Simultâneas ocorrências de vibrações de cabos de pontes estaiadas sob ação combinada de chuva de vento têm sido observadas ao redor do mundo nos últimos 20 anos. Este mecanismo tem causado grande preocupação aos engenheiros de pontes e pesquisadores por provocar grandes amplitudes de vibração. O melhor conhecimento do fenômeno evitará que perigosas oscilações induzidas pelo efeito combinado de chuva e vento ocorram evitando que medidas sejam tomadas apenas após a ocorrência de acidentes. Foi possível determinar, neste trabalho, as características aerodinâmicas de cabos de pontes estaiadas submetidos à ação combinada de chuva e vento no que diz respeito à influência dos filetes sobre as forças aerodinâmicas (arrasto e sustentação) e sobre o desprendimento de vórtices em três modelos seccionais. O modelo M1 foi posicionado horizontalmente com vento incidente normal ao eixo longitudinal, o modelo M2 foi posicionado horizontalmente com vento incidindo obliquamente ao eixo longitudinal e o modelo M3 representa um cabo inclinado típico de ponte estaiada. Os filetes nas posições = 1 θ 60° e = 2 θ 110° aumentaram as sucções na esteira do M3 consideravelmente. Para qualquer posição dos filetes no M3 não ocorreram mudanças em seus coeficientes de sustentação. Os coeficientes de arrasto aumentaram com a presença dos filetes, no entanto não apresentaram mudanças nos valores com a variação da posição dos filetes. Em modelos horizontais, a presença dos filetes pode causar supressão ou amplificação da intensidade do desprendimento de vórtices dependendo da localização dos filetes. Para o M3 notou-se aumento da intensidade do desprendimento de vórtices para qualquer posição dos filetes. A maior intensidade ocorreu para = 1 θ 50° e = 2 θ 110°. Para todos os modelos com filetes, o desprendimento de vórtices é mais forte em escoamento turbulento. Independente da presença dos filetes, o modelo M3 apresentou freqüências de desprendimento de vórtices mais baixas que as freqüências de desprendimento do vórtice de Kármán convencional. Verifica-se, portanto, o efeito de vórtice axial. Para Re < 1,2 x 105 o filete inferior não tem influência sobre o escoamento. Entretanto, para Re > 1,2 x 105 o filete inferior passa a afetar nitidamente o escoamento em torno do cilindro. Para o modelo inclinado o filete inferior apresentou influência no escoamento para todos os valores de Re. / Simultaneous occurrences of cable vibrations under combined action of wind and rain have been observed around the world in cable-stayed bridges in the last 20 years. This mechanism has caused great concern to bridge engineers and researchers due to the large vibration amplitudes. A better knowledge of the phenomenon may prevent that dangerous oscillations induced by the combined effect of rain and wind occur, compromising the usefulness and safety of cable-stayed bridges, besides to avoiding the necessity of measures taken only after some accident occurrence. It was possible to determine, in this study, the aerodynamic characteristics of cables submitted to the combined action of rain and wind regarding the influence of rivulets on aerodynamic forces (drag and lift) and on the vortex shedding in three sectionals models. The M1 model was positioned horizontally with perpendicular wind incidence to the longitudinal axis, the M2 model was positioned horizontally with oblique wind to the longitudinal axis and the M3 model is a typical, cable of cable-stayed bridges. The rivulets positioned in the 60° (upper) position and the 110° (lower) position increase considerably the negative pressures in the M3 model wake. For any rivulets position, the M3 do not change their lift coefficients. The drag coefficients increased with the rivulet presence, however its position seems to make no difference in the values of the coefficients. In horizontal models, the rivulets can suppress or cause amplification in the vortex shedding intensity, depending of their position. For the M3 model, the vortex shedding intensity increases for all rivulets positions. The greater intensity occurred when the upper and lower rivulets were at 50° and 110°, respectively. For all models with rivulets, the vortex shedding is stronger in turbulent flow. Independent of the rivulets presence, the vortex shedding frequencies at the inclined model (M3) presented lower frequencies than the conventional Karman vortex shedding. This shows, therefore, the effects of the axial vortex. For Re < 1.2 x 105 the lower rivulet has no influence on the flow. However, for Re > 1.2 x 105 the lower rivulets affect significantly the flow around the cylinder. For the inclined model the lower rivulet has no influence on the flow for all Re range.

