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

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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.