In order to more accurately consider the effect of the dynamic vehicle loading caused by the road surface condition (RSC) on the fatigue damage accumulation of bridge components, the deterioration process of the RSC of steel bridges under the given traffic and environmental loading condition was first investigated, and the number of vehicle passages required for the RSC to deteriorate from one class to the next was obtained. Then, the three-dimensional bridge and vehicle models were established respectively. Coupling vibration equations based on the displacement and the interaction force relationships at the contact points of the bridge and vehicle models were solved by the modal superposition technique and the fourth-order Runge-Kutta method in the time domain. In terms of numerical simulations, the impact factors for stress range and the equivalent number of stress cycles, induced by each vehicle passage were obtained under the different RSCs of the main girder of five I-type simply supported steel girder bridges with different span lengths based on AASHTO bridge design specifications. Finally, impact factors and the number of stress cycles for fatigue design, two parameters directly affecting fatigue lifetime of bridges in AASHTO bridge design specifications were optimized by considering the fatigue damage accumulation effect of dynamic vehicle loading on bridge members during the deterioration process. The procedure of applying the proposed method to improve the Chinese code for fatigue design and evaluation of steel bridges was also discussed. The results show that the impact factor (0.15) specified in AASHTO bridge design specifications for fatigue design is suitable for bridges with span lengths larger than 23m, while for the fatigue design of shorter-span steel bridges, larger impact factor should be adopted. The value of 1 may be adopted as the number of stress cycles for the main girders of steel bridges with span lengths larger than 23 m and the number of stress cycles can be calculated with the proposed equation for bridges with span lengths shorter than 23 m. The proposed approach can be applied to improve the Chinese code for fatigue design and evaluation of steel bridges.
Key words
bridge engineering /
optimization of parameter for fatigue design /
vehicle-bridge coupled model /
impact factor for stress range /
number of stress range /
RSC /
fatigue damage accumulation
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