Construction of Expert System for Assessment of Fatigue Damages in Steel Bridges

桥梁长期或半永久地暴露在自然环境和随时间变化的汽车、火车等荷载作用下。因此，疲劳损伤是既有桥梁中最常见、最令人担忧的事故。本研究的目的是构建钢桥疲劳损伤评估专家系统，为该系统提供基础知识。主要研究内容如下：通过对桥梁构件变幅截面力的模拟，研究了公路桥梁的疲劳设计荷载。讨论了影响线形状、长度、桥梁梁数、车道数、横向荷载分布等参数对桥梁疲劳损伤的影响，并利用有限元方法分析了主梁上翼缘与竖向加劲肋连接部位的疲劳损伤原因，分析了焊缝处局部应力与摆动支撑构件截面力的关系，提出了一种简便的计算摆动支撑构件截面力的方法，并利用大量疲劳数据检验了角焊疲劳裂纹发生率。试验结果对疲劳损伤构件的剩余寿命评估和修复方法的选择有一定的参考价值。构建了一个基于知识的专家系统，用于参考公路钢桥各部位以往出现的疲劳损伤情况，辅助工程师的判断。该系统由三个子系统组成：显示待检件清单、评定疲劳损伤等级、提出改造方法。

Bridges are exposed to a natural environment and time-depend fluctuating loads due to motorcars, trains and so on for a long or semipermanent time. Fatigue damage, therefore, is the most frequent and anxious accidents in existing bridges. The objective of this study is to construct the expert system for assessment of fatigue damage in steel bridges and to offer the basic knowledge for the system. Main contents of the study are follows.Fatigue design load of highway bridges are studied by means of the simulation of variable amplitude sectional forces in bridge components. The differences of fatigue damages due to various parameters ; the shape and length of influence line, the number of girders in a bridge, the number of lanes and lateral load distribution, are discussed.In order to make clear the cause of fatigue damage at the connection weld between upper flange of main girder and vertical stiffener with a function of connection plate to sway bracing member, the relationship between the local stresses at the weld and the sectional force of sway bracing member is analyzed by using finite element method, and a simple procedure for evaluating the sectional force of sway bracing member is proposed.Aspect ratios of fatigue cracks in fillet welds are examined by use of many fatigue data. The results of the examination are useful in evaluating the remaining life of fatigue damaged components and selecting the repair method.A knowledge-based expert system is constructed to refer the past fatigue damages appeared at various parts of steel highway bridges and to assist engineers's judgment. The system consists of three subsystems : presenting the list of parts to be inspected, appraising the grade of fatigue damages, and proposing the method of retrofit.