| Orthotropic steel bridge decks are widely used in the construction projects of modern large-span bridge due to their great seismic performance and short construction period.Under the cyclic load of vehicles,due to its complicated structural formation and force transmission path,the welding location produces severe local stress concentration,which eventually leads to fatigue damage and shortening service life.The welding residual stress which widely exists inside the welded structure will drastically affect the fatigue property of the structure by shortening the fatigue strength life and promoting the initial crack propagation under the action of fatigue load,thereby shortening the fatigue life of the structure.Therefore,the influence of welding residual stress should be fully considered in the fatigue performance study of orthotropic steel bridge decks.This article takes the standard beam section of Taizhou Yangtze River Highway Bridge as the engineering background,based on the hot spot stress method and considers the influence of welding residual stress.Through the finite element simulation calculation,the distribution of the hot spot stress on the vulnerable welding details of the orthotropic steel bridge deck under the vehicle load was analyzed and fatigue performance was evaluated.The specific work is as follows:(1)The development status and research results of fatigue problems of orthotropic steel bridge decks were introduced,and based on the basic principles and applicable range,several relatively comprehensive evaluation methods were compared;then the formation process of welding residual stress and the influence mechanism on the fatigue life of the steel structure were introduced.(2)The finite element software ANSYS was used to conduct and analyze multi-scale modeling of the Taizhou Bridge,and through the steel box girder segment model analysis,the transverse stress influence range of the transverse bridge was determined to be 5 U ribs × longitudinal bridge to 1 diaphragm spacing,and the most unfavorable lane was determined to be the heavy lane;through the local model analysis of the orthotropic steel bridge deck,the fatigue vehicle load model was simplified to be a single wheel model with a ground area of 0.1m × 0.2m,and it was determined that the most unfavorable loading condition happens when the fatigue details are directly above.(3)Sub-model method was used to conducted a refined solid model as for exploring the effect of grid size,element type and extrapolation method on stress distribution and hot spot stress values.Based on grid stability,rationality of stress distribution,and conservative calculation results,solid95 element with IIW linear extrapolation was recommended to calculated the hot spot stress,and the corresponding grid size was divided into 4 layers with a thickness of 20 mm in the longitudinal direction and 0.5t in the transverse direction.(4)A test was conducted for the joint of roof-U ribs to explore its fatigue performance.Three fatigue vulnerable points were selected to measure the stress by using the hot spot stress method and the nominal stress method,then the test result was compared with the finite element calculation results to determine the suitable modeling method for different vulnerable points.(5)Considered the influence of welding residual stress and based on Goodman formula,a method to modify the stress amplitude obtained from finite element analysis was proposed,so as to achieved the corresponding results of the finite element simulation results and the S-N curve based on the measured data of fatigue test.Taking Taizhou Yangtze River Highway Bridge as the engineering background,the frequency spectrum of hot spot stress of the roof-U rib details was calculated by the mixed shell-solid finite element model.Based on the finite element result modification method proposed in this paper,and according to the Miner linear cumulative damage principle,the fatigue life of the welding details was estimated. |
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