A new philosophy in structural health monitoring was explored, with the view to the creation of a smart mining bolt: one which would bear the normal load of any bolt used in South African gold mining tunnels, but at the same time be capable of monitoring its own level of damage. To this end, a survey of various smart materials currently used in structural health monitoring applications, was conducted, and a group known as strain memory alloys isolated as holding the most promise in this regard. Strain memory alloys give an indication of peak strain based on an irreversible transformation from paramagnetic austenite to ferromagnetic martensite, which occurs in direct proportion to the amount of strain experienced by the material. A measurement of magnetic permeability can therefore be correlated to peak strain. An extensive study of the alloying chemistry, material processing and transformation characteristics was therefore carried out, including an analytical model for the quantification of the energy associated with martensitic nucleation, at a dislocation-disclination level. The conditions within typical South African gold mining tunnels were evaluated, and a smart mining bolt design produced, based on the loading and environmental conditions present. Several material formulations were then proposed, melted, tested and evaluated against the relevant strength, corrosion and transformation criteria. A suitable material was selected and further tested. A working prototype bolt has been produced, and in situ tests of complete bolts, are scheduled to take place shortly. / Thesis (Ph.D.)-University of Natal, Durban, 2003.

Block shear is a limit state that should be accounted for during the design of the steel tension members. This failure mechanism combines a tension failure on one plane and a shear plane on a perpendicular plane. Although current design specifications present equations to predict block shear load capacities of the connections, they fail in predicting the failure modes. Block shear failure of a structural connection along a staggered path may be the governing failure mode. Code treatments for stagger in a block shear path are not exactly defined. A parametric study has been conducted and over a thousand finite element analyses were performed to identify the parameters affecting the block shear failure in connections with multiple bolt lines and staggered holes. The quality of the specification equations were assessed by comparing the code predictions with finite element results. In addition, based on the analytical findings new equations were developed and are presented herein.

The research objectives for this project were to explicitly define the anchor bolt corrosion problem in the state of Georgia and recommend action to the Georgia Department of Transportation. The bearing assembly of concern is the plate bearing assembly, in which carbon steel and/or bronze plates are anchored by either carbon steel or stainless steel anchor bolts. Inspection report data revealed that anchor bolt corrosion was ubiquitous for all environments in Georgia; the problem was reported for 27% of the steel girder bridges throughout the state. Based on a synthesis of the field investigations, bolt failure analyses, laboratory experimental testing, and review of GDOT inspection report surveys, the corrosion of carbon steel anchor bolts is caused universally by concentration cell corrosion. Other corrosion mechanisms of concern are galvanic and crevice corrosion, which are both enhanced by the current bearing design. Corrosion protection provided through zinc galvanization cannot sufficiently protect the carbon steel bolt for its entire service life. Corrosion potential and cyclic polarization data confirmed that ASTM Type 304, Type 316, Type 2101, and Type 2205 were protected from concentration cell and localized corrosion in the simulated bearing environment. Therefore, it is recommended that the stainless steel anchor bolts of these types be use in future designs and that the bolts should be electrically separated from all dissimilar metals using a Nylon or Teflon washer to prevent preferential corrosion of carbon steel. It is further recommended that the bronze lube plate should be eliminated entirely and that the bearing type should be a reinforced elastomeric bearing. Maintenance of existing sliding plate bearings should include regular cleaning by brushing away debris from the bearing surfaces, and bridges with carbon steel anchor bolts should be retrofitted to provide additional lateral restraint according to current maintenance procedures.

