[pt] A utilização de pneus usados é uma técnica interessante para reforço de solos, sob o aspecto ambiental. Os pneus usados constituem uma matéria-prima abundante e de custo reduzido. A técnica de utilização de pneus em obras geotécnicas vem sendo difundida no Brasil desde meados dos anos 90, com a construção do muro experimental de solopneus da PUC-Rio, em colaboração com a Fundação Geo-Rio e a Universidade de Ottawa (Canadá). O presente trabalho tem por objetivo apresentar a metodologia para avaliação da resistência ao arrancamento de malhas de pneus. Os pneus podem ser dispostos em um plano horizontal e amarrados entre si, formando uma malha de reforço. Podem ser utilizados pneus inteiros ou com uma das bandas laterais cortadas. A sobrecarga atuando no reforço provém do confinamento provocado pela altura do aterro de solo, construído sobre a malha de pneus. Os ensaios de arrancamento dos pneus no campo utilizaram uma estrutura metálica de reação, atirantada, a qual foi desenvolvida especificamente para o programa experimental sobre reforço de solos. Os resultados permitiram idealizar um mecanismo de ruptura envolvido no processo de arrancamento das malhas de pneus, bem como a verificação das características de resistência e deformabilidade deste tipo de reforço. / [en] The use of scrap tires as soil reinforcement is an environmentally interesting technique. Scrap tires are an abundant and low cost waste material. The technique for using tires in geotechnical construction is becoming popular in Brazil since the construction of an experimental gravity wall made with soil and tires in 1995. This wall was part of a research project by carried out by PUC-Rio in collaboration with Geo-Rio and University of Ottawa. The objective of this work is to present a methodology to evaluate the pull-out behaviour of tire meshes. The tires can be placed in a horizontal plane and tied with rope or wire, forming a reinforcement mesh. The surcharge on these meshes comes from the confinement due to the height of a soil embankment built on the mesh. Field pull-out tests were performed on these reinforcement meshes, using a metallic reaction structure, which was developed specifically for this experimental research. The results allowed the idealization of a shearing mechanism based on the pull-out of tire meshes, as well as the verification of the strength and deformability characteristics of the reinforcement.

On se propose d’analyser le régime transitoire de décrochage à l’aide de la simulation numériqueinstationnaire de type DNS. Cette approche permet de reproduire avec fidélité l’écoulementdans la région critique de Bulbe de Décollement Laminaire au bord d’attaque, encoreimpossible à modéliser ou mesurer avec précision. Après une étape de validation, la sensibilitédu BDL au niveau de turbulence extérieure est étudiée et comparée favorablement à celleétablie récemment dans la littérature. La phase d’établissement du décollement massif depuisle BDL est reproduite en réalisant de petites variations d’incidence à travers l’angle critiqued’apparition du décrochage. Ce raisonnement ”aux petites perturbations” permet de reproduirel’éclatement du BDL communément rattaché au décrochage statique. La déstabilisation de larégion de BDL est alors étudiée à l’aide d’une base de données instationnaires et moyennes quipermet pour la première fois de rendre compte des déformations 3D du BDL. Conservant ceprotocole, et faisant varier la vitesse du profil, on est en mesure d’évaluer l’influence de cettedernière sur le régime transitoire. Des mouvements de rotation de plus forte amplitude angulaireont permis de mettre en évidence un mécanisme de décrochage sensiblement différent duprécédent. La couche de mélange surplombant le BDL s’enroule alors pour donner naissance àun tourbillon énergétique (Leading Edge Vortex), communément associé au décrochage dynamique.Enfin, l’analyse du champ de vitesse moyen a permis de valider un critère empiriqued’apparition de l’éclatement du BDL, qui s’est révélé pertinent aussi bien pour les mouvementsde faible amplitude que ceux plus amples. / High fidelity numerical simulation is used to study the transitory flow involved during the staIl ofan airfoil at high angle of attack. The nearly DNS resolution in the Laminar Separation Bubbleprovides the required accuracy to reproduce this complex flow that still represents a challenge forboth experimentation and modeling. The numerical procedure is comprehensively validated withparticular attention to the LSB region. The sensitivity of the LSB to an external disturbance ismonitored on the airfoil and is favorably compared with a recent study on flat plate in the literature.The destabilization of the LSB during staIl is reproduced with a small variation of the angle ofattack through the critical angle. The LSB bursting, typical of a static leading edge staIl, is thusreproduced. A comprehensive study of the unsteady events during the transitory flow is performedby means of a high frequency sampling of spanwise and short time averaged data base. Ofparticular interest is the 3D deformation of the flow captured by using a large spanwisecomputational domain (one chord length). The influence of the motion dynamic is then explored.The transitory is significantly affected by a high angular amplitude motion. The shear-Iayer in theLSB undergoes a roll-up which is found to be responsible for the formation of the Leading EdgeVortex, typical of a dynamic staIl configuration. An empirical criterion for the prediction of burstingis then assessed using the statistical data base. Results are found to surprisingly match the incipientof staIl in both static and dynamicaJ conditions.

