Research On Vehicle-borne Fatigue Of Stiffened Girder Based On Long-term Monitoring Of Suspension Bridge In Mountain Area

In recent years,with the increase of vehicle holding rate,the traffic volume of highway-bridges has also increased,and due to the repeated action of live loads such as vehicle load and wind load,as well as the frequent overloading of trucks and buses,the fatigue damage problem of steel truss beam suspension bridges during operation is becoming more and more serious.The fatigue performance of each member of steel truss beam is becoming more and more important to the safety of the bridge structure.Therefore,it is necessary to study the fatigue performance of steel truss beam under the combined effect of vehicle loads and other external loads.Taking a steel truss beam suspension bridge as the engineering background,based on the measured data of long-term monitoring,the fatigue performance of typical members of steel truss beam suspension bridge in mountainous region is studied,and the method for predicting its fatigue life is given..The main work is as follows:(1)The commonly used methods and basic theories in fatigue life research at home and abroad are investigated,and then established the ANSYS model of the full bridge based on the support engineering.After verifying and modifying the model,the model is loaded with the standard fatigue vehicle model III in the 《Specifications for Design of Highway Steel Bridge》JTG D64-2015.The model vehicle is simulated to cross the bridge at a constant speed,and according to the response of the main truss structure,the most unfavorable member in the main beam is selected as the typical member.Based on the measured data of a suspension bridge health monitoring system,strain data of a typical rod is selected,converted into stress and a stress history curve is drawn.Then the stress history curve is counted with the rain flow counting method program written in Matlab,and the stress spectrum of typical rod corresponding to the measured strain is obtained.(2)Based on the traffic volume data of a steel truss beam suspension bridge from the beginning of 2017 to the end of 2019.According to the statistical results and the vehicle classification data,16 typical car models were selected as the counterparts for traffic volume data classification and processing.Based on the statistical results,five standard fatigue vehicles suitable for the suspension bridge are converted,the converted standard fatigue vehicles are loaded into the model and the stress history curves of typical rods are extracted.And the stress amplitude statistics are again made with the rain flow counting method.Finally,the typical rod stress spectrum based on the measured traffic volume data is obtained.(3)By referring to the current highway steel bridge code,railway steel bridge code and the latest research results,the appropriate level of fatigue structure detail is selected,and the fatigue life S-N curve suitable for this steel truss beam suspension bridge is obtained.Then,the damage degree is calculated and evaluated by combining the stress spectrum obtained from the measured strain and the stress spectrum obtained from the measured traffic volume,and stripped the damage caused by the live load other than the vehicle to the typical rod innovatively.The future change trend is predicted separately.At the same time,the change trend of traffic volume in the future is forecasted.Finally,the prediction results of the two types of loads are combined to predict the fatigue durability of the stiffening beam of the support engineering.