Neste trabalho desenvolve-se uma formulação teórica consistente para a análise não-linear, física e geométrica, de pórticos planos de aço, através do Método dos Elementos Finitos (MEF), considerando barras com imperfeições iniciais e tensões residuais nas suas seções transversais, visando analisar os critérios de resistência adotados para projeto das colunas de aço, baseados no conceito de resistência-última, e estudar o comportamento não-linear dos pórticos de aço considerando estes dois fatores. São feitas considerações qualitativas sobre a influência das imperfeições iniciais e das tensões residuais no cálculo da resistência das colunas. e é dada uma visão geral sobre a evolução dos critérios usados na prática para dimensionamento das colunas de aço. Apresenta-se o desenvolvimento da teoria geral, que leva em conta a presença das tensões residuais auto-equilibradas nas equações de equilíbrio do elemento. Este desenvolvimento é feito dentro de uma formulação Lagrangiana utilizando a técnica corrotacional para a dedução consistente da matriz de rigidez tangente do elemento de pórtico plano com imperfeição inicial. Para implementação desta formulação é desenvolvido um programa em linguagem FORTRAN para micro-computador capaz de fazer a análise não-linear elasto-plástica de pórticos planos, baseado num processo incremental-iterativo. Utiliza-se o modelo de fatias para avaliar os coeficientes de rigidez do elemento, modelo este que se mostrou bastante adequado, permitindo o acompanhamento da plastificação ao longo da altura da seção e a consideração de qualquer modelo de distribuição das tensões residuais. Finalmente, os exemplos apresentados mostram a grande potencialidade da formulação desenvolvida. São analisados vários casos cujos resultados são comparados com os obtidos por outros autores, demonstrando a precisão e correção da teoria proposta. A aplicação na análise de pórticos de andares múltiplos confirma a validade da formulação e demonstra a sua aplicabilidade nos casos práticos. / A consistent finite element formulation to consider material and geometric nonlinearities of steel plane frames is presented. Residual stresses and initial imperfections are considered to evaluate steel columns failure criteria based on the ultimate strength and also to investigate the nonlinear behavior of steel plane frames. Some qualitative considerations are made on the initial imperfections and residual stresses influence on the practical steel columns design. A general theory considering self equilibrated residual stresses is developed based on the Lagrangian formulation. Corotacional technique is used to obtain the tangent stiffness matrix of plane frame taking the initial imperfection into account. A stand alone code has been written in FORTRAN and implemented on a microcomputer platform to perform incremental-iterative analysis of nonlinear elastoplastic plane frame problems. The frame element is made up of layers such that the plastic region can be readily identified and any kind of residual stresses through the cross section area can be taken into account in the analysis. Some examples are presented and their results compared to others in the literature. The multistory building analyses using the plane frame element presented in this research has shown to be very effective and useful to practical applications.

Management of data imprecision has become increasingly important, especially with the advance of technology enabling applications to collect and store huge amount data from multiple sources. Data collected in such applications involve a large number of variables and various types of data imperfections. These data, when used in knowledge discovery applications, require the following: 1) computationally efficient algorithms that works faster with limited resources, 2) an effective methodology for modeling data imperfections and 3) procedures for enabling knowledge discovery and quantifying and propagating partial or incomplete knowledge throughout the decision-making process. Bayesian Networks (BNs) provide a convenient framework for modeling these applications probabilistically enabling a compact representation of the joint probability distribution involving large numbers of variables. BNs also form the foundation for a number of computationally efficient algorithms for making inferences. The underlying probabilistic approach however is not sufficiently capable of handling the wider range of data imperfections that may appear in many new applications (e.g., medical data). Dempster-Shafer theory on the other hand provides a strong framework for modeling a broader range of data imperfections. However, it must overcome the challenge of a potentially enormous computational burden. In this dissertation, we introduce the joint Dirichlet BoE, a certain mass assignment in the DS theoretic framework, that simplifies the computational complexity while enabling one to model many common types of data imperfections. We first use this Dirichlet BoE model to enhance the performance of the EM algorithm used in learning BN parameters from data with missing values. To form a framework of reasoning with the Dirichlet BoE, the DS theoretic notions of conditionals, independence and conditional independence are revisited. These notions are then used to develop the DS-BN, a BN-like graphical model in the DS theoretic framework, that enables a compact representation of the joint Dirichlet BoE. We also show how one may use the DS-BN in different types of reasoning tasks. A local message passing scheme is developed for efficient propagation of evidence in the DS-BN. We also extend the use of the joint Dirichlet BoE to Markov models and hidden Markov models to address the uncertainty arising due to inadequate training data. Finally, we present the results of various experiments carried out on synthetically generated data sets as well as data sets from medical applications.