Desde 1988, ao redor do mundo, têm sido relatadas, ocorrências de vibrações de cabos de pontes estaiadas sob ação combinada de chuva de vento. Este mecanismo tem sido de grande interesse dos engenheiros de pontes e pesquisadores, por provocar vibrações de grandes amplitudes em cabos de pontes estaiadas. Estas vibrações, que são predominantemente transversais à direção do vento, foram observadas apenas sob condições de chuva leve e baixa velocidade do vento ocorrendo simultaneamente. As oscilações são provocadas principalmente pela formação e pelo movimento de filetes d´água que se dispõem ao longo da superfície dos cabos e modificam continuamente a distribuição de pressões em volta destes. Devido à alta flexibilidade, massa relativamente pequena e amortecimento extremamente baixo, o sistema de cabos de pontes estaiadas pode estar sujeito a largos movimentos dinâmicos induzidos pela ação combinada de chuva e vento. As grandes amplitudes atingidas reduzem a vida útil dos cabos e de suas conexões e em consequência causam danos aos dutos de proteção contra corrosão. Além disso, as oscilações excessivas podem provocar choques entre cabos adjacentes e causar situações de desconforto ao usuário. O melhor conhecimento do fenômeno evitará que perigosas oscilações induzidas pelo efeito combinado de chuva e vento ocorram evitando que medidas sejam tomadas apenas após a ocorrência de acidentes e não na fase de projeto. O objetivo principal deste trabalho foi investigar os mecanismos relacionados ao efeito combinado de chuva e vento através da identificação e quantificação da influência dos filetes sobre coeficientes aerodinâmicos e sobre a esteira de modelos seccionais. Modelos seccionais de diâmetros 110 mm e 200 mm foram posicionados verticalmente com vento incidente normal ao eixo longitudinal e posicionados verticalmente com vento incidindo obliquamente ao eixo. Os números de Strouhal apresentaram valores diferentes, variando de forma aleatória entre 0,18 e 0,27, em função do diâmetro do cabo e posição dos filetes. Existe, portanto a presença de vórtices de kármám (St=0,2), vórtices de alta velocidade reduzida (St=0,18) e vórtices de alta frequência (St=0,28), sendo estes dois últimos ocorrendo devido a presença dos filetes. Foi confirmada através dos gráficos de densidade espectral a existência de amplificação ou diminuição da intensidade do desprendimento dos vórtices em função da posição do filete superior podendo ocorrer até a supressão dos vórtices. Os modelos inclinados não apresentaram resultados visíveis para a análise de desprendimento de vórtices através de anemometria. Isso pode ter ocorrido devido a presença outros efeitos do vento que normalmente ocorrem sobre cabos inclinados. O escoamento axial, por exemplo, (que ocorre na direção axial do cabo e a sotavento da seção) pode ter sido impedido de se representar na câmara de ensaio do túnel, pois o escoamento pode encontrar as paredes ou pisos como obstáculo ao fluxo. Puderam-se reunir dados experimentais de cabos de diâmetros, posições de filetes e tipos de escoamentos diferentes. Estes resultados servem como base de dados para diversos modelos teóricos já desenvolvidos para estudo do fenômeno. / Since 1988, around the world, have been reported occurrences of cable-stayed bridges cables vibrations under combined action of rain wind. This mechanism has caused great concern to bridge engineers and researchers due to the large vibration amplitudes. These vibrations, which are predominantly cross-wind, were observed only under conditions of light rain and low wind speed occurring simultaneously. The oscillations are caused mainly by the formation and movement of water rivulets over the cables surface in the axial direction, which modify continuously the pressure distribution around the cable. Due to the high flexibility, relatively small mass and low damping, the cables system of cable-stayed bridges may be subject to large dynamic movements induced by the combined action of rain and wind. The large amplitudes reduce the lifetime of the cables and their connections, resulting in damage to the corrosion protection ducts. Moreover, the fluctuations can cause shocks between adjacent cables and cause user discomfort. A better knowledge of the phenomenon may prevent that dangerous oscillations induced by the combined effect of rain and wind occur, compromising the usefulness and safety of cable-stayed bridges, besides to avoiding the necessity of measures taken only after some accident occurrence. The main objective of this study was to investigate the mechanisms related to the combined effect of rain and wind by the identification and quantification of the rivulet influence on aerodynamic coefficients and sectional models wake. Sectional models diameters of 110 mm and 200 mm was positioned vertically with perpendicular wind incidence to the longitudinal axis and positioned vertically with oblique wind incidence to the longitudinal axis. The Strouhal numbers showed different values, varying randomly between 0.18 and 0.27 due the cable diameter and rivulet position. Therefore is noted the kármám vortex presence (St = 0.2), low frequency vortex (St = 0.18) and high frequency vortex (St = 0.28), the latter two occurring due the rivulet presence. Was confirmed by spectral density the amplification and the reduction of the vortex shedding intensity due rivulet position occurring until the vortex suppress. The inclined models showed no visible results for the vortex shedding analysis by anemometry. This may be occurring due the presence of other effects of the wind that normally occur on inclined cables. The axial flow, for example, (which occurs in the axial direction of the) may have been unable to be represented due the tunnel dimensions. Experimental data of cable diameters, rivulet positions and different flow was collected. These results serve as a database for theoretical models already developed for studying of the phenomenon.

