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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
21

Comportamento de um solo residual levemente cimentado : estimativa de capacidade de carga para estacas submetidas a esforços transversais

Carretta, Mariana da Silva January 2018 (has links)
Fundações profundas, quando solicitadas ao carregamento lateral, são regidas por três critérios de projeto: resistência última do solo, carga última do elemento estrutural e deflexão máxima. Esses critérios atuam em conjunto e é necessário que sejam analisados dessa forma, visto que a falha de um deles é capaz de acarretar o colapso de todo sistema. No que tange à resistência do solo, metodologias de capacidade de carga existentes traduzem o comportamento de solos granulares e coesivos. Dada a particularidade da atuação de solos residuais na mecânica dos solos, não há uma metodologia abrangente para estacas sujeitas a solicitação de carregamento lateral nesse tipo de solo, o qual apresenta comportamento intermediário e estrutura levemente cimentada. Em vista disso, o presente trabalho propõe um método de estimativa de capacidade de carga para estacas carregadas horizontalmente, quando inseridas em solo residual e em casos em que as mesmas apresentam topo locado em superfície de solo tratado. Dessa forma, dados de provas de carga lateral pré-existentes e ensaios de laboratório executados ao longo da pesquisa serviram como base para a proposição do método, fundamentado no comportamento do material quando solicitado ao carregamento lateral Ensaios de resistência à compressão simples, compressão oedométrica, compressão isotrópica e ensaios triaxiais com medidas de módulo cisalhante demonstram que há um ponto em que se dá a quebra da estrutura cimentada do solo, passando o mesmo a se apresentar num arranjo desestruturado, refletido em maiores deformações. Uma relação linear é capaz de equacionar a capacidade de carga, tanto para estacas inseridas em solo residual quanto para estacas executadas em solo com camada superficial melhorada. Essa relação é estabelecida entre a carga de ruptura das estacas ensaiadas e a área de solo adjacente à mesma, mobilizada pelo carregamento. Os resultados demonstram que a capacidade de carga das estacas estudadas é regida pela tensão de plastificação do material. O equacionamento proposto possibilita a obtenção da carga de ruptura com base em ensaios simples e de fácil execução, tal como o ensaio de resistência à compressão simples que estabelece relação direta com a tensão de plastificação do solo estudado. / Deep foundations, when requested to lateral loading, are governed by three design criteria: ultimate soil strength, piles’ ultimate load, and maximum deflection. These criteria act together and must be analyzed in this way, since the failure of one of them is capable of causing the collapse of the entire system. Regarding soil resistance, the current bearing capacity methodologies describe the behavior of granular and cohesive soils. Given the particular behavior of the residual soils in the soil mechanics, there is no comprehensive methodology for piles subject to lateral loads and inserted in this soil type, which presents an intermediate behavior and a lightly cemented structure. Thus, the present work proposes an estimated bearing capacity for crosswise loaded piles, when inserted in residual soil and in soil with the top layer cemented. So, data from preexisting lateral loading tests and laboratory tests, performed during the research, served as a basis for the proposition of the method, based on the behavior of the material when requested to lateral loading Unconfined compression tests, oedometer consolidation tests, isotropic compression, and triaxial tests with measures of shear modulus demonstrate that there is a point where the soil's cemented structure breaks down, presenting itself in a destructured arrangement, reflected by larger strains. A linear relationship is capable of equating the bearing capacity for both, piles inserted in residual soil and piles carried out in soil with improved surface layer. This relationship is established between the rupture load of the piles tested and the area of soil adjacent to it mobilized by the loading. The results shows that the piles' bearing capacity is governed by the yield stress of the material. The proposed equation makes it possible to obtain the rupture load based on simple and easy tests, such as the unconfined compression test that establishes a direct relationship with the yield stress of the studied soil.
22

Efeito de grupo em estacas carregadas transversalmente associadas a solos melhorados

