A unified approach for the design of steel structures under low and/or high cycle fatigue

Abstract

In this paper, a method is presented trying to unify both design and damage assessment methods for high and low cycle fatigue. In particular it is shown that, by interpreting the stress range Δω as the ideal stress range associated to the real strain range Δϵ in an ideal perfectly elastic material, high and low cycle fatigue test data can be interpreted by the same Wöhler (S-N) lines usually given in recommendations for (high cycle) fatigue design of steel structures. Furthermore, local buckling can be regarded as a notch effect, an effect which is intrinsic to the various shapes, because it is strictly correlated to their geometrical properties (in particular of the slenderness ratios b/t and h/t w of the flanges and the web). It is also shown that, in the case of variable amplitude loading histories reprocessed by the rainflow cycle counting method, a linear damage cumulation rule together with the previously defined S-N curves (a procedure usually adopted in high cycle fatigue) can lead to a reliable collapse criterium for low cycle fatigue also.