Dissertations / Theses on the topic 'Hybrid Composite Plate'

Cette thèse porte sur le développement d'un traducteur ultrasonore multi-élément capacitif à couplage air (MEACUT) et son utilisation dans le domaine du contrôle non destructif (CND) de matériaux. Un modèle est employé pour simuler numériquement ce traducteur, et pour optimiser sa conception. Un prototype est ensuite fabriqué, puis caractérisé expérimentalement pour quantifier ses performances. Son originalité réside dans le fait qu'il possède une large bande passante en fréquence, tout en offrant la possibilité d'une focalisation variable. Ce prototype est alors employé pour la détection d'un endommagement causé par impact, dans une plaque composite. Il est clairement constaté que la résolution spatiale du procédé d'inspection employé (C-scan) est fortement améliorée grâce aux performances techniques du MEACUT. Enfin, un modèle hybride 3D est développé pour simuler, rapidement et intégralement, ce procédé de CND. Le très bon accord obtenu entre prédictions numériques et mesures expérimentales laisse présager que cet outil de simulation pourra servir à mettre au point d'autres expérimentations de CND, qui pourront à leur tour exploiter les performances du MEACUT<br>This thesis focuses on the development of a Multi-Element Air-coupled Capacitive Ultrasonic Transducer (MEACUT) and its use in the field of non-destructive testing (NDT) of materials. A numerical model is used to simulate the translator, and to optimize its design. A prototype is then built and experimentally characterized to quantify its performance. Its originality lies in the fact that it has a broad frequency bandwidth while offering the possibility of a dynamic focusing. This prototype is then used for the detection of damage caused by impact, in a composite plate. It is clearly found that the spatial resolution of the inspection process employed (C-scan) is greatly improved thanks to the technical performance MEACUT. Finally, a 3D hybrid model is developed to simulate quickly and fully, the process of NDT. The good agreement obtained between numerical predictions and experimental measurements suggests that this simulation tool can be used to develop other NDT experiments, which may in turn exploit the performance of MEACUT

Delamination is a frequent cause of failure in laminated structures, particularly under compressive loads. The presence of delaminations in composite laminates reduces their overall stiffness. In addition, delaminations tend to grow rapidly under postbuckling loads, causing further reductions in the structural strength and leading ultimately to a sudden structural failure. Recently, many studies have been carried out to investigate the effects of delaminations on the buckling and vibration behaviour of composite structures. Finite element analysis is often used to perform these due to its ability to model complex geometries, loading and boundary conditions, but this comes at a high computational cost. The exact strip method provides an efficient alternative approach using an exact dynamic stiffness matrix based on a continuous distribution of stiffness and mass over the structure, so avoiding the discretization to nodal points that is implicit in finite element analysis. However due to its prismatic requirements, the exact strip method can model damaged plates directly only if the damaged region extends along the whole length of the plate. This thesis introduces a novel combination of exact strip and finite element analysis which can be used to model more complex cases of damaged plates. Comparisons with pure finite element analysis and a previous technique based on the exact strip method demonstrate the capability and efficiency of this hybrid method for a range of isotropic and composite plates.

Das Forschungsvorhaben liefert einen Beitrag zum Schweißen von Gleich- und Mischmaterialverbindungen aus Naturfaserverstärkten Kunststoffen (NFK) sowie deren Verarbeitung im Compoundieren und Spritzguss. Es wurde holzfasergefülltes (WPC) und flachsfasergefülltes (FFC) Polypropylen (PP) mit unterschiedlichen Füllgraden verwendet. Der Einsatz synthetisch-organsicher Fasern (PET-Fasern) im Compound zielte darauf ab, besonders die Schlagzähigkeit zu verbessern. Im Bereich des Urformens wurden Aussagen zur Verarbeitbarkeit, zu rezepturabhängigen Kurz- und Langzeiteigenschaften sowie Aussagen zur Dauergebrauchsfähigkeit erarbeitet. Die Anwendbarkeit der Fügeverfahren Heizelement- (HE-Schweißen) und Vibrationsschweißen (VIB-Schweißen) konnte für Gleich- und Mischmaterialverbindungen sowohl ohne als auch mit angepasster Energieeinbringung nachgewiesen werden. In diesem Zusammenhang können Aussagen zur Rezepturabhängigkeit, Verfahrensführung, Parameterauswahl, Prüfkriterien sowie den technischen Grenzen der Schweißverbindung unter kurzzeitmechanischer Beanspruchung getroffen werden. Weiterhin wird ein Beitrag zur Dauergebrauchsfähigkeit unter UV-Globalbewitterung und thermischer Alterung sowie zu langzeitmechanischen Eigenschaften von NFK-Schweißverbindungen geliefert.

