Esta pesquisa propõe-se estudar a viabilidade de um ensaio de aderência aço-concreto apropriado (Appropriate Bond Test - ABT) para estimativa da resistência à compressão axial do concreto, objetivando empregá-lo como complemento ao controle de qualidade do concreto armado em campo. Originalmente os autores Lorrain e Barbosa (2008) apresentaram a utilização de um ensaio de aderência apropriado, denominado APULOT, para estimar a resistência à compressão do concreto, aumentando as possibilidades de controle tecnológico do concreto armado em canteiros de obras. Os mesmos propõem uma adaptação do método pull-out test (POT) tradicional, normalizado pela RILEM CEB/FIP RC6:1983, por ser este um ensaio de baixa complexidade e de custo reduzido. Para viabilizar o uso de um ensaio de aderência apropriado como ensaio de controle tecnológico do concreto em canteiro de obras é necessário definir um padrão para o mesmo e adaptá-lo da prática experimental do laboratório para o campo. O presente trabalho buscou avaliar os seguintes parâmetros: (1) Tipo de carregamento do ensaio (pull-out e push-in); (2) Influência do tipo de configuração geométrica das barras de aço; (3) Análises da preparação, moldagem, cura e estocagem dos corpos de prova do ABT; (4) Análises quanto à execução do ABT referentes à idade de ruptura, taxa de carregamento e tipo de ruptura; (5) Implementação do ABT em canteiro de obras, avaliando a sua potencialidade de efetuar estimativas da resistência à compressão a partir dos dados da tensão de aderência. Para tanto, foram ensaiadas 26 composições de concreto de classes distintas, com idades entre 3 e 28 dias. Foram, ainda, testadas 8 configurações distintas de barras de aço com diâmetros nominais de 8 e 12,5 mm. Os resultados obtidos mostram que, sob condições padronizadas de ensaio e adotando os coeficientes adequados, a correlação entre a tensão máxima de aderência e a resistência à compressão do concreto é satisfatória, fortalecendo o propósito de consolidar este ensaio como uma alternativa complementar para controle de qualidade do concreto armado. / This research proposes a study on the feasibility of bond test steel-concrete appropriate (Appropriate Bond Test - ABT) to estimate the compressive strength of concrete, aiming to use them as a supplement in the quality control of concrete in situ. Originally the authors Lorrain and Barbosa (2008) proposed the use of a modified bond test, called APULOT to estimate the compressive strength of the concrete, increasing the possibilities for technological control of reinforced concrete on construction sites. They propose an adaptation of the traditional method pull-out test (POT), normalized by the CEB / FIP RC6: 1983, because it is a test of low complexity and low cost. To enable the use of the test as a test technological control of concrete in construction site is necessary to define a standard for yourself and adapt it practice experimental laboratory to the field. This study evaluated the following parameters: (1) Type of load test (pull-out and push-in); (2) Influence of the type of geometric configuration of steel bar; (3) Analyses of preparation, molding, curing and storage of specimens of ABT; (4) Review of the implementation of ABT on age rupture, loading rate and type of fracture; (5) Implementation of ABT in construction site, evaluating its potential to make estimates of compressive strength from the data of bond stress. Therefore, 26 different compositions of concrete classes, aged between 3 and 28 days, were tested. Were also tested 8 different configurations of steel bars with nominal diameters of 8 and 12.5 mm. The results indicate that, under standard testing and adopting the appropriate coefficients conditions, the correlation between the maximum bond stress and the compressive strength of concrete is satisfactory, strengthening the purpose of consolidating this test as a complementary alternative to quality control reinforced concrete.