Master of Architecture

This research is aimed at investigating and analyzing the rain-windinduced cable vibration phenomena experienced in cables of cable-stayed bridges and also the countermeasures employed by engineers to mitigate the large-amplitude vibration problem reported by various researchers around the world. In order to investigate the problem of the water rivulet creation at the top of the cable surface, a single-degree-of-freedom (SDOF) analytical model was developed and analyzed. This thesis studies the aerodynamic instability of cables in cable-stayed bridges by doing literature review of a typical in-situ test, developing a single degree-of-freedom (SDOF) analytical model, and an ANSYS finite element model. Furthermore, a linear viscous damper that acts as a countermeasure to the large amplitudes of vibration is reported and analyzed. The suppression characteristics and damper effectiveness of such countermeasure are summarized. / Includes bibliography. / Thesis (M.S.)--Florida Atlantic University, 2014. / FAU Electronic Theses and Dissertations Collection

[Truncated abstract] As a consequence of the increase in terrorist incidents, many comprehensive researches, both experimental and numerical modelling of structure and blast interaction, have been conducted to examine the behaviour of civilian structures under dynamic explosion and its impact. Nevertheless most of the works in literature are limited to response of simple structures such as masonry walls, reinforced concrete beams, columns and slabs. Although these studies can provide researchers and structural engineers a good fundamental knowledge regarding blast load effect, it is more likely for blast load to act upon entire structures in actual explosion events. The interaction between blast load and structures, as well as the interaction among structural members may well affect the structural response and damage. Therefore it is necessary to analyse more realistic reinforced concrete structures in order to gain an extensive knowledge on the possible structural response under blast load effect. Among all the civilian structures, bridges are considered to be the most vulnerable to terrorist threat and hence detailed investigation in the dynamic response of these structures is essential. This thesis focuses on the study of the response of a modern cable-stayed bridge under blast loadings. ... Firstly, analysis is conducted to examine the failure of four main components namely pier, tower, concrete back span and steel composite main span under close proximity dynamic impact of a 1000 kg TNT equivalent blast load. Secondly, based on such results, the remainder of the bridge structure is then tested by utilizing the loading condition specified in the US Department of Defence (DoD) guideline with the aim to investigate the possibility of bridge collapse after the damage of these components. It is found that failure of the vertical load bearing elements (i.e. pier and tower) will lead to catastrophic collapse of the bridge. Assuming that terrorist threat cannot be avoided, hence protective measures must be implemented into the bridge structure to reduce the damage induced by explosive blast impact and to prevent bridge from collapse. As such, a safe standoff distance is determined for both the pier and tower under the blast impact of 10000 kg TNT equivalent. This information would allow the bridge designer to identify the critical location for placing blast barriers for protection purpose. For the case of bridge deck explosion, carbon fibre reinforced polymer (CFRP) is employed to examine in respect of its effectiveness in strengthening the concrete structure against blast load. In this research, appropriate contact is employed for the numerical model to account for the epoxy resin layer between the CFRP and concrete. In addition, to ensure that the CFRP can perform to its full capacity, anchors are also considered in the numerical study to minimize the chance of debonding due to the weakening of the epoxy. The results reveal that although severe damage can still be seen for locations in close proximity to the explosive charge, the use of CFRP did reduce the dynamic response of the bridge deck as compared to the unprotected case scenario. Further investigation is also carried out to examine the change in damaged zone and global response through variation in CFRP thickness.

