Fatigue Analysis On Key Parts Of A Dual-purpose Steel Cable-stayed Bridge For Highway And Railway Based On Measured Traffic Flow

This article takes the Chongqing Dong Shui Men a Dual-purpose Steel Cable-stayed Bridge for Highway and Railway Yangtze River Bridge as the research engineering background.With theoretical analysis,the fatigue performance of the key areas based on the measured traffic flow data is studied.The bridge is a dual-use cable-stayed bridge with two towers and a single cable plane truss girder.The highway and railway are laid separately on the upper and lower bridge decks.Under the combined effect of track load and highway load,coupled with the doubling of urban traffic flow,the fatigue performance of key areas of this cable-stayed bridge needs to be verified.First of all,this article summarizes the research history and current status of fatigue performance which is cable-girder anchorage areas of long-span cable-stayed bridges at home and abroad.And it introduces the theoretical basis and calculation methods of fatigue which included: a.Fatigue concept and its failure principle;b.Linear accumulation principle of fatigue damage;c.Method for counting fatigue frequency spectrum(rain flow counting method);d.Theory of equivalent fatigue load conversion.It also introduces the grey system theory and GM(1,1)mathematical model used for the prediction of time series data such as traffic flow.Secondly,build a bridge model with software MIDAS/CIVIL.Then the local weak area of the main beam under constant live load is analyzed as the key part of the fatigue design.Due to its complex structure and concentrated stress,the cable-girder anchorage zone of cable-stayed bridges causes fatigue problems.The moving load analysis of the whole bridge was performed to extract the cable force influence line at the same time.Then,based on the measured traffic flow data,the number of passing vehicles within the designed service life of the bridge is predicted.This article combines the previous literature and the comparison of national standards to select the appropriate fatigue vehicles axle weight and wheelbase.The influence line loading is performed to obtain the cable force internal force history curve of the cable beam anchoring zone.Through the rain flow counting method,the fatigue load is sorted out.Through the fatigue equivalent load theory,a series of fatigue loads of unequal amplitude and unequal average value are converted into constant amplitude load spectra under 2 million times of action.Finally,according to the force transfer condition of the anchorage zone of the cablestayed bridge,the plate shell element model of the local zone is established by using ANSYS software.Set the displacement boundary conditions and load conditions,determine the structural details that need to be fatigue checked,apply the fatigue load,and calculate the corresponding stress amplitude.The fatigue design content in China,British,American,and European Standard,respectively,were used to check and calculate them.Ultimately,it is concluded that the anchorage zone of the cable and beam of the bridge can withstand the effects of two types of traffic loads on the public rail within the design service life under the standards of various countries.