O parafuso como elemento de ancoragem de sistemas de fixação vertebral já é há muito utilizado. Porém a forma de distribuição da tensão gerada por ele na região de ancoragem não está ainda bem clara. O método de elementos finitos (MEF) é um método matemático desenvolvido no século passado e permite, quando em um estudo estático, avaliar reações internas de estruturas ao se aplicar uma força. Este estudo teve por objetivo analisar as tensões e deformações internas geradas por parafusos do sistema de fixação vertebral por meio do MEF. Os Parafusos USS1 de 5, 6 e 7 mm de diâmetro e 45 mm de comprimento (Grupo 1 G1, Grupo 2 G2 e Grupo 3 - G3) e os parafusos USS2 anterior, USS2 posterior de 6,2mm de diâmetro e USS1 de 6 mm de diâmetro e 30 mm de comprimento (Grupo 4 G4, Grupo 5 G5 e Grupo 6 - G6) foram utilizados neste estudo. Para validação dos modelos foram utilizados: ensaio mecânico de arrancamento do parafuso em corpos de prova de poliuretana com densidade de 0,16 g/cm3 e resultados de ensaios de arrancamento encontrados na literatura. Foi confeccionado um modelo tridimensional para cada conjunto parafuso e poliuretana estudado no programa SolidWorks®2006. Foram confeccionados 30 corpos de prova em poliuretana para validação de G1, G2 e G3, sendo 10 corpos de prova para cada grupo. O orifício piloto foi realizado por broca de 3,8 mm para G1 e 4,8 mm para G2 e G3. Os modelos dos grupos G4, G5 e G6 foram validados por resultados encontrados na literatura de ensaios em poliuretana de mesma densidade e orifício piloto realizados por sonda de 3,8 mm para G4 e G5 e 4,8mm para G6. A análise pelo método de elementos finitos, foi realizada no programa ANSYS®Workbench 10.0. A validação foi obtida pela comparação da rigidez relativa obtida no ensaio mecânico e o resultado da simulação pelo MEF. Foram encontradas divergências de 8,3% para G1, 3,1% para G2, 0,5% para G3, 14,4% para G4, 9,5% para G5 e 10,3% para G6, sendo todas consideradas aceitáveis. Validados os modelos, os grupos G4 e G6, utilizados na fixação anterior, foram submetidos à força de compressão, tração e dobramento lateral. Os grupos G5 e G6, empregados na fixação posterior, foram submetidos à força de compressão, tração, flexão e extensão. Na fixação anterior as menores tensões foram encontradas para G4 e as maiores para G6 para todas as forças aplicadas. Na fixação posterior as menores tensões foram encontradas para G5 e as maiores para G6 para todas as forças aplicadas. As maiores tensões foram geradas ao se realizar o dobramento lateral na fixação anterior e a extensão na fixação posterior. / Screws have been used to stabilize spine fixation systems. However, stress distribution around them is not clear yet. The finite element method (FEM) is a mathematic model developed in the last century and allows evaluating internal reactions of the structure submitted to a load in a static analysis. The present study aimed to evaluate stress and internal deformation caused by screws of the spine fixation system using FEM. USS1 screws measuring 5, 6 and 7 mm in diameter and 45 mm in length (Group 1 G1, Group 2 G2 and Group 3 G3) and the screws USS2 anterior, USS2 posterior measuring 6.2 mm in diameter and USS1 measuring 6 mm in diameter and 30 mm in length (Group 4 G4, Group 5 G5 and Group 6 G6) were used in the present study. For validation models, mechanical tests evaluating pull-out strength in polyurethane samples presenting density of 0.16 g/cm3, and results of pull-out tests related in the literature were used. Threedimensional (3D) models were built for each screw-polyurethane sample set using SolidWorks® 2006 software. Thirty polyurethane samples were made for G1, G2 and G3 validation, 10 for each group. The pilot hole was made using a 3.8 mm drew for G1, and 4.8 mm for G2 and G3. The G4, G5 and G6 models were validated based on literature results that used polyurethane of same density and pilot hole made using 3.8 mm probe for G4 and G5, and 4.8 mm for G6. The FEM analysis was performed using ANSYS®Workbench 10.0 software. Validation was reached by comparing relative stiffness obtained in mechanical tests and results of FEM simulation. Differences of 8.3% for G1, 3.1% for G2, 0.5% for G3, 14.4% for G4, 9.5% for G5, and 10.3% for G6 were found, but all values were considered acceptable. Validated the models, G4 and G6 groups, used for anterior fixation, were submitted to compression, traction and lateral bending load. The G5 and G6 groups, used for posterior fixation, were submitted to compression, traction, flexion and extension force. In the anterior fixation, lower stress were found for G4, and greater for G6 at all applied forces. In the posterior fixation, lower stress were found for G5 and greater for G6 at all applied forces. Greater stress were caused simulating lateral bending in the anterior fixation, and extension in the posterior fixation.

