Research On Fatigue Load And Fatigue Life Assessment Of Orthotropic Steel Deck In Port Highway Bridge

In recent years,the fatigue problem of orthotropic steel deck of port Highway bridge become more and more prominent along with the increase of traffic load.Under the commission of Key Project of Chinese National Programs for Fundamental Research and Development(2016YFC0701202),Ministry of Transport Construction Technology Projects(2015318 J41 270)and Fundamental Research Project for the Central University(106112015CDJZR155508),taking the orthotropic steel deck of a port highway bridge as an example,this paper analyzes the characteristics of fatigue load and stress of the orthotropic steel deck,and the fatigue life is evaluated.The main research contents and conclusions are as follows:(1)Based on one year’s vehicle load data of the port highway bridge,the vehicles are devided into 7 categories according to the axle number and wheelbase.The distribution of traffic volume and vehicle weight are analyzed,and Lane 4 is determined to be the main research object of fatigue load and fatigue life.Then the least square method is used to fit the distribution of axle load and wheelbase.Finally,the fatigue load spectrum is calculated.According to the fatigue load spectrum of port highway bridge,it is found that the weight of all equivalent fatigue vehicles is bigger than 10 t,and four or more axes trucks account for 85.9%.(2)Firstly,rib-to-deck at the floorbeam weld(P1),rib-to-floorbeam weld(P2),floorbeam cutout(P3),rib-to-deck weld(P4),rib splice weld(P5)are selected as the research objects.Then the finite element model of orthotropic steel deck is established,and the moving wheel load is applied in the scope of 14m×1.8m(vertical×transverse)of the model.Finally,the stress influence surfaces of structural details were calculated by hot spot stress method,and the stress characteristics of orthotropic steel deck is obtained.it is found that the effective transverse influence range of the stress of structural details are less than 1.2m.Thus,there is no load effect superposition between the wheels in tansverse,and it can only consider one set of wheel load in tansverse when the stress of orthotropic steel decks is calculated.Besides,the unfavorable load positions of structural details are determined.(3)Based on the fatigue load spectrum and stress influence surfaces,the fatigue stress history of structural details were calculated by programming the simulation of the vehicle running on the orthotropic steel deck.And then,through using the simpli-fied Rain-flow Counting method to count stress circulations,the fatigue stress spectrum is obtained.At last,fatigue life of structural details is evaluated.It is show that the fatigue damage contribution of four or more axes vehicles is accounted for more than 90% to structural details,and The proportions of the Five-axle vehicle and the second type of Six-axle vehicle are about 35%.The proportion of the second type of Three-axle vehicle is less than 1%,because it has light axle load and large wheelbase.Besides,the fatigue life of structural details are less than its designed service life(100 years).And the fatigue life of P2,P3 and P4 were 4.3 years,6.1 years and 5.5 years,respectively.