PSI - Issue 19

Mladen Lukić / Procedia Structural Integrity 19 (2019) 655–664 Author name / Structural Integrity Procedia 00 (2019) 000–000

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2.2.2. Sub-task 2: Enhanced ease of use CEN/TC 250 is committed to enhancing ease of use in the development of the second generation of Eurocodes. All tasks in the work programme include a requirement to improve the ease of use of existing Eurocode parts and ensure that new parts are drafted with an emphasis on ease of use, all to the extent that it can be technically justified whilst safeguarding the core of essential technical requirements. That is expected to be achieved by improving clarity, simplifying routes through the standard, avoiding or removing rules of little practical use in design and avoiding additional and/or empirical rules for particular structure or structural- element types, all to the extent that it can be technically justified whilst safeguarding the core of essential technical requirements. 2.2.3. Sub-task 3: Partial safety factors for fatigue strength Choice of partial safety factors for fatigue strength given in the standard is based on IIW Fatigue recommendations and not clearly connected with the Consequence Classes (CCs) defined in EN 1990 (2002). Therefore, these factors may need to be adjusted / (re)calibrated to the Consequence Classes in order to control the required safety level. Fig. 1 gives a comparison between the values in Table 3.1 in the current standard and the values in the same table as proposed in the Danish National Annex. The fundamental work in this sub-task, finding out what the proper values of the partial factors are, is expected to be done by others. The Project Team will need to review and incorporate this material into the subsequent drafts of the standard, adapting it when necessary to ensure that it is consistent with the rest of its work. The key benefit will be making the standard safety levels corresponding to those given in EN 1990 (2002) to allow for a consequent application of EN 1090-2 (2018) on a suitable execution quality. Its output would be a revised Table 3.1 in EN 1993-1-9 (2005). 2.2.4. Sub-task 4: Hot spot stress method in fatigue Finite Element Methods (FEM) are used more and more in construction. The fatigue strength tables given in EN 1993-1-9 (2005) specifying the strength in terms of nominal stresses are not suitable for such an analysis. There is some information given in Annex B of the standard, but that information is incomplete and lack precision especially when applied to modern structures, in terms of their geometry and execution. A revision based on other standards (DNV, GL rules) and CIDECT guides needs to be carried out. The fundamental work of this sub-task has been undertaken by an ad-hoc group created within TC 250/SC 3. The Project Team will need to review and incorporate this material into the drafts of the standard, adapting it when necessary to ensure that it is consistent with the rest of its work. The key benefit will be the use of Finite Element Methods based on a common certified approach and in accordance with general rules given in EN 1993-1-9 (2005). Its output would be a modified and reworked Annex B of current EN 1993-1-9 (2005). There is a great chance that elements on effective notch stress method will be added as well, either in the reworked Annex B or as a completely separate annex to the new version of the standard. 2.2.5. Sub-task 5: Fatigue loads on orthotropic decks The application of today’s fatigue load models from EN 1991-2 (2003) to orthotropic bridge decks may result in a comparatively short fatigue life which has not been confirmed in reality. There is a need for adjustment or Design method Consequence of failure Low High Safe life 1.15 1.35 1.15 Damage tolerant 1.00 Design method Consequence of failure CC1 CC2 CC3 Safe life 1.26 1.54 1.00 1.88 1.00 Damage tolerant 1.00 Fig. 1. (a) Table 3.1 in EN 1993-1-9; (b) Table 3.1 in EN 1993-1-9 DK NA