In the design of cable-stayed bridges, the construction analysis is very important since the worst stresses are usually reached during the construction process. In addition, if the bridge is made of concrete, the effects of time dependent phenomena have great importance. Some commercial software are able to simulate the construction process, but one of their main drawbacks is that they simulate in a backward approach where creep is difficult to analyze. In this thesis a new criterion to define the Objective Service Stage (OSS) is presented which takes the constructive process into account. Tensioning operations are very expensive, so the main goal is to define the pretension forces in the stays such that only one pretension operation is necessary in each stay.  Furthermore, an algorithm has been developed to simulate the construction process of cable-stayed bridges erected by cantilever method. This algorithm includes the creep effects into the structure. The Dischinger simplification, which is explained in this document, has been improved in order to better take into account the loading time and the age of the concrete in every stage. The creep simulation of the algorithm has been validated with some patch tests. The developed algorithm has been implemented in a full scale FEM model adapted from the Giribaile Dam project developed in 1990. In this study case, the new OSS criterion is implemented. Moreover, the axial forces in the stays, the bending moments, and the displacements are analyzed during the construction process and a comparison is carried out between two cases: with and without taking creep into account. With the new OSS criterion, the Objective Service Stage is achieved without taking the creep into account. However the creep effects, which are of huge importance in concrete bridges built by cantilever method, require the definition of an OSS which considers time dependent phenomena.

As pontes estaiadas são pontes que consistem de um tabuleiro suportado por cabos retos e inclinados (estais) fixados nos mastros. Este tipo de estrutura é altamente hiperestática, bastante sensível à seqüência construtiva, mas mesmo assim aceitando, por conta a flexibilidade do tabuleiro uma considerável gama de esforços de instalação dos estais. É importante escolher uma distribuição inicial apropriada para esses esforços sob carregamento permanente tal que a flexão no tabuleiro seja limitada. A presente pesquisa tem como objetivo estudar diferentes métodos para a obtenção de uma boa distribuição de esforços nos estais em pontes estaiadas. Os métodos estudados nesta pesquisa são: o método do tabuleiro articulado (uma articulação em cada cruzamento com os estais - MTA), o método de anulação dos deslocamentos (MAD), o método de anulação das reações em apoios fictícios (MAR) e o método de anulação dos deslocamentos ao longo do processo construtivo. A idéia final de todos eles é obter para o tabuleiro uma resposta próxima à de uma viga continua. Porém, se for necessário, pode-se controlar também os deslocamentos do mastro. Os três primeiros métodos são estudados para a configuração final da ponte, mas também foram verificados seus resultados considerando o processo construtivo, já que durante esta etapa ocorrem variações nos esforços internos da ponte alterando assim o resultado final. Todos os resultados são comparados com a finalidade de escolher um método que além de controlar a configuração final da ponte apresente uma distribuição aceitável de esforços ao final da construção. Desta forma, pode-se obter uma boa estimativa dos esforços de instalação dos estais. / Cable-stayed bridges consists of a deck supported by inclined and straight cables anchored to the pylons. This type of structure is highly hyperestatic and quite sensitive to the construction sequence, but yet supporting a considerable range of loadings from the cable installation due to the deck flexibility. Nevertheless, due to the deck flexibility the cables can accept a considerable range of loadings. It is important to choose an appropriate initial distribution for those loadings under permanent load, so that the bending moment on the bridge deck is limited. The main goal of this research is to study the different methods for obtaining a good load distribution in cables in cable-stayed bridges. The methods that are studied in this research are: The articulated deck method (there is a joint in every cable-deck junction - MTA), the zero displacement method (MAD), the ficticious support force equilibrium method (MAR), and the construction process zero displacement method. The objective of them all is to obtain a deck bending moment similar to that of a continuous beam. However, if necessary, the displacements of the pylon can be controlled. The first three methods are studied for the bridge final configuration. However, their results for the initial configuration during the construction process are also verified, since there are significant bridge internal loading variations which may change the final outcome. All the results are evaluated in order to choose a method that not also controls the bridge final configuration, but also presents an acceptable cable loading distribution at the end of the construction. This way, a good estimative of the loadings from the pylons installation can be obtained.

