Structural Static Reliability Analysis Of Self-anchored Suspension Bridges

Due to its aesthetic appearance and adaptability for poor foundation, self-anchored suspension bridge becomes one of the most widespread bridge types used in cities. From the beginning of the 21st century, more than 20 self-anchored suspension bridges have been built in China. So far the design of self-anchored suspension bridges are limited to deterministic analysis. However taking into account the stochastic variations of structural material parameters, geometry factors and external loadings, the reliability analysis of self-anchored suspension bridges are seldom investigated. As a highly indeterminate structure, the failure of some components of a self-anchored suspension bridge doesn't mean failure of the whole structure, system reliability is a key issue in the design and construction of self-anchored suspension bridges. In this dissertation the static reliability of long-span self-anchored suspension bridges was investigated and main results obtained are listed as follows:(1) As the limit state functions of complex engineering structures are inexplicit, a uniform design method and support vector machines (UDM-SVM)-based approach was proposed, which is an improvement of the traditional response surface method.. Three algorithms, i.e. grid search, genetic algorithm and particle swarm optimization methods, were adopted to determine the parameters of the model of SVM. The proposed UDM-SVM response surface method was applied to the reliability analysis of the structure, and a relevant program was then developed. With several numerical examples, the proposed method and program were demonstrated to be accurate and effective, and the efficiency of computation could be greatly improved.(2) The reliability analysis of Liede Bridge and Sanchaji Bridge under serviceability limit-state was carried out with the proposed UDM-SVM response surface method. When the main span was fully occupied with traffic loads, the reliability index of maximum displacement of main girder of Liede Bridge and Sanchaji Bridge were 3.92 and 3.94 respectively, which showed that both the two bridges owned high reliability under serviceability limit-state. The impact of the mean and coefficient of variation of random variables on the reliability index were also analyzed. The results showed that the section areas and Young's modulus of main cables, Young's modulus and inertia moment of steel stiffening girder were the main influential factors on the maximum deflection of stiffening girder.(3) With co-rotational formulation, the material and geometric stiffness matrix of a plane beam and bar element were deduced. The material nonlinearity of beam-column element was considered on the basis of the displacement method, from which the formula of response gradients in direct differentiation method was deduced. The nonlinear finite element method and first-order reliability method were combined, based on which the reliability approach was proposed and a program was developed, numerical examples were then computed to validate the accuracy and high efficiency of the proposed approach and program.(4) The nonlinear static stochastic finite element analysis program was used to assess the reliability of Liede Bridge and Sanchaji Bridge under ultimate limit states, taking account of the possible failure of girder, main cable, cable tower and suspension cables. The stochastic finite element method based on direct differentiation method was directly applied in the system reliability of long-span self-anchored suspension bridge. The results showed that the main tower and main beam of Liede Bridge failed at level 1 under different traffic loads. When the main span was fully occupied with traffic loads, the system reliability index at level 1 was 3.9439. For Sanchaji Bridge, its suspension cables failed at level 1. When searching for level 2, the system reliability index at level 2 was 5.9170. The results showed that two bridges processed high security under ultimate limit states. The sensibility analysis showed that the resistance of element sections had the most remarkable impact on element reliability index. Dead loads, live loads and bending stiffness of main girder had large impact on reliability of main beam, main cables and main tower.(5) A model test with 1:10 scale and spatial analysis were carried out on the shell shaped tower of Liede Bridge. The test and calculation indicated that strength of cable tower could meet the requirements of design specifications; the tower was safe under the construction load and operational load. And there was no visible crack under testing overloads. The results showed that the tower owned strong overload ability and high safety coefficient.(6) The main tower of Liede Bridge was modeled with elastic-plastic fiber beam-column elements, taking the geometry and material nonlinearity into consideration. The stress reliability of the main tower was assessed and the sensitivity analysis was conducted.