Tese de Doutoramento em Engenharia Civil<br>This research work deals with development of a novel retrofitting element for RC structures designated as “Hybrid Composite Plate (HCP)”. This prefabricated element is composed of a thin strain hardening cementitious composite (SHCC) plate reinforced with either near surface mounted CFRP (NSM-CFRP) laminates, designated as HCP(L), or externally bonded CFRP (EB-CFRP) sheets, designated as HCP(S). From the materialstructural point of view, this system benefits from the high ductility of SHCC and the high tensile strength of CFRP in retrofitting of RC structures. HCP is essentially tailored to be significantly free of the shortcomings identified in the most advanced available retrofitting techniques, such as textile reinforced mortar (TRM) and conventional FRP systems. Furthermore, it is possible to attach this proposed system to the RC members by means of either adhesive, chemical anchors or a combination thereof. The investigation carried out is mainly dedicated to the development of HCP and assessment of its structural efficiency for upgrading/repairing RC members with a variety of retrofitting demands. In this framework, series of experimental tests are executed to assess HCP retrofitting efficiency for upgrading shear, flexural and energy dissipation capacity of RC members. Results of these experimental tests confirmed HCP’s high potential for retrofitting RC structures. An analytical approach is presented to estimate the ultimate flexural capacity of the beams with an HCP attached to their soffit, which is further complemented with a numerical strategy to predict the load-deflection response of such retrofitted beams. The proposed analytical and numerical approaches accurately predict the flexural capacity and load-deflection response, of flexurally strengthened beams using HCP. Finally, adopting a combination of experimental tests and finite element modelling, recommendations for an optimized HCP(L) and its connection with concrete are provided. The local bond stress-slip models at the interface of CFRP-SHCC and interface of HCP(L)- concrete are determined. Based on results obtained, equations correlating the pull force capacity of the HCP(L) to the CFRP-SHCC bond length for CFRP laminates with two different axial stiffness are derived.<br>Esta tese apresenta a investigação realizada para o desenvolvimento de um novo elemento visando o reforço de estruturas de betão armado (BA) designado por Hybrid Composite Plate (HCP). Este elemento consiste num painel pré-fabricado composto por uma fina camada de material de matriz cimentícia apresentando comportamento de endurecimento em tração ( SHCC) reforçada laminados de matriz polimérica reforçada com fibras de carbono (CFRP) inseridos à superfície (Near Surface Mounted), designado por HCP(L), ou com manta de CFRP aplicada segundo a técnica de colagem exterior (externally bonded, EB-CFRP), designadas por HCP(S). Do ponto de vista estrutural, este sistema beneficia da alta ductilidade do SHCC e da elevada resistência à tração do CFRP no reforço de estruturas de BA. O HCP afigura-se como uma solução apropriada essencialmente por não apresentar as deficiências identificadas nas técnicas mais avançadas de reforço estrutural atualmente disponíveis, tais como TRM (Textile Reinforced Mortar) e sistemas FRP (Fiber Reinforced Polymer). O sistema proposto permite uma ligação aos elementos de BA através de resina epóxi, ancoragem química ou uma combinação entre estes. A investigação realizada foi dedicada ao desenvolvimento do HCP e avaliação da sua eficiência estrutural para melhorar ou reparar elementos de BA para uma variedade de exigências de reforço. Com este objetivo, uma série de ensaios foram realizados para avaliar a eficiência do reforço do HCP ao corte, flexão e capacidade de dissipação de energia de elementos de BA. Uma formulação analítica foi desenvolvida para estimar a resistência à flexão de vigas de BA reforçadas com HCP ligado à sua face inferior. Esta abordagem foi completada com um modelo numérico para prever a resposta carga-deformação destas vigas. A formulação analítica e o modelo numérica propostos previram com precisão, respetivamente, a capacidade de flexão e a resposta carga-deformação de vigas reforçadas com HCP. Finalmente, com base na combinação de resultados de ensaios experimentais e modelos de elementos finitos, são fornecidas recomendações para a otimização do HCP(L) e a sua ligação ao betão. Para a caracterização das interfaces CFRP-SHCC betão-HCP(L) foram determinadas leis tensão versus deslizamento. Com base nos resultados obtidos, apresentamse as equações que relacionam a capacidade de carga à tração do HCP(L) com o comprimento de ligação do CFRP-SHCC composto por camadas de CFRP dotadas de rigidez distinta.<br>Fundação para a Ciência e a Tecnologia (FCT) SFRH/BD/65663/2009.<br>Fundação para a Ciência e a Tecnologia (FCT) PTDC/ECM/114511/2009

