Cabos são componentes estruturais utilizados desde a antiguidade, principalmente em aplicações onde o carregamento axial é elevado, enquanto a flexão e torção são relativamente baixos. Exemplos de aplicação atuais incluem sustentação de pontes, ancoragem de plataformas offshore, elevadores, transporte em minas, guindastes, entre outros. O estudo de seu comportamento mecânico envolve fatores que agregam considerável complexidade na elaboração de modelos numéricos ou analíticos que representem seu comportamento. Dentre esses fatores se destacam as tensões de contato que surgem entre as pernas do cabo à medida que deslizam em relação às outras, a geometria helicoidal, a rotação das pernas em torno da alma do cabo ao ser estendido (i.e., variação do ângulo da hélice do cabo) além de, no caso de cabos compósitos, um comportamento anisotrópico. Tendo em vista a indisponibilidade de uma solução analítica completa para cabos compósitos, buscou-se através do presente trabalho calibrar um modelo numérico elaborado em software comercial de elementos finitos, contemplando fatores comumente desprezados pelos modelos analíticos simplificados. Foram executados ensaios de tração na alma de cabos de compósitos com fibras de carbono de geometria 1×10 (nove fios envolvendo a alma) para determinar o módulo de elasticidade longitudinal e utilizada a teoria da micromecânica para avaliar as demais constantes de engenharia. O cabo foi modelado em tração, onde uma extremidade foi engastada e a outra teve rotação restrita e deslocamento longitudinal livre, e também em flexão em quatro pontos, deixando uma das extremidades com rotação livre e a outra com rotação e deslocamento longitudinal livre, com os demais graus de liberdade restritos. Em seguida foi conduzida uma análise de sensibilidade das principais variáveis que governam o problema, de onde se concluiu que o passo do cabo, o diâmetro de seus fios e o módulo de elasticidade longitudinal são as mais relevantes. O desvio da deformação de ruptura em tração e do deslocamento em flexão obtidos numericamente em relação aos dados experimentais obtidos foi de 10,8 % e 14,6 %, respectivamente. Após o processo de calibração, que fez uso do método de Programação Linear Sequencial para buscar o valor das variáveis de projeto que minimizassem o erro entre os dados experimentais e numéricos, o desvio encontrado reduziu para 2,4 % e 0,1 %, respectivamente. / Wire ropes have been used since ancient times, especially in applications were the axial stress is high and flexural and torsional stresses are relatively low. Current application include bridges, offshore platforms, elevators, mine hoisting, cranes, among others. Study of their mechanical behavior encompasses many factors, bringing considerable complexity in the construction of numerical or analytical models that represent their behavior, including contact stresses between rods as they slide past one another, helical geometry, rotation of wires around the core when in extension (i.e. variation in helix angle) and also, for composite cables, the anisotropic behavior. In view of the unavailability of a comprehensive analytical solution, this work focuses on the calibration of a numerical model built on a finite element software incorporating factors commonly neglected by simplified analytical approaches. Tensile tests were performed on the core of carbon fiber composite cables, 1×10 geometry (nine rods surrounding the core), to evaluate its longitudinal elastic modulus and employed micromechanics theory to obtain the remaining engineering constants. The cable was then modeled under tensile stress, where one end was fully constrained and the other could not rotate but was free to move in the longitudinal direction. Under 4-point bending, where one end was free only to rotate, while the other was free to move in longitudinal direction and to rotate, whereas the remaining degrees of freedom were constrained. After that, sensitivity analysis of the main variables governing the problem was conducted, concluding that cable pitch, rod diameter and longitudinal elastic modulus of the rods are the most relevant parameters. Deviation between ultimate strain under tensile stress and displacement under bending numerically obtained with those from experiments were 10.8 % and 14.6 %, respectively. After the calibration process, which used Sequential Linear Programing to search for the design variables values that minimized error between numerical and experimental data, the finite element model could reproduce the tensile stress and bending behavior with deviations of 2.4 % and 0.1 %, respectively.