La corrosion des armatures constitue la principale cause de dégradation des ouvrages en béton armé, et occasionne des coûts élevés de maintenance/réparation. Pour prévenir ce problème sur ouvrages neufs, une solution consiste à renforcer les structures en béton par des armatures non-métalliques de type Polymère Renforcé de Fibres (PRF), généralement à base de fibres de verre, de carbone ou d'aramide. Il existe aujourd'hui plusieurs textes réglementaires consacrés aux armatures PRF, notamment aux USA, au Canada et au Japon, et de nombreux ouvrages en béton armé par barres en PRF ont d'ailleurs été construits dans ces pays. Cependant, si l'utilisation de ces nouvelles armatures semble à priori prometteuse, elle suscite encore des réserves de la part des maîtres d'ouvrages, notamment en France. Il subsiste en effet des incertitudes sur le comportement à long terme des structures renforcées par PRF, et plus particulièrement sur la durabilité en milieu alcalin des armatures à matrice vinylester ou époxy renforcée par des fibres de verre (PRFV), qui sont actuellement les plus utilisées, ou encore sur le vieillissement de l'interface PRF/béton. Dans ce contexte, la présente étude vise à développer pour la première fois en France, un ensemble de méthodologies permettant, d'une part, de caractériser les principales propriétés physiques, mécaniques et d'interface des différentes armatures en PRF disponibles sur le marché, mais également d'évaluer la durabilité d'armatures en PRFV (les plus représentatives du marché) et de l'interface PRFV/béton à travers des procédures pertinentes de vieillissements accélérés. La première partie de l'étude a donc été consacrée à la caractérisation physique et mécanique d'une sélection d'armatures du commerce, confectionnées à base de fibres de verre, de carbone ou d'aramide, et au comportement mécanique de l'interface entre ces PRF et le béton. Outre la caractérisation microstructurale des PRF par techniques de microscopie et d'analyse thermique, la mise en place de dispositifs d'essais de traction et de flexion 3 points à appuis rapprochés (Short-beam test) a permis d'accéder respectivement aux propriétés mécaniques en traction (module d'élasticité, résistance) et à la résistance au cisaillement inter-laminaire des armatures. Des essais spécifiques d'arrachement (Pull-out) ont ensuite permis d'évaluer l'influence de différents paramètres (type de fibre, diamètre et géométrie de surface des barres) sur le mécanisme de transfert d'effort à l'interface armature/béton. Une grande originalité de l'approche proposée réside dans l'instrumentation d'une partie des corps d'épreuve par des capteurs de déformation à fibre optique disposés au niveau de l'interface armature/béton ; ce dispositif de mesures réparties permet d'accéder à des informations locales comme le profil des déformations de traction de l'armature, et d'en déduire la longueur d'ancrage des différentes armatures dans le béton. En complément de l'étude expérimentale précédente, un travail de modélisation analytique et numérique a été initié en vue de simuler les essais d'arrachement et d'appréhender plus finement les mécanismes d'interface mis en jeu entre l'armature et le béton lors de ces essais. Dans cette optique, un modèle analytique d'interface a tout d'abord été proposé, puis introduit dans un modèle aux éléments finis (modèle d'endommagement de zones cohésives). Enfin, un protocole de vieillissement accéléré a été appliqué à des barres en PRFV seules ou noyées dans un milieu cimentaire. Les caractéristiques résiduelles des armatures et des interfaces ont été évaluées à différentes échéances de vieillissement (jusqu'à 240 jours). Hormis