博士<br>中原大學<br>化學研究所<br>97<br>Abstract This dissertation divided into two parts. The preparation of polyimide nanocomposite hollow fiber includes two kinds of additive, plate clay or spherical silica, is the first part. The preparation of polyvinyl alcohol and polyacrylonitrile plate nanocomposite membrane contain silver nanoparticle is the second part. Silver nitrite converts into silver nanoparticle by using in-situ photochemical reduction and direct chemical reduction. In this research, the structure and performance of a series of organic-inorganic hybrid materials will be investigated. In the first part, casting solution contains polyimide, NMP, and nanoparticle (flat clay or spherical silica) was used to prepare asymmetric polyimide nanocomposite hollow fiber membrane. The effect of additives on the morphology, membrane formation mechanisum, mechanical properties, and pervaporation performance of the asymmetric polyimide nanocomposite hollow fiber membrane was investigated. The results revealed that the addition of nano-filler in the spinning solution and increasing the filler amount can promote the formation of macrovoids in nonocomposite hollow fiber membrane. Otherwise, the exchange rate between the solvent and nonsolvent during the membrane formation process increases resulting in an asymmetric PI hollow fiber membrane with a wider wall thickness. The material composition will affect the thermal stability, mechanical strength and the separation performance of vapor permeation of aqueous ethanol solution. The elongation at break, strength at break, and work of rupture increase with nano-filler is a unique phenomenum different than general polymer. Moreover, water contact angle increasing presents self-clearing performance. The second part, a series of nano-scale silver polymer composite films were prepared from polyvinyl alcohol silver ions chelate aqueous solution. Silver ions transfer to silver by in-situ photochemical reduction using UV-irradiation. Other way, polyacrylonitrile silver ions chelate in N,N-dimethylformamide (DMF) will change into silver by direct chemical reduction. The reduction of silver ion in nano-composite films were confirmed by UV/vis optical absorption, Fourier-transformation infrared spectroscopy (FTIR), SEM-mapping, and X-ray diffraction (XRD). The surface morphology of nano-scale silver polymer composite films were investigated by atomic force microscopy (AFM), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The amount of nano-scale silver in polymer composite films will affect the thermal stability, contact angle and antibacterial activities. In this study, we found that the structural morphology of PVA-Ag+ chelate films change vastly due to the changes in loading amount. However, silver nano-particles produced by in situ reduction UV-irradiation shown particles on the surface of PVA films. The surface morphology of PVA-Ag0 and PAN-Ag0 membrane is similar. PVA-Ag+ is effective prohibite the growth of Escherichia coli and Staphylococus aureus in 0.5 wt% silver nitrite loading. PVA-Ag0 and PAN-Ag0 films are effective in prohibiting the growth of Escherichia col. Furthermore, we demonstrated that the hybrid composite films have good hydrophobic characterization owing to the presence of nano-scale silver. From DSC experimental results, the glass transition (Tg) and melting temperatures decreases with increasing AgNO3 loading owing to destroy of the crystalline.

Dissertação de Mestrado em Engenharia Mecânica apresentada à Faculdade de Ciências e Tecnologia da Universidade de Coimbra.<br>The traditional carbon fibre-reinforced composites offer excellent mechanical properties while having a low density, which makes them an ideal solution for the applications where weight is a major concern. The self-reinforced composites (SRC’s) consist of polymer fibres reinforcing a matrix made from the same material. In fact, it is by partially melting the fibres that the matrix is created. This type of composites provide a high toughness but lack the high stiffness and strength needed in structural applications. Hybrid composites are a combination of at least two types of fibres in a matrix. By hybridizing self-reinforced polypropylene (SRPP) with unidirectional (UD) carbon fibre reinforced polypropylene (CFRPP), it is expected to combine properties of both composite types. The goal is to have a stiff and strong composite while maintaining a high toughness. This thesis aims to understand how the material properties of a hybrid composite influence the flexural properties in a corrugated plate. The flexural properties of hybrid composites have been studied but always in flat surfaces. Also, the low compressive properties of polymer fibres make it difficult to capture the flexural properties. By using this type of surface, the flexural properties should not be as highly dependent on the position of the carbon fibre (CF) laminae in relation to the neutral plane as they are for flat laminates. Experimental work has been performed to understand the dependence of the flexural properties of hybrid composite materials on the carbon fibre volume fraction (Vf) and position. The experimental work was supported by a numerical modelling study. This study established preliminary knowledge needed for further developments of the model. In combination with the experimental work, the limitations of the current model are pointed out. The achievement of a more advanced model in the future, that can predict the behaviour of these hybrid composite materials when subjected to bending, is possible. The main conclusions of this work were that the stiffness of a corrugated hybrid composite plate is not influenced by the position of the UD CFRPP layers. This property only changes with the CF Vf. The maximum flexural load and displacement at this point are also influenced by the CF content and by the thickness of the UD CFRPP layers. The other work we ever did together. Without the experience of working with him, there would be a lot of things I would not have learned. To Carlos Lavoura and José Canhola, my mentors in my rowing experience. They were the ones who guided me throughout ten years of rowing, making me a better athlete and a better person. For giving me the will to never give up on my goals and dreams, thank you.