Thesis (M.S.C.E.)--University of Toledo, 2007. / Typescript. "Submitted as partial fulfillment of the requirements for The Master of Science in Civil Engineering." "A thesis entitled"--at head of title. Bibliography: leaves 55-56.

Thesis (Ph.D.)--Hong Kong University of Science and Technology, 2008. / Includes bibliographical references. Also available in electronic version.

The creep and shrinkage of concrete and the relaxation of cables cause long-term redistribution of internal forces and time-dependent deformations in concrete structures, steel-concrete composite structures and concrete cable-stayed bridges. They should be properly modelled for accurate prediction of their long-term behaviour and its effect on instantaneous structural responses at service. An equivalent stress relaxation model is proposed for prestressing tendons based on the intrinsic stress relaxation, from which the equivalent creep coefficients can be obtained through a recursive algorithm. Based on the equivalent stress relaxation model, an accurate finite element analysis of time-dependent behaviour by time integration has been devised considering concrete creep, concrete shrinkage and cable relaxation. Concrete members are modelled by beam-column elements while tendons are modelled by truss elements with nodes connected to the beam axis by perpendicular rigid arms. It is found that the proposed relaxation model with time integration can provide a reliable method as well as benchmark solutions for time-dependent analysis. The numerical results obtained indicate that the interactions among these factors should be properly considered in analysing the long-term performance of concrete bridges. Although time integration provides a reliable method for time-dependent analysis, both the computing time and memory requirement increase drastically with the number of time steps as the time-dependent strains of concrete and tendons within a time interval depend on the loading history up to that time. It is therefore necessary to develop a more efficient method to conduct time-dependent analysis. The relaxation-adjusted elasticity modulus is introduced on the basis of equivalent creep coefficients of tendons. Then, an efficient tendon sub-element is put forward to cope with cables with arbitrary profiles. Finally, a more general single-step method is devised using the classical age-adjusted elasticity modulus to account for external loading and creep effect, the shrinkage-adjusted elasticity modulus to consider shrinkage effect and its interaction with concrete creep, and the relaxation-adjusted elasticity modulus to consider the effect of cable relaxation based on the finite element method. The numerical results obtained indicate not only the accuracy of the single-step method but also the significance of interaction among various time-varying factors. Based on the time integration or single-step method, a systematic method is developed to monitor the long-term variations of dynamic properties of cable-stayed bridges taking into account various time-varying factors and geometric nonlinearities. Numerical studies show that, although geometric nonlinearities tend to reduce the natural frequencies, the time-dependent behaviour of concrete more than offsets it and tends to increase the natural frequencies in the long run. A generic method is further presented to investigate the long-term dynamic response of vehicle-bridge interaction systems taking account of time-dependent behaviour. The vehicles are represented by a combination of mass-spring-damper systems while the bridge is modelled by finite elements. The surface roughness of bridge deck is simulated by spectral representation method and introduced to the coupled system properly. Based on the method, the individual and combined effects of various time-varying factors are studied in detail using various numerical examples. / published_or_final_version / Civil Engineering / Doctoral / Doctor of Philosophy

Thesis (M.S.C.E.)--University of Toledo, 2009. / Typescript. "Submitted as partial fulfillment of the requirements for The Master of Science in Civil Engineering." "A thesis entitled"--at head of title. Bibliography: leaf 66.

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No description available.

Em estruturas estaiadas de pontes e viadutos, a determinação das forças dos estais necessariamente está relacionada à ação direta dos carregamentos mais a interação com a deformabilidade do estaiamento, incluindo principalmente o sistema tabuleiro e mastro. Por outro lado, é necessário conhecer estas forças ao longo das fases de montagem, assim como sua adequada implantação na estrutura e a determinação de possíveis ajustes nas forças devido ao processo construtivo da ponte, garantindo assim que os esforços desejados sejam alcançados e a correta distribuição espacial das forças do estaiamento. O conhecimento das forças dos estais é de extrema importância no controle dos deslocamentos e esforços da estrutura em questão, tendo este trabalho foco no greide e nos esforços finais do tabuleiro da ponte estaiada. As forças podem ser obtidas a partir da solução de um problema fundamental que consiste na determinação de acréscimos de força nos estais, necessários para atingir ou controlar um vetor de deslocamentos, ou um vetor de momentos fletores. De maneira geral, no caso de pontes construídas com aduelas (balanços sucessivos), para cada aduela anexada os esforços e deslocamentos são alterados nas aduelas já executadas, e principalmente nos estais já montados. A montagem deve garantir o greide final do tabuleiro e o conjunto de esforços desejados, o que se consegue com uma criteriosa definição dos esforços de montagem dos cabos. No mais, em função da sequência construtiva e do programa de tensionamento dos estais estabelecido para a obra, pode se tornar necessária a aplicação de uma correção sequencial das forças dos estais para se chegar às forças finais previstas em projeto.Será apresentado neste trabalho o procedimento de controle do greide final e dos esforços do tabuleiro da ponte e o de montagem dos estais, sendo este último, dividido na definição das forças dos cabos ao longo da montagem, na implantação destas forças na estrutura e num procedimento de correção sequencial das forças dos estais a partir da determinação de forças de ajuste. / In cable-stayed structures of bridges and viaducts, the determination of the stay forces is necessarily related to the direct action of loads plus interaction with the deformability of the staying, including especially the system deck and mast. On the other hand, it is necessary to know these forces along the assembly phases, as well as their proper implementation in the structure and determination of possible adjustments in forces due to bridge construction process, ensuring that the desired forces are achieved and the correct spatial distribution of forces of the staying. The knowledge of the stay forces is extremely important in controlling of the displacements and forces of the structure in question, having this work focus on shape and final forces of the cable-stayed bridge deck. The forces can be obtained from the solution to a fundamental problem that consists in the determination of increases strength in the stays, required to reach or control an array of displacements, or a vector of bending moments. In general, in the case of bridges constructed with staves (cantilever procedure), for each attached stave the forces and displacements are changed in staves already implemented, and especially in the stays already assembled. The assembly must ensure final shape of the deck and all forces desired, what can be achieved with a careful definition of the assembly forces of the cable. In addition, according to the sequence of constructive and the program tensioning of the stays established for the construction, may become necessary to apply a sequential correction of the strengths of the stays to reaching at the final forces provided in project.It will be presented in this work the procedure of control final shape and bridge deck forces and the assembly of stays, the latter divided in defining the forces of the cables along the assembly, deployment of these forces in the structure and a sequential correction procedure of the stay forces from the determination of adjustment forces.

