Hot Spot Stress Analysis Of The Construction Details Of Highway Orthotropic Deck And Fatigue Research

Fatigue problems of orthotropic steel decks gradually appear in the long term serving life in spite of its wide application on modern steel bridges thanks to some specific advantages. Since nominal stress is difficult to be determined due to complicated structure of orthotropic steel decks and huge amount of S-N curves needed, the process of fatigue assessment according to the traditional nominal stress method is difficult. To solve the above problems, one orthotropic deck steel box girder is chosen in this thesis for characterizing stress distribution of orthotropic steel deck in the finite element model of entire steel box girder under the action of wheel load. The fatigue vehicle models from different standards are used for calculations to study their effect about fatigue on bridge deck details. The structural hot-spot stress of bridge deck is analyzed based on the model of local details while the fatigue life estimation is done with the help of hot-spot stress method and nominal stress method. The thesis mainly contains:Current research on steel structural fatigue performance theories and methods of fatigue life assessment is summarized followed by comparison of differences and advantages of each method. Different types of fatigue cracks in orthotropic steel decks are organized and their origins are analyzed in the aspect of production, structural characterizations and loading conditions. Carry out contrast analysis of the related researches on fatigue loads of highway bridges and their simulating models are summarized in the scope of worldwide.In order to understand the stress characteristics of orthotropic steel deck under the action of wheel loads, Finite Element Model of one orthotropic deck steel box girder is established with the help of ANSYS to characterize its stress distribution. Stress histories of four different structural details are calculated which help the analysis of their stress distribution and characteristics. Calculate the difference of fatigue effects under different standards fatigue vehicle model for local connection detail of bridge deck with longitudinal web plate and determine fatigue load model for fatigue assessment of orthotropic steel deck structural detail with the situation of China.The calculation formula of Dong method is extended to3D form based on3D structural model and then reduced to simplified Dong method for3D structural model. To apply the hot-spot stress method on the fatigue life estimation, hot-spot stress is calculated through linear surface extrapolation method, through thickness at the weld toe method and Dong method on the local connection detail of bridge deck with longitudinal web plate in the local structure model established by sub-model with the help of ANSYS. The effects of FEM parameters are also analyzed for the three different methods mentioned above, Carry out contrast calculation of the3D Dong method and simplified3D Dong method, the effect of the distance between reference surface and crack extended surface, is analyzed in the formula based on simplified3D Dong method. Through above calculation and analysis, determine the suitable parameter of finite element modeling and calculation formula for the three hot-spot stress method.Local structural details are modeled through sub-model with the help of ANSYS. Based on vehicle load spectrum model, fatigue life is assessed for the local connection details of bridge deck and longitudinal web plate using hot-spot stress method and nominal stress method, fatigue check is then processed in standard fatigue vehicle model, the reason of the difference of the above two methods of fatigue assessment results is discussed. It is concluded that the hot spot stress method can be convenient for evaluating the fatigue life of this detail.