PSI - Issue 57

Mathias Euler et al. / Procedia Structural Integrity 57 (2024) 298–306 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

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1. Introduction Crane runways are the supporting structures of an overhead-travelling bridge crane as shown in Figure 1a. They are subjected to travelling single forces from the crane that are also known as wheel loads. These loads are introduced into the top flange of the crane runway beam through a crane rail in case of a top-running bridge crane as shown in Figure 1b. The rail disperses the wheel loads and transmits them into the web of the crane runway beam. The flange-to-web connection in Figure 1b can be realized as welded T-joint with partial penetration (light crane service) or with full penetration (heavy crane service). In case of partial penetration welded joints, a non-fusion region between flange and web remains afterwelding. A contact between flange and web in this region cannot be expected for this kind of welded connection due to unavoidable manufacturing tolerances in practice. Therefore, it is assumed by EN 1993-6 (2006) for design purposes that the wheel loads are exclