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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nominal stresses in bolts and rods have been introduced. In addition, a new informative Annex E provides guidance on the calculation of nominal stresses in preloaded bolts and rods.

Fig. 4. Relevant nominal stresses in welds: T joint with (a) fillet weld, (b) partial penetration butt welds

3.2. Improved S-N curves

The draft standard prEN 1993-1-9 (2022) differentiates between four sets of fatigue resistance curves for the nominal stress method. This is an extension compared to EN 1993-1-9 (2005) that contains only two sets of curves, one set with a slope parameter m = 3 fornominalstresses and one set with a slope parameter m = 5 for shear stresses, see figures 7.1 and 7.2 in EN 1993-1-9 (2005), together with a further set of curves with m = 5 for structural hollow section joints subject to nominal stresses. As the set for structural hollow section joints is not illustrated, the existence of a second slope parameter for variable amplitude loading with stress ranges above and below the fatigue limit was unclear. The draft standard clarifies this issue through illustrations of all sets of fatigue resistance curves. The fatigue resistance curves of welded constructional details with detail category 71 and above that are subject to normal stresses remain unchanged compared to EN 1993-1-9 (2005). For details classified below detail category 71, the standard draft assumes a lower fatigue limit   D , as the beginning of the infinite life region is altered to 10 million stress cycles. This more unfavourable behavior is not a novelty in prEN 1993-1-9 (2022) as it is already taken into account by the detail categories marked with asterisk (*) in EN 1993-1-9 (2005). As the concept of these special detail categories has frequently been misunderstood by many practitioners, they are deleted and replaced by an individual set of curves in prEN 1993-1-9 (2022) as shown in Figure 5.

Nominal stress range [N/mm²]

Number of cycles Fig. 5. Example of revised fatigue resistance curves for welded details in draft standard prEN 1993-1-9 (2022)