Born, Ricardo Bergan January 2015 (has links)
O conjunto estaca-solo submetido a carregamentos horizontais é caracterizado por um comportamento não-linear. A propagação das tensões no solo próximo à estaca decai rapidamente em função do espaçamento, porém para estacas próximas, caracterizando um grupo de estacas, pode haver uma sobreposição de tensões, gerando zonas com tensões elevadas, que formam áreas de plastificação maiores. A interação da sobreposição destas zonas plastificadas, resultam em maiores deformações para o grupo de estacas, ante comparadas com o equivalente de soma da capacidade individual de cada estaca (Chaudhry, 1994). Deste comportamento, deriva-se o chamado efeito de grupo, que age como um redutor da eficiência total das estacas. Através de modelos numéricos tridimensionais, avaliou-se o efeito de espaçamento entre estacas em solo natural, onde fatores de eficiência do grupo foram propostos. O comportamento de estacas carregadas lateralmente é conhecido por ter seu comportamento diretamente relacionado com as características da parte superior do solo. Recomendações feitas há mais de 30 anos já lidavam com este comportamento {e.g. Simons eMenzies (1975); Broms (1972)}, e tratavam com soluções que melhoravam a capacidade de carga lateral, com a substituição da parte superior do solo por um material mais rígido. Embora estas soluções melhorassem a capacidade de carga lateral, a técnica reflete uma prática de substituição de material. Neste trabalho, uma técnica de melhoramento de solo, lidando com areia cimentada é apresentada, estudando numericamente o comportamento de grupos de estacas submetidos a carregamentos laterais. As conclusões apontam fatores de eficiência próximos a unidade em espaçamentos superiores a 6 diâmetros, porém com a tendência a inexistir somente em espaçamentos superiores a 10 diâmetros. A inserção da camada de solo cimento no topo do grupo de estaca, mostrou uma expressiva melhora de seu comportamento, eliminando por total a perda de eficiência devido ao efeito de grupo. / The soil-pile set when subjected to lateral loads is characterized by a non-linear behavior. The stress distribution on the soil near the pile decays rapidly in magnitude with radial distance, but for closely spaced piles within a group, these yielded zones of the soil around individual piles overlap, forming larger yielded zones in the soil surrounding the pile group. The interaction arising due to overlapping of these yielded zones results in a larger deflection for the group of piles before the lateral resistance equivalent to that for a single pile (Chaudhry, 1994). Based on this behavior, the group effect is derived, which acts as a reducer of the piles efficiency. Through tridimensional numerical models, the effects of the pile spacing in natural soil were evaluated, and group efficiency factors had been proposed. The behavior of laterally loaded piles is well known to be straightly related to characteristics of the upper part of the soil. Recommendations of over 30 years in past already dealt with this behavior {e.g. Simons and Menzies (1975); Broms (1972)}, and treated with solutions that improved the lateral resistance, by substituting the upper part of the soil with a more rigid material. Besides those solutions improved the lateral resistance, the technique reflects a practice of material replacement. Here, a ground improvement technique, dealing with cemented sand is presented, studying numerically the behavior of piles subjected to lateral forces. Conclusions shows group efficiency factors close to unity on spacing larger than 6 diameters, but tending to disappear only on spacing larger than 10 diameters. The insertion of a soil cement layer on the top of the pile group has shown an expressive improvement on its behavior, eliminating the loss of efficiency due to the group effect.
23

Computational Fluid Dynamics Simulations of Membrane and Resin-based Chromatography

Umatheva, Umatheny January 2019 (has links)
Many of the industrial processes, used by manufacturers to produce biologics, have not been significantly updated since their original design and conception. And thus, there is a great opportunity to update and optimize manufacturing processes. Downstream purification is often considered the bottleneck of the manufacturing process and when biologics are being purified for clinical applications, the final purity is paramount. As a result, pharmaceutical products are subjected to multiple concentration, conditioning, and chromatographic steps. The pharmaceutical industry is constantly and slowly evolving and is always looking to improve efficiency. Simulations and modeling are becoming more commonly used in the pharmaceutical industry as a tool to strategically design and test new production and separation processes developed at the research and development scale. In this thesis, computational fluid dynamics (CFD) modeling was used to develop more efficient bioseparation processes by (1) using a cuboid module geometry and (2) chromatographic medium with product-specific affinity ligands. The laterally-fed class of chromatography modules has a unique cuboidal geometry, with lateral feeding of the sample in the channel above the bed and lateral collection of permeate. CFD simulations and experimental results have shown that the laterally-fed class of chromatography devices can produce sharper elution peaks, have better peak resolution, and consequently purer product fractions than conventional membrane and resin-based chromatographic formats. The enhanced performance by the laterally-fed class of chromatography devices is attributed to improved system fluidics and narrow solute residence time distribution. One other approach to improving efficiency is to address the tradeoff between purity and recovered yield, due to the non-specific binding nature of many commercial resins and membranes. Purification using high-affinity biological ligands selected on specificity to the target molecule could be a feasible solution. A purification scheme for pertactin was developed with final eluate purity of 90% and approximately 100% recovery. / Thesis / Master of Applied Science (MASc)
24