A evolução das pontes estaiadas modernas mostra a procura da engenharia de pontes por sistemas estruturais cada vez mais leves e esbeltos. No intuito de dar contexto ao problema de análise de estruturas esbeltas, de maneira geral e desde a perspectiva da concepção, se discutem os vários arranjos estruturais que podem se obter ao combinar o pilão, o sistema de suspensão por estais e o tabuleiro, elementos que compõem qualquer sistema estrutural de ponte estaiada. Este trabalho apresenta um método de análise estrutural estático não linear que considera os efeitos decorrentes da mudança da geometria da estrutura sob carregamentos (não linearidade geométrica) e os efeitos da resposta não linear da seção de concreto estrutural quando solicitada por flexão oblíqua composta (comportamento não linear do material). O programa ANLST foi elaborado para obter as relações momento-normal-curvatura e as rigidezes secantes na flexão oblíqua composta para uma seção de concreto de geometria arbitraria, esses resultados são integrados com uma análise elástica de segunda ordem, que é executada no programa SAP2000 para análise estrutural por elementos finitos. Mostra-se a formulação do método de análise elástica de segunda ordem pelo princípio dos deslocamentos virtuais, que leva em consideração os efeitos dos deslocamentos finitos dos nós do modelo para a resposta da estrutura, por meio da matriz de rigidez geométrica do elemento barra no espaço. Finalmente são apresentados dois exemplos de estruturas planas para validar o método e um exemplo de uma estrutura espacial para a aplicação do método. Todos esses exemplos mostram que os esforços e deslocamentos de segunda ordem, em este tipo de estruturas, não podem ser desprezados. / Modern cable stayed bridges evolution shows the bridge engineering searching for lightweight and slender structural systems. Trying to give context for the problem of analysis of slender structures, of a general mode and from the conception perspective, is discussed the several structural layouts that can be obtained from the combination of pylon, cable stayed suspension system and girder, elements that compose any structural system of cable stayed bridges. This work presents a method of non-linear static structural analysis that consider the resulting effects of geometry change under loading (geometric non linearity), and the effects of nonlinear response of the structural concrete section when it is loading for biaxial bending and axial force interaction (material non linearity). The ANLST program was developed to obtain the moment-axial-curvature relationships and the secant stiffness for biaxial bending and axial force interaction for a concrete section of arbitrary geometry. These results are integrated with the second order elastic static analysis, which is executed in the finite element program SAP2000 for structural analysis. A formulation of method for second order elastic analysis is shown by the virtual displacement principle, which leads in consideration the effects of finite displacement of the model\'s nodes for the structural behavior, by means of geometric stiffness matrix for space frame element. Finally are shown two examples of plane structures for the validation of the method and one example of space structure for the application of the method. All of these examples showed that second order forces and displacements can\'t be despised in this type of structures.