<br>Os tradicionais materiais compósitos reforçados com fibras de carbono oferecem excelentes propriedades mecânicas enquanto mantêm uma baixa densidade, o que faz deles uma solução ideal para aplicações nas quais o peso é um fator a considerar. Os materiais compósitos auto-reforçados consistem em fibras poliméricas que reforçam uma matriz do mesmo material. De fato, é ao fundir parcialmente as fibras que se obtém a matriz. Este tipo de materiais compósitos proporciona uma elevada tenacidade mas não tem a alta rigidez e resistência mecânica necessária em aplicações estruturais. Os materiais compósitos híbridos resultam da combinação de dois tipos de fibras numa matriz. Ao hibridizar polipropileno auto-reforçado com polipropileno reforçado com fibras de carbono unidirecionais, é esperada a combinação das propriedades dos dois tipos de compósitos. O objetivo é que se tenha um compósito rígido e resistente enquanto se mantém uma alta tenacidade. Esta dissertação tem como objetivo a compreensão de como as propriedades materiais de um compósito híbrido influenciam as propriedades à flexão numa placa enrugada. As propriedades à flexão de compósitos híbridos já foram estudadas, mas sempre em superfícies planas. Além disso, as fracas propriedades compressivas das fibras poliméricas tornam difícil capturar as propriedades à flexão destas. Ao usar este tipo de superfície, as propriedades à flexão não deverão ser tão dependentes da posição das camadas de fibras de carbono em relação ao plano neutro como se verifica para laminados. O trabalho experimental foi realizado para entender a dependência das propriedades à flexão de um material compósito híbrido com a variação da fração volúmica e posição das fibras de carbono. O trabalho experimental foi suportado por um estudo de modelação numérica. Este estudo estabeleceu conhecimentos preliminares necessários para desenvolvimentos futuros do modelo. Em combinação com o trabalho experimental, as limitações do modelo atual são enunciadas. O desenvolvimento de um modelo mais avançado no futuro, que possa prever o comportamento destes materiais compósitos híbridos quando sujeitos a flexão, é possível. As principais conclusões deste trabalho são que a rigidez dos compósitos híbridos em placas enrugadas não é influenciada pela posição das camadas de fibras de carbono. Esta propriedade apenas varia com a fração volúmica de fibras de carbono. A carga de flexão máxima e deslocamento também são influenciados pelo conteúdo de fibras de carbono e pela espessura das camadas de fibras de carbono unidirecionais. O trabalho de modelação confirmou o comportamento da rigidez mas o modelo não é capaz de prever as outras propriedades. Ainda é possivel fazer um grande desenvolvimento do modelo.

碩士<br>國立臺北科技大學<br>機電整合研究所<br>99<br>The structural components of composite materials are often subjected to elevated temperatures during their service life. In such circumstances, high thermally induced compressive stresses will be developed in the constrained composite plates and consequently will lead to buckling; and thus significantly degrade their performance. So, thermal buckling and stability characteristics are one of the major design criteria for composite laminated plates for their optimal usage. In order to fully exploit their strength, an accurate prediction of their buckling load carrying capacity is essential. In the present work, the Hamilton’s energy principle is used to governing partial differential equations of hybrid composite plate in a general state of non-uniform initial stresses includes thermal effects are formulated from Mindlin plate theory. The Galerkin method is used to reduce the governing partial differential equations to ordinary differential equations. Thermal buckling is presented for hybrid composite plates under thermal loading and arbitrary initial stresses. Two types of thermal loadings, namely; uniform temperature rise and linear temperature rise are considered. The critical buckling temperatures, vibration frequency and buckling load are obtained from the linear eigenvalue problems. The effects of various parameters for hybrid composite plates will be studied. The analysis results show that the thickness ratio and initial stress has a great impact to the critical temperature parameter of the hybrid composite plates. The ratio of has an apparent influence on natural frequency and buckling load. And buckling load is also affected by thickness ratio.

碩士<br>淡江大學<br>機械工程研究所<br>83<br>Compared to the usual displacement-based model, these are several benefits for the hybrid stress finite element method, such as high accuracy, fast convergence, and the interface stress continuity being statis fied in the analysis of composite laminated plates. Since there is no shear locking problem in this model, the full Gaussian integration is adopted and then the spurious zero energy mode, the full Gaussian integration is adopted and the the spurious zero energy mode is avoided. Two different hybrid models are used to develop single-layer plate element and multi-lateer plate element based on the Mindlin plate theory. In the first element, the six three-dimensional midplane stress fucntions. After the in-plane stresses are assumed, the transverse stresses are derived through the satisfaction of stress equilibrium and enforcement of stress boundary conditions. On th other hand, the second element is formulated by assuming the in-plane strain fields on the beginning. The in-plane stresses are then obtained. The stress equilibrium, interface transverse stress continuity, and the traction-free boundary conditions on the surface are enforced to derive the transverse stress field. Based on the Hellinger-Reissner principle, the governing equations of the hybrid stress finite element method are obtained. In the thesis, the static, stress, and free vibration analyses are accomplished. The effects of thickness-to-length ratio, the width-to-length ration. and the stacking sequences are investigated. Compared to the previous literatures, the accuracy and applicability are validated in several benchmark problems.

