Дисертації з теми "Sections finies"
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1
Benyamine, Charif Abdallah. "Sections finies d'inégalités multiplicatives de Hilbert et multiplicateurs de l'espace de Dirichlet." Thesis, Bordeaux, 2022. http://www.theses.fr/2022BORD0187.
Анотація:
Nous étudions deux problèmes. Le premier concerne les sections finies de l'inégalité multiplicative de Hilbert. Nous donnons le comportement asymptotique de la meilleure constante $lambda_n$ dans l'inégalité$$Big|sum_{i,j=2}^{n}frac{a_ioverline{a_j}}{ijlog(ij)}Big|leq lambda_n sum_{i=2}^n|a_i|^2.$$Nous donnons aussi le comportement asymptotique de la version $ell^p$ des sections finies de l'inégalité multiplicative de Hilbert.Le deuxième problème concerne l'appartenance des fonctions distance à l'algèbre des multiplicateurs de l'espace de Dirichlet. Les fonctions distance sont les fonctions extérieures dont les valeurs au bord ne dépendent que de la distance par rapport à un ensemble fermé du cercle unité de mesure nulle. Nous donnons une estimation de l'intégrale de Dirichlet d'une fonction distance pour qu'elle appartienne à l'algèbre des multiplicateursWe study two problems. The first one concerns finite sections of the Hilbert multiplicative inequality. We give the asymptotic behaviour of the best constant $lambda_n$ in the inequality$$Big|sum_{i,j=2}^{n}frac{a_ioverline{a_j}}{ijlog(ij)}Big|leq lambda_n sum_{i=2}^n|a_i|^2.$$We also give the asymptotic behaviour of the $ell^p$ version of the finite sections of the Hilbert multiplicative inequality.The second problem concerns the membership of the multiplier algebra of the Dirichlet space of so-called distance functions, namely outer functions whose boundary values depend only on distance to a closed subset of measure zero. We establish an estimate for the Dirichlet integral of such function to belong to the multiplier algebras of the Dirichlet space
2
Blanquier, Éric. "Le modèle de Polyakov, Nambu et Jona-Lasinio et ses applications pour décrire les particules sub-nucléaires." Toulouse 3, 2013. http://thesesups.ups-tlse.fr/2119/.
Анотація:
Pour étudier la physique nucléaire des hautes énergies et les phénomènes associés, comme la transition de phase quark-gluon-plasma/matière hadronique, le modèle de Nambu et Jona Lasinio (NJL) constitue une alternative intéressante à la Chromodynamique Quantique, non solvable aux énergies considérées. En effet, le modèle NJL permet de décrire la physique des quarks à températures et densités finies. D'autre part, afin de tenter de corriger une limitation de ce modèle, l'absence de confinement, il a été proposé un couplage des quarks/antiquarks à une boucle de Polyakov, formant le modèle PNJL. L'objectif de cette thèse est de voir les possibilités offertes par les modèles NJL et PNJL, afin de décrire les particules sub-nucléaires pertinentes (quarks, mésons diquarks et baryons), d'étudier leurs interactions et de mener une étude dynamique avec ces particules. Après un rappel des outils pertinents, nous avons modélisé les quarks effectifs u, d, s, et les mésons. Ensuite, nous avons décrit les baryons comme des états liés quarks-diquarks. Une part du travail a concerné le calcul des sections efficaces liées aux réactions possibles avec ces particules. Nous avons incorporé ces travaux dans un code de calcul pour étudier le refroidissement d'un plasma de quarks/antiquarks et son hadronisation. Dans cette étude, chaque particule évolue dans un système où la température et les densités sont des paramètres locaux. Les interactions entre particules sont de deux types : interactions par collisions et interactions à distance, notamment entre quarks. Finalement, nous avons étudié les propriétés de notre approche : qualités, limitations et évolutions possiblesTo study the high energy nuclear physics and the associated phenomenon, as the QGP/hadronic matter phase transition, the Nambu and Jona-Lasinio model (NJL) appears as an interesting alternative of the Quantum Chromodynamics, not solvable at the considered energies. Indeed, the NJL model allows describing the quarks physics, at finite temperatures and densities. Furthermore, in order to try to correct a limitation of the NJL model, i. E. The absence of confinement, it was proposed a coupling of the quarks/antiquarks to a Polyakov loop, forming the PNJL model. The objective of this thesis is to see the possibilities offered by the NJL and PNJL models, to describe relevant sub-nuclear particles (quarks, mesons, diquarks and baryons), to study their interactions, and to proceed to a dynamical study involving these particles. After a recall of the useful tools, we modeled the u, d, s effective quarks and the mesons. Then, we described the baryons as quarks-diquarks bound states. A part of the work concerned the calculations of the cross-sections associated to the possible reactions implying these particles. Then, we incorporated these works in a computer code, in order to study the cooling of a quarks/antiquarks plasma and its hadronization. In this study, each particle evolves in a system in which the temperature and the densities are local parameters. We have two types of interactions: one due to the collisions, and a remote interaction, notably between quarks. Finally, we studied the properties of our approach: qualities, limitations, and possible evolutions
3
Ori, Miklós. "Local Buckling of Doubly-Symmetric I-Sections Subjected to Warping Torsion : The limitations of the Reduced Cross-Section Method under unconventional loading." Thesis, KTH, Bro- och stålbyggnad, 2019. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-251031.
Анотація:
In regular design practice, when it comes to conventional loading, such as uniaxial compression and bending, the local buckling of thin plates is taken care of through cross section classification. The effect of warping torsion, which also gives rise to normal stresses in the section, however, is typically not considered in the process. Present work aimed to uncover the influence of warping torsion on the phenomena of local plate buckling and to investigate the limitations of the effective width method when it was applied against its intended use. In the case of varying results, a simple correction to the calculation method was to be developed to improve accuracy. The examined I-sections were tested to failure and results were obtained with two different approaches: with finite element method and a Eurocode-based hand-calculation. The finite element models were refined to closely mimic physical experiments and their results were accepted as the true resistance of the sections, while the calculation method tried to capture the structural response in a practical, easily understandable way. The calculated results showed reasonably good accuracy with that of the finite element analysis. However, what really stood out was how similar the change in resistance was when the section parameters were manipulated. Through a properly chosen function, this allowed for the creation of an exponent that could modify the calculated results to achieve an even greater accuracy. The eccentricity of the applied load on the system was also manipulated to alter the proportion of normal stresses due to the two examined effects. It became clear that the stresses from warping in the applied calculation model were underestimated and the otherwise conservative method of effective width lost much of its safety margin when its application was extended to warping as well. Consequently, the consideration of stresses from warping in the regular design process and stability control of commonly used thin walled open sections seemed to be justified. The effective width method could not reliably cover the issue with retaining its original margin of safety.
4
Sousa, Yuri Teixeira e. "Kinematically exact elastoplastic analysis of steelo rods with compact cross sections." Universidade de São Paulo, 2017. http://www.teses.usp.br/teses/disponiveis/3/3144/tde-05122017-134523/.
Анотація:
In this work, we present the formulation and implementation of two elastoplastic constitutive equations for kinematically exact thin-walled rod models. The first uses the fact that first order strains due to cross sectional shear stresses and warping are considered to formulate a small strains three-dimensional elastoplastic constitutive model. Given the kinematical hypothesis of non-deformability of the cross section in the projection of its plane, we may also assume that plastic deformations may occur due only to the cross sectional normal stresses, thereby allowing us to formulate a second, simple one-dimensional framework. Our approach adopts a standard additive decomposition of the strains together with a linear elastic relation for the elastic part of the deformation. Both ideal plasticity and plasticity with (linear) isotropic hardening are considered. The models have a computational implementation within a finite element thin-walled rod model and, following the kinematics adopted, we implement this equation on models with consideration of the warping of the cross sections, having 7 degrees of freedom. The formulation and implementation presented is validated by the analysis of problems known in the literature and comparison of the results. We believe that simple elastoplastic models combined with robust thin-walled rod finite element may be a useful tool for the analysis of thin-walled rod structures, such as, e.g., steel structures.Neste trabalho, apresentamos a formulação e implementação de duas equações constitutivas elastoplásticas simples para modelos de barra de parede fina cinematicamente exatos. O primeiro usa o fato de deformações de primeira ordem devido a esforço cortante na seção transversal e empenamento serem considerados para formular um modelo constitutivo elastoplástico tridimensional para pequenas deformações. Dada a hipótese cinemática de não deformabilidade da seção transversal da barra na projeção de seu plano, podemos também assumir que deformações plásticas ocorrem devido apenas às tensões normais à seção transversal, nos permitindo formular um segundo modelo unidimensional simples. Nossa abordagem adota uma decomposição aditiva padrão das deformações com uma relação elástica linear para a parte elástica das deformações. Tanto plasticidade ideal quanto plasticidade com encruamento isótropo (linear) são considerados. Os modelos resultantes têm uma implementação computacional com elementos finitos de barras e, de acordo com a cinemática adotada, implementamos esta equação com consideração do empenamento das seções transversais, possuindo 7 graus de liberdade. A formulação e implementação apresentadas são validadas pela análise de problemas conhecidos na literatura e comparação dos resultados. Acreditamos que modelos elastoplásticos simples combinados com um elemento finito de barras robusto podem ser uma ferramenta útil para a análise de estruturas reticuladas como, por exemplo, estruturas de aço.
5
Carrier, Michel. "Comportement dynamique des poutres composites a section quelconque : etude par elements finis correspondants." Toulouse 3, 1988. http://www.theses.fr/1988TOU30085.
Анотація:
Element fini monodimensionnel, prenant en compre: heterogeneite, couplages elastiques et dynamiques dus a la non-coincidence des centres de torsion, de masse et elastique, et le gauchissement (effets secondaires). Notion de parametres integraux, equilibre ou interviennent les coefficients de cisaillement. Logiciel pour l'analyse modale des frequences de vibration d'une poutre libre-libre; comparaison a experiences menees en parallele et extension au cas de poutres a phases orthotropes, un axe etant confondu avec celui de la poutre
6
Carrier, Michel. "Comportement dynamique des poutres composites à section quelconque étude par éléments finis correspondante /." Grenoble 2 : ANRT, 1988. http://catalogue.bnf.fr/ark:/12148/cb37612482b.
7
Calloo, Ansar. "Développement d'une nouvelle modélisation de la loi de choc dans les codes de transport neutronique multigroupes." Phd thesis, Université de Grenoble, 2012. http://tel.archives-ouvertes.fr/tel-00909705.
