New framework for calibration of partial safety factors for fatigue design

In Eurocode standards, three verification schemes are proposed for fatigue design under variable amplitude loadings: 1) Based on constant amplitude fatigue limit; 2) Based on constant amplitude equivalent stress range at 2 ⋅ 106 cycles; 3) Based on accumulated damage. Characteristic values of fatigue resistance and load effects as well as partial safety factors are introduced in design equations in order to achieve a target reliability level. In this paper a new framework for calibration of fatigue partial safety factors is presented. Three different fatigue limit state functions are formulated for direct comparison with the three verification schemes proposed in Eurocodes. The variable amplitude S-N curves used in this framework are defined using an original probabilistic approach. The presented framework is then applied to two typical bridge fatigue sensitive welded joints. The comparison of results with partial safety factors values recommended in Eurocodes shows that the Eurocode-based partial safety factors should be revised by considering different fatigue sensitive details and by further differentiating between the three verification schemes.