Terremotos recientes han demostrado la gran vulnerabilidad de algunos puentes ante movimiento fuerte. Los de tipo atirantado constituyen una tipología estructural muy atractiva, y que actualmente es empleada para muchos fines prácticos, por lo que es necesaria su protección sísmica. Entre las actuales estrategias de protección, el uso de dispositivos pasivos es la más robusta, económica y apropiada opción para mejorar el desempeño sísmico de estructuras, de entre los que destacan los sistemas de disipación de energía adicional como una buena alternativa. Debido a sus capacidades, fácil recambio y mantención, así como su buen comportamiento mecánico, los amortiguadores de fluidos viscosos son un excelente sistema de disipación de energía para proteger grandes estructuras contra eventos sísmicos intensos. Es por ello que el análisis, evaluación y comparación de la respuesta sísmica no lineal de puentes atirantados de hormigón, con y sin la incorporación de amortiguamiento viscoso suplementario, con el propósito de investigar su efectividad ante eventos sísmicos, es el principal objetivo de esta investigación aplicada. Para alcanzar lo antes expuesto, se definieron previamente ocho modelos teóricos de puentes atirantados basados en los internacionalmente conocidos puentes de Walter [Walter, 1999], considerando variaciones del esquema de atirantamiento, nivel del tablero, tipo de tablero y espaciamiento de los cables. Como punto de partida para el análisis dinámico no lineal, se realizó un análisis estático no lineal para todos los casos. Luego, se llevó a cabo una caracterización dinámica de los puentes mediante un análisis modal. Como primera aproximación a la respuesta sísmica de los modelos, se ejecutó un análisis mediante espectros de respuesta para cada caso, con el propósito de comparar el comportamiento sísmico en función de las principales variaciones consideradas, y para seleccionar los dos modelos más representativos para ser analizados usando análisis no lineal paso-a-paso. En seguida, se analizaron las estructuras elegidas en el paso previo mediante uso de análisis temporal no lineal por integración directa, sin la consideración de amortiguamiento viscoso suplementario, y tomando en cuenta sismos de campo lejano y campo cercano. En este sentido, se aplicaron cinco eventos sísmicos artificiales para el análisis de campo lejano, y cinco eventos reales que incorporasen pulsos de velocidad de período largo para el análisis de campo cercano, según el Capítulo 3. Finalmente, el análisis de la ubicación óptima de los amortiguadores, un estudio paramétrico tendiente a seleccionar los parámetros óptimos de los mismos, y el análisis paso-a-paso no lineal considerando los amortiguadores viscosos definitivos, fueron investigados con la idea de comparar las respuestas en función de la naturaleza del evento sísmico y el tipo de atirantamiento de los cables, considerando los mismos eventos sísmicos antes expuestos. Los resultados de la investigación muestran que la aplicación de amortiguamiento viscoso suplementario es una eficiente estrategia para incrementar el amortiguamiento de una estructura, absorbiendo una gran cantidad de la energía de entrada, y controlando la respuesta de estructuras de período largo, sobre todo en la dirección longitudinal, en donde se manifiestan las mayores respuestas. Más de un 55% de la energía de entrada puede ser disipada usando éstos dispositivos, los cuales resultan ser igualmente efectivos para sismos de campo lejano y campo cercano, con independencia del esquema de atirantamiento empleado, por lo que constituyen una excelente estrategia de protección pasiva. Debido a la gran no linealidad de éstas estructuras, el método del espectro de respuesta debe ser considerado sólo como primera aproximación al problema, y para propósitos comparativos. Para resultados más precisos, y para aplicaciones de diseño, el análisis no lineal paso-a-paso es siempre la mejor opción. Por otro lado, ésta investigación prueba el despreciable efecto del esquema de atirantamiento en la respuesta sísmica, así como el importante aumento de la respuesta cuando son tomados en cuenta los efectos tipo pulso de la directividad de la falla, característicos de sismos de fuente cercana. / Recent seismic events have demonstrated the vulnerability of some bridges under strong ground motions. Cable-stayed bridges are an attractive bridge typology currently used for many practical purposes, constituting important structural systems to be protected against earthquakes. Amongst the current seismic protection strategies, the use of passive devices is the most robust, economic and well-suited option to improve the seismic performance of structures, in which additional energy dissipation systems is good choice. Because of their capacities, easy replacement and maintenance, as well as their interesting mechanical properties, fluid viscous dampers could be an excellent additional energy dissipation system to protect large structural systems against strong earthquakes. For that reason, the analysis, assessment and comparison of the nonlinear seismic response of concrete cable-stayed bridges, with and without the incorporation of nonlinear fluid viscous dampers in order to investigate their effectiveness for seismic protection purposes, is the main objective of this applied research. To reach the proposed objectives, firstly, eight theoretical cable-stayed bridge models based on the well-known Walter's Bridges [Walter, 1999] were defined; considering variations of the stay cable layout, deck level, deck type and stay spacing. As a starting point of the nonlinear dynamic analysis, a nonlinear static analysis was performed for all the cases. After that, the dynamic characterization of the models was carried out by means of a modal analysis. As a first approach of the seismic response of the bridges, response