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

Long bridges tend to develop large deformations under the action of intense dynamical loads such as wind or earthquakes. Unless these deformations are controlled in some fashion, the structure might suffer damage or even collapse. One possible solution to this problem is to apply external forces to the bridge through suspension cables. This work presents an active robust control scheme to suppress the vibrations caused by the vertical ground motion due to an earthquake of a cable-stayed bridge. It is proven both mathematically and through computer simulation that the active nonlinear controller is capable of reducing the amplitude of the vibrations to an arbitrarily small size. This may save the bridge structure during a strong earthquake. It is shown that the control scheme performs satisfactorily even if parts of the system fail during an earthquake. An alternative method to derive the control law using finite elements is also presented. / Graduation date: 1993

Long-span cable-stayed bridges have gained increasing popularity due to their appealing aesthetics, increased stiffness compared to the suspension bridges, and relatively small size of bridge components. For cable-stayed bridges with steel girders in particular, fatigue has been one of the most important failure modes and the prediction of the remaining fatigue lives has been the primary focus in recent years. To enable the evaluation of fatigue performance, a reasonable baseline finite element model reflecting the real structural behaviour is indispensable. This thesis describes the establishment of baseline finite element models of cable-stayed bridges for fatigue analysis considering the mean stress effect. Ting Kau Bridge in Hong Kong is chosen as a real life example to demonstrate the practical application of the methods developed. Firstly, the initial cable forces of the finite element model of the cable-stayed bridge are calibrated to ensure that the initial geometry of the finite element model under permanent loading agrees with that specified on the as-built drawings within reasonable tolerance. The traditional cable force adjustment method is often a trial-and-error process which is empirical, time-consuming and occasionally difficult in convergence. An optimization method based on the Kriging surrogate model is therefore developed in order to establish the relation between the deck geometry and he initial cable forces of the cable-stayed bridge. The efficiency of the proposed approach is further verified using Ting Kau Bridge against the traditional method. Furthermore, the initial finite element model developed on the basis of engineering blueprints is updated by modifying the uncertain parameters so as to achieve a refined model using the Kriging predictor. An objective function can be formulated in terms of the discrepancy between the theoretical and measured responses captured by the Wind and Structural Health Monitoring System (WASHMS) installed on the bridge. A novel feature of the proposed method is that it enables the simultaneous use of static load testing data and the dynamic information, which is not feasible by using the conventional sensitivity-based approaches. Finally, the fatigue lives of selected critical components of Ting Kau Bridge are worked out with different methods including the deterministic and probabilistic approaches based on the baseline finite element model. In the deterministic approach, the equivalent annual standard fatigue vehicle spectrum is built based on the WASHMS measurements to estimate the damage accumulation and predict fatigue lives. In the probabilistic approach, a probabilistic loading model is proposed to simulate the vehicles running along the bridge by using the available information collected by the weigh-in-motion system. Combined with the traffic load model, a statistical approach is employed to obtain the stress time-histories, and the probability density curve of the fatigue life can be obtained. One significant advantage of the proposed method is that the diurnal variation of traffic flow within different time intervals can be accounted for properly. The results of these approaches are compared with one another. As the mean stress effect is significant in the estimation of fatigue lives, the baseline calibration of cable-stayed bridges is considered essential. / published_or_final_version / Civil Engineering / Doctoral / Doctor of Philosophy