Анотація:
Dans le cadre de la conception des réacteurs, les schémas de calculs utilisant des codes de cal- culs neutroniques déterministes sont validés par rapport à un calcul stochastique de référence. Les biais résiduels sont dus aux approximations et modélisations (modèle d'autoprotection, développement en polynômes de Legendre des lois de choc) qui sont mises en oeuvre pour représenter les phénomènes physiques (absorption résonnante, anisotropie de diffusion respec- tivement). Ce document se penche sur la question de la pertinence de la modélisation de la loi de choc sur une base polynômiale tronquée. Les polynômes de Legendre sont utilisés pour représenter la section de transfert multigroupe dans les codes déterministes or ces polynômes modélisent mal la forme très piquée de ces sections, surtout dans le cadre des maillages énergétiques fins et pour les noyaux légers. Par ailleurs, cette représentation introduit aussi des valeurs négatives qui n'ont pas de sens physique. Dans ce travail, après une brève description des lois de chocs, les limites des méthodes actuelles sont démontrées. Une modélisation de la loi de choc par une fonction constante par morceaux qui pallie à ces insuffisances, a été retenue. Cette dernière nécessite une autre mod- élisation de la source de transfert, donc une modification de la méthode actuelle des ordonnées discrètes pour résoudre l'équation du transport. La méthode de volumes finis en angle a donc été développée et implantée dans l'environ- nement du solveur Sn Snatch, la plateforme Paris. Il a été vérifié que ses performances étaient similaires à la méthode collocative habituelle pour des sections représentées par des polynômes de Legendre. Par rapport à cette dernière, elle offre l'avantage de traiter les deux représenta- tions des sections de transferts multigroupes : polynômes de Legendre et fonctions constantes par morceaux. Dans le cadre des calculs des réacteurs, cette méthode mixte a été validée sur différents motifs : des cellules en réseau infini, des motifs hétérogènes et un calcul de réflecteur. Les principaux résultats sont : - un développement polynômial à l'ordre P 3 est suffisant par rapport aux biais résiduels dus aux autres modélisations (autoprotection, méthode de résolution spatiale). Cette modéli- sation est convergée au sens de l'anisotropie du choc sur les cas représentatifs des réacteurs à eau légère. - la correction de transport P 0c n'est pas adaptée, notamment sur les calculs d'absorbant B4 C.
8
Maranda, Richard. "Analyses par éléments finis de poteaux mixtes avec section d'acier en I de classe 4." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1998. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape11/PQDD_0006/MQ42915.pdf.
9
Boubez, Toufic I. "Three-dimensional finite-element mesh generation using serial sections." Thesis, McGill University, 1986. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=63804.
10
Goudet, Catherine A. "Finite element analysis of diseased cross-sections of human carotid arteries." Thesis, Georgia Institute of Technology, 1995. http://hdl.handle.net/1853/16816.
11
Cheng, Shanshan. "Fire performance of cold-formed steel sections." Thesis, University of Plymouth, 2015. http://hdl.handle.net/10026.1/3316.
Анотація:
Thin-walled cold-formed steel (CFS) has exhibited inherent structural and architectural advantages over other constructional materials, for example, high strength-to-weight ratio, ease of fabrication, economy in transportation and the flexibility of sectional profiles, which make CFS ideal for modern residential and industrial buildings. They have been increasingly used as purlins as the intermediate members in a roof system, or load-bearing components in low- and mid-rise buildings. However, using CFS members in building structures has been facing challenges due to the lack of knowledge to the fire performance of CFS at elevated temperatures and the lack of fire design guidelines. Among all available design specifications of CFS, EN1993-1-2 is the only one which provided design guidelines for CFS at elevated temperatures, which, however, is based on the same theory and material properties of hot-rolled steel. Since the material properties of CFS are found to be considerably different from those of hot-rolled steel, the applicability of hot-rolled steel design guidelines into CFS needs to be verified. Besides, the effect of non-uniform temperature distribution on the failure of CFS members is not properly addressed in literature and has not been specified in the existing design guidelines. Therefore, a better understanding of fire performance of CFS members is of great significance to further explore the potential application of CFS. Since CFS members are always with thin thickness (normally from 0.9 to 8 mm), open cross-section, and great flexural rigidity about one axis at the expense of low flexural rigidity about a perpendicular axis, the members are usually susceptible to various buckling modes which often govern the ultimate failure of CFS members. When CFS members are exposed to a fire, not only the reduced mechanical properties will influence the buckling capacity of CFS members, but also the thermal strains which can lead additional stresses in loaded members. The buckling behaviour of the member can be analysed based on uniformly reduced material properties when the member is unprotected or uniformly protected surrounded by a fire that the temperature distribution within the member is uniform. However if the temperature distribution in a member is not uniform, which usually happens in walls and/or roof panels when CFS members are protected by plaster boards and exposed to fire on one side, the analysis of the member becomes very complicated since the mechanical properties such as Young’s modulus and yield strength and thermal strains vary within the member. This project has the aim of providing better understanding of the buckling performance of CFS channel members under non-uniform temperatures. The primary objective is to investigate the fire performance of plasterboard protected CFS members exposed to fire on one side, in the aspects of pre-buckling stress distribution, elastic buckling behaviour and nonlinear failure models. Heat transfer analyses of one-side protected CFS members have been conducted firstly to investigate the temperature distributions within the cross-section, which have been applied to the analytical study for the prediction of flexural buckling loads of CFS columns at elevated temperatures. A simplified numerical method based on the second order elastic – plastic analysis has also been proposed for the calculation of the flexural buckling load of CFS columns under non-uniform temperature distributions. The effects of temperature distributions and stress-strain relationships on the flexure buckling of CFS columns are discussed. Afterwards a modified finite strip method combined with the classical Fourier series solutions have been presented to investigate the elastic buckling behaviour of CFS members at elevated temperatures, in which the effects of temperatures on both strain and mechanical properties have been considered. The variations of the elastic buckling loads/moments, buckling modes and slenderness of CFS columns/beams with increasing temperatures have been examined. The finite element method is also used to carry out the failure analysis of one-side protected beams at elevated temperatures. The effects of geometric imperfection, stress-strain relationships and temperature distributions on the ultimate moment capacities of CFS beams under uniform and non-uniform temperature distributions are examined. At the end the direct strength method based design methods have been discussed and corresponding recommendations for the designing of CFS beams at elevated temperatures are presented. This thesis has contributed to improve the knowledge of the buckling and failure behaviour of CFS members at elevated temperatures, and the essential data provided in the numerical studies has laid the foundation for further design-oriented studies.
12
Nukala, Ramanand. "Efficient finite element modeling of WT sections subjected to uniaxial tension." Morgantown, W. Va. : [West Virginia University Libraries], 2001. http://etd.wvu.edu/templates/showETD.cfm?recnum=2091.
Анотація:
Thesis (M.S.)--West Virginia University, 2001.Title from document title page. Document formatted into pages; contains vii, [90] p. : ill. (some col.). Includes abstract. Includes bibliographical references (p. 62-63).
13
Lentz, W. Karl. "Optimum coupling in thin-walled, closed section composite beams." Diss., Georgia Institute of Technology, 1997. http://hdl.handle.net/1853/12018.
14
Hassan, Rusul. "Distortional Lateral Torsional Buckling Analysis for Beams of Wide Flange Cross-sections." Thèse, Université d'Ottawa / University of Ottawa, 2013. http://hdl.handle.net/10393/24008.
Анотація:
Structural steel design standards recognize lateral torsional buckling as a failure mode governing the capacity of long span unsupported beams with wide flange cross-sections. Standard solutions start with the closed form solution of the Vlasov thin-walled beam theory for the case of a simply supported beam under uniform moments, and modify the solution to accommodate various moment distributions through moment gradient expressions. The Vlasov theory solution is based on the assumption that cross-sectional distortional effects have a negligible effect on the predicted elastic critical moment. The present study systematically examines the validity of the Vlasov assumption related to cross-section distortion through a parametric study.
A series of elastic shell finite element eigen-value buckling analyses is conducted on simply supported beams subject to uniform moments, linear moments and mid span point loads as well as cantilevers subject to top flange loading acting at the tip. Cross-sectional dimensions are selected to represent structural steel cross-section geometries used in practice. Particular attention is paid to model end connection details commonly used in practice involving moment connections with two pairs of stiffeners, simply supported ends with a pair of transverse stiffeners, simply supported ends with cleat angle details, and built in fixation at cantilever roots.
The critical moments obtained from the FEA are compared to those based on conventional critical moment equations in various Standards and published solutions. The effects of web slenderness, flange slenderness, web height to flange width ratio, and span to height ratios on the critical moment ratio are systematically quantified. For some combinations of section geometries and connection details, it is shown that present solutions derived from the Vlasov theory can overestimate the lateral torsional buckling resistance for beams.
15
Serey, Valentin. "Sélectivité modale d'ondes ultrasonores dans des guides d'ondes de section finie à l'aide d'éléments piézoélectriques intégrés pour le SHM." Thesis, Bordeaux, 2018. http://www.theses.fr/2018BORD0403/document.
Анотація:
Les systèmes SHM (Structural Health Monitoring) basés sur la propagation d’ondes ultrasonores guidées sont utilisés pour des structures de grandes dimensions, par exemple dans les secteurs de l’aéronautique ou du génie civil. Les ondes de Lamb ou SH sont généralement employées car elles se propagent sur de longues distances dans des structures planes tout en sondant l’épaisseur des pièces. Cependant, des modes moins conventionnels se propagent dans les guides d’ondes de section droite finie, tels que les barreaux, les rails ou les tuyaux. Le nombre de modes peut être très élevé dans ce type de guide, et il est important de bien sélectionner un mode particulier.Les méthodes actuelles de sélectivité modale, basées sur l’emploi de plusieurs émetteurs,considèrent habituellement des éléments PZT identiques (même sensibilité, même réponse en fréquence...) et ne prennent pas en compte les conditions réelles de montage et leurs éventuelles imperfections (couplage variable entre traducteurs, mauvais alignement, différence de réponse de l’électronique...). Ce travail présente une méthodologie générale pour la sélectivité modale dans des guides à section droite finie, à l’aide de plusieurs éléments piézoélectriques disposés à leur surface. Cette sélectivité est basée sur la mesure expérimentale préalable, à l’aide d’un vibromètre laser 3D, des amplitudes des modes générés par chaque élément excité individuellement.Une procédure d’optimisation permet d’inverser le problème afin de maximiser l’amplitude du mode désiré, alors obtenue en excitant simultanément tous les émetteurs. Le problème à inverser requiert la connaissance des courbes de dispersion ainsi que des déformées modales des modes,obtenues en utilisant la méthode SAFE 2D. La méthodologie est testée à travers des simulations numériques et des mesures expérimentales sur un barreau d’aluminium de section rectangulaire instrumenté avec huit éléments PZT à sa surface. L’efficacité de la méthode pour générer différents modes purs, mais aussi pour détecter et localiser des défauts calibrés, est démontrée sur le barreau d’aluminium. Son fort potentiel pour des applications de SHM de structures plus complexes est étudié, tels qu’un rail ou un assemblage collé de matériaux compositesSHM systems (Structural Health Monitoring) based on ultrasonic guided waves propagation are used for large structures, e.g. in Aerospace or Civil Engineering. Lamb or SH waves are usually employed as they propagate over long distances in plate-like structures while probing the entire thickness. However less conventional modes propagate in wave guides with finite crosssection,such as bars, rails or pipes. The number of modes can be very high even at low frequencyin this type of guide, and it is important to carefully select a specific mode. Current methods for modal selectivity, based on the use of several emitters, usually consider identical PZT elements(same sensitivity, same frequency response, etc.) and do not account for real experimental conditions and possible differences (variable coupling between transducers, flawed alignment,variable electronic response, etc.). This work presents a global methodology for modal selectivity in waveguides with finite cross-section, using several piezoelectric elements attached to their surface. This selectivity is based on experimental measurements, with a 3D laser vibrometer,of the amplitudes of the modes generated by each emitter. An optimization process allows to inverse the problem in order to maximize the amplitude of the desired mode, then generated by exciting all the emitters at once. This process requires knowing dispersion curves as well as the displacements of the various modes, calculated with SAFE 2D method. The methodology is tested through numerical simulations and experiments on an aluminium rectangular bar instrumented with 8 PZT elements on top. The method efficiency to generate different pure modes,and to detect and locate calibrated defects, is demonstrated for the aluminium bar. Its potential for SHM application of more complex structures is studied, like a rail or an adhesively bonded composite structure
16
Marone-Hitz, Pernelle. "Modélisation de structures spatiales déployées par des mètres ruban : vers un outil métier basé sur des modèles de poutre à section flexible et la méthode asymptotique numérique." Thesis, Ecole centrale de Marseille, 2014. http://www.theses.fr/2014ECDM0011/document.
