PSI - Issue 19

Jennifer Hrabowski et al. / Procedia Structural Integrity 19 (2019) 267–274 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

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When designing outside the scope, SCFs can be determined using finite element analysis (FEA); where Zhao et al. (2001) or Hobbacher (2016) provide good guidance. Generally, FEA result in smaller SCFs than recommended by Zhao et al. (2001), which is probab ly due to specimens’ imperfections and safety margins. In both, the nominal stress as well as the structural stress concept, the previously determined stress range is then compared to a fatigue strength curve. While the S-N-curve is defined in the nominal stress concept via the DC or FAT class, it is specified in the structural stress concept as a function of the wall thickness. These are valid for RHS up to 25 mm and for CHS up to 50 mm (Zhao et al. 2001 and ISO 14347 2008). As the evaluation in Fig. 5 shows, skillful weld seam guidance and execution can considerably increase the fatigue strength of a construction. In any case, it is recommended to place value on high quality welds. To further increase the fatigue strength, it is also possible to apply one of various methods of post weld treatment. The presented fatigue test results for hollow section K-joints made of steel grades up to S700 are in good accordance with Eurocode 3-1-9 (2010), which is also valid for the investigated joints made of higher strength steel grades. The fatigue strength curves represent a lower limit for the fatigue design. Since the fatigue strength of hollow section joints strongly depends on the dimensionless parameters, such as e.g. the wall thickness ratio  , this should already be considered in the planning by selecting appropriate parameters. Experiments as well as numerical analysis point out, that the fatigue resistance is, beneath the dimensions and the geometrical parameters, also depending on the weld execution and shape. This is not considered in the design rules but can be used to build fatigue resistant structures. So, for the CHS K-joints with over-welded gap, the fatigue resistance could be increased by two classes from DC 71 to DC 90. By careful planning and execution, fatigue-proof hollow-section constructions can be realized, which is also valid when using high strength steels. Acknowledgements The authors like to thank FOSTA Forschungsvereinigung Stahlanwendung e.V. and CIDECT for funding the presented research. They also thank the staff members of TNO and the Research Center for Steel, Timber and Masonry of Karlsruhe Institute of Technology for performing the fatigue tests and the good cooperation in the research project. DNV GL-PR-C203: 2016. Fatigue Design of offshore steel structures, Recommended Practice C203, Det Norske Veritas, EN 1090-2:2018-09. Execution of steel structures and aluminium structures - Part 2: Technical requirements for steel structures; German version EN 1090-2, September 2018. EN 1993-1-9: 2010-12. Eurocode 3: Design of steel structures - Part 1-9: Fatigue; German version EN 1993-1-9:2005 + AC:2009, December 2010 FOSTA P1132 / CIDECT 7AB. Fatigue behaviour of hollow sections joints and high strength steel, running research project Herion, S., Fleischer, O., Koenig, D., 2014. Comparison of different configurations of thick-walled K-joints with gap made of RHS and CHS. Proceedings of the 24th International Offshore and Polar Engineering Conference. Busan, Korea, June 15-20, 2014. Herion, S., 2018. Fatigue of hollow section structures - Current research and developments. Tubular Structures XVI – Heidarpour & Zhao (Eds) Taylor & Francis Group, London, ISBN 978-0-8153-8134-1. Hobbacher, A.F., 2016. Recommendations for Fatigue Design of Welded Joints and Components, Second Edition, IIW-Doc. IIW-2259-15 ex XIII 2460-13/XV-1440-13, International Institute of Welding (1996) and Springer International Publishing Switzerland. ISO 14347: 2008-12. Fatigue - Design procedure for welded hollow-section joints – Recommendations, December 2008 Kuhlmann, U.; Mangerig, I., Bucak, O. et al, 2015. Ermuedungsgerechte Fachwerke aus Rundhohlprofilen mit dickwandigen Gurten – Fatigue resistant trusses of circular hollow sections with thick-walled chords, FOSTA P815. Duesseldorf, Germany. Puthli, R.S. et al., 2006. Beurteilung des Ermüdungsverhaltens von Krankonstruktionen bei Einsatz hoch- und ultra-hochfester Stähle, Final report P 512, Forschungsvereinigung Stahlanwendung e.V., Düsseldorf, Germany Zhao, X.L., Herion, S., Packer, J.A., Puthli, S., Sedlacek, G., Wardenier, J., Weynand, K., van Wingerde, A.M. and Yeomans, N.Y., 2001. Constructions with hollow steel sections 8: Design guide for circular and rectangular hollow section welded joints under fatigue loading. CIDECT. TÜV-Verlag, Koeln, Germany. References 4. Conclusions