Estruturas Mistas de Aço-Concreto têm sido usadas extensivamente na construção de pontes e viadutos urbanos, especialmente a partir da segunda metade do século XX. A popularidade desse tipo de solução, com seções caixão, cresceu devido a sua alta capacidade à flexão, rigidez à torção e uma seção transversal fechada que reduz a superfície exposta a corrosão. Este trabalho discorre sobre o comportamento estrutural, procedimentos de análise e verificação em Estado Limite Último (ELU) de pontes mistas de seção caixão com aplicação de protensão externa. Em vista da escassez de literatura sobre o assunto e inexistência de norma brasileira, o trabalho objetiva produzir um roteiro de análise para a determinação da capacidade à flexão em ELU de estruturas mistas de seção caixão protendidas. Embasado na norma americana AASHTO-LRFD:2012 e na revisão bibliográfica, propôs-se um estudo de caso para verificação/dimensionamento analíticos da estrutura, tratando de Momentos Fletores Resistentes (positivos e negativos), Esforço Cortante Resistente e conectores de cisalhamento. Após esta etapa inicial, aplicou-se protensão à estrutura e, por meio de métodos analíticos, e auxílio do método dos trabalhos virtuais, obtiveram-se as perdas de protensão e a relação entre a deformação adicional do cabo de protensão em função do momento externo aplicado à estrutura. Deste modo pôde-se fazer o equilíbrio de forças horizontais, através do método da Bissecção, e obter-se o valor de incremento de Momentos Fletores Positivos e Negativos Resistentes da estrutura. Observou-se, com a protensão, um aumento de resistência importante na região de Momentos Fletores Negativos em ELU (~40%); para a região de flexão positiva esse incremento foi pouco superior a 7%, em relação à estrutura nãoprotendida. Por fim, modelou-se a estrutura em elementos finitos de casca com o software SAP2000, a fim de confrontar a análise inicial, feita em modelo de barras de pórtico espacial, preconizada pela norma AASHTO-LRFD:2012. Os resultados mostram que o modelo em barras de pórtico espacial, em termos de deslocamentos e tensões, é adequado à análise deste tipo de estrutura. / Steel-Concrete Composite Strutures have been used extensively in the construction of bridges and urban viaducts, especially from the second half of the twentieth century. The popularity of this type of solution, with box sections, has increased due to its high flexural capacity and torsion stiffness combined with a closed cross section that reduces the exposed surface to corrosion. This paper discusses the structural behavior, analysis and verification procedures in the Ultimate Limite State (ULS) of Composite Box Girder Bridges with application of external prestressing. In view of the paucity of literature on the subject and the absence of Brazilian standard, this work aims to produce a analysis script to determine the flexural capacity of prestressed composite box girder structures in ULS. Grounded in the American Standard AASHTO-LRFD:2012 and the literature review, we propose a case study for analytical verification/dimensioning of the structure, concerning positive and negative bending moments, shear and shear connectors. After this initial stage, prestressing was applied to the structure, and with de aid of analytical methods, and the virtual work method, the prestress losses and the relation between the additional strain of the tendons and the external applied moment were obtained. Thus, it was possible to make the horizontal forces balance through the Bisection Method and obtain the increment of positive and negative flexion strength. It was observed, with prestressing, an important increase of capacity in the negative bending region for ULS (~40%); for the positive bending region, the increase was somewhat higher than 7%, compared with the non-prestressed structure. Finally, a finite element model with shell elements was held with aid of the software SAP2000 to confront the initial analysis, made in space frame bars model, recommended by AASHTO-LRFD:2012 standard. The results show that the space frame bars model, in terms of displacements and stresses, is appropriate to analyze this type of structure.