博士<br>國立成功大學<br>航空太空工程研究所<br>79<br>A new element-partial hybrid stress element-is proposed for three-dimensional analysis of thick laminated composite plates. Through dividing the six stress components into a flexural part（圖表省略） and a transverse shear part（圖表省略） the variational form of this element which is modified from the Hellinger-Reissner principle is presented. While flesural stresses are calculated from a displacement field via constitutive relations, transverse shear stresses are computed from assumed stresses. For the displacement field, a twenty-node hexahedron element is employed in each layer. In selection of assumed transverse shear, only interface traction continuity and traction-free boundary conditions need be satisfied. Equations of motion are automatically imposed by the variational form. As a result, a concise and self-consistent formulation is achieved. The element stiffness matrix so derived is directly composed of the standard patterns of the conventional displacement and the hybrid stress elements. The mass matrix is simply consistent mass regardless of the assumed stress field. With the above properties, the interface traction discontinuity for transverse shear encountered by general displacement methods (including higher-order plate elements) can be overcome. Moreover, the tedious and troublesome work of searching a statically equilibrating stress field for all the six stress components in hybrid stress models can be avoided. The inconsistency of hybrid stress elements, using the statically equilibrating stress field for dynamic problems, can be removed at the same time. Consequently, this new element combines the benefits of the conventional displacement and the hybrid stress methods, while discards the main disadvantages of both methods simultaneously. With the element so developed, static and dynamic analyses are carried out in the dissertation. Through thickness variations of the reponses and fundamental frequencies of laminated plates are examined. Comparisons between the present results and available solutions demonstrate the accuracy and efficiency of this new element. Behavior of the proposed element is also investigated and compared with that of the displacementbased and the hybrid stress elements. 本文中提出一個對複合厚板做三維分析的新元素一部份混成元素。該元素所根據的變 分式導源於修正後的Hellinger-Reissner原理。其基本精神在於將六個應力分量分成 撓曲部份（圖表省略） 及橫向剪切部份（圖表省略） 前者由位移場經組成律求出，而後者則由假設應力場求得。元素中每一層的位移場是 以二十個節點的六面體元素來模擬。而在選取橫向剪應力場時，僅需滿足各層間的應 力連續條件及零外力邊界條件。運動方程式則自動於變分式中滿足。如此所得元素之 勁度矩陣為傳統位移元素和混成元素的組合式。依此法便可降低引用一般位移元素時 所產生的誤差，如：各層間橫向剪應力不連續以及上下自由表面剪應力不為零。同時 亦可避免在傳統混成元素因選用滿足靜態平衡式的應力場而產生不一致的現象。故此 元素可擷取傳統位移元素及混成元素之精華，而儘量摒棄其缺陷。 本文亦探討所提出之元素於層板的靜態及動態分析上之應用。其中包含了沿層板厚度 方向的反應及層板的基本頻率。為驗證此元素之準確性及有效性，文中亦將由本元素 所得之結果與文獻上的資料作一比較。對於該元素的基本行為也有詳盡的探討並與傳 統的位移元素和混成元素比較。

碩士<br>逢甲大學<br>纖維與複合材料學系<br>101<br>In this study, we discuss the effects of different K-numbers on the notched strengths of woven hybrid composite plates. Finite Element software-ANSYS-and a Point Stress Criterion are used for the study of fracture strength predictions for plates that are made of woven hybrid laminate composite and contain various holes of different radii. First, the Stiffness Averaging Method was used to calculate the engineering moduli of woven hybrid composite plates. The calculations were then input into ANSYS to analyze the stress distribution around each hole. Then, a Point Stress Criterion was used to calculate the characteristic length for each hole size. Based on linear theory, the characteristic length with the ratio of the hole diameter and the specimen width (D/W) by a power-law are used to predict the strength of the plates for each hole size. The predictions were compared with experimental results. The results indicate that this method works quite accurately to predict the fracture strength of a plate that is made of surface layer of woven fabrics for 3K, 6K with center hole woven hybrid laminate composite, with only a three percent margin of error. The notched strength and unnotched strength of the plate made of surface layer of woven fabric for 3K has the higher value.

碩士<br>逢甲大學<br>纖維與複合材料學系<br>99<br>The purpose of this study is to establish a method to predict the strength of woven hybrid composite plates with a center hole. First, the Stiffness Averaging Method was used to calculate the engineering moduli of woven hybrid composite plates. The calculations were then input into ANSYS to analyze the stress distribution around the hole. Then, Point Stress Criterion was used to calculate the characteristic length for each hole size. Based on linear theory, the characteristic length with the ratio of the hole diameter and the specimen width (D/W) by a power-law are used to predict the strength of the plates for each hole size. The results were compared with experimental results. The maximum error of notched strength of drilling was 3.26%; the maximum error of water jet was 5.57%. The two different methods of opening holes are under 6% error. The results show a good consistency, so using this method is effective for predicting the strength of the plates for each hole size.

