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D.Ing. (Electrical And Electronic Engineering) / Please refer to full text to view abstract

The reliability of the main cable of a suspension bridge is crucial to the reliability of the entire bridge. Throughout the life of a suspension bridge, its main cables are subject to corrosion due to various factors, and the deterioration of strength is a slowly evolving and dynamic process. The goal of this research is to find the pattern of how the strength of steel wires inside a suspension bridge cable changes with time. Two methodologies are proposed based on the analysis of five data sets which were collected by testing pristine wires, artificially corroded wires, and wires taken from three suspension bridges: Severn Bridge, Forth Road Bridge and Williamsburg Bridge. The first methodology is to model wire strength as a random process in space whose marginal probability distribution and power spectral density evolve with time. Both the marginal distribution and the power spectral density are parameterized with time-dependent parameters. This enables the use of Monte Carlo methods to estimate the failure probability of wires at any given time. An often encountered problem -- the incompatibility between the non-Gaussian marginal probability distribution and prescribed power spectral density -- which arises when simulating non-Gaussian random processes using translational field theory, is also studied. It is shown by copula theory that the selected marginal distribution imposes restrictions on the selection of power spectral density function. The second methodology is to model the deterioration rate of wire strength as a stochastic process in time, under Ito's stochastic calculus framework. The deterioration rate process is identified as a mean-reversion stochastic process taking non-negative values. It is proposed that the actual deterioration of wire strength depends on the deterioration rate, and may also depend on the state of the wire strength itself. The probability distribution of wire strength at any given time can be obtained by integrating the deterioration rate process. The model parameters are calibrated from the available data sets by matching moments or minimizing differences between probability distributions.

The purpose of this study is to assist wire companies to identify buying behaviour amongst consumers of their products. For the purpose of this study the product will be wire products and the specific target market will be farmers in the Eastern Free State. The primary objective of the study is to identify factors that play a role in the buying behaviour of farmers in the Eastern Free State when purchasing wire products. By knowing exactly the buying criteria of wire products amongst farmers and seasonable cycles of purchasing will form the basis of strategic marketing planning. This study was conducted in two phases. Phase one consisted of a literature review and phase two of an empirical research. The empirical research consisted of a quantitative research design; more specifically, descriptive research that employed cross–sectional analysis of the quantitative data collected from a sample by means of a structured questionnaire. The results show that 76% of the respondents are older than 41 years of age. The population for this study is, therefore, a more matured one. Regarding their buying behaviour, the purchase frequency shows that the majority purchase wire products on a monthly basis and 40% on an annual basis. Most of them (78%) purchase their wire products from the co–operative. Wire products are an integral part of farming activities and in general the respondents are very positive about the industry. Most important considerations identified are that the wire industry should keep in touch with its market, never be out of orders, keep up the fast service that is currently provided, and that reputable products should be kept in stock. / Thesis (M.B.A.)--North-West University, Potchefstroom Campus, 2012.

The purpose of this study is to assist wire companies to identify buying behaviour amongst consumers of their products. For the purpose of this study the product will be wire products and the specific target market will be farmers in the Eastern Free State. The primary objective of the study is to identify factors that play a role in the buying behaviour of farmers in the Eastern Free State when purchasing wire products. By knowing exactly the buying criteria of wire products amongst farmers and seasonable cycles of purchasing will form the basis of strategic marketing planning. This study was conducted in two phases. Phase one consisted of a literature review and phase two of an empirical research. The empirical research consisted of a quantitative research design; more specifically, descriptive research that employed cross–sectional analysis of the quantitative data collected from a sample by means of a structured questionnaire. The results show that 76% of the respondents are older than 41 years of age. The population for this study is, therefore, a more matured one. Regarding their buying behaviour, the purchase frequency shows that the majority purchase wire products on a monthly basis and 40% on an annual basis. Most of them (78%) purchase their wire products from the co–operative. Wire products are an integral part of farming activities and in general the respondents are very positive about the industry. Most important considerations identified are that the wire industry should keep in touch with its market, never be out of orders, keep up the fast service that is currently provided, and that reputable products should be kept in stock. / Thesis (M.B.A.)--North-West University, Potchefstroom Campus, 2012.

Este trabalho apresenta um estudo do processo de cromatização de arames galvanizados da Linha de Galvanização 2 da Gerdau Riograndense através do entendimento das variáveis de processo que podem ser alteradas com o intuito de proporcionar uma resistência à oxidação branca maior do que a fornecida com os parâmetros de processo utilizados atualmente. Amostras de arames foram coletadas diretamente da linha de galvanização e submetidas a ensaios acelerados de corrosão em câmaras de umidade saturada (NBR 8095 e ISO 6270-2)16 e de névoa salina (NBR 8094 e ASTM B 117)15. Com base nos resultados obtidos destes ensaios são propostas alterações nas variáveis de processo, como por exemplo, tempo de imersão no tanque de cromatizante, avaliando o aumento ou não do poder protetivo. Os resultados obtidos até agora mostraram que as configurações operacionais da Linha de Galvanização 2 não oferecem uma condição para a formação de uma camada protetora eficiente. Espera-se com este trabalho justificar junto à Empresa a necessidade de alteração de parâmetros de processo para que se consiga obter significativo aumento no poder protetivo conferido pelo cromatizante ao arame galvanizado, e assim, ter condições de disponibilizar ao mercado um produto com qualidade superior no que tange a resistência à oxidação branca. / This work presents a study about the chromatization process for galvanized steel wires in the Galvanizing Line 2 of the Gerdau Riograndense through the understanding of variables of the process that can be modified to provide a superior white corrosion resistance than the one which is provided actually. Samples of wires were collected directly from the galvanizing line and submitted to accelerated corrosion tests in the saturated humidity chamber (NBR 8095 and ISO 6270-2)16 and the salt spray chamber (NBR 8094 and ASTM B 117)15. Based in the results from this tests changes in the process variables are proposed like immersion time in the chromatizating bath to evaluate the increase or decrease of the protective action. The results obtained so far showed that the operational configurations of the Galvanizing Line 2 do not offer a good condition to create an efficient protective layer on the wire. The expectation of this work is to justify to the company that changes in the parameters process are necessaries to get a significant increasing of the protective chromatizating action on the galvanized wire and this way to have conditions to offer to costumers a product with superior quality about white corrosion resistance.

