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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.
1

EFFECT OF HORIZONTAL PILES ON THE SOIL BEARING CAPACITY FOR CIRCULAR FOOTING ABOVE CAVITY

Arosemena, Rafael L 01 May 2007 (has links)
The design of foundation in normal soil conditions is governed by bearing capacity, minimum depth of foundation and settlement. However, foundation design in karst regions needs to consider an additional criterion associated to the possibility of subsurface subsidence and ravelling sinkholes. Under this environment, alternative techniques are needed to improve the subsurface soil. In this study general background information is given to understand the geological characteristics of Central Florida and why this area is considered to be a karst region and susceptible to sinkholes formation. Traditional foundation design techniques on karst regions are addressed in this paper. Finally, the use of a network of three subsurface horizontal piles is proposed and the effect on stress increase and soil bearing capacity for footing due to the horizontal piles is investigated. Finite element computer software is used to analyze the stress distribution under different conditions and the results are discussed. The objective of this study is to determine whether or not horizontal piles under a circular footing at the sinkhole site is a viable solution to reduce the stress increase in the soil induced by the footing load. The horizontal piles located at a certain depth below the center of the footing intercepts the cone of pressure due to the footing load. Also, it is the purpose of this research to determine the effect on the soil bearing capacity for footing due to the proposed horizontal piles at the sinkhole prone area. In 1983 Baus, R.L and Wang, M.C published a research paper on soil bearing capacity for strip footing above voids. In their research, a chart for soil bearing capacity for strip footing located above a void was presented. However, in this paper we present a chart for circular footing size as a function void location and a design chart for circular footing size with a network of three underground piles. The result indicates that with the horizontal piles placed above the cavity, the stress increase caused by the footing load substantially decreases as compared to the situation of no horizontal piles, thus increases the soil bearing capacity for the normal design of footing size. The approach of using the horizontal piles placed in between the footing and the subsurface cavity is a new concept that has not been experienced previously. The results are strictly based on the analytical model of finite element program. Before full implementation for the construction practice, further research and experimental work should be conducted. / M.S.C.E. / Department of Civil and Environmental Engineering / Engineering and Computer Science / Civil Engineering MSCE
2

Field measurements of the linear and nonlinear shear moduli of cemented alluvium using dynamically loaded surface footings

Park, Kwangsoo 27 September 2010 (has links)
In this dissertation, a research effort aimed at development and implementation of a direct field test method to evaluate the linear and nonlinear shear modulus of soil is presented. The field method utilizes a surface footing that is dynamically loaded horizontally. The test procedure involves applying static and dynamic loads to the surface footing and measuring the soil response beneath the loaded area using embedded geophones. A wide range in dynamic loads under a constant static load permits measurements of linear and nonlinear shear wave propagation from which shear moduli and associated shearing strains are evaluated. Shear wave velocities in the linear and nonlinear strain ranges are calculated from time delays in waveforms monitored by geophone pairs. Shear moduli are then obtained using the shear wave velocities and the mass density of a soil. Shear strains are determined using particle displacements calculated from particle velocities measured at the geophones by assuming a linear variation between geophone pairs. The field test method was validated by conducting an initial field experiment at sandy site in Austin, Texas. Then, field experiments were performed on cemented alluvium, a complex, hard-to-sample material. Three separate locations at Yucca Mountain, Nevada were tested. The tests successfully measured: (1) the effect of confining pressure on shear and compression moduli in the linear strain range and (2) the effect of strain on shear moduli at various states of stress in the field. The field measurements were first compared with empirical relationships for uncemented gravel. This comparison showed that the alluvium was clearly cemented. The field measurements were then compared to other independent measurements including laboratory resonant column tests and field seismic tests using the spectral-analysis-of-surface-waves method. The results from the field tests were generally in good agreement with the other independent test results, indicating that the proposed method has the ability to directly evaluate complex material like cemented alluvium in the field. / text
3

Análise dos modelos estruturais para determinação dos esforços resistentes em sapatas isoladas / Analysis of structural models to determine limit forces in spread footing

