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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

Assessment of the structural integrity of timber bridges using dynamic approach.

Choi, Fook Choon January 2007 (has links)
In this study, a systematic approach was adopted to investigate, numerically and experimentally, localised defects and/or damage in timber bridges, such as rot, using modal based damage detection techniques. An existing damage detection method namely damage index (DI) method that utilises modal strain energy before and after damaged state was adopted. One contribution of this study was to modify the Dl method by an additional step of normalising the modal curvature, which would minimise the dominance of higher modes. In the numerical models, a comparative study of the effects of numerical integration techniques used in a damage detection process was carried out. The results show that when mode shape curvature integrations use the rectangular rule for the numerical integration, it yields better results than the trapezoidal rule. In the numerical examples using a finite element model of timber beam, the modified DI (MDI) methods were found to perform better than its original form for locating'" single and multiple damage scenarios. For the DI methods, two types of formulations were adopted and modified, and they are denoted as modified damage index I (MDI-I) and modified damage index II (MDI-II). Another modal based damage detection method, namely changes in flexibility (CIF), was adopted for locating damage. It was found that the ClF method performed reasonably well for single damage but not multiple damage scenarios. As part of the study, the modified damage index methods were utilised for evaluating severity of damage. For the :MDI-I method, the formulation was not derived to evaluate damage severity directly. Instead, a hybrid of the MDI-I and CIF methods (HMC), was proposed for evaluating severity of damage in terms of loss of '1' (moment of inertia). Using three levels of damage, i.e. light (L), medium (M) and severe (S), the HMC method is able to predict the medium and severe damage quite well, but it is less efficient for light damage scenarios. For the MDI-II method, further manipulation of the algorithm can predict the severity of damage in terms of loss of'I'. This method is able to predict the medium and severe damage quite well but is not as good for the light damage. Both methods, HMC and MDI-II, for predicting severity of damage, required some adjustment using a weighting factor in order to obtain reasonable results. An experimental modal analysis (EMA) test program of timber beams was undertaken. This was done to verify the robustness of the modified damage index methods for detecting location and estimating severity of damage. The laboratory investigation was conducted on the corresponding changes of modal parameters due to loss of section. The MDI methods were used to detect location of damage and to evaluate the severity of damage in the test beams. A mode shape reconstruction technique was utilised to enhance the capability of the damage detection algorithms with limited number of sensors. The test results and analysis show that location of damage is quite accurately estimated with the available sensors. The methods demonstrate that they are less mode dependant and can detect damage with a higher degree of confidence. The MDI methods also show that they are able to predict the severe damage well, but it is less accurate for the medium damage and not as good for light damage. The damage index II (DI-II) method extended to plate-like structures (DI-II-P) was adopted and evaluated for detecting damage. Based on finite element analysis (FEA) results of a laboratory timber bridge, the DI-II-P method which utilises two dimensional (2-D) mode shape curvature was employed to detect location of damage. The results show that the tnethod based on 2-D mode shape curvature is able to locate damage quite well, numerically. A supplementary work using the DI-II-P method in a timber plate model was carried out. The results also show that the method was able to predict the damage location well. A process of updating a laboratory timber bridge, analytically, is presented. A finite element model was developed and updated with experimental modal data. Material properties of timber beam (girders) and plywood (deck) as well as the screw connection between deck and girder were experimentally investigated. These test results were then used for the finite element modelling. The model has been developed sequentially starting with a preliminary model having very simple features. It followed by the advanced model calibrated with the experimental modal data employing a global objective function, consisting of errors of natural frequencies and modal assurance criterion. The calibrated finite element model shows a good correlation to the experimental model with minor adjustments to the real material properties and boundary conditions. The calibrated model can reasonably be used to study the damaged behaviour of the laboratory timber bridge. The bridge model was then used to verify the numerical results for detecting damage. The bridge was inflicted with various damage scenarios with loss of section similar to the timber beam models. The limited number of data was expanded using the 2-D cubic spline. Using the reconstructed data for detecting damage yields better results than just using 'as is' data. Using the undanlaged and dmnaged modal data, the D I-II -P method was employed to detect the location of damage. The results of using the first nine modes showed that generally the severe damage is able to be located by the method. It performs reasonably well for the medium damage but does not perform as good in the light damage scenarios. However, in some cases the method can present some problems in identifying severe damage, which may be due to lack of normalisation of mode shape curvature. Complementary work was undertaken using the method 'On a timber plate, experimentally. The results showed that the damage detection process in the timber plate is less efficient compared to the laboratory timber bridge. A comprehensive comparative study was carried out based on the results of the numerical and experimental investigation of damage detection on timber beam, laboratory timber bridge and timber plate. For the timber beam, both damage detection methods, MDI-I and MDI-II, were capable of detecting medium and severe damage in the numerical and experimental studies. However, the light damage was not identified well using the experimental data in the presence of noise. To estimate damage severity in the timber beam, the HMC method performed well for the medium and severe damage. The method did not work well in estimating severity of light damage. Similar conclusions can be drawn in using the MDI-II method to estimate the damage severity. The results of applying the DI-II-P method (using 9 modes) to locate damage in the laboratory timber bridge showed that numerical and experimental data are capable of detecting all severe damage for damage cases with less than three damage locations. While for light and medium damage, the experimental data did not work well as compared to the numerical one. For the timber plate (a complementary work), the numerical and experimental results also showed that they are able to detect the severe damage well. However, there were serious false positives appearing in the light damage cases in the experimental results.
2