Анотація:
Les dimensions des satellites spatiaux tendent à croître fortement alors que le volume disponible dans la coiffe des lanceurs est limité. L'utilisation de structures déployables permet de résoudre cette contradiction. Afin de développer l'offre disponible, le département Recherche de Thales Alenia Space étudie les mètres rubans comme solution innovante de déploiement. La première structure envisagée est un télescope déployé par le déroulement de six mètres rubans assurant également le positionnement du miroir secondaire. D'autres structures déployables utilisant les propriétés des mètres rubans sont également en cours d'étude : mât, panneaux solaires, etc.Il convient alors de se doter d'outils de modélisation spécifiques pour modéliser les scénarios de déploiement et multiplier les configurations envisagées. Deux précédentes thèses ont conduit à l'élaboration de modèles énergétiques de poutre à section flexible, rendant compte du comportement plan des rubans ([Guinot2011]) puis de leur comportement tridimensionnel ([Picault2014]). Cette thèse présente différentes contributions autour de ces modèles de poutre à section flexible. Les hypothèses du modèle ont été améliorées. Le re-positionnement de la ligne de référence sur le barycentre des sections conduit à des résultats plus proches des scénarios physiques (apparition et disparition des plis sur le ruban). A ce jour, les hypothèses et les équations du modèle sont définitivement formalisées. Nous avons établi les équations locales 1D (équilibre, comportement) dans le cas des comportements tridimensionnels avec le souci de la plus grande généralité. Établir ensuite les équations dans des cas dérivés simplifiés (restriction aux comportements 2D, section faiblement courbée) nous a permis d'obtenir un certain nombre de solutions analytiques et les équations à implémenter dans l'outil métier.Nous avons développé sur le logiciel de continuation ManLab les premiers éléments d'un outil métier performant dédié à la modélisation des mètres rubans. Nous avons ainsi pu réaliser deux contributions principales :- Un outil généraliste, performant en temps de calcul, permettant d'étudier les systèmes différentiels 1D (BVP, Boundary Value Problems). Les équations locales des modèles de poutre à section flexible ont été implémentées dans cet outil, avec une discrétisation par interpolation polynomiale et collocation orthogonale.- Un élément fini spécifique pour les poutres à section flexible et son implémentation dans ManLab.Ces éléments ont permis de réaliser différentes simulations numériques conduisant à une meilleure compréhension du comportement des mètres rubans grâce aux diagrammes de bifurcation associés à plusieurs essais significatifsDimensions of spatial satellites tend to grow bigger and bigger, whereas the volume in launchers remains very limited. Deployable structures must be used to meet this contradiction. To expand the offer of possible solutions, the Research Department of Thales Alenia Space is currently studying tape springs as an innovative deployment solution. The first structure to be considered is a telescope that is deployed by the uncoiling of six tape springs that also ensure the positioning of the secondary mirror. Other deployable structures that use the properties of tape springs are under investigation : mast, solar panels,...Specific modeling tools then appear compulsory to model deployment scenarios and multiply the tested configurations. Two previous PhD thesis lead to the development of energetic rod models with flexible cross-sections that account for planar ([Guinot2011])and three dimensional behavior of tape springs ([Picault2014]). This PhD thesis presents several contributions on these rod models with flexible cross-sections. The hypotheses of the model were improved. Re-positioning the reference rod line so that it passes through the sections' centroids leads to results that are closer to experimental scenarios (creation and disappearance of folds in the spring). The hypotheses and equations of the model are now definitively formalized.We have derived the 1D local equations in the three-dimensional behavior case in the most generalist way. Then, the derivation of the equations in simplified cases (restriction to 2D behavior, shallow cross-section) enabled us to obtain several analytic solutions and the equations to implement in the specific modeling tool.We have developed on the continuation software ManLab the first elements towards a home made, efficient modeling tool dedicated to the modeling of tape springs. Two main contributions can be listed :- A generalist tool, efficient in calculus times, to study 1D differential problems (BVP, Boundary Value Problems). The local equations of the rod models with flexible cross sections were implemented in this tool, with a discretization based on polynomial interpolation and orthogonal collocation.- A specific finite element for rods with flexible cross sections and its implementation in ManLab.These elements enabled us to perform several numerical simulations and have a better understanding of the behavior of tape springs thanks to full bifurcation diagrams obtained for significant tests
17
El, Hassania Kamal. "Etude numérique et expérimentale du comportement des poutres à parois minces et à sections ouvertes." Metz, 1998. http://docnum.univ-lorraine.fr/public/UPV-M/Theses/1998/El_Hassania.Kamal.SMZ9856.pdf.
Анотація:
Le travail de la présente thèse se résume en deux grandes parties. La première concerne l'étude numérique et expérimentale du comportement des poutres à parois minces et à sections ouvertes en torsion non uniforme. Le modèle théorique est basé sur le modèle de Vlassov. La partie numérique présente le modèle élément finis de type poutre 3D à sept degrés de liberté par nœud ; dont le septième degré de liberté est le gauchissement. Les calculs numériques sont traités par le code d'éléments finis Abaqus et comparés d'une part aux résultats théoriques de Vlassov et d'autre part à nos résultats expérimentaux. L'effet du gauchissement est similaire à celui de la flexion. Dans la seconde partie on s'intéresse au phénomène de déversement des poutres à parois minces et à sections ouvertes. Cette instabilité fait intervenir le comportement des poutres en flexion torsion avec gauchissement. On étudie en particulier l'incidence des conditions aux limites vis à vis du gauchissement et l'effet du point d'application des charges sur la résistance des poutres au déversement. Les solutions numériques par éléments finies sont comparées aux solutions analytiques proposées dans le règlement européen EC3. Le comportement post critique est ensuite étudié en utilisant la méthode de Riks. On étudie en particulier : - l'effet de l'excentricité de la charge par rapport au centre de torsion - l'effet du point d'application de la chargeThis work contains two parts. The first one concerns the experimental and numerical study of behavior of thin walled beams with a non-uniforrn torsion. It is based on the Vlassov's theory. The numerical part uses the finite element method. A 3D beam with warping are considered. The numerical simulations are treated on Abaqus code are compared to theoretical and to experimental results. The warping effect is the same as the flexion. In the second part, the lateral-buckling phenomenon of thin walled beam is studied. The impact of boundary conditions, and especially the warping on the resistance of beams to lateral buckling is exposed. The load height effect is also considered. Numerical solutions by finite element method are compared to analytical solutions proposed in the European regulation EC3. The post critical behavior is then studied by using the method of Riks. We studies especially: - the loading eccentricity effect by report to the center of twist -The load height effect
18
Green, Vicki L. "Investigation of Structural Responses for Flexible Pavement Sections at the Ohio-SHRP Test Road." Ohio University / OhioLINK, 2008. http://rave.ohiolink.edu/etdc/view?acc_num=ohiou1213280487.
19
Martin, Maverick. "Structures spatiales déployables constituées de mètres rubans : analyse et implémentation de modèles de poutre à section flexible." Thesis, Aix-Marseille, 2017. http://www.theses.fr/2017AIXM0571/document.
Анотація:
Les mètres rubans sont utilisés comme dispositif de déploiement car ils sont légers, compacts, se déploient de manière autonome et ont une capacité d'auto-blocage en position déployée. Ces structures élancées de forme cylindrique présentent un comportement complexe avec formation de plis localisés. Leur modélisation est donc difficile : bien que des modèles de poutre à section flexible (RFleXS) aient été développés. Les travaux réalisés consistent à développer des outils numériques d'aide au dimensionnement de structures déployées par des rubans. Un modèle RFleXS adimensionné dédié aux rubans peu profonds est introduit et analysé, mettant en évidence des liens avec le modèle de barre d'Ericksen régularisé. Ces liens expliquent la formation de plis et caractérisent les trois zones constitutives d'un pli. On détermine de façon analytique le nombre et la position des points de bifurcation des branches de solution obtenues pour un essai de flexion pure d'un ruban. Un enrichissement de la cinématique de section est intégré dans les modèles RFleXS. Les simulations de flexion de ruban montrent alors une bonne corrélation avec les modèles de coque. Une nouvelle formulation des modèles RFleXS est implémentée et conduisant au développement de deux outils numériques : un code de calcul par éléments finis complet et un élément à deux noeuds intégré dans un code commercial. Des essais de flexion réalisés sur des rubans composites viennent compléter ces travaux afin de confronter les simulations numériques à des essais réels. Bien que des écarts soient observés, le comportement global du ruban est bien retranscrit par les modèles de poutre à section flexibleDue to their lightness, compactness, their autonomous deployment and their ability to self-locking while deployed, tape-springs are considered to deploy structures. These slender and cylindrical structures highlight a complex behaviour because of the formation of localised folds. Tape-springs are then difficult to model but a rod model with flexible cross-section (RFleXS) has been developed in order to characterise the tape-spring behaviour.The purpose of this PhD was to develop numerical tools dedicated to design structures deployed by tape-spings. A dimensionless form of the RFleXS model dedicated to shallow tape spring has been developed and links with a regularised Ericksen's bar have been made. These links help to explain folds creation and to determine characteristics of the three constitutive areas of a fold. Analysis of the dimensionless model leads to determine the finite number and the position of bifurcation points for the pure bending of a tape-spring. The cross-section kinematic is enriched; simulations of bending tests then show a good correlation with shell models. A new implementation of RFleXS models is introduced, leading to the creation of two numerical tools: a full finite element software and a one-dimensional element with two nodes incorporated in Abaqus. Some bending experiments have been performed in order to compare simulations with measured data. Even if discrepancies are observed, these comparisons show that the tape-spring overall behaviour is well predicted by rod models with flexible cross-section
20
Jeong, Woo Yong. "Structural analysis and optimized design of general nonprismatic I-section members." Diss., Georgia Institute of Technology, 2014. http://hdl.handle.net/1853/53020.
