Fatigue Analysis Of Orthotropic Steel Deck Of Large-Span Steel Truss Arch Bridge And Structural Improvement

At present,large span steel bridges are commonly designed with orthotropic steel decks.Domestic and international engineering experience shows that large span orthotropic steel decks are prone to fatigue cracks during service life,which affects the operational safety of the bridge and increases bridge maintenance costs.Therefore,it is important to analyze the fatigue performance,service life evaluation of orthotropic steel deck and propose structural measures to postpone fatigue cracks in large span steel bridge.This thesis takes the orthotropic bridge panels of Mingzhu Bay Bridge with three-truss arch bridge with long span are taken as the research background.The typical fatigue details which are easy to crack are analyzed by tests and finite element method.The fatigue performance and life evaluation of the panels are studied based on nominal stress and linear elastic fracture mechanics.At the same time,for the practical application of long-span bridge,in order to reduce the stress amplitude generated by vehicle vibration,prolong fatigue life and maintenance interval,the improvement suggestions of orthotropic bridge panel structure are put forward.The main research contents and achievements are as follows:(1)Comparative analysis of fatigue design codes for steel bridges.The fatigue codes of the USA,UK,Europe and China were compared in terms of fatigue design criteria,fatigue loading models,fatigue strength S-N curves and fatigue testing.The study shows that the S-N curves of each code are derived from the relevant data of constant amplitude fatigue loading,and the fatigue test is designed for safe life,but there are differences in fatigue design guidelines and fatigue detail classification to lay the foundation for the fatigue performance assessment of orthogonal anisotropic bridge decks.(2)Panel-U rib fatigue tests.Six full-size specimens containing U-rib were designed and tested in static and fatigue tests.The accuracy of the finite element model is verified by static load test.Three points of concern were determined in the fatigue test,namely,the welding point between the U rib and the top plate,the welding position between the U rib and the diaphragm,and the curved opening of the diaphragm.The S-N curve,the regression equation and the stress amplitude of different detail types of the concerns were proposed.(3)Fatigue life assessment of steel bridge panels.The 5U rib finite element model was established by Abaqus,relying on the Dload subroutine to apply dynamic vehicle loads to it,and stress analysis was carried out for three different loading cases of normal load,25%overload and 50% overload respectively to obtain stress-time history curves and cycle counts of the points of interest.Based on the nominal stress,fracture mechanics,Miner’s linear cumulative damage theorem was used to obtain that the bridge deck slab could meet the bridge design reference period(100 years)under both normal load and 25% overload,and when the overload reached 50%,the fatigue at the U-rib and cross-sectional weld location no longer met the requirements.(4)Bridge deck panel structure improvement research.In order to reduce the stress amplitude of the steel deck and improve the service life of the bridge,curved stiffened rib steel deck structure,iron-based memory alloy deck structure,steel-wood composite deck structure and ribbed steel deck structure were proposed,and the stress analysis and life comparison of curved rib steel bridge panel by finite element,we know that the stress of curved rib bridge deck is reduced by about 15% and the life is increased by about 40%.