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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

A 3-D Pseudo-Rigid-Body Model for Rectangular Cantilever Beams with an Arbitrary Force End-Load

Chimento, Jairo Renato 07 April 2014 (has links)
This dissertation introduces a novel three-dimensional pseudo-rigid-body model (3-D PRBM) for straight cantilever beams with rectangular cross sections. The model is capable of capturing the behavior of the neutral axis of a beam loaded with an arbitrary force end-load. Numerical integration of a system of differential equations yields approximate displacement and orientation of the beam's neutral axis at the free end, and curvatures of the neutral axis at the fixed end. This data was used to develop the 3-D PRBM which consists of two torsional springs connecting two rigid links for a total of 2 degrees of freedom (DOF). The 3-D PRBM parameters that are comparable with existing 2-D model parameters are characteristic radius factor (mean: γ = 0.8322), bending stiffness coefficient (mean: KΘ = 2.5167) and parametric angle coefficient (mean: cΘ = 1.2501). New parameters are introduced in the model in order to capture the spatial behavior of the deflected beam, including two parametric angle coefficients (means: cΨ = 1.0714; cΦ = 1.0087). The model is verified in a few locations using ANSYSTM and its use in the design of compliant mechanisms is illustrated through spatial compliant versions of crank slider and double slider mechanisms.
2

Pseudo-Rigid-Body Models for Approximating Spatial Compliant Mechanisms of Rectangular Cross Section

Ramirez, Issa Ailenid 13 November 2014 (has links)
The objective of the dissertation is to develop and describe kinematic models (Pseudo-Rigid-Body Models) for approximating large-deflection of spatial (3D) cantilever beams that undergo multiple bending motions thru end-moment loading. Those models enable efficient design of compliant mechanisms, because they simply and accurately represent the bending and stiffness of compliant beams. To accomplish this goal, the approach can be divided into three stages: development of the governing equations of a flexible cantilever beam, development of a PRBM for axisymmetric cantilever beams and the development of spatial PRBMs for rectangular cross-section beam with multiple end moments. The governing equations of a cantilever beam that undergoes large deflection due to force and moment loading, contains the curvature, location and rotation of the beam. The results where validated with Ansys, which showed to have a Pearson's correlation factor higher than 0.91. The resulting deflections, curvatures and angles were used to develop a spatial pseudo-rigid-body model for the cantilever beam. The spatial pseudo-rigid-body model consists of two links connected thru a spherical joint. For an axisymmetric beam, the PRB parameters are comparable with existing planar PRBMs. For the rectangular PRBM, the parameters depend on the aspect ratio of the beam (the ratio of the beam width over the height of the cross-section). Tables with the parameters as a function of the aspect ratio are included in this work.
3

Computation of Live Load Deflections for a Composite, Steel-Girder Bridge

Jefferson, Thomas Seth 01 December 2016 (has links)
Current specifications of the American Association of State Highway and Transportation Officials (AASHTO) include restrictions on the live load deflections of highway bridge girders. Conventional practice, which utilizes hand calculations to estimate girder deflections, assumes that all girders of a highway bridge deflect to the same degree. In addition, the conventional equations do not account for AASHTO specifications requiring the evaluation of extreme force effects. As such, the accuracy of the conventional approach for calculating girder deflections is under question. The purpose of this study is, therefore, to check the accuracy of the conventional approach by testing the two aforementioned assumptions made by the equations. A composite steel girder bridge example has been selected from Design of Highway Bridges: An LRFD Approach, Third Edition by Richard M. Barker and Jay A. Puckett. The design example specifies the dimensions for all structural elements, as well as the girder type and spacing. The design example does not include specifications for the bridge bearings, and so bearing pads are designed according to the Illinois Department of Transportation (IDOT) Bridge Manual (2012). This study consists of two steps. First, a hand-calculated live load deflection for the bridge example is derived from the conventional approach (assuming all girders deflect to the same degree and without consideration for extreme force effects). Next, the finite element analysis software, NISA/Display IV, is utilized to model and analyze the real-world deflections of the bridge model. Three live loading conditions are applied to the finite element model, in accordance with AASHTO specifications. For first live load condition, the live loads are positioned at the center of each traffic lane. The second and third conditions apply extreme force effects to an interior girder and exterior girder, respectively. The results for each finite element analysis are then compared with the conventional, hand-calculated deflection. The results of this study contradict the two aforementioned assumptions made by the conventional equations for calculating girder deflections. Firstly, this study demonstrates that interior girders experience a significantly greater live load deflection than interior girders. More importantly, the results indicate that the conventional equations underestimate the live load deflection of an interior girder subjected to extreme force effects. None of the results, however, suggest that the bridge example is at risk of excessive deformation, and so the extent to which these drawbacks present a concern can be left to the discretion of the engineer.
4

