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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

Nonlinear analysis of smart composite plate and shell structures

Lee, Seung Joon 29 August 2005 (has links)
Theoretical formulations, analytical solutions, and finite element solutions for laminated composite plate and shell structures with smart material laminae are presented in the study. A unified third-order shear deformation theory is formulated and used to study vibration/deflection suppression characteristics of plate and shell structures. The von K??rm??n type geometric nonlinearity is included in the formulation. Third-order shear deformation theory based on Donnell and Sanders nonlinear shell theories is chosen for the shell formulation. The smart material used in this study to achieve damping of transverse deflection is the Terfenol-D magnetostrictive material. A negative velocity feedback control is used to control the structural system with the constant control gain. The Navier solutions of laminated composite plates and shells of rectangular planeform are obtained for the simply supported boundary conditions using the linear theories. Displacement finite element models that account for the geometric nonlinearity and dynamic response are developed. The conforming element which has eight degrees of freedom per node is used to develop the finite element model. Newmark's time integration scheme is used to reduce the ordinary differential equations in time to algebraic equations. Newton-Raphson iteration scheme is used to solve the resulting nonlinear finite element equations. A number of parametric studies are carried out to understand the damping characteristics of laminated composites with embedded smart material layers.
2

Nonlinear analysis of smart composite plate and shell structures

Lee, Seung Joon 29 August 2005 (has links)
Theoretical formulations, analytical solutions, and finite element solutions for laminated composite plate and shell structures with smart material laminae are presented in the study. A unified third-order shear deformation theory is formulated and used to study vibration/deflection suppression characteristics of plate and shell structures. The von K??rm??n type geometric nonlinearity is included in the formulation. Third-order shear deformation theory based on Donnell and Sanders nonlinear shell theories is chosen for the shell formulation. The smart material used in this study to achieve damping of transverse deflection is the Terfenol-D magnetostrictive material. A negative velocity feedback control is used to control the structural system with the constant control gain. The Navier solutions of laminated composite plates and shells of rectangular planeform are obtained for the simply supported boundary conditions using the linear theories. Displacement finite element models that account for the geometric nonlinearity and dynamic response are developed. The conforming element which has eight degrees of freedom per node is used to develop the finite element model. Newmark's time integration scheme is used to reduce the ordinary differential equations in time to algebraic equations. Newton-Raphson iteration scheme is used to solve the resulting nonlinear finite element equations. A number of parametric studies are carried out to understand the damping characteristics of laminated composites with embedded smart material layers.
3

Análise crítica do controle construtivo de pavimentos com a viga de Benkelman: aplicação ao caso da ampliação do Aeroporto Internacional Tom Jobim no Rio de Janeiro. / Critical analysis on the control of pavement construction using Benkelman beam: application to the case of the expansion of Tom Jobim International Airport in Rio de Janeiro.

Vellasco, Bruno Quilici 30 July 2018 (has links)
Há algumas décadas a viga de Benkelman vem sendo utilizada como um meio de controlar a qualidade das camadas de pavimento recém executadas, ao aferir as deflexões máximas na superfície dos materiais. Apesar disto, não existe qualquer referência que auxilie na determinação das deflexões admissíveis, uma vez que nenhuma norma técnica trata sobre os valores aceitáveis para a liberação das camadas. Neste contexto, as responsáveis pela definição dos parâmetros de controle passam a ser as projetistas, que muitas vezes não possuem conhecimento suficiente sobre os materiais de pavimentação para cumprir esta tarefa. O resultado disto são valores de controle sem fundamentos e inconsistentes, que são incapazes de representar de forma fidedigna as condições de campo, gerando uma série de dificuldades em obra. Sendo assim, este trabalho tem por objetivo fazer uma reflexão crítica sobre o modo como as deflexões de controle são definidas pelas projetistas, analisando as considerações de projeto que podem levar a resultados incoerentes em campo e propondo diretrizes para o aperfeiçoamento desta prática. Para isto, foi feita uma revisão bibliográfica sobre os principais fatores que podem afetar os valores de módulos de resiliência dos materiais e, consequentemente, as medidas de deflexões. Complementarmente, foram revisados valores de módulos de resiliências obtidos em laboratório e retroanalisados em pista. Em seguida, foi estudado o caso da obra de ampliação do Aeroporto Internacional Tom Jobim no Rio de Janeiro, em que resultados insatisfatórios de deflexões obtidas em campo levaram a uma revisão dos parâmetros de controle, revelando os principais equívocos cometidos pela projetista e os pontos críticos do processo de determinação dos valores de controle. Com base nisto, foi feita uma análise crítica das deflexões revisadas, mostrando como a variação de alguns critérios e parâmetros pode afetar os resultados e o que isto representa em termos práticos para o controle deflectométrico. Por fim, foi realizado um refinamento dos valores de deflexões de controle definidos pela projetista. / For decades, the Benkelman beam has been used to assure the quality of pavement construction by measuring the maximum deflections on top of the materials. Nevertheless, there are neither technical standards nor any references that determine a range of acceptable values for deflection. In this context, the definition of these parameters of control is the responsibility of the designers, who mostly do not have the expertise to complete the task. Consequently, the control values tend to be inconsistent and unable to represent in a reliable way the site conditions, creating a number of constraints/shortcomings. Hence, the objective of this dissertation is to undertake a critical analysis on the way the acceptable deflections are determined by the designers, evaluating the project assumptions that can lead to incoherent results on site and proposing guidelines for the improvement of this practice. For this, the main factors that can affect the elasticity of the materials and its deflections were reviewed, in addition to typical values of resilient modulus obtained in laboratory and from backanalysis. Next, the case of the Rio de Janeiro International Airport expansion project was studied. On that occasion, the deflections measured on site during the construction of the pavements were constantly greater than the control values indicated in the project. A revision of the parameters was undertaken by the designer to identify the reasons for the discrepancies and thus, unveiling the critical points of the process. Based on that, a critical analysis on the revised deflections was carried out, showing how the variation of some criteria and parameters can affect the results and what this represents in practical terms for the deflectometric control. Finally, a refinement of the acceptable deflections defined by the designer was proposed.
4

