Abstract
This chapter describes the range of application of the structural hot-spot stress approach including its limitations and gives some important definitions for correct application and understanding of the subsequent chapters: Fillet welds are classified into load carrying and non-load carrying ones, whereby also partial-load carrying fillet welds exist. Hot-spots at weld toes occur on a plate surface (type “a” hot-spot) or at a plate edge (type “b” hot-spot), being treated differently in the following. Afterwards, a definition of the structural hot-spot stress is given, based on membrane and shell bending stresses, being reasonable for type “a” hot spots, while some problems regarding the definition for type “b” hot-spots are discussed. Furthermore, a structural stress concentration factor is defined, being particularly useful for the consideration of secondary bending stresses due to misalignment. Finally, size effects are discussed.
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Misalignment is addressed in different ways in the IIW Fatigue Design Recommendations [2], depending on its source:
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Some misalignment effects are already taken into account in the fatigue classes referred to nominal stresses. The same is true for the structural hot-spot stress classes, but only for the small amount corresponding to up to 5% stress increase [2]. Particularly for butt joints, cruciform joints and transverse attachments, additional misalignment effects resulting from fabrication inaccuracy and welding distortion should be taken into account by increasing the stress or dividing the fatigue class by K m.
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Designed eccentricities, as shown in Fig. 2.8d, should be taken into account by calculating the extra shell bending stress.
However, in this Designer’s Guide, it is recommended that all sources of extra stress, including misalignments resulting from fabrication inaccuracy and welding distortion, are taken into consideration in the stress calculations.
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References
Fricke, W.: IIW guideline for the assessment of weld root fatigue. Weld. World 57, 753–791 (2013)
Hobbacher, A.F.: Recommendations for fatigue design of welded joints and components. 2nd edn. Springer (2016)
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Niemi, E., Fricke, W., Maddox, S.J. (2018). The Structural Hot-Spot Stress Approach to Fatigue Analysis. In: Structural Hot-Spot Stress Approach to Fatigue Analysis of Welded Components . IIW Collection. Springer, Singapore. https://doi.org/10.1007/978-981-10-5568-3_2
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DOI: https://doi.org/10.1007/978-981-10-5568-3_2
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