| Orthotropic steel deck gets wider recognition and application in modern bridge construction thanks to its specific advantages. However, many bridges have appeared fatigue cracks in different degree, which has caused serious influence in the serviceability and safety of the structure.The structure of orthotropic steel deck is complicated because of longitudinal and transverse ribs being welded on the deck, the residual stress and stress concentration produced by welding have extremely adverse effect on fatigue strength. In this thesis, in order to obtain residual stress distributions of orthotropic steel deck as a whole, especially on the location where is easy to have cracks, it is simulated for welding process and the value of residual stress in orthotropic steel deck. The thesis mainly contains:First of all, it introduces its fatigue problems caused by welding as well as the orthotropic steel deck, generalizes the definition, classification, causes and effects of welding residual stress respectively, summarizes some test methods, briefly describes the elimination methods to reduce residual stress and gives further introduction combining with the experiment as well.Secondly, it is targeted to discuss the applications and characteristics of finite element analysis theory in the welding, then summarizes the key technologies of FEM in simulation. The basic forms of heat transfer in the process of welding and the basic equations of FEM analysis have been put forward. Also the discrete methods are further elaborated when it involves in nonlinear transient problems. Then it briefly illustrates the theories and principles of the analysis in the stress field.Thirdly, the thermal analysis methods based on ANSYS are summarized. Simulation steps of the stress field are summarized in detail as well as the temperature field, and the key problems are:how to establish and divide the model, which kind of unit and model of the heat source should be chosen, how to choose the boundary conditions and apply the load, how to achieve the coupling between the temperature field and stress field and determine the time of load step, even what method should be chosen to make heat source move and weld metal gradually fill.Finally, calculation model is established by reference to the actual model on the basis of theoretical study. The temperature field and stress field of orthotropic steel deck are simulated by 3D FEM. Selecting hexahedron entity unit without intermediate nodes and the material parameter within a certain temperature range, dividing the model reasonably, choosing room temperature as boundary conditions, utilizing double ellipsoid heat source model according to the actual situation, assessing the parameters of heat source, and simulating the movement of welding heat source by APDL will help to complete the simulation of the temperature field. Limiting the displacement of rigid body, applying temperature load, and simulating metal gradually filling by element birth and death technology will help to complete the simulation of the stress field. The temperature field and residual stress field distributions of the weld between U rib and bridge panel are priority to calculating, and then the residual stress distributions after welding the transverse ribs with different typical details are given. Through the comparison and analysis, it can point out which one is the better detail. Also the changes on the weld residual stress of U rib are being analyzed after welding transverse rib. The results of the calculation are checked by the experimental data. It provides important basis for optimizing the welding structure as well as choosing the more reasonable welding form. At the same time, the thesis will lay a foundation for evaluating the fatigue strength with its residual stress field which is from the results of numerical simulation. |
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