O objetivo do estudo foi analisar tridimensionalmente, por meio do Método de Elementos Finitos (MEF), o comportamento biomecânico de um incisivo central superior hígido sob condição de oclusão fisiológica e posteriormente comparar com diferentes simulações de situações clínicas de dentes tratados endodonticamente e restaurados com coroas totais cerâmicas, variando a quantidade de remanescente dental e o tipo de retentor intra-radicular (núcleo metálico fundido- NMF, fibras de vidro- RFV e zircônio- RZ). Foram construídos modelos tridimensionais do incisivo central superior sem e com 2 mm de remanescente dentinário na porção coronária. Uma carga de 10 N foi aplicada de forma normal no terço incisal, nas cristas marginais mesial e distal, da superfície palatal. A análise dos dados foi realizada pelo programa computacional NeiNastran® - Noran Engineering, Inc. Os resultados de deslocamento e tensão máxima principal foram obtidos mostrando que houve diferenças significativas na distribuição de tensão entre o dente hígido e o com retentor intra-radicular. O grupo com NMF apresentou o comportamento mais similar ao dente hígido (controle), seguidos do retentor de fibra de vidro com remanescente e sem remanescente dental. Os grupos que apresentaram maior diferença em relação ao controle foram os retentores de zircônia sem e com remanescente de dentina. Considerando- se a presença de remanescente dentinário na porção coronária (2mm) para os grupos restaurados com retentores pré- fabricados, os RFV apresentaram uma redução do estresse na interface dente/restauração em comparação com RZ. Pode-se concluir que a utilização de núcleos metálicos fundidos apresentou comportamento biomecânico mais similar ao dente hígido. / The purpose of this study was to evaluated by three-dimensional finite element analysis the biomechanical behavior of a healthy maxillary central incisor under physiological load comparing with different clinical conditions of endodontically treated teeth restored with all-ceramic crowns, with various remaining tooth structure and post-and-core systems (cast metal post- MP, glass fiber post- GFP and zirconium post- ZP). Three-dimensional models were performed with and without 2 mm of dental remaining in coronary portion. A load of 10 N was applied in normal way at the incisal third of the palatine surface in the mesial and distal marginalis ridges. Data analysis was performed by the computer program NeiNastran ® - Noran Engineering, Inc. The results of maximal stress and displacement demonstrated significant differences in the tensile distribution in healthy (control) and restored tooth. The MP showed similar performance in comparison with healthy tooth, followed by GFP with and without remaining tooth structure. The teeth restored with ZP showed higher difference than control group. This study demonstrated that presence of the coronary remaining dentin (2mm) decreases the stress concentration at the interface crown/restoration using GFP in comparison with ZP. Conclusion that cast metal post can reduce the stress level in maxillary central incisor and showed biomechanical behavior similar than healthy teeth.

O tratamento cirúrgico do câncer bucal pode resultar em graves seqüelas das estruturas anatômicas envolvidas na fisiologia da cavidade bucal. A extensão e a localização da ressecção cirúrgica, assim como a condição dental, são determinantes do planejamento da prótese obturadora. Este trabalho emprega a Análise de Elementos Finitos para o estudo do comportamento biomecânico de uma prótese obturadora maxilar Classe IV de Aramany, em um modelo digital desenvolvido a partir de uma TC de um indivíduo adulto. O modelo tridimensional desenvolvido no programa Rhinoceros® versão 3.0 foi utilizado para a geração da malha de elementos finitos no programa FEMAP/NASTRAN®. Uma força de 120 N foi aplicada nas plataformas oclusal e incisal, correspondentes aos dentes posteriores e anteriores da prótese obturadora, para observação das forças de tensão geradas no tecido ósseo maxilar. Os resultados são apresentados sob a forma de análise qualitativa, indicada pela escala de Tensão Máxima Principal, e análise quantitativa, representada por valores em Mega Pascal (MPa). Observou-se que o carregamento posterior provoca tensão de tração e tensão de compressão, independentemente da região óssea avaliada, induz a uma maior tensão de tração em todas as regiões ósseas observadas e a uma maior tensão de compressão na região média anterior do palato. O carregamento anterior gera tensão de tração em todas as regiões ósseas consideradas e acarreta maior tensão de tração do que tensão de compressão, independentemente da região óssea avaliada. Concluiu-se que ocorre uma tendência de rotação da prótese em direção à área de ressecção cirúrgica, tanto para o carregamento posterior como para o carregamento anterior. O nível das tensões de tração e de compressão observado neste estudo indica que o comportamento biomecânico da prótese obturadora maxilar Classe IV de Aramany encontra-se dentro dos limites fisiológicos do tecido ósseo maxilar. / The surgical treatment of oral cancer may result in severe sequel of the anatomical structures involved in oral physiology. The extension and location of surgical resection, as well as the dental condition, enjoin the prosthetic planning of the obturator prostheses. This study employs the finite elements analysis to evaluate the biomechanical behavior of Aramany Class IV obturator prostheses, in a digital model developed from a computerized tomography of an adult individual. A tridimensional model was constructed applying the software Rhinoceros® version 3.0 and then it was used to develop the finite element mesh in the software FEMAP/NASTRAN®. A 120 N load was applied to the occlusal and incisal surfaces correspondent to the prosthetic teeth. The qualitative analysis was based on Principal Maximum Tension Scale and the quantitative analysis was expressed in Mega Pascal values. Results demonstrated that the posterior load generates tensile and compression stress and a higher tension stress regardless of the osseous region, as well as a higher compression stress on the anterior medial area of residual palate. Anterior load provokes tensile stress in each of the osseous regions evaluated, in addition to a higher tensile then compression stresses, despite of the osseous region. Therefore, it was concluded that the prostheses tends to rotate towards surgical resection areas during posterior and anterior loading. The amount of tensile and compression stresses observed herein indicates that the biomechanical behavior of Aramany Class IV obturator prostheses is within the physiological limits of the maxillary osseous tissue.

