Fatigue class combination model to quantify the influence of multiple weld imperfections on fatigue strength

Fabrication-related defects are inherent in every weld, playing a crucial role in steel structures exposed to fatigue. These defects significantly impact the fatigue strength of the welded joint. However, the existing connection between fatigue strength values and the quality level of welded joints has been insufficient. While EN 1090-2, EN 1993-1-9, in combination with EN ISO 5817 specify permissible sizes for weld imperfections for fatigue-stressed joints, the connection lacks a scientific foundation, and true limits remain unknown. To address this gap, a methodology has been developed to determine FAT classes based on the size of weld imperfections. Through fatigue tests on welded details with imperfections and subsequent numerical investigations utilizing local fatigue concepts, a quantitative relationship between fatigue strength and weld imperfection size has been established. This forms the basis for the development of the “Fatigue Class Combination Model” (FCCM), detailed in this paper. This model efficiently considers multiple imperfections in a probabilistic manner within the FAT Class. By implementing this method, the need for time-consuming rework of welds is mitigated in the future, enhancing the verification concept for sufficient safety against fatigue failure with improved cost and resource efficiency. • Identifying the effects of different weld imperfections on the fatigue strength of structural steel details. • Quantifying the influence of weld imperfections by numerical simulations and local concepts. • Detailed measurements of imperfection curves over the length of welds converted into stress increase curves. • Probabilistic derivation of a combination model considering multiple influences on fatigue.