O presente trabalho teve como objetivo principal estudar, em caráter essencialmente numérico via ANSYS v9.0, a elevação de temperatura em seções transversais de elementos estruturais de aço e mistos de aço e concreto, com vistas a uma avaliação das equações propostas pelo método simplificado de cálculo da NBR 14323:1999, em especial, para situações em que não ocorra aquecimento uniforme por todos os lados do elemento. São apresentados modelos numéricos de seções transversais de elementos estruturais de aço, mistos de aço e concreto e, em caráter complementar, de madeira, em situação de incêndio, para avaliar a evolução dos níveis de temperatura ao longo do tempo. São também construídos e analisados modelos numéricos com vistas à análise do efeito da elevação de temperatura no comportamento mecânico em vigas de aço de um edifício de interesse. A determinação dos níveis de temperatura em seções transversais de elementos estruturais, obtidas com base nas prescrições normativas da NBR 14323:1999, conduzem a resultados satisfatórios, porém, com temperaturas próximas as temperaturas máximas obtidas numericamente. Para os casos usuais não contemplados pela NBR 14323:1999 fica evidente a necessidade do emprego de modelo avançado de cálculo ou de estudos com vistas ao desenvolvimento de ferramentas analíticas para emprego em tais situações. Com relação à análise do efeito da elevação de temperatura no comportamento mecânico, os fatores de redução de resistência para as vigas em situação de incêndio obtidos via ANSYS resultaram inferiores àqueles obtidos via TCD v5.0, com base na análise da seção transversal e procedimentos normativos. / This research presents a study, within the context of numerical analysis with ANSYS v9.0, in which the main goal has been driven to obtain the rise of temperature in steel and composite steel-concrete structural elements cross sections with the purpose of evaluating the temperature determination by normative equations proposed in brazilian standard NBR 14323:1999, considering the simple calculation model, specially in situations with not uniform exposition of the elements cross sections to the fire. Numerical models of steel, composite steel-concrete and wooden structural elements cross sections in fire situation are presented to evaluate the levels of temperature throughout the time. Numerical models to analyze the effect of the rise of temperature in the mechanical behavior of steel beams of a building of interest are also presented. The temperature levels obtained for structural elements by prescriptions of NBR 14323:1999 lead to satisfactory results but with temperatures near to the maximum temperatures obtained numerically. For the usual cases not contemplated by the NBR 14323:1999, is evident the necessity of employing advanced calculation models or studies for the development of analytical methods for such situations. With respect to the analysis of temperature rising effects in the mechanical behavior, the reduction factors for the resistance in fire situation, obtained by ANSYS, resulted smaller than those ones obtained by TCD v5.0, with base on the analysis of elements cross sections and normative procedures.

Este trabalho apresenta uma abordagem abrangente das estruturas mistas aço-concreto, com ênfase em edifícios, e dos principais elementos que compõem esse sistema: as vigas mistas, simplesmente apoiadas e contínuas, as lajes mistas e os pilares mistos. São abordados os aspectos construtivos, o comportamento estrutural e os procedimentos para dimensionamento recomendados pelas principais normas aplicáveis, enfatizando a norma norte-americana do AISC e o EUROCODE 4. O projeto em situação de incêndio também é analisado, considerando o comportamento e o dimensionamento de elementos mistos frente à ação do fogo. No final, são desenvolvidos exemplos de dimensionamento, onde procura-se comparar e discutir os resultados obtidos pelas principais normas / This study consists of a broad analysis of composite structures, with particular emphasis on buildings, and the principal elements that make up this system, i.e., continuous and simply supported composite beams, composite slabs and composite columns. Several aspects of construction are broached, as well as structural behavior and the procedures for design recommended by the main codes, mainly the American AISC and the EUROCODE 4 codes. Fire design is also analyzed, considering the behavior and design of composite elements under fire conditions. The study concludes with some examples of design, comparing and discussing the results achieved by the principal codes