Анотація:
Tapered I-section members have been employed widely for the design of long-span structures such as large clear-span buildings, stadiums, and bridges because of their structural efficiency. For optimized member design providing maximum strength and stiffness at minimum cost, general non-prismatic (tapered and/or stepped cross-sections) as well as singly-symmetric cross-sections have been commonly employed. Fabricators equipped to produce web-tapered members can create a wide range of optimized members from a minimal stock of different plates and coil. Linearly tapered web plates can be nested to minimize scrap. In many cases, the savings in material and manufacturing efficiencies lead to significant cost savings relative to the use of comparable rolled shapes. To employ Design Guide 25 (DG25) which provides guidance for the application of the provisions of the AISC Specification to the design of frames composed of general non-prismatic members, designers need a robust and general capability for determining the elastic buckling loads. Furthermore, robust tools are needed to facilitate the selection of optimum non-prismatic member designs based on minimum cost.
This research addresses the calculation of the elastic buckling loads for general non-prismatic members subjected to general loadings and bracing conditions (typically involving multiple brace points along a given member). This research develops an elastic buckling analysis tool (SABRE2) that can be used to define general geometries, loadings and bracing conditions and obtain a rigorous calculation of the elastic buckling load levels. The three-dimensional finite element equations using open section thin-walled beam theory are derived and formulated using a co-rotational approach including load height effects of transverse loads, stepped flange dimensions, and bracing and support height effects. In addition, this research addresses an algorithmic means to obtain automatic optimized member and frame designs using the above types of members based on Genetic Algorithms (GA). These capabilities are implemented in the tool SABRE2D, which provides a graphical user interface for optimized member and frame design based on updated DG25 provisions and the elastic buckling load calculations from SABRE2.
21
Assenso, Antwi Akwasi. "LOCATION AND CONFIGURATION OF REDUCED BEAM SECTION CONNECTION EFFECTS ON STRENGTH, STIFFNESS AND DUCTILITY OF MOMENT STEEL FRAMES." OpenSIUC, 2018. https://opensiuc.lib.siu.edu/dissertations/1532.
Анотація:
Moment resistant frames are mainly used in resisting lateral loads in buildings. During the 1994 Northridge Earthquake, some of these moment steel frame connections could not undergo inelastic deformation which led to many structural damages. New connection systems were proposed and tested which performed better than the pre-Northridge moment frame connections. Reduced beam section (RBS) connection is one of the most widely used connections after the Northridge Earthquake. Instead of increasing the steel at beam-column, the RBS connection rather removed steel from the flange of the beam. This connection thus gives the designer the option of deciding where the yield will occur in the frame. This research studies the three different parameters used in describing the location and configuration of the radius cut reduced beam section by employing finite element modeling. Variations in ductility, strength and elastic displacement were observed as these parameters were changed. Reducing the flange thus helped with ductility but affected the lateral load carrying capacity and stiffness of the frame.
22
Kucukarslan, Sertac. "A Finite Element Study On The Effective Width Of Flanged Sections." Master's thesis, METU, 2010. http://etd.lib.metu.edu.tr/upload/12612180/index.pdf.
Анотація:
Most of the reinforced concrete systems are monolithic. During construction,
concrete from the bottom of the deepest beam to the top of slab, is placed at
once. Therefore the slab serves as the top flange of the beams. Such a beam is
referred to as T-beam. In a floor system made of T-beams, the compressive
stress is a maximum over the web, dropping between the webs. The
distribution of compressive stress on the flange depends on the relative
dimensions of the cross section, span length, support and loading conditions.
For simplification, the varying distribution of compressive stress can be
replaced by an equivalent uniform distribution. This gives us an effective
flange width, which is smaller than the real flange width. In various codes
there are recommendations for effective flange width formulas. But these
formulas are expressed only in terms of span length or flange and web
thicknesses and ignore the other important variables. In this thesis, three-dimensional finite element analysis has been carried out on
continuous T-beams under different loading conditions to assess the effective
flange width based on displacement criterion. The formulation is based on a
combination of the elementary bending theory and the finite element method,
accommodating partial interaction in between. The beam spacing, beam span
length, total depth of the beam, the web and the flange thicknesses are
considered as independent variables. Depending on the type of loading, the
numerical value of the moment of inertia of the transformed beam crosssection
and hence the effective flange width are calculated. The input data and
the finite element displacement results are then used in a nonlinear regression
analysis and two explicit design formulas for effective flange width have been
derived. Comparisons are made between the proposed formulas and the ACI,
Eurocode, TS-500 and BS-8110 code recommendations.
23
Ba-abbad, Mazen. "Reliability-based Design Optimization of a Nonlinear Elastic Plastic Thin-Walled T-Section Beam." Diss., Virginia Tech, 2004. http://hdl.handle.net/10919/27895.
Анотація:
A two part study is performed to investigate the application of reliability-based design
optimization (RBDO) approach to design elastic-plastic stiffener beams with Tsection.
The objectives of this study are to evaluate the benefits of reliability-based
optimization over deterministic optimization, and to illustrate through a practical
design example some of the difficulties that a design engineer may encounter while
performing reliability-based optimization. Other objectives are to search for a
computationally economic RBDO method and to utilize that method to perform
RBDO to design an elastic-plastic T-stiffener under combined loads and with
flexural-torsional buckling and local buckling failure modes. First, a nonlinear
elastic-plastic T-beam was modeled using a simple 6 degree-of-freedom non-linear
beam element. To address the problems of RBDO, such as the high non-linearity and
derivative discontinuity of the reliability function, and to illustrate a situation where
RBDO fails to produce a significant improvement over the deterministic
optimization, a graphical method was developed. The method started by obtaining a
deterministic optimum design that has the lowest possible weight for a prescribed
safety factor (SF), and based on that design, the method obtains an improved
optimum design that has either a higher reliability or a lower weight or cost for the
same level of reliability as the deterministic design. Three failure modes were
considered for an elastic-plastic beam of T cross-section under combined axial and
bending loads. The failure modes are based on the total plastic failure in a beam
section, buckling, and maximum allowable deflection. The results of the first part
show that it is possible to get improved optimum designs (more reliable or lighter
weight) using reliability-based optimization as compared to the design given by
deterministic optimization. Also, the results show that the reliability function can be
highly non-linear with respect to the design variables and with discontinuous
derivatives. Subsequently, a more elaborate 14-degrees-of-freedom beam element
was developed and used to model the global failure modes, which include the
flexural-torsional and the out-of-plane buckling modes, in addition to local buckling
modes. For this subsequent study, four failure modes were specified for an elasticplastic
beam of T-cross-section under combined axial, bending, torsional and shear
loads. These failure modes were based on the maximum allowable in-plane, out-ofplane
and axial rotational deflections, in addition, to the web-tripping local buckling.
Finally, the beam was optimized using the sequential optimization with reliabilitybased
factors of safety (SORFS) RBDO technique, which was computationally very
economic as compared to the widely used nested optimization loop techniques. At
the same time, the SOPSF was successful in obtaining superior designs than the
deterministic optimum designs (either up to12% weight savings for the same level of
safety, or up to six digits improvement in the reliability for the same weight for a
design with Safety Factor 2.50).Ph. D.
24
Lucassen, Mattheüs. "Infuence of the modelling of truss joints made of hollow tube sections in finite element models." Thesis, KTH, Skolan för industriell teknik och management (ITM), 2019. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-263912.
Анотація:
Several boom segments form the crane boom. These segments are often truss structures formed out of circular hollow sections, which are welded together forming the truss joints. A adequate modelling of these truss joints is very important for operational strength and life. Due to the large boom sizes, efficient models are used in the finite element method, generally built of beam elements. These models have problems capturing the proper bending moments working in the truss joints. This is caused by a insufficient portrayal of the joint stiffness. In the literature several modelling techniques with beam elements are proposed, which capture the joint stiffness better. These different modelling methods are implemented in a parametric boom section and compared with a shell element FE model. From this comparison the most appropriate modelling method is selected, which improve the portrayal of internal loads and nominal stresses. With these improved nominal stress values, it is investigated to implement a different fatigue assessment. The structural stress can be calculated from the nominal stress in combination with stress concentration factor (SCF) equations. To implement the structural stress method as fatigue assessment, several modelling and extrapolation methods have been compared. Which lead to a method for evaluating the structural stress in a efficient matter. This method is compared with existing SCF K truss joint equations, from which a new set of SCF equations is derived. These equations are constructed from a larger dataset, hold a wider validity range and fit better with the FE models. When applying these SCF equations with the improved beam modelling method in a boom section, the structural stress is not adequately captured. This is caused by unsymmetrical stressed braces in the K truss joints. Both the modelling methods and SCF equations account for uniformly stressed braces forming the truss joints. More research needs to be conducted to this uneven behaviour. If the structural stress method needs to be implemented with efficient FE models, submodels out of shell elements combined with beam elements are recommended. For fatigue evaluation with the nominal stress method, beam models which account for the local joint flexibility give sufficient realistic results.Flera kranarmsegment bildar kranarmen. Dessa segment är ofta fackverk utformade av cirkulära ihåliga profiler, som är sammansvetsade och bildar fackverkslederna. En ordentlig modellering av dessa fackförband är mycket viktig för dess driftsstyrka och livslängd. På grund av storleken används finita elementmetoden, vanligtvis uppbyggt av balkelement. Dessa modeller har problem med att beräkna de korrekta böjmomenten som uppstår i fackverkslederna. Detta orsakas av en otillräcklig beskrivning av ledstyvheten. I litteraturen föreslås flera modelleringstekniker med balkelement som tar hänsyn till ledens styvhet bättre. Dessa olika modelleringsmetoder implementeras i en parametrisk kranarmsektion och jämförs med en FE-modell med skalelement. Med denna jämförelse väljs den mest lämpliga modelleringsmetoden, vilket bör förbättra skildringen av interna belastningar och nominella spänningar. Med dessa förbättrade nominella spänningsvärden, undersöks det att genomföra en annan utmattningsbedömning. Den strukturella spänningen kan beräknas utifrån den nominella spänningen i kombination med spänningskoncentrationsfaktor- (SCF) ekvationerna. För att implementera strukturella spänningsmetoden som utmattningsbedömning, har flera modellerings- och extrapoleringsmetoder jämförts. Detta leder till en metod för att utvärdera den strukturella spänningen effektivt. Denna metod jämförs med befintliga SCF-ekvationer, från vilka en ny uppsättning SCF-ekvationer härleds. Dessa ekvationer är konstruerade från en större datauppsättning, har ett bredare giltighetsområde och passar bättre med FE-modellerna. När man applicerar dessa SCF-ekvationer med den förbättrade balkmodelleringsmetoden i en kranarmsektion, uppsamlas strukturella spänningar inte tillräckligt, detta orsakas av ojämna spänningar i diagonalelementen i fackverkslederna. Både modelleringsmetoderna och SCF-ekvationerna tar hänsyn till jämnt spända diagonalelement som uppstår i fackverkslederna. Mer forskning bör göras över detta ojämna beteende. Om den strukturella spänningsmetoden måste implementeras med effektiva FE-modeller, rekommenderas undermodeller av skalelement kombinerade med balkelement. För utmattningsutvärdering med den nominella spänningsmetoden, ger balkmodeller som tar hänsyn till den lokala ledflexibiliteten tillräckligt realistiska resultat.
