M.S.

published_or_final_version / Civil Engineering / Doctoral / Doctor of Philosophy

Thesis (M.C.E.)--University of Delaware, 2006. / Principal faculty advisor: Michael J. Chajes, Dept. of Civil & Environmental Engineering. Includes bibliographical references.

Thesis (M.S. in Engineering)--University of Texas at Austin, 2005. / Vita. Includes bibliographical references.

Cable stayed bridges are the state of the art in long span bridges. Developments in cable response analysis and computer hardware and software have allowed engineers to design and build many cable stayed bridges. Bridges of many different configurations with longer and longer spans are being built. With the long spans and high axial loads in the deck, the stability of cable stayed bridges becomes a growing concern. Current analysis procedures use a parabolic approximation to the true catenary response of cables, which is quite accurate for tight cables; however, for near instability conditions with the accompanying large deflections and consequently loose cables, a catenary model is called for. Herein, a study is conducted on the elastic stability of cable stayed bridges utilizing a true catenary model of cable response. A dimensional analysis of cable stayed bridge stability is undertaken as well as deck maximum deflection and moment under service load conditions. A computer program written by this author is the analysis tool used in this work. The program is given the acronym ULA which stands for Ultimate Load Analysis. ULA is a nonlinear plane frame program with catenary cable elements and an interactive graphics interface. The dimensional analysis is carried out by comparing the computer model of a cable stayed bridge to the theoretical model of a beam on an elastic foundation. Two preliminary simplified cable stayed bridge backspan models are studied first in order to develop the dimensionless ratios that are applicable to the bridge response and to gain an insight into the cable stayed bridge behaviour. The final model is that of an entire cable stayed bridge. Because of the multitude of parameters governing cable stayed bridge behaviour it is not possible to describe all cable stayed bridges. Instead, the dimensionless behaviour of a standard model is examined and the sensitivity of this standard to various parameter variations is given in the form of dimensionless charts. Finally, a preliminary design and analysis aid is developed from the dimensionless charts and is then applied to two existing bridge designs. / Applied Science, Faculty of / Civil Engineering, Department of / Graduate

As pontes extradorso surgiram na última década do Século XX, principalmente pelo extraordinário desenvolvimento tecnológico do concreto protendido, que possibilitou uma solução simples e econômica para a construção de pontes. A Odawara Blueway Bridge, construída em 1995 no Japão, foi a primeira ponte extradorso do mundo. Depois dessa obra, dezenas de outras pontes foram construídas com esse sistema estrutural, principalmente na Ásia, comprovando sua viabilidade técnica e econômica. Todavia, não se tem conhecimento de algum estudo que mostre em que faixa de extensão de vãos as superestruturas de pontes extradorso são economicamente vantajosas em relação a outros sistemas estruturais. Neste trabalho foi realizada uma investigação visando um estudo comparativo entre as superestruturas de pontes em viga reta de concreto protendido e as pontes extradorso, ambas construídas pelo método dos balanços progressivos. Na investigação realizada verificou-se que as pontes extradorso são economicamente competitivas com a ponte em viga reta de concreto protendido, principalmente na faixa de vãos entre 100 e 200 metros. / The extradosed bridges had appeared in the last decade of XX Century, mainly because the extraordinary technological development of the prestressed concrete made possible a simple and economic solution for the construction of bridges. The Odawara Blueway Bridge, built in 1995 in Japan, was the world\'s first extradosed bridge. After that, dozens of other bridges were built with the same structural type, most in Asia, proving it\'s economic and technique advantages. However, there is no knowledge of any study that show on witch span lengths the extradosed bridges are economically advantageous in comparison with others structural types. This work intended to do this study, comparing the superstructures of conventional prestressed concrete bridges and extradosed bridges, both built with de balanced cantilever method. On this investigation confirms that extradosed bridges are economically competitive with prestressed concrete bridges, mainly with span lengths between 100 and 200 meters.