Tese de Doutoramento em Engenharia Civil<br>The main purpose of this thesis is to assess the potentialities of Hybrid Composite Plates (HCPs) for the shear strengthening of reinforced concrete (RC) beams. HCP is a thin plate of Strain Hardening Cementitious Composite (SHCC) reinforced with Carbon Fiber Reinforced Polymer (CFRP) laminates applied according to the Near Surface Mounted technique (NSM). Due to the excellent bond conditions between SHCC and CFRP laminates, these reinforcements provide the necessary tensile strength capacity to the HCP, while the high post-cracking tensile deformability and resistance of SHCC avoids the occurrence of premature fracture failure of this cement composite in the stress transfer process between these two materials when the HCP is crossed by a shear crack. Different HCPs with different CFRP laminates percentage are adopted for the shear strengthening of the beams. Two different processes are investigated to apply the HCPs to the beam’s concrete substrate: by using epoxy adhesive; in addition to the epoxy adhesive it is also used mechanical anchors. From the results it was verified that when epoxy adhesive is only used, the shear strengthening contribution of the HCPs is limited by the tensile strength of the concrete substrate of the strengthened beams. Mechanical anchors were therefore used in order to prevent a premature debonding of the HCPs and apply a certain confinement to the concrete in the zone of the beam to be strengthened, resulting favorable effects in terms of shear strengthening. Experimental programs with intact and damage RC beams are carried out to assess the shear strengthening contribution of HCPs. The results obtained from these tests are also used for determining the predictive performance of the analytical model developed to evaluate the shear resistance of RC beams strengthened with HCPs. To further explore the potentialities of HCPs for the shear strengthening of RC beams, advanced numerical simulations are performed by using a FEM-based computer program, whose adequate predictive performance is demonstrated by simulating the experimental tests carried out.<br>O principal objetivo desta tese é avaliar as potencialidades de um novo tipo de painel compósito hibrido no reforço ao corte de vigas de betão armado (BA). Este fino painel, designado na língua inglesa por Hybrid Composite Plate e com a abreviatura HCP, é composto por argamassa reforçada com fibras, a qual após endurecida é reforçada por finas lâminas de polímero reforçado com fibras de carbono (CFRP) aplicadas segundo a técnica “Instalação próxima da superfície” que na bibliografia em Inglês é conhecida por NearSurfaceMounted (NSM). Estes laminados de CFRP são instalados em finos entalhes executados no painel e colados com resina epóxi. Esta argamassa apresenta comportamento de endurecimento em tração, designada na língua inglesa por StrainHardeningCementitious Composite (SHCC), pelo que após o início da fendilhação da matriz desenvolve capacidade crescente de resistência à tração até nível de extensão relativamente elevado.O elevado desempenho em tração do SHCC permite mobilizar eficazmente a elevada resistência em tração dos laminados de CFRP, pois as microfibras que reforçam o SHCC evitam a ocorrência de rotura precoce por fratura durante o processo de transferência de tensões destes para o meio circundante, situação esta que ocorre quando o HCP é atravessado por fenda de corte que se desenvolve na viga a reforçar. Diferentes configurações de HCP foram investigadas para o reforço ao corte de vigas de BA, em especial a percentagem e inclinação de laminados de CFRP e o processo de fixar os HCPs às faces laterais da viga a reforçar. No que respeita a este último aspeto, dois métodos foram estudados, um em que o HCP é aplicado recorrendo apenas a adesivo epóxi, e um outro em que para além do adesivo epóxi o painel é fixo recorrendo a ancoragens mecânicas. Os programas de ensaios experimentais evidenciaram a elevada eficácia desta técnica de reforço, principalmente quando os HCP são aplicados com adesivo e ancoragens, pois o nível de reforço garantido pelo HCP aplicado exclusivamente por adesivo está limitado pela resistência à tração do betão do substrato da viga a reforçado, dado ocorrer destacamento precoce do HCP. Este destacamento é evitado recorrendo a ancoragens mecânicas, as quais permitem ainda introduzir algum confinamento no betão da viga a reforçar dado poderem ser aplicadascom uma certa pós-tensão, resultando maior eficácia de reforço ao corte de vigas de BA conseguida com a presente técnica. Recorrendo a conceitos e formulações existentes no quadro do comportamento e reforço ao corte de vigas de BA, foram desenvolvidas duas novas formulações, cuja capacidade preditiva foi avaliada não somente com os resultados obtidos nos programas experimentais executados, mas também recorrendo a resultados experimentais existentes na bibliografia da especialidade. No intuito de melhor compreender as potencialidades da técnica de reforço desenvolvida neste trabalho, recorrendo a estudos paramétricos, foi inicialmente avaliada a capacidade preditiva de um modelo constitutivo existente no programa de elementos finitos FEMIX, fazendo a simulação dos ensaios executados experimentalmente. Constatou-se que o modelo constitutivo que modela o amolecimento em tração e em corte do processo de abertura e deslizamento de uma fenda em betão permite simular com elevado rigor quer a resposta deformacional, como o padrão de fendilhação registado nos ensaios experimentais. Utilizando este modelo, foram efetuados estudos paramétricos para evidenciar a influência de parâmetros relevantes na eficácia da técnica de reforço proposta.

