The design of composite laminated panels is a combinatorial problem when the orientation of the fibers in each layer is restricted to a discrete pool of angles. Additionally, composite laminates often have many optimal and near-optimal designs, and the designer may benefit by knowing many of those designs. Genetic algorithms are well suited for laminate design because they can handle the combinatorial nature of the problem and they permit the designer to obtain many near-optimal designs. However, their computational cost is high for most structural optimization problems. This work describes several attempts to reduce the cost of optimizing composite laminates using genetic algorithms. First, the use of a genetic algorithm to maximize the buckling load of a fixed thickness composite laminate is studied. Various genetic parameters, including population size, probability of mutation, and probability of crossover are optimized by numerical experiments. A new genetic operator - stack swap - is proposed and shown to be effective in reducing the cost of the optimization. Second, the genetic algorithm is revised and improved for minimum thickness design of composite laminated plates. The influence on the genetic search of the penalty functions enforcing failure constraints is studied. Combining fixed and proportional penalty functions is found to be the most efficient strategy. Improved selection, mutation, and stack swap operators are proposed. The use of an operator called scaling mutation that projects designs towards the feasible domain is investigated. The improvements in the genetic algorithm are shown to reduce the average price of the search by more than 50%. Next, the improved genetic algorithm for minimum thickness laminate design is applied to a more complex wing box-beam optimization problem. Tuning the genetic algorithm on this problem shows that, because the maximum length of a search is limited, the optimal population size does not grow with the size of the design space. If the probability of applying stack swap is reduced with the number of independent laminates in the wing box, stack swap enhances the performance of the genetic search on the wing box -beam problem. Finally, the possibility of running many searches is investigated. It is empirically shown that several short searches can be more efficient than a long one, especially when high levels of reliability are required. An example is given where a genetic algorithm is specifically modified for better efficiency in the context of repeated short runs. A procedure is studied that enables predicting reliability at later stages of the search. / Ph. D.

Este trabalho aborda o estudo da aderência aço-concreto em pilares mistos preenchidos através de revisão bibliográfica e de investigação experimental. De modo esquemático, a aderência é dividida em três parcelas: adesão, aderência mecânica e atrito, que em conjunto compõem a aderência natural. Adicionalmente, podem ser empregados conectores de cisalhamento, que são dispositivos mecânicos fixados nas superfícies internas dos tubos, como meio de ampliar a resistência ao escorregamento. Foram realizados ensaios do tipo pushout em alguns tipos de modelos de pilar preenchido: modelos simples, com adição de conectores tipo pino com cabeça, com cantoneiras na interface aço-concreto e semelhantes aos anteriores mais elementos de ligação. Com os resultados obtidos traçaram-se comportamentos força x escorregamento do concreto, força x deformações axiais nos materiais e curvas de distribuição de força ao longo do comprimento dos modelos. Concluiu-se que conectores tipo pino com cabeça e cantoneiras são uma excelente alternativa como dispositivos auxiliares na transferência de tensões de cisalhamento na interface aço-concreto. Entretanto, é necessário garantir resistência à ligação para que esses mecanismos sejam mobilizados / This research presents a study of influence of bond on concrete-filled steel tubes by means of a bibliography review and an experimental investigation. The bond strength counts on three mechanisms: adhesion of the concrete to the steel surface, friction and wedging of the concrete core. In order to improve the shear resistance of the steel-concrete interface, shear connectors can be used. A series of push-out tests of rectangular concrete-filled steel tubes was conducted in the specimens without mechanical shear connectors, specimens with stud bolt shear connectors and specimens with angles. They were also tested the corresponding beam-column connections. The results are shown in curves force x slip of concrete, force x axial strain of materials and distribution of axial load to the steel and to the concrete. The results of the tests permitted identify the mechanisms of natural bond and indicated that the stud bolts and the angles are excellent alternatives as auxiliary mechanisms to transfer shear between the concrete and steel in the concrete filled composite column. However, it is necessary to guarantee the connection enough strength in order to permit these resistance be developed

