Research On Fatigue Life Of Modular Expansion Joint Based On Miner Cumulative Damage Theory

With the development of Chinese transportation industry and the increase in traffic volume,the requirements for highway bridge structures have gradually increased.The modular bridge expansion joint is widely used as a large-scale bridge expansion device.It is easily damaged during use.That will further damage the bridge structure if this phenomenon has not been Paid enough attention.At the same time,the replacement of the bridge expansion joint will also affect public transportation.This Paper based on Miner linear cumulative damage theory has estimated the working life of modular expansion joint.The main research results are as follows:(1)Through the field investigation of the bridge expansion joint used in China at present and the analysis of disease forms about different kinds of bridge expansion joint used in diverse environments,the main reason why bridge expansion joints are broken is fatigue damage produced by long-term vehicle load.(2)Through calculating the middle beam profile steel and anchorage concrete of the modular bridge expansion joint under the vehicle load of a highway in the northwest region by Midas FEA,even in the most unfavorable condition,the middle beam profile steel and anchorage concrete still does not reach their yield strength,the conclusion that the destruction form of middle beam profile steel and anchorage concrete is fatigue damage can be proved.(3)The conclusion that as the stiffness of the elastic support of the telescopic device decreases,the stress peak of the middle beam profile steel in the bridge expansion joint will increase continuously can be proved by Midas FEA analysis.When the elastic support stiffness degrades to original 30 percents,the tensile and pressure stress of the middle beam profile steel will increase drastically;the shedding of the elastic support will also cause a sharp increase in the tensile and pressure stress of the middle beam profile steel.(4)After summarizing the traffic volume of an expressway bridge in the northwest region,the simplified vehicle load spectrum is obtained.The rain flow counting method is used to calculate the concrete stress amplitude of the beam steel and anchorage zone in the bridge expansion joint and the corresponding cycle number.The working life of modular bridge expansion joint has been estimated.The working life of the modular bridge expansion joint is 23.3 years.Considering the degeneration of the modular bridge expansion joint's elastic support,the working life is 17.6 years.The shedding of the elastic support has a great influence on the fatigue life of the modular expansion device,and the expansion device will be destroyed in a year or so after the elastic support slips.When using steel fiber reinforced concrete as the anchoring area concrete of the telescopic device,the service life of the expansion joint can be effectively improved.(5)The residual stress in the welded joint between the beam steel and the beam in the modular bridge expansion joint was obtained by thermal-structural analysis in ANSYS,and the stress concentration factor at the weld was determined by the linear extrapolation method of welding provided by The International Institute of Welding(IIW).The fatigue resistance curve(S-N curve)which is concluded that the beam in the telescopic device is damaged before the weld with the support beam.modular bridge expansion joint is determined.