In the present work, the non-linear vibrations and the corresponding dynamic fracture mechanics of cables of cable-stayed bridges are studied. The cables are among the most critical components in cable-stayed bridges and there are different damage sources such as corrosion, vibration, fatigue and fretting fatigue that can significantly affect them, thereby reducing the cable’s service life and even producing their failure. Cable-Parametric Resonance is the specific non-linear vibration studied in this research. This type of vibration occurs due to displacements presented at the cable supports. These displacements are induced by the wind and traffic loads acting on the pylon and deck of the bridge. Under certain conditions, unstable cable-vibration of significant amplitude can be registered. Therefore, numerical and experimental analyses are carried out in order to describe this phenomenon and to determine the corresponding instability conditions. Two non-linear models of cable-parametric resonance are studied to predict the cable response. In the simulation method, the non-linear components are treated as external forces acting on the linear systems, which are represented by Single Degree of Freedom systems and described by digital filters. A clear non-linear relationship between the excitation and the cable response is observed in the simulations and the experiments. The corresponding experimental analysis is based on a scaled model (1:200) of the Öresund bridge and a good agreement between the numerical and experimental results is found. After obtaining the relationship between the cable response and the excitation, the cable instability conditions are determined. This is done by finding the minimum displacement required at the cable supports in order to induce nonlinear cable vibration of considerable amplitude. The instability conditions are determined within a wide range of excitation frequencies and conveniently expressed in a simplified and practical way by a curve. The determination process is rather fast and offers the possibility to evaluate all bridge cable stays in a rather short time. Finally, the dynamic fracture mechanics of the cable is considered by studying the fracture toughness characteristics of the material under dynamic conditions. Finite Element simulations on a pre-cracked three-point bending specimen under impact loading are performed. The observed cable instability is equivalently considered as the associated response to impact load conditions, and a crack as a defect on the wires of a cable stay. The simulations are based on an experimental work by using the Split Hopkinson pressure bar (Jiang et al). The dynamic stress intensity factor KI(t) up to crack initiation is then obtained by different methods. The numerical estimations based on the specimen’s crack tip opening displacement (CTOD) and mid-span displacement were closest to the experimental results. It is observed that a better estimation of the dynamic stress intensity factor relies on a proper formulation of the specimen’s stiffness. / Lic March 2011

Nos últimos anos, a utilização de pontes estaiadas tem evoluído rapidamente e novos conceitos estruturais têm surgido, como por exemplo: o desenvolvimento de seções flexíveis e esbeltas, o aumento do comprimento dos vãos e a aplicação de pontes estaiadas em múltiplos vãos. Torna-se necessário portanto uma compreensão profunda do comportamento estrutural desse sistema. No processo de projeto as decisões mais importantes são geralmente feitas nas fases iniciais quando a síntese predomina sobre a análise numérica, tornando fundamental o entendimento do comportamento físico da estrutura na fase de pré-dimensionamento. Na concepção de uma ponte estaiada inúmeras alternativas estruturais são possíveis, por exemplo: pode-se utilizar um ou dois planos de cabos em diferentes arranjos, mastros e tabuleiros com seções transversais diversas e diferentes tipos de vinculação externa. Para um dado problema, mais de uma solução pode ser viável, no entanto algumas delas propiciarão a maior eficiência, sob o ponto de vista de consumo de materiais, facilidades construtivas, prazo de execução e comportamento físico da estrutura. Neste trabalho foram analisadas diferentes concepções estruturais com o objetivo de fornecer subsídios para as decisões tomadas no início do projeto estrutural de uma ponte estaiada. Para tanto, a partir do entendimento preliminar do comportamento físico de diferentes sistemas, foram definidas alternativas estruturais para análise estática através de modelos de elementos finitos tridimensionais. A análise e a comparação dos resultados permitiram um aprofundamento daquele entendimento. Além disso, alguns aspectos relevantes no projeto de pontes estaiadas foram estudados, tais como: o pré-dimensionamento dos estais, a definição da força de protensão inicial dos mesmos, o estudo do problema de fadiga nos cabos e a elaboração de modelos simplificados para análise preliminar do comportamento do tabuleiro e da torre. / In the last years, the use of cable-stayed bridges has increased a lot and new design concepts have appeared, such as: the development of slender and flexible deck sections, the increase in span length and the application of cable-stayed bridges in multiple spans. It is thus necessary a thorough understanding of the structural behavior of this system. During the design process the most important decisions are usually taken in the initial phases, when the synthesis prevail over the numerical analysis, which requires the understanding of the physical structural behavior in the preliminary design. The design of cable-stayed bridges involves many structural alternatives, for example: it is possible to use one or more cable planes in different arrangements, a wide range of pylons and decks cross sections and different types of external connections. For a given problem, more than one solution can be feasible, however some of them will provide a greater efficiency, from the point of view of material consumption, construction facilities, time of execution and physical behavior of the structure. This study analyzes different structural conceptions with the purpose of helping in the decisions made in the beginning of a cable-stayed bridge structural project. For this, from the preliminary understanding of the physical behavior of different systems, some structural alternatives were defined and a static analysis using finite element models was carried out. The analysis and comparison of results allowed an improved understanding of the problem. Furthermore, some relevant aspects in cable-stayed bridges were studied, such as: the preliminary stay design, the definition of initial prestressing force in the stays, the study of the fatigue behavior of the cables and the development of simple models to simulate the response of the bridge decks and pylons.

