A Study on Fatigue Evaluation Procedure for Steel Bridge Members

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Fatigue design load, design stress range histogram, fatigue strength evaluation procedure, and interactive program for fatigue evaluation are investigated in order to construct fatigue evaluation procedure for steel bridge members. This study summarized as follows.Stress variation analyses with the aid of influence line and Monte Calro simulation of traffic flow are performed under usual traffic condition. On the basis of the analytical results, the fatigue design stress range histogram for highway bridges are proposed. Proposed fatigue design load is the three axles truck of 20tf weight and the design histogram is to utilize two-parameter Weibul distribution.Fatigue crack propagation analyses for typical structural details are performed under many types of variable-amplitude stresses which approximately express the stresses in various steel structures. On the basis of analytical results, the relationship between threshold stress range to give the fatigue damage and the degree of fatigue damage is verified. By combining the relationship with the linear damage conception, a new procedure is proposed to predict the fatigue life of the structural details under variable-amplitude stresses.An interactive program has been developed for checking the safety of steel highway bridges against fatigue, and estimating fatigue life and remaining life easily. This program consist of three subprograms. The first is that analyze the stress variations caused by passing of various vehicles, the second is that determine allowable stress range based on the Recommendations for Fatigue Design Method of Japanese Society of Steel Construction, and the last is that check the safety by comparison of the stress variation to the allowable stress range.