An experimental program was conducted at the Ferguson Structural Engineering Laboratory of The University of Texas at Austin, under the auspices of Texas Department of Transportation (TxDOT) Research Project 5831, to investigate the tensile stresses that develop in the end regions of pretensioned concrete U-beams at transfer of prestress. Understanding the effect of these “bursting” and “spalling” stresses is essential in order to design standard details that might lead to reliably-serviceable end regions. Two full-scale beam specimens, designed to be worst-case scenarios for bursting and spalling, were fabricated. Each beam had one square and one highly skewed end. Extensive instrumentation, including strain gages on transverse and lateral reinforcing bars, was employed in the end regions of these U-beams. Experimentally determined bursting and spalling stresses in these bars were compared to results of past projects (from the literature) investigating I-beams and inverted T-beams. Preliminary recommendations are made for changes in the standard reinforcing details for U-beam end regions. Such recommended details will be tested in the upcoming phase of Research Project 5831. / text

Fabrication of SWCNT-PMMA and Activated Charcoal- PMMA composites was carried out by the compression moulding technique. Then Mechanical and Electrical properties of the composites were investigated. The morphological studies of composites showed a) good dispersion of fillers and b) good interaction between fillers and matrix. Electrical conductivity of SWCNT-PMMA composites was increased by 9 orders of magnitude (at 0.8 % volume fraction of SWCNT) and that of AC-PMMA composites increased by 16 orders of magnitude (at 17 % volume fraction of AC). The percolation threshold of both composites turned out to be lower compared to the theoretical values. A significant improvement in mechanical properties was obtained ??? particularly in AC-PMMA composites which showed a 400 % improvement in Vickers microhardness ??? raising the polymer matrix abrasion property literally to that of Aluminium alloys (Dobrazanski et al 2006). In conclusion, it is to be noted that Activated Charcoal - PMMA composites have a great potential for cost effective conducting polymer composite production by the use of cheap filler: In addition, the compression moulding technique shows good potential for cost effective fabricating technique for amorphous polymers with high electrical and mechanical properties.

Lesões cervicais não cariosas têm etiologia multifatorial, com ênfase na ação de ácidos, abrasivos e cargas mecânicas aplicadas à distância do local da lesão, mas que concentram tensão na região cervical, que é o local da lesão. O mecanismo de ação das cargas aplicadas à distância não foi ainda elucidado. Pensou-se que seria mediado por micro fraturas que fariam se desprender fragmentos de tecido (abfração); mas isto não explicaria a formação de lesões produzidas na presença de compressão, mesmo concentrada, nem a interação sinérgica na presença de ácidos. Além disso, as fraturas nunca foram localizadas no tecido. Uma outra hipótese considera os tecidos dentários como esponjas rígidas, deformáveis, capazes de expelir a sua própria água quando comprimidos ou absorver fluidos circundantes quando tracionados. Quando a carga fosse removida e o tecido recuperasse sua forma original, o fluido faria o caminho inverso. Assim, a ciclagem mecânica forçaria a circulação de fluidos circundantes no tecido e, se fossem ácidos, facilitaria a dissolução do tecido, tanto sob tração quanto sob compressão. A proposta do estudo foi avaliar a penetração de fluido traçador (nitrato de prata a 10 %) no esmalte de espécimes submetidos ou não a cargas cíclicas excêntricas que provocam compressão ou tração. Os espécimes foram construídos a partir de incisivos bovinos, cortados em paralelepípedos de 3x3x8,2 mm, com entalhe na dentina para formar um pescoço de 2x2 mm de seção transversal. Os espécimes, exceto uma faixa central do esmalte vestibular de 1,5x5 mm foram protegidos da penetração do traçador com verniz. Foram aplicados 1.200 ciclos mecânicos de carga excêntrica para produzir tensões de tração ou compressão no esmalte, com 5 s de carga de 40 N e 25 s sem carga. Um grupo controle não recebeu nem carga nem exposição ao traçador; outro controle recebeu apenas exposição ao traçador, sem carga; outros dois grupos controles receberam carga (de tração ou compressão) enquanto imersos em água e, imediatamente depois, foram expostos ao traçador durante 600 min. Os dois grupos teste foram expostos simultaneamente aos ciclos de carga (de tração ou de compressão) e ao traçador. A prata do traçador foi precipitada por exposição a fixador radiográfico e, posteriormente, à luz de fotopolimerizador (5 min). Para localizar o traçador os espécimes foram micro tomografados, radiografados e, posteriormente, foram cortados longitudinalmente para obter uma fatia central de 1 mm