Edja Laurindo da Silva 17 August 1998 (has links)
Esta dissertação de mestrado discute e analisa os critérios especificados em normas brasileiras e internacionais sobre projetos de sapatas isoladas em concreto armado, com relação a determinação dos esforços solicitantes, dimensionamento e detalhamento das armaduras. O trabalho contém as recomendações essenciais para o projeto e a construção de sapatas isoladas, como o tipo de fundação rasa mais freqüentemente utilizado. São discutidos os critérios apresentados no Boletim número 73 do CEB (1970), da norma brasileira \" Projeto e execução de obras de concreto armado\", NBR 6118 (1982), do Código Modelo do CEB - FIP (1991), Código de Projeto de Edifícios do ACI 318/1995, Eurocode 2 (1992) e do Texto Base para Revisão da NB 1/78(1992) e alguns modelos de cálculo não normalizados mas encontrados na literatura técnica. Observa-se em alguns desses códigos a omissão com relação ao dimensionamento no estado limite último de sapatas isoladas, onde foram, portanto, adaptados critérios indicados para lajes maciças. Exemplos de projetos de sapatas isoladas submetidas a ação centrada, excêntrica com plano de ação do momento paralelo a um dos lados do pilar e sapata com ação centrada e momentos paralelos aos dois lados do pilar são analisados para facilitar o entendimento dos conceitos emitidos pelas várias normas citadas e que são utilizadas comumente pelo meio técnico. Observou-se nos exemplos apresentados que para as tensões normais de tração foram encontradas armaduras mínimas ou valores próximos aos mínimos. Para os valores das forças cortantes e forças para verificar a punção, em alguns casos, se aproximaram das forças últimas. Foi notado que geralmente os efeitos das tensões cisalhantes determinam não só as alturas das sapatas mas também todo o seu dimensionamento. / This Thesis discusses and analyses the footing design criteria of Brazilian Code and also some international codes, in regarding to internal forces determination, dimensioning and reinforcement distribution. This work has essential recommendations to design and construct spread footing, such as the most frequently used types of shallow foundation. Criteria presented in the CEB/1970, NBR 6118/1982, CEB MC-90, ACI 318/1995, EC-2/92, and in the text which can be used as the basis for revised version of the Brazilian Code NB 1/78(1992) are discussed as well as some design models that are not yet normalized but it can be found at technical literature. lt can be observed in some of these Codes that since they do not take into consideration the ultimate limit state in spread footing design, some criteria that are applicable to slabs were adapted for this study. Some examples of spread footing under compression load design, spread footing under eccentric load having flexure plane in one side of column and in both side of column, are analysed to help understanding the concepts on the cited Codes. lt was noted on the examples that it was founded the minimum reinforcement when the structure was submitted to tension stress. Shear forces and forces used to verify punching shear effects reached the ultimate forces in some cases. lt was observed that shear tension effects determine the footing high as well as every footing dimensions.
4

Behaviour of strip footing on fiber-reinforced model slopes

Mirzababaei, M., Inibong, E., Mohamed, Mostafa H.A., Miraftab, M. January 2014 (has links)
No / Laboratory scale model slopes reinforced with waste carpet fibers were made in a rigid tank with dimensions of 800 mm x 300 mm x 500 mm. Bearing capacities of the strip footing rested on non-reinforced and fiber-reinforced model slopes with 1%, 3% and 5% fiber content were compared at 20% footing displacement ratio. The influence of location of footing on the bearing capacity was studied with placing the footing at different edge distances from the crest of the footing (i.e., 150 mm, 100 mm and 0). Suction probe sensors were installed at appropriate locations on the rear side of the model slope to measure the pore-water pressure generated due to the footing pressure. Results showed that fiber reinforcement increased the bearing resistance of the model slopes significantly. Inclusion of 5% fiber increased the bearing resistance by 271% compared to that of non-reinforced model slope at the footing edge distance ratio of 3. The location of footing was found to affect the load-carrying capacity of the fiber-reinforced model slope. The increase in the edge distance ratio of the footing increased the load-carrying capacity of the model slope.
5