La thèse comprend 8 chapitres, 3 annexes, 191 figures, 43 tableaux, 13 photos et 181 références bibliographiques. Le corps du texte totalise 135 pages et les annexes 120 pages. Le chapitre 1 constitue lintroduction dans laquelle le contexte et les objectifs de la recherche sont définis. Le chapitre 2 présente létat de la question concernant les colonnes faites de tubes en acier remplis de béton (CFSHS columns - concrete filled steel hollow section columns). Leur comportement à température ordinaire et sous conditions dincendie est analysé ainsi que les paramètres significatifs qui guident leur comportement. Les propriétés du béton auto-plaçant sont aussi examinées dans ce chapitre. Le chapitre 3 est consacré à la présentation du code de calcul SAFIR développé à lUniversité de Liège pour la simulation du comportement structural à température ordinaire et sous conditions dincendie. Le logiciel a été utilisé pour simuler des résultats dessais expérimentaux présentés dans la littérature, et quelques calibrations sont proposées. En utilisant le modèle décrit au chapitre 3, la charge ultime à température ordinaire des colonnes CFSHS est calculée en considérant différents paramètres. On considère essentiellement des tubes de petites dimensions avec un pourcentage élevé darmatures ou contenant un autre profilé métallique. Ce type délément nest pas couvert par les Eurocodes. Des simulations ont été réalisées en vue dexaminer si les méthodes classiques de lEurocode 4 (EN1994-1-1) sont applicables à ce type de section et de voir quelle courbe de flambement est la plus appropriée. Le chapitre 5 décrit la recherche expérimentale réalisée à lUniversité de Liège relative au comportement au feu des colonnes CFSHS. Les essais expérimentaux ont été simulés par SAFIR, tant en ce qui concerne la répartition de la température à lintérieur des éléments que le comportement structural. Un des objectifs de ces calculs était de vérifier si les propriétés thermiques et mécaniques du béton auto-plaçant sont proches de celles du béton ordinaire. En vue de fournir aux bureaux détudes des outils pratiques de dimensionnement, une formule permettant dévaluer la résistance au feu des colonnes CFSHS est proposée dans le chapitre 6. Le domaine dapplicabilité a été étendu par rapport aux études précédentes. Une formule pour colonnes courtes de section carrée a dabord été établie sur base de simulations effectuées à laide de SAFIR en considérant linfluence des paramètres principaux. On examine ensuite si cette formule est aussi applicable à dautres types de profilés. La formule a été étendue en cas des colonnes élancées et à celui des colonnes chargées excentriquement. Létude expérimentale du chapitre 5 est limitée à des sections dassez petites dimensions (< 300 mm), essentiellement pour des problèmes de capacité de mise en charge des laboratoires. En vue de recueillir des informations pratiques pour des profilés de plus grandes dimensions pour lesquels on peut atteindre des résistances au feu de 2 heures et plus, des simulations numériques additionnelles sont présentées dans le chapitre 7, avec des résultats utilisables en bureau détudes. Le chapitre 8 donne les conclusions de létude et présente des suggestions pour des recherches futures.

SectionBuilder is an innovative finite element based tool, developed for analysis and design of composite beam cross-sections. The tool can handle the cross-sections with parametric shapes and arbitrary configurations. It can also handle arbitrary lay-ups for predefined beam cross-section geometries in a consistent manner. The material properties for each layer of the cross-section can be defined on the basis of the design requirements. This tool is capable of dealing with multi-cell composite cross-sections with arbitrary lay-ups. It has also the benefit of handling the variation of thickness of skin and D-spars for beams such as rotor blades. A typical cross-section is considered as a collection of interconnected walls. Walls with arbitrary lay-ups based on predefined geometries and material properties are generated first. The complex composite beam cross-sections are developed by connecting the walls using various types of connectors. These connectors are compatible with the walls, i.e., the thickness of the layers of the walls must match with those of the connectors at the place of connection. Cross-sections are often reinforced by core material for constructing realistic rotor blade cross-sections. The tool has the ability to integrate core materials into the cross-sections. A mapped mesh is considered for meshing parametric shapes, walls and various connectors, whereas a free mesh is considered for meshing the core materials. A new algorithm based on the Delaunay refinement algorithm is developed for creating the best possible free mesh for core materials. After meshing the cross-section, the tool determines the sectional properties using finite element analysis. This tool computes sectional properties including stiffness matrix, compliance matrix, mass matrix, and principal axes. A visualization environment is integrated with the tool for visualizing the stress and strain distributions over the cross-section.

Este trabalho aborda o estudo da aderência aço-concreto em pilares mistos preenchidos através de revisão bibliográfica e de investigação experimental. De modo esquemático, a aderência é dividida em três parcelas: adesão, aderência mecânica e atrito, que em conjunto compõem a aderência natural. Adicionalmente, podem ser empregados conectores de cisalhamento, que são dispositivos mecânicos fixados nas superfícies internas dos tubos, como meio de ampliar a resistência ao escorregamento. Foram realizados ensaios do tipo pushout em alguns tipos de modelos de pilar preenchido: modelos simples, com adição de conectores tipo pino com cabeça, com cantoneiras na interface aço-concreto e semelhantes aos anteriores mais elementos de ligação. Com os resultados obtidos traçaram-se comportamentos força x escorregamento do concreto, força x deformações axiais nos materiais e curvas de distribuição de força ao longo do comprimento dos modelos. Concluiu-se que conectores tipo pino com cabeça e cantoneiras são uma excelente alternativa como dispositivos auxiliares na transferência de tensões de cisalhamento na interface aço-concreto. Entretanto, é necessário garantir resistência à ligação para que esses mecanismos sejam mobilizados / This research presents a study of influence of bond on concrete-filled steel tubes by means of a bibliography review and an experimental investigation. The bond strength counts on three mechanisms: adhesion of the concrete to the steel surface, friction and wedging of the concrete core. In order to improve the shear resistance of the steel-concrete interface, shear connectors can be used. A series of push-out tests of rectangular concrete-filled steel tubes was conducted in the specimens without mechanical shear connectors, specimens with stud bolt shear connectors and specimens with angles. They were also tested the corresponding beam-column connections. The results are shown in curves force x slip of concrete, force x axial strain of materials and distribution of axial load to the steel and to the concrete. The results of the tests permitted identify the mechanisms of natural bond and indicated that the stud bolts and the angles are excellent alternatives as auxiliary mechanisms to transfer shear between the concrete and steel in the concrete filled composite column. However, it is necessary to guarantee the connection enough strength in order to permit these resistance be developed