A presente dissertação versa sobre a determinação do parâmetro de adesão entre nata de cimento e rocha. Este parâmetro é de fundamental importância no dimensionamento de grampos e tirantes ancorados, sistemas de contenção frequentemente executados que utilizam da técnica de ancoragem. Ensaios de arrancamento in loco são comumente realizados para avaliar essa tensão de aderência, no entanto, muitas vezes, apenas se tornam viáveis financeiramente durante a etapa de execução das obras. A metodologia Composite Cylinder Bond Test (CCBT) permite a determinação da adesão de maneira mais simples e com menor custo, por meio de ensaios de laboratório utilizando corpos de prova mistos de rocha e nata de cimento, sendo, por isto, uma interessante alternativa para a etapa de definição paramétrica de projetos. Neste contexto, foram estudadas três litologias sedimentares do município de Caçapava do Sul/RS – aqui chamadas de conglomerado, arenito muito fino e arenito médio – pertencentes à Formação Varzinha. A caracterização dessas litologias foi realizada por meio de lâminas delgadas e outros ensaios de caracterização de laboratório A classificação textural do conglomerado é de conglomerado arenoso, o arenito muito fino é classificado como arenito lamoso e o arenito médio é classificado como arenito. Do ponto de vista composicional, o arenito muito fino é classificado como arcóseo, enquanto o arenito médio é classificado como arcóseo lítico. Noventa ensaios CCBT, além de ensaios de resistência à compressão simples das rochas e da nata de cimento foram realizados. As tensões de adesão médias obtidas dos ensaios de laboratório foram de 2,52 MPa para o conglomerado, 1,84 MPa para o arenito muito fino e 1,43 MPa para o arenito médio. Foi realizada uma avaliação de intervalos de confiança de valores de tensão de adesão, conforme a distribuição t-student. Concluiu-se que não apenas a resistência das rochas influencia nessa capacidade de adesão, mas também a capacidade de absorção d’água e a porosidade. Maiores valores dessas duas propriedades na rocha favorecem a adesão entre os dois materiais. Os valores encontrados em laboratório são compatíveis com dados de literatura de campo em rochas similares. / This dissertation evaluates the determination of the adhesion parameter between cement grout and rock. This parameter is of great importance on design of two systems frequently executed that use the technique of anchoring: rock anchors and bolts. Pull out field tests are commonly carried out to evaluate this bond strength, however, they are normally only economically feasible during the construction stage. The Composite Cylinder Bond Test (CCBT) methodology allows the adhesion determination in a simpler and cheaper way, by laboratory tests using mixed samples of rock and cement grout. Therefore, the CCBT is an interesting alternative to project definition of adhesion values. In this context, three different sedimentary lithologies from Caçapava do Sul/RS, Southern Brazil, were studied. The lithologies – called here as conglomerate, fine sandstone and medium sandstone – belong to Varzinha Formation. The characterization of these lithologies were made by thin sections and characterization laboratory tests The textural classification of the conglomerate was sandy conglomerate, the fine sandstone was classified as muddy sandstone, and the medium sandstone was classified as sandstone. In the view of their composition, the fine sandstone was classified as arkose, while the medium sandstone was classified as lithic arkose. Ninety CCBT tests, besides unconfined compression tests on rock and cement grout specimens were carried out. The average adhesion values obtained from laboratory tests were 2,52 MPa for the conglomerate, 1,84 MPa for the fine sandstone and 1,43 MPa for the medium sandstone. An evaluation of confidence intervals of adhesion was also carried out, according to t-student distribution. It was concluded that the adhesion strength was influenced not only by the unconfined compressive strength of the rocks, but also by their water absorption and porosity. Larger values of these two properties increased the adhesion between the two materials. The values obtained from laboratory tests are compatible with literature field data in similar rocks.