une diminution des propriétés mécaniques des barres soumises à une immersion directe en solution alcaline, cette condition pouvant être considérée comme très sévère par rapport aux conditions de service, il n'a pas été observé de dégradation des propriétés d'adhérence PRF/béton par rapport à l'état initial / Corrosion of the steel reinforcing bars (rebars) is the main process involved in the degradation of reinforced concrete (RC) structures, and has large repercussions on the maintenance/reparation expenses. To prevent such degradations on new infrastructures, the use of corrosion-free reinforcements, such as Fiber Reinforced Polymer (FRP) bars based on glass, carbon or aramid fibers, is gaining interest. Specific guidelines are already available in several countries (USA, Canada or Japan for instance), that define the design principles and good practices for this type of internal rebars; beside, many FRP RC structures have been built and are in service in these countries. Although the development of these new reinforcing bars is quite promising, infrastructures owners are still reluctant for their wide-scale use, especially in France. There are still major concerns regarding the long term behavior of FRP RC structures, and more particularly, the durability of glass fibers reinforced polymers (GFRP) when subjected to an alkaline environment, and the ageing behavior of the GFRP/concrete bonding as well. In this context, the present study aims at developing for the first time in France, a set of methodologies that allows : to characterize the main physical/mechanical properties of different types of FRP bars from the marketto assess the durability of GFRP bars (the most common type of bar) and their interface with concrete through relevant accelerated ageing procedures. The first part of this study was thus devoted to the physical/mechanical characterization of a selection of commercially available FRP rebars, based on glass, carbon or aramid fibers, and to the mechanical behavior of corresponding FRP/concrete interfaces. Beside the microstructural characterization of the various FRP materials by microscopy and thermal analysis techniques, tensile and short beam tests were developed in order to determine the tensile properties (Young's modulus and strength) and the interlaminar shear strength (ILSS) of the bars. Specific pull-out tests then made it possible to evaluate the influence of several parameters (type of fibers, diameter and surface geometry of the bars) on the mechanism of load transfer at the bar/concrete interface. A main originality of the proposed approach relied on the instrumentation of several test bodies by optical fiber strain sensors, which were installed along the bar/concrete interface. Such a distributed measurement system provided local information in the form of tensile strain profiles of the bars along the interface, and made it possible to determine the effective transfer length of the various types of FRP bars. As a complement to the previous experimental study, an analytical and numerical modeling work was initiated to simulate the pull-out tests and investigate more closely the interfacial mechanisms involved in the FRP bar/concrete bond behavior. In this line, an improved interface model was first proposed, which was then implemented in a finite element model (cohesive zone model formulated in the context of damage mechanics).Finally, an accelerated ageing protocol was developed and applied to the GFRP bars, either alone or embedded in a concrete medium. The retention properties of both bars and interfaces were determined after various periods of exposure (up to 240 days). Except a drop of tensile properties observed for GFRP bars that were directly immersed in an alkaline solution, which is considered as a very severe environment compared to actual service conditions, no significant loss of interfacial properties was detected on aged specimens compared to the initial state