Análise dos modelos estruturais para determinação dos esforços resistentes em sapatas isoladas / Analysis of structural models to determine limit forces in spread footing

Silva, Edja Laurindo da 17 August 1998 (has links)
Esta dissertação de mestrado discute e analisa os critérios especificados em normas brasileiras e internacionais sobre projetos de sapatas isoladas em concreto armado, com relação a determinação dos esforços solicitantes, dimensionamento e detalhamento das armaduras. O trabalho contém as recomendações essenciais para o projeto e a construção de sapatas isoladas, como o tipo de fundação rasa mais freqüentemente utilizado. São discutidos os critérios apresentados no Boletim número 73 do CEB (1970), da norma brasileira \" Projeto e execução de obras de concreto armado\", NBR 6118 (1982), do Código Modelo do CEB - FIP (1991), Código de Projeto de Edifícios do ACI 318/1995, Eurocode 2 (1992) e do Texto Base para Revisão da NB 1/78(1992) e alguns modelos de cálculo não normalizados mas encontrados na literatura técnica. Observa-se em alguns desses códigos a omissão com relação ao dimensionamento no estado limite último de sapatas isoladas, onde foram, portanto, adaptados critérios indicados para lajes maciças. Exemplos de projetos de sapatas isoladas submetidas a ação centrada, excêntrica com plano de ação do momento paralelo a um dos lados do pilar e sapata com ação centrada e momentos paralelos aos dois lados do pilar são analisados para facilitar o entendimento dos conceitos emitidos pelas várias normas citadas e que são utilizadas comumente pelo meio técnico. Observou-se nos exemplos apresentados que para as tensões normais de tração foram encontradas armaduras mínimas ou valores próximos aos mínimos. Para os valores das forças cortantes e forças para verificar a punção, em alguns casos, se aproximaram das forças últimas. Foi notado que geralmente os efeitos das tensões cisalhantes determinam não só as alturas das sapatas mas também todo o seu dimensionamento. / This Thesis discusses and analyses the footing design criteria of Brazilian Code and also some international codes, in regarding to internal forces determination, dimensioning and reinforcement distribution. This work has essential recommendations to design and construct spread footing, such as the most frequently used types of shallow foundation. Criteria presented in the CEB/1970, NBR 6118/1982, CEB MC-90, ACI 318/1995, EC-2/92, and in the text which can be used as the basis for revised version of the Brazilian Code NB 1/78(1992) are discussed as well as some design models that are not yet normalized but it can be found at technical literature. lt can be observed in some of these Codes that since they do not take into consideration the ultimate limit state in spread footing design, some criteria that are applicable to slabs were adapted for this study. Some examples of spread footing under compression load design, spread footing under eccentric load having flexure plane in one side of column and in both side of column, are analysed to help understanding the concepts on the cited Codes. lt was noted on the examples that it was founded the minimum reinforcement when the structure was submitted to tension stress. Shear forces and forces used to verify punching shear effects reached the ultimate forces in some cases. lt was observed that shear tension effects determine the footing high as well as every footing dimensions.
6

A influÃncia da terceira parte na mudanÃa de footing em chats educacionais / The influence of the third part in changing educational footing in chats