A presente dissertação versa sobre a determinação do parâmetro de adesão entre nata de cimento e rocha. Este parâmetro é de fundamental importância no dimensionamento de grampos e tirantes ancorados, sistemas de contenção frequentemente executados que utilizam da técnica de ancoragem. Ensaios de arrancamento in loco são comumente realizados para avaliar essa tensão de aderência, no entanto, muitas vezes, apenas se tornam viáveis financeiramente durante a etapa de execução das obras. A metodologia Composite Cylinder Bond Test (CCBT) permite a determinação da adesão de maneira mais simples e com menor custo, por meio de ensaios de laboratório utilizando corpos de prova mistos de rocha e nata de cimento, sendo, por isto, uma interessante alternativa para a etapa de definição paramétrica de projetos. Neste contexto, foram estudadas três litologias sedimentares do município de Caçapava do Sul/RS – aqui chamadas de conglomerado, arenito muito fino e arenito médio – pertencentes à Formação Varzinha. A caracterização dessas litologias foi realizada por meio de lâminas delgadas e outros ensaios de caracterização de laboratório A classificação textural do conglomerado é de conglomerado arenoso, o arenito muito fino é classificado como arenito lamoso e o arenito médio é classificado como arenito. Do ponto de vista composicional, o arenito muito fino é classificado como arcóseo, enquanto o arenito médio é classificado como arcóseo lítico. Noventa ensaios CCBT, além de ensaios de resistência à compressão simples das rochas e da nata de cimento foram realizados. As tensões de adesão médias obtidas dos ensaios de laboratório foram de 2,52 MPa para o conglomerado, 1,84 MPa para o arenito muito fino e 1,43 MPa para o arenito médio. Foi realizada uma avaliação de intervalos de confiança de valores de tensão de adesão, conforme a distribuição t-student. Concluiu-se que não apenas a resistência das rochas influencia nessa capacidade de adesão, mas também a capacidade de absorção d’água e a porosidade. Maiores valores dessas duas propriedades na rocha favorecem a adesão entre os dois materiais. Os valores encontrados em laboratório são compatíveis com dados de literatura de campo em rochas similares. / This dissertation evaluates the determination of the adhesion parameter between cement grout and rock. This parameter is of great importance on design of two systems frequently executed that use the technique of anchoring: rock anchors and bolts. Pull out field tests are commonly carried out to evaluate this bond strength, however, they are normally only economically feasible during the construction stage. The Composite Cylinder Bond Test (CCBT) methodology allows the adhesion determination in a simpler and cheaper way, by laboratory tests using mixed samples of rock and cement grout. Therefore, the CCBT is an interesting alternative to project definition of adhesion values. In this context, three different sedimentary lithologies from Caçapava do Sul/RS, Southern Brazil, were studied. The lithologies – called here as conglomerate, fine sandstone and medium sandstone – belong to Varzinha Formation. The characterization of these lithologies were made by thin sections and characterization laboratory tests The textural classification of the conglomerate was sandy conglomerate, the fine sandstone was classified as muddy sandstone, and the medium sandstone was classified as sandstone. In the view of their composition, the fine sandstone was classified as arkose, while the medium sandstone was classified as lithic arkose. Ninety CCBT tests, besides unconfined compression tests on rock and cement grout specimens were carried out. The average adhesion values obtained from laboratory tests were 2,52 MPa for the conglomerate, 1,84 MPa for the fine sandstone and 1,43 MPa for the medium sandstone. An evaluation of confidence intervals of adhesion was also carried out, according to t-student distribution. It was concluded that the adhesion strength was influenced not only by the unconfined compressive strength of the rocks, but also by their water absorption and porosity. Larger values of these two properties increased the adhesion between the two materials. The values obtained from laboratory tests are compatible with literature field data in similar rocks.