25
Chakravarty, Uttam Kumar. "Section builder: a finite element tool for analysis and design of composite." Diss., Atlanta, Ga. : Georgia Institute of Technology, 2008. http://hdl.handle.net/1853/22640.
Анотація:
Thesis (Ph. D.)--Aerospace Engineering, Georgia Institute of Technology, 2008.Committee Chair: Bauchau, Olivier; Committee Member: Craig, James; Committee Member: Hodges, Dewey; Committee Member: Mahfuz, Hassan; Committee Member: Volovoi, Vitali.
26
Lowder, Margaret Loraine. "Distribution of Stress in Three-Dimensional Models of Human Coronary Atherosclerotic Plaque Based on Acrylic Histologic Sections." Diss., Georgia Institute of Technology, 2007. http://hdl.handle.net/1853/16137.
Анотація:
Each year in the United States over a million people experience a myocardial infarction. The majority of these attacks are caused by coronary artery plaque cap rupture with subsequent thrombus formation. Because rupture is a mechanical event and the tendency of a plaque to rupture is due in part to increases in the mechanical stresses in the fibrous cap, mechanical analyses are important to understanding plaque stability.
Histology is the only method capable of identifying plaque features that are associated with vulnerability. Therefore, minimally distorted histologic sections should serve as a basis for constructing the models used in mechanical analyses. Further, because substantial longitudinal variations in geometry and mechanical properties often exist, models should be three-dimensional (3-D). Finally, given the complex geometries of atherosclerotic plaques and the fact that they are composed of different materials, the finite element (FE) method should be used to determine the distribution of stress under physiological loading. Until now, a critical need has existed to determine the distribution of stress in 3-D FE models of human coronary atherosclerotic plaques based on minimally distorted histologic sections.
In this research study, a method to measure and correct for distortions caused by acrylic histologic processing was first created. The devised strain-based method yields a limited set of parameters needed for a first order correction. Thus, corrections can be easily implemented using FE methods. Next, a methodology to create 3-D finite FE models of human coronary atherosclerotic plaques based on stable acrylic histologic sections was developed. Models of plaques, ranging in disease severity, were generated using the developed methodology. Lastly, the distributions of stress in these models were obtained and the effects of some plaque features on stresses were determined.
Results from this study confirm that morphological description of a plaque is not sufficient to predict plaque rupture. The findings suggest that in many cases the 3-D stress field within a plaque must be known in order to assess plaque stability. Finally, the results show that patient specific models must be developed if the 3-D stress field within a plaque is to be determined.
27
Persson, Daniel. "Efficient Calculations of Two-Dimensional Radar Cross-Section Using DGFEM." Thesis, Uppsala universitet, Avdelningen för beräkningsvetenskap, 2020. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-424009.
Анотація:
A two-dimensional discontinuous Galerkin finite element method algorithm in the time domain was developed for calculation of the radar cross-section of an arbitrary object. The algorithm was formed using local nodal basis functions in each element and coupling them via numerical upwind flux. Both transverse electric and transverse magnetic polarization, as well as three different dispersive material models, were handled. The computational domain was effectively truncated with low reflections using the uniaxial perfectly matched layer method. Two different time stepping methods were used, low-storage explicit Runge-Kutta and Leap-Frog, to allow for flexibility in the time step and application of a stabilization method. The algorithm was verified with geometries, which have analytical expressions, and an existing validated code. The algorithm was also compared to an existing algorithm, which utilized the continuous finite element method with implicit time stepping, and showed outstanding performance regarding computation time and memory allocation. Since the developed algorithm had explicit time stepping could no general conclusions favoring any of the methods beyond these specific algorithms be made. The results still encouraged continued development of the DGFEM algorithm, where the expansion into three dimensions and optimizations could be explored further.
28
Wilkinson, Timothy James. "The Plastic Behaviour of Cold-Formed Rectangular Hollow Sections." University of Sydney. Department of Civil Engineering, 2000. http://hdl.handle.net/2123/843.
Анотація:
The aim of this thesis is to assess the suitability of cold-formed rectangular hollow sections (RHS) for plastic design. The project involved an extensive range of tests on cold-formed Grade C350 and Grade C450 (DuraGal) RHS beams, joints and frames. A large number of finite element analyses was also carried out on models of RHS beams. The conclusion is that cold- formed RHS can be used in plastic design, but stricter element slenderness (b/t) limits and consideration of the connections, are required. Further research, particularly into the effect of axial compression on element slenderness limits, is required before changes to current design rules can be finalised. Bending tests were performed on cold-formed RHS to examine the web and flange slenderness required to maintain the plastic moment for a large enough rotation suitable for plastic design. The major conclusions of the beam tests were: (i) Some sections which are classified as Compact or Class 1 by current steel design specifications do not maintain plastic rotations considered sufficient for plastic design. (ii) The current design philosophy, in which flange and web slenderness limits are independent, is inappropriate. An interaction formula is required, and simple formulations are proposed for RHS. Connection tests were performed on various types of knee joints in RHS, suitable for the column - rafter connection in a portal frame. The connection types investigated were welded stiffened and unstiffened rigid knee connections, bolted plate knee joints, and welded and bolted internal sleeve knee joints, for use in RHS portal frames. The ability of the connections to act as plastic hinges in a portal frame was investigated. The most important finding of the joint tests was the unexpected fracture of the cold-formed welded connections under opening moment before significant plastic rotations occurred. The use of an internal sleeve moved the plastic hinge in the connection away from the connection centre- line thus eliminating the need for the weld between the RHS, or the RHS and the stiffening plate, to carry the majority of the load. The internal sleeve connections were capable of sustaining the plastic moment for large rotations considered suitable for plastic design. Tests on pinned-base portal frames were also performed. There were three separate tests, with two different ratios of vertical to horizontal point loads, simulating gravity and horizontal wind loads. Two grades of steel were used for comparison. The aims of the tests were to examine if a plastic collapse mechanism could form in a cold-formed RHS frame, and to investigate if plastic design was suitable for such frames. In each frame, two regions of highly concentrated curvature were observed before the onset of local buckling, which indicated the formation of plastic hinges and a plastic collapse mechanism. An advanced plastic zone structural analysis which accounted for second order effects, material non-linearity and member imperfections slightly overestimated the strength of the frames. The analysis slightly underestimated the deflections, and hence the magnitude of the second order effects. A second order plastic zone analysis, which did not account for the effects of structural imperfections, provided the best estimates of the strengths of the frames, but also underestimated the deflections. While cold-formed RHS did not satisfy the material ductility requirements specified for plastic design in some current steel design standards, plastic hinges and plastic collapse mechanisms formed. This suggests that the restriction on plastic design for cold-formed RHS based on insufficient material ductility is unnecessary, provided that the connections are suitable for plastic hinge formation, if required. A large number of finite element analyses were performed to simulate the bending tests summarised above, and to examine various parameters not studied in the experimental investigation. To simulate the experimental rotation capacity of the RHS beams, a sinusoidally varying longitudinal local imperfection was prescribed. The finite element analysis determined similar trends as observed experimentally, namely that the rotation capacity depended on both the web slenderness and flange slenderness, and that for a given section aspect ratio, the relationship between web slenderness and rotation capacity was non-linear. The main finding of the finite element study was that the size of the imperfections had an unexpectedly large influence on the rotation capacity. Larger imperfections were required in the more slender sections to simulate the experimental results. There should be further investigation into the effect of varying material properties on rotation capacity.
29
Brackus, Travis R. "Destructive Testing and Finite-Element Modeling of Full-Scale Bridge Sections Containing Precast Deck Panels." DigitalCommons@USU, 2010. https://digitalcommons.usu.edu/etd/861.
Анотація:
Full-depth, precast panel deck systems are becoming more common in bridge installation and repair. The objective of these systems is to achieve the performance of cast-in-place systems while simultaneously saving time and money. The structural behavior of these systems has been the subject of scrutiny in recent research. The Utah Department of Transportation demolished a steel I-girder bridge containing a precast panel deck system and provided two full-scale specimens for this project. Destructive testing was performed at Utah State University on the specimens to investigate three failure modes: flexural, beam shear, and punching shear. Finite-element models were created using ANSYS software to replicate experimental behavior. Overall, it was found that the elastic, post-elastic, and ultimate behavior of the full-scale bridge sections containing precast panel deck systems can be accurately predicted in analytical models.
Another aspect of this project was to investigate changes in dynamic behavior as the system was subjected to flexural yield and failure. Point loads were applied and removed in increments, and dynamic testing was conducted at each load level. It was found that significant damage is somewhat noticeable by monitoring the changes in natural frequencies.
30
Sanni, Bakouregui Abdoulaye. "Étude du comportement d'une section d'essais de chaussée de BAC avec des armatures en PRFV." Mémoire, Université de Sherbrooke, 2017. http://hdl.handle.net/11143/9863.
Анотація:
Au Québec, l’épandage des sels de déglaçage pendant l’entretien hivernal des routes est l’une des causes de la corrosion des armatures en acier dans les ouvrages routiers en béton armé. La corrosion de l’acier crée des tensions internes dans le béton, ce qui entraine l’éclatement du béton qui enrobe l’armature d’acier. La durée de vie des infrastructures routières est par conséquent réduite et les coûts d’entretien sont augmentés.
Le présent projet de recherche est né d’une collaboration entre le ministère des Transports, de la Mobilité durable et de l’Électrification des Transports (MTMDET) et l’Université de Sherbrooke. Il vise à étudier l’utilisation des barres en polymères renforcés de fibres de verre (PRFV), non sujettes à la corrosion dans les dalles en béton armé continu (BAC).
Dans cette étude, une section de chaussée de 300 mètres de long a été instrumentée pendant la reconstruction de l’autoroute 40 Ouest à Montréal, pour caractériser le comportement à court et à long terme des dalles en BAC avec des armatures en PRFV. Les résultats expérimentaux montrent que les conditions climatiques affectent considérablement le comportement à la fissuration des dalles en BAC de PRFV et d’acier. Une analyse par éléments finis d’une section de la chaussée a été également réalisée avec le logiciel Abaqus en vue d’étudier l’influence de plusieurs paramètres tels que le taux d’armature longitudinale, les propriétés des barres de PRFV et leur profondeur, l’épaisseur de la dalle, le coefficient de dilatation thermique du béton et l’espacement des armatures transversales sur le comportement de la dalle en BAC de PRFV. Le modèle par éléments finis a été validé avec les résultats expérimentaux obtenus en chantier. Les résultats numériques montrent que le coefficient de dilatation thermique du béton, le taux d’armature longitudinale, les propriétés des barres de PRFV et leur positionnement dans la dalle, l’épaisseur de la dalle constituent les paramètres qui influencent le plus le comportement des dalles en BAC. Pour le dimensionnement des dalles en BAC de PRFV, des taux d’armature ainsi que des propriétés de barres de PRFV ont été proposés en tenant compte des résultats expérimentaux ainsi que de l’analyse par éléments finis.
