| There are a lot of welding details in steel truss bridge which affect the safe use of beidge and it must be considered in design. With the steel truss bridge span increasing, variety of new structure details with new manufacturing process have been applied. However designers usually cannot grasp the fatigue property of the structure details, that will bring bad impacts on bridge design and management work.There are many weld seams around the access hole detail in oblique web member of steel truss where the stress gradient is significant. Fatigue failure usually starts at the detail which needs to focus attention on. A fatigue test was carried out for testing the fatigue performance of the structure detail. Besides that, several characteristic parameters in the paris formula about the structure detail were studied based on fracture mechanics. The major contents are summarized as follows:1. The basic principle of fatigue life evaluation methods based on S-N curve or linear elastic fracture mechanics are introduced. And it is considered that the latter one apply to the fatigue performance evaluation of welded steel bridges better after comparing the superiority and inferiority of both form many aspects.2、The method that establishing discontinuous displacement field with Heaviside funcion and jump function in extended finite element method(X-FEM) is described in detail. In addition, the X-FEM is applied to numerical calculation for stress intensity factor and the computational efficiency and calculation accuracy is evaluated by comparing with the analytical solution. It is considered that applying the X-FEM to discontinuity problems can keep the high calculation accuracy and make the calculation process more simplified than finite element method(FEM).3. The specimen whose stress characteristics is similar to the access hole detail is designed for fatigue test. On this basis, the fatigue life of the access hole detail under the conditions that the nominal stress amplitude is respectively 63MPa,81MPa or 99MPa. It is found that the starting-crack location is always at the weld toe near the access hole on the flange plate. So that the region’s fatigue performance needs to focus attention on.4. The expression of S-N curve which suitable for the access hole detail is derived based on the fatigue test data. And the limit of stress amplitude of this detail under 2 million times cyclic loading is also calculated.5. Analysis on the influence law of several characteristic parameters in the paris formula on prediction results of fatigue life is carried on. It is found that the parameters C, m and α0 have a great influence on the prediction results and the three parameters depend on each other. Therefore, it is necessary to reasonably determine the parameters to ensure the prediction accuracy of fatigue life.6. The stress intensity factors of specimen during each stage of cracking process are calculated by X-FEM. On this basis, the parameters C and m are reasonably determined with the fatigue test data, in order to provide reference for the fatigue design of similar structure details. |
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