A utilização do elemento estrutural viga mista aço-concreto, que consiste da associação de vigas de aço (perfil do tipo I) com lajes de concreto (maciça ou com forma de aço incorporada), têm sido considerável nas obras de engenharia civil, tanto no contexto mundial como no Brasil. Parte da eficiência desse elemento estrutural está diretamente relacionada ao trabalho em conjunto de ambos os materiais, ou seja, do tipo de interação entre aço e concreto. Para um comportamento estrutural adequado das vigas mistas, essa interação é garantida por meio de elementos metálicos denominados conectores de cisalhamento, cujas principais funções consistem em transferir forças de cisalhamento longitudinais do concreto para o aço na interface entre laje e viga, bem como impedir a separação vertical entre laje de concreto e perfil metálico, movimento conhecido como uplift. Nesse sentido, o presente trabalho tem como objetivo principal uma pesquisa com base em referências bibliográficas sobre o assunto vigas mistas, bem como é proposta a elaboração de um modelo numérico tridimensional para viga mista, objetivando simular satisfatoriamente seu comportamento estrutural, em temperatura ambiente e em situação de incêndio, cujos resultados serão comparados com valores, obtidos numérica e experimentalmente, extraídos de trabalhos apresentados por outros pesquisadores. Para a modelagem numérica, utilizou-se o código de cálculo ABAQUS 6.3-1, elaborado com base nos métodos dos elementos finitos (MEF) / Composite steel-concrete beam have been commonly considered in steel-framed building used in civil engineering, not only in Brazil but also in the worldwide context. The efficiency of this structural element is directly related with the type of interaction between steel beam and concrete slab, which is assured using metallic elements called shear connectors, with the objective to transfer longitudinal shear forces from concrete slab to steel beam, in the interface, and avoid the vertical separation between concrete slab and steel beam (uplift). In this sense, the aim of the present work is to carry out a bibliographical review about composite steel-concrete beam, as well as propose a three dimensional non-linear procedure for modeling only full shear connection in composite beam. The three-dimensional numerical models constructed must be capable of predicting de response of composite beam, in ambient temperature an also in elevated temperatures (fire conditions). The computer program ABAQUS 6.3-1, based on finite element method, was used to analyze the numerical modeling. The accuracy of the three-dimensional numerical models are demonstrated by analyses of the results obtained with the models which are compared with the experimental results, obtained and presented by others researches

No Brasil, a pequena gama disponível de perfis laminados e o custo relativamente elevado dos perfis soldados, têm impulsionado o emprego dos perfis formados a frio nos edifícios de pequeno porte, em associação com as tradicionais lajes de vigotas pré-moldadas, constituindo um sistema misto cujo comportamento estrutural ainda é pouco conhecido. Embora haja similaridades com as clássicas vigas mistas em perfis laminados e soldados e laje maciça, é fundamental investigar o comportamento estrutural das vigas mistas em perfis formados a frio, uma vez que (i) os conectores de cisalhamento devem apresentar compatibilidade estrutural e construtiva com as vigas as quais serão concectados, (ii) pela reduzida capacidade de rotação das vigas de aço, comprometendo os modelos de cálculo que admitem, por hipótese, a plastificação total da seção mista para a determinação do momento fletor resistente e (iii) pela dificuldade de posicionamento da armadura transversal (armadura de costura). Neste trabalho foi desenvolvido um estudo teórico e experimental sobre conectores em perfil U formado a frio e vigas mistas constituídas por perfis formados a frio e laje de vigotas pré-moldadas. O estudo dos conectores, por meio de ensaios de cisalhamento direto, permitiu a avaliação da influência da altura e espessura na resistência e rigidez, e ainda permitiu ajustar a expressão da norma americana AISC:2005, estabelecida para cálculo da resistência de conectores em perfil U laminado, aos perfis formados a frio. Da análise das vigas mistas simplesmente apoiadas, por meio de simulações numéricas e ensaios experimentais, verificou-se a influencia da: armadura de costura, do posicionamento dos conectores em relação às vigotas treliçadas e do deslizamento na interface e suas implicações principalmente na determinação do deslocamento vertical. Os resultados indicaram que se deve adotar um momento fletor resistente inferior ao momento de plastificação total da seção mista, e que a posição e taxa de armadura transversal interferem no panorama de fissuração da laje, mas têm pequena influência na resistência da viga mista. / In Brazil, the lack of hot-rolled members and high cost of welded steel beams have increased the use of composite beams made of cold-formed steel beams and floor system with lattice girder beams, whose structural behavior is not perfectly understood. Although this system is similar to the one composed of hot-rolled steel beams and concrete slabs, it is important to study its structural behavior due to some reasons: (i) the shear connectors must have structural and constructive compatibility with the beams they are connected, (ii) the small rotations of the steel beams jeopardize the concept of total yielding of composite section, which is currently used to evaluate the resistant moment, (iii) the complexity in placing the conventional shear reinforcement. This work presents an