Research On Stress Intensity Factor And Propagation Path Of Fatigue Crack In Steel Structures

Based on linear elastic fracture mechanics and Haihe Bridge, this paper studiesthe propagation mechanism of the existed cracks under cycled vehicle loads.The formula presented by Paris has become the most popular one to determinethe propagation rate of fatigue cracks. This formula introduce a parameter-stressintensity factor (SIF). There are many methods to determine the SIF of crack tip, suchas analytical methods and finite element method based on simulation. In part one,three types of cracks have been studied. Using software ABAQUS, J-integral method,extrapolation method and node displacement method are applied to determine the SIF.After calculating, we compare the results of the three methods with results fromanalytical function to confirm the accuracy of each finite element method. Besides wecompare the results from different element types and mesh sizes to testify theapplicability of these methods under various circumstance.Through the analysis, the most accurate and effective method is selected to beapplied in the research of L-crack in square steel tube. We obtain the SIF of web andflange when the tube bears the tensile pressure or moment. Then we combine theresults of cracks with different length. We perform the regression analysis with theresults and obtain a fitting equation which can be seen as the analytical formula ofsquare steel tube with L-crack. Later, we add the tensile formula to moment formulaand apply the combined one to rectangular steel tube under both tensile pressure andmoment. The results of the combined formula fit perfectly to the calculation results.In the last part of this paper, we take advantage of extended finite elementmethod (XFEM) to simulate the propagation path of crack. The analysis based onlocal model of Haihe Bridge which has microsmall crack. The simulated vehicle loadsare applied to the U-rib to forecast the propagation tendency of the existed cracks. Wealso use the finite element method to testify the results of XFEM. In the end, weestimate the remnant life of the bridge using formula Paris.