Análise crítica do controle construtivo de pavimentos com a viga de Benkelman: aplicação ao caso da ampliação do Aeroporto Internacional Tom Jobim no Rio de Janeiro. / Critical analysis on the control of pavement construction using Benkelman beam: application to the case of the expansion of Tom Jobim International Airport in Rio de Janeiro.

Bruno Quilici Vellasco 30 July 2018 (has links)
Há algumas décadas a viga de Benkelman vem sendo utilizada como um meio de controlar a qualidade das camadas de pavimento recém executadas, ao aferir as deflexões máximas na superfície dos materiais. Apesar disto, não existe qualquer referência que auxilie na determinação das deflexões admissíveis, uma vez que nenhuma norma técnica trata sobre os valores aceitáveis para a liberação das camadas. Neste contexto, as responsáveis pela definição dos parâmetros de controle passam a ser as projetistas, que muitas vezes não possuem conhecimento suficiente sobre os materiais de pavimentação para cumprir esta tarefa. O resultado disto são valores de controle sem fundamentos e inconsistentes, que são incapazes de representar de forma fidedigna as condições de campo, gerando uma série de dificuldades em obra. Sendo assim, este trabalho tem por objetivo fazer uma reflexão crítica sobre o modo como as deflexões de controle são definidas pelas projetistas, analisando as considerações de projeto que podem levar a resultados incoerentes em campo e propondo diretrizes para o aperfeiçoamento desta prática. Para isto, foi feita uma revisão bibliográfica sobre os principais fatores que podem afetar os valores de módulos de resiliência dos materiais e, consequentemente, as medidas de deflexões. Complementarmente, foram revisados valores de módulos de resiliências obtidos em laboratório e retroanalisados em pista. Em seguida, foi estudado o caso da obra de ampliação do Aeroporto Internacional Tom Jobim no Rio de Janeiro, em que resultados insatisfatórios de deflexões obtidas em campo levaram a uma revisão dos parâmetros de controle, revelando os principais equívocos cometidos pela projetista e os pontos críticos do processo de determinação dos valores de controle. Com base nisto, foi feita uma análise crítica das deflexões revisadas, mostrando como a variação de alguns critérios e parâmetros pode afetar os resultados e o que isto representa em termos práticos para o controle deflectométrico. Por fim, foi realizado um refinamento dos valores de deflexões de controle definidos pela projetista. / For decades, the Benkelman beam has been used to assure the quality of pavement construction by measuring the maximum deflections on top of the materials. Nevertheless, there are neither technical standards nor any references that determine a range of acceptable values for deflection. In this context, the definition of these parameters of control is the responsibility of the designers, who mostly do not have the expertise to complete the task. Consequently, the control values tend to be inconsistent and unable to represent in a reliable way the site conditions, creating a number of constraints/shortcomings. Hence, the objective of this dissertation is to undertake a critical analysis on the way the acceptable deflections are determined by the designers, evaluating the project assumptions that can lead to incoherent results on site and proposing guidelines for the improvement of this practice. For this, the main factors that can affect the elasticity of the materials and its deflections were reviewed, in addition to typical values of resilient modulus obtained in laboratory and from backanalysis. Next, the case of the Rio de Janeiro International Airport expansion project was studied. On that occasion, the deflections measured on site during the construction of the pavements were constantly greater than the control values indicated in the project. A revision of the parameters was undertaken by the designer to identify the reasons for the discrepancies and thus, unveiling the critical points of the process. Based on that, a critical analysis on the revised deflections was carried out, showing how the variation of some criteria and parameters can affect the results and what this represents in practical terms for the deflectometric control. Finally, a refinement of the acceptable deflections defined by the designer was proposed.
5