Os pontos com maior fragilidade em estruturas de madeira são as ligações, pois nelas ocorrem as maiores concentrações de tensões. Dentre os tipos de conectores mais utilizados nas ligações temos os pinos metálicos, no quais se enquadra o parafuso comum. Para o dimensionamento de ligações por pinos metálicos, dois parâmetros são utilizados: a resistência ao escoamento do aço e a resistência da madeira ao embutimento. O objetivo deste trabalho foi comparar os métodos de ensaio de documentos normativos (ABNT NBR 7190:1997, EN 383:2007, ASTM D5764:2007, EUROCODE 5:2004, NDS:2001 e LRFD:1996) com a finalidade de estabelecer uma proposta de método de ensaio para a determinação da resistência da madeira ao embutimento. Foram realizados ensaios na direção paralela e na direção normal às fibras para seis espécies de madeira (Paricá, Pinus elliottii, Pinus oocarpa, Jatobá, Lyptus e Cupiúba), utilizando vários diâmetros (8 mm, 10 mm, 12 mm e 16 mm) para os pinos metálicos. Baseado na análise dos resultados obtidos foi proposta a adoção do método de ensaio baseado na EN 383:2007. Os resultados experimentais para a resistência ao embutimento tem maior aprovação com o parâmetro resistência à compressão paralela às fibras, atualmente adotado pela ABNT NBR 7190:1997. Além disso, esse método recomenda dimensões que facilitam a confecção dos corpos de prova, principalmente na direção normal às fibras. / Main fragility in timber structures occurs in the connections, because to stress concentrations. Most of connections use bolts laterally loaded, a metal dowel-type fastener. Two parameters are used for design of the connections with metal dowel-type in timber structures: yield strength of metal dowel and embedment strength of wood. The aim of this study was to compare the test methods of Codes (ABNT NBR 7190:1997, EN 383:2007, ASTM D5764:2007, EUROCODE 5:2004, NDS:2001 and LRFD:1996) in order to establish a proposed test method for the determination of the embedment strength of wood. The tests were performed applying load in the direction parallel and in the direction perpendicular to the grain for six species of wood (Paricá, Pinus elliottii, Pinus oocarpa, Jatobá, Lyptus and Cupiúba) using several diameters (8 mm, 10 mm, 12 mm and 16 mm) for the metal dowels. Based on the analysis of the results, is proposed adopting the test method based on EN 383:2007. The experimental results for the embedment strength has better fit with the strength parameter currently used by ABNT NBR 7190:1997, compression parallel to the grain. In addition, this method recommends dimensions that facilitate the specimens preparation, mainly in the direction perpendicular to the grain.

Orientador: Itamar Ferreira / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Mecanica / Made available in DSpace on 2018-08-12T15:59:53Z (GMT). No. of bitstreams: 1 Marcelo_AndreLuiz_M.pdf: 9740567 bytes, checksum: 965e448ceb0965ed5555dfa95cc7f5c6 (MD5) Previous issue date: 2008 / Resumo: Parafusos de alta resistência mecânica (classe ISO 10.9) fabricados com dois aços de origens diferentes são utilizados para investigar a influência da temperatura de revenido, da seqüência do processo de fabricação (laminação da rosca antes e após o tratamento térmico) e da quantidade de inclusões contidas no aço, no limite de fadiga e também qual o critério de falha por fadiga existente na literatura que melhor se aplica a parafusos de alta resistência mecânica com laminação da rosca antes do tratamento térmico. Parafusos M8 com rosca grossa foram divididos em sete grupos diferentes, três fabricados com aço nacional (AISI 4135) e tratados termicamente após laminação da rosca com temperaturas de revenido 490, 520 e 550 ºC, e quatro fabricados com aço japonês (SCM 435H), porém, desses quatro grupos, três foram idênticos aos fabricados com aço nacional e um último grupo teve a rosca laminada após tratamento térmico, com temperatura de revenido de 550 ºC. Nesses grupos foram realizadas análises metalográficas e de micro-inclusões, ensaios de tração, microdureza Vickers e fadiga e, por último, uma análise fratográfica dos parafusos que falharam durante o ensaio de fadiga, utilizando microscopia eletrônica de varredura. Os ensaios de fadiga foram realizados com pré-carga constante de 700 MPa, razão de carga por volta de 0,8, e utilizando o método estatístico "staircase" para a determinação do limite de fadiga. Além disso, foram realizados alguns ensaios de fadiga adicionais, com baixa razão de carga, 1 , 0 ??R , para um grupo