Fatigue Reliability Evaluation Of Steel Bridge Deck By Combining Multi-scale Model With Fine Simulation Of Vehicle Flow

Since the last century,steel box girder and orthotropic steel deck have become the most important structural form in bridge construction.The latter is widely used because of its high bearing capacity and good economic benefits.At present,the prominent problem of steel bridge deck is fatigue.Its numerous structural details and weld joints lead to stress concentration and repeated cycles in the process of bearing wheel load,which is the main reason for crack development and structural failure.In the research of steel bridge deck fatigue,finite element simulation is a commonly used analysis method;compared with real bridge test and model test,this method can reduce the research cost and simulate the content that is difficult to realize in actual operation,which is an important supplement to the test method,but the model accuracy and calculation efficiency are also the key problems to be solved in finite element simulation 。 In this paper,a large-span cable-stayed bridge is taken as an example.Based on the vehicle load information collected by WIM system,by introducing the sampling method of related random variables,the key parameters of traffic flow load are correlated sampled,and then the random traffic flow samples are generated.The fatigue details of the main girder steel deck are loaded and analyzed,and the fatigue reliability of different details is calculated.The specific research contents are as follows:1.Based on the multi-point constraint method,the spatial multi-scale model of cablestayed bridge is established,and the whole bridge,beam segment and fatigue detail model are established by using the member system element,shell element and solid element respectively.Based on the dynamic and static load tests,the single beam model is modified by using the zero order optimization algorithm,and the multi-scale model is verified.The results show that the modified multi-scale model can better reflect the overall and local stress characteristics of the structure,and the multi-point constraint method can be used to connect different types of elements to meet the calculation accuracy requirements;when the grid size is less than 1 / 4 of the plate thickness,the calculated hot spot stress error of the weld details is small and tends to converge gradually;2.Based on the traffic flow data collected by WIM system,this paper analyzes the traffic flow load parameters of a highway,focusing on the representative vehicle types and their proportion,daily traffic volume and axle load parameters;establishes the stratified sampling method of related random variables,samples the key parameters of random traffic flow,and generates random traffic flow samples.The advantages of cmcs-cl sampling method in the consideration of the correlation of random variables and the representativeness of samples are verified by an example;3.Based on the S-N curve method,the fatigue limit state equation is established,and the stress history and fatigue load spectrum of different details are obtained through the load analysis of LHS sampled vehicle samples through influence line loading.The Kriging agent model is used to predict the fatigue load spectrum of different vehicle models under different axle loads.The reliability analysis program is compiled to calculate the fatigue details in the random vehicle flow In addition,three traffic flow parameters,such as traffic volume,vehicle type ratio and traffic volume growth,are analyzed to analyze the influence of each parameter on fatigue reliability.The results show that there is a great risk of cracking in the fatigue details of the steel deck,and the fatigue life is lower than the designed service life;4.Calculate the stress size and distribution of the steel deck of the cable-stayed bridge under the large-scale transportation load,respectively calculate and analyze the local stress distribution and the stress history of key details of the steel box girder in the middle span under the large-scale transportation load,and calculate the fatigue damage caused by the large-scale vehicle to the key details.The results show that the overall stress level of the steel box girder is not high and there is stress concentration in some details,but the fatigue damage caused by the vehicle is small,which will not affect the durability and safety of the structure..