Fatigue Reliability Research On Cable Of Low Tower Cable-stayed Bridge Under Random Heavy-duty Traffic Loads

The low-rise cable-stayed bridge is the new bridge structure which appeared in China at the end of the 20 th century.Due to its reasonable force,beautiful shape and strong adaptability,it has been widely used in China for more than a decade.As the important force-transmitting member of the main tower and the pylon in the cablestayed bridge of the low-rise tower,the cable is subjected to the load effect of 30% of the whole bridge,and its stress state directly affect the safe operation of the whole bridge.Therefore,it is very necessary to study the fatigue characteristics of the cable.Based on the Wuhai Yellow River Bridge in Wuhai,Inner Mongolia,the fatigue reliability of the cable of the low-rise cable-stayed bridge is studied in this article.The main research contents of this thesis are as follows:(1)Geting the stress influence line of the cable.The finite element model of the full bridge is established using the finite element software MIDAS/Civil,and the modal analysis was carried out.The impact coefficient of the full bridge is determined according to the specification.Taking the road design grade load as the moving load,the static and dynamic analysis of the cable is carried out.The most representative cable is selected and the stress influence line is extracted.(2)Establishing a heavy load fatigue load model.A traffic survey of the road sections near the bridge site is conducted,and the obtained data is statistically analyzed by mathematical statistics theory which determine the distribution types and parameters of various factors in the traffic flow data,including vehicle composition,vehicle weight,vehicle spacing,etc.Based on MATLAB platform,the Monte Carlo method is adopted to establish the heavy-duty vehicle fatigue load model.(3)Calculating the fatigue reliability of the cable using MATLAB software.The obtained heavy-duty traffic fatigue load model is applied to the stress influence line of the cable to obtain the stress history of the cable.The numerical analysis method is used to fit and obtain the probability model of the equivalent stress amplitude of the cable.Based on the S-N curve of 1860 steel strands and combined with the nonlinear continuous cumulative damage principle of CDM,the fatigue reliability of the cable of the low tower cable-stayed bridge is calculated by the important sampling Monte Carlo method.(4)Studying the effects of traffic growth and vehicle overload on the fatigue life of the cable.Using the MATLAB software to build the gray model GM(1,1),which can predict the growth of future traffic volume of this road segment,so as to calculate the cumulative fatigue damage amount in the increasing traffic flow pull-down cable.In addition,the overload phenomenon is also a factor that often occurs in the 110 national highway and affect the fatigue damage of the cable.By controlling the overload ratio of the vehicle,the overload rate and the time of overload occurrence,the cumulative fatigue damage of various pull-down conditions is obtained.According to the above calculation results,the fatigue reliability of the long cable is smaller compared with the short cable;The increase of traffic volume greatly reduce the fatigue life of the cable,resulting in the cable entering the stage of rapid destruction after 100 years;The ratio of overloaded vehicles and the overload rate will reduce the fatigue life of the cable,and they should be strengthen controlled in practice;The effect of overload on the cable is irreversible.The earlier the overload control,the longer the fatigue life of the cable.