Fatigue Analysis Of Steel Bridge Decks Based On Bridge Health Monitoring Data

Orthotropic steel bridge decks have been widely used in long-span bridge decks because of the advantages of light weight,low structural height,strong bearing capacity,ease of assembly and convenient construction.However,due to unfavorable factors such as welding residual stress,short influence line,and high cyclic stress of vehicle load,fatigue cracking is prone to occur.The expansion of fatigue cracks will endanger the durability and safety of the deck structure.At present,many bridges around the world have cracks in the details of the orthotropic steel deck structure.Based on the actual monitoring data of the health monitoring system of Chongqing Wanzhou Pailou Yangtze River Bridge,this paper analyzes the fatigue life of its typical fatigue details of the orthotropic steel bridge deck.According to the vehicle data of the dynamic weighing system,the distribution of traffic flow and vehicle characteristics are studied,and the applicable fatigue vehicle model of each lane is deduced according to the linear fatigue damage accumulation criterion.From the characteristics of the actual traffic flow,it is found that the size and composition of the traffic flow in each lane are quite different.Therefore,compared with the fatigue load specified in the fatigue codes of various countries,the fatigue vehicle model determined in this paper is more suitable for the fatigue life analysis of the bridge deck of Chongqing Wanzhou Pailou Yangtze River Bridge.The steel box girder mid-span segment model and the lane 1 sub-model were established through ANSYS,and the multi-lane load effect was considered when the fatigue life of the lane 1 orthotropic steel bridge deck was evaluated.It not only considers the fatigue damage caused by traffic flow in lane 1,but also considers the impact of traffic flow in adjacent lanes on its fatigue life.The most unfavorable loading position of the fatigue vehicle model in the transverse bridge direction of the two lanes is determined by the transverse load,and the longitudinal load is carried out on this basis to simulate the uniform speed of the vehicle on the bridge deck pavement,and the stress spectrum under the action of the fatigue vehicle is obtained.And calculate the degree of fatigue damage in accordance with the European Eurocode standard.The monitoring strain data at the top plate and the U-rib weld is processed and the rain flow is counted using matlab to obtain the daily stress spectrum and compare it with the finite element calculation result.Convert the daily stress spectrum into an equivalent stress amplitude,and statistical analysis finds that the daily equivalent stress amplitude and the number of daily cycles accord with the log-normal distribution.Derive its vehicle flow growth model and vehicle weight growth model based on the WIM system measured data and relevant data related to the design of Wanzhou Pailou Yangtze River Bridge.According to the Paris formula,and using the stress intensity factor of the crack tip at the top plate and U-rib weld to derive its fatigue fracture model.The fatigue function function of the roof and the U-rib weld is established by the daily equivalent stress spectrum and the fatigue fracture model,and the fatigue reliability evaluation result during the design reference period is calculated considering the annual traffic volume and the annual vehicle weight increase.