GeÃrgia Maria Feitosa e Paiva 30 April 2013 (has links)
FundaÃÃo de Amparo à Pesquisa do Estado do Cearà / CoordenaÃÃo de AperfeiÃoamento de Pessoal de NÃvel Superior / Conselho Nacional de Desenvolvimento CientÃfico e TecnolÃgico / nÃo hà / Esta tese tem como objetivo analisar atà que ponto e sob quais circunstÃncias a presenÃa da terceira parte influencia ou interfere nos chats educacionais virtuais por meio das mudanÃas de footing dos participantes desses chats e da polidez linguÃstica que eles investem em momentos de mudanÃa. Para tanto, tomamos como base os estudos de Goffman (1967; 1981), Brown; Levinson (1978; 1987), Leech (1983; 2005), e as investigaÃÃes de Paiva (2004), Paiva; Rodrigues-Junior (2008) e Pereira (2009). Para a realizaÃÃo da pesquisa, contamos com a colaboraÃÃo dos alunos e dos professores das disciplinas SociolinguÃstica, LinguÃstica Textual e Leitura e ProduÃÃo de Textos AcadÃmicos, ofertadas no curso de graduaÃÃo Letras-PortuguÃs da Universidade Federal do CearÃ. Cada participante respondeu a um questionÃrio com questÃes que visaram compreender seus hÃbitos e afinidades com a ferramenta chat educacional virtual. Depois de tabular e cruzar as informaÃÃes presentes nos questionÃrios, e de analisar quinze chats, verificamos que a figura do professor conteudista nÃo somente atua como terceira parte ou zona de influÃncia como tambÃm chega a interferir na mudanÃa de footing dos participantes da interaÃÃo. O tipo de mudanÃa de footing mais significativo à o de formato de produÃÃo, no qual foi possÃvel observar que na presenÃa da terceira parte tutores e alunos procuram ser mais animadores do que responsÃveis ou autores. TambÃm na presenÃa da terceira parte, os alunos evitaram inserir frames de longa duraÃÃo. Com relaÃÃo à mudanÃa de footing por estrutura de participaÃÃo, a presenÃa da terceira parte parece ter condicionado a exclusÃo momentÃnea do tutor na interaÃÃo durante a sua presenÃa, que, por sua vez, excluiu alunos, neste mesmo momento interacional. Estes resultados demonstram que o movimento interno Ãs interaÃÃes sociais (footing) realizadas em chats educacionais virtuais à bastante sensÃvel à presenÃa de membro hierarquicamente superior, podendo inclusive se prolongar na sua ausÃncia. Com esta investigaÃÃo, concluÃmos que a escolha de determinadas estratÃgias de polidez como use marcadores de identidade e grupo, inclua ouvinte e falante na mesma atividade, nominalize, distancie-se do ator e adicione formalidade; distancie-se dos pronomes eu e vocà auxiliam no estabelecimento e na mudanÃa de footings pelos participantes, pois demonstram o nÃvel de engajamento empreendido, sinalizando em quais momentos o observador interfere na projeÃÃo de suas faces. / This research aims at analyzing what extent and under what circumstances the presence of third part influences or interferes with the educational virtual chats through changes in participantsâ footing in these chats and linguistic politeness that they invest in turning points.Our work in this dissertation seeks to achieve this relationship which, in our view, seems inseparable for understanding social relations. Therefore, as the basis of our studies we take Goffman (1967, 1981), Brown; Levinson (1987, 1978), Leech (1983, 2005), and more recently, investigations by Paiva; Rodrigues-Junior (2008), Paiva (2004) and Pereira (2009). To achieve the researchâs aims, we had the collaboration of students and teachers from Sociolinguistics, Linguistics and Textual Reading and Production of Academic Texts disciplines, offered in the Portuguese Literature course at the Federal University of CearÃ. The participants answered a questionnaire that aimed to understand their habits and affinities with educational virtual chat tools. After crossing and tabling the information provided in the questionnaires and analyzing fifteen chats, we found that the figure of the content teacher does not only act as a third part or zone of influence, but also he/she interferes in some instances to the changing in participants of the interactionâs footing. The most significant type of footing change is in the format of production, in which tutors and students demonstrate that in the presence of the third part, they seek to be more impeller than sponsors or authors. Also, in the presence of the third part, students avoid inserting frames of long duration. Regarding the change of footing for participation structure, the presence of the third part seems to have conditioned the momentary exclusion of the tutor interaction during its presence, which in turn, excluded students, even in this moment of interaction. These results demonstrate that the internal motion to social interactions (footing) held in virtual educational chats is very sensitive to the presence of higher-ranking member, and it can even extend during its absence. With this investigation, we can conclude that the choice of certain politeness strategies, such as use group and identity markers, include listener and speaker in the same activity, nominalize, hold off yourself from the author and add formality, hold off yourself from pronouns such as I and you assist in establishing and changing footings by the participants because they demonstrate the level of engagement undertaken, signaling to which moments the observer interferes with the projection of their faces.
7

