Main Cable Fatigue Life Research Of Long-Span Suspension Bridge

Cable structure bridges such as suspension bridges and cable-stayed bridges have become the first choice for long-span bridges,which make our daily life colorful and also provide great convenience to transportation.Among the cable structure bridges,As cable system is one of important members for load-bearing of the bridges,its safety and durability play a vital role on ensuring normal operation of the bridges.Therefore,the study on safety of the cable system,especially on the life-cycle fatigue performance,is necessary.This paper totally discusses the theoretical evaluation of the fatigue performance and the cable fatigue life of long-span suspension bridges.The specific research contents can be summarized as follows:At first, the bridge structure must face to complicate and random vehicle load during daily operation, and pulse of the load is also complicate and changeable,but in laboratory we cannot be provided the related loading mode.In order to be closer to the real situation and effectively complete the structure fatigue life analysis,it is necessary to simplize the real load reasonably to a relatively simple form of load.According to the actual amount of traffic,we can get the frequency of vehicles passing the bridge. In this paper, combined with the domestic geographical features of supporting project and foreign specifications, it is summed up that three reasonable and convenient fatigue live load can be used(Ml、M2、M3).Secondly, based on the finite element calculating program, the initial shape of the main cable of Lancang River Bridge is analyzed,so the initial state of the main cable of the bridge is more realistic.Combined with finite element program analysis results and the local traffic situation,the fatigue load under different conditions can be summed up,then "the maximum stress amplitude"and "the most easily fatigue position" can also be figured out.These results will be used as original data for next step--atigue performance and fatigue life assessment.Next, the main cable supposed to be continuum media. According to the whole bridge finite element model analysis results,using nominal stress method and local stress-strain mefhod,we can calculate the main cable’s fatigue life and fatigue crack initiation life,(main cable adhere to cable tower area, for example,under M3 load condition,fatigue life is 2481590 times(73.73years),fatigue crack initiation life is 202743), the proposed theory calculation and simulation analysis parameters values are recommended.Finally,focus on main cable’s fatigue crack expansing rate, calculated the fatigue crack propagation life.Combined with the fatigue life and fatigue crack initiation life calculation results, summarized the fatigue crack propagation life calculation formula for this bridge, determined important parameters recommended values as m=3,C=1.592X 10-13, reasonable and effective data support will be supplied for future study.