Možnosti stroje Vernet Behringer při CNC programování / Vernet Behringer tools for CNC programming

Mana, Marek January 2014 (has links)
The master’s thesis is focused on the possibilities of machining lines of the company Vernet – Behringer. The theoretical part is a brief inclusion of the control system ProNC2 between selected commercially available control systems and are compared ways of programming CNC machine tools. On the machine tool of company Vernet – Behringer are processed mainly thin-walled components, that is why is part of the work focuses on the issue of machining thin-walled parts, the distribution of deflection tools and machined parts. The next part of thesis deals with the design and processing of technical documentation for the machined model part. The practical part deals with the possibilities of the machine and method of programming the control system ProNC2. Programming and practical production on machine were proceeded in company SSI Schäfer s.r.o. The work is focused on practical verification of the production process using simulation and production itself. Finally, it was performed technical - economic evaluation of production.
6

Evaluation of the In-Servic Performance of the Tom's Creek Bridge

Neely, William Douglas 26 May 2000 (has links)
The Tom's Creek Bridge is a small-scale demonstration project involving the use of fiber-reinforced polymer (FRP) composite girders as the main load carrying members. The project is intended to serve two purposes. First, by calculating bridge design parameters such as the dynamic load allowance, transverse wheel load distribution and deflections under service loading, the Tom's Creek Bridge will aid in modifying current AASHTO bridge design standards for use with FRP composite materials. Second, by evaluating the FRP girders after being exposed to service conditions, the project will begin to answer questions about the long-term performance of these advanced composite material beams when used in bridge design. This thesis details the In-Service analysis of the Tom's Creek Bridge. Five load tests, at six month intervals, were conducted on the bridge. Using mid-span strain and deflection data gathered from the FRP composite girders during these tests the above mentioned bridge design parameters have been determined. The Tom's Creek Bridge was determined to have a dynamic load allowance, IM, of 0.90, a transverse wheel load distribution factor, g, of 0.101 and a maximum deflection of L/488. Two bridge girders were removed from the Tom's Creek Bridge after fifteen months of service loading. These FRP composite girders were tested at the Structures and Materials Research Laboratory at Virginia Tech for stiffness and ultimate strength and compared to pre-service values for the same beams. This analysis indicates that after fifteen months of service, the FRP composite girders have not lost a significant amount of either stiffness or ultimate strength. / Master of Science
7

Determination of AASHTO Bridge Design Parameters through Field Evaluation of the Rt. 601 Bridge: A Bridge Utilizing Strongwell 36 in. Fiber-Reinforced Polymer Double Web Beams as the Main Load Carrying Members

Restrepo, Edgar Salom 18 December 2002 (has links)
The Route 601 Bridge in Sugar Grove, Virginia spans 39 ft over Dickey Creek. The Bridge is the first to use the Strongwell 36 in. fiber reinforced polymer (FRP) double web beam (DWB) in its superstructure. Replacement of the old bridge began in June 2001, and construction of the new bridge was completed in October 2001. The bridge was field tested in October 2001 and June 2002. This thesis details the field evaluation of the Rt. 601 Bridge. Using mid span deflection and strain data from the October 2001 and June 2002 field tests, the primary goal of this research was to determine the following AASHTO bridge design parameters: wheel load distribution factor g, dynamic load allowance IM, and maximum deflection. The wheel load distribution factor was determined to be S/5, a dynamic load allowance was determined to be 0.30, and the maximum deflection of the bridge was L/1500. Deflection results were lower than the AASHTO L/800 limit. This discrepancy is attributed to partial composite action of the deck-to-girder connections, bearing restraint at the supports, and contribution of guardrail stiffness. Secondary goals of this research were to quantify the effect of diaphragm removal on girder distribution factor, determine torsion and axial effects of the FRP girders, compare responses to multiple lane symmetrical loading to superimposed single lane response, and compare the field test results to a finite element and a finite difference model. It was found that diaphragm removal had a small effect on the wheel load distribution factor. Torsional and axial effects were small. The bridge response to multilane loading coincided with superimposed single lane truck passes, and curb-stiffening effects in a finite difference model improved the accuracy of modeling the Rt. 601 Bridge behavior. / Master of Science

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