experimental and theoretical analysis on channel cold-formed connectors and composite beams made of cold-formed steel beams and concrete slabs with lattice girder beams. The push out tests of shear connectors evaluated the influence of their height and thickness on strength and stiffness of the system, and made possible to adjust the empiric expression of AISC:2005, originally developed for hot-rolled channel connectors, to fit the behavior of cold-formed connectors. Additionally, the influence of transverse reinforcement, relative position of connectors to lattice girder beams and interface slippage on vertical displacements were evaluated through numerical and experimental analysis. The results showed that the resistant moment is smaller than the calculated considering total yielding of the cross section. Besides this, the position and amount of transverse reinforcement amount have strong influence on crack configuration but not on the strength of the system.

Estruturas Mistas de Aço-Concreto têm sido usadas extensivamente na construção de pontes e viadutos urbanos, especialmente a partir da segunda metade do século XX. A popularidade desse tipo de solução, com seções caixão, cresceu devido a sua alta capacidade à flexão, rigidez à torção e uma seção transversal fechada que reduz a superfície exposta a corrosão. Este trabalho discorre sobre o comportamento estrutural, procedimentos de análise e verificação em Estado Limite Último (ELU) de pontes mistas de seção caixão com aplicação de protensão externa. Em vista da escassez de literatura sobre o assunto e inexistência de norma brasileira, o trabalho objetiva produzir um roteiro de análise para a determinação da capacidade à flexão em ELU de estruturas mistas de seção caixão protendidas. Embasado na norma americana AASHTO-LRFD:2012 e na revisão bibliográfica, propôs-se um estudo de caso para verificação/dimensionamento analíticos da estrutura, tratando de Momentos Fletores Resistentes (positivos e negativos), Esforço Cortante Resistente e conectores de cisalhamento. Após esta etapa inicial, aplicou-se protensão à estrutura e, por meio de métodos analíticos, e auxílio do método dos trabalhos virtuais, obtiveram-se as perdas de protensão e a relação entre a deformação adicional do cabo de protensão em função do momento externo aplicado à estrutura. Deste modo pôde-se fazer o equilíbrio de forças horizontais, através do método da Bissecção, e obter-se o valor de incremento de Momentos Fletores Positivos e Negativos Resistentes da estrutura. Observou-se, com a protensão, um aumento de resistência importante na região de Momentos Fletores Negativos em ELU (~40%); para a região de flexão positiva esse incremento foi pouco superior a 7%, em relação à estrutura nãoprotendida. Por fim, modelou-se a estrutura em elementos finitos de casca com o software SAP2000, a fim de confrontar a análise inicial, feita em modelo de barras de pórtico espacial, preconizada pela norma AASHTO-LRFD:2012. Os resultados mostram que o modelo em barras de pórtico espacial, em termos de deslocamentos e tensões, é adequado à análise deste tipo de estrutura. / Steel-Concrete Composite Strutures have been used extensively in the construction of bridges and urban viaducts, especially from the second half of the twentieth century. The popularity of this type of solution, with box sections, has increased due to its high flexural capacity and torsion stiffness combined with a closed cross section that reduces the exposed surface to corrosion. This paper discusses the structural behavior, analysis and verification procedures in the Ultimate Limite State (ULS) of Composite Box Girder Bridges with application of external prestressing. In view of the paucity of literature on the subject and the absence of Brazilian standard, this work aims to produce a analysis script to determine the flexural capacity of prestressed composite box girder structures in ULS. Grounded in the American Standard AASHTO-LRFD:2012 and the literature review, we propose a case study for analytical verification/dimensioning of the structure, concerning positive and negative bending moments, shear and shear connectors. After this initial stage, prestressing was applied to the structure, and with de aid of analytical methods, and the virtual work method, the prestress losses and the relation between the additional strain of the tendons and the external applied moment were obtained. Thus, it was possible to make the horizontal forces balance through the Bisection Method and obtain the increment of positive and negative flexion strength. It was observed, with prestressing, an important increase of capacity in the negative bending region for ULS (~40%); for the positive bending region, the increase was somewhat higher than 7%, compared with the non-prestressed structure. Finally, a finite element model with shell elements was held with aid of the software SAP2000 to confront the initial analysis, made in space frame bars model, recommended by AASHTO-LRFD:2012 standard. The results show that the space frame bars model, in terms of displacements and stresses, is appropriate to analyze this type of structure.

