| Due to its advantages such as simple structure,short construction period,economy and so on,the small and medium span reinforced concrete rib girder bridges account for a high proportion among all kinds of bridges.However,the resistance performance of materials,such as concrete and steel have gradually degrades because of the gradual growth of traffic volume,operation time extension as well as load level continually raising up,which leads to fatigue cumulative damage with different degrees on local structures and it can be a potential safety hazard for normal operation.However,as to local component fatigue problems,yet there's have no detailed rules for fatigue design and fatigue life prediction in the existing design and evaluation standard for highway reinforced concrete bridges in our country.Based on the research status of fatigue problem of the reinforced concrete structure at home and abroad and the fatigue damage basic theory.Finite element software,Midas/FEA was used to establish space solid models of the model beam.During the fatigue simulation analysis,the Von Mises stress and Goodman and Gerber correction methods of average stress were taken into consideration.Based on the fatigue analysis models established by using traditional fatigue analysis methods,S-N curve and Miner linear cumulative damage criterion,the influence law of stress levels,distance-span ratios and width-height ratios on the fatigue performance of rib beam bridge diaphragms was studied.The main research contents and results are as follows:(1)Based on the existing stangard drawing,the original beam was designed.Trussing model of the original beam was established by adopting Midas/Civil software,to verify the bridge design reasonable with new design specification.According to the similarity theory,the scale model was designed with the scale of 1:2 and the similarity coefficient was calculated,which can provide theoretical basis for the finite element simulation and indoor model fatigue tests.(2)Through the analysis of fatigue numerical simulation,the internal relation between diaphragms fatigue life and fatigue load stress levels was revealed.When the stress level Smax is less than or equal to 0.25,the fatigue life curve tends to be smooth,whivh can be thought there is no fatigue problems of the structure at this point.The decline rate of fatigue life increases continuously with stress levels increasing with the stress level 0.25<Smax?0.60.The falling rate of fatigue life is significantly speeding up when the stress level Smax is more than 0.60.(3)Through drafting the study scheme of diaphragms fatigue performance,the variation rule of fatigue life and damage of diaphragms under different distance-span ratios and width-height ratios layouts were analyzed.By contrast analysis,the result shows that fatigue life of the model beam improve continuously and damage degree decrease gradually with the reduce of diaphragms distance-span ratios and the increases of width-height ratios.It is economic and reasonable when distance-span ratios is about equal to 3.85 and width-height ratios value is about 0.17 of the diaphragm.This paper can provides certain theoretical basis for fatigue damage accumulation analysis of reinforced concrete rib girder bridges in service,and has certain value as a reference for further improving the anti-fatigue design theory of reinforced concrete diaphragm. |
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