Fatigue life estimation of steel girder of Yangpu cable-stayed bridge due to buffeting

As the main span of modern cable-stayed bridges becomes longer and longer, the buffeting-induced fatigue damage problem of steel girders located in strong wind regions may have to be taken into consideration in the design of the bridge. This paper presents a method in the mixed frequency-time domain for estimating the fatigue life of steel girders of the Yangpu cable-stayed Bridge due to buffeting. In the suggested method, the joint probability density function of wind speed and wind direction at the deck level of the bridge is first established. The power spectra of the critical stress of the girder are then derived from the power spectra of the generalized coordinates of the bridge for different wind speeds and wind directions. The derived stress spectra are no longer a narrow spectrum when the background component of stress response is included. Thus, the time histories of the critical stress are simulated from their power spectra and the stress cycle distributions are estimated in terms of rainflow count method. The formulae derived based on the modified Miner law and the random vibration theory are finally used for estimating the fatigue life of the bridge girder. The results show that the effects of wind direction on the fatigue life of the Yangpu Bridge are significant. The predicted fatigue life due to buffeting is much longer than the design life of the bridge. (C) 1999 Elsevier Science Ltd. All rights reserved.