de espessura para avaliação em lupa, com luz refletida ou transmitida. A micro tomografia foi ineficaz devido aos artefatos formados. As radiografias marcaram apenas as regiões de maior concentração do traçador. A avaliação dos cortes em lupa binocular permitiu concluir que existem variações de padrão de coloração natural do esmalte de incisivos bovinos, que todos os espécimes expostos ao traçador, independentemente do grupo experimental, apresentaram alguma infiltração, pelo menos numa camada fina e uniforme da superfície exposta. Além da fina camada marcada, existe variação de padrões de penetração do traçador, mesmo entre os que receberam um mesmo tratamento experimental, o que pode ser devido a variações inevitáveis no histórico de cada dente. Isto, apesar de se tornar um inconveniente para identificar um possível efeito de bombeamento, poderia ser identificado também como um indicador de que podem existir diferenças na velocidade e profundidade de penetração no esmalte de outras moléculas como, por exemplo, as dos ácidos. Em resumo, o corante traçador penetrou no esmalte dos espécimes de incisivos bovinos sem diferenças claras de padrão de penetração entre os diferentes grupos e pode ser um método eficaz para comprovar a hipótese de circulação forçada, mas exigirá novos estudos. / Non-carious cervical lesions have a multifactorial aetiology, with emphasis on the action of acids, abrasives and mechanical loads applied at a distance from the site of the lesion, which concentrates tension at the lesion site. The mechanism of action of loads applied at a distance has not yet been elucidated. It was thought that it would be mediated by microfractures that would cause fragments of tissue (abfração) to be released, but this would not explain the formation of lesions produced in the presence of compression, even concentrated, nor the synergistic interaction in the presence of acids. Also, no fractures were located in the tissue. Another hypothesis considers dental tissues as rigid, deformable sponges capable of expelling their water when compressed or absorbing surrounding fluids under traction. When the load was removed, and the tissue regained its original shape, the fluid would do the reverse way. Thus, mechanical cycling would force the circulation of surrounding fluids into the tissue and, if they were acidic, would facilitate dissolution of the tissue, both under traction and under compression. The study aimed to evaluate the penetration of tracer fluid (10% silver nitrate) in the enamel of specimens subjected or not to eccentric cyclic loads that cause compression or traction. The specimens were constructed from bovine incisors, cut in parallelepipeds of 3x3x8.2 mm, with a notch in dentin to form a neck of 2x2 mm cross-section. The specimens, except a central vestibular enamel strip of 1.5x5 mm, were protected from penetration of the tracer with varnish. 1,200 eccentric load mechanical cycles were applied to produce tension or compression in the enamel, with 5 s of 40 N load and 25 s without load. A control group received neither load nor exposure to the tracer; another control received only exposure to the tracer, without load; two other control groups received loading (tensile or compression) while immersed in water and immediately exposed to the tracer for 600 min. The two test groups were exposed simultaneously to the load (traction or compression) cycles and the tracer. The silver from the tracer was precipitated by exposure to a radiographic fixer and, subsequently, by the light of a curing light source (5 min). To locate the tracer the specimens were micro-scanned, radiographed and later cut longitudinally to obtain a central slice of 1 mm thickness for evaluation in a magnifying glass, light reflected or transmitted. Microtomography was ineffective due to artefacts formed. The radiographs marked only the regions with the highest concentration of the tracer. The evaluation with stereo microscopy allowed to conclude that there are variations in the natural staining pattern of bovine incisor enamel; that all the specimens exposed to the tracer, independently of the experimental group, showed some infiltration, at least in a thin and uniform layer of the exposed surface. In addition to the thin layer marked, there is a variation of tracer penetration patterns, even among those who received the same experimental treatment, which may be due to inevitable variations in the history of each tooth. This fact, although an inconvenience to identify a possible pumping effect, could also be identified as an indicator that there may be differences in the speed and depth of enamel penetration of other molecules, such as those of acids. In summary, tracer dye penetrated the enamel of bovine incisor specimens without clear differences in penetration pattern between the different groups and may be an effective method to prove the hypothesis of forced circulation, but will require further studies.