In dieser Arbeit wird das Verhalten von Normal- und Stahlfaserbeton (engl. steel fiber reinforced concrete (SFRC)) unter quasi-statischer und dynamischer Belastung untersucht. Der Fokus der Arbeit liegt dabei auf den Untersuchungen unter dynamischer Belastung. Frühere Forschungen haben gezeigt, dass die Zugabe von Stahlfasern viele der gewünschten technischen Eigenschaften des erhärteten Betons, wie Bruchzähigkeit, Biegefestigkeit, Ermüdungsfestigkeit, Temperaturwechselbeständigkeit sowie Rissbildung, erheblich verbessern kann. In diesem Zusammenhang weisen viele experimentelle und numerische Studien darauf hin, dass die Festigkeit solcher Verbundwerkstoffe ratenabhängig ist, d.h. sie wird durch die Erhöhung der dynamischen Belastung stark beeinflusst. Dieser Effekt gilt sowohl für die Verbundwerkstoffkomponenten Beton und Stahlfasern als auch für die Verbundwechselwirkung zwischen ihnen. Das Phänomen ist allgemein als Dehnraten-Effekt bekannt. Im Rahmen dieser Forschungsarbeit wurden numerische Untersuchungen durchgeführt, um den Einfluss der Zugabe von Stahlfasern in die Betonmatrix systematisch zu analysieren und die Abhängigkeit dieses Materials von der Belastungsrate zu untersuchen. Es wurden drei numerische Studien durchgeführt. In der ersten Studie wurde das Verbundverhalten zwischen Stahlfaser und der angrenzenden Betonmatrix mit verschiedenen Ansätzen mit der Finite-Elemente-Software LS-DYNA untersucht. Die Ergebnisse wurden mit zur Verfügung stehenden experimentellen Daten verglichen. In der zweiten Studie wurde das Verhalten von unverstärktem und stahlfaserverstärkten Betonplatten unter Impakt-Belastung untersucht. Die Modelle wurden entwickelt und kalibriert. Die Qualität und Zuverlässigkeit der Modelle wurden in einer Reihe von numerischen Fallstudien bewertet. Die berechneten Ergebnisse wurden durch Vergleich mit den zur Verfügung stehenden experimentellen Daten verifiziert. Das dynamische Verhalten von unverstärktem Beton und faserverstärktem Beton wurde in der dritten Studie untersucht, wobei sowohl das Druck- als auch das Zugverhalten untersucht wurden. Diese Untersuchungen zielten darauf ab, den Beitrag der Stahlfasern zur globalen Festigkeit bzw. zum Widerstandsverhalten von unverstärktem und faserverstärktem Material unter dynamischer Belastung zu untersuchen, wobei dem Einfluss der Stahlfasern auf die Rissentwicklung des faserverstärkten Betons wenig Beachtung geschenkt wurde. Darüber hinaus sind der Beitrag des Materialeffekts und seine Fähigkeit, das dynamische Verhalten von glattem und faserverstärktem Beton zu erfassen, von Interesse. Der Schwerpunkt liegt hier auf dem vorgeschlagenen Materialmodell für den Beton. Es wird gezeigt, dass das vorgeschlagene Betonmodell das druck- und zugdynamische Verhalten des unverstärkten und des faserverstärkten Betons gut abbilden und die experimentellen Ergebnisse realistisch vorhersagen kann. Schließlich folgten numerische Fallstudien zur Abhängigkeit der Ergebnisse von der Netzgröße, dem Fasergehalt, dem Verhältnis von Faserlänge zu -durchmesser, der Betonfestigkeit und der Belastungsrate. Die Parameter mit dem größten Einfluss wurden identifiziert und analysiert, und eine Schlussfolgerung wurde gezogen. Es wurde gezeigt, dass die zuvor genannten Parameter aktiv am Gesamtverhalten der Materialien beteiligt sind und eine wesentliche Rolle dabei spielen können.