Study of the effect of structural variables of die on die deflections

Dedhia, Sanjay Z. January 1997 (has links)
No description available.
5

Agregado reciclado de construção e demolição com adição de aglomerantes hidráulicos como sub-base de pavimentos. / The use construction and demolition waste aggregate with hydraulic binders for pavement subbase.

Beja, Igor Amorim 06 December 2013 (has links)
O uso de resíduos de construção e demolição (RCD) vem ganhando espaço crescente em aplicações na engenharia. Este material adquiriu maior importância a partir da década de 70, com seu emprego ampliado como material granular em concretos de cimento para obras civis e no setor de infraestrutura, principalmente como camadas de pavimentos. O presente trabalho tem por objetivo compreender o comportamento físico e mecânico do agregado reciclado de resíduos de construção e demolição com adição de aglomerantes, a cal hidratada e cimento Portland. Foram construídos três trechos experimentais de uma via urbana com uso de RCD misto na sub-base dos pavimentos: (i) um sem aglomerantes adicionais, (ii) um com adição em usina de 3% de cal hidratada, e (iii) um com adição em usina de 3% de cimento Portland. Todas as amostras coletadas em usina foram caracterizadas em laboratório e foram analisados os comportamentos mecânicos das três diferentes misturas por meio de ensaios de (i) resistência à compressão simples aos 7 dias de cura para os materiais com aglomerantes, (ii) ensaios de módulo de resiliência a 7, 28 e 60 dias de cura para todas as misturas, e (iii) ensaios de deformação permanente com diferentes tensões. Analisando os resultados das misturas a 60 dias de cura, a mistura em RCD apresentou com o menor ganho em módulo de resiliência, enquanto que a mistura de RCD com 3% cimento, apresentou os maiores módulos, e a mistura RCD com adição em 3% de cal obteve um valor pouco abaixo daquele com cimento. Quanto ao comportamento à deformação permanente, verificou-se que a baixos níveis de tensão, todas as misturas apresentaram baixas deformações e comportamento similar. Em maiores níveis de diferença de tensões principais, as misturas estabilizadas apresentaram comportamento estável e as misturas em RCD obtiveram deformação permanente mais significativa. Com o monitoramento deflectométrico foi possível realizar retroanálise, e estimar os módulos de resiliência in situ, cujos valores foram similares aos encontrados em laboratório. Passados quase dois anos, o comportamento funcional e estrutural dos trechos experimentais é satisfatório. / The use of construction and demolition waste (CDW) has been increasing in engineering applications the use of CDW has become more important since the 70s as granular material in cement concrete applications in civil engineering and transportation infrastructure, mainly as pavement layers. This study aims to understand the physical and mechanical behavior of recycled aggregate from construction and demolition waste with the addition of hydraulic binders, as hydrated lime and Portland cement. Three experimental urban pavement sections were constructed using CDW as subbase material: (i) the first one using CDW, (ii) the second one using CDW with 3% of hydrated lime (mixed in the plant), and (iii) the third one employing CDW with 3% of cement (also mixed in the plant). All samples collected in the plant were characterized in laboratory. The mechanical behavior of these materials and mixtures were analyzed through the following tests: (i) compressive strength after 7 days of curing for materials with hydraulic binders, (ii) resilient moduli after 7, 28, and 60 days of curing for all mixes, and (iii) permanent deformation. By analyzing the responses of the mixture after 60 days of curing, the CDW mixture presented, as a crushed stone, the smallest gain on resilient modulus, whereas mixture with 3% cement with CDW had the highest modulus. The mixture with 3 % hydrated lime with CDW showed resilient modulus smaller than the mixture with cement. The permanent deformations at low stress levels were low and similar for the three tested materials. On the other hand, at higher stress level, the stabilized mixtures exhibited stable behavior, and the mixture with CDW shows a significant permanent deformation. The backcalculation based on the measurement of field deflections showed values of resilient moduli in situ similar to the laboratory results. After almost two years, the performance of the experimental sections is considered satisfactory.
6