Over the past decades, many industries have heavily spent on computerizing their work environments with the intention to simplify and expedite access to information and its processing. Typical of real-world data are various types of imperfections, uncertainties, ambiguities, that have complicated attempts at automated knowledge discovery. Indeed, it soon became obvious that adequate methods to deal with these problems were critically needed. Simple methods such as "interpolating" or just ignoring data imperfections being found often to lead to inferences of dubious practical value, the search for appropriate modification of knowledge-induction techniques began. Sometimes, rather non-standard approaches turned out to be necessary. For instance, the probabilistic approaches by earlier works are not sufficiently capable of handling the wider range of data imperfections that appear in many new applications (e.g., medical data). Dempster-Shafer theory provides a much stronger framework, and this is why it has been chosen as the fundamental paradigm exploited in this dissertation. The task of association rule mining is to detect frequently co-occurring groups of items in transactional databases. The majority of the papers in this field concentrate on how to expedite the search. Less attention has been devoted to how to employ the identified frequent itemsets for prediction purposes; worse still, methods to tailor association-mining techniques so that they can handle data imperfections are virtually nonexistent. This dissertation proposes a technique referred to by the acronym DS-ARM (Dempster-Shafer based Association Rule Mining) where the DS-theoretic framework is used to enhance a more traditional association-mining mechanism. Of particular interest is here a method to employ the knowledge of partial contents of a "shopping cart" for the prediction of what else the customer is likely to add to it. This formalized problem has many applications in the analysis of medical databases. A recently-proposed data structure, an itemset tree (IT-tree), is used to extract association rules in a computationally efficient manner, thus addressing the scalability problem that has disqualified more traditional techniques from real-world applications. The proposed algorithm is based on the Dempster-Shafer theory of evidence combination. Extensive experiments explore the algorithm's behavior; some of them use synthetically generated data, others relied on data obtained from a machine-learning repository, yet others use a movie ratings dataset or a HIV/AIDS patient dataset.

This dissertation concerns failure modelling with material imperfections and element erosion in finite element analyses. The aim has been to improve the element erosion technique, which is simple to use and implement and also computationally inexpensive. The first part of the dissertation serves as an introduction to the topic and as a summary of the methodologies presented in the following part. The second part consists of seven appended papers. In paper A the standard element erosion technique is used for projectile penetration. In papers B and C a methodology that accounts for size effects is developed and applied to crack initiation in armour steel and tungsten carbide. A methodology to better predict the stress state at crack tips with coarse meshes is presented and applied to armour steel in paper D. Papers E and F concern the development of selective mass scaling which allows for larger time steps in explicit methods. Finally, in paper G the previously presented methodologies are used in combination and validated against experimental results on tungsten carbide. The computations show good agreement with the experimental results on failure initiation for both materials, while the computational results on the propagation of cracks show better agreement for the armour steel than for the tungsten carbide. / On the day of the public defence of the doctoral thesis, the status of articles I, III and IV was Accepted and article VII was Submitted.