Syftet med denna studie var att undersöka elevers och studie- och yrkesvägledares upplevelser av studieavbrott i Komvux vuxenutbildning. Studien tar upp vad som har orsakat studieavbrotten och om vuxenutbildningen hade kunnat göra något för att hjälpa eleverna att undvika dessa. En kvalitativ forskningsansats användes för studien med inspiration från fenomenografisk metodansats. Kvalitativa halvstrukturerade intervjuer genomfördes. Datainsamlingen skedde dels med stöd av en chatt-dialog med de elever som hade avbrutit sina studier och ansikte mot ansikte i intervjuer med studie- och yrkesvägledare. Datainsamlingen omfattar tio intervjuer med studie- och yrkesvägledare och med nio elever. Alla elever har deltagit i gymnasial teoretisk Komvux, men valt att avbryta sina studier. Ett teoretiskt ramverk användes för att analysera och kategorisera orsakerna till studieavbrotten. Kategorierna omfattade begreppen "pull out", "push out" och "fall out". Teorin hämtades från tidigare studier som har haft avsikten att titta närmare på just orsaker bakom studieavbrott. Resultatet visade att de tre kategorierna fanns representerade även i resultatet i den här studien orsaker bakom studieavbrott inom Komvux verksamhet. Ett tema som framkom under analysen av data som kan ses väsentligt att följa upp var enskilda studieplaneringar och lokala insatser. Det var något som i hög grad efterfrågades av de studerande för att klara studierna och även lyftes fram av studie- och yrkesvägledarna i samtalen. Anpassningar för att svara upp mot enskilda studerandes behov av stöd för sina studier saknades. Uppdraget och behovet behöver tydliggöras i organisationen. Studien har därmed synliggjort och lyft fram ny kvalitativ information

Abstract The reinforcement of concrete with steel fibres changes the failure of the composite material from catastrophic brittle failure to pseudo-ductile behaviour as a result of crack-bridging by the fibres, and the additional work which is absorbed by fibre pull-out. A good understanding of the properties of the fibre-reinforced concrete depends on an understanding of the fibre pull-out process. The main aim of the current study is to investigate, both experimentally and numerically, the pull-out behaviour of a single hooked end steel fibre from epoxy matrix, where epoxy was chosen to replace concrete in order to enable visualisation of the pull-out process. The experimental and numerical results both contribute to the development of a physical understanding of the mechanism of pull-out. Experimental studies included the evaluation of the mechanical properties of hooked end steel fibre and epoxy matrix by means of tensile tests, the manufacturing of pull-out specimens consisting of a single hooked end steel fibre embedded in epoxy matrix, and the experimental characterisation of the fibre pull-out. The significant features (peaks and minima) of the load vs. displacement graph were correlated to stills taken from a video of the pull-out process, in which the plastic deformation of the fibre is evident. Small deformations (spalling) were also observed in the matrix. A model is proposed for the mechanisms which interact during the pull-out process. / Dissertation (MEng)--University of Pretoria, 2013. / gm2014 / Mechanical and Aeronautical Engineering / unrestricted

Mortar is the cementitious binding material placed between masonry blocks to create a composite system. The American Society of Testing and Materials (ASTM), along with other organizations, have established the testing of prismatic mortar specimens for evaluating mechanical properties, like compressive strength. Mortar joints, however, possess vastly different characteristics compared to prismatic specimens, especially in terms of geometry and water content. These differences prevent a direct comparison of compressive strength between prismatic specimens and actual mortar joints in the assembly. The objective of this study was to analyze Type S mortar joints, with particular emphasis on specimen shape and water content, to draw accurate comparisons of compressive strength to ASTM prescribed mortar prismatic specimens.To examine the effect of water on mortar compressive strength, three different water contents were evaluated across nearly all testing series. Cubic (2-in) and cylindrical (2 by 4-in) mortar specimens were prepared and tested according to ASTM guidelines to verify the compressive strength relationship described