Study On Fatigue Damage Of Bridge Rigid Suspenders Based On Time Series Analysis

Recently there has been plenty of bridge collapse accidents caused by the fatigue crack of suspender,so it's very necessary to carry out research on the fatigue damage of bridge suspender during the service period.But the residents' motor vehicle ownership is growing with the development of China's economy,so we should consider the trend of fatigue index when we analysis the fatigue damage of suspender according to the existing health monitoring data.The main content of this thesis includes:(1)Introducing the concept,common models and characteristic function of time series,exploring the possibility of combining time series with suspender fatigue analysis to improve the current methods of calculating fatigue damage and fatigue lifetime,elaborating the creation process of time series model and the extended application of least square method;(2)Putting forward a calculating method of suspender fatigue accumulating damage based on Miner linear rule and the S-N curve of Tianyuan bridge suspender's detail,calculating the daily fatigue equivalent stress amplitude and daily fatigue damage of suspenders,researching the distribution of stress amplitude and the relativity between distribution and fatigue damage,it proves side suspender's response process and change regulation to fatigue stress cycles are similar to the second side suspender's.However,the side suspender's highest cycle stress amplitude Ah,most decreasing cycle stress amplitude Ad and fatigue equivalent stress amplitude Seq are all greater than the second side suspender's.Moreover,the research shows that the main contribution to suspender fatigue is caused by the stress cycle which has low loop counts and high stress amplitude,this kind of stress cycle can bring about fatigue damage three to eight times greater than the stress cycle which has high loop counts and low stress amplitude;(3)Creating ARMA models on the basis of the calculated data which contains daily fatigue equivalent stress amplitude and daily fatigue damage of suspenders,deducing these data's change regulation after making sure that the ARMA models can pass the residual test,predicting the slightly rising trend of the next 100 days' data,the error is no more than 10%shows that predicting effect is good.Ultimately using three methods which are according to existed data merely,considering motor vehicles load increasing,basing on ARMA models predicting data to calculate Tianyuan bridge suspenders' residual fatigue lifetime.No matter using which method the result shows that the side suspender's fatigue lifetime is far less than the second side suspender's and the midspan suspender's,it tells us when maintaining the bridge we need to pay attention to the side suspender 's fatigue damage condition.This thesis investigates the bridge suspender's fatigue damage contribution from high amplitude stress cycle and low amplitude stress cycle,analyzing suspenders'fatigue trend with time series theory,the results can provide several guidance to bridge suspender fatigue research.