During construction of dams, rock bolts are in general installed in the interface between concrete and rock as an extra safety measure against overturning failure. These bolts are however not allowed to be taken into consideration for the stability calculations of large dams. New standards and new design criterias have increased the requirements of the safety of the old dams, leading to a need for expensive rehabilitation and strengthening. It is possible that consideration of these bolts in stability calculations may lead to money being saved. In order to do so more information about the long term strength of these bolts is needed. One way of getting this information has been the destructive testing of old dugout bolts found during reconstruction works. At the Lima hydropower station in Sweden, this kind of testing was made. The test rig used had a design where a piston pressed down on the rock around the bolt in order to pull it out. The question was raised if this could affect the failure load of the bolt. In this thesis, an attempt was made to answer this question using finite element methods. Models of a rock bolt was made in Abaqus, where one model included the piston and one where it was not. The connection between the bolt and the rock was modelled with nonlinear springs and friction, and the results were then compared between the cases and with experimental data. The results showed that the resulting force-deformation curves may be affected by the piston in cases where the dominant failure mode was adhesive failure, which would influence failure loads and deformations. Since so little was known about the properties of the rock and grout at Lima however, it is difficult to say to which extent the test rig has affected these results.

Made available in DSpace on 2014-07-29T15:03:36Z (GMT). No. of bitstreams: 1 pretext.pdf: 126548 bytes, checksum: 75b886ac104c5eb27a1e4f83ca04924f (MD5) Previous issue date: 2008-10-28 / The reinforced concrete structures are subject to interference from many factors that affect its stability and its performance and may generate the need for interventions and eventual reinforcement. There are several techniques of enhancing that can be employed and in the case of columns, the increase of the section with reinforced concrete is quite usual. This type of enhancement requires the attendance requirements to ensure its effectiveness, among which stand out in importance: meeting the needs and characteristics of project, the appropriate sizing, and the adhesion between concrete of different ages. Although the reinforcement of structures involve risk situations, and in many cases, are costly and uncertain, does not exist in the country a specific normalization for their specific design and implementation, thus they have been executed considering the normative disposals for project and execution of structures of armed concrete and in personal experiences. This research was evaluated the behavior of reinforced concrete columns required to flexural compression, with an initial section of 120 mm x 250 mm and height of 2000 mm in the compressed section and enhanced with a layer of 35 mm of self compact concrete and anchors. Was varied the amount of anchors and kept the other variables such as the concrete strength of the original columns and the enhanced columns, the initial rate of reinforcement, the eccentricity of the load test, the thickness of the reinforcement and the preparation of the substratum method. The strengthened columns had presented increasing load by increasing the amount of anchors used in the interface between the concrete of different ages. The improvement in the performance of the interface was observed, slowing the sputting and in one case, the column with a larger amount of anchors, with the crushing of concrete and sputting, almost simultaneously. There was a reduction of displacements caused by the decrease in ductility. These evidences indicate that the adopted technique of reinforcement if showed efficient, promoting consolidation of the composed section better / As estruturas de concreto armado estão sujeitas à interferência de diversos fatores que alteram sua estabilidade e seu desempenho podendo gerar a necessidade de intervenções e eventualmente reforço. Diversas são as técnicas de reforço que podem ser empregadas e, no caso dos pilares, o aumento da seção com concreto armado é bastante usual. Esse tipo de reforço exige o atendimento a requisitos que garantam a sua eficácia, dentre os quais se destacam em importância: o atendimento às necessidades e características de projeto; o adequado dimensionamento; e a aderência entre concretos de diferentes idades. Apesar de o reforço de estruturas envolver situações de risco e, em muitos casos, ser oneroso e incerto, não existe no país uma normalização específica para seu projeto e execução; assim têm sido executados considerando as disposições normativas para projeto e execução de estruturas de concreto armado e em experiências pessoais. Nesta pesquisa foi avaliado o comportamento de pilares de concreto armado solicitados à flexo-compressão reta, com uma seção inicial de 120 mm x 250 mm e altura de 2000 mm e reforçados na região comprimida com uma camada de 35 mm de concreto auto-adensável e chumbadores. Foi variada a quantidade de chumbadores e mantidas as demais variáveis como: as resistências dos concretos dos pilares originais e do reforço, a taxa de armadura inicial, a excentricidade de ensaio do carregamento, a espessura da camada de reforço e o método de preparação do substrato. Os pilares reforçados apresentaram ganhos crescentes de carga com o aumento da quantidade de chumbadores utilizada na interface entre os concretos de diferentes idades. Foi observada melhora no desempenho da interface, retardando o desplacamento e em um dos casos, no pilar com maior quantidade de chumbadores, ocorrendo o desplacamento e esmagamento do concreto quase simultaneamente. Houve redução dos deslocamentos horizontais dos pilares, provocada pela diminuição da ductilidade. Estas evidências indicam que a técnica de reforço adotada se mostrou eficiente, promovendo melhor consolidação da seção composta