A Study On The Method Of Fatigue Design Of Highway Steel Bridge

Although steel bridge has the advantages of light-weight and big-span, due to thelong-term and cycle effect of vehicle, coupled with its own defect such as weld defects,sudden-changed cross-section and stress concentration, it will generate fatigue cracks at theweak positions. Currently, Chinese fatigue design criterion is relatively old and backward,and the discription of characteristics of the highway steel bridge fatigue is insufficient. Thehighway steel bridge fatigue design criterion is still in the revision status. This paper aimedat the status quo，carried out research and analysis on the the method of fatigue design ofhighway steel bridge. Specifically, this paper mainly did the following work:1）From the anti-fatigue design formula, the classification of the fatigue details andthe forms of fatigue load of the relatively advanced specifications including AASHTO, BS5400, Eurocode, Japanese specification and Chinese steel design specification, railwaysteel bridge specification and highway bridge steel structure and wood structure designspecification.Based on the two kinds of fatigue design code and calculation formula of infinite lifeand safety life design of AASHTO, the design method of combining the three-gradestep-by-step fatigue and service life control of BS5400, absolute safety design and damagetolerance design on three levels (infinite life design, equivalent damage design and damageaccumulation design) of Eurocode, and infinite life and service life design code andcalculation formula of Japanese specification. This paper pointed out the part needs to beupdated of our code and calculation formulas which is suitable for our country highwaybridge design.Study on the differences of fatigue details, fatigue strength and Characteristics of theS-N curve among foreign codes, this paper pointed out the dividing principles of fatiguedetails and noticeable problems that should be adopted, and pointed out the fatigue detailsthat still need more fatigue test or new fatigue test to determine the fatigue details andfatigue strength. This paper provided the reference and suggestion for out highway steelbridge design.Based on the study of fatigue load of AASHTO, BS5400, Eurocode and Japanesecodes, this paper provided the main form of fatigue load. And derivation method of thestandard fatigue load model was briefly discussed. Based on the simply supported girderbridge, this paper made study on the bending moment of cross section in the middle-spancaused by standard fatigue load model of AASHTO, BS5400and Eurocode, T-load of Japanese codes, and our country highway-Ⅰ, highway-Ⅱand city-A, city-B live loadvehicles. This paper provided the stress cycle number under difference vehicles to providethe reference for our country highway steel bridge fatigue load..2）According to the relatively advanced specifications about the fatigue of orthotropicsteel deck including AASHTO, Eurocode and Japanese specification, this paper studied thefatigue strength of typical fatigue details of the orthotropic steel deck of Daxie SecondBridge. The methods and formula of calculation of all these three specifications are similarto each other. But there are difference between the fatigue detail and fatigue load forms.Through the analysis of the results this paper obtained the main factors that impacted thefatigue strength of orthotropic steel deck and the stress of fatigue details under the fatigueload. And Chinese specification is still lack of some fatigue test data on orthotropic steeldeck, so the fatigue of steel deck details could refer to relatively advanced classificationnorms.