La fabrication des structures composites conduit à une variabilité élevée de ses paramètres mécaniques. La thèse a comme objectif global de développer des méthodes économiques et robustes pour étudier la variabilité de la réponse statique ou dynamique des structures composites modélisées par éléments finis, prenant en compte les propriétés matériaux (modules d'élasticité, coefficients de Poisson, masses volumiques...) et physiques (épaisseurs et orientations des fibres) incertaines. Deux méthodes stochastiques : Certain Generalized Stresses Method (CGSM) et Modal Stability Procedure (MSP), sont développées. La méthode CGSM considère une hypothèse mécanique, les efforts généralisés sont supposés indépendants des paramètres incertains. Elle permet d'évaluer la variabilité de la réponse statique. La méthode MSP, proposée pour étudier la variabilité d'une structure en dynamique, est basée sur l'hypothèse considérant que les modes propres sont peu sensibles aux paramètres incertains. Les hypothèses mécaniques et une unique analyse par éléments finis permettent de construire un méta-modèle exploité dans une simulation de Monte Carlo. Le coût de calcul de ces méthodes stochastiques est donc réduit considérablement. De plus, elles présentent les avantages de ne pas limiter le nombre de paramètres incertains ou le niveau de variabilité d'entrée, et d'être compatibles avec tout code éléments finis standard. Quatre exemples académiques de plaque et coque composite sont traités avec la méthode CGSM, deux exemples académiques de plaque composite carrée et un exemple de plaque raidie sont traités avec la méthode MSP. La variabilité de la réponse statique (déplacement et critère de rupture) et dynamique (fréquence propre), soit la moyenne, l'écart-type, le coefficient de variation et la distribution, est évaluée. Les résultats statistiques obtenus par les méthodes proposées sont comparés avec ceux obtenus par une simulation de Monte Carlo directe, considérée comme la méthode de référence. La comparaison montre que les méthodes développées fournissent des résultats de bonne qualité et qu'elles sont très performantes en temps de calcul. Un indicateur d'erreur est également proposé, permettant de donner une estimation du niveau d'erreur des résultats obtenus par les méthodes CGSM ou MSP par rapport à la méthode de référence, sans réaliser un grand nombre d'analyses par éléments finis. / The manufacture of composite structures leads to a high variability of mechanical parameters. The objective of this work is to develop economic and robust methods to study the variability of the static or dynamic response of composite structures modeled by finite elements, taking into account uncertain material (elastic moduli, Poisson's ratios, densities... ) and physical (thicknesses and fiber orientations) properties. Two methods are developed: the Certain Generalized Stresses Method (CGSM) and the Modal Stability Procedure (MSP). The CGSM considers a mechanical assumption, the generalized stresses are assumed to be independant of uncertain parameters. lt allows to evaluate the variability of static response. The MSP, proposed to study the variability of structures in dynamics, is based on the assumption that the modes shapes are insensitive to uncertain parameters. These mechanical assumptions and only one fïnite element analysis allow to construct a metamodel used in a Monte Carlo simulation. As a result, the computational cost is reduced considerably. Moreover, they are not limited by the number of considered parameters or the level of input variability, and are compatible with standard finite element software. Four academic examples of composite plate and shell are treated with the CGSM, while two academic examples of composite square plate and an example of stiffened plate are studied by the MSP. The variability of static response (displacement and failure criterion) and dynamic response (natural frequency), namely mean value, standard deviation, coefficient of variation and distribution, is evaluated. The results obtained by the proposed methods are compared with those obtained by the direct Monte Carlo simulation, considered as the reference method. The comparison shows that the proposed methods provide quite accurate results and highlights their high computational efficiency. An error indicator is also proposed, which allows to provide an estimation of the error level of the results obtained by the CGSM or MSP compared to the reference method, without performing a large number of finite element analyses.

