| Steel-concrete composite girder bridges,which take advantages of light weight of steel bridges and the resistance of concrete bridge deck,are becoming more widely applicated in China.During the service period of composite girder bridges,they are affected by the direct effect of vehicle loads and indirect effect of environmental corrosion.The resulting fatigue damage is constantly threatening the safety of such bridges.Scholars at domestic and overseas have done a lot of researches on the effect of environmental corrosion on the fatigue strength of steel girders,and some meaningful results were obtained.However,studies on the variation rule of fatigue life under the combined effect of fatigue load and environmental corrosion are scarce.Also,the impact of environmental corrosion has not been considered in the fatigue design and fatigue assessment of composite girder bridges in the China’s existing specifications.Therefore,it is of great significance for the safety of the composite girder bridge in China to study the variation rule of the fatigue life of the composite girder bridge under the effects of the environmental corrosion and vehicle loads,and to propose a simplified calculation method suitable for engineering applications.Moreover,the parameters of standard fatigue truck model for fatigue assessment in China’s "General Specifications for Design o f Highway Bridges and Culverts" were mainly stemed from European Standard.While,whether the model is applicable to calculate the fatigue life of highway bridges in China is still question able.In allusion to the problems mentioned above,this paper first ly studied the rationality of the fatigue truck model in the specification,and pointed out that the existing model had some limitations.Secondly,based on the analysis of the traffic data from existing references,two optimized fatigue truck models were proposed.Thirdly,the FE model of a typical steel-concrete composite girder bridge was established based on the current specifications.By using the obtained fatigue truck model,the fatigue life of this bridge under different vehicle weights,traffic volumes and environmental corrosion levels was calculated,and then the effect of corrosion on the fatigue life under different truck traffic was studied.The main research contents are as follows:(1)Based on a systematically summarization of the load spectrum of equivalent vehicle model in 6 representative regions recorded in the existing literatures and Miner linear cumulative damage theory,the fatigue damage ratios of simple beam bridge under real vehicle load spectrum and standard fatigue truck were calculated.Then,the applicability of the standard fatigue truck was analyzed.In the basis of the traffic data in the literatures,the axial weight ratios and axle spacings of the fatigue truck model were optimized.The results can provide a reference for the formulation of the standard fatigue truck in the Chinese regulation.(2)Based on the ANSYS finite element model of a typical steel-concrete composite beam bridge,stress-time curve and corresponding stress amplitude of different fatigue-prone details under different environmental corrosions,fatigue truck weights and average daily truck traffic volumes were obtained by using moving point loads method.Then,the fatigue life and the corresponding fatigue life reduction ratio due to the corrosion of composite girder bridge under various conditions were calculated,and the variation rule of vehicle weights and traffic volumes on fatigue life reduction ratios were analyzed.Based on the result of numerical analysis,the concept of corrosion fatigue correction factor,i.e.the ratio of fatigue life considering the effect of corrosion to fatigue life not considering the effect of corrosion,was proposed and used to quantify the effect of environmental corrosion in the fatigue analysis of bridges.Finally,the influence of steel beam size on the corrosion fatigue correction factor was analyzed. |
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