específico, com a finalidade de analisar os critérios de falha por fadiga já existentes. A análise metalográfica revelou que em todos os grupos a microestrutura característica foi martensita revenida e a única diferença foi encontrada no grupo com laminação da rosca após tratamento térmico que apresentou linhas de laminação muito bem definidas nos contornos dos filetes da rosca. A análise de micro-inclusões mostrou que o aço nacional possui uma quantidade de inclusões muito superior ao aço japonês. Os ensaios de microdureza e de tração revelaram que os parafusos com laminação da rosca após tratamento térmico possuem níveis de resistência mecânica inferior somente aos grupos revenidos a 490 ºC. Todos os grupos com laminação da rosca antes do tratamento térmico apresentaram praticamente o mesmo limite de resistência à fadiga, mostrando que, neste caso, variações de até 60 ºC no tratamento de revenido não interferiram no limite de fadiga. Por outro lado, o grupo com laminação da rosca após tratamento térmico apresentou um limite de fadiga de aproximadamente 9% superior ao grupo tratado nas mesmas condições, porém com laminação da rosca antes do tratamento térmico. Esta melhora está relacionada ao alinhamento dos grãos nos contornos dos filetes da rosca e à introdução de tensões residuais de compressão na superfície da rosca. Com os ensaios de fadiga adicionais, foi possível mostrar que o critério que mais se ajusta a parafusos de alta resistência mecânica com laminação da rosca após tratamento térmico é o VDI 2230, que apresenta uma tensão alternada constante independente da razão de carga. / Abstract: High strength bolts, class ISO 10.9, were manufactured with two different steels in order to investigate the influence of tempering temperature, the sequence of manufacture process (threads rolled before and after heat treatment), and the inclusions amount contained in steels, in the bolt fatigue behavior and also what criterion of fatigue failure existent in literature is the best for application on high strength bolts with the threads rolling before heat treatment. M8 bolts with coarse threads were separated in seven different groups, three manufactured with Brazilian steel (AISI 4135) and heat treated, after the process of thread rolling, with tempering temperatures of 490, 520, and 550 ºC, and four groups were manufactured with Japanese steel (SCM 435H), however, three groups were identical of the bolts manufactured with national steel and a last one group had the threads rolled after heat treatment with tempering temperature of 550 ºC. In all groups were carried out metallographic and inclusion analyses, tension, microindentation hardness, and fatigue tests, and a fractographic analysis of bolts failed in the fatigue tests, using a scanning electron microscope. The fatigue tests were carried out with constant preload of 700 MPa, stress ratio about 0.8, and it was used the staircase statistical method for determine the fatigue limit. Besides, additional fatigue tests were carried out, with low stress ratio ( 1 . 0 ??R ), in order to analyze the existents criteria of fatigue failure. The results of metallographic analysis showed that the characteristic microstructure in all groups was tempered martensite and the only difference between the groups was the alignment of the grains around the root of the thread that occurred in the group which was heat treated before the threads rolling. The inclusion analysis revealed that the Brazilian steel has an amount of inclusions very superior than Japanese steel. The tension and microindentation hardness tests showed that the bolts with threads rolling after heat treatment have strength level lower than solely the groups tempered at 490 ºC. All the groups with threads rolling before heat treatment presented practically the same fatigue limit. It shows that variations of up to 60 ºC in the tempering temperature don't interfere in the fatigue limit. On the other hand, the group with threads rolling after heat treatment presented fatigue limit approximately 9% superior than the group treated in the same conditions, however with threads rolling before heat treatment. This improve is related with the alignment of the grains around the root of the thread and the introduction of residual compressive stress near the surface of the bolts. With the results of the additional fatigue tests, it was possible to analysis some criteria of fatigue failure and show that the best criterion of failure, existent in the literature, for high strength bolts with thread rolling after heat treatment is the VDI 2230, which presents a constant alternating stress independently of the stress ratio. / Mestrado / Materiais e Processos de Fabricação / Metre em Engenharia Mecanica

