PSI - Issue 57

Elena Sidorov et al. / Procedia Structural Integrity 57 (2024) 316–326 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

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In analogy to wheel loaded flange-to-web connections, the nominalstress  nom in rail welds (double fillet welds) should be obtained from Eq. (1) where p is the maximum verticalforce in both welds per unit length, that is referred to as ‘ weld pressure ’ in this paper, and a is the size of the single weld. (1) For continuous rail welds , Euler (2017) proposes to calculate the maximum weld pressure in the rail welds by means of Eq.(2) where eff is the effective loaded length specific of continuous rail welds that is determined by an analytical model based on the theory of elasticity. Tabled values of eff for the most important types of hot-rolled beams and rail sizes can be found in (Euler & Kuhlmann, 2018) together with a corresponding detail category 56 (   C = 56 N/mm²) for the fatigue verification. The detail category was derived from fatigue tests with travelling and stationarily pulsating wheel loads (Kuhlmann et al. 2015, 2016). eff / = p F (2) The fatigue behaviour of intermittent rails welds had been systematically investigated for the first time by Kuhlmann et al. (2022). For chain intermittent rail welds , the calculation of the maximum weld pressure according to Eq. (3) is recommended where b r and h r are the dimensions of the crane rail, see Figure 1d. This equation assumes an ideal contact between rail and flange of the crane runway beam. Unavoidable surface irregularities of the rail and/or the flange are neglected. This nominalstress definition corresponds with a detail category 40 (   C = 40 N/mm²). In contrast to continuous rail welds, the stop-starts of the intermittent rail welds have additionally to be checked against fatigue. See further details in (Kuhlmann et al. 2022). nom / (2 ) = p a 

+ F

p

=

(3)

b h

r

r

In this paper, Equation (3) is investigated in detail by means of a parametric study in order to check whether the rail dimensions are the only decisive geometric parameters on the nominalstress of the rail welds. Particular focus is laid on the influence of the contact surface conditions between rail and flange.

3. Experimental investigation of rail-flange contact in case of chain intermittent rail welds Ideal contact between crane rail and flange of the crane runway beam cannot be achieved in practice due to following reasons: (i) macroscopic imperfections of the members, for example spherical surfaces of rail and flange; (ii) microscopic imperfections in the form of surface roughness of rail and flange; (iii) thermal deformation of the members during welding, for example slight upward bending of the flange. For these reasons, the interaction at the interface between crane rail and flange is denoted as ‘technical contact’ in this paper. Technical contact of two touching surfaces is characterized by alternating sub-areas with and without contact as shown in Figure 3a. The surfaces exhibit a small distance in the sub-areas without contact that is called ‘ gap ’ in the following. With respect to the surface roughness, plastic deformation of the surface peaks under loading as shown in Figure 3b can reduce the initial gap. However, the complete closure of the gap between rail and flange – also in view of the other aforementioned influences – is usually prevented by the rail welds that behave elastically under service loads. Therefore, the proportion of the wheel load F , that is transferred by the rails welds (weld pressure p ) in Figure 3c, directly depends on the properties of the technical contact. Kuhlmann et al. (2022) investigated the rail-flange contact of test girders that were produced by three different steel construction companies under typical production conditions. The crane rails were fastened by chain intermittent fillet welds. Non-destructive feeler gauge measurements (thickness: 0,05 mm) identified a technicalcontact alongthe rail edges for all test girders.