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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

Protection of buried structures from groundshock

Woodley, S. L. January 1997 (has links)
No description available.
2

The Influence of Loading on the Corrosion of Steel in Cracked Ordinary Portland Cement and High Performance Concretes

Jaffer, Shahzma Jafferali January 2007 (has links)
Most studies that have examined chloride-induced corrosion of steel in concrete have focused on sound concrete. However, reinforced concrete is seldom uncracked and very few studies have investigated the influence of cracked concrete on rebar corrosion. Furthermore, the studies that have examined the relationship between cracks and corrosion have focused on unloaded or statically loaded cracks. However, in practice, reinforced concrete structures (e.g. bridges) are often dynamically loaded. Hence, the cracks in such structures open and close which could influence the corrosion of the reinforcing steel. Consequently, the objectives of this project were (i) to examine the effect of different types of loading on the corrosion of reinforcing steel, (ii) the influence of concrete mixture design on the corrosion behaviour and (iii) to provide data that can be used in service-life modelling of cracked reinforced concretes. In this project, cracked reinforced concrete beams made with ordinary Portland cement concrete (OPCC) and high performance concrete (HPC) were subjected to no load, static loading and dynamic loading. They were immersed in salt solution to just above the crack level at their mid-point for two weeks out of every four (wet cycle) and, for the remaining two weeks, were left in ambient laboratory conditions to dry (dry cycle). The wet cycle led to three conditions of exposure for each beam: (i) the non-submerged region, (ii) the sound, submerged region and (ii) the cracked mid-section, which was also immersed in the solution. Linear polarization resistance and galvanostatic pulse techniques were used to monitor the corrosion in the three regions. Potentiodynamic polarization, electrochemical current noise and concrete electrical resistance measurements were also performed. These measurements illustrated that (i) rebar corroded faster at cracks than in sound concrete, (ii) HPC was more protective towards the rebar than OPCC even at cracks and (iii) there was a minor effect of the type of loading on rebar corrosion within the period of the project. These measurements also highlighted the problems associated with corrosion measurements, for example, identifying the actual corroding area and the influence of the length of rebar. The numbers of cracks and crack-widths in each beam were measured after the beam’s initial exposure to salt solution and, again, after the final corrosion measurements. HPC beams had more cracks than the OPCC. Also, final measurements illustrated increased crack-widths in dynamically loaded beams, regardless of the concrete type. The cracks in both statically and dynamically loaded OPCC and HPC beams bifurcated at the rebar level and propagated parallel to the rebar. This project also examined the extent of corrosion on the rebars and the distribution of corrosion products in the concrete and on the concrete walls of the cracks. Corrosion occurred only at cracks in the concrete and was spread over a larger area on the rebars in HPC than those in OPCC. The damage due to corrosion was superficial in HPC and crater-like in OPCC. Regardless of the concrete type, there was a larger distribution of corrosion products on the crack walls of the dynamically loaded beams. Corrosion products diffused into the cement paste and the paste-aggregate interface in OPCC but remained in the crack in HPC. The most voluminous corrosion product identified was ferric hydroxide. Elemental analysis of mill-scale on rebar which was not embedded in concrete or exposed to chlorides was compared to that of the bars that had been embedded in uncontaminated concrete and in cracked concrete exposed to chlorides. In uncontaminated concrete, mill-scale absorbed calcium and silicon. At a crack, a layer, composed of a mixture of cement paste and corrosion products, developed between the mill-scale and the substrate steel. Based on the results, it was concluded that (i) corrosion occurred on the rebar only at cracks in the concrete, (ii) corrosion was initiated at the cracks immediately upon exposure to salt solution, (ii) the type of loading had a minor influence on the corrosion rates of reinforcing steel and (iv) the use of polarized area led to a significant underestimation of the current density at the crack. It is recommended that the effect of cover-depth on (i) the time to initiation of corrosion and (ii) the corrosion current density in cracked concrete be investigated.
3

The Influence of Loading on the Corrosion of Steel in Cracked Ordinary Portland Cement and High Performance Concretes