Development and evaluation of new cementless revision acetabular components for total hip arthroplasty / type TC / Objective: The aim of the clinical part of the study was to introduce a new revision oval cup type TC, and evaluate its reliability and utility in revision endoprosthesis. Due to the different structure of the implant, we aimed to objectively demonstrate the remodeling of bone tissue in its vicinity. In the experimental part of the work we verified the hypothesis that the use of locking screws has an effect on the bond strength of the implant with bone tissue, and therefore on the primary stability of the acetabular component. Method: We evaluated 31 patients that underwent revision hip surgery between 2004 and 2008. The mean follow-up was 7.1 years (range 5.3 to 9.3 years, minimum 5 years after surgery). Osteointegration of the implant and remodeling of bone tissue around the implant and its ribs were evaluated by digital radiography and computed tomography, and clinical results according to Harris. The experiment was based on the execution of pull-out tests after the implantation of TC cups in cadaveric bovine pelves. We evaluated the dependence of tensile forces in the axis of the implant on extraction of the metal cup from the bone bed. Four tests were conducted with the cup fixed...

The current research project mainly aims to investigate the corrosion resistance and bond performance of steel reinforced recycled aggregate concrete incorporating nano-silica under both normal and corrosive environmental conditions. The experimental part includes testing of 180 pull-out specimens prepared from 12 different mixtures. The main parameters studied were the amount of recycled aggregate (RCA) (i.e. 0%, 25%, 50% and 100%), nano silica (1.5% and 3%), steel embedment length as well as steel bar diameter (12 and 20mm). Different levels of corrosion were electrochemically induced by applying impressed voltage technique for 2, 5, 10 and 15 days. The experimental observations mainly focused on the corrosion level in addition to the ultimate bond, failure modes and slips occurred. Experimental results showed that the bond performance between un-corroded steel and recycled aggregate concrete slightly reduced, while a significant degradation was observed after being exposed to corrosive conditions, in comparison to normal concrete. On the other hand, the use of nano silica (NS) showed a reasonable bond enhancement with both normal and RCA concretes under normal conditions. However, much better influence in terms of bond and corrosion resistance was observed under advancing levels of corrosion exposure, reflecting the improvement in corrosion resistance. Therefore, NS was superbly effective in recovering the poor performance in bond for RCA concretes. More efficiency was reported with RCA concretes compared to the conventional concrete. The bond resistance slightly with a small amount of corrosion (almost 2% weight loss), then a significant bond degradation occurs with further corrosion. The influence of specific surface area and amount of nano silica on the performance of concrete with different water/binder (w/b) ratios has been also studied, using 63 different mixtures produced with three different types of colloidal NS having various surface areas and particle sizes. The results showed that the performance of concrete is heavily influenced by changing the surface area of nano silica. Amongst the three used types of nano silica, NS with SSA of 250 m2 /g achieved the highest enhancement rate in terms of compressive strength, water absorption and microstructure analysis, followed by NS with SSA of 500 m2/g, whilst NS with SSA of 51.4 m2 /g was less advantageous for all mixtures. The optimum nano silica ratio in concrete is affected by its particle size as well as water to binder ratio. The feasibility of the impact-echo method for identifying the corrosion was evaluated and compared to the corrosion obtained by mass loss method. The results showed that the impact echo testing can be effectively used to qualitatively detect the damage caused by corrosion in reinforced concrete structures. A significant difference in the dominant frequencies response was observed after exposure to the high and moderate levels of corrosion, whilst no clear trend was observed at the initial stage of corrosion. Artificial neural network models were also developed to predict bond strength for corroded/uncorroded steel bars in concrete using the main influencing parameters (i.e., concrete strength, concrete cover, bar diameter, embedment length and corrosion rate). The developed models were able to predict the bond strength with a high level of accuracy, which was confirmed by conducting a parametric study. / Higher Education Institute of the Libyan Government

