PSI - Issue 75

Florian Kalkowsky et al. / Procedia Structural Integrity 75 (2025) 581–592 Florian Kalkowsky et al. / Structural Integrity Procedia 00 (2019) 000 – 000

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1. Introduction Bolted connections are a common joining technique for steel structures, such as high-rack warehouses, escalator or elevator frames, where modular assembly of the finished coated components is required. EN 1993-1-8 (2010) distinguishes between shear-loaded and tension-loaded connections, whereby shear connections in steel structures are divided into slip-resistant (category B & C) and bearing type connections (category A). The execution of these connections differs fundamentally as for the slip-resistant connections a defined surface treatment and defined preload is necessary. In contrast, bolting assemblies in bearing type connections can only be tightened to target level II for serviceability reasons (close gaps, minimize slippage or increase deformation rigidity) and therefore the bolt preload is not a design-relevant parameter. A positive-fit load transfer is therefore assumed in strength verification, which for this type of connection results in a combined notch effect from geometric discontinuity due to the hole drilling and the contact between the fastener and the hole wall in the jointed components. However, Eurocode 3 only provides the formulation of different detail categories (DC’s) , which does not consider further main factors such as the material strength and the stress concentration influencing fatigue strength of components in bolted connections. The aim of the investigations of bearing type connections is to demonstrate there are various factors influencing the fatigue resistance of components in bolted connections and further developments of the existing design rules according to Eurocode 3 are necessary. For this purpose, different bearing type connection configurations were tested in fatigue tests at constant amplitude loading and were compared with the existing DC’s from the current Eurocode 3 and 2 nd generation. Based on this comparison the possibility of using the effective notch stress approach for a better description of the fatigue behaviour should also be demonstrated. The results were checked for plausibility using this approach. Based on this a derivation of the DC for the verification according to Eurocode 3 is presented based on the nominal stress concept, which allows to include important parameters in the fatigue strength verification in future. 2. State of the Art 2.1. Fatigue resistance of bearing type connections according to Eurocode 3 The verification of fatigue strength according to Eurocode 3 is essentially based on the nominal stress concept, even though the structural stress concept and, in the 2 nd generation FprEN 1993-1-9 (2024), the effective notch stress concept will also be implemented, these can only be applied to welded joints. The fatigue strength verification with nominal stresses is fulfilled by an acting stress range ∆ E which is equal or smaller than the resistance value ∆ R . ∆σ E ≤∆σ R (1) In the Eurocode 3 the fatigue strength is defined by the DC’s (∆ C |∆ C ) and a related slope parameter of a specific constructional detail at C =2 ∙ 10 6 number of cycles. These values can be applied to components made of S235 to S700 to the same extent, sufficient protection against corrosion and exposure to temperatures below 150 °C. The derivation of the different DC’s is essentially based on a statistical evaluation of fatigue test data published worldwide dating back to 1960s and in accordance with the evaluation procedure specified in Annex D of EN 1990 (2021). Often only a limited database can be assigned to a particular constructional detail, and the parameters of the test boundary conditions are often only incompletely documented. For the derivation of the DC for components in bearing type connections the database from Valtinat et al. (2000) was used and resulted in the DC 50 acc. to EN 1993-1-9 (2010) which is shown in Table 1. A comprehensive consideration of bearing type connections to extend the database by Valtinat et al. (2000); Brown (2006); Josi et al. (1999); Wilson et al. (1938); Steinhardt et al. (1954) was done by Maljaars et al. (2021) and led to the new formulation in FprEN 1993-1-9 (2024) to describe the notch effect in the components, which is also shown in Table 1.