by ASTM and to be used as comparative data. In addition, a small masonry wall was assembled and cured in a laboratory to simulate true properties of mortar joints. Mortar joints subjected to testing were a combination of thin slices cut from prismatic specimens as well as in-place bed joints cured between concrete masonry units (CMU). Two unorthodox test methods, the double punch test (DPT) and helix pull-out test (HPT), were selected as methods for assessing mortar joints. In addition, confining effects from neighboring material common to DPT were evaluated as a function of specimen face dimensions. The compressive strength ratio obtained through testing of 2-in cubic and 2 by 4-in cylindrical specimens was lower than ASTM recommendations. This may have been in part due to testing cylindrical specimens with rough surfaces and no capping material. DPT confinement on 2-in square and 2-in diameter circular specimens was found to be equivalent. Thinly sliced specimens tested in DPT showed increases in compressive strength as water content and specimen thickness decreased. As a whole, DPT results on thin mortar slices showed promise for accurate comparison to prismatic mortar specimens. In-place mortar joints tested in HPT showed moderate to high scatter. In addition, evaluation via HPT was determined to be more appropriate for qualitative rather than quantitative assessments of in-situ mortar.

No description available.

[EN] At present, hybrid structures in flexural elements are being gradually incorporated in the field of civil and building structures. The low weight and high durability of these structures make use viable. Hybrid structures are usually composed of polymeric materials reinforced with glass or carbon fibers (GFRP or CFRP) in structural shapes of any type of section, in I, in box, trough-shaped, as elements working in tension, and the concrete in the compressed head of the resistant section. Due to this, the union of these materials and their excellent qualities allow for optimizing their mechanical performance in these positions. The failure modes of these structures have different opinions (points of view) among researchers. Therefore, this thesis focuses first of all on the possibility of designing a beam with ductile failure mode that moves the break to the compressed head by fiber reinforced concrete(Appendix I). It is found in this study that it is not possible to analyze this option because after "shielding" all possible failure modes of the structure the break occurs by the grazing effort between GFRP and concrete , without checking the influence of HRF. For this reason, the study is redirected and focused on the bond between GFRP and concrete by analyzing the influence of a series of surface treatments applied to the GFRP profile and the use of mechanical fasteners. To do this without losing sight of applications in civil engineering and construction, and after analyzing the scientific information available, given that there are no standard tests of this type of hybrid beams trials, the need to provide a simple testing methodology arises to enable the study of this phenomenon. That is why the adaptation of the pull-out test, usually for bars, is presented for rectandular section profiles. The complexity of this adaptation is solved by providing a number of modalities to the approach depending on the degree of confinement of the concrete over GFRP profile and the possibility of applying torque to the prestressed bolts, finally generating patterns 2C, 1CA, 1CE and 1CL. These patterns in turn are represented in the forms of connecting profiles with "in situ" concrete: flange profile embedded in the compression layer, or the top of the flange profile in contact with the compression layer. In the modality 2C, the concrete is passively confining all faces of the GFRP profile; in the form 1CA, the concrete confines the two main faces of elements but one of them does not have surface treatment; in the form 1CE, one side of the profile is confined with surface treatment and the other one is not in contact with the concrete; and finally, in 1CL one side is in contact with the concrete and the other one is liberated from this to access profile and give torque to conduct a post-tensioning of the mechanical fastener, thus achieving an active confinement of concrete over GFRP profile. Once clarified trial methodology, it is proceed to the characterization of the different proposed