Das Zugtragverhalten von bewehrten und unbewehrten Bauteilen wird von einer Vielzahl von Faktoren beeinflusst. Maßgeblich wird es von der Festigkeit des verwendeten Betons, dem Verbundverhalten zwischen Bewehrung und Beton sowie vom vorhandenen Spannungszustand im Bauteil bestimmt. In der Regel werden im täglichen Planungsgeschäft des Ingenieurs einaxiale Spannungszustände unter Berücksichtigung der Materialeigenschaften des Betons aus den Standardprüfungen betrachtet. Jedoch treten in einer Vielzahl von Anwendungen mehraxiale Spannungszustände auf. Beispielhaft sollen hier Bereiche von zweiachsig spannenden Deckenplatten, in Bereichen von Rahmenecken, rotationssymmetrischen Bauwerkshüllen sowie bei Brückenbauwerken mit durchlaufender Fahrbahn im Bereich der Stützen genannt werden. Normative Regelungen sehen bisher im Falle einer zweiaxialen Druckbeanspruchung lediglich die Erhöhung der Druckfestigkeit bzw. Verbundspannung vor. Regelungen zur Festigkeit des Betons unter zweiaxialer Zugbelastung existieren dagegen nicht. Daraus abgeleitet stellt sich die Frage, welchen Einfluss eine zweiaxiale Zugbeanspruchung auf das Festigkeits- und Verformungsverhalten von unbewehrten und bewehrten Bauteilen ausübt. Mit Blick auf übliche Konstruktionsbetone sollen diese Fragestellungen für einen Beton C20/25 und C40/50 geklärt werden. Im Rahmen eines Forschungsvorhabens wurden hierzu Versuche an unbewehrten Betonsscheiben und gemischt bewehrten Bauteilen durchgeführt. Das im CEB-FIP MODELL CODE 90 vorgestellte Modell zur Beschreibung des einaxialen Spannungs-Dehnungs-Verhaltens bildet das reale Verhalten von Beton unter zweiaxialer Zugbelastung nur ungenügend ab. Hierfür werden Modelle zur Beschreibung des Verformungsverhaltens von Beton unter Berücksichtigung von zweiaxialen Spannungszuständen für einen Beton C20/25 und C40/50 entwickelt. Weiterhin werden Bruchkriterien für die zwei Betonsorten vorgestellt, mit denen die Zugfestigkeit des Betons unter zweiaxialer Zugbelastung bestimmt werden kann. Während bei einem Beton C20/25 die zweiaxiale Zugfestigkeit annähernd der einaxialen Zugfestigkeit entspricht, so nimmt die Zugfestigkeit des Betons C40/50 unter zweiaxialer Zugbelastung um ca. 25% ab. Hinsichtlich der Bruchdehnungen unter zweiaxialer Zugbelastung wurde festgestellt, dass diese mit steigendem Spannungsverhältnis 1 : 2 abnehmen. Darüber hinaus bilden die Modelle zur Bestimmung des Spannungs-Dehnungs-Verhaltens des unbewehrten Betons die Versuchsergebnisse sehr gut ab. Mit Hilfe der hier vorliegenden Ergebnisse können somit das Verformungs- und Festigkeitsverhalten von Beton unter zweiaxialer Zugbelastung sehr gut abgebildet werden. In Bauteilversuchen wurde das Verformungsverhalten unter zweiaxialer Zugbelastung von gemischt bewehrten Bauteilen untersucht. Die Bestimmung der Verformungen erfolgte hierbei mittels Dehnmessstreifen auf der Betonoberfläche, dem schlaffen Bewehrungsstahl und dem im nachträglichen Verbund liegenden Spannglied. Ein indirekter Nachweis des Einflusses auf das Verbundverhalten des Spanngliedes erfolgte. Es wurde aufgezeigt, dass unter zweiaxialer Zugbelastung die Dehnungen im Spannstahl infolge der Längsrissbildung über dem Hüllrohr abnehmen. Dies lässt die Aussage zu, dass die Verbundwirkung des Spanngliedes durch eine orthogonal wirkende Zugbelastung negativ beeinflusst wird. Aufbauend auf den Versuchsergebnissen wird eine Empfehlung für den Einsatz von Dehnmessstreifen zur Bestimmung der Verformungen auf einbetonierten Betonstählen gegeben. Die Berechnung der Erstrisslasten aus den Bauteilversuchen mit den entwickelten Bruchkriterien hat eine sehr gute Übereinstimmung ergeben. / The tensile load-bearing characteristics of structural elements made of reinforced or non-reinforced concrete is influenced by a number of factors. Mainly it depends on the strength of the concrete, the interaction between the concrete and the rebar, and the state of stress in the concrete element. Traditionally the designing engineer examines uni-axial stress conditions under consideration of the material properties