A Method in Mixed Frequency time domain for Fatigue Life Estimation of Steel Girders of Cable stayed Bridges Due to Buffeting

A method in the mixed frequency time domain for estimation the fatigue flife of steel girders of cable stayed bridges due to buffeting is developed in this paper. In this method, the joint probability density function of wind speed and wind direction at the deck level of the bridge is first established. The derived stress spectra are of wide band frequency properties when the background component of stress response is included. Thus, the time histories of the critical stress are simulated from its power spectra and the stress cycle distributions are estimated in terms of rainflow count method. The formulae derived based on the modified Miner′s law and the random vibration theory are used for estimating the fatigue life of the bridge girder due to buffeting considering the effects of wind direction. The Yangpu Bridge, a cable stayed bridge with a main span of 602m, is finally taken as an example, and the results show that the effects of wind direction on the fatigue life of the Yangpu Bridge is significant. The predicted fatigue life due to buffeting is much longer than the design life of the bridge.