bond variables like a series of surface treatments such as sandblasting, and textured resins and a combination of both. Also fixed and moveable mechanical fastening elements are used providing them with a torque, sometimes only for fixing the profile GFRP and in other cases to achieve an active confinement of the concrete on the profile. After the results, a proposal for characterizing the bond parameters is made and a variety of behavioral models based on bond stress-slip curves are analyzed, bringing innovations to the scientific community. / [ES] En la actualidad, poco a poco, se están incorporando las estructuras híbridas en elementos a flexión en el sector de las estructuras civiles y de edificación. El bajo peso y la gran durabilidad de estas estructuras hacen viable su utilización. Las estructuras híbridas están compuestas generalmente por materiales poliméricos reforzados con fibras de vidrio o carbono (GFRP o CFRP) en forma de perfiles estructurales de cualquier tipo de sección en I, en caja, en forma de artesa, como elementos que trabajan a tracción, y el hormigón en la cabeza comprimida de la sección resistente. Es por ello que la combinación de estos materiales y sus excelentes cualidades permiten optimizar su rendimiento mecánico en dichas posiciones. Los modos de fallo de estas estructuras presentan diversidad de criterios entre los investigadores, y es por ello que en esta Tesis Doctoral se realiza en primer lugar un estudio (Anexo I) sobre la posibilidad de diseñar una viga con un modo de fallo dúctil, trasladando la rotura a la cabeza comprimida con hormigones reforzados con fibras. Así, en este estudio se comprueba que no es posible analizar dicho modo de fallo ya que tras "blindar" todos los posibles modos de fallo de la estructura la rotura se produce por esfuerzo rasante entre el perfil de GFRP y el hormigón, sin llegar a comprobar la influencia del hormigón reforzado con fibras. Por ello se redirige el estudio y se inicia el análisis de la adherencia del GFRP y el hormigón, analizando la influencia de una serie de tratamientos superficiales aplicados al perfil de GFRP, así como el uso de elementos de fijación mecánica. Para ello, y sin perder de vista las aplicaciones en obra civil y edificación, y después de analizar la información científica disponible, visto que no existen ensayos normalizados para el estudio de este tipo de vigas híbridas, se plantea la necesidad de aportar una metodología de ensayo sencilla que posibilite el estudio de este fenómeno. Es por ello que se plantea la adaptación del ensayo de pull-out, habitual para barras, para su aplicación a perfiles de sección rectangular. La complejidad de esta adaptación se resuelve aportando una serie de modalidades al método, siendo el grado de confinamiento del hormigón sobre el perfil de GFRP y la posibilidad de aplicar par de apriete para postesar la tornillería lo que genera las modalidades de 2C, 1CA, 1CE y 1CL. Estas modalidades a su vez se ven representadas en las formas de conexión de los perfiles de GFRP con el hormigón en obra: ala o alma del perfil embebido en la capa de compresión, o la cara superior del ala del perfil en contacto con la capa de compresión. En la modalidad 2C el hormigón se encuentra confinando pasivamente todas las caras del perfil de GFRP; en la modalidad 1CA el hormigón confina las dos caras principales, pero una de ellas no tiene tratamiento superficial; en la modalidad 1CE el hormigón confina pasivamente la cara del perfil que ha sido tratada superficialmente , mientras que la otra cara no está en contacto con el hormigón; y por último, en la modalidad 1CL una cara está en contacto con el hormigón y la otra está liberada de éste para tener acceso al perfil en la probeta híbrida y poder darle el par de apriete para realizar un postesado del elemento de fijación mecánica, consiguiendo así un confinamiento activo del hormigón sobre el perfil de GFRP. Una vez clarificada la metodología del ensayo se procede a la caracterización de las distintas variables de adherencia propuestas, como son una serie de tratamientos superficiales tales como arenados, resinas y texturizados, así como combinaciones entre ellos; también se utilizan elementos de fijación mecánica fijos y con desplazamiento dotándolos de un par de apriete, unas veces solo para su fijación al perfil de GFRP y en otros casos para conseguir un confinamiento activo del hormigón sobre el perfil. / [CA] En l'actualitat, a