Fatigue Reliability Analysis Of Cables Of Long Span Cable-stayed Bridges Considering The Combined Effects Of Wind And Traffic Vehicle

Stayed cables are susceptible to vibrations due to winds and traffic loads.Recently,the fatigue of stayed cables has gradually become the focus of attention.It is of great significance to evaluate their fatigue life and reliability.The Shanghai-Suzhou-Nantong rail-cum-road Yangtze River Bridge is taken as the engineering background.The fatigue damage of stay cables under the combined action of wind and traffic vehicles is calculated numerically,based on which the fatigue life is evaluated.The main research contents are as follows:(1)The current research status on the fatigue problem of the stayed cables due to winds,vehicles and the combined action of winds and vehicles are introduced at home and abroad.The research significance,framework and main content of this paper are elaborated.(2)The random wind load model as well as the fatigue damage analysis model were established.The stress and fatigue damage of stayed cables under different wind parameters were simulated by re-developing the software ANSYS.The annual fatigue damage of stayed cables was analyzed based on the probability model considering the simultaneous distribution of wind speed and direction.(3)On the basis of local traffic statistics,the random parameters for the calculation such as automobile type,weight,speed,flow and spacing were simulated.The random traffic flow model was therefore established.The most unfavorable cable was determined accordingly.In addition,the fatigue damage calculation under different automobile parameters was carried out.(4)The model of moving train vehicles was established.Both the stress distribution and fatigue damage of stayed cables were calculated and analyzed under different train speeds,axle loads,composition and multi-line running conditions.Based on the statistical analysis of the train traffic in one year,the annual fatigue damage of stayed cables was analyzed.(5)The fatigue reliability analysis model of stayed cables was established.The fatigue reliability under the combined action of random winds and vehicles was analyzed.The fatigue life of cables was further assessed.The results show that: 1)Under the random wind loads,the stress amplitude of the cable is increasing with the increase of the wind attack angle and the wind speed.It is more unfavorable under the action of the positive attack angle.The position of the most unfavorable cable will change with the wind attack angle.As the wind attack angle is in the range of-6° to +6°,the most unfavorable cable is the shorter cable in the main span,otherwise transfer to the longer cable.2)Under the random traffic flow,the stress amplitude of the cable decreases with the increase of the cable length,while increases with the increasing of the traffic flow.3)Under the multi-train vehicles,with the increase in the number of vehicles on the bridge,the stress amplitude of the cable tends to increase.Compared with the case of a single train passing through,the stress amplitude of the cable increases by 108.8% on average when there are four trains on the bridge at the same time.4)The fatigue reliability within 10 years of the shorter cable in the main span is around 3.9 and 3.54,respectively,under the combined action of winds and traffic flow,and the combined action of wind,traffic flow and moving trains.