Submitted by Cláudia Bueno (claudiamoura18@gmail.com) on 2016-03-31T19:38:48Z No. of bitstreams: 2 Dissertação - Jeovan Pereira das Virgens - 2015.pdf: 10009095 bytes, checksum: a8f3d2a6914adbb0c7cdcf49732ffc57 (MD5) license_rdf: 23148 bytes, checksum: 9da0b6dfac957114c6a7714714b86306 (MD5) / Approved for entry into archive by Luciana Ferreira (lucgeral@gmail.com) on 2016-04-04T11:45:04Z (GMT) No. of bitstreams: 2 Dissertação - Jeovan Pereira das Virgens - 2015.pdf: 10009095 bytes, checksum: a8f3d2a6914adbb0c7cdcf49732ffc57 (MD5) license_rdf: 23148 bytes, checksum: 9da0b6dfac957114c6a7714714b86306 (MD5) / Made available in DSpace on 2016-04-04T11:45:04Z (GMT). No. of bitstreams: 2 Dissertação - Jeovan Pereira das Virgens - 2015.pdf: 10009095 bytes, checksum: a8f3d2a6914adbb0c7cdcf49732ffc57 (MD5) license_rdf: 23148 bytes, checksum: 9da0b6dfac957114c6a7714714b86306 (MD5) Previous issue date: 2015-10-16 / This paper presents the experimental study of reinforcement concrete columns reinforced with wedge bolts and a 35 mm self compacting concrete jacket at the most compressed face. Nine columns with a 2000 mm height subjected to flexure and bending with initial eccentricity of 60 mm, named as: original column (Po) with a cross section of 120 mm x 250 mm; reference column (Pref) with a cross section of 155 mm x 250 mm and seven columns with a initial cross section of 120 mm x 250 mm, and later reinforced by the addition of 35 mm reinforcing layer, and various configurations of wedge bolts at its most compressed face. Except for the original column (Po), the columns were submitted to a 42.5 mm load eccentricity due to the attached concrete layer at the compressed face. Although failure of the wedge bolts did not accour, it was not possible to prevent detachment of the reinforcing layer. The results indicate that it is possible to structural rehabilitate reinforce concrete columns with the use of the strengthening methodology used in this research, resulting in average load capacity gains of 3,71 times compared to original column load (Po). / O presente trabalho apresenta o estudo experimental de pilares de concreto armado reforçados com parafusos chumbadores e acréscimo de camada com 35 mm de concreto autoadensável na face comprimida. Nove pilares, com alturas de 2000 mm, foram submetidos à flexão composta reta com excentricidade inicial de 60 mm, assim discriminados: um pilar original (Po) com seção transversal de 120 mm x 250 mm; um pilar de referência (Pref) com seção transversal de 155 mm x 250 mm e sete pilares, inicialmente moldados com seção transversal de 120 mm x 250 mm, e após, reforçados através da adição de camada de reforço de 35 mm e diversas configurações de posições de parafusos chumbadores na face comprimida. Exceto o pilar original (Po), os pilares foram submetidos à excentricidade inicial de carga de 42,5 mm, devido ao acréscimo da camada de reforço na face comprimida. Apesar de não ocorrer ruptura dos parafusos chumbadores, não foi possível evitar o desplacamento da camada de reforço. Os resultados obtidos indicam que é possível a reabilitação estrutural de pilares de concreto armado com o uso da metodologia de reforço empregada, obtendo ganho de capacidade de carga média de 3,71 vezes em relação ao pilar original (Po).

Submitted by Erika Demachki (erikademachki@gmail.com) on 2015-03-05T20:16:17Z No. of bitstreams: 2 Dissertação - Marília Gonçalves Marques - 2014.pdf: 6536401 bytes, checksum: 080ea60c6004cee2f33a28aab0065b39 (MD5) license_rdf: 23148 bytes, checksum: 9da0b6dfac957114c6a7714714b86306 (MD5) / Approved for entry into archive by Erika Demachki (erikademachki@gmail.com) on 2015-03-05T20:16:35Z (GMT) No. of bitstreams: 2 Dissertação - Marília Gonçalves Marques - 2014.pdf: 6536401 bytes, checksum: 080ea60c6004cee2f33a28aab0065b39 (MD5) license_rdf: 23148 bytes, checksum: 9da0b6dfac957114c6a7714714b86306 (MD5) / Made available in DSpace on 2015-03-05T20:16:35Z (GMT). No. of bitstreams: 2 Dissertação - Marília Gonçalves Marques - 2014.pdf: 6536401 bytes, checksum: 