Fatigue Damage And Life Assessment For Long Span Bridges Under Stochastic Traffic Flow

With the development of our country's economy and the increase of urban traffic volume,the trafic load of the bridge is increasing day by day.However,under the repeated action of random traffic load,the stress of the structural components changes with the cycle and accumulates continuously,resulting in fatigue damage,which will seriously threaten the operation safety and safety of the long-span steel bridge.Service life.Therefore,reasonable evaluation of fatigue performance of long-span steel bridge structures and key components has become an important part of life-cycle performance evaluation of bridge structures.In this paper,the fatigue life assessment and fatigue reliability research of Aizhai Bridge and Dongping River Bridge are carried out based on field measurement and numerical simulation respectively.The main contents of the research are as follows:(1)The characteristics of the two main methods used to obtain fatigue stress spectrum are compared and analyzed.The background and significance of this study are elaborated.Furthermore,the research methods of fatigue reliability based on S-N curve and linear damage theory and the counting method of extracting stress cycle are correlated.It provides theoretical and methodological guidance for the study of bridge fatigue reliability.(2)The shell-beam hybrid element finite element model of the bridge is established by using ANSYS software,and the key components and key sections of the bridge are determined by analysis.According to the key sections of key components,real-time strain monitoring was carried out for 6 days.Through pretreatment of measured data,more accurate stress response was obtained.The probability distribution model of fatigue load spectrum of small samples of key components was established by using nuclear density estimation method,and the fatigue of key components measured by bridge was studied.Reliability provides guarantee for the safe operation of the bridge.(3)Using ANSYS finite element software,the finite element model of the standard section shell element of the main girder in the middle span of Dongping River Bridge is established,and the stress influence surface functions of two kinds of weld details at key U-rib positions are calculated.Based on the dynamic weighing system of a bridge,a stochastic traffic flow model is established.The stress time history response of the details of steel box girder under sparse,general and intensive operation conditions is obtained by numerical simulation method.The length of each stress response is five minutes.The fatigue reliability of weld details in key positions of bridges was studied by using the probability distribution model of fatigue load spectrum fitting two kinds of weld details.