A Theoretical Structural Impairment Detection System for Timber Railway Bridges

Orsak, John 2012 May 1900 (has links)
The objective of this research is to develop a theoretical Structural Impairment Detection System (SIDS) for timber railway bridges. Due to fatigue, the timber stringers in timber railway bridges develop shear cracks. These shear cracks lead to higher bridge deflections, higher stresses in the stringers and rail, and shorter fatigue life of the system. A SIDS is proposed which links wheel path accelerations obtained from traversing freight cars to the condition of the bridge. In order to develop the SIDS, two models of timber railway bridges with various levels of structural impairment were developed. The first model was a quasi-static model developed from classical beam theory and implemented in MATLAB. The second model was a dynamic, finite element model created in LS-DYNA. Traversing axle loads were imposed on the models. The results obtained from the model were the wheel paths the axles take as they traverse the bridge. The paths were expressed as vertical displacements as a function of position on the bridge. Wheel path accelerations were obtained by numerically differentiating the vertical displacements. The accelerations were then used to train neural networks to have an input of an acceleration vector and an output of a bridge condition vector. The neural networks were trained on results from both models under three train speeds: 40 mph, 30 mph, and 20 mph. The networks were able to determine the correct bridge condition 90% of the time when the train speed was 40 mph and 70% of the time when the train speed was 30 mph. The networks were not successful in determining bridge condition when the train speed was 20 mph.
3

Pontes protendidas de Eucalipto citriodora / Pre-stressed timber bridge of Eucalyptus citriodora