poc a poc, s'estan incorporant les estructures híbrides en elements a flexió en el sector de les estructures civils i d'edificació. El baix pes i la gran durabilitat d'aquestes estructures fan viable la seua utilització. Les estructures híbrides estan compostes generalment per materials polimèrics reforçats amb fibres de vidre o carboni (GFRP o CFRP) en forma de perfils estructurals de qualsevol tipus de secció en I, en caixa, en forma d'artesa, com a elements que treballen a tracció, i el formigó en el cap comprimit de la secció resistent. És per açò que la unió d'aquests materials i les seues excel·lents qualitats permeten optimitzar el seu rendiment mecànic en aquestes posicions. Les maneres de fallada d'aquestes estructures presenten diversitat de criteris entre els investigadors, és per açò que en aquesta Tesi Doctoral, en primer lloc es realitza un estudi (Annex I) per a estudiar la possibilitat de dissenyar una biga amb una manera de fallada dúctil traslladant el trencament al capdavant comprimit amb formigons reforçats amb fibra (HRF). Es comprova, en aquest estudi, que no és possible analitzar aquesta possibilitat ja que després de "blindar" totes les possibles maneres de fallada de l'estructura, el trencament arriba per esforç rasant entre el perfil de GFRP i el formigó, sense arribar a comprovar la influència del HRF. És per açò que es redirigeix i s'inicia l'estudi en l'adherència del GFRP i el formigó, analitzant la influència d'una sèrie de tractaments superficials aplicats al perfil de GFRP així com l'ús d'elements de fixació mecànica. Per açò, i sense perdre de vista les aplicacions en obra civil i edificació, i després d'analitzar l'informació científica disponible, vist que no existeixen assajos normalitzats per a l'estudi d'aquest tipus de bigues híbrides, es planteja la necessitat d'aportar una metodologia d'assaig senzilla que possibilite l'estudi d'aquest fenomen. Es planteja mitjançant l'assaig de pull-out habitual per a barres, la seua aplicació en perfils de secció rectangular. La dificultat d'aquesta adaptació es resol aportant una sèrie de modalitats al mètode, sent el grau de confinament del formigó sobre el perfil de GFRP i la possibilitat d'aplicar parell d'estrenya per a postesar els caragols el que genera les modalitats de 2C, 1CA, 1CE i 1CL. Aquestes modalitats es veuen representades en les formes de connectar els perfils amb el formigó en obra: ala del perfil embegut en la capa de compressió, o la cara superior de l'ala del perfil en contacte amb la capa de compressió. En la modalitat 2C el formigó es troba confinant passivament totes les cares del perfil de GFRP, en la modalitat 1CA el formigó confina les dues cares principals, però una d'elles no té tractament superficial, en la modalitat 1CE el formigó confina pasivament la cara del perfil que està tractada supercialment, mentres que l'altra cara no està en contacte amb el formigó, i finalment a la modalitat 1CL una cara està en contacte amb el formigó i l'altra està alliberada d'aquest per a tenir accés al perfil en la proveta híbrida i poder donar-li el parell d'estrenya per a realitzar un postesat de l'element de fixació mecànica, aconseguint així un confinament actiu del formigó sobre el perfil de GFRP. Una vegada aclarida la metodologia de l'assaig es procedeix a la caracterització de les diferents variables d'adherència proposades, com són una sèrie de tractaments superficials tals com arenats, resines i texturitzats, així com combinacions entre ells; també s'utilitzen elements de fixació mecànica fixos i amb desplaçaments aplicant-los un parell d'estrenya, unes vegades solament per a la seua fixació al perfil de GFRP i en altres casos per a aconseguir un confinament actiu del formigó sobre el perfil. / Albiol Ibáñez, JR. (2015). Estudio experimental de la adherencia entre laminados de GFRP y el hormigón [Tesis doctoral]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/58866

