PSI - Issue 57

Mladen Lukić et al. / Procedia Structural Integrity 57 (2024) 550 – 559 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

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verification (given in this annex), as schematically shown in Figure 2. Many of the rules are based on the IIW recommendations (Hobbacher, 2016; Niemi et al., 2016). Annex B and most of the annexes of prEN 1993-1-9 (2022) are organized to be self-standing. They have a coherent and similar structure as the main document with following subsections: fatigue action effect, calculation of stress ranges, fatigue resistance, fatigue resistance modifications, verification. As the computation of hot spot stress often requires specific expertise, the national choice for the conditions of application of the method is given. It is important to emphasize that the application range is limited to welded constructional details with potential fatigue cracks starting from a weld toe; even if techniques do exist to apply the method to other cases they are not standardised. With its range of application being limited compared to the nominal stress or the effective notch stress method (Annex C), those may have to be used in addition for other potential initiation sites in a constructional detail. The application range of the method was extended to structural hollow section joints and to orthotropic bridge decks, for which further guidance is given in the technical specification TS 1993-1-901 (2023). The method now makes a distinction between three different hot spot types as shown in Figure 7, both for extrapolatingthe stress and for the detail resistance: • type “a”: cracking at a plate surface , where the stress varies considerably through thickness of the plate with crack; • type “b”: cracking at a plate edge, where the stress at the hot spot is independent of the plate or cross-sectional wall thickness, such as longitudinal attachments; • type “c”: cracking at the weld toe of a lattice girder joint made of structural hollow sections, where the hot spots and the extrapolation method are specifically defined. The first two types are directly taken from the IIW recommendations (Hobbacher, 2016). The type “c” is taken from the CIDECT recommendations, adopted as ISO 14347 (2008).

Fig. 7. Definition of hot spot types ‘a’, ‘b’ and ‘c’: (a) plated structure with stress distribution at the hot spots, (b) tubular joint with illustration of hot spots. Key: 1 – chord, 2 – brace, 3 – crown heel, 4 – crown toe, 5 – saddle

For the characteristic fatigue resistance curves and detail category tables, there is a differentiation between hot spot types. For types “a” and “b”, the set of fatigue resistance curves contains only three curves with slope parameters m 1 = 3 and m 2 = 5 (similarly to the basic set for the nominalstress method).Table B.1 in the draft standard gives the detail categories for butt welds, fillet welded attachments and fillet welds in cruciform joints . For type “c”, a specific set is given where m 1 varies with the detail category, while the knee point positions and m 2 = 5 are identical to the basic set for nominal stress method. Table B.2 in the draft standard gives the corresponding detail categories. The tables have been drafted to offer the same level of information as the tables for the nominal stress method. 5. Introduction of effective notch stress method (Annex C) The effective notch stress (ENS) method has been developed to extend the applicability of prEN 1993-1-9 (2022) to fatigue verifications of details not covered by the nominal stress or the hot spot stress methods and is based on the IIW recommendations (Hobbacher, 2016). Similar conditions as for Annex B have been set, thus a national choice for