of the concrete based on standard tests. However, multiple-stress conditions apply for a number of application of such elements, e.g. in concrete slabs designed for bi-axial load bearing, in the joints of frames, in axial symmetrical constructions, or in the intersections of column and deck of multi-span bridges. The commonly used design standard recommends the increase of the compression strength of the concrete or the bond stress for cases of bi-axial load-bearing caused by compression. However, no recommendations are given for the design strength of a concrete under bi-axial tensile stress. Therefore it is interesting to know how a bi-axial tensile stress is influencing the load-bearing and deformation behaviour of structural elements made of reinforced or non-reinforced concrete. This has been investigated for two commonly used concretes (C20/25 and C40/50). Part of an earlier research programme was to perform trials on slabs made of reinforced and non-reinforced concrete. In result a model CEB-FIP MODELL CODE 90 was introduced to describe the deformation of the slab due to a uni-axial stress. However, the model does not satisfactory describe the real behaviour of the slab under a bi-axial tensile stress. In this dissertation a new model will be presented to describe the deformation behaviour of a Concrete C20/25 and a Concrete C40/50 under bi-axial tensile stress. Furthermore, criteria for the two concretes are introduced to describe the ultimate limit state under bi-axial tensile stress. It has been found the bi-axial tensile strength of a Concrete C20/25 is comparable to its uni-axial strength. In difference, the tensile strength of a Concrete C40/50 is decreased by 25% when subject to bi-axial stress. The ultimate limit stress due to bi-axial tensile stress decreases with increasing ratio of the stress 1 : 2. The Strains 1 and 2 are the strains as a result of the biaxial tensile forces in the main directions. The presented model to describe the strain-stress behaviour of an unreinforced concrete is found to agree well with the observations from the trials. Based on the results of this thesis it is possible to describe the strain-stress behaviour of concrete under bi-axial tensile stress. The stress-strain behaviour of structural elements has been investigated under bi-axial tensile stresses. Strains have been monitored with strain-gauges fixed to the surface of the concrete, to the rebars and to the post-tensioning tendons. Therefore, the influence to the interaction of tendon and concrete has been demonstrated indirectly. Furthermore, it has been shown the strain of the tendon decreases following the development of cracks along the grout tube due to the application of bi-axial tensile stress. It can be concluded the bound of the tendon is influenced adversely by tensile stresses applied in perpendicular direction. Recommendations are given for the application of strain-gauges to measure strains of rebars set in concrete. Based on these trials, the estimation of the critical stress to develop initial cracks has been found in good agreement to the presented criteria.

The presented dissertation is focused on research in the field of dowels and design of concrete pavements using the finite element method. The theory part describes the history and the currently used techniques in the world and in the Czech Republic. The practice part of the dissertation contains a description of design methods, diagnostics of concrete pavements by using FWD and a description of laboratory tests on beams with inserted dowels. The results of measurements and modelling are verified on real operating conditions on testing fields. Based on the dissertation results, the amendment of the Czech standard ČSN 73 6123-1 regarding the position of dowels were proposed and approved. In addition, methodological guidelines of the Ministry of Transport regarding the measurements of the dowels and tie bars position and diagnostic by FWD was approved. The conclusion of the work summarizes and emphasizes the results of the dissertation.