Fonte, Thalita Fernandes da 20 February 2004 (has links)
O conceito de pontes de madeira em tabuleiro laminado protendido surgiu na década de 70, no Canadá, como forma de reabilitação para tabuleiros laminados pregados. Diversas pesquisas foram desenvolvidas para verificar o desempenho estrutural e a durabilidade do sistema, e estes estudos comprovaram a eficácia do método. Devido ao enorme déficit de pequenas e médias pontes em todo o seu território, o Brasil tem buscado cada vez mais materiais e tecnologias alternativas economicamente competitivas para sua construção. Partindo de pesquisas desenvolvidas em outros países, desde 1993 começaram a ser desenvolvidas pesquisas nacionais para verificar a viabilidade em se utilizar madeiras brasileiras para construção de pontes, e a resposta, mais uma vez, foi positiva. Este trabalho tem como objetivos o estudo teórico e experimental das pontes de eucalipto protendidas transversalmente, através do projeto e construção da primeira ponte protendida de madeira da América do Sul. Por meio de provas de carga, foi avaliado o desempenho da ponte e a influência dos guarda-rodas e defensas na rigidez do tabuleiro. Os resultados mostram que o sistema protendido de eucalipto é uma ótima alternativa para o Brasil. / The concept of pre-stressed laminated timber bridges come from 70s, in Canada, as an alternative for the rehabilitation of damaged nailed laminated timber decks. Many researches were developed to verify the structural performance and the durability of the system, which corroborated the system\'s high efficience. Because of a great deficit in short-span and medium-span bridges in Brazil, the country has searched more and more competitive materials and technologies for their construction. Based on studies developed in other countries, since 1993 Brazil has developed studies to verify the viability of using brazilian woods to build such bridges, and the answer was positive. The present work aims to investigate the project and behavior of transversally pre-stressed timber bridges of eucalyptus, through the project and construction of the first stress-laminated timber bridge in South America. The bridge performance was evaluated as well as the influence of the guard-rail system in the deck stiffness, across proof loading. The results showed that this system is a good alternative for bridge construction in Brazil.
4

Pontes protendidas de Eucalipto citriodora / Pre-stressed timber bridge of Eucalyptus citriodora

Thalita Fernandes da Fonte 20 February 2004 (has links)
O conceito de pontes de madeira em tabuleiro laminado protendido surgiu na década de 70, no Canadá, como forma de reabilitação para tabuleiros laminados pregados. Diversas pesquisas foram desenvolvidas para verificar o desempenho estrutural e a durabilidade do sistema, e estes estudos comprovaram a eficácia do método. Devido ao enorme déficit de pequenas e médias pontes em todo o seu território, o Brasil tem buscado cada vez mais materiais e tecnologias alternativas economicamente competitivas para sua construção. Partindo de pesquisas desenvolvidas em outros países, desde 1993 começaram a ser desenvolvidas pesquisas nacionais para verificar a viabilidade em se utilizar madeiras brasileiras para construção de pontes, e a resposta, mais uma vez, foi positiva. Este trabalho tem como objetivos o estudo teórico e experimental das pontes de eucalipto protendidas transversalmente, através do projeto e construção da primeira ponte protendida de madeira da América do Sul. Por meio de provas de carga, foi avaliado o desempenho da ponte e a influência dos guarda-rodas e defensas na rigidez do tabuleiro. Os resultados mostram que o sistema protendido de eucalipto é uma ótima alternativa para o Brasil. / The concept of pre-stressed laminated timber bridges come from 70s, in Canada, as an alternative for the rehabilitation of damaged nailed laminated timber decks. Many researches were developed to verify the structural performance and the durability of the system, which corroborated the system\'s high efficience. Because of a great deficit in short-span and medium-span bridges in Brazil, the country has searched more and more competitive materials and technologies for their construction. Based on studies developed in other countries, since 1993 Brazil has developed studies to verify the viability of using brazilian woods to build such bridges, and the answer was positive. The present work aims to investigate the project and behavior of transversally pre-stressed timber bridges of eucalyptus, through the project and construction of the first stress-laminated timber bridge in South America. The bridge performance was evaluated as well as the influence of the guard-rail system in the deck stiffness, across proof loading. The results showed that this system is a good alternative for bridge construction in Brazil.
5

Estudo de pontes de madeira com tabuleiro multicelular protendido / Study of timber bridges with multicellular prestressed decks