31
Vassart, Olivier. "Analytical model for cellular beams made of hot rolled sections in case of fire." Phd thesis, Université Blaise Pascal - Clermont-Ferrand II, 2009. http://tel.archives-ouvertes.fr/tel-00860914.
Анотація:
Cette thèse a permis de développer un modèle analytique pour la prédiction de la température critique de poutrelle cellulaire fabriquée à base de profilés laminés en situation d'incendie. Ces résultats seront basés sur la mise au point d'un nouveau modèle analytique de poutrelle cellulaire isostatique soumise au feu. Pour assurer la fiabilité du modèle developpé, les étapes suivantes ont été considérées : La réalisation de tests en grande échelle en laboratoire ; La mise au point d'un modèle éléments finis dans le logiciel SAFIR ; La validation du modèle éléments finis en comparaison des essais en laboratoire ; Le développement du modèle analytique simplifié ; La validation de cette méthode analytique par une étude paramétrique utilisant le modèle éléments finis. Le modèle éléments finis et le modèle analytique sont capable de reproduire avec un niveau satisfaisant de précision le comportement complexe des poutrelles cellulaires en cas d'incendie
32
Boissonnade, Nicolas. "Mise au point d'un élément fini de type poutre à section variable et autres applications à la construction métallique." Clermont-Ferrand 2, 2002. http://www.theses.fr/2002CLF21394.
Анотація:
Le but de ce travail est le développement d'un outil numérique de calcul rapide et efficace pour poutres à parois minces et section ouverte et variable ; une formulation "éléments finis" a été retenue ici, à travers un élément de poutre, parce qu'elle offre le meilleur compromis entre facilité d'obtention et qualité des résulats. Pour pouvoir asseoir de la meilleure façon possible les bases théoriques de cet élément, un modèle analytique complet pour poutres à parois minces et section variable est tout d'abord développé. L'accent est mis sur les phénomènes de torsion, primordiaux pour l'étude spatiale des poutres à section variable, et sur le traitement des rotations dans l'espace. Le modèle mécanique et les hypothèses de comportement sont finalement résumés dans le choix d'un champ de déplacements approprié. Les expressions des déformations non linéaires et des équations d'équilibre en sont déduites, et, en particulier, l'équation différentielle du déversement des poutres en I monosymétriques à semelles constantes et hauteur d'âme linéairement variable, très importante en pratique, est mise en évidence. On montre ensuite comment ces concepts théoriques peuvent être appliqués de façon simple à l'étude du comportement réel des poutres et fléchies. Sur la base du champ de déplacements et des expressions des déformations retenus, un élément fini de type poutre est proposé en formulation corotationnelle totale, avec un soin particulier quant à la prise en compte correcte des modes rigides et des phénomènes de locking. Les qualités de convergence et de précision de l'élément sont testées à travers différents cas de chargement et d'appui, pour tous les types d'analyse statique, y compris le cas le plus complexe de l'analyse non linéaire géométrique et matérielle. Les résultats obtenus sont comparés avec différentes références numériques disponibles, en particulier avec des éléments finis de coques, et la concordance entre ces différentes sources est excellente
33
Carlson, Ryne. "Flexural Strength of Steel Beams with Holes in the Tension Flange." University of Cincinnati / OhioLINK, 2019. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1563527519192391.
34
Geara, Fadi. "Contribution à l'étude de la torsion des poutres en voiles minces et des poutres à profil dissymétrique." Châtenay-Malabry, Ecole centrale de Paris, 1998. http://www.theses.fr/1998ECAP0598.
Анотація:
Cette recherche est une contribution à l'étude de la torsion des poutres en voiles minces ouverts et des poutres à sections transversales non symétriques. En effet, dans le cas des poutres en voiles minces ouverts, on a développé la statique de la torsion suivant la théorie de Vlassov, c'est-à-dire en tenant compte du gauchissement qui accompagne en général la torsion, et ses effets sur les éléments de structure. Notre travail commence par la résolution de l'équation différentielle de la torsion gênée pour diverses conditions aux limites et différents chargements. Des exemples numériques ont concrétisé l'importance de la prise en compte du gauchissement dans le cas des éléments minces. L'étude a été complétée par la formulation de la poutre continue soumise à la torsion et par une étude numérique comparative avec la méthode des éléments finis en utilisant une modélisation en éléments coques et montrant la concordance entre les deux méthodes. D'autre part, dans le cas des poutres a profil dissymétrique, le centre de torsion n'est pas en général confondu avec le centre de gravité. Notre travail était de prendre en compte cette excentricité et d'introduire son effet dans la matrice de rigidité d'un élément de poutre droite, ainsi que ses effets sur les sollicitations et les déplacements des éléments de structure. L'étude a été complétée par plusieurs exemples schématisant l'intérêt de l'utilisation de la matrice de rigidité modifiée.
35
Radi, Neto José. "Simulação numérica do comportamento pós-fissuração de vigas de concreto armado pelo método dos elementos finitos." Universidade Federal de Uberlândia, 2007. https://repositorio.ufu.br/handle/123456789/14224.
Анотація:
Coordenação de Aperfeiçoamento de Pessoal de Nível SuperiorThis work presents a numerical method for the evaluation of internal forces and displacements in reinforced concrete straight beams considering cracking and the influence of longitudinal and transversal reinforcement. In order to simulate cracking behavior, the elasticity module of the cracked element is reduced depending on the dimensions of the finite element. The physical non-linear behavior of concrete and steel is also considered. The finite element method was used for a rectangular element with four nodes representing the concrete. A hinged end bar element in tension and compression was used for steel. The numerical results obtained compared satisfactorily with the experimental ones available in the technical literature. The results were analyzed by graphs and tables. The analysis showed the proposed method is actually appropriate for reinforced concrete beams simulations.
O presente trabalho apresenta um método numérico para a determinação dos esforços e deslocamentos em vigas retas de concreto armado levando em consideração a fissuração e a influência das armaduras longitudinais e transversais. Para simular numericamente as fissuras, o elemento fissurado tem seu módulo de elasticidade reduzido em função das dimensões do elemento finito. Também é considerada a não-linearidade física dos materiais aço e concreto. Empregou-se o método dos elementos finitos com elementos retangulares de quatro nós para o concreto e elementos do tipo barra com capacidade de tração ou compressão para o aço. A validação do sistema computacional foi feita através de comparações entre resultados numéricos do programa com resultados experimentais desenvolvidos por outros pesquisadores. Os resultados são comparados entre si através das respostas mostradas em gráficos e tabelas mostrando que o método utilizado é bastante apropriado para a análise de vigas de concreto armado.
Mestre em Engenharia Civil
36
Picault, Elia. "Un modèle de poutre à section mince flexible - Application aux pliages 3D de mètres rubans." Phd thesis, Aix-Marseille Université, 2013. http://tel.archives-ouvertes.fr/tel-00921931.
Анотація:
Ce travail a pour cadre une collaboration entre le LMA et Thales Alenia Space. Nous nous intéressons au comportement des structures flexibles et plus particulièrement des mètres rubans qui ont la particularité de pouvoir, grâce à l'aplatissement de la section, s'enrouler ou développer des pliages localisés. Une première thèse a permis d'une part la mise au point d'un nouveau type de mètre ruban au déroulement maîtrisable thermiquement et d'autre part le développement d'un modèle plan de poutre à section flexible. Dans le travail de thèse présenté ici, nous proposons une version étendue de ce modèle adaptée à la simulation du comportement dynamique tridimensionnel des mètres rubans en grands déplacements et en grandes rotations. Ce modèle est dérivé de la théorie des coques et repose sur l'introduction d'hypothèses cinématiques et sthéniques adaptées. La déformation de la section est caractérisée par celle de sa ligne moyenne qui peut se déformer dans son plan par flexion et torsion mais non par extension, ainsi que hors de son plan par gauchissement de torsion. Les fortes variations de forme de la section dans son plan peuvent alors être décrites par une cinématique de type Elastica, tandis qu'une cinématique de type Vlassov est utilisée pour définir le gauchissement dans le repère local attaché à la section. Le modèle unidimensionnel est obtenu par intégration sur la section des expressions de la théorie des coques, une approche énergétique permet ensuite de formuler le problème associé qui est résolu grâce au logiciel de modélisation par éléments finis COMSOL.
37
Deterre, Cécile. "Étude dans les états finals dileptoniques de différentes propriétés des paires top-antitop avec les détecteurs D0 et ATLAS." Phd thesis, Université Pierre et Marie Curie - Paris VI, 2012. http://tel.archives-ouvertes.fr/tel-00725209.
Анотація:
Les études de différentes propriétés des paires top-antitop dans l'état final dileptonique sont présentées dans cette thèse. Deux analyses ont été réalisées dans des expériences différentes : l'une à D0 auprès du Tevatron, l'autre dans ATLAS auprès du LHC. Les deux collisionneurs étant différents, les mesures qui y sont réalisées sont complémentaires pour les études des propriétés du top. La première analyse, réalisée dans l'expérience D0, a consisté à faire une mesure simultanée de la section efficace de production des paires top-antitop et du rapport d'embranchement t -> Wb Cette mesure a été réalisée dans le canal dileptonique avec un lot de données correspondant à une luminosité de 5,4 fb⁻¹. Elle a ensuite été combinée avec la mesure réalisée dans le canal semileptonique pour obtenir une précision de 8% sur la section efficace, comparable à la précision des calculs théoriques. La deuxième analyse présentée, réalisée dans l'expérience ATLAS , a consisté à mesurer l'asymétrie de charge du quark top dans le canal dileptonique avec le lot de données enregistré par ATLAS en 2011, soit 4,7 fb⁻¹. Les résultats ont ensuite été combinés avec le résultat du canal semileptonique obtenu avec 1 fb⁻¹. On mesure : A^C(ttbar) = 0,029 +- 0,018 (stat.) +- 0,014 (syst.), ce qui est compatible avec la prédiction du modèle standard de 0,004 +- 0,001.
38
Hotz, Carl. "MOMENT REDUCTION ANALYSIS OF BUILT-UP I-SECTION EXPOSED TO UNIFORM CORROSION." University of Akron / OhioLINK, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=akron1525293365942438.
39
Guler, Togan Kemal. "Thermo-mechanical Finite Element Analysis And Design Of Tail Section For A Ballistic Missle." Master's thesis, METU, 2012. http://etd.lib.metu.edu.tr/upload/12615165/index.pdf.
Анотація:
During the flight of missiles, depending on the flight conditions, rotation of missiles around its centerline can cause instabilities. To override this issue, missile generally is designed in 2 sections. In the missile, the rear tail section and the front section are to rotate freely by means of bearings. Tail section on which bearings are mounted is designed according to thermal loads due to flow of hot gasses through the nozzle and mechanical loads due to inertial load, interference fit and thread preload which appear during flight of missile.