O princípio estrutural das pontes estaiadas não é tão recente quanto as pontes propriamente ditas. Em algumas estruturas, tais como passarelas, embarcações e tendas, já se usavam cabos como sustentação. Com a evolução da tecnologia e dos materiais, houve a possibilidade de um aperfeiçoamento dessas técnicas e sua utilização nas mais diversas áreas. As pontes estaiadas surgiram como uma alternativa eficaz para transpor grandes vãos, possibilitando a utilização de estruturas mais leves, esbeltas e econômicas. Este trabalho apresenta a evolução das pontes estaiadas no mundo e no Brasil, enfatizando os seus aspectos históricos, as novas tecnologias empregadas nestes projetos, as diversas possibilidades de geometria da estrutura e os métodos construtivos empregados nestas pontes. Para as pontes estaiadas ao redor do mundo, é elaborada uma análise geral, demonstrando sua importância ao longo da história e as vantagens que as mesmas propiciaram para o suprimento das necessidades da humanidade. Fazendo uma análise especial das pontes estaiadas brasileiras, é elaborada uma listagem das mesmas por ordem cronológica, indicando suas principais características. Finalmente, para as pontes estaiadas nacionais de maior destaque, é feita uma análise mais detalhada das suas principais características quanto ao vão central, geometria da ponte, processo construtivo, curiosidades sobre o empreendimento e período de construção. / The structural principle of cable stayed bridges is not as recent as the bridges themselves. In some structures such as catwalks, boats and tents, cable were already used as a support. With the evolution of technology and materials, there was the possibility of an improvement of these techniques and their use in several areas. The cable-stayed bridges have emerged as an effective alternative to large- span bridge, allowing the use of lighter, slim and economical structures. This paper presents the evolution of cable-stayed bridges in the world and in Brazil, emphasizing the historical aspects, the new technologies employed in these projects, the various possibilities for the geometry of the structure and the construction methods employed in these bridges. A general analysis of cable stayed bridges around the world is done, being shown their importance throughout history and the advantages that they have brought to fulfill the needs of mankind A special analysis of cable stayed bridges in Brazil will be is made a list of them in a chronological order is presented and their main features are examined. Finally, for the most prominent Brazilian cable stayed bridges national prominence, a more detailed analysis of its key features is done, being examined the central span, the bridge geometry, the constructive process, curiosities about the new development and the construction period.

As pontes estaiadas vêm sendo cada vez mais utilizadas no país, seja pela competitividade alcançada em função do domínio da tecnologia por parte dos empreiteiros e calculistas, seja pelo apelo estético. Os cabos, principais componentes deste sistema estrutural, que conferem o caráter altamente hiperestático e o comportamento não linear da estrutura são, em muitos modelos, numericamente simulados como um elemento de treliça, com a sua rigidez calculada em função da geometria e nível de carregamento do cabo. No presente trabalho é verificada a influência da componente tangencial do peso próprio do cabo, desprezada por Dishinger no cálculo da rigidez equivalente do elemento de cabo, comparada com o método proposto por Hajdn. Os resultados também são comparados com os da modelagem do cabo discretizado em elementos de treliça, seguindo a Formulação Posicional dos Elementos Finitos, que se mostrou bastante eficaz para simulação do cabo isolado, onde a capacidade de representar o comportamento do cabo foi verificada através de exemplos que mostram aspectos do comportamento não linear do mesmo. / Cable stayed bridges are being increasingly used in Brazil due to the recent master on this technology by the builders and designers and because of its aesthetics appealing. The principal components of this type of bridge, the cables, responsible for high non-linear behavior of the structure, are frequently modeled as truss element with its stiffness evaluated according to the tension and horizontal projection of the span of the cable. On the present paper the influence by neglecting the tangential component of the weight of the cable on Dishingers formula is investigated. The results are compared with the formula by Hajdn and with a model in which the cable is discretized in truss bars in a program based on the Positional Finite Element Method which has presented good results to describe the non-linear behavior of the cable.