Typical Fatigue Disease Assessment And Prediction Of Orthotropic Steel Deck

Fatigue is a typical deterioration of steel bridges,and fatigue assessment is a cut edge issue in steel structure research.In recent years,China has detected a large number of fatigue cracks in steel bridges and most of them are expanding with daily use.In the ordinary inspection and evaluation of steel bridges,find a simple and accurate way to evaluate and predict the fatigue cracks of steel bridges is necessary.The paper based on the traditional fatigue assessment theory,combined with design specifications of different countries as well as design guidelines of welding society and classification society,summarizing the fatigue vehicle model and the details of typical steel structure diseases,established an FE Model to analyze fatigue problems of the Nanjing Yangtze River Bridge.The model is used to analyze the parameters of fatigue influence,and the stress influence surface model suitable for the research of orthotropic steel bridge deck is obtained.The fatigue impact assessment of the Nanjing Yangtze River Bridge was carried out by using the stress influence surface model,and the evaluation results were consistent with the occurrence of fatigue disease.The research results can be used to predict the fatigue of steel bridge orthogonal orthotropic steel bridge deck.This article discussed the following:(1)Referring to the design specifications JTG D64,AASHTO and Eurocode and engineering guidelines and based on the traditional fatigue theory,the evaluation process and use scope of the nominal stress method and the hot spot stress method are discussed.The vehicle model of fatigue load of common steel bridges is also summarized.(2)According to the fatigue cracks found in the project,the details of the eight most common fatigue diseases of steel bridges are summarized,and the characteristics of the structural details and the causes of damage are analyzed.(3)According to the fatigue test results of the Nanjing Yangtze River Bridge,by analyzing the cracking degree of 7 types of typical fatigue cracks of orthotropic steel bridge decks,it is found that fatigue crack concentration occurs in the rib to deck welds,the rib to floor-beam welds and the floor-beam cutout fatigue details.The details of the weld and the details of the cutout have obvious spatial distribution characteristics,which are directly related to the lateral distribution of the vehicle and the vehicle load.(4)Established a refined finite element model by using the general finite element software ANSYS for parameter analysis which based on using the hot spot stress method,the study considers the pavement diffusion effect,wheel size effect,wheel load longitudinal stress superposition and wheel track lateral probability distribution,research results show that the vehicle spatial distribution model has a direct impact on the fatigue effect.(5)Analyzed typical fatigue diseases of the rib to deck welds,the rib to floor-beam welds and the floor-beam cutout fatigue details of the Yangtze River Third Bridge which based on the fatigue detail stress influence surface model,the effects of wheel load stress superposition and wheel track distribution are discussed.The applicable range of vehicle impact surfacemodel and the sensitivity factors of fatigue details are studied.The evaluation results show that the equivalent stress amplitude caused by the coupling and multi-axle vehicles of common heavy vehicles in China is significantly affected by the wheel load stress superposition effect.The simplified fatigue load model in JTG D64 has a limited scope of application.The influence of wheel track distribution on the fatigue effect of fatigue details is consistent.The vehicle distribution reduction factor can be introduced on the basis of the influence line model to simplify the equivalent stress calculation.