Mechanical Behaviors Of Beam-arch Bridges And Extradosed Cable-stayed Bridges

Hybrid bridges includes beam-arch bridges, suspension bridges, cable-stayed bridges and so on. These types of bridge have one thing in common that they are all composed of beams bearing bending moment, arch or column resisting compression and cable or suspender under tension. These kinds of structure are beneficial for reducing the load that is carried by beams and enhancing safety coefficient. In recent years, beam-arch bridges, self-anchored suspension bridges and extradosed cable-stayed bridges are more and more chosed by designers. However, there is a common feature for these strutures that they are all hybrid system composed by different components such as beam, arch, tower, cable, steev. Because of the hybrid bridge contains several components, the mechanical characteristics analysis is difficult and how to decide the size or stiffness of every component becomes a problem.This paper is a study about mechanical characteristics of components for hybrid bridges using energy method. Ritz Method, as a approximate analysis method of energy method, has been used in this paper to analyse the deformation curve of components in structures and proportion of loads that the components bear. The energy calculation of structural elements using Ritz Method based on principle of minimum potential energy has been finished by three steps. The first step was changing infinite degree of freedom to finite degree of freedom. That was to make a hypothesis that the displacement function has several limited variables. Then, the potential energy was expressed by those functions with the variables. Finally, those variables have been work out by calculating the extreme value of the potential energy. Then the finite element method of structural analysis was started and by comparing the results between energy calculation and the finite element analysis. it would be clear whether the hypothesis of displacement is correct. Finally, predigestion and modification was applied to drawing accurate formulae by which a simplified method of structural analysis would be proposed.This set of analysis has been applied to analysis and preliminary design of beam-arch bridge and extradosed cable-stayed bridge respectively.Main contents of this paper: (1) The formulae were developed for beam-arch through bridge subjected to a uniformly distributed load, to calculate the load shared ratio of arch and deflections of beam and arch. For a series of bridges with varying structural parameters, the results obtained by the proposed method were generally in accord with those by finite element analysis (FEA). To minimize the discrepancy between the results of the current approach and FEA, a modification factor was employed to improve the accuracy of the proposed formulae. Finally, a parametric study was conducted to investigate the influences of various structural parameters on the load shared ratio between the arch and the beam.(2) The formulae were developed for extradosed cable-stayed bridge subjected to a uniformly distributed load, to calculate the equivalent membrane tension. The equivalent load factor for load shared ratio of stay cable was discussed. For a series of bridges with varying structural parameters, the results obtained by the proposed method were accurate enough for concept or preliminary design. Finally, a parametric study was conducted to investigate the influences of various structural parameters on the load shared ratio of stay cable.The formulae and the parametric study results will provide a useful guidance in the preliminary design of the bridges with similar structural styles.