Cette thèse a pour objectifs de développer une modélisation aussi fine que possible des structures aciers et mixtes acier-béton sous sollicitations cycliques avec prise en compte d'une part du comportement des assemblages et d'autre part des non-linéarités géométriques et du contact à l'interface acier-béton. Notre attention porte en particulier sur l'assemblage de type poutre acier/mixte sur poteau métallique par platine d'extrémité boulonnée. L'objectif étant de proposer un modèle «élément fini» d'assemblage qui reproduit aussi fidèlement que possible le comportement cyclique de ce dernier pour ensuite l'assembler à un élément fini de poutre non-linéaire acier ou mixte avec prise en compte, pour ce dernier, du soulèvement à l'interface. Le travail se compose de 3 parties distinctes. Un premier modèle qui se base sur la méthode des composantes a été développé ayant pour objectif de suivre la déformation de chaque composante au cours des cycles et de prendre en compte les non-linéarités induites par la séparation entre la platine d'extrémité et la semelle du poteau auquel elle est boulonnée. Ce modèle type composantes, a été développé pour une rangée de boulons. Dans le cas le plus fréquent, de deux rangées de boulons, une résistance de groupe (en plus des résistances individuelles de chacune des rangées) est susceptible de se développer. Pour rendre compte de ce phénomène, nous avons implanté le modèle proposé par Cerfontaine qui repose sur la définition d'une surface de charge et une règle d'écoulement associée pour déterminer les allongements des ressorts équivalents. Seul le cas de plasticité parfaite est considéré. Il est mis en évidence que l'influence de l'effet de groupe s'avère non négligeable sur le comportement post-élastique de l'assemblage et donc de la structure. Dans une seconde phase, nous proposons un modèle de poutre métallique classique en grands déplacements (approche co-rotationnelle) avec rotules généralisées aux extrémités. Nous faisons l'hypothèse que les déformations plastiques sont concentrées aux rotules dont le comportement plastique est contrôlé par une surface de charge asymétrique (anisotrope) qui peut prendre différentes formes selon la valeur donnée à un facteur q dit « facteur de forme». Chacune de ces rotules plastiques comprend un ressort longitudinal pour l'effort normal Net un ressort spiral pour le moment fléchissant M. L'interaction (M-N) entre ces deux efforts dans le domaine plastique est régie par le critère de plasticité. Le modèle de rotule plastique généralisé proposé permet de rendre compte de l'adoucissement cyclique, de la ductilité et du « pinching effect ».Nous montrons aux travers de plusieurs exemples la pertinence mais également les limites d'une telle approche. Dans une troisième partie, nous proposons un nouvel élément fini de poutre mixte (à 6 ddl par nœud) en petits déplacements avec prise en compte de la non-linéarité matérielle de la poutre ainsi que du contact entre l'acier et le béton. Une stratégie efficace de type nœud mobile (Flying Node) est proposée pour déterminer l'étendue de la surface de contact au sein d'un élément fini et d'adapter le maillage de l'élément poutre/poteau. Pour la résolution du problème de contact, la technique du Lagrangien Augmenté a été retenue. On montre que dans certaines situations, le soulèvement modifie la redistribution des efforts. / The goal of this thesis is to develop computational tools for the nonlinear analysis of steel and composite steel-concrete structures under cyclic loading taking into account the actual behaviour of joint, material and geometry non-linearities and contact conditions at the steel-to-concrete interface. In particular, our efforts focuses on typical bolted end-plate connection between steel or composite beam and steel column. The objective is to develop a new «joint finite element" able to reproduce accurately the cyclic behavior of the beam-to-column connection. Next this model is combined with a non-linear steel/composite beam element considering slip and possible uplift at the interface. The thesis consists of three major parts. The first part deals with the behavior of a steel beam-to-column bolted end-plate connection under arbitrarily cyclic loading. The proposed model is based on an improved component method that closely follows the deformation of each component taking into account non-linearities induced by possible gap between the column flange and the end-plate. This model has been developed for a single row connection. In the case of multiple row bolted connection group effects may develop. Possible group effect between two bolt-rows has been implemented considering the model proposed by Cerfontaine based on the definition of the multi-surface yield criterion and the associated flow rule that govern deformation of equivalent springs. Only the case of perfect plasticity is considered. It is shown that the influence of the group effect is not negligible on the nonlinear response of the joint. In the second part, we have developed a flexible co-rotational two-noded beam with generalized elasto-plastic hinges at the beam ends. It is assumed that plastic deformations concentrate at these hinges. These hinges have the ability to elongate/shorten along the beam axis and to rotate. A family of asymmetric and convex yield surfaces of super-elliptic shape is considered for the plastic behavior of the hinges. By varying the roundness factor, an infinite nun1ber of yield surface are obtained. It is shown that the nonlinear response of bolted connections subjected to both bending and tension are conveniently modeled with such a yield surface. It was observed that cyclic loading produces pinching effect, cyclic softening and ductile behavior. Advantages and limitations of the approach are discussed. Finally, the third part is dedicated to the problem of contact at the interface of steel-concrete composite beams. A "new" finite element for composite steelconcrete beam is proposed. The beam element has 6 degrees of freedom per node. The concrete beam is allowed to separate from the steel beam. An efficient contact algorithm is proposed. The Flying node concept is introduced and used to determine the extent of the contact area within a single element and modify the mesh of the beam structure. The contact problem is solve using the Augmented Lagrangian Method. The influence of contact on the loading capacity of the beam and its influence on some design variables are highlighted.

This master's thesis deals with design, strength calculation and technological solution of wing-fuselage joint for composite four-seater aeroplane certificated by CS-23. Design is focused on optimal space utilization, low weight and simple manufacturing and assembly. Main output is technical documentation consisting of drawings and technological lay-ups. Conceptual design was chosen after analysis and weight estimation. With strenght calculation for composite materials it was possible to design composition of primary parts and also specify manufacture processes. Assigment was solved by unusuall conceptual design, which claims higher precision manufacturing, but it saves weight.