Strut-and-tie model design examples for bridge

Williams, Christopher Scott 16 February 2012 (has links)
Strut-and-tie modeling (STM) is a versatile, lower-bound (i.e. conservative) design method for reinforced concrete structural components. Uncertainty expressed by engineers related to the implementation of existing STM code specifications as well as a growing inventory of distressed in-service bent caps exhibiting diagonal cracking was the impetus for the Texas Department of Transportation (TxDOT) to fund research project 0-5253, D-Region Strength and Serviceability Design, and the current implementation project (5-5253-01). As part of these projects, simple, accurate STM specifications were developed. This thesis acts as a guidebook for application of the proposed specifications and is intended to clarify any remaining uncertainties associated with strut-and-tie modeling. A series of five detailed design examples feature the application of the STM specifications. A brief overview of each design example is provided below. The examples are prefaced with a review of the theoretical background and fundamental design process of STM (Chapter 2). • Example 1: Five-Column Bent Cap of a Skewed Bridge - This design example serves as an introduction to the application of STM. Challenges are introduced by the bridge’s skew and complicated loading pattern. A clear procedure for defining relatively complex nodal geometries is presented. • Example 2: Cantilever Bent Cap - A strut-and-tie model is developed to represent the flow of forces around a frame corner subjected to closing loads. The design and detailing of a curved-bar node at the outside of the frame corner is described. • Example 3a: Inverted-T Straddle Bent Cap (Moment Frame) - An inverted-T straddle bent cap is modeled as a component within a moment frame. Bottom-chord (ledge) loading of the inverted-T necessitates the use of local STMs to model the flow of forces through the bent cap’s cross section. • Example 3b: Inverted-T Straddle Bent Cap (Simply Supported) - The inverted-T bent cap of Example 3a is designed as a member that is simply supported at the columns. • Example 4: Drilled-Shaft Footing - Three-dimensional STMs are developed to properly model the flow of forces through a deep drilled-shaft footing. Two unique load cases are considered to familiarize the designer with the development of such models. / text
8

Bearing capacity and immediate settlement of shallow foundations on clay

Strahler, Andrew W. 14 March 2012 (has links)
Shallow foundations are extensively used to support structures of all sizes and derive their support from near surface soils. Thus, they are typically embedded up to a few meters into the soil profile. Designers of shallow foundations are required to meet two limit states: overall failure of the soil beneath the foundation (bearing capacity) and excessive settlement. Existing bearing capacity design methods use an assumed shearing plane within the soil and perfectly plastic soil behavior to estimate the ultimate resistance available. The immediate settlement of a shallow foundation is typically approximated using an elasticity-based method that does not account for actual, nonlinear soil behavior. A load test database was developed from footing load tests reported in the literature to assess the accuracy and uncertainty in existing design methodologies for calculating bearing capacity and immediate settlement. The assessment of uncertainty in bearing capacity and immediate settlement was accomplished through the application of a hyperbolic bearing pressure-displacement model, and the adaptation of the Duncan-Chang soil constitutive model to footing displacements. The prediction of bearing capacity using the general bearing capacity formula was compared to the bearing capacity extrapolated from the load test database using a hyperbolic bearing pressure-displacement model. On average the general bearing capacity formula under-predicts the bearing capacity and exhibits a significant amount of variability. The comparison was used to develop resistance statistics that were implemented to produce resistance factors for an LRFD based design approach using AASHTO load statistics. The Duncan-Chang model was adapted to predict bearing pressure displacement curves for footings in the load test database and used to estimate governing soil parameters. Bearing pressure-displacement curves fitted to the observed curves were used to back calculate soil stiffness. The soil stiffness was used with an elasticity-based displacement prediction method to evaluate the accuracy of the method. Finally, the back-calculated modulus from the fitted Duncan-Chang model was used to assess the accuracy and uncertainty associated with the elasticity-based K-factor, a correlation based stiffness parameter. In general the comparisons indicate that the current design procedures over-predict the bearing pressure associated with a given displacement and exhibit a significant amount of uncertainty. / Graduation date: 2012
9

