Fatigue Assessment Of Caiyuanba Bridge Based On Fully Coupled Method

The method of fully coupled fatigue damage analysis based on damage mechanicscan be used to study the occurrence、development and destruction in the whole processof evolution about fatigue damage. It also can be used to analyze the fatigue damage ofdetails more meticulously and accurately, but there is less study comparatively in largeand complex bridge, including compare with other fatigue damage assessment methodsbecause of the complex principle and other factors. With the UMAT technology of finiteelement software ABAQUS, thesis establish fully coupled fatigue damage analysisalgorithms by variable stiffness based on the principles of damage mechanics. Then it’sapplied to assessment damage about a welding integral node of a large bridge fatigueand compared with the traditional fatigue analysis methods.The main research content and research findings include:①The principle of fully coupled fatigue damage analysis based on damagemechanics, choose the elastic modulus as damage variables, use high-cycle fatiguedamage evolution model, then compile fatigue assessment subroutine FATIGUE withthe UMAT technology of finite element software ABAQUS;②The test simulations of fillet weld node without loading by subroutineFATIGUE show that the calculated D-N curve and the law of crack propagation matchexperiment; the test simulations of arris weld node with deep and shallow penetrationshow that the calculated S-N curves match experiment;③Thesis establish fine finite element model for a welding integral node B-7of alarge bridge, local stress analysis shows that the stress level of the node is low, and themaximum stress range is located in the roof of the track beams with the verticalconnecting plate of the welding integral node (called A) and the end near the largegusset plate of the roof of vertical connecting plate (called B);④Combined the measured stress spectrum value by the rain flow countingmethod with subroutine FATIGUE, the results of fully coupled fatigue damageevolution analysis for the welding integral node B-7show that based on the linearMiner’s rule fatigue damage at A along the weld extends to B and damage at B extendsalong the parallel direction to the large gusset plate; the results based on damagemechanics analysis are similar to the Miner’s rule, but the damage at B extends aroundthe vertical connecting plate, in addition to the damage which appear at the large gusset plate intersection of welding, and through-thickness direction at later period;⑤The fatigue damage analysis of the welding integral node B-7based ontraditional method and damage mechanics method show that: there is a certaininteraction between the fatigue damage field and the stress field, because the fullydecoupled method can not calculate such mutual affect, so the fatigue life will be higherand results in fatigue assessment are not accurate and safe; the linear Miner’s rule whichis widely used in engineering is conservative for fatigue life assessment, but notconducive to the accurate assessment of fatigue cumulative damage.