spectrum analysis was performed in order to compare the seismic behaviour as function of the main variations considered, and to select the two most representative bridges to be analyzed using nonlinear time history analysis. The following stage was the seismic analysis of the selected bridge models from the previous step, applying nonlinear direct integration time history analysis, without additional energy dissipation devices, and considering both far-fault and near-fault ground motions. In these sense, five artificially generated earthquake events were considered for the far-fault analysis, as long as five real earthquake events containing long-period velocity pulses were included for the near-fault analysis, according to Chapter 3. Finally, the analysis of the optimal layout of the dampers, a parametric study to select the optimal damper parameters and the nonlinear step-by-step analysis considering the incorporation of the definitive fluid viscous dampers were investigated in order to compare the seismic responses as a function of the earthquake nature and stay cable layout, taking into account the same earthquake events before mentioned. Results of this investigation show that application of fluid viscous dampers as additional passive energy dissipation systems is a very efficient strategy to increase the damping of a structure, absorbing a significant amount of the seismic input energy, and controlling the seismic response of long-period structures, mainly in the longitudinal direction, where the main responses occur. More than 55% of the input energy can be dissipated with these devices, being equally efficient for far-fault and near-fault ground motions, independent on the stay cable layout, which constitutes a very promising strategy to protect cable-stayed bridges against earthquakes. Because of the highly nonlinear behaviour of those structures, response spectrum analysis must be considered only as first approach to the seismic response and for comparative purposes. For more accurate analysis results, and for design applications, nonlinear time-history analysis is a necessary choice. Likewise, it is demonstrated that the effect of the stay cable layout on the nonlinear seismic response of the bridges is not very important, as well as an important increase of the seismic response when forward rupture directivity pulse effects are considered, a characteristic of near-source ground motions.

A evolução das pontes estaiadas modernas mostra a procura da engenharia de pontes por sistemas estruturais cada vez mais leves e esbeltos. No intuito de dar contexto ao problema de análise de estruturas esbeltas, de maneira geral e desde a perspectiva da concepção, se discutem os vários arranjos estruturais que podem se obter ao combinar o pilão, o sistema de suspensão por estais e o tabuleiro, elementos que compõem qualquer sistema estrutural de ponte estaiada. Este trabalho apresenta um método de análise estrutural estático não linear que considera os efeitos decorrentes da mudança da geometria da estrutura sob carregamentos (não linearidade geométrica) e os efeitos da resposta não linear da seção de concreto estrutural quando solicitada por flexão oblíqua composta (comportamento não linear do material). O programa ANLST foi elaborado para obter as relações momento-normal-curvatura e as rigidezes secantes na flexão oblíqua composta para uma seção de concreto de geometria arbitraria, esses resultados são integrados com uma análise elástica de segunda ordem, que é executada no programa SAP2000 para análise estrutural por elementos finitos. Mostra-se a formulação do método de análise elástica de segunda ordem pelo princípio dos deslocamentos virtuais, que leva em consideração os efeitos dos deslocamentos finitos dos nós do modelo para a resposta da estrutura, por meio da matriz de rigidez geométrica do elemento barra no espaço. Finalmente são apresentados dois exemplos de estruturas planas para validar o método e um exemplo de uma estrutura espacial para a aplicação do método. Todos esses exemplos mostram que os esforços e deslocamentos de segunda ordem, em este tipo de estruturas, não podem ser desprezados. / Modern cable stayed bridges evolution shows the bridge engineering searching for lightweight and slender structural systems. Trying to give context for the problem of analysis of slender structures, of a general mode and from the conception perspective, is discussed the several structural layouts that can be obtained from the combination of pylon, cable stayed suspension system and girder, elements that compose any structural system of cable stayed bridges. This work presents a method of non-linear static structural analysis that consider the resulting effects of geometry change under loading (geometric non linearity), and the effects of nonlinear response of the structural concrete section when it is loading for biaxial bending and axial force interaction (material non linearity). The ANLST program was developed to obtain the moment-axial-curvature relationships and the secant stiffness for biaxial bending and axial force interaction for a concrete section of arbitrary geometry. These results are integrated with the second order elastic static analysis, which is executed in the finite element program SAP2000 for structural analysis. A formulation of method for second order elastic analysis is shown by the virtual displacement principle, which leads in consideration the effects of finite displacement of the model\'s nodes for the structural behavior, by means of geometric stiffness matrix for space frame element. Finally are shown two examples of plane structures for the validation of the method and one example of space structure for the application of the method. All of these examples showed that second order forces and displacements can\'t be despised in this type of structures.