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Fatigue reliability in future generations of Eurocodes

One of the aims in preparation of the new generation of Eurocodes is the development of technical bases for the extension of existing procedures. The current procedure for the fatigue limit state verification is based on the deterministic S-N concept which should be given a probabilistic alternative. In the latter, the values of statistical parameters of resistance and actions are to be entered in the fatigue limit state function. Contrary to resistance, statistical parameters for the effects of actions are still based on the data that are incomplete or not updated, notably concerning the evaluation of load history of fatigue-exposed structures. This paper proposes a procedure to extend the current fatigue limit state verification using probabilistic methods with a particular stress placed on the effects of actions. In the first phase of the procedure the effects of actions are presented by a stress range spectrum. In the second phase this spectrum is approximated with various probability density functions. Depending on the choice of probability density functions, different fatigue limit state functions are defined. Solving a selected fatigue limit state function allows to determine the fatigue reliability level, expressed by reliability indices as operating values of failure probability for different detail categories. A contribution to the current fatigue limit state verification will be a possibility to compare the calculated reliability indices with their target values for fatigue as given in EN 1990. Preliminary analyses have shown that it might be difficult to maintain a uniform slope angle of the fatigue strength curves for all detail categories as such an assumption turns the calculated reliability of different categories very uneven. This paper can be one among the already mentioned bases for initiating discussion on fatigue concepts in the future generation of Eurocodes.

Fatigue; Reliability index; Fatigue limit state function; New generation of Eurocode

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