Reliability Analysis Of Composite Beam Cable-stayed Bridge

Compared to the concrete cable-stayed bridge and steel cable-stayed bridge, the composite beam cable-stayed bridge has the following advantages: long-span capacity, light weight, reasonable cost, short construction period, full use of respective material etc., which has a rapid development in last decade. At present, researches about composite beam cable-stayed bridge are concentrated on the field of deterministic structure analysis, which can’t know how the random structural parameters and random loads impact on the safety of structure. If the reliability theory which based on probability theory is applied to a structural analysis of composite beam cable-stayed bridge, the safety and reliability of composite beam cable-stayed bridge could be controlled scientifically and accurately. The Jiujiang rebuilding cable-stayed bridge is taken as the engineering background, and the reliability of composite beam cable-stayed bridge under various situations is investigated and analyzed, the main contents include the following aspects:(1) Based on Newmark geometric model, considering the concrete slab、steel beam and shear connectors as a whole element, and making use of the T.L. formulation, a nonlinear composite beam element model was developed which had taken the interface slip effect into consideration;(2) Based on the nonlinear composite beam element model and the characteristic of composite beam, the structural response gradients of composite beam were obtained by use of the DDM method, meanwhile the reliability index was achieved by use of the FORM method and the improved HL-RF iteration. According to the proposed method, a stochastic finite element program of composite beam written in C++ as well as Matlab was developed. Several numerical examples were computed to validate the accuracy of the proposed approach;(3) Taking advantage of the proposed stochastic finite element program of composite beam, a stochastic finite element analysis was directly applied to the analysis of composite beam cable-stayed bridge during construction stage,the reliability for elevation control of composite beam during construction stage was analyzed, meanwhile the sensitivity of structure parameter which might have an effect on the elevation control was also analyzed, and some useful conclusions were obtained;(4) As cables contain huge tensions, which would generate great axial pressure in the bridge tower and part of beams, thus the tower and part of beams should be considered as beam-columns to calculate the ultimate load. The limit state functions of composite beam and tower were developed by using the force-moment interaction equation, and the system reliability both at level 1 and level 2 of the composite beam cable-stayed bridge under the ultimate limit-state was analyzed by using theβ-unzipping method which was used to search the main failure modes;(5) The support vector classification machine (SVC) and Kriging model were introduced into the study of structure reliability. Based on the experiment design of initial input training sample which was selected by use of the Latin Hypercube Sampling (LHS) method, considering the SVC/Kriging model as the response surface function in which the parameters were optimized by using genetic algorithm, an improved SVC/Kriging–based response surface method was proposed which combined with the Monte Carlo sampling method. The main idea of the proposed method is: choosing some new training points from the test sample according to the value of a defined―important‖critical function during the iterative process, and adding these new training points into the initial training sample to update the whole training sample, finally the approximate limit state function of SVC/Kriging would be more close to the real limit state function within the regions where the Monte Carlo population is located by updating the training sample continuously. Several numerical examples were computed to validate the accuracy and high efficiency of the proposed approach;(6) The seismic response of bridge structure was characterized by nonlinear and complexity, which caused more difficulties in the reliability analysis. Compared to other reliability methods, the response surface method was regarded as an effective way to solve such problems. Therefore, the proposed improved SVC/Kriging–based response surface method was utilized to analyze the first excursion dynamic reliability issue. Meanwhile, the influence from the randomness of structure parameters was also analyzed.