<p>Demand for lightweight, cost-effective, structural components is driving the development of continuous fiber thermoplastic tow preforms, also known as 3D-tow or tow reinforcements, to add material performance to hybrid-molded structures as an alternative to metal components. Tow reinforcements offer the performance advantages of continuous fiber composites within molded structures. The tow reinforcements also feature more tailorability of performance compared to fabric or organo-sheet reinforced hybrid-molded structures, improving their potential for design optimization. However, the added complexity of 3D-tow reinforcement structure requires the development of unique design principles and computer aided engineering (CAE) methodologies to effectively design components which meet manufacturing and performance requirements. </p> <p><br></p> <p>A systematic evaluation of design considerations was performed comparing parts manufactured with various design features, configurations, and materials. Choosing the structural profile and balance of material properties was shown to be an important component of achieving the desired performance especially where the tow reinforcement must work in conjunction with the overmolding material to provide structural performance. </p> <p><br></p> <p>By experimentally testing representative structures with features found on automobile components and molded sports equipment, performance was evaluated for a range of material combinations and reinforcement content. Tow reinforcements were made from continuous glass or carbon fiber reinforced PA6 prepreg tape and injection overmolded with unfilled or glass fiber filled PA6 adding a shear web and rib structures. Tow reinforcement significantly reduced warpage, and in tensile loading, demonstrated potential for 340\% strength increase over parts without tow. However, three-point bend performance was dominated by the overmolding material. High strain to break overmolding materials are recommended to avoid premature overmolding material cracking. </p> <p><br></p> <p>Tensile performance of tow reinforced structures is not accurately captured by conventional modeling processes. When wrapped around load introduction points, the fibers of a thick tow traverse a shorter distance at the inner radius than the outer radius leading to waviness on the inner region of each wrap. The Hsaio and Daniel model was used to predict local elastic properties of the wavy fiber composite and spatially varying material properties were applied to 3D finite element models of a suspension link. Neglecting fiber waviness overpredicted experimental tensile stiffness and strength by 36\% and 33\% respectively while modeling waviness overpredicted stiffness and strength by only 9\% and 14\% respectively. Tow wrap configuration, waviness propagation, and material parameters have significant effect on tensile performance while the tow has little effect on compressive performance.</p> <p><br></p> <p>In addition to fiber waviness, tow bundles also spread to reconcile path length differences. A method for accounting for tow spread orientations was developed and combined with fiber waviness modeling techniques. The effects of simulating the resulting fiber orientations and effective elastic properties was used to model representative beams in tension and bending load cases and compared to previous experimental results. Accounting for fiber waviness in tension demonstrated greatly improved part stiffness predictions. Spread tow bundles improved predicted strength and stiffness over simulations where tow was constrained to a uniform cross section. Increased tow reinforcement increased bending stiffness, but failure behavior was significantly influenced by the overmolding material.  </p> <p><br></p> <p>The studies in this work identified key performance attributes of 3D-tow reinforced hybrid composite structures. Design principles and modeling techniques were developed in this work, providing improved performance predictions which brings the technology closer to widespread adoption. </p>