The current research project mainly aims to investigate the corrosion resistance and bond performance of steel reinforced recycled aggregate concrete incorporating nano-silica under both normal and corrosive environmental conditions. The experimental part includes testing of 180 pull-out specimens prepared from 12 different mixtures. The main parameters studied were the amount of recycled aggregate (RCA) (i.e. 0%, 25%, 50% and 100%), nano silica (1.5% and 3%), steel embedment length as well as steel bar diameter (12 and 20mm). Different levels of corrosion were electrochemically induced by applying impressed voltage technique for 2, 5, 10 and 15 days. The experimental observations mainly focused on the corrosion level in addition to the ultimate bond, failure modes and slips occurred. Experimental results showed that the bond performance between un-corroded steel and recycled aggregate concrete slightly reduced, while a significant degradation was observed after being exposed to corrosive conditions, in comparison to normal concrete. On the other hand, the use of nano silica (NS) showed a reasonable bond enhancement with both normal and RCA concretes under normal conditions. However, much better influence in terms of bond and corrosion resistance was observed under advancing levels of corrosion exposure, reflecting the improvement in corrosion resistance. Therefore, NS was superbly effective in recovering the poor performance in bond for RCA concretes. More efficiency was reported with RCA concretes compared to the conventional concrete. The bond resistance slightly with a small amount of corrosion (almost 2% weight loss), then a significant bond degradation occurs with further corrosion. The influence of specific surface area and amount of nano silica on the performance of concrete with different water/binder (w/b) ratios has been also studied, using 63 different mixtures produced with three different types of colloidal NS having various surface areas and particle sizes. The results showed that the performance of concrete is heavily influenced by changing the surface area of nano silica. Amongst the three used types of nano silica, NS with SSA of 250 m2 /g achieved the highest enhancement rate in terms of compressive strength, water absorption and microstructure analysis, followed by NS with SSA of 500 m2/g, whilst NS with SSA of 51.4 m2 /g was less advantageous for all mixtures. The optimum nano silica ratio in concrete is affected by its particle size as well as water to binder ratio. The feasibility of the impact-echo method for identifying the corrosion was evaluated and compared to the corrosion obtained by mass loss method. The results showed that the impact-echo testing can be effectively used to qualitatively detect the damage caused by corrosion in reinforced concrete structures. A significant difference in the dominant frequencies response was observed after exposure to the high and moderate levels of corrosion, whilst no clear trend was observed at the initial stage of corrosion. Artificial neural network models were also developed to predict bond strength for corroded/uncorroded steel bars in concrete using the main influencing parameters (i.e., concrete strength, concrete cover, bar diameter, embedment length and corrosion rate). The developed models were able to predict the bond strength with a high level of accuracy, which was confirmed by conducting a parametric study. / Higher Education Institute in the Libyan Government MONE BROS Company in Leeds (UK) for providing recycled aggregates BASF and Akzonobel Companies for providing nano silica NS, Hanson Ltd, UK, for suppling cement

[pt] A técnica de reforço de solo por inclusão de materiais geossintéticos vem se consolidando de forma acelerada em todo o mundo, com aplicações diretas em estabilização de encostas e de aterros sobre solos moles. A utilização de geogrelhas como elemento de reforço apresenta-se como uma alternativa promissora, embora ainda pouco difundida no Brasil. O presente trabalho tem por objetivos avaliar a resistência ao arrancamento de diferentes tipos de geogrelhas e analisar os mecanismos de interação entre solo e geogrelha. Para tal, foi realizado um extenso programa de ensaios de arrancamento no laboratório e no campo. Os equipamentos utilizados, a preparação das amostras e as metodologias dos ensaios estão apresentados em detalhe. Os ensaios de arrancamento no campo utilizaram uma estrutura de reação fixa, específica para ensaios de arrancamento de grandes dimensões, e foram realizados no campo experimental da PUC-Rio, em Jacarepaguá. Nestes ensaios, três tipos de geogrelhas foram utilizadas para o arrancamento em aterros de solo arenoso e solo residual. Os ensaios de arrancamento no laboratório foram executados em uma caixa de arrancamento cúbica de grandes dimensões (1m de aresta), no