Jaffer, Shahzma Jafferali January 2007 (has links)
Most studies that have examined chloride-induced corrosion of steel in concrete have focused on sound concrete. However, reinforced concrete is seldom uncracked and very few studies have investigated the influence of cracked concrete on rebar corrosion. Furthermore, the studies that have examined the relationship between cracks and corrosion have focused on unloaded or statically loaded cracks. However, in practice, reinforced concrete structures (e.g. bridges) are often dynamically loaded. Hence, the cracks in such structures open and close which could influence the corrosion of the reinforcing steel. Consequently, the objectives of this project were (i) to examine the effect of different types of loading on the corrosion of reinforcing steel, (ii) the influence of concrete mixture design on the corrosion behaviour and (iii) to provide data that can be used in service-life modelling of cracked reinforced concretes. In this project, cracked reinforced concrete beams made with ordinary Portland cement concrete (OPCC) and high performance concrete (HPC) were subjected to no load, static loading and dynamic loading. They were immersed in salt solution to just above the crack level at their mid-point for two weeks out of every four (wet cycle) and, for the remaining two weeks, were left in ambient laboratory conditions to dry (dry cycle). The wet cycle led to three conditions of exposure for each beam: (i) the non-submerged region, (ii) the sound, submerged region and (ii) the cracked mid-section, which was also immersed in the solution. Linear polarization resistance and galvanostatic pulse techniques were used to monitor the corrosion in the three regions. Potentiodynamic polarization, electrochemical current noise and concrete electrical resistance measurements were also performed. These measurements illustrated that (i) rebar corroded faster at cracks than in sound concrete, (ii) HPC was more protective towards the rebar than OPCC even at cracks and (iii) there was a minor effect of the type of loading on rebar corrosion within the period of the project. These measurements also highlighted the problems associated with corrosion measurements, for example, identifying the actual corroding area and the influence of the length of rebar. The numbers of cracks and crack-widths in each beam were measured after the beam’s initial exposure to salt solution and, again, after the final corrosion measurements. HPC beams had more cracks than the OPCC. Also, final measurements illustrated increased crack-widths in dynamically loaded beams, regardless of the concrete type. The cracks in both statically and dynamically loaded OPCC and HPC beams bifurcated at the rebar level and propagated parallel to the rebar. This project also examined the extent of corrosion on the rebars and the distribution of corrosion products in the concrete and on the concrete walls of the cracks. Corrosion occurred only at cracks in the concrete and was spread over a larger area on the rebars in HPC than those in OPCC. The damage due to corrosion was superficial in HPC and crater-like in OPCC. Regardless of the concrete type, there was a larger distribution of corrosion products on the crack walls of the dynamically loaded beams. Corrosion products diffused into the cement paste and the paste-aggregate interface in OPCC but remained in the crack in HPC. The most voluminous corrosion product identified was ferric hydroxide. Elemental analysis of mill-scale on rebar which was not embedded in concrete or exposed to chlorides was compared to that of the bars that had been embedded in uncontaminated concrete and in cracked concrete exposed to chlorides. In uncontaminated concrete, mill-scale absorbed calcium and silicon. At a crack, a layer, composed of a mixture of cement paste and corrosion products, developed between the mill-scale and the substrate steel. Based on the results, it was concluded that (i) corrosion occurred on the rebar only at cracks in the concrete, (ii) corrosion was initiated at the cracks immediately upon exposure to salt solution, (ii) the type of loading had a minor influence on the corrosion rates of reinforcing steel and (iv) the use of polarized area led to a significant underestimation of the current density at the crack. It is recommended that the effect of cover-depth on (i) the time to initiation of corrosion and (ii) the corrosion current density in cracked concrete be investigated.
4

Frequency analysis of accelerometer measurements on trains

Majala, Jonas January 2017 (has links)
No description available.
5

Comportamento de tubulões escavados a céu aberto, submetidos a carregamentos dinâmicos, em solo colapsível / not available

Campelo, Nilton de Souza 13 April 2000 (has links)
Provas de carga dinâmicas em sete tubulões, de oito metros de comprimento e 0,60 m de diâmetro de fuste, sendo quatro com 1,5 m de base alargada, são apresentadas. Resistências mobilizadas determinadas pelo PDA e pela utilização de métodos que empregam medidas de repique elástico, em particular, os métodos de CHELLIS-VELLOSO e UTO et al. (1985) são comparadas. Várias seqüências de carregamento foram efetuadas, de modo a se ter uma ideia da influência de carregamentos sucessivos no comportamento dos tubulões. Constatou-se que o método de CHELLIS-VELLOSO apresentou resultados sofríveis em relação às resistências encontradas pelas análises CAPWAP, mas que melhoram à medida que sucessivos carregamentos são impostos aos tubulões, por causa do gradual comportamento de tubulões escavados em tubulões \"cravados\", pelo acúmulo de tensões residuais de cravação. Este fato pode ser corroborado pela aplicação do Princípio de Hamilton aos tubulões, fazendo crer que a realização de um ensaio de carregamento dinâmico em elementos de fundação moldados in loco necessita de uma suficiente penetração líquida deste elemento no terreno - da ordem do seu diâmetro, se este for de seção uniforme -, ou seja, sua transformação em um elemento de comportamento \"cravado\". Em alguns tubulões, provas de carga dinâmicas foram efetuadas com o solo em estado natural e inundado, a fim de se determinar a influência da colapsibilidade na resistência mobilizada, conforme o nível de energia aplicado. Verificou-se que em um tubulão submetido a uma inundação prévia do terreno por 48 h, as resistências mobilizadas foram inferiores às encontradas nos demais, para um mesmo nível de energia, muito provavelmente pela ação deletéria da água na colapsibilidade do solo em tela. / Dynamic Loading Tests (DLT) on seven caissons 8 m length and 0,60 m shaft diameter are presented, being four caissons with 1,5 m enlarged base diameter. Mobilized resistances determined both through PDA and rebound measurement methods as CHELLIS-VELLOSO and UTO et al. (1985) are compared. SeveraI successive loadings were performed in order to obtain assessment of the influence of the loading sequence in the caisson behavior. It was observed what CHELLIS-VELLOSO method showed very poor agreement with the obtained resistances through the CAPWAP analysis. Nevertheless, it was noted what the more the caissons are submitted to successive loadings, the closer are the results between CAPWAP analysis and CHELLIS-VELLOSO method, because the cast-in-place caisson is gradually switched to a driving caisson due to driving residual stress accumulations. To allow this to happen, it is necessary to have a net set value close to the shaft diameter in caisson without enlarged base. These facts were confirmed through the application Hamilton\'s Principle to tested caissons. In some caissons DLT were performed with natural and soaked soil conditions in order to know the collapsible influence in the mobilized resistances. lt was verified what 48 hours previous soaked soil resulted in lowest resistances than observed in the other caissons to the same energy level. This fact may justify the harmful action of the water in the reduction of resistance in collapsible soils.
6