Η πρόσφατη έρευνα για τους καθοριστικούς παράγοντες σε επίπεδο επιχείρησης της σταθερής επένδυσης έχει τονίσει τη σημασία των επεξηγηματικών μεταβλητών ώς προσεγγιστικές για την εσωτερική χρηματοδότηση των εταιριών που κρατούν σταθερά τα μέτρα των σταθερών ευκαιριών ή το κόστος του κεφαλαίου. Τέτοιες μελέτες έχουν βασιστεί στις αποκλίσεις από τα νεοκλασσικά υποδείγματα επένδυσης με τις τέλειες αγορές κεφαλαιαου στην κατεύθυνση των υποδειγμάτων βασισμένων στις ασυμμετρικές πληροφορίες στις χρηματαγορές. Αυτές οι αποκλίσεις στηρίζονται στην γνώση των θεωρητικών υποδειγμάτων του χρηματοοικονομικού συμβολαίου υπό συνθήκες ασυμμετριών στην πληροφόρηση χρησιμοποιώντας την δυσμενή επιλογή ή/και τον ηθικό κίνδυνο, στα οποία οι μετακινήσεις στα εσωτερικά κεφάλαια προβλέπουν μετακινήσεις στα έξοδα επένδυσης, κρατώντας σταθερές ευκαιρίες επένδυσης. Ο σκοπός αυτής της διατριβής είναι να διαμορφωθεί ο αντίκτυπος του χρηματοοικονομικού περιορισμού στις αποφάσεις επένδυσης των εταιρειών στην Ελλάδα και στην Ευρώπη. Η διατριβή εφαρμόζει ένα δυναμικό υπόδειγμα επένδυσης, όπου οι χρηματοοικονομικές μεταβλητές και η πραγματική επένδυση συνδέονται σε μία προσπάθεια να ερευνηθεί το πρόβλημα της ατέλειας στις κεφαλαιαγορές. Ένα περαιτέρω βήμα προς τα εμπρός είναι να ερευνηθούν οι πιθανές ασυμμετρίες στις αποφάσεις επένδυσης σχετικά με την κατάσταση των προσδοκιών των επιχειρηματιών που δίνει έμφαση στο ρόλο του επιχειρηματικού κύκλου. Προκειμένου να παρασχεθεί μια πλήρης εικόνα του προβλήματος των αποφάσεων επένδυσης, εκτός από το κεφάλαιο, εισάγουμε τον όρο της ζήτησης εργασίας. Ειδικότερα, μελετάμε την πιθανή επίδραση στη ζήτηση εργασίας των ατελειών της αγοράς κεφαλαίου, τις θεσμικές ακαμψίες της αγοράς εργασίας υπό την μορφή της δύναμης των ενώσεων, και τον αντίκτυπο της αβεβαιότητας. Υιοθετούμε μια δυναμική μεθοδολογία χρονικώς επαναλαμβανομένων διαστρωματικών στοιχείων (panel data) χρησιμοποιώντας την μέθοδο των εκτιμητών των Γενικευμένων Ροπών-Generalised Method of Moments- (GMM) σε ένα σύνολο στοιχείων εισηγμένων Ελληνικών επιχειρήσεων κατά τη διάρκεια της περιόδου 1993-2001. Επιπλέον, εξετάζουμε ένα σύνολο στοιχείων σε κλαδικό επίπεδο για τις περισσότερες από τις ηπειρωτικές ευρωπαϊκές χώρες για την περίοδο από το 1987 εώς το 2003. / Recent research on determinants of firm-level fixed investment has stressed the importance of proxies for firms’ internal finance as explanatory variables, holding constant measures of firm opportunities or the cost of capital. Such studies have been based on departures from neoclassical investment models with perfect capital markets in the direction of models based on asymmetric information in financial markets. These departures build on insights from theoretical models of financial contracting under asymmetric information, using adverse selection and/or moral hazard examples, in which movements in internal funds predict movements in investment spending, holding constant investment opportunities. The purpose of this thesis is to model the impact of financial distress on the investment decisions of firms in Greece and in Europe. To do so, the thesis builds a dynamic investment model, where financial variables and real investment are linked in an attempt to explore the problem of imperfection in capital markets. A further step forward is to investigate potential asymmetries in agents’ investment decisions relative to the state of expectation highlighting the role of business cycle. In order to provide a full picture of the investment decision problem, apart from capital, we introduce the term of labour demand. In particular, we explore the potential effect on labour demand of capital market imperfections, labour market institutional rigidities in the form of union power, and the impact of uncertainty. We employ a dynamic panel data methodology, a GMM estimation technique, is used on a panel data set of Greek firms over the 1993-2001 period. In addition, a panel data set on a sectoral level for most of the continental European countries is also exploited for the period from 1987 to 2003.