The primary purpose of this thesis is to find out the mechanism of cracking formation during filtration as well as improve the dewatering efficiency of Limestone and Vietnam coal. They are both fine materials, which negatively affect the filtration process. Experiments are executed by changing parameters like solid volume fraction of initial suspension, the height of filter cake and the applied pressure difference using the conventional pressure filtration. Permeability ratio is used as the relevance output parameter to quantify the degree of cracking. Otherwise, saturation and residual moisture content on filter cake are also calculated to evaluate the extent of dewatering. Almost the mechanism of cracking is assumpted and proved. Countermeasures are suggested to prevent the probability and degree of cracking on filter cake. Otherwise, steam pressure filtration is applied as a new method allow improve the dewatering efficiency and reduce the cracking.:Contents Abstract iii Acknowledgment v Contents vi List of Figure viii List of Tables xvi List of Symbols xvii Abbreviation xix 1. Background 1 1.1. The Filtration process 1 1.2. Conventional pressure filtration and steam pressure filtration 3 1.3. Filtration theory 6 1.4. Cake deliquoring - immiscible fluid displacement in porous media 16 1.5. Tensile stress between particles 20 1.6. Coal processing/ washing 24 2. Literature review 34 2.1. Cracking on filter cake and the dewatering process with and without cracking 34 2.2. Summary and focus of research 47 3. Material, methods and the result of capillary pressure curve and tensile stress versus saturation 51 3.1. Material used 51 3.1.1. Limestone 51 3.1.2. Vietnam Coal 52 3.2. Conventional filtration rig and steam pressure filtration rig 55 3.2.1. Conventional filtration rig 55 3.2.2. Steam pressure filtration rig 57 3.3. Filtration experimental 58 3.4. Relevant parameter 59 3.5. Analyze technique 65 3.6. Tensile stresses depend on saturation during deliquoring 66 4. The influence of operating parameters on cracks formation in case of limestone 69 4.1. Capillary pressure curve and tensile stress during the filtration in the case of limestone 69 4.2. Test were conducted using conventional pressure filtration 76 4.2.1. Particle size distribution effect 76 4.2.2. The solid volume fraction of suspension effect 82 4.2.3. Height of filter cake (filter cake deep/ filter cake thickness) effect 92 4.2.4. Pressure difference effect 101 4.3. The difference in the crack formation by using steam pressure filtration 111 4.4. General conclusion 116 5. The influence of operating parameters on cracks formation in the case of Vietnam coal 118 5.1. Capillary pressure curve and tensile stress during filtration in case of Vietnam coal 118 5.2. Test were conducted using conventional pressure filtration 122 5.2.1. The influence of the solid volume fraction on crack formation and saturation 122 5.2.2. The influence of the height of filter cake on crack formation and saturation 127 5.2.3. The influence of pressure difference on crack formation and saturation 134 5.3. Estimate the efficiency dewatering as well as the crack formation using steam pressure filtration 139 5.4. General conclusion 146 6. Overall conclusion and recommendation 148 6.1. Overall conclusion 148 6.2. Recommendation 150 References 152 Appendices 156 Appendix A: Data from CCWP. 156 Appendix B: Data from the crack formation with various operation parameters using conventional pressure filtration (CPF). 159 Appendix C: Data from steam pressure filtration. 167 Appendix D: Miscellaneous Information. 177

Das Zugtragverhalten von bewehrten und unbewehrten Bauteilen wird von einer Vielzahl von Faktoren beeinflusst. Maßgeblich wird es von der Festigkeit des verwendeten Betons, dem Verbundverhalten zwischen Bewehrung und Beton sowie vom vorhandenen Spannungszustand im Bauteil bestimmt. In der Regel werden im täglichen Planungsgeschäft des Ingenieurs einaxiale Spannungszustände unter Berücksichtigung der Materialeigenschaften des Betons aus den Standardprüfungen betrachtet. Jedoch treten in einer Vielzahl von Anwendungen mehraxiale Spannungszustände auf. Beispielhaft sollen hier Bereiche von zweiachsig spannenden Deckenplatten, in Bereichen von Rahmenecken, rotationssymmetrischen Bauwerkshüllen sowie bei Brückenbauwerken mit durchlaufender Fahrbahn im Bereich der Stützen genannt werden. Normative Regelungen sehen bisher im Falle einer zweiaxialen Druckbeanspruchung lediglich die Erhöhung der Druckfestigkeit bzw. Verbundspannung vor. Regelungen zur Festigkeit des Betons unter zweiaxialer Zugbelastung existieren dagegen nicht. Daraus abgeleitet stellt sich die Frage, welchen Einfluss eine zweiaxiale Zugbeanspruchung auf das Festigkeits- und Verformungsverhalten von unbewehrten und bewehrten Bauteilen ausübt. Mit Blick auf übliche Konstruktionsbetone sollen diese Fragestellungen für einen Beton C20/25 und C40/50 geklärt werden. Im Rahmen eines Forschungsvorhabens wurden hierzu Versuche an unbewehrten Betonsscheiben und gemischt bewehrten Bauteilen durchgeführt. Das im CEB-FIP MODELL CODE 90 vorgestellte Modell zur Beschreibung des einaxialen Spannungs-Dehnungs-Verhaltens bildet das reale Verhalten von Beton unter zweiaxialer Zugbelastung nur ungenügend ab. Hierfür werden Modelle zur Beschreibung des Verformungsverhaltens von Beton unter Berücksichtigung von zweiaxialen Spannungszuständen