Yes / Limited information related to the application of nano silica in recycled aggregate concretes has been available in the literature. However, investigations on the effect of nano silica on the bond performance of reinforcement embedment length in recycled aggregate concrete have not been conducted yet. Therefore, the present study aimed at investigating the bond strength for recycled aggregate concretes incorporating nano silica under different levels of corrosive environments. The experimental work consisted of testing 180 pull-out specimens prepared from different mixtures. The main parameters studied were the amount of recycled aggregate (i.e. 0%, 25%, 50% and 100%), nano silica (1.5% and 3%), embedment length (5 and 13Ø) as well as reinforcement diameter (12 and 20mm). Different levels of corrosion were electrochemically induced by applying impressed voltage technique for 2, 5, 10 and 15 days. Finally, the experimental results were compared with the existing models. Experimental results showed that the bond performance between un-corroded steel and RCA 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 a small quantity of NS (1.5%) showed between 8 and 21% bond enhancement with both normal and RCA concretes under normal conditions. However, much better influence was observed with the increase of corrosion periods, reflecting the improvement in corrosion resistance. NS particles showed a more effective role with RCA concretes rather than conventional concretes in terms of enhancing bond and corrosion resistance. Therefore, it was superbly effective in recovering the poor performance in bond for RCA concretes. By doubling the content of NS (3%), the bond resistance slightly enhanced for non-corroded samples, while its influence becomes more pronounced with increasing RCA content as well as exposure time to corrosion.

Yes / This paper investigates the bond performance of recycled coarse aggregate (RCA) concrete with un-corroded/corroded reinforcing steel bars, with the main parameters being RCA content, corrosion level, bar diameter and embedment length. For this purpose, 60 pull-out specimens containing different percentages of RCA (i.e. 0%, 25%, 50% and 100%) and steel bars of two diameters (12 and 20 mm) and different embedment lengths were tested. In order to establish various levels of corrosion, specimens were exposed to an electrochemical corrosion for 2, 5, 10 and 15 days. The bond strength between RAC concrete and un-corroded/corroded steel are compared to current codes and equations proposed by other researchers. Experimental results showed that larger corrosion rate of steel bars was observed with the increase of the replacement level of RCA due to its high porosity and water absorption. The use of RCA had a slight influence on bond strength for un-corroded specimens compared to that obtained from conventional concrete. Furthermore, the bond strength of RCA concrete was strongly affected by corrosion products; bond strength slightly enhanced for up to about 2% corrosion rate, and then significantly decreased as the corrosion time further increased, similar to that of conventional concrete. However, the rate of bond degradation between RCA concrete and corroded steel bars was much faster than that observed in corroded conventional concrete.

Yes / In this study, bond properties of glass fibre reinforced polymer (GFRP) bars embedded in high-strength concrete (HSC) were experimentally investigated using a pull-out test. The experimental program consisted of testing 84 pull-out specimens prepared according to ACI 440.3R-12 standard. The testing of the specimens was carried out considering bar diameter (9.5, 12.7 and 15.9 mm), embedment length (2.5, 5, 7.5 and 10 times bar diameter) and surface configuration (helical wrapping with slight sand coating (HW-SC) and sand coating (SC)) as the main parameters. Twelve pull-out specimens reinforced with 16 mm steel bar were also tested for comparison purposes. Most of the specimens failed by a pull-out mode. Visual inspection of the tested specimens reinforced with GFRP (HW-SC) bars showed that the pull-out failure was due to the damage of outer bar surface, whilst the detachment of the sand coating was responsible for the bond failure of GFRP (SC) reinforced specimens. The bond stress – slip behaviour of GFRP (HW-SC) bars is different from that of GFRP (SC) bars and it was also found that GFRP (SC) bars gave a better bond performance than GFRP (HW-SC) bars. It was observed that the reduction rate of bond strength of both GFRP types with increasing the bar diameter and the embedment length was reduced in the case of high-strength concrete. Bond strength predictions obtained from ACI-440.1R, CSAeS806, CSA-S6 and JSCE design codes were compared with the experimental results. Overall, all design guidelines were conservative in predicting bond strength of both GFRP bars in HSC and ACI predictions were closer to the tested results than other codes.