The relining of deteriorated gravity flow and pressure pipes with polymeric liners is now popular practice. In the water industry, health concerns and challenges associated with re-opening water services in a lined small diameter pipe have limited the use of liners. Sanexen Environmental Services Inc. in Montreal, Canada, manufactures a cured-in-place liner system which can restore water service connections after lining from within the pipe, using a remote controlled robot. The installation of the liner within cast iron water pipes can result in the formation of geometric imperfections (wrinkles) as the external diameter of the liner often exceeds the internal diameter of the host pipe. Previous studies have suggested that the wrinkles have a detrimental effect on the structural performance of the liner. In this study, experimental and analytical investigations were conducted to evaluate further the effect of the wrinkles on the circumferential (hoop) strength of the liner. The experimental investigation involved testing 33-25 mm wide ring samples of the liner with and without wrinkles, using the split-disk test method which is defined by ASTM Standard D2290. The laboratory tests were conducted to examine the effects on the response of the liner of loading rate, cyclic loading, and presence of different wrinkle configurations. A series of two-tailed Mann-Whitney statistical tests were conducted on the obtained test data. The analytical investigation examined the behavior of two of the three types of wrinkles observed in the liner using finite element models. The results from the models were evaluated using the experimental results. This study confirmed that the wrinkles were a source of weakness in the liner as failure was initiated at the wrinkle in all the test samples. It also showed that their presence may or may not result in a reduction in the ultimate hoop tensile capacity of the liner depending on wrinkle pattern. The loading rate had no significant effect on the first cracking load of the resin within the wrinkle. However, lower ultimate hoop tensile capacities were observed at very slow loading rates. Under the 50-year cyclic loading, the resin within the wrinkle was susceptible to cracking while the jackets of the wrinkle remained intact. / Thesis (Master, Civil Engineering) -- Queen's University, 2008-09-16 22:38:10.234

As de torres treliçadas estaiadas são muito utilizadas e são foco de atenção na pesquisa da engenharia moderna, apresentando-se como um desafio na avaliação das excitações que sobre elas atuam, assim como a determinação das respostas dos elementos que as compõem. Para realizar um estudo neste sentido se realiza no presente trabalho a avaliação estrutural de uma torre treliçada estaiada, localizada na Universidade de Passo Fundo. Esta torre se encontra instrumentada, registrando velocidades de vento de forma contínua, sendo possível determinar nos registros existentes ventos característicos de tormentas TS e EPS. Se conta também com a caracterização dinâmica desta torre para qual foram determinadas suas freqüências naturais de vibração. Utilizando a informação supracitada foram criados modelos estruturais de diferentes níveis de complexidade que foram calibrados utilizando as informações disponíveis. A excitação devida a tormentas foi montada, comparando espectros de excitação clássicos disponíveis na literatura técnica e os registros experimentais de tormentas reais disponíveis. Também foi analisado um montante da torre submetido à compressão onde sua seção transversal é uma cantoneira de abas iguais. Foi determinada a carga de colapso deste perfil considerando as não linearidades físicas e geométricas incorporadas no mesmo. Foi prestada singular atenção ao estudo da influência das imperfeições, utilizando para isto expressões propostas pela bibliografia especializada e o quadro de imperfeições que foi extraído do escaneamento tridimensional de um montante real. Finalmente os diferentes aspectos estudados são discutidos nesta dissertação os quais permitem conhecer melhor o comportamento estrutural de torres estaiadas, em forma global, dos componentes que as compõem e das solicitações que atuam sobre elas. A forma em que se estudaram estes aspectos sem duvida enriqueceram a discussão do complexo tema da incerteza de modelo um dos atuais frentes na pesquisa da engenharia moderna. / The analysis of frames guyed masts are widely used and are the focus of attention in the research of modern engineering, presenting a challenge in the evaluation of excitations that act on them, and determining the responses of the component elements. To undertake a study to that effect, in this essay is made the evaluation of a structural truss of guyed masts, located at the University of Passo Fundo. This tower has equipments that record wind speeds in a continuous manner, being able to determine data about TS and EPS storms in the existing records. It also determines the natural frequencies of vibration as a dynamic characteristic of the tower. Using the above information, structural models of different levels of complexity were created, being calibrated using the available data. The excitement caused by storms was created by comparing the excitation spectra classics available in the technical literature and the experimental records of actual storms available. Also discussed was an amount subject to compression of the tower where its cross section is a corner of tabs equal. Was determined from the load profile given the collapse of physical and geometric nonlinearities embedded in it. Individual attention was given to the study of the influence of imperfections, using it to expressions proposed by the specialized literature and the framework of imperfection that was extracted from three-dimensional scanning of an actual amount.