| The orthotropic steel bridge deck has the advantages of light weight, high strength, large bearing capacity, fast installation speed and wide application range. However, the fatigue problem of welding structural details is still a research emphasis of modern orthotropic steel deck plate. Besides, with the increasing of vehicle load and the raising total volume of traffic in the life-time of bridge, the fatigue cracking phenomenon of welding structure details is becoming more and more serious. According to the steel box beam construction of the Chongqing Jiangjin Zhongdu Yangtze River Bridge, this dissertation systematically studied the analysis method, mechanical behavior and fatigue properties of orthotropic plate.The main research contents are as follows:1. The stress behavior of orthotropic steel bridge deck of Highway Bridge was studied based on the finite element method. Research shows that the welding structural details are mainly under the influence of the force form the second system and the third system, which is specifically shown as global bending action, global shearing action, local supporting action and local shearing action. Also, the influence degrees on different welding details that caused by the effects mentioned above were qualitatively analyzed, and it came to a conclusion that the global shearing action and local supporting action are the dominant influence factors of the stress behavior of structural details. What’s more,we extracted the stress influence surface of different structural details by means of finite element method,and comprehensively analyzed stress influence degree of different structural details when vehicle load is in different lane position.2. The hot spot stress calculation theory of OSD welding details was studied, and thoroughly analyzed the influence on calculation result of the hot spot caused by element type,mesh precision and extrapolation method, and according to the analysis results, perfected the analysis process of hot spot stress calculation method for the OSD welding details. It is recommended that the Solid 95 element is used for modeling, and the precision of the finite element model should be improved as far as possible in order to reduce the degree of dispersion of the results. The accuracy and reliability of the numerical simulation model used in the hot spot stress method was verified based on the method of full-scale model test, and the mechanical characteristics of OSD structure details that are subjected to different acting was studied.3. With such methods as field investigation, finite element analysis and numerical simulation of probability model, the author researched several problems such as vehicle load space distribution of highway steel structural bridge, fatigue transverse probability coefficient,parameters of highway traffic load characteristics in Southwest China, etc. And a simulation program of Monte Carlo is written based on fatigue load spectrum of highway. A fatigue load spectrum model is suggested to be applied in calculation for OSD structure of highway steel structural bridge in Southwest China. And the author respectively used the preceding fatigue loading spectrum model and the fatigue load model specified in the Specifications for Design of Highway Steel Bridge (JTG D64-2015) to calculate fatigue equivalent stress of simply supported girder bridge. Research shows that transverse probability coefficient of stress fatigue for OSD construction details of steel highway bridge should be 0.9. Given the limitation of equivalent damage coefficient /,the equivalent stress obtained by the fatigue load model in the D64 specification is greater when traffic flow of single lane is less than 5 X 108times. However, the equivalent stress calculated from the Monte Carlo load model is greater when traffic flow of single lane is more than 5 × 108 times.4. The full scale fatigue model test of the orthotropic plate welding structural details of Chongqing Jiangjin Zhongdu Yangtze River Bridge was conducted, and the loading cycle times of the experiment was confirmed by Miner’s linear cumulative damage theory. The results show that the fatigue cracks appear at the weldment of the notch between the stiffening rib web and the diaphragm, the longitudinal fatigue cracks appear at the weldment of the top plate and stiffening rib web while no fatigue cracks appear at the notch of the diaphragm,however, great tensile stress does exist there. The fatigue strength at the weldment of the notch between the stiffening rib web and diaphragm is greater than that of the category 90 in the Eurocode. The fatigue strength at the weldment of the top plate and the stiffening rib web is greater than that of the category 225 in the IIW. While, the fatigue strength of the cutout of the diaphragm is greater than the category 140 of the in the Eurocode. And affected by welding residual stress, fatigue cracking still emerged in the area of pressure stress cycling.5. By studying the fatigue multi-lane coefficient of multi-lane steel highway bridge, the author presents a calculation method for fatigue multi-lane coefficient, which is based on Carlo Monte method. And general probability method, D64 standard formula method and Monte Carlo method were separately used to calculate the fatigue multi-lane coefficient of OSD structure details of multi-lane steel highway bridge. Then the author analyzed the principle and superiority-inferiority of each method and studied the affecting parameters of the fatigue multi-lane coefficient. Ultimately, the fatigue multi-lane coefficient of OSD welded roof structure details of steel highway bridge was decided to be 1.0. Meanwhile, the fatigue multi-lane coefficient of welded structure details of stiffening rib web plate was decided to be 1.2,and the fatigue multi-lane coefficient of the structure of diaphragm cut was decided to be 1.5. |
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