Góes, Jorge Luís Nunes de 30 May 2005 (has links)
As pontes de madeira com tabuleiro multicelular protendido são uma das mais recentes tecnologias usadas na construção das modernas pontes de madeira. Nesta tese é realizado o estudo teórico e experimental do comportamento estrutural destas pontes. Os principais métodos de cálculo são apresentados e discutidos. A investigação experimental foi realizada em dois modelos reduzidos em escala 1:3 com as mesmas dimensões externas mas diferente quantidade de nervuras. Os modelos foram ensaiados com diferentes posições de carregamento enquanto os deslocamentos, deformações e forças nas barras, eram monitorados. Os resultados obtidos demonstraram que os modelos de Placa Ortotrópica Equivalente e Elementos Finitos podem ser empregados para o dimensionamento das pontes de madeira com tabuleiro multicelular protendido. O método de Viga Equivalente pode ser empregado desde que utilizado o correto Fator de Distribuição de Carga. Os estudos realizados neste trabalho, indicam a viabilidade da utilização deste sistema estrutural para pontes com vãos de 12 a 25 m / Timber bridges with multicellular prestressed decks is one of the most recent technology for modern timber bridges construction. In this thesis the theoretical and experimental study of the structural behavior of these bridges is accomplished. The main calculation methods are introduced and discussed. Two reduced models on scale 1:3, with the same external dimensions but different number of webs, were used for the experimental investigation. The models were tested with different load positions meanwhile displacements, strains and bar forces were measured. The obtained results have show that either model of Equivalent Orthotropic Plate or Finite Elements can be used for the design of this type of bridge. The Equivalent Beam model can also be employed as long as the correct Load Distribution Factor is chosen. The accomplished studies demostrate that this structural system is viable for bridges with span from 12 to 25 m
6

Pontes protendidas de madeira com cordoalhas engraxadas: perda da protensão / Stress-laminated timber bridge with wire rope greased: stress relaxation

Ceferino, Gloria Esther Urrea 05 April 2013 (has links)
As pontes protendidas transversalmente de madeira vêm sendo pesquisadas no Brasil desde o ano 1995, com madeiras de reflorestamento e outros materiais nacionais. Os resultados mostram a viabilidade da utilização desse sistema na construção de pontes de madeira, sejam em vias rurais, urbanas e até mesmo em rodoviárias no país, a fim de viabilizar melhoras ao acesso onde se faz necessário, além de contribuição nos quesitos de segurança estrutural, em função do trafego. Este trabalho tem como objetivos os estudos teórico e experimental de pontes de madeiras protendidas transversalmente com cordoalhas engraxadas, focando, principalmente, a análise do desempenho da ponte e os estudos das influências da temperatura e da umidade no mecanismo de perda de protensão de tabuleiros laminados com madeiras. / Since 1995 Stress-Laminated Timber Bridge built with reforestation wood and other national materials have been researched in Brazil. The results show feasibility to use this system for build timber bridges, in rural and urban roads, and even in federal highways, in order to facilitate access improvements where needed, plus contribution as safe structural depending on the traffic. The aims of this paper is analyze of theoretical and experimental stress-laminated Timber Bridge with wire rope, focusing, mainly, bridges field performance and thermal response and moisture content as influence in stress relaxation in wood lumber slab.
7

Análise de pontes de madeira protendidas transversalmente formadas por vigas-T / Analysis of transversely stressed timber bridges composed of T beams

