Development of System to Evaluate Fatigue Damage of Steel Highway Bridge on the basis of Dynamic Response Analysis and Structural Reliability Theory

公路桥梁车辆振动对局部疲劳损伤的影响虽然不小，但在寿命估算中往往被忽略。此外，在寿命设计中没有充分考虑等幅应力循环引起的结构材料损伤的大的不确定性。另一方面，利用结构可靠度理论，各种结构的极限状态设计方法也逐渐建立起来，本文旨在发展一种精确计算公路桥梁结构构件在车辆荷载作用下动应力的分析方法，并对其在使用期内的疲劳损伤进行统计评估，结果表明：（1）建立了考虑路面不平度影响的桥梁与车辆相互作用的三维动力学方程。在有限元分析中，桥面板采用矩形单元，主梁、横撑和井式扶手采用梁单元。此外，一个移动的车辆被建模为一个八自由度。(2)基于上述方程进行动力响应分析，得到的主梁动位移、桥面板动应变等数值结果与现场试验结果吻合较好。(3)考虑到材料在一定应力范围内疲劳寿命的离散性，提出了一种较为简单的随机载荷作用下构件疲劳损伤的统计分析方法。(4)采用上述分析方法，根据实测数据，模拟移动车辆引起的桥梁构件随机变化的应力水平，可以计算桥梁在运营期内因交通荷载引起的疲劳破坏概率。

Although the effcts of vibrations of highway bridges due to moving vehicles upon local fatigue damage are not necessarily small, they have been often neglected in estimating their lifetime. Furthermore, the large uncertainties of damage of structural material induced by a stress cycle of constant amplitude are not sufficiently considered in the lifetime design. On the otherhand, the limit state design method for various structures has been gradually established by use of the structural reliability theory.This study was carried out to develop an analytical method to accurately calculate dynamic stress of structural members of highway bridges under traffic vehicles and to statistically evaluate its fatigue damage during the service period.As a result, the following conclusions could be drawn :(1) Three-dimensional kinetic equations for interactions between a bridge and vehicles were formulated in consideration of road surface roughness. Then, a deck plate was modeled by rectangular elements in applying finite element analysis ; main girders, sway bracings and well-style handrails were by beam elements. Furthermore, a moving vehicle was modeled by an eight degree of freedom.(2) Numerical results, such as the dynamic displacement of the main girders or the dynamic strain of the deck plate, by dynamic response analysis based on foregoing equations showed good agreement with field test results.(3) A relatively simple, analytical method to evaluate statistically fatigue damage of structural members excited by random forces was developed in consideration of scatter of fatigue life of matearials under a regular stress range.(4) Using the above mentioned analytical method, it was demonstrated that probabilities of fatigue failure of bridges due to traffic loads during its service period could be calculated with randomly variable stress levels of bridge members induced by moving vehicles simulated on the basis of abserved data.