The purpose of this thesis is to determine the most suitable structural parameters according to the flight conditions of missile.
The geometrical and load parameters which have effect on the results were determined. Finite element model is formed by using FEA software. After that, transient nonlinear thermo-mechanical analyses are performed and the most effective parameter on VM (Von-Mises) stress and force is determined.
DOE (Design of Experiments) method was used to determine the most suitable values for the structural parameters. Totally 27 different configurations are studied to achieve to the most suitable values for variable set.
It is observed that VM stress and force results for all configurations are within the ±%5 ranges. So this means parameters don&rsquo
t affect the systems response very much. By taking manufacturing processes into consideration, configuration with the highest bearing inner/outer ring interference is taken. From the comparison of the results, the most suitable configuration is obtained after checking forces and VM stress on the bearings.
40
Vootukuri, Venkat Ramana Reddy. "COMPARISON OF STRENGTH, DUCTILITY AND STIFFNESS FOR RADIUS CUT AND STRAIGHT CUT OF REDUCED BEAM SECTION." OpenSIUC, 2019. https://opensiuc.lib.siu.edu/theses/2536.
Анотація:
In 1994 there was an earthquake occurred in Northridge, California which caused damage in structures built with Steel Moment Frames (SMF) due to the brittle fractures in the beam and column connections. It has led to the major modifications and improvements in the connection detailing prior to the earthquake occurred in the Northbridge. These changes came up with better materials for welding and introduced the use of cover plate and Reduced Beam Section (RBS). RBS connections are the most widely used connection today and it allows the SMF systems to yield extensively and deform plastically by avoiding brittle fracturing at connections. The most important factors that affect the response along with the design of Steel Moment Frames (SMF) and Reduced Beam Section (RBS) connections are connection strength, stiffness, connection type, use of deep columns and phenomena associated with its instability, the strength of ductility of the column panel zone-beam instability.
41
Ozyurt, Emre. "Behaviour of welded tubular structures in fire." Thesis, University of Manchester, 2015. https://www.research.manchester.ac.uk/portal/en/theses/behaviour-of-welded-tubular-structures-in-fire(15601ab3-8f6c-4e64-ba1a-6201e66e9e16).html.
Анотація:
This thesis presents the results of a research project to develop methods to carry out fire safety design of welded steel tubular trusses at elevated temperatures due to fire exposure. It deals with three subjects: resistance of welded tubular joints at elevated temperatures, effects of large truss deflection in fire on member design and effects of localised heating. The objectives of the project are achieved through numerical finite element modelling at elevated temperatures using the commercial Finite Element software ABAQUS v6.10-1 (2011). Validation of the simulation model for joints is based on comparison against the test results of Nguyen et al. (2010) and Kurobane et al. (1986). Validation of the simulation model for trusses is through checking against the test results of Edwards (2004) and Liu et al. (2010).For welded tubular joints, extensive numerical simulations have been conducted on T-, Y-, X-, N- and non-overlapped K-joints subjected to brace axial compression or tension, considering a wide range of geometrical parameters. Uniform temperature distribution was assumed for both the chord and brace members. Results of the numerical simulations indicate for gap K- and N-joints (two brace members, one in tension and the other in compression) and for T-, Y- and X-joints with the brace member under axial tensile load (one brace member only, in tension), it is suitable to use the same ambient temperature calculation equation as in the CIDECT (2010) or EN 1993-1-8 (CEN, 2005a) design guides and simply replace the ambient temperature strength of steel with the elevated temperature value. However, for T-, Y- and X-joints under brace compression load (one brace member only, in compression), the effect of large chord deformation should be considered. Large chord deformation changes the chord geometry and invalidates the assumed yield line mechanism at ambient temperature. For approximation, the results of this research indicate that it is acceptable to modify the ambient temperature joint strength by a reduction factor for the elastic modulus of steel at elevated temperatures. In the current fire safety design method for steel truss, a member based approach is used. In this approach, the truss member forces are calculated at ambient temperature based on linear elastic analysis. These forces are then used to calculate the truss member limiting temperatures. An extensive parametric study has been carried out to investigate whether this method is appropriate. The parametric study encompasses different design parameters over a wide range of values, including truss type, joint type, truss span-to-depth ratio, critical member slenderness, applied load ratio, number of brace members, initial imperfection and thermal elongation. The results of this research show that due to a truss undergoing large displacements at elevated temperatures, some truss members (compression brace members near the truss centre) experience large increases in member forces. Therefore, using the ambient temperature member force, as in the current truss fire safety design method, may overestimate the truss member critical temperature by 100 °C. A method has been proposed to analytically calculate the increase in brace compressive force due to large truss deformation. In this method, the maximum truss displacement is assumed to be span/30. A comparison of the results calculated using the proposed method against the truss parametric study results has shown good agreement with the two sets of results, with the calculation results generally being slightly on the safe side. When different members of a truss are heated to different temperatures due to localised fire exposure, the brace members in compression experience increased compression due to restrained thermal expansion. To calculate the critical temperature of a brace member in a localised heated truss, it is necessary to consider this effect of restrained thermal expansion. It is also necessary to consider the beneficial effects of the adjacent members being heated, which tends to reduce the increase in compressive force in the critical member under consideration. Again, an extensive set of parametric studies have been conducted, for different load ratio, slenderness and axial restraint ratio. The results of this parametric study suggest that to calculate the critical temperature of a brace member, it is not necessary to consider the effects of the third or further adjacent members being heated. For the remainder of the heated members, this thesis has proposed a linear elastic, static analysis method at ambient temperature to calculate the additional compressive force (some negative, indicating tension) in the critical member caused by the heated members (including the critical member itself and the adjacent members). The additional compressive force is then used to calculate the limiting temperature of the critical member. For this purpose, the approximate analytical equation of Wang et al. (2010) has been demonstrated to be suitable.
42
Perera, Nilakshi. "Structural behaviour and design of innovative hollow flange steel plate grinders." Thesis, Queensland University of Technology, 2018. https://eprints.qut.edu.au/123310/1/Liyanage%20Nilakshi%20Piyahasi_Perera_Thesis.pdf.
Анотація:
This thesis proposes a new Hollow Flange Steel Plate Girder (HFSPG) by welding industrially available cold-formed Rectangular Hollow Sections (RHS) to a web plate for use in long span construction. Design procedures presented in the national and international design guidelines were reviewed and suitable improvements were made to accurately predict the structural behaviour and capacities of HFSPGs by undertaking detailed experimental and numerical studies into their unique structural behaviour. Local buckling/yielding, global buckling and local-global interaction failures were all considered in this thesis.
43
Silva, Raphael Santos da. "Avaliação de ligações K e T entre perfis estruturais tubulares circulares." Universidade do Estado do Rio de Janeiro, 2012. http://www.bdtd.uerj.br/tde_busca/arquivo.php?codArquivo=5589.
Анотація:
Coordenação de Aperfeiçoamento de Pessoal de Nível SuperiorO difundido uso de perfis estruturais tubulares, principalmente devido às vantagens associadas ao comportamento estrutural e estético, levou a uma intensa utilização nos países da Europa, Sudeste Asiático, América do Norte e na Austrália. Países como Canadá, Inglaterra, Alemanha e Holanda fazem uso intensivo dessas estruturas e contam com uma produção corrente, industrializada e contínua com alto grau de desenvolvimento tecnológico. O aumento da oferta deste tipo de perfis, aliado a recentes pesquisas nesta área, leva o Brasil a se inserir neste cenário mundial. Entretanto, as normas brasileiras que regem o dimensionamento destes perfis ainda não se encontram atualizadas, principalmente no que tange ao dimensionamento de ligações de perfis tubulares. Considerando esta perspectiva, este trabalho apresenta uma análise de ligações tipo K e T com perfis tubulares circulares (CHS). Propõe-se estabelecer um quadro comparativo entre as formulações analíticas de dimensionamento proposta pelo Eurocode 3 Parte 1.8, 2 edição do guia de projeto de ligações tubulares do CIDECT, projeto de norma brasileira PN 02.125.03-004 e critérios de deformação limite. Para cada um dos tipos de ligações analisadas, desenvolveu-se um modelo em elementos finitos no programa Ansys, calibrado e validado com resultados experimentais e numéricos existentes na literatura. As não-linearidades física e geométrica foram incorporadas aos modelos, a fim de se mobilizar totalmente a capacidade resistente da ligação. A não-linearidade do material foi considerada através do critério de plastificação de Von Mises através de uma lei constitutiva tensão versus deformação bilinear. A não-linearidade geométrica foi introduzida no modelo através da Formulação de Lagrange Atualizado considerando-se a previsão de grandes deformações de forma a permitir a redistribuição de carregamento na ligação após o escoamento inicial. Esta dissertação propõe ainda, a modelagem de uma treliça planar constituída de perfis tubulares, objetivando estabelecer uma comparação entre um nó isolado e um nó da treliça planar.
The widespread adoption of hollow section structures, mainly due to the advantages associated with the structural and aesthetic behavior, led to an intense use in the countries of Europe, Southeast Asia, North America and Australia. Countries like Canada, England, Germany and Holland use these structures intensively and have a current industrialized production with an associated high level of technological development. Increasing the supply of such profiles, combined with recent investigations in this area, leads the Brazil to enter in this world stage. However, the Brazilian standards that governing the design of these profiles are not yet updated, especially the tubular joints design. Given this perspective, this work presents an analysis of connections such as "K" and " T" with circular hollow sections. A comparison between the analytical design formulations proposed by Eurocode 3 Part 1.8, 2nd edition of the guide design of tubular joints of the CIDECT, Brazilian standard PN 02.125.03-004 and limit deformation criteria was performed. For each of the joints types analyzed, a finite element model was developed in ANSYS program, later to be calibrated and validated with experimental and numerical results present in literature. The models physical and geometrical non-linearities have been incorporated in the model to mobilize the joint full load capacity. The material nonlinearity was considered by Von Mises criteria through stress versus strain bilinear constitutive law. The geometric non-linearity was introduced in the model by Lagrange Updated Formulation considering the expected large deformation to allow redistribution of load in the joint after the initial yielding. This work also proposes the modeling of a planar truss made of circular hollow section structures to establish a comparison between a single joint and the response of joint as a part of a full scale truss structure.
44
Akman, Mehmet Nazim. "Analysis Of Thin Walled Open Section Tapered Beams Using Hybrid Stress Finite Element Method." Master's thesis, METU, 2008. http://etd.lib.metu.edu.tr/upload/2/12609246/index.pdf.
Анотація:
In this thesis, hybrid stress finite element is formulated for the analysis of the isotropic, thin walled, open section beams with variable cross sections. The beam element has two nodes each having seven degrees of freedom. Assumption of stress field is sufficient to determine the element stiffness matrix. Axial, flexural and torsional effects are taken into account in the analysis. The methodology can be applied both to the tapered and the uniform beams. Throughout this study, firstly element cross-sectional properties are computed using the flow analogy of the inter-connected elements which may have different thicknesses. Then another computer program calculates the displacements and stresses at the nodes along the beam. The results obtained are compared to the results taken from literature and commercial FEM program Nastran.