080ea60c6004cee2f33a28aab0065b39 (MD5) license_rdf: 23148 bytes, checksum: 9da0b6dfac957114c6a7714714b86306 (MD5) Previous issue date: 2014-04-11 / Strengthening of reinforced concrete columns by jacketing is one of the most common structural rehabilitation techniques in Brazil. For adequate performance, it is necessary, among others, to avoid detachment of the new concrete layer (strengthening material) from the old concrete substrate when the strengthened member is again in service conditions. This paper describes the test results of eight reinforced concrete rectangular columns subjected to combined compression and one-axis bending to evaluate the efficiency of using sleeve wedge bolts across the new concrete/old concrete interface to avoid detachment. The strengthening technique, in this case, consisted of adding a layer of self-compacting concrete to one column face. Two columns tested were monolithic and named PO (original column) e PR (reference column). The other six columns were strengthened using a new 35 mm thick self-compacting concrete layer attached to the column face subjected to highest compressive stresses. Column PO had a 120mm by 250 mm rectangular cross section and its results gave information about column behavior without the use of strengthening. Column PR had a 155mm by 250 mm rectangular cross section and its cross section dimensions matched the strengthened columns but it was cast monolithically. To improve bond conditions between the existing concrete and the new concrete, the concrete surface was roughened and the outermost aggregate was exposed using hydro jetting. Holes along the concrete surface were made to insert the wedge bolts responsible for increasing the bond between the two concrete surfaces. The difference among the six strengthened columns consisted in the position and amount of bolts used. Results indicate the position and amount of the bolts significantly alters the strength capacity of the strengthened columns since premature rupture by concrete detachment was delayed. The reinforcement used was increased approximately three times the ultimate load of the original column, indicating the good performance of reinforcement. / ANÁLISE DO COMPORTAMENTO DE PILARES DE CONCRETO ARMADO REFORÇADOS COM CHUMBADORES E CONCRETO AUTO ADENSÁVEL O reforço de pilares de concreto armado por encamisamento é uma das técnicas de reabilitação estrutural mais utilizada no Brasil. Para que este tipo de intervenção funcione, é preciso entre outras coisas evitar o desplacamento entre o concreto adicionado (material do reforço) e o concreto antigo (substrato) quando a peça reabilitada é colocada novamente em serviço. Neste trabalho são descritos os resultados dos ensaios de oito pilares de concreto armado, submetidos à flexo-compressão reta, com o intuito de avaliar a eficiência do uso de chumbadores metálicos cruzando a interface de ligação entre os concretos moldados em idades distintas, para evitar o desplacamento entre estes materiais. Dos oito pilares ensaiados, dois eram referências e foram denominados de PO (pilar original) e PR. (pilar referência). Os outros seis foram reforçados acrescentando-se uma camada de concreto auto-adensável de 35 mm à face comprimida. O pilar PO, tinha seção transversal de 120 x 250 mm, e forneceu informações sobre o comportamento da peça antes da execução do reforço. O pilar PR tinha seção transversal de 155 x 250 mm, e forneceu informações sobre o comportamento de uma peça monolitica de seção idêntica a dos pilares após o reforço. Para executar a intervenção, inicialmente escarificou-se, por hidrojateamento, a zona de interface a ser formada pelo contato entre o concreto do reforço e do substrato. Posteriormente, fizeram-se furos ao longo desta superfície, onde foram inseridos os chumbadores mecânicos responsáveis por aumentar a aderência entre os concretos. A diferença entre os seis pilares reforçados consistia justamente na variação da posição e da quantidade dos chumbadores usados em cada peça. Os resultados obtidos indicaram que a quantidade e a posição destes chumbadores interferiram significativamente na capacidade portante dos pilares reforçados, pois retardavam a ocorrência de uma ruptura prematura por desplacamento entre os concretos do reforço e do substrato. O reforço utilizado aumentou aproximadamente três vezes a carga de ruptura do pilar original, indicando o bom desempenho do reforço.