Análise das deformações do concreto e do comportamento de vigas submetidas à flexão simples / Concrete strains and beams under single flexion behavior analysis

Fernandes, Solange Aparecida 08 January 1996 (has links)
Desde o seu surgimento, na França, o concreto armado vem evoluindo, com alterações nos materiais constituintes, nas dosagens e nos processos construtivos. Esta evolução tem como consequência uma variação no seu comportamento. Portanto, torna-se necessária a atualização das normas, que são as responsáveis por suas especificações. Com base na evolução do concreto, as normas, como o EC-2/89, CEB/90 e a NB-1, vem sendo substancialmente atualizadas, baseando-se em novos ensaios. Este trabalho aborda alguns aspectos que estão sendo alterados no estudo das deformações que ocorrem no concreto e no aço. Com base na análise de resultados, são feitas algumas considerações que podem contribuir para as modificações da NB-1, ora em desenvolvimento, e para futuros trabalhos sobre os temas abordados. / Since it appears, in France, the reinforced concrete has been developing, with changes in its component materials, in its doses and in its constructive process. This evolution has as result a change of its behavior. So, it makes necessary to bring the standards that are responsible for its specifications up to date. Based on the concrete evolution, the standards, as the EC-2/89, CEB/90 and the NB-1, have been essentially brought up to date based on new tests. This essay broaches some points of view that are being changed in the steel. Based on the result analysis, I do some considerations that can contribute for the modernization of the NB-1, for the time in development, and for future essays about the topics broached.
7

Prediction of deformations in post-tensioned prestressed suspended slabs in tall buildings.

Vincent, Thomas J. January 2009 (has links)
The research presented in this thesis focuses on the accuracy of predicting deflections and cambers in partially prestressed suspended slabs. Precision in predicting this behaviour accurately is complex due to the large number of variables which affect the behaviour of suspended prestressed slabs. This level of complexity is particularly relevant for post tensioned slabs due to the numerous on site construction steps. Many of the variables are hard to determine accurately due to their tendency to be unique for each construction site. Variables such as ambient temperatures, concrete material properties, stressing times, applied loads, loading times, prop movement and humidity are all examples of these properties. Hence, when predicting the behaviour of post tensioned suspended slabs of a multi storey building there always remains a degree of uncertainty. The research presented in this thesis addresses crucial areas of this topic and ultimately aims to supply reinforced concrete designers and constructors with additional confidence when predicting this behaviour. The requirement for this project surfaced during the design stages of 151 Pirie, a multistorey building constructed in Adelaide, Australia. The design project for 151 Pirie was particularly complex due to a very ambitious construction timeline. The strict construction timeline was imposed due to the contractual agreement of early occupancy of the top three floors (of a 9 storey building). The client purchasing the top floors required functioning office space within a matter of months. This contract created a construction priority of erecting the bare structural requirements up to and including the top three floors in the shortest possible time. Fittings and services to the top three floors was then the secondary priority. Fitting and services to the lower floors (which would usually be achieved before the upper floors) would be performed at a later date. Excessive deflection limits of the slabs due to the accelerated construction were a major concern for the client. The effect on the deformation performance due to the accelerated construction was difficult to predict for the designer. Therefore, this project was born to help supply confidence to the designer and concrete supplier for this construction scenario. This research project was designed to assist in the close monitoring and recording of the construction process of 151 Pirie. Due to the nature of data collection, data from this construction site would be limited in its benefits for the current construction. However, the data obtained would be vital for future projects by providing a log of onsite slab performance data as well as explanations of delays or other general outcomes with the construction process. Therefore, the aim of this research is to present the issues that were faced, the methods used to overcome these issues as well as displaying the vast amounts of site specific data documented within this project for future reference. In this research a wide range of concrete material properties were collected and monitored closely on site as well as in the laboratory. The experimental testing created large detailed database of concrete material properties as well as other relevant factors such as surveyed deflections and construction timing. Concrete material properties were the primary focus of this research due to their direct effect on member performance. The database was sufficiently large to allow a meaningful statistical data analysis to be performed on the compressive strength (f’[subscript]c), modulus of elasticity (E[subscript]c) and tensile strength (f’[subscript] t) of the concrete samples. This analysis supplied a detailed understanding of the statistical relationship between different concrete material properties. A Monte Carlo simulation was performed, with multiple deflection and camber models, to create a statistical distribution of predicted deflections and cambers from the statistical distribution of concrete material properties. This statistical output is then critically analysed and compared to the surveyed data. Proposed improvements to the process of predicting deflections and cambers have been outlined. These improvements have then been utilised in the construction of a finite element style program. Finally, the multiple predictions of column strip and mid panel deformation are compared to the short term surveyed deflections. It is summarised that the improvements suggested and implemented in the finite style analysis yield results with a higher degree of accuracy. The accuracy and benefits of the suggested improvements has been justified and proven by the application of multiple examples and a parametric study. / http://proxy.library.adelaide.edu.au/login?url= http://library.adelaide.edu.au/cgi-bin/Pwebrecon.cgi?BBID=1366459 / Thesis (M.Eng.Sc.) -- University of Adelaide, School of Civil, Environmental and Mining Engineering, 2009
8

