Research On Fatigue Load For Orthotropic Deck Of Highway Steel Bridge

Orthotropic steel deck is widely used because of its light weight, high strength, and the convenience of construction in recent years. However, it sufferes severe fatigue problems due to complex mechanical properties, significant stress concentration and other factors. On the other hand, after the initiation and expansion of local fatigue cracks, orthotropic steel deck can hardly be effectively repaired. To determine fatigue load reasonably is the basis of obtainning excellent anti-fatigue design and making accurate assessment of the fatigue life of the bridge. Different from the strength design load in accordance with the most adverse conditions, fatigue load should be determined based on the variety of actual traffic vehicle load with mathematical statistics taking account of structural response. The work of this paper includes:(1) The course of development of the steel deck was reviewed. The types and location of steel deck fatigue cracks were summarized. The relevant provisions of the fatigue loading on the steel bridge at BS5400, Eurocode, AASHTO and Code for Design of Highway Steel Bridges (draft for development) were compared comprehensively?(2) The mechanism of steel bridge fatigue was explained. Three steel bridge fatigue damage accumulation theory models, such as the non-linear, bilinear and linear ones, were expatiated with a comprehensive comparison and the linear one was taken as the basis of the analysis in this paper;(3) The influence surface of principal stress of the target fatigue detail (critical section in web of cross girder due to cut outs) was obtained by FE analysis on the background of the Hong Kong-ZhuHai-Macao Bridge. General conclusions based on the FE results include: The influence line along the bridge of principal stress of the target detail is approximately6to10meters in length, while the one across the bridge varies greatly according to the location of the target fatigue detail;(4) The probability distribution models with parameter values of the types, weight, spacing and vehicle lateral position of vehicles for the Hong Kong-Zhuhai-Macao Bridge were determined based on statistic data of actual transport vehicles at Lantau Link and HuMen Bridge as well as related literatures. EXCEL VBA-based program was completed based on the Monte Carlo method and Random traffic vehicles were obtained. (5) It is applicable to merge similar vehicle types into one with equivalent axle weight and distance formulas according the calculation results of target details at the Hong Kong-Zhuhai-Macao Bridge. The standard fatigue vehicle just for target details was obtained theoretically.