Har du någonsin åkt genom en tunnel och undrat hur det kommer sig att det tunga berget över dig inte kollapsar in i detta hålrum? Har du lagt märke till underliga metallpinnar som sticker ut ur väggar och tak? Dessa metallpinnar är bultar, och de är en del av säkerhetsåtgärderna som ser till att tunnlar över hela Sverige är säkra att färdas i. När en tunnel byggs är det viktigt att ta reda på vilka egenskaper som berget har för att kunna avgöra hur stora säkerhetsåtgärder som bör implementeras. Dessa egenskaper kan vara sådant som sprickors utbredning och orientering, hur mycket vatten som finns i sprickorna, vad berget består av och krafter som påverkar berget. Säkerhetsarbetet kring tunnlar kan göra skillnaden mellan liv och död, men hur ska man forska kring detta? I ett labb kan man med hjälp av en modell undersöka vad som fungerar bäst, men även det minsta möjliga för att förhindra kollaps. I detta arbete har en modell som representerar ett tunneltak använts. Den används till undervisning för förståelse av bultar. Modellen var en upphöjd stålram med avtagbar botten, stålramen var kvadratisk med 82 cm sidolängd. I denna ram placerades skruvar och järnvägsmakadam för att simulera ett tunneltak med bultar i mindre skala. Järnvägsmakadam är krossat berg med en kornstorlek på ca 32 till 64 mm. Skruvarna trycker ihop makadamen med hjälp av brickor för att tryck ska uppstå och trycket mäts med tryckgivare som är placerade i modellen. Arbetet som har utförts med hjälp av modellen syftar till att utveckla metoder för hur sådana försök bör utföras i framtiden. Tidigare försök har gjorts och då har det observerats att denna modell har varit stabil när skruvarna spänts till 7 Nm (Newtonmeter) vridmoment och att den kollapsade av minimal påverkan när skruvarna spändes till 5 Nm. Därför gick vi in i detta arbete med hypotesen att modellens lägre gräns för stabilitet fanns strax under 5 Nm. Vid de tidigare försöken mättes inte trycket i modellen och vi hade därför ingen hypotes om detta. Försöken utfördes på olika vis. Skruvarna spändes i olika mönster och med olika vridmoment, makadamen placerades också på olika sätt när modellen byggdes upp. Som resultat ställdes vridmoment och tryck upp i tabeller och diagram. Det skulle visa sig att hypotesen om att den lägre gränsen var nära 5 Nm vridmoment inte stämde. Modellen hölls uppe även när skruvarna endast spändes till 2 Nm. Både när modellens bottenlager var fördelaktigt och ofördelaktigt uppbyggt ur ett stabilitetsperspektiv så höll modellen vid 2 Nm. Lägre vridmoment än 2 Nm kunde inte testas i brist på känsligare verktyg. / Have you ever traveled through a tunnel and wondered why the heavy rock above you doesn’t collapse on top of you? Have you noticed the odd metal rods that sticks out from the walls and ceiling? These metal rods are bolts, a part of the security measures that make sure that tunnels all over Sweden are safe to travel through. When a tunnel is built, it is important to know the properties of the rock to be able to assess what type of security measures that need to be applied. These properties can be fractures and their orientation, the composition of the rock and the forces that are present. The security work regarding tunnels can be the difference between life and death, but how can research in this field be carried out? Model experiments in a laboratory can be of great use to investigate the most efficient way to stabilize the rock, but also the minimal effort required to prevent collapse. For this report a model that represents the roof of a tunnel has been used. The model is used for learning about rock bolts and consisted of an elevated 82 cm square steel frame with a detachable floor. Bolts and crushed rock were placed within the frame to simulate a tunnel roof in a smaller scale. The crushed rock had a grain size of 32 to 64 mm. The bolts in combination with small metal discs compress the rock to produce pressure, and the induced pressure is measured with pressure indicators placed within the model. The experiments conducted with this model aims to develop potential new methods for future uses and experiments. Previous experiments with this type of model have shown that the model is stable when the bolts have been tightened to 7 Nm (Newton Meters) torque, and subsequently collapsed with minimal influence when the bolts were tightened to 5 Nm. Therefore, the hypothesis of this report was based on previous experiments, where the lower limit of the model seemed to be close to 5 Nm. The previous experiments didn’t measure the pressure throughout the strained rock mass, and therefore there is no hypothesis regarding this. The experiments were conducted in different ways. The bolts were tightened both in different patterns and with different torques, and the crushed rock were placed differently throughout the experiments as the model was being built. The following result of torque and pressure were presented in tables and graphs. The result showed that the hypothesis regarding the lower boundary being close to 5 Nm was not correct. The model stayed in place even when the bolts were tightened as low as 2 Nm. The model was stable at 2 Nm both with a favorable and unfavorable bottom layer of rock. Therefore, it is required to tension the bolt with torque lower than 2 Nm to determine the lower limit of stability, but that could not be tested due to the lack of proper tools.