45
Gao, Sasa. "Development of a new 3D beam finite element with deformable section." Thesis, Lyon, 2017. http://www.theses.fr/2017LYSEI026/document.
Анотація:
Le nouvel élément de poutre est une évolution d'un élément de Timoshenko poutre avec un nœud supplémentaire situé à mi-longueur. Ce nœud supplémentaire permet l'introduction de trois composantes supplémentaires de contrainte afin que la loi constitutionnelle 3D complète puisse être utilisée directement. L'élément proposé a été introduit dans un code d'éléments finis dans Matlab et une série d'exemples de linéaires/petites contraintes ont été réalisées et les résultats sont systématiquement comparés avec les valeurs correspondantes des simulations ABAQUS/Standard 3D. Ensuite, la deuxième étape consiste à introduire le comportement orthotrope et à effectuer la validation de déplacements larges / petites contraintes basés sur la formulation Lagrangienne mise à jour. Une série d'analyses numériques est réalisée qui montre que l'élément 3D amélioré fournit une excellente performance numérique. En effet, l'objectif final est d'utiliser les nouveaux éléments de poutre 3D pour modéliser des fils dans une préforme composite textile. A cet effet, la troisième étape consiste à introduire un comportement de contact et à effectuer la validation pour un nouveau contact entre 3D poutres à section rectangulaire. La formulation de contact est dérivée sur la base de formulation de pénalité et de formulation Lagrangian mise à jour utilisant des fonctions de forme physique avec l'effet de cisaillement inclus. Un algorithme de recherche de contact efficace, qui est nécessaire pour déterminer un ensemble actif pour le traitement de contribution de contact, est élaboré. Et une linéarisation constante de la contribution de contact est dérivée et exprimée sous forme de matrice appropriée, qui est facile à utiliser dans l'approximation FEM. Enfin, on présente quelques exemples numériques qui ne sont que des analyses qualitatives du contact et de la vérification de l'exactitude et de l'efficacité de l'élément de 3D poutre proposéThe new beam element is an evolution of a two nodes Timoshenko beam element with an extra node located at mid-length. That extra node allows the introduction of three extra strain components so that full 3D stress/strain constitutive relations can be used directly. The second step is to introduce the orthotropic behavior and carry out validation for large displacements/small strains based on Updated Lagrangian Formulation. A series of numerical analyses are carried out which shows that the enhanced 3D element provides an excellent numerical performance. Indeed, the final goal is to use the new 3D beam elements to model yarns in a textile composite preform. For this purpose, the third step is introducing contact behavior and carrying out validation for new 3D beam to beam contact with rectangular cross section. The contact formulation is derived on the basis of Penalty Formulation and Updated Lagrangian formulation using physical shape functions with shear effect included. An effective contact search algorithm is elaborated. And a consistent linearization of contact contribution is derived and expressed in suitable matrix form, which is easy to use in FEM approximation. Finally, some numerical examples are presented which are only qualitative analysis of contact and checking the correctness and the effectiveness of the proposed 3D beam element
46
Deulin, Xavier. "Contribution à l'étude des phénomènes de transport des photons dans les milieux turbides par la méthode des éléments finis : Application à la thermocoagulation des tissus biologiques par laser." Paris, ENSAM, 2003. http://www.theses.fr/2003ENAM0010.
Анотація:
L’objet de ce travail a consisté à modéliser et à simuler les phénomènes de transport des photons dans la matière turbide à partir d’une équation de transfert radiatif déduite de l’équation de Boltzmann par intégration et pouvant être résolue commodément par la méthode des éléments finis en régime permanent et non-stationnaire. Le terme de source est explicité pour un faisceau diffusant et les conditions aux limites sur les frontières, éclairées ou non, sont obtenues par des bilans énergétiques. Les simulations effectuées ont eu pour objet d’étudier l’influence des propriétés optiques du milieu sur la répartition des flux et les puissances captées par une fibre optique, puis de traiter le cas de milieux hétérogènes, et enfin d’appréhender les phénomènes complexes de thermocoagulation des tissus biologiques par laser en résolvant les équations couplées du transfert radiatif et de la chaleurThe goal of this work was to modelise and simulate transport phenomena of photons into turbid media with the radiative transfer equation obtained from Boltzmann’s equation by integration and which can be easily solved by the Finite Element Method. The source term was explicated for a diffuse laser beam and the boundary conditions were obtained by establishing energetic balances. The goal of the numerical simulation was first to study the role played by optical coefficients on the fluence rate distribution. Second to analyse the case of heterogeneous media like multilayered media and embedded heterogeneities. And finally, to apprehend complex phenomena of tissue coagulation by laser in solving the coupled equations of heat and radiative transfer
47
Yang, Jie. "Structural behaviour of concrete-filled elliptical column to I-beam connections." Thesis, University of Bradford, 2017. http://hdl.handle.net/10454/16022.
Анотація:
Concrete-filled tubular (CFT) columns have been widely adopted in building structures owing to their superior structural performance, such as enhanced load bearing capacity, compared to hollow tubes. Circular, square and rectangular hollow sections are most commonly used in the past few decades. Elliptical hollow section (EHS) available recently is regarded as a new cross-section for the CFT columns due to its attractive appearance, optional orientation either on major axis or minor axis and improved structural efficiency. The state of the research in terms of elliptical columns, tubular joints between EHSs and connections with CFT columns, etc., are reviewed in this thesis, showing a lack of investigations on EHSs, especially on beam to elliptical column connections which are essential in framed structures. The structural behaviour of elliptical column to I-beam connections under bending is studied in this thesis to fill the research gap. Overall ten specimens with various joint assemblies were tested to failure to highlight the benefits of adopting concrete infill and stiffeners in the columns. A three-dimensional finite element model developed by using ABAQUS software is presented and verified against obtained experimental results, which shows acceptable accuracy and reliability in predicting failure modes of the connections and their moment capacities. Parametric studies were performed to access the main parameters that affecting the bending behaviour of the connections. A simple hand calculation method in terms of ultimate moment capacity is proposed according to experiments conducted for connections with concrete-filled columns.
48
Ghosh, Jayanto K. "Finite element simulation of non-Newtonian flow in the converging section of an extrusion die using a penalty function technique." Ohio : Ohio University, 1989. http://www.ohiolink.edu/etd/view.cgi?ohiou1172094913.
49
Rajagopal, Anurag. "Advancements in rotor blade cross-sectional analysis using the variational-asymptotic method." Diss., Georgia Institute of Technology, 2014. http://hdl.handle.net/1853/51877.
Анотація:
Rotor (helicopter/wind turbine) blades are typically slender structures that can be modeled as beams. Beam modeling, however, involves a substantial mathematical formulation that ultimately helps save computational costs. A beam theory for rotor blades must account for (i) initial twist and/or curvature, (ii) inclusion of composite materials, (iii) large displacements and rotations; and be capable of offering significant computational savings compared to a non-linear 3D FEA (Finite Element Analysis). The mathematical foundation of the current effort is the Variational Asymptotic Method (VAM), which is used to rigorously reduce the 3D problem into a 1D or beam problem, i.e., perform a cross-sectional analysis, without any ad hoc assumptions regarding the deformation. Since its inception, the VAM based cross-sectional analysis problem has been in a constant state of flux to expand its horizons and increase its potency; and this is precisely the target at which the objectives of this work are aimed. The problems addressed are the stress-strain-displacement recovery for spanwise non-uniform beams, analytical verification studies for the initial curvature effect, higher fidelity stress-strain-displacement recovery, oblique cross-sectional analysis, modeling of thin-walled beams considering the interaction of small parameters and the analysis of plates of variable thickness. The following are the chief conclusions that can be drawn from this work:
1. In accurately determining the stress, strain and displacement of a spanwise non-uniform beam, an analysis which accounts for the tilting of the normal and the subsequent modification of the stress-traction boundary conditions is required.
2. Asymptotic expansion of the metric tensor of the undeformed state and its powers are needed to capture the stiffnesses of curved beams in tune with elasticity theory. Further improvements in the stiffness matrix can be achieved by a partial transformation to the Generalized Timoshenko theory.
3. For the planar deformation of curved laminated strip-beams, closed-form analytical expressions can be generated for the stiffness matrix and recovery; further certain beam stiffnesses can be extracted not only by a direct 3D to 1D dimensional reduction, but a sequential dimensional reduction, the intermediate being a plate theory.
4. Evaluation of the second-order warping allows for a higher fidelity extraction of stress, strain and displacement with negligible additional computational costs.
5. The definition of a cross section has been expanded to include surfaces which need not be perpendicular to the reference line.
6. Analysis of thin-walled rotor blade segments using asymptotic methods should consider a small parameter associated with the wall thickness; further the analysis procedure can be initiated from a laminated shell theory instead of 3D.
7. Structural analysis of plates of variable thickness involves an 8×8 plate stiffness matrix and 3D recovery which explicitly depend on the parameters describing the thickness, in contrast to the simplistic and erroneous approach of replacing the thickness by its variation.
50
Correia, Sebastiao. "Diffusion multiple dans les systèmes désordonnés composés de diffuseurs de taille finie et approche du groupe de renormalisation pour la description des systèmes d'électrons en interaction." Phd thesis, Université Louis Pasteur - Strasbourg I, 2000. http://tel.archives-ouvertes.fr/tel-00001525.
Анотація:
Dans une première partie, certaines caractéristiques de la propagationd'un électron dans des systèmes désordonnés sont étudiées au moyen
d'un développement perturbatif utilisant la série de Watson.
L'utilisation de potentiels de taille finie répartis de façon
aléatoire pour modéliser le désordre nécessite l'introduction de
matrices de diffusion hors couche d'énergie, qui permettent ensuite de
calculer analytiquement chaque élément de la série de Watson. Des
corrections au libre parcours moyen élastique de Boltzmann, en
dimensions 2 et 3, sont obtenues à l'aide de la moyenne d'ensemble du
propagateur de l'électron. La taille du diffuseur y joue un rôle
important.
La resommation exacte de la série de Watson sous forme matricielle
permet une étude numérique de la section efficace totale de diffusion
du système désordonné. Celle-ci montre un comportement inattendu lors
du passage du régime balistique au régime diffusif.
La deuxième partie concerne le transport d'électrons en interaction
dans les systèmes désordonnés. Le désordre y est modélisé par un
champ d'impuretés statiques. L'utilisation d'outils de la théorie des
champs permet d'envisager une approche non perturbative de ces
systèmes désordonnés dans lesquels l'interaction entre électrons peut
être à l'origine d'une transition entre le régime métallique et le régime
isolant.
Une nouvelle approche s'inspirant du groupe de renormalisation est
ensuite appliquée au calcul d'équations de flot décrivant l'évolution
des constantes de couplage d'un système d'électrons en interaction.
L'approximation à l'ordre d'une boucle permet de vérifier que ces
équations de flot conduisent aux résultats donnés par la théorie des
perturbations (RPA).