Im Luftfahrtbereich haben sich kohlenstofffaserverstärkte Kunststoffe (CFK) wegen ihrer hohen spezifischen Festigkeiten und Steifigkeiten längst als Konstruktionswerkstoffe etabliert. In der Großserienfertigung von Automobilkarosserien kommt diese Materialgruppe jedoch nur zögerlich zum Einsatz. Offensichtlich sprechen noch viele Argumente für den Einsatz von metallischen Werkstoffen: Denn auch Leichtmetalle und pressgehärtete Stähle ermöglichen immer höhere Leichtbaugrade, ohne dabei signifikante Kostensteigerungen zu generieren. Zudem sind Fertigungs- und Montageabläufe für Metallkarosserien etabliert und weitgehend frei von Entwicklungsrisiken. Vor diesem Hintergrund erscheint es schwer, mit neuen Leichtbaumaterialien und den zugehörigen Bauweisen einen Durchbruch erzielen zu können. Dabei zeigt das Produktsegment der Supersportwagen schon deutlich, dass zusätzliche Leichtbaupotentiale durch beanspruchungsgerecht gestaltete und optimierte CFK-Strukturen für den Automobilbau eröffnet werden. Bislang lassen sich derartig optimierte CFK-Strukturen jedoch kaum wettbewerbsfähig in Großserie realisieren. An dieser Stelle ergeben sich Chancen und zugleich neue Herausforderungen für die Produktentwickler: Zum einen sind Faserverbundbauweisen zu erarbeiten, mit denen die Leichtbaupotentiale von CFK weitgehend ausgereizt werden. Zum anderen ist die automatisierte Fertigung bei hohen Taktraten zu ermöglichen. Die Lösung beider Teilaufgaben setzt den Einsatz geeigneter materialspezifischer Konstruktionsmethoden voraus.

The concept of semi-rigid composite connection has been widely researched in the past; however, most of the researches are limited to composite joints with metal deck ¿ooring and solid concrete slabs. Composite construction incorporating precast concrete hollowcore slabs (HCU) is a recently developed composite ¿oor system for buildings. The research on the structural behaviour of the semi-rigid composite joints with HCU is new and without any previous experimental database. In this paper, eight full-scale tests of beam-to-column semi-rigid composite joints with steel beams and precast hollowcore slabs are reported. The variables are stud spacing, degree of the shear connections, area of the longitudinal reinforcement and slab thickness. The test set-up and instrumentation is described in detail. The experimental behaviour is analysed and based on the test data the structural behaviour of these semi-rigid composite joints is discussed. Based on the experimental data, a simpli¿ed method to predict rotation and moment capacity for this type of composite connection is proposed.

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Civil and Environmental Engineering, 2012. / Cataloged from PDF version of thesis. / Includes bibliographical references (p. 115-117) / Highway bridges are exposed to numerous elemental and loading issues that are extremely difficult for a designer to anticipate and account for during design. The current state of practice is to design a bridge deck for a certain life span and then turn the bridge over to maintenance personnel who attempt to prolong the life of the deck through a variety of repair and rehabilitation measures. These repair measures are rarely, if ever, considered during the design process of the bridge deck. Numerous researchers have looked at making bridges, specifically decks, more repairable. The majority of these research efforts have focused on the bridge deck system as a whole. Other researchers have looked at individual elements of the bridge deck to girder connection to see if the required strength could be achieved while making the connections easier to take apart. One of the main components in the bridge deck to girder system is the steel shear stud connection, which is used to create composite action between the deck and the girder. Numerous researchers have studied this connection from a strength perspective, and the strength equations for the shear connection have been codified. Shear connections using headless studs have been researched as well, but always as a part of a larger deck to girder connection system. The headless stud has never been researched to see how it responds to a shear loading. This study looks at headless studs with varying levels of debonding along the stud shaft to analyze the impact on the load resistance that the levels of debonding would have. Granular materials for the shear transfer of load are also looked at. The results show that, as expected, the headless, debonded shear studs can carry less load than a bonded stud, but the difference in load carrying capacity is within the suggested over-estimation range of the codes that other researchers have suggested. These results suggest that the use of headless, debonded shear studs in a deck to girder connection is a feasible way to make that connection more repairable. / Funded by the U.S. Dept. of the Army. / by Berndt F. Spittka / S.M.