碩士<br>逢甲大學<br>機械與電腦輔助工程學系<br>101<br>The aim of this thesis is to simulate, predict and analyze the notched fracture strength of hybrid composite plates with different woven Fabric on the surface layer by Point Stress Criterion and Finite Element Software ANSYS. A modified point stress criterion (PSC) was adopted to predict the strength of notched plate in this study. First, the effective elastic moduli of specimens were predicted by stiffness averaging method. Those moduli were then put into ANSYS for analyzing the stress distribution in the notched plate. The characteristic length of each plate was then figured out by modified PSC, and the power law relationship between the characteristic length and the ratio of hole diameter to specimen width was also established. The characteristic length of different hole diameter can thus be predicted. Employing the theory of superposition in linear elasticity and the predicted characteristic length, the notched strength of woven hybrid composite plates were finally predicted and compared to experimental data. The results indicate that the notched strength of woven hybrid composite plates can be accurately predicted by the methodology in this study, and the error between the predicted value and its corresponding experimental data is within 3 %.

The purpose of this research is to investigate the seismic behavior of plane moment resisting frames (MRFs) consisting of concrete filled steel tube (CFT) columns and steel I beams through targeted studies utilizing advanced computational methodologies calibrated on the basis of existing experimental results and to propose a preliminary performance-based seismic design method for this kind of frames. A computational study is conducted first to investigate the nonlinear cyclic response of square concrete-filled steel tubes (CFT) in bending and compression. An accurate nonlinear finite element model is created and its validity is established by comparing its results with those of existing experiments. Using this finite element model, extensive parametric studies are performed to provide information on the hysteretic and deteriorating behavior of CFT columns. Thus, on the basis of this computational study, three simple yet sufficiently accurate concentrated plasticity hysteretic models for simulating the cyclic behavior of square concrete-filled steel tube (CFT) columns, are developed. The seismic behavior of plane MRFs consisting of I steel beams and CFT columns is investigated next. More specifically, the effect of modelling details of each individual component of CFT-MRFs, such as the CFT columns, the beam-column connections, the panel zones and the steel I beams, on their seismic behavior is studied through comparisons against available experimental results. Then, fragility curves are constructed for composite frames for various levels of modelling sophistication through nonlinear time history analyses involving three typical CFT-MRFs which have been designed according to the European seismic design codes. On the basis of these fragility curves, one can select the appropriate modelling level of sophistication that can lead to the desired seismic behavior for a given seismic intensity. The third part of this work deals with the establishment of all the necessary ingredients for this kind of composite frames to be seismically designed by the performance-based hybrid force-displacement (HFD) seismic design method, which combines the advantages of the well-known force-based and displacement-based seismic design methods. Thus, extensive parametric studies are conducted involving nonlinear dynamic analysis of 96 frames under 100 seismic motions in order to create a databank with the response quantities of interest. Based on regression analysis, simple formulae for estimating the maximum roof displacement, the maximum inter-storey drift ratio, the maximum rotation ductility along the height of the frame and the behavior factor are developed. Comparison of the proposed design method with those adopted by current seismic design codes demonstrates that the proposed procedure seems to be more rational and controls deformation better than current seismic design codes. Nonlinear time history analyses proved the consistency of the proposed method to accurately estimate inelastic deformation demands and the tendency of the current seismic design codes to overestimate the maximum roof displacement and underestimate the maximum inter-storey drift ratio along the height of the frames. Finally, comparisons between CFT-MRFs and all steel ones reveal that the CFT-MRFs seem to have better seismic behavior than the all steel ones and seem to be more economical structures.