Long-span Cable-stayed The Fatigue Life Typical Structure Details Assessment

Since the sixties in last century, fatigue cracks is belonged to the shortage of knowledge on fatigue of steel structures in the design process of bridges, which caused a lot of steel bridge appeared fatigue cracks. This fatigue cracks didn't get timely treatment, leading to catastrophic accidents. In accordance with the investigation of fatigue and fracture committee of ASCE, over 80 percent of steel structural damages are related to structural fatigue. The steel structural fatigue of bridges gradually become an important problem in bridge engineering field. With the rising number of the steel structure, the fatigue problem of birage has become an important topic of the bridge engineering.In consideration to the practical problems involved in fatigue study of steel bridges, the characteristics of fatigue design curves of typical structural details are analyzed and discussed by means of the proposed normal fatigue vehicle model. Meanwhile, on the basis of S-N curve, the analysis method of fatigue life and the concrete technological flow are presented. Taking East Hubei Yangtze River Bridge as an example, the evaluation of fatigue life is carried out. The main research results are listed in the below:At first, the method is introduced for us to obtain the load spectrum of typical vehicles and the normal fatigue vehicle model. Through comparisons between American code AASHTO,UK code BS5400,and European code Eurocode 1, the calculation methods of fatigue load spectrum are discussed in detail.Secondly, it is made to summarize and discuss the characteristics of fatigue damage of steel bridges,the mechanism of deterioration of weld details as well as typical structural details closely related to fatigue damage. In addition, the principles, method and steps of designing fatigue resistant steel structures are provided accordingly. And the suggestions are given to improve the fatigue strength of weld details.Thirdly, with respect to the practical problems involved in fatigue study of steel bridges, the fatigue design curves with various amplitudes are suggested. According to this point, it is carried out to calculate the fatigue life of East Hubei Yangtze River Bridge.