Alves, Nívea Mara Pereira 03 April 2002 (has links)
Neste trabalho é estudada uma variação do sistema estrutural de ponte de madeira com tabuleiro laminado protendido, em que a seção transversal é formada por vigas-T. As nervuras destas vigas são de madeira laminada colada e o tabuleiro de madeira serrada. São analisadas pontes da classe 30, com uma ou duas faixas de tráfego, dimensionando-se os elementos estruturais para diversas situações de projeto, e avaliando-se as influências das espécies e classes de resistência das madeiras e dos fatores geométricos (largura da nervura, altura do tabuleiro e espaçamento entre nervuras) na altura das nervuras. O procedimento de cálculo utilizado no dimensionamento das pontes de madeira formadas por vigas-T baseia-se no método WVU. Para o desenvolvimento deste trabalho, o método foi adaptado aos critérios da Associação Brasileira de Normas Técnicas, \"NBR 7188/84 - Cargas móveis em pontes rodoviárias e passarelas de pedestres\" e \"NBR 7190/97 - Projeto de estruturas de madeira\", e programado em software MATHCAD©. Os resultados obtidos indicam que não existe influência significativa na altura da nervura, ao se utilizar madeira da classe C 30 ou C 40 no tabuleiro, ou ao se variar a altura do tabuleiro de 15 até 25 cm. O modelo teórico é avaliado experimentalmente, por meio de modelo reduzido na escala geométrica de 1:5, obtendo-se boa concordância entre os valores experimentais e os teóricos. / In this work it is studied a variation of the structural system of timber bridge with transversely laminated deck, in which the transversal section is composed of T-beams. The stringers of those beams are made of glued laminated timber and the deck of sawed timber. Bridges of class 30 are analyzed, with one or two traffic lanes, where the structural elements are designed for different project situations, and evaluated the influences of specimens and wood classes and geometric factors (width of stringer, depth of deck and spacing of stringers) in the depth of stringers. The calculus procedure used in the design of the timber bridges composed of T-beams is based on the WVU Method. To the development of this work, the method was adapted to the criteria of the Brazilian standards \"NBR 7188/84 - Live Loads in Highway Bridges and Pedestrian Bridges\" and \"NBR 7190/97 - Project of Timber Structures\" and programmed in MATHCAD© software. The results obtained show that there is no significant influence in the depth of stringer, either by using wood class C 30 or C 40, or by varying the height of the deck from 15 to 25 cm. The theoretical model is evaluated experimentally, by means of a reduced model at 1:5 geometric scale, being obtained well agreement between experimental and theoretical values.
8

Análise de pontes de madeira protendidas transversalmente formadas por vigas-T / Analysis of transversely stressed timber bridges composed of T beams

Nívea Mara Pereira Alves 03 April 2002 (has links)
Neste trabalho é estudada uma variação do sistema estrutural de ponte de madeira com tabuleiro laminado protendido, em que a seção transversal é formada por vigas-T. As nervuras destas vigas são de madeira laminada colada e o tabuleiro de madeira serrada. São analisadas pontes da classe 30, com uma ou duas faixas de tráfego, dimensionando-se os elementos estruturais para diversas situações de projeto, e avaliando-se as influências das espécies e classes de resistência das madeiras e dos fatores geométricos (largura da nervura, altura do tabuleiro e espaçamento entre nervuras) na altura das nervuras. O procedimento de cálculo utilizado no dimensionamento das pontes de madeira formadas por vigas-T baseia-se no método WVU. Para o desenvolvimento deste trabalho, o método foi adaptado aos critérios da Associação Brasileira de Normas Técnicas, \"NBR 7188/84 - Cargas móveis em pontes rodoviárias e passarelas de pedestres\" e \"NBR 7190/97 - Projeto de estruturas de madeira\", e programado em software MATHCAD©. Os resultados obtidos indicam que não existe influência significativa na altura da nervura, ao se utilizar madeira da classe C 30 ou C 40 no tabuleiro, ou ao se variar a altura do tabuleiro de 15 até 25 cm. O modelo teórico é avaliado experimentalmente, por meio de modelo reduzido na escala geométrica de 1:5, obtendo-se boa concordância entre os valores experimentais e os teóricos. / In this work it is studied a variation of the structural system of timber bridge with transversely laminated deck, in which the transversal section is composed of T-beams. The stringers of those beams are made of glued laminated timber and the deck of sawed timber. Bridges of class 30 are analyzed, with one or two traffic lanes, where the structural elements are designed for different project situations, and evaluated the influences of specimens and wood classes and geometric factors (width of stringer, depth of deck and spacing of stringers) in the depth of stringers. The calculus procedure used in the design of the timber bridges composed of T-beams is based on the WVU Method. To the development of this work, the method was adapted to the criteria of the Brazilian standards \"NBR 7188/84 - Live Loads in Highway Bridges and Pedestrian Bridges\" and \"NBR 7190/97 - Project of Timber Structures\" and programmed in MATHCAD© software. The results obtained show that there is no significant influence in the depth of stringer, either by using wood class C 30 or C 40, or by varying the height of the deck from 15 to 25 cm. The theoretical model is evaluated experimentally, by means of a reduced model at 1:5 geometric scale, being obtained well agreement between experimental and theoretical values.
9

