Fatigue strength verification of bearing type connections with mechanical fasteners - A comparison of Eurocode 3 and effective notch stress concept

The fatigue strength verification is a key factor in the design of cyclical loaded steel and lightweight steel structures. Mechanically fastened joints represent hotspots in these structures that require special attention. The fatigue strength verification acc. to the Eurocode 3 is based on the nominal stress concept with defined detail categories for different constructional details. This method is still the preferred verification procedure due to the ease of use. Most of the influencing parameters on fatigue resistance are already covered by the corresponding detail category of a constructional detail. This allows the verification to be carried out without the need for precise knowledge of these parameters. Associated with this is also a conservatism in the design of some of the constructional details, which is demonstrated by new studies on the fatigue resistance of bearing type connections with mechanical fasteners. In these studies, the material strength and the joint configuration (double covered joint, variation of hole and edge distances, number and type of fasteners) were systematically changed to determine their effects on fatigue resistance. A promising alternative to the nominal stress concept is the effective notch stress concept for non-welded constructional details. This concept makes it possible to consider the two main effects of material strength and the notch effect for bearing type connections in the design. Due to the missing preload in bearing type connections they transfer the acting loads by bearing contact. This results in a combination of different stress increasing effects in the components, which requires a more detailed description by numerical studies for verification. By comparing the test-assisted S-N curves (nominal stress concept) with synthetic S-N curves (effective notch stress concept) the deficits of the existing design rules are highlighted. In addition, a new design proposal for the bearing type connection with mechanical fasteners based on the notch stress concept is proposed.