Comportamento de tubulões escavados a céu aberto, submetidos a carregamentos dinâmicos, em solo colapsível / not available

Nilton de Souza Campelo 13 April 2000 (has links)
Provas de carga dinâmicas em sete tubulões, de oito metros de comprimento e 0,60 m de diâmetro de fuste, sendo quatro com 1,5 m de base alargada, são apresentadas. Resistências mobilizadas determinadas pelo PDA e pela utilização de métodos que empregam medidas de repique elástico, em particular, os métodos de CHELLIS-VELLOSO e UTO et al. (1985) são comparadas. Várias seqüências de carregamento foram efetuadas, de modo a se ter uma ideia da influência de carregamentos sucessivos no comportamento dos tubulões. Constatou-se que o método de CHELLIS-VELLOSO apresentou resultados sofríveis em relação às resistências encontradas pelas análises CAPWAP, mas que melhoram à medida que sucessivos carregamentos são impostos aos tubulões, por causa do gradual comportamento de tubulões escavados em tubulões \"cravados\", pelo acúmulo de tensões residuais de cravação. Este fato pode ser corroborado pela aplicação do Princípio de Hamilton aos tubulões, fazendo crer que a realização de um ensaio de carregamento dinâmico em elementos de fundação moldados in loco necessita de uma suficiente penetração líquida deste elemento no terreno - da ordem do seu diâmetro, se este for de seção uniforme -, ou seja, sua transformação em um elemento de comportamento \"cravado\". Em alguns tubulões, provas de carga dinâmicas foram efetuadas com o solo em estado natural e inundado, a fim de se determinar a influência da colapsibilidade na resistência mobilizada, conforme o nível de energia aplicado. Verificou-se que em um tubulão submetido a uma inundação prévia do terreno por 48 h, as resistências mobilizadas foram inferiores às encontradas nos demais, para um mesmo nível de energia, muito provavelmente pela ação deletéria da água na colapsibilidade do solo em tela. / Dynamic Loading Tests (DLT) on seven caissons 8 m length and 0,60 m shaft diameter are presented, being four caissons with 1,5 m enlarged base diameter. Mobilized resistances determined both through PDA and rebound measurement methods as CHELLIS-VELLOSO and UTO et al. (1985) are compared. SeveraI successive loadings were performed in order to obtain assessment of the influence of the loading sequence in the caisson behavior. It was observed what CHELLIS-VELLOSO method showed very poor agreement with the obtained resistances through the CAPWAP analysis. Nevertheless, it was noted what the more the caissons are submitted to successive loadings, the closer are the results between CAPWAP analysis and CHELLIS-VELLOSO method, because the cast-in-place caisson is gradually switched to a driving caisson due to driving residual stress accumulations. To allow this to happen, it is necessary to have a net set value close to the shaft diameter in caisson without enlarged base. These facts were confirmed through the application Hamilton\'s Principle to tested caissons. In some caissons DLT were performed with natural and soaked soil conditions in order to know the collapsible influence in the mobilized resistances. lt was verified what 48 hours previous soaked soil resulted in lowest resistances than observed in the other caissons to the same energy level. This fact may justify the harmful action of the water in the reduction of resistance in collapsible soils.
7