Estudo de pontes de madeira com tabuleiro multicelular protendido / Study of timber bridges with multicellular prestressed decks

Jorge Luís Nunes de Góes 30 May 2005 (has links)
As pontes de madeira com tabuleiro multicelular protendido são uma das mais recentes tecnologias usadas na construção das modernas pontes de madeira. Nesta tese é realizado o estudo teórico e experimental do comportamento estrutural destas pontes. Os principais métodos de cálculo são apresentados e discutidos. A investigação experimental foi realizada em dois modelos reduzidos em escala 1:3 com as mesmas dimensões externas mas diferente quantidade de nervuras. Os modelos foram ensaiados com diferentes posições de carregamento enquanto os deslocamentos, deformações e forças nas barras, eram monitorados. Os resultados obtidos demonstraram que os modelos de Placa Ortotrópica Equivalente e Elementos Finitos podem ser empregados para o dimensionamento das pontes de madeira com tabuleiro multicelular protendido. O método de Viga Equivalente pode ser empregado desde que utilizado o correto Fator de Distribuição de Carga. Os estudos realizados neste trabalho, indicam a viabilidade da utilização deste sistema estrutural para pontes com vãos de 12 a 25 m / Timber bridges with multicellular prestressed decks is one of the most recent technology for modern timber bridges construction. In this thesis the theoretical and experimental study of the structural behavior of these bridges is accomplished. The main calculation methods are introduced and discussed. Two reduced models on scale 1:3, with the same external dimensions but different number of webs, were used for the experimental investigation. The models were tested with different load positions meanwhile displacements, strains and bar forces were measured. The obtained results have show that either model of Equivalent Orthotropic Plate or Finite Elements can be used for the design of this type of bridge. The Equivalent Beam model can also be employed as long as the correct Load Distribution Factor is chosen. The accomplished studies demostrate that this structural system is viable for bridges with span from 12 to 25 m
10

Pontes protendidas de madeira com cordoalhas engraxadas: perda da protensão / Stress-laminated timber bridge with wire rope greased: stress relaxation

Gloria Esther Urrea Ceferino 05 April 2013 (has links)
As pontes protendidas transversalmente de madeira vêm sendo pesquisadas no Brasil desde o ano 1995, com madeiras de reflorestamento e outros materiais nacionais. Os resultados mostram a viabilidade da utilização desse sistema na construção de pontes de madeira, sejam em vias rurais, urbanas e até mesmo em rodoviárias no país, a fim de viabilizar melhoras ao acesso onde se faz necessário, além de contribuição nos quesitos de segurança estrutural, em função do trafego. Este trabalho tem como objetivos os estudos teórico e experimental de pontes de madeiras protendidas transversalmente com cordoalhas engraxadas, focando, principalmente, a análise do desempenho da ponte e os estudos das influências da temperatura e da umidade no mecanismo de perda de protensão de tabuleiros laminados com madeiras. / Since 1995 Stress-Laminated Timber Bridge built with reforestation wood and other national materials have been researched in Brazil. The results show feasibility to use this system for build timber bridges, in rural and urban roads, and even in federal highways, in order to facilitate access improvements where needed, plus contribution as safe structural depending on the traffic. The aims of this paper is analyze of theoretical and experimental stress-laminated Timber Bridge with wire rope, focusing, mainly, bridges field performance and thermal response and moisture content as influence in stress relaxation in wood lumber slab.

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