Research On Reliability And Failure Modes Correlation Of Bridge Based On Support Vector Machine And Copula Theory

Bridge structure plays a critical role in highway traffic,and its reliability is closely related to the security of pedestrian and vehicle.Due to the complexity of structure and load,the performance function of structural reliability is highly nonlinear implicit function,which causes extensive computation and complex solution process by traditional reliability solving method.Meanwhile,most of the analysis about bridge reliability have simplified or ignored the correlation between failure modes,which leads to the result error.In view of the above problems,a scientific substitution model which can make the implicit function explicit is introduced to solve the reliability of bridge structure with reasonable consideration of the correlation among failure modes,which makes it more applicable in engineering structures and thus produces significant practical significance.Taking the bridge in Huangshi as the engineering background,the reliability of bridge structure during construction stage and normal use stage was analyzed by Support Vector Machine(SVM).The reliability of bridge system when considering correlation between failure modes by Copula theory was acquired.The sensitivity analysis was performed on numerous parameters related to reliability of bridge structure.The key parameters were controlled to ensure the target reliability of the bridge during the normal use stage.The main research contents of this dissertation are as follows:Firstly,the computational procedure of structural reliability adopting Support Vector Machine was written by MATLAB.The fitting effect of SVM classification model influenced by different parameters and sample numbers was discussed in this dissertation.Then,the result of reliability solved by SVM method in two function examples was compared with the results solved by response surface method,Monte Carlo method and first-order second-moment method to verify the accuracy and feasibility of SVM method.Secondly,the reliability of bridge during the construction stage and normal use stage was calculated based on SVM model.The testing research on C50 concrete was conducted to fit the time varying behavior of elastic modulus of material during bridge construction.The finite element models of continuous rigid frame bridge during cantilever stage and normal use stage were established by MIDAS/Civil software.Then based on SVM model,the reliability of bridge during normal use stage and the elevation control reliability under the different allowable deviation of deflection during the construction stage were calculated with Monte Carlo method.Thirdly,the correlation of failure modes was analysed through Copula theory.The Copula models of failure probability about two-component series system and two-component parallel system were built based on Copula theory.Then,the reliability of single span elastic-plastic frame example was calculated by Copula function model to validate the rationality and necessity of this model,which laid the foundation for the reliability calculation of bridge system considering correlation between failure modes in the following passage.Fourthly,the system reliability of bridge structure when considering correlation between failure modes was calculated based on Copula model.The structural system of continuous rigid frame bridge was divided into several subsystems.Corresponding Copula function was selected according to the scatter plot of performance function value and characteristic of two-component frequency histogram of each subsystem.The relevant parameters of the function model were obtained by semi-parametric estimation method.Then,the optimal Copula function model was selected by the square Euclidean distance.According to the optimal Copula function model,the failure probability of each subsystem was calculated,and the system reliability of bridge structure when considering correlation between failure modes was further obtained.Finally,the sensitivity analysis was performed in parameters related to reliability of continuous rigid frame bridge in normal operation stage.The random parameters with great influence on the reliability of bridge structure were estimated by changing the mean and standard deviation of random variable in accordance with 5% increase or decrease,which were considered as the key controlling parameters in the bridge design,construction and structure optimization.