Este trabalho apresenta um estudo do processo de cromatização de arames galvanizados da Linha de Galvanização 2 da Gerdau Riograndense através do entendimento das variáveis de processo que podem ser alteradas com o intuito de proporcionar uma resistência à oxidação branca maior do que a fornecida com os parâmetros de processo utilizados atualmente. Amostras de arames foram coletadas diretamente da linha de galvanização e submetidas a ensaios acelerados de corrosão em câmaras de umidade saturada (NBR 8095 e ISO 6270-2)16 e de névoa salina (NBR 8094 e ASTM B 117)15. Com base nos resultados obtidos destes ensaios são propostas alterações nas variáveis de processo, como por exemplo, tempo de imersão no tanque de cromatizante, avaliando o aumento ou não do poder protetivo. Os resultados obtidos até agora mostraram que as configurações operacionais da Linha de Galvanização 2 não oferecem uma condição para a formação de uma camada protetora eficiente. Espera-se com este trabalho justificar junto à Empresa a necessidade de alteração de parâmetros de processo para que se consiga obter significativo aumento no poder protetivo conferido pelo cromatizante ao arame galvanizado, e assim, ter condições de disponibilizar ao mercado um produto com qualidade superior no que tange a resistência à oxidação branca. / This work presents a study about the chromatization process for galvanized steel wires in the Galvanizing Line 2 of the Gerdau Riograndense through the understanding of variables of the process that can be modified to provide a superior white corrosion resistance than the one which is provided actually. Samples of wires were collected directly from the galvanizing line and submitted to accelerated corrosion tests in the saturated humidity chamber (NBR 8095 and ISO 6270-2)16 and the salt spray chamber (NBR 8094 and ASTM B 117)15. Based in the results from this tests changes in the process variables are proposed like immersion time in the chromatizating bath to evaluate the increase or decrease of the protective action. The results obtained so far showed that the operational configurations of the Galvanizing Line 2 do not offer a good condition to create an efficient protective layer on the wire. The expectation of this work is to justify to the company that changes in the parameters process are necessaries to get a significant increasing of the protective chromatizating action on the galvanized wire and this way to have conditions to offer to costumers a product with superior quality about white corrosion resistance.

Resumo: O objetivo deste trabalho foi investigar e modelar matematicamente a influência das variáveis do processo de têmpera e revenimento no limite de resistência à tração de arames de aço trefilado SAE 9254 com diâmetros de 2,00mm e 6,50mm. Para isso, utilizaram-se as ferramentas estatísticas de delineamento de experimentos e de regressão múltipla com aplicação de análise de componentes principais. Os resultados revelaram quais variáveis do processo têm influência significativa na variável resposta. Os modelos matemáticos obtidos pela regressão múltipla predizem com boa precisão a propriedade mecânica limite de resistência à tração. / Abstract: The purpose of this work was to investigate and to model mathematically the influence of the quench hardening and draw tempering process variables on the tensile strength of SAE 9254 drawn steel wires with 2,00 mm and 6,50mm diameter. To this end, the statistical tools of design of experiments and multiple regression with application of principal components analysis were employed. The results revealed the process variables that significantly affect the response variable. The mathematical models obtained by multiple regression were able to predict, with a reasonable accuracy, the mechanical property of the tensile strength. / Orientador: Messias Borges Silva / Coorientador: Rosinei Batista Ribeiro / Banca: Marco Antonio Carvalho Pereira / Banca: Gilbert Silva / Mestre

Made available in DSpace on 2014-06-11T19:30:10Z (GMT). No. of bitstreams: 0 Previous issue date: 2009-02-19Bitstream added on 2014-06-13T19:39:26Z : No. of bitstreams: 1 pimenta_cd_me_guara.pdf: 442019 bytes, checksum: 6f6f8b2d9fedc6b5b27318f6af0026ee (MD5) / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / O objetivo deste trabalho foi investigar e modelar matematicamente a influência das variáveis do processo de têmpera e revenimento no limite de resistência à tração de arames de aço trefilado SAE 9254 com diâmetros de 2,00mm e 6,50mm. Para isso, utilizaram-se as ferramentas estatísticas de delineamento de experimentos e de regressão múltipla com aplicação de análise de componentes principais. Os resultados revelaram quais variáveis do processo têm influência significativa na variável resposta. Os modelos matemáticos obtidos pela regressão múltipla predizem com boa precisão a propriedade mecânica limite de resistência à tração. / The purpose of this work was to investigate and to model mathematically the influence of the quench hardening and draw tempering process variables on the tensile strength of SAE 9254 drawn steel wires with 2,00 mm and 6,50mm diameter. To this end, the statistical tools of design of experiments and multiple regression with application of principal components analysis were employed. The results revealed the process variables that significantly affect the response variable. The mathematical models obtained by multiple regression were able to predict, with a reasonable accuracy, the mechanical property of the tensile strength.