| The fatigue crack of the orthotropic steel decks(OSDs)is harmful to the bridge and difficult to repair.The fatigue design approach based on nominal stress is widely used for most OSDs.However,in practical engineering,the fatigue life of the deck is far from the expected life when fatigue crack occurs.In this paper,three optimization approaches for evaluating the fatigue performance of the deck-rib weld joints in the OSDs are presented:simplified nodal force structural stress approach,notch stress approach,and fatigue life evaluation approach considering the influence of welding residual stress.Based on the three optimal design approaches,the fatigue life of Jiangyin Yangtze River Bridge is analyzed.The main research work and achievements of this paper are as follows:In view of the structural characteristics and force characteristics of the deck-rib welding details,a simplified nodal force structural stress approach is proposed.And the accuracy and mesh sensitivity of the calculation results by the proposed approach are investigated.Based on the fatigue experiment results of the deck-rib component in the OSDs,the effectiveness of the master S-N curve is verified.And the master S-N curves under ultrahigh cycles are discussed in the different slopes and knee points.A multi-scale shell-solid model of Jiangyin Yangtze River Bridge is established and the influence of heavy vehicles on the bridge fatigue life is discussed.The effects of notch type and notch radius on notch stress are studied.Base on the test results of the deck-rib components,the slope and fatigue strength categories of the notch stress fatigue design curves under different notch types and notch radii are given.According to the recommended notch type and the corresponding fatigue design curve for deck-rib welding details,the fatigue life of Jiangyin Yangtze River Bridge is calculated based on notch stress approach.And the influences of S-N curve slope under ultrahigh cycles of the notch stress approach and vehicle overweight on bridge fatigue life are discussed.The distribution characteristics of weld residual stress of deck-rib welding details in OSDs are studied and verified by experiments.Based on the theory of metal fatigue,a full range S-N curve(M-S-N curve)considering the mean stress modification is proposed,and a fatigue life evaluation approach considering the influence of welding residual stress is established.The relaxation effect of welding residual stress under external cyclic load and the influence of average stress on fatigue life of welded joints were investigated.Based on the multi-scale model of Jiangyin Bridge and birth-death element method,the real stress coupling welding residual stress and vehicle load stress is obtained for the deck-rib welding details.Based on the real stress,the fatigue life of deck-rib welding details of Jiangyin Bridge under different vehicle weights and different thickness is calculated by using the M-S-N curve,and the results are compared with those of the nominal stress approach,simplified nodal force structural stress approach and notch stress approach.For the deck-rib welding details of the OSDs,it is recommended to use the approach of considering the welding residual stress influence to evaluate the fatigue life:that is,according to the real stress coupling the welding residual stress and vehicle load stress in the welding details,the M-S-N curve considering the mean stress modification is used to calculate the fatigue life.When the notch stress method is adopted for calculation,the notch type of the weld toe is tangent,and the notch radius is 1mm.The fatigue design curve should adopt the fatigue strength category FAT205,and the slope of S-N curve under number of cycle N?10~7 and N(29)10~7(ultrahigh cycle)is 3.5 and 5,respectively.When only the fatigue life of the weld toe is considered,the simplified nodal force structural stress approach is recommended for calculation,the slope of the main S-N curve under the high cycles should be 5. |
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