<br>Ο σκοπός της παρούσας έρευνας είναι να διερευνήσει τη σεισμική συμπεριφορά επίπεδων καμπτικών πλαισίων με υποστυλώματα από τετραγωνικές χαλύβδινες κοιλοδοκούς γεμισμένες με σκυρόδεμα και με μεταλλικές δοκούς τύπου Ι και να προτείνει μία μέθοδο αντισεισμικού σχεδιασμού με βάση την επιτελεστικότητα για αυτόν τον τύπο κατασκευών. Αρχικά, διεξάγεται μία υπολογιστική μελέτη ώστε να διερευνηθεί η μη-γραμμική ανελαστική απόκριση υπό ανακυκλιζόμενη φόρτιση και σταθερή θλίψη των τετραγωνικών σύμμικτων υποστυλωμάτων. Ένα ακριβές και προηγμένο μοντέλο πεπερασμένων στοιχείων δημιουργείται όπου η ακρίβεια των αποτελεσμάτων του ελέγχεται μέσω συγκρίσεων των αναλυτικών λύσεων με υπαρκτά πειραματικά δεδομένα. Κατόπιν, χρησιμοποιώντας αυτό το μοντέλο πεπερασμένων στοιχείων, πραγματοποιoύνται εκτενείς παραμετρικές μελέτες με σκοπό να παραχθούν πληροφορίες σχετικά με την υστερητική συμπεριφορά των σύμμικτων υποστυλωμάτων. Έτσι, στη βάση αυτής της υπολογιστικής μελέτης, τρία απλά και αρκετά ακριβή υστερητικά μοντέλα συγκεντρωμένης πλαστιμότητας αναπτύσσονται για την προσομοίωση της συμπεριφοράς σύμμικτων υποστυλωμάτων υπό ανακυκλιζόμενη φόρτιση και σταθερή θλίψη. Έπειτα, διερευνάται η σεισμική συμπεριφορά επίπεδων καμπτικών πλαισίων με σύμμικτα υποστυλώματα και με μεταλλικές δοκούς τύπου Ι. Πιο συγκεκριμένα εξετάζεται η επίδραση της λεπτομερής μοντελοποίησης των επιμέρους δομικών στοιχείων μια κατασκευής, όπως των σύμμικτων υποστυλωμάτων, των μεταλλικών δοκών, των κόμβων διατμητικής παραμόρφωσης και των συνδέσεων, στη σεισμική συμπεριφορά των πλαισίων μέσω συγκρίσεων με υπαρκτά πειραματικά δεδομένα. Επιπλέον, διαμορφώνονται καμπύλες τρωτότητας για τρία σύμμικτα πλαίσια σχεδιασμένα με τους Ευρωπαϊκούς κανονισμούς για διάφορα επίπεδα μοντελοποίησης χρησιμοποιώντας μη-γραμμικές αναλύσεις χρονοιστορίας. Στη βάση αυτών των καμπυλών τρωτότητας, κάποιος μπορεί να επιλέξει το κατάλληλο επίπεδο πολυπλοκότητας της μοντελοποίησης των σύμμικτων πλαισίων ώστε να οδηγηθεί στην επιθυμητή συμπεριφορά για μια δεδομένη σεισμική ένταση. Το τρίτο μέρος της παρούσας έρευνας πραγματεύεται την ανάπτυξη της διαδικασίας που απαιτείται από την Υβριδική Δυνάμεων-Μετατοπίσεων (ΥΔΜ) μέθοδο αντισεισμικού σχεδιασμού με βάση την επιτελεστικότητα, η οποία συνδυάζει τα πλεονεκτήματα της μεθόδου των δυνάμεων και της μεθόδου των μετακινήσεων, ώστε να εφαρμόζεται για τον αντισεισμικό σχεδιασμό σύμμικτων καμπτικών πλαισίων. Έτσι, πραγματοποιούνται εκτενείς παραμετρικές μελέτες περιλαμβάνοντας μη-γραμμικές δυναμικές αναλύσεις σε 96 πλαίσια υπό 100 σεισμικές καταγραφές με σκοπό τη δημιουργία τράπεζας δεδομένων με αποκρίσεις ενδιαφέροντος. Κατόπιν αναλύσεων γραμμικής παλινδρόμησης, απλές σχέσεις προτείνονται που απαιτούνται από την ΥΔΜ μέθοδο οι οποίες συνδέουν τη μέγιστη μετακίνησης κορυφής των πλαισίων με τη στοχευόμενη μέγιστη γωνιακή παραμόρφωσης των ορόφων ή την τοπική στροφική πλαστιμότητα των μελών και την απαιτούμενη συνολική πλαστιμότητας του πλαισίου με τον συντελεστή συμπεριφοράς q. Η σύγκριση της προτεινόμενης ΥΔΜ μεθόδου αντισεισμικού σχεδιασμού με εκείνης που προτείνεται από τον Ευρωπαϊκό κανονισμό αποδεικνύει ότι η προτεινόμενη διαδικασία φαίνεται να είναι πιο ακριβής και ελέγχει καλύτερα τις παραμορφώσεις. Μη-γραμμικές αναλύσεις χρονοιστορίας δείχνουν την συνέπεια της ΥΔΜ να εκτιμά με ακρίβεια τις απαιτήσεις των ανελαστικών παραμορφώσεων στα διάφορα επίπεδα επιτελεστικότητας σε αντίθεση με την τάση του κανονισμού να υποεκτιμά τη μέγιστη γωνιακή μετακίνησης ορόφων και να υπερεκτιμά την μέγιστη μετακίνηση κορυφής. Τέλος, συγκρίσεις σύμμικτων πλαισίων με σχεδιασμένα πλαίσια εξ’ ολοκλήρου από χάλυβα σύμφωνα με την ΥΔΜ, δείχνουν ότι τα σύμμικτα πλαίσια έχουν καλύτερη σεισμική συμπεριφορά από τα μεταλλικά και φαίνεται να είναι πιο οικονομικές κατασκευές.