A Study on Fatigue Evaluation Procedure for Steel Bridge Members

研究了疲劳设计荷载、设计应力范围直方图、疲劳强度评估程序和疲劳评估交互程序，构建了钢桥构件疲劳评估程序。本文主要研究内容如下：利用影响线和蒙特卡罗方法对正常交通条件下的交通流进行了应力变化分析。在此基础上，提出了公路桥梁疲劳设计应力范围直方图。建议的疲劳设计载荷为20tf的三轴货车，设计直方图采用双参数威布尔分布。对典型结构细节在多种变幅应力作用下进行了疲劳裂纹扩展分析，这些应力近似表示各种钢结构中的应力。在分析结果的基础上，验证了疲劳损伤门槛应力范围与疲劳损伤程度之间的关系。将该关系与线性损伤概念相结合，提出了一种新的变幅应力作用下结构细节疲劳寿命预测方法，并开发了用于公路钢桥疲劳安全性校核、疲劳寿命和剩余寿命估算的交互式程序。该程序由三个子程序组成。首先是分析各种车辆通过时的应力变化，其次是根据日本钢结构学会疲劳设计方法的建议确定许用应力范围，最后是通过应力变化与许用应力范围的比较来进行安全性校核。

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.