ASSESSMENT OF LIVE LOAD DEFLECTIONS IN A SIMPLE SPAN COMPOSITE BRIGDE WITH PRESTRESSED PRECAST CONCRETE GIRDERS

Duran, Heriberto C 01 May 2016 (has links)
The purpose of this study is to investigate how accurately the distribution factor method estimates the live load deflections under the principles of the 2012 AASHTO LRFD Bridge Design Specifications (AASHTO LRFD specifications) compared to the results of the NISA finite element analysis software. The simple span bridge model analyzed is developed very similarly to the design example of the PCI Bridge Design Manual. The main difference is a shorter span length and smaller AASHTO-PCI bulb tee sections. Three main finite element models are created to estimate the live load deflections under the recommended live load conditions as per AASHTO LRFD specifications. The first model is simulated with simple support conditions. The purpose of this model is two-fold: compare the deflections to the distribution factor method and to the deflections of the second model that is simulated with elastomeric steel reinforced bearing pads. Thus, the stiffnesses of the elastomeric bearing pads of the second model are varied within the AASHTO LRFD specifications acceptable limits and under low temperature conditions the stiffness is increased accordingly for two cases. The purpose is to investigate if the stiffness have any significant affect on the deflections of the girders. Then a third model is created to investigate if the removal of the intermediate diaphragms have any affect on the deflections. The results of the first and second models, including the models with the allowed varied stiffnesses of the bearing pads, found only the interior girders deflecting up to 4% more and the exterior girders were deflecting up to 5.55% less than the estimates of the distribution factor method. In the case when the diaphragms are removed, the deflections of the inner most interior girders are deflecting up to 10.85% more compared to the same girders of the model which includes the intermediate diaphragms and the bearing pads. In the unique case of the second model where the bearing pads may stiffen significantly under low temperatures, the girders are deflecting up to 23% less than when at room temperature conditions. All these findings and other summarized results are discussed in greater detail in this study.
9

Agregado reciclado de construção e demolição com adição de aglomerantes hidráulicos como sub-base de pavimentos. / The use construction and demolition waste aggregate with hydraulic binders for pavement subbase.

