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

虽然由于车辆运动引起的公路桥梁振动对桥梁局部疲劳损伤的影响并不一定小，但在估计桥梁寿命时往往忽略了这些影响。此外，在寿命设计中没有充分考虑结构材料在等幅应力循环下损伤的较大不确定性。另一方面，利用结构可靠度理论，逐渐建立了各种结构的极限状态设计方法。本研究旨在建立一种准确计算交通车辆作用下公路桥梁结构构件动应力的分析方法，并对其服役期间的疲劳损伤进行统计评估。结果表明：(1)考虑路面粗糙度，建立了桥梁与车辆相互作用的三维动力学方程。然后，采用矩形单元对甲板板进行有限元建模；主梁、横撑和井式扶手由梁构件构成。在此基础上，建立了八自由度运动车辆模型。(2)根据上述方程进行动力响应分析得到的主梁动位移或甲板动应变等数值结果与现场试验结果吻合较好。(3)考虑到材料疲劳寿命在一定应力范围内的离散性，提出了一种相对简单的结构构件在随机力作用下疲劳损伤的统计分析方法。(4)利用上述分析方法，在观测数据的基础上，通过模拟车辆对桥梁构件的随机变应力水平，可以计算出桥梁在服务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.