| In recent years, due to the sustained and rapid development of the national economy, highway traffic volume, number of heavy vehicles and speed has increased significantly. The construction of highway bridge has also entered a period of rapid development. Due to the advantages of lightweight, high strength and easy to factory production, steel bridge becomes popular. The proportion of live load has increased because of the widely used of lightweight, high strength materials and substantial increase of highway traffic volume. Then, fatigue problems have become increasingly prominent. The current code "Specification for Design of Steel Structure and Timber Structure Highway Bridges and Culverts"(JTJ025-86) has been implemented more than25years. It has long been unable to meet the needs of the development of highway steel bridge in our country. In this paper, on the basis of a project of stainless steel suspender fatigue analysis of a three-span continuous steel arch bridge and a project of863Program (2007AA11Z133), a series of work has been done. The main contents are as follow:(1) The constant amplitude sine wave fatigue tests had been done on a stainless steel suspender with a diameter of55mm and two stainless steel suspenders with a diameter of70mm. Material of these suspenders is stainless steel of05Cr17Ni4Cu4Nb. The fatigue life, fatigue failure locations and fracture appearance were obtained.(2) The symmetric tension-compression fatigue limits had been estimated by theoretical methods, and the value was226MPa for the stainless steel suspender body with a diameter of55mm and250MPa for the stainless steel suspender body with a diameter of70mm, respectively. On the basis of the measured stress and strain of suspender body, the variation relationship of strain range with load cycles had been analyzed. The results showed that one of the stainless steel suspender body with a diameter of70mm appeared tiny damage after about3million cyclic loading, and no damage was found in other two suspender bodies.(3) The trilinear constitutive model was proposed. The stress analysis had been performed on the threaded connections of suspenders with finite element software ANSYS. The conclusive results were drawn from the analysis including load distributions on the thread teeth and the locations and values of maximum Von Mises stress and strain.(4) The Manson-Coffin formula of05Cr17Ni4Cu4Nb stainless steel was proposed. The fatigue lives of the two suspenders with a diameter of70mm had been estimated with the nominal stress method, and the value were976500cycles and2365130cycles, respectively. The fatigue crack initiation lives of the two suspenders with a diameter of70mm had been estimated with the local stress-strain method and the value were314230cycles and444919cycles, respectively. Then, the fatigue crack initiation lives of the two suspenders with a diameter of70mm were estimated with FE-SAFE, and the value were441165cycles and695132cycles, respectively. The results showed that the nominal stress method to accurately predict the fatigue life of a particular component is almost impossible, FE-SAFE has higher accuracy than local stress-strain method on estimating the fatigue initiation life, and it suitable for the user with rich theoretical knowledge of fatigue analysis.(5) The stress intensity factor formula for thread root was proposed. An analysis of the fatigue crack propagation lives of stainless steel suspenders had been performed. The recommendation values of Paris equation parameters of05Cr17Ni4Cu4Nb stainless steel were proposed as m=3, C=3.96×10-13.(6) The comparative analysis had been performed on the anti-fatigue design of BS5400, AASHTO, Eurocode1and Eurocode3, as well as TB10002.2-2005. The suggestions of fatigue load model, detail categories and design fatigue curves, as well as anti-fatigue design method were proposed on the anti-fatigue design of China's highway steel bridge.The detail category of threaded connection of stainless steel suspender was recommended to be taken as71MPa, and considered size effect when the nominal diameter d>30mm. The size effect factor is ks=(30/d)0.25.The finite element model of arch bridge was established with finite element software Midas Civil to perform an axial force analysis of the suspenders of arch bridge under the fatigue load model3of Eurocode1. The fatigue assessment had been performed on the stainless steel suspenders with the simple fatigue assessment method of Eurocode3and the detail category of threaded connection of stainless steel suspender recommended in this paper. The results showed that the fatigue resistance of the stainless steel suspenders with a diameter of70mm meet design requirement, and only9of the stainless steel suspenders with a diameter of55mm meet the anti-fatigue design requirement, the fatigue design requirements of the remaining45stainless steel suspenders with a diameter of55mm are not met. The suggestions of dedign modification were proposed and met the anti-fatigue design requirement.
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