A FULL RANGE S-N CURVE FOR FATIGUE EVALUATION OF ORTHOTROPIC BRIDGE DECKS IN STEEL BOX-GIRDERS

The full range S-N curve plays a fundamental role in the fatigue evaluation of orthotropic bridge decks in steel box-girders when using the sequential law. The general full range S-N curve model, which covers the low-cycle range, the finite-life region, and the high-cycle region, is deduced theoretically based on the S-N curve in the finite-life region specified in design specifications for steel bridges. Furthermore, a full range S-N curve model used for evaluating the fatigue performance of orthotropic bridge decks in steel box-girders is developed. In the model, the fatigue damage accumulation factor and the fatigue strength amplification coefficient are adopted to compute the fatigue damages caused by small stress amplitudes in the high-cycle region and the influence of plastic strain on the fatigue strength in the low-cycle region, respectively. The effects of low stress amplitude caused by cars and sustained wind and high stress amplitudes caused by earthquakes and strong winds are estimated. Subsequently, the parameters in the proposed model are explained from the geometrical point of view. The full range S-N curve with the best goodness of fit and the full range S-N curve for fatigue evaluation with 99% reliability are formulated by using the data obtained from fatigue tests of rib-to-deck joints. The results indicate that the full range S-N curve model developed in this paper has strong ability to describe the accumulative characteristics of fatigue damage of orthotropic bridge decks in steel box-girders under fatigue loading with variable amplitudes. The proposed full range S-N curve is expected to provide a reference for fatigue evaluation of orthotropic bridge decks in steel box-girders.