Dynamic response of laterally-loaded piles

Thammarak, Punchet 20 October 2009 (has links)
The laterally-loaded pile has long been a topic of research interest. Several models of the soil surrounding a pile have been developed for simulation of lateral pile behavior, ranging from simple spring and dashpot models to sophisticated three-dimensional finite-element models. However, results from the available pile-soil models are not accurate due to inherent approximations or constraints. For the springs and dashpots representation, the real and imaginary stiffness are calculated by idealizing the soil domain as a series of plane-strain slices leading to unrealistic pile behavior at low frequencies while the three-dimensional finite-element analysis is very computationally demanding. Therefore, this dissertation research seeks to contribute toward procedures that are computationally cost-effective while accuracy of the computed response is maintained identical or close to that of the three-dimensional finite-element solution. Based on the fact that purely-elastic soil displacement variations in azimuthal direction are known, the surrounding soil can be formulated in terms of an equivalent one-dimensional model leading to a significant reduction of computational cost. The pile with conventional soil-slice model will be explored first. Next, models with shear stresses between soil slices, including and neglecting the soil vertical displacement, are investigated. Excellent agreement of results from the proposed models with three-dimensional finite-element solutions can be achieved with only small additional computational cost. / text
25

Lateral Resistance of H-Piles and Square Piles Behind an MSE Wall with Ribbed Strip and Welded Wire Reinforcements

Luna, Andrew I. 01 May 2016 (has links)
Bridges often use pile foundations behind MSE walls to help resist lateral loading from seismic and thermal expansion and contraction loads. Overdesign of pile spacing and sizes occur owing to a lack of design code guidance for piles behind an MSE wall. However, space constraints necessitate the installation of piles near the wall. Full scale lateral load tests were conducted on piles behind an MSE wall. This study involves the testing of four HP12X74 H-piles and four HSS12X12X5/16 square piles. The H-piles were tested with ribbed strip soil reinforcement at a wall height of 15 feet, and the square piles were tested with welded wire reinforcement at a wall height of 20 feet. The H-piles were spaced from the back face of the MSE wall at pile diameters 4.5, 3.2, 2.5, and 2.2. The square piles were spaced at pile diameters 5.7, 4.2, 3.1, and 2.1. Testing was based on a displacement control method where load increments were applied every 0.25 inches up to three inches of pile deflection. It was concluded that piles placed closer than 3.9 pile diameters have a reduction in their lateral resistance. P-multipliers were back-calculated in LPILE from the load-deflection curves obtained from the tests. The p-multipliers were found to be 1.0, 0.85, 0.60, and 0.73 for the H-piles spaced at 4.5, 3.2, 2.5, and 2.2 pile diameters, respectively. The p-multipliers for the square piles were found to be 1.0, 0.77, 0.63, and 0.57 for piles spaced at 5.7, 4.2, 3.1, and 2.1 pile diameters, respectively. An equation was developed to estimate p-multipliers versus pile distance behind the wall. These p-multipliers account for reduced soil resistance, and decrease linearly with distance for piles placed closer than 3.9 pile diameters. Measurements were also taken of the force induced in the soil reinforcement. A statistical analysis was performed to develop an equation that could predict the maximum induced reinforcement load. The main parameters that went into this equation were the lateral pile load, transverse distance from the reinforcement to the pile center normalized by the pile diameter, spacing from the pile center to the wall normalized by the pile diameter, vertical stress, and reinforcement length to height ratio where the height included the equivalent height of the surcharge. The multiple regression equations account for 76% of the variation in observed tensile force for the ribbed strip reinforcement, and 77% of the variation for the welded wire reinforcement. The tensile force was found to increase in the reinforcement as the pile spacing decreased, transverse spacing from the pile decreased, and as the lateral load increased.
26