Laboratório de Geotecnia do CEDEX, na Espanha. No programa experimental no laboratório, foram utilizados os mesmos tipos de geogrelhas e de solos, de modo a facilitar as comparações e análises dos resultados. As influências do tipo de geogrelha, do tipo de solo, da tensão confinante e dos procedimentos de ensaioforam analisadas em detalhe no que se refere à rigidez e à resistência ao arrancamento das geogrelhas. / [en] The technique of soil reinforcement by inclusion of geosynthetics has been subject to significant development worldwide, with direct applications in slope stabilization and earthfills over soft deposits. The use of geogrids as a soil reinforcement element is an attractive alternative, although still with very little application in Brazil. This work presents the results of an investigation into soil- geogrid interaction by means of pull-out tests. Both field and laboratory pull-out tests were carried out in order not only to make clear the pull-out mechanism but also to determine the parameters for design and analysis of reinforced soil structures. The testing equipments, specimen preparation and testing procedures are described in detail. The field pull-out tests were performed with three different types of geogrids in a research area in Jacarepagua, Rio de Janeiro. Sandy and residual soil surcharge fills of 0,5 to 2m in height were used. Details of the anchored reaction structure are also presented. The laboratory pull-out tests were performed in the geotechnical laboratory at CEDEX, in Spain, with the same types of geogrids and soils. Details of the cubical pull-out box (1m in dimensions) are presented. The influence of the type of geogrid, type of soil, confining pressure and tests procedures on the pull-out stiffness and resistance of the geogrids are discussed by analysing the results of the experimental program. / [es] La técnica de refuerzo del suelo por inclusión de materiales geosintéticos se ha consolidado de forma acelerada en todo el mundo. La utilización de geochapas como elemento de refuerzo se presenta como una alternativa promisora, aunque poco difundida en Brasil. Este trabajo tiene por objetivos evaluar la resistencia al arrancamento de diferentes tipos de geogrelhas y analizar los mecanismos de interacción entre suelo y geochapa. Para tal, se realizó un extenso programa de ensayos de arrancamento en el laboratorio y en el campo. Los equipos utilizados, la preparación de las muestras y las metodologías de los ensayos están descritos detalladamente. Los ensayos de arrancamento en el campo utilizaron una extructura de reacción fija, específica para ensayos de arrancamento de grandes dimensiones, y fueron realizados en el campo experimental de la PUC-Rio, en Jacarepaguá. En estos ensayos, se utilizaron tres tipos de geogrelhas para el arrancamento en aterros de suelo arenoso y suelo residual. Los ensayos de arrancamento en el laboratorio fueron ejecutados en una caja de arrancamento cúbica de grandes dimensiones (1m de arista), en el Laboratorio de Geotecnia del CEDEX, España. En el programa experimental en laboratorio, se utilizaron los mismos tipos de geogrelhas y de suelos, de modo que facilitara las comparaciones y análisis de los resultados. Las influencias del tipo de geochapa, del tipo de suelo, de la tensión confinante y de los procedimentos de ensayo se analizaron detalladamente.

In composite beam design, headed stud shear connectors are commonly used to transfer longitudinal shear forces across the steel¿concrete interface. Present knowledge of the load¿slip behavior and the shear capacity of the shear stud in composite beam are limited to data obtained from the experimental push-off tests. For this purpose, an effective numerical model using the finite element method to simulate the push-off test was proposed. The model has been validated against test results and compared with data given in the current Code of Practices, i.e., BS5950, EC4, and AISC. Parametric studies using this model were preformed to investigate variations in concrete strength and shear stud diameter. The finite element model provided a better understanding to the different modes of failure observed during experimental testing and hence shear capacity of headed shear studs in solid concrete slabs

The paper presents a meso-scopic modeling framework for the simulation of three-phase composite consisting of a brittle cementitious matrix and reinforcing AR-glass yarns impregnated with epoxy resin. The construction of the model is closely related to the experimental program covering both the meso-scale test (yarn tensile test and double sided pull-out test) and the macro-scale test in the form of tensile test on the textile reinforced concrete specimen. The predictions obtained using the model are validated using a-posteriori performed experiments.