[pt] Sistemas de piso misto, quando comparados a lajes de concreto armado, são uma solução estrutural mais eficiente e econômica. O comportamento geral desses elementos mistos depende da conexão de cisalhamento entre o aço e a laje de concreto. O sistema de piso misto pré-moldado com aberturas de alma apresenta uma solução eficiente e útil que ajuda a reduzir a altura do piso. Este trabalho relata os resultados de ensaios em escala real de vigas mistas e os ensaios de cisalhamento direto da ligação aço-concreto. Além dos ensaios experimentais, uma análise nãolinear em Elementos Finitos foi conduzida com o objetivo de recalcular os resultados dos ensaios com precisão suficiente usando um conjunto de parâmetros consistente. O sistema de piso misto é composto por uma viga de aço assimétrica parcialmente embutida no concreto, e o mecanismo de transferência de cisalhamento foi estabelecido através de uma inovadora conexão de cisalhamento por aderência, atrito e efeito pino (por armaduras transversais passando através de furos na alma). Os resultados dos ensaios indicaram uma ligação rígida produzida pela aderência e atrito da mesa do perfil embutida no concreto, bem como a possibilidade da viga mista de desenvolver sua capacidade resistente ao momento fletor. O modelo analítico proposto fornece uma maneira eficiente de analisar e projetar vigas mistas com mesa de compressão embutida no concreto da laje. / [en] Composite floor systems, when compared to reinforced concrete slabs, are a more cost-effective structural solution. The overall behaviour of these composite members depends on the shear connection between steel and the concrete encasement. The pre-cast composite flooring system with hollowcore section presents an efficient and useful solution that helps to reduc the flooring height. This thesis reports the results of full-scale tests in composite beams and the associated composite connection push-out tests. In addition to the tests, a nonlinear Finite Element analysis was conducted to recalculate the experimental results with sufficient precision using a consistent set of parameters. The system was composed of a partially encased asymmetric steel beam, and the shear transfer mechanism was established through an innovative shear connection by chemical bonding, friction, and dowel action (by transversal reinforcing bars passing through the web s holes). The tests results indicated that a rigid connection was produced by the chemical bonding and friction of the embedded flange profile in the concrete slab, as well as the composite beam s ability to develop its plastic bending moment capacity. The proposed analytical model provides an efficient way for analysing and designing a composite beam with encased compression flanges.

Composite structures can lower the weight of an airliner significantly. The increased production cost, however, requires the application of cost-effective design strategies. Hence, a comparative value is required which is used for the evaluation of a design solution in terms of cost and weight. The direct operating cost (DOC) can be used as this comparative value; it captures all costs that arise when the aircraft is flown. In this work, a cost/weight optimization framework for composite structures is proposed. It takes into account manufacturing cost, non-destructive testing cost and the lifetime fuel consumption based on the weight of the aircraft, thus using a simplified version of the DOC as the objective function. First, the different phases in the design of an aircraft are explained. It is then focused on the advantages and drawbacks of composite structures, the design constraints and allowables, and non-destructive inspection. Further, the topics of multiobjective optimization and the combined optimization of cost and weight are addressed. Manufacturing cost can be estimated by means of different techniques; here, feature-based cost estimations and parametric cost estimations proved to be most suitable for the proposed framework. Finally, a short summary of the appended papers is given. The first paper contains a parametric study in which a skin/stringer panel is optimized for a series of cost/weight ratios (weight penalties) and material configurations. The weight penalty, defined as the specific lifetime fuel burn, is dependent on the fuel consumption of the aircraft, the fuel price and the viewpoint of the optimizer. It is concluded that the ideal choice of the design solution is neither low-cost nor low-weight but rather a combination thereof. The second paper proposes the inclusion of non-destructive testing cost in the design process of the component, and the adjustment of the design strength of each laminate according to the inspection parameters. Hence, the scan pitch of the ultrasonic testing is regarded as a variable, representing an index for the (guaranteed) laminate quality. It is shown that the direct operating cost can be lowered when the quality level of the laminate is assigned and adjusted in an early design stage. / QC 20101112