Igor Amorim Beja 06 December 2013 (has links)
O uso de resíduos de construção e demolição (RCD) vem ganhando espaço crescente em aplicações na engenharia. Este material adquiriu maior importância a partir da década de 70, com seu emprego ampliado como material granular em concretos de cimento para obras civis e no setor de infraestrutura, principalmente como camadas de pavimentos. O presente trabalho tem por objetivo compreender o comportamento físico e mecânico do agregado reciclado de resíduos de construção e demolição com adição de aglomerantes, a cal hidratada e cimento Portland. Foram construídos três trechos experimentais de uma via urbana com uso de RCD misto na sub-base dos pavimentos: (i) um sem aglomerantes adicionais, (ii) um com adição em usina de 3% de cal hidratada, e (iii) um com adição em usina de 3% de cimento Portland. Todas as amostras coletadas em usina foram caracterizadas em laboratório e foram analisados os comportamentos mecânicos das três diferentes misturas por meio de ensaios de (i) resistência à compressão simples aos 7 dias de cura para os materiais com aglomerantes, (ii) ensaios de módulo de resiliência a 7, 28 e 60 dias de cura para todas as misturas, e (iii) ensaios de deformação permanente com diferentes tensões. Analisando os resultados das misturas a 60 dias de cura, a mistura em RCD apresentou com o menor ganho em módulo de resiliência, enquanto que a mistura de RCD com 3% cimento, apresentou os maiores módulos, e a mistura RCD com adição em 3% de cal obteve um valor pouco abaixo daquele com cimento. Quanto ao comportamento à deformação permanente, verificou-se que a baixos níveis de tensão, todas as misturas apresentaram baixas deformações e comportamento similar. Em maiores níveis de diferença de tensões principais, as misturas estabilizadas apresentaram comportamento estável e as misturas em RCD obtiveram deformação permanente mais significativa. Com o monitoramento deflectométrico foi possível realizar retroanálise, e estimar os módulos de resiliência in situ, cujos valores foram similares aos encontrados em laboratório. Passados quase dois anos, o comportamento funcional e estrutural dos trechos experimentais é satisfatório. / The use of construction and demolition waste (CDW) has been increasing in engineering applications the use of CDW has become more important since the 70s as granular material in cement concrete applications in civil engineering and transportation infrastructure, mainly as pavement layers. This study aims to understand the physical and mechanical behavior of recycled aggregate from construction and demolition waste with the addition of hydraulic binders, as hydrated lime and Portland cement. Three experimental urban pavement sections were constructed using CDW as subbase material: (i) the first one using CDW, (ii) the second one using CDW with 3% of hydrated lime (mixed in the plant), and (iii) the third one employing CDW with 3% of cement (also mixed in the plant). All samples collected in the plant were characterized in laboratory. The mechanical behavior of these materials and mixtures were analyzed through the following tests: (i) compressive strength after 7 days of curing for materials with hydraulic binders, (ii) resilient moduli after 7, 28, and 60 days of curing for all mixes, and (iii) permanent deformation. By analyzing the responses of the mixture after 60 days of curing, the CDW mixture presented, as a crushed stone, the smallest gain on resilient modulus, whereas mixture with 3% cement with CDW had the highest modulus. The mixture with 3 % hydrated lime with CDW showed resilient modulus smaller than the mixture with cement. The permanent deformations at low stress levels were low and similar for the three tested materials. On the other hand, at higher stress level, the stabilized mixtures exhibited stable behavior, and the mixture with CDW shows a significant permanent deformation. The backcalculation based on the measurement of field deflections showed values of resilient moduli in situ similar to the laboratory results. After almost two years, the performance of the experimental sections is considered satisfactory.
10

Análise das deformações do concreto e do comportamento de vigas submetidas à flexão simples / Concrete strains and beams under single flexion behavior analysis

Solange Aparecida Fernandes 08 January 1996 (has links)
Desde o seu surgimento, na França, o concreto armado vem evoluindo, com alterações nos materiais constituintes, nas dosagens e nos processos construtivos. Esta evolução tem como consequência uma variação no seu comportamento. Portanto, torna-se necessária a atualização das normas, que são as responsáveis por suas especificações. Com base na evolução do concreto, as normas, como o EC-2/89, CEB/90 e a NB-1, vem sendo substancialmente atualizadas, baseando-se em novos ensaios. Este trabalho aborda alguns aspectos que estão sendo alterados no estudo das deformações que ocorrem no concreto e no aço. Com base na análise de resultados, são feitas algumas considerações que podem contribuir para as modificações da NB-1, ora em desenvolvimento, e para futuros trabalhos sobre os temas abordados. / Since it appears, in France, the reinforced concrete has been developing, with changes in its component materials, in its doses and in its constructive process. This evolution has as result a change of its behavior. So, it makes necessary to bring the standards that are responsible for its specifications up to date. Based on the concrete evolution, the standards, as the EC-2/89, CEB/90 and the NB-1, have been essentially brought up to date based on new tests. This essay broaches some points of view that are being changed in the steel. Based on the result analysis, I do some considerations that can contribute for the modernization of the NB-1, for the time in development, and for future essays about the topics broached.

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