Applications Of Method Of Characteristics And Upper Bound Limit Analysis To Different Bearing Capacity Problems

Ghosh, Priyanka 12 1900 (has links) (PDF)
No description available.
10

Previsão de recalques por colapso de sapatas assentes em solo natural e compactado / Prediction of collapse settlements of footings built over natural and compacted soil

Soares, Fábio Visnadi Prado 26 January 2018 (has links)
Submitted by Fábio Visnadi Prado Soares null (fvps@hotmail.com) on 2018-02-28T12:38:57Z No. of bitstreams: 1 Dissertação - Soares, F V P - 2017 - VF - REPOSITORIO.pdf: 6006217 bytes, checksum: c8b6c04c1ed994f7a112e592011d919b (MD5) / Approved for entry into archive by Maria Marlene Zaniboni null (zaniboni@bauru.unesp.br) on 2018-02-28T17:41:25Z (GMT) No. of bitstreams: 1 soares_fvp_me_bauru.pdf: 6006217 bytes, checksum: c8b6c04c1ed994f7a112e592011d919b (MD5) / Made available in DSpace on 2018-02-28T17:41:25Z (GMT). No. of bitstreams: 1 soares_fvp_me_bauru.pdf: 6006217 bytes, checksum: c8b6c04c1ed994f7a112e592011d919b (MD5) Previous issue date: 2018-01-26 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / O comportamento dos solos não saturados é um tema amplamente estudado, tanto por meio de ensaios de laboratório quanto de campo. Fenômenos como o colapso dos solos são relativamente bem explicados pelos modelos elastoplásticos existentes, dos quais o Modelo Básico de Barcelona é um dos mais utilizados e difundidos no meio acadêmico. Apesar dos avanços obtidos, ainda existe certa escassez de estudos que comparem o comportamento previsto por tais modelos a resultados de situações reais de engenharia. Esta pesquisa teve como objetivo simular numericamente resultados de recalques devidos a carregamentos e inundação de provas de carga em placa e de protótipos de sapata construídas sobre solo natural e compactado em cava. Com os resultados buscou-se analisar a eficiência da técnica de compactação para mitigar o problema do colapso do solo. Para isso, ensaios de compressão triaxial e edométricos com sucção controlada, bem como ensaios de curva de retenção e condutividade hidráulica foram realizados para determinação dos parâmetros constitutivos hidráulicos e mecânicos do solo natural e compactado que foram utilizados no programa Code_Bright para simulação numérica dos resultados de campo. Os resultados demonstraram a capacidade do modelo em reproduzir o comportamento do solo no campo. Demonstraram também que o uso da compactação do solo que preconiza compactar em cava uma camada de espessura equivalente à largura da sapata é viável para redução da colapsibilidade, mas depende do nível das tensões atuantes nas fundações e da tolerância aos recalques. Tensões propagadas para a camada de solo natural superiores à tensão de pré-adensamento do solo natural saturado provocarão recalques por colapso quando o solo for umedecido. / The behaviour of unsaturated soils is a widely studied theme around the world, both by utilising laboratory and field tests. Phenomena like soil collapsibility are relatively well explained by the existing elastoplastic models, among which the Barcelona Basic Model is the most widely used in the academic field. Despite the recent advances, there is still a scarcity of papers that compare the behaviour predicted by constitutive models and results of real engineering problems. This research aims to numerically simulate the results of settlement due to loading and wetting of load tests built both on undisturbed and compacted soil. The results were analysed in order to study the efficacy of the soil compaction technique in mitigating soil collapse. Suction controlled triaxial compression and oedometer tests, as well as soil water retention curve and hydraulic conductivity experiments were conducted to determine the hydraulic and mechanic parameters used in the software Code_Bright to numerically simulate field results. The results highlight the capability of the model in reproducing the analysed field behaviour. They also show that the technique that involves compaction of the soil equal to the footing’s width is viable to reduce its collapsibility, but its efficacy will also depend on the tensions applied on the foundation and on the tolerable settlement values. Tensions that are propagated to the natural soil layer that are higher than its preconsolidation stress will cause collapse settlements and wetted.

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