Research On Fatigue Load Spectrum Of Mountain Low-grade Highway Bridge Based On Cellular Automaton

There are a large number of low-grade roads in mountainous areas of Yunnan Province,and road transportation is the main mode of transportation.Over-limited and over-load is extremely common.The key to ensuring the operation safety of the bridge structure is using accurate fatigue load spectrum to anti-fatigue design and fatigue life evaluation.At present,the research on fatigue load spectrum of low-grade highway bridges in mountainous areas is very limited.At the same time,Stochastic traffic flow simulation is developing from static traffic flow to actual traffic flow,the key of research is to accurately obtain traffic load data.Based on the measured traffic load data on low-grade highways in mountainous areas of Yunnan Province,this paper studies the vehicle classification,fatigue vehicle load spectrum,cellular automata simulated traffic flow load,and fatigue life analysis of steel box girders bridges.The main contents include:(1)Through the weight-in motion(WIM)system on a low-grade highway in the mountainous area of Yunnan Province,the actual traffic load data for 29 consecutive days was obtained,and the system clustering method was used to analyze the model.Statistical analysis and K-S test are carried out on the distribution parameters of vehicle weight,vehicle speed,vehicle length,wheelbase,axle weight and vehicle time interval of various types of vehicles,and the probability distribution and characteristic parameter values obeyed by various types of vehicles are obtained.(2)Based on the measured traffic load data and the model division results,a typical vehicle load spectrum including 14 typical models is proposed.According to the fatigue damage equivalent principle,the special vehicle load spectrum including the five types of vehicles is simplified,and the standard vehicle fatigue train is simplified according to the principle of maximum fatigue contribution rate.(3)On the basis of the traditional cellular automaton model,the cell length and the update time step are refined,and the open boundary of the vehicle-time equivalent vehicle generation probability is adopted.According to the vehicle lane change rule,the driving rule and the traffic load characteristic parameter,The refined cellular automaton traffic load flow model was established by Matlab.After verifying the accuracy of the model,the fatigue stress history of the steel box girder spanning the midsole is obtained.The fatigue stress spectrum was obtained by counting the fatigue stress history using the "rain flow counting method".(4)The fatigue load spectrum and the effective stress spectrum of the cellular load flow are used as the fatigue model.The nominal stress method is used to estimate the crack formation life and the fracture mechanics method is used to estimate the crack propagation life.The fatigue life of the steel box girder is estimated by combining the two.The effect of crack size and critical crack size on fatigue life.The agreement between the fatigue load spectrum and the cellular load flow fatigue model is compared,and the correction coefficient of the fatigue load spectrum calculation result is proposed.