für einen Beton C20/25 und C40/50 entwickelt. Weiterhin werden Bruchkriterien für die zwei Betonsorten vorgestellt, mit denen die Zugfestigkeit des Betons unter zweiaxialer Zugbelastung bestimmt werden kann. Während bei einem Beton C20/25 die zweiaxiale Zugfestigkeit annähernd der einaxialen Zugfestigkeit entspricht, so nimmt die Zugfestigkeit des Betons C40/50 unter zweiaxialer Zugbelastung um ca. 25% ab. Hinsichtlich der Bruchdehnungen unter zweiaxialer Zugbelastung wurde festgestellt, dass diese mit steigendem Spannungsverhältnis 1 : 2 abnehmen. Darüber hinaus bilden die Modelle zur Bestimmung des Spannungs-Dehnungs-Verhaltens des unbewehrten Betons die Versuchsergebnisse sehr gut ab. Mit Hilfe der hier vorliegenden Ergebnisse können somit das Verformungs- und Festigkeitsverhalten von Beton unter zweiaxialer Zugbelastung sehr gut abgebildet werden. In Bauteilversuchen wurde das Verformungsverhalten unter zweiaxialer Zugbelastung von gemischt bewehrten Bauteilen untersucht. Die Bestimmung der Verformungen erfolgte hierbei mittels Dehnmessstreifen auf der Betonoberfläche, dem schlaffen Bewehrungsstahl und dem im nachträglichen Verbund liegenden Spannglied. Ein indirekter Nachweis des Einflusses auf das Verbundverhalten des Spanngliedes erfolgte. Es wurde aufgezeigt, dass unter zweiaxialer Zugbelastung die Dehnungen im Spannstahl infolge der Längsrissbildung über dem Hüllrohr abnehmen. Dies lässt die Aussage zu, dass die Verbundwirkung des Spanngliedes durch eine orthogonal wirkende Zugbelastung negativ beeinflusst wird. Aufbauend auf den Versuchsergebnissen wird eine Empfehlung für den Einsatz von Dehnmessstreifen zur Bestimmung der Verformungen auf einbetonierten Betonstählen gegeben. Die Berechnung der Erstrisslasten aus den Bauteilversuchen mit den entwickelten Bruchkriterien hat eine sehr gute Übereinstimmung ergeben. / The tensile load-bearing characteristics of structural elements made of reinforced or non-reinforced concrete is influenced by a number of factors. Mainly it depends on the strength of the concrete, the interaction between the concrete and the rebar, and the state of stress in the concrete element. Traditionally the designing engineer examines uni-axial stress conditions under consideration of the material properties of the concrete based on standard tests. However, multiple-stress conditions apply for a number of application of such elements, e.g. in concrete slabs designed for bi-axial load bearing, in the joints of frames, in axial symmetrical constructions, or in the intersections of column and deck of multi-span bridges. The commonly used design standard recommends the increase of the compression strength of the concrete or the bond stress for cases of bi-axial load-bearing caused by compression. However, no recommendations are given for the design strength of a concrete under bi-axial tensile stress. Therefore it is interesting to know how a bi-axial tensile stress is influencing the load-bearing and deformation behaviour of structural elements made of reinforced or non-reinforced concrete. This has been investigated for two commonly used concretes (C20/25 and C40/50). Part of an earlier research programme was to perform trials on slabs made of reinforced and non-reinforced concrete. In result a model CEB-FIP MODELL CODE 90 was introduced to describe the deformation of the slab due to a uni-axial stress. However, the model does not satisfactory describe the real behaviour of the slab under a bi-axial tensile stress. In this dissertation a new model will be presented to describe the deformation behaviour of a Concrete C20/25 and a Concrete C40/50 under bi-axial tensile stress. Furthermore, criteria for the two concretes are introduced to describe the ultimate limit state under bi-axial tensile stress. It has been found the bi-axial tensile strength of a Concrete C20/25 is comparable to its uni-axial strength. In difference, the tensile strength of a Concrete C40/50 is decreased by 25% when subject to bi-axial stress. The ultimate limit stress due to bi-axial tensile stress decreases with increasing ratio of the stress 1 : 2. The Strains 1 and 2 are the strains as a result of the biaxial tensile forces in the main directions. The presented model to describe the strain-stress behaviour of an unreinforced concrete is found to agree well with the observations from the trials. Based on the results of this thesis it is possible to describe the strain-stress behaviour of concrete under bi-axial tensile stress. The stress-strain behaviour of structural elements has been investigated under bi-axial tensile stresses. Strains have been monitored with strain-gauges fixed to the surface of the concrete, to the rebars and to the post-tensioning tendons. Therefore, the influence to the interaction of tendon and concrete has been demonstrated indirectly. Furthermore, it has been shown the strain of the tendon decreases following the development of cracks along the grout tube due to the application of bi-axial tensile stress. It can be concluded the bound of the tendon is influenced adversely by tensile stresses applied in perpendicular direction. Recommendations are given for the application of strain-gauges to measure strains of rebars set in concrete. Based on these trials, the estimation of the critical stress to develop initial cracks has been found in good agreement to the presented criteria.