Incremental Compilation and Dynamic Loading of Functions in OpenModelica

Klinghed, Joel, Jansson, Kim January 2008 (has links)
<p>Advanced development environments are essential for efficient realization of complex industrial products. Powerful equation-based object-oriented (EOO) languages such as Modelica are successfully used for modeling and virtual prototyping complex physical systems and components. The Modelica language enables engineers to build large, sophisticated and complex models. Modelica environments should scale up and be able to handle these large models. This thesis addresses the scalability of Modelica tools by employing incremental compilation and dynamic loading. The design, implementation and evaluation of this approach is presented. OpenModelica is an open-source Modelica environment developed at PELAB in which we have implemented our strategy for incremental compilation and dynamic loading of functions. We have tested the performance of these strategies in a number of different scenarios in order to see how much of an impact they have on the compilation and execution time.</p><p>Our solution contains an overhead of one or two hash calls during runtime as it uses dynamic hashes instead of static arrays.</p>
8

Moving to a Smart Distribution Grid through Automatic Dynamic Loading of Substation Distribution Transformers

January 2011 (has links)
abstract: Dynamic loading is the term used for one way of optimally loading a transformer. Dynamic loading means the utility takes into account the thermal time constant of the transformer along with the cooling mode transitions, loading profile and ambient temperature when determining the time-varying loading capability of a transformer. Knowing the maximum dynamic loading rating can increase utilization of the transformer while not reducing life-expectancy, delaying the replacement of the transformer. This document presents the progress on the transformer dynamic loading project sponsored by Salt River Project (SRP). A software application which performs dynamic loading for substation distribution transformers with appropriate transformer thermal models is developed in this project. Two kinds of thermal hottest-spot temperature (HST) and top-oil temperature (TOT) models that will be used in the application--the ASU HST/TOT models and the ANSI models--are presented. Brief validations of the ASU models are presented, showing that the ASU models are accurate in simulating the thermal processes of the transformers. For this production grade application, both the ANSI and the ASU models are built and tested to select the most appropriate models to be used in the dynamic loading calculations. An existing application to build and select the TOT model was used as a starting point for the enhancements developed in this work. These enhancements include: &#61599; Adding the ability to develop HST models to the existing application, &#61599; Adding metrics to evaluate the models accuracy and selecting which model will be used in dynamic loading calculation &#61599; Adding the capability to perform dynamic loading calculations, &#61599; Production of a maximum dynamic load profile that the transformer can tolerate without acceleration of the insulation aging, &#61599; Provide suitable output (plots and text) for the results of the dynamic loading calculation. Other challenges discussed include: modification to the input data format, data-quality control, cooling mode estimation. Efforts to overcome these challenges are discussed in this work. / Dissertation/Thesis / M.S. Electrical Engineering 2011
9

Numerical Modelling of Liquid Containing Structure under Dynamic Loading

Barakati, Adel January 2015 (has links)
Abstract Liquid containing tanks (LCTs) are used in water distribution systems and in the industry for storing water, toxic and flammable liquids and are expected to be functional after severe earthquakes. The failure of a large tank during seismic excitation has implications far beyond the economic value of the tanks and their contents. Then seismic design becomes a high necessity for this type of structure. However, tanks differ from buildings in two ways: first, during seismic excitation, the liquid inside the tank exerts a hydrodynamic force on tank walls, base, and roof in addition to the hydrostatic forces. Second, LCTs are generally required to remain watertight. Many current standards and guidelines such as ACI 350.3-06, ACI 371R-08, ASCE7, API650, EUROCODE8 and NZSEE 1986 code, cover seismic designs which are based primarily on theoretical analysis. This analysis is still not enough to fully describe the behavior of this structure under seismic oscillation noting that the theoretical analysis is based on a linear model and two dimensional spaces. So the focus of this study is to measure two important dynamic parameters which are the natural period and the maximum sloshing height of the water under harmonic motion by conducting an experimental investigation and computational fluid dynamic (CFD) simulation. Open-foam is the numerical tool chosen in this study. There is currently no study done with this tool to measure the behavior of the water inside a square tank neither under seismic motion nor harmonic oscillation.Finally, a comparison between the experimental, the analytical and the numerical results will be presented to confirm the level of validity of each method. Then a conclusion is made to summarize this research and to propose future works.
10

Efficacy of gapseal® in preventing microleakage at the dental implant abutment interface

Badi Mohamed, Hadeel Mohamed January 2021 (has links)
Magister Chirurgiae Dentium (MChD) / Dental implants have proven to be a success in the past decades, however the inevitable presence of microgaps at the implant abutment interface leading to microleakage is still a distressing concern. Microbial leakage can lead to peri-implant disease and bone loss and reduces implants' success rates. Measures to decrease the effect of the microgap were introduced; amongst them is the application of silicone sealing gels, such as GapSeal®.

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