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 Table 1. Detail categories ∆ C for bearing type connections acc. to EN 1993-1-9 (2010) and FprEN 1993-1-9 (2024) Detail category Description Requirements DIN EN 1993-1-9:2010-12 50 m = 3 One sided or double covered symmetrical connection with non-preloaded bolts in normal clearance holes. No load reversals. Δσ to be calculated on the net cross-section.

583

3

FprEN 1993-1-9:2024-10

For all members containing a potential crack site, Δ should be calculated with Δ = Δ net [ + ( − 0 ) 3 ] where σ net is the net cross-section stress. For non-preloaded normal bolts in holes with normal clearance: =1 ; =1.6 ; =2.7 . It applies = max( 2 ;2 2 ) . Holes drilled or reamed.

Double covered symmetrical joint subject to normal stress with non-preloaded normal bolts in holes with normal clearance without load reversal. One-sided fully supported connection subject to normal stress with non-preloaded normal bolts in holes with normal clearance without load reversal.

90 m 1 = 5

80 m 1 = 5

A graphical comparison between the DC’s of components in bearing type connections with non-preloaded normal bolts in holes with normal clearance and without load reversal acc. to EN 1993-1-9 (2010) and FprEN 1993-1-9 (2024) is given in Table 1. The decisive influencing parameters of the formulation to determine the modified nominal stresses acc. to the FprEN 1993-1-9 (2024) are the edge distance 2 and the spacing between two holes perpendicular to the load direction 2 . Both parameters determine the nominal cross-section which is used in the calculation of the nominal stress. For the adjustment in FprEN 1993-1-9 (2024), it remains to be noted that the DC 50 often cannot be met for the case 2 <2 2 and thus an unsafe design is currently present. 2.2. Fatigue strength verification acc. to FKM-Guideline for non-welded components The fatigue strength verification with nominal stress acc. to the FKM-Guideline (2020) offers the possibility of a purely analytical or FEA supported strength verification. In contrast to the verification according to Eurocode 3, most of the influencing parameters are directly considered as input parameters in the strength verification. Due to this comprehensive consideration of these parameters in the design, a better predication about the fatigue strength is possible. The fatigue strength verification based on nominal stress is generally divided into eight steps. Fig. 1 shows the procedure of the analytical fatigue strength assessment. The assessment starts from the point of the fatigue endurance limit of the base material for zero mean stress W,zd . By consideration of all constructive influences from the real application by the design factor WK,zd this value is reduced to the component fatigue endurance limit for zero mean stress WK,zd . This factor considers the notch effect t,zd , support effect σ , surface roughness R,σ , surface treatment V and effects from specific coatings S . Often the load ratio differs from pure reversed = -1, so the relevant load ratio must be considered in the calculation by the mean stress factor AK,zd . With the resistance value of the component fatigue endurance limit depending on actual mean stress AK,zd , finally an assessment of the component fatigue strength for variable amplitudes is possible. This verification can be performed for the fatigue strength of finite life, fatigue endurance limit or variable amplitudes by the factor BK,zd . The fatigue endurance limit for non-welded components made of steel is defined as the allowable stress amplitude at D = 1 ∙ 10 6 load cycles. For the finite life calculation, the S-N curve is described by a constant slope of = 5 in the finite life region according to Haibach's (1968) proposal. In general, the described calculation method of fatigue strength verification based on nominal stresses is limited to rod-shaped components. However, there is the possibility of a transfer to components for which a reasonable net cross-section can be defined.