εκείνης της περιόδου, το Νικηφόρο Θεοτόκη, και τυπώθηκε στη Βιέννη το 1766-1767. Όπως αποδεικνύεται, αυτό το βιβλίο είναι το πρώτο έντυπο κείμενο, που εισήγαγε και υποστήριξε συνολικά τη Νευτωνική φυσική στον ευρύτερο ελλαδικό χώρο. Οι κύριες πηγές που χρησιμοποιήθηκαν από το Θεοτόκη ήταν, το βιβλίο του Ολλανδού πειραματιστή Peter van Musschenbroek "elementa physicae" και το πολύτομο έργο "fisica sperimentale" του Γάλλου φυσικού επιστήμονα Abbe Nollet, δύο ευρωπαίους επιστήμονες που, μέσω της επιστημονικής παραγωγής τους, είχαν μια σημαντική επίδραση στην προοδευτική λογιοσύνη εκείνης της περιόδου. Τα χαρακτηριστικά των "στοιχείων φυσικής" διερευνώνται λεπτομερειακά και καταγράφεται η επίδραση του Θεοτόκη στους μεταγενέστερους λόγιους καθώς και η εξέλιξη που είχε η φυσική σκέψη μέχρι την έναρξη της επανάστασης του 1821

Proactivity in supply chain management systems

Proactive computing refers to the ability of computer systems to anticipate the needs of their operational environment before they occur and act accordingly to prevent undesired events. This preventive capability is based on the ability of proactive systems to understand their operating environment through recognition and event analysis and appropriate event management. Proactive computing is used in highly dynamic areas such as the supply chains. The supply chain environment is characterized by dynamic changes. These changes happen due to a multitude of events caused by external or internal factors. Events affect the supply chain functionality and either create opportunities for exploitation or cause deviations from predetermined levels of operation. Event management that deviates from predefined operating levels is where Supply Chain Event Management is implemented.SCEM is a supply chain management approach by locating, analyzing and processing events to optimize its operation. The combination of proactive computing and SCEM is the research area of this study. The enhancement of SCEM's capabilities through the use of proactive computing aims to create a proactive framework where either the events themselves or their adverse effects will be prevented before affecting supply chain performance. This thesis examines supply chain proactivity and explores ways to achieve it. Examining and analyzing particularly the environment of the supply chain, its participants, as well as events that adversely affect supply chain performance alternative ways are proposed to avoid the negative effects of divergences. For the implementation of the study, a bibliographic research was conducted in the field of Proactive Computing, Event Driven Computing, SCEM, in the field of Fuzzy Logic, Situation Awareness and Bayes Network.Η προδραστική πληροφορική (proactive computing) αναφέρεται στην ικανότητα των υπολογιστικών συστημάτων να προλαμβάνουν λειτουργικές ανάγκες του περιβάλλοντος τους πριν αυτές εκδηλωθούν. Η ικανότητα προληπτικής λειτουργίας βασίζεται σε δυνατότητες που έχουν τα προδραστικά συστήματα να αντιλαμβάνονται και να κατανοούν γεγονότα που συμβαίνουν στο περιβάλλον λειτουργίας τους, προβαίνοντας στην κατάλληλη διαχείριση. Η προδραστική πληροφορική βρίσκει εφαρμογή σε έντονα δυναμικές περιοχές όπως αυτή της εφοδιαστικής αλυσίδας.Το περιβάλλον της εφοδιαστικής αλυσίδας χαρακτηρίζεται από δυναμικές αλλαγές. Οι αλλαγές αυτές οφείλονται σε ένα πλήθος παραμέτρων όπως εξωτερικούς είτε εσωτερικούς παράγοντες. Οι παράγοντες αυτοί δημιουργούν γεγονότα που επιδρούν στη λειτουργία της εφοδιαστικής αλυσίδας και είτε δημιουργούν ευκαιρίες προς εκμετάλλευση είτε δημιουργούν αποκλίσεις από προκαθορισμένα επίπεδα λειτουργίας. Η διαχείριση γεγονότων που δημιουργούν αποκλίσεις από προκαθορισμένα επίπεδα λειτουργίας είναι ο χώρος όπου το Supply Chain Event Management εφαρμόζεται.Το SCEM είναι μια προσέγγιση διαχείρισης της εφοδιαστικής αλυσίδας μέσω του εντοπισμού, ανάλυσης και επεξεργασίας γεγονότων με σκοπό τη βελτιστοποίηση του συνόλου της εφοδιαστικής αλυσίδας. Ο συνδυασμός προδραστικής πληροφορικής και SCEM είναι ο ερευνητικός τομέας στο οποίο εντάσσεται αυτή η μελέτη. Η επαύξηση των δυνατοτήτων του SCEM με χρήση της προδραστικής πληροφορικής στοχεύει στη δημιουργία ενός προδραστικού πλαισίου όπου είτε τα ίδια τα γεγονότα είτε οι αρνητικές επιδράσεις αυτών θα προλαμβάνονται πριν επηρεάσουν την απόδοση της εφοδιαστικής αλυσίδας.Στην παρούσα διπλωματική διατριβή εξετάζεται η προδραστικότητα στην εφοδιαστική αλυσίδα και διερευνώνται τρόποι ώστε να επιτευχθεί αυτή. Ειδικότερα εξετάζονται το περιβάλλον της εφοδιαστικής αλυσίδας, οι συμμετέχοντες σε αυτή καθώς και τα γεγονότα (events) τα οποία επηρεάζουν αρνητικά την απόδοση της εφοδιαστικής αλυσίδας και προτείνονται τρόποι ώστε να αποφευχθούν οι αρνητικές επιδράσεις των αποκλίσεων.Για την υλοποίηση της μελέτης έγινε βιβλιογραφική έρευνα στου τομείς του Proactive Computing, Event Driven Computing, SCEM, στο χώρος της ασαφής λογικής (Fuzzy Logic) στο χώρο του Situation Awareness και των Bayes Network