The Influence of Pile Shape and Pile Sleeves on Lateral Load Resistance

Russell, Dalin Newell 01 March 2016 (has links)
The lateral resistance of pile foundations is typically based on the performance of round piles even though other pile types are used. Due to lack of data there is a certain level of uncertainty when designing pile foundations other than round piles for lateral loading. Theoretical analyses have suggested that square sections will have more lateral resistance due to the increased side shear resistance, no test results have been available to substantiate the contention. Full-scale lateral load tests involving pile shapes such as circular, circular wrapped with high density polyethylene sheeting, square, H, and circular with a corrugated metal sleeve have been performed considering the influence of soil-pile interaction on lateral load resistance. The load test results, which can be summarized as a p-y curve, show higher soil resistance from the H and square sections after accounting for differences in the moment of inertia for the different pile sections. The increased soil resistance can generally be accounted for using a p-multiplier approach with a value of approximately 1.25 for square or 1.2 for H piles relative to circular piles. It has been determined that high density polyethylene sheeting provides little if any reduction in the lateral resistance when wrapped around a circular pile. Circular piles with a corrugated metal sleeve respond to lateral loading with higher values of lateral resistance than independent circular piles in the same soil.
27

A Model Study On The Effects Of Wall Stiffness And Surcharge On Dynamic Lateral Earth Pressures

Cilingir, Ulas 01 July 2005 (has links) (PDF)
A model study on laterally braced sheet pile walls retaining cohesionless soil was conducted using 1-g shaking table. Lateral dynamic earth pressures, backfill accelerations and dynamic displacement of walls were measured. Input accelerations were kept between 0.03g to 0.27g. A data acquisition system consisting of dynamic pressure transducers, accelerometers, displacement transducer, signal conditioning board and a data acquisition card compatible with a personal computer was used during the study. Three different walls with thicknesses of 6.6, 3.2 and 2.0 mm were used in order to investigate the effects of changing wall stiffness value on lateral seismic pressures developed on the wall. In addition to that, steel blocks were placed on top of the backfill in order to simulate a surcharge effect of 1.57 kPa to 3.14 kPa during shaking. Amplification of input acceleration, incremental seismic lateral thrusts and corresponding maximum dynamic pressures, application point of the resultant, effect of stiffness and surcharge on maximum seismic lateral thrust and dynamic wall deflections were calculated by processing raw data stored. The results were compared to previous model studies and some analytical methods available.
28

Full-Scale Lateral-Load Tests of a 3x5 Pile Group in Soft Clays and Silts

Snyder, Jeffrey L. 15 March 2004 (has links) (PDF)
A series of static lateral load tests were conducted on a group of fifteen piles arranged in a 3x5 pattern. The piles were placed at a center-to-center spacing of 3.92 pile diameters. A single isolated pile was also tested for comparison to the group response. The subsurface profile consisted of cohesive layers of soft to medium consistency underlain by interbedded layers of sands and fine-grained soils. The piles were instrumented to measure pile-head deflection, rotation, and load, as well as strain versus pile depth.
29

Linear Instability Of Laterally Strained Constant Pressure Boundary Layer Flows

Tyagi, P K 09 1900 (has links)
The linear instability of laterally diverging/converging flows is an important aspect towards understanding the laminar-transition process in many viscous flows. In this work the linear instability of constant pressure laterally diverging/converging flow has been investigated. The laminar velocity field for laterally diverging/converging flows, under the source/sink approximation, has been reduced to two-dimensional flows. This reduction is alternative to the Mangier transformation used earlier. For a constant pressure laterally strained flow, the laminar velocity is found to be governed by the Blasius equation for flow over a flat plate. The non-parallel linear instability of constant pressure laterally strained flows has been examined. The instability equation is found to be same as that for the Blasius flow. This implies that the stability is same as that for the Blasius flow. A lateral divergence/convergence is shown to alter the Reynolds number from that in a two-dimensional flow. The instability of a laterally converging/diverging flow thus can be obtained from the available results for the Blasius flow by scaling the Reynolds numbers. This leads to the result that while a diverging flow is more unstable than the Blasius flow, a converging flow is more stable. Some additional relevant results are also presented.
30

Klinikinių, instrumentinių ir laboratorinių tyrimų prognozinė reikšmė diagnozuojant prostatos vėžį pacientams, turintiems padidėjusią prostatos vėžio riziką / Prognostic value of clinical, instrumental and laboratory investigations for detection of prostate cancer in high risk patients

Vaičiūnas, Kęstutis 08 September 2008 (has links)
Prostatos vėžys yra dažniausia vyrų onkologinė liga JAV, Vakarų Europoje bei Lietuvoje. Dėl senstančios visuomenės ateityje bus nustatoma dar daugiau naujų prostatos vėžio atvejų. Lietuvos vėžio registro duomenimis 1995 – 2005 metais vidutinis metinis prostatos vėžio sergamumo didėjimas - 14,5 proc. per metus. Vyrų sergamumas prostatos vėžiu Lietuvoje 2005 metais siekė 125,9/100000 atvejų, o mirtingumas nuo šios ligos siekė 31/100000 atvejų. Vyrų mirtingumas nuo prostatos vėžio antras pagal dažnį po plaučių vėžio su vėžiu susijusio mirtingumo grupėje. Todėl daugelis tyrėjų pabrėžia, kad norint mažinti mirtingumą, reikia ankstinti prostatos vėžio nustatymo laiką. Pradėta Lietuvos vyrų ankstyvosios prostatos vėžio diagnostikos programa ir dažnas prostatos specifinio antigeno nustatymas lėmė padidėjusį apsilankymų pas urologus skaičių ir padidino prostatos biopsijų kiekį. Norint efektyviai ir optimaliai ištirti šiuos pacientus, reikia daug materialinių išteklių ir laiko.Šio darbo tikslas buvo optimizuoti pacientų su padidėjusia prostatos vėžio rizika ištyrimą ir stebėjimą bei nustatyti ryšį tarp prostatos vėžio rizikos veiksnių ir prostatos vėžio diagnozavimo padidėjusios rizikos grupėje. Darbo uždaviniai: 1. Išanalizuoti prostatos vėžio nustatymo dažnį pirmąja ir kartotinėmis lateralinėmis sekstantinėmis prostatos biopsijomis ir įvertinti jų efektyvumą. 2. Nustatyti amžiaus, rūkymo, alkoholio vartojimo, prostatos vėžio šeiminės anamnezės, viršsvorio ir padidėjusio cholesterolio... [toliau žr. visą tekstą] / Prostate cancer is the most frequent malignant disease in men in United States, Western Europe and in Lithuania. Due to ageing population incidence of prostate cancer will rise even more in the future. Since the year 2003 prostate cancer became the most common form of cancer diagnosed in men in Lithuania (more than 1500 new prostate cancer cases a year). There were 2005 of new prostate cancer cases diagnosed in the year 2005. According to Lithuanian Cancer Registry data during the years 1995-2005 the prevalence of prostate cancer was increasing 14.5 percent annually. Prostate cancer was detected in 24.3 percent of all cancer cases in men in the year 2005 in Lithuania and in 48.3 percent of them disease was detected in the stages I and II. In the year 2005 the prevalence of prostate cancer in Lithuanian men was 125.9 per 100000 population and mortality was 31 per 100000 population. Prostate cancer is a second common form of death after lung cancer in cancer-associated mortality group in Lithuania. Prostate cancer mortality ranged between 19 and 55 per 100000 in Europe and it was 23.2 per 100000 populations in the year 2006 in European Union. Many authors stress that it is important to diagnose prostate cancer in the early stages in order to reduce prostate cancer mortality rate. The aim of the study was to optimize investigation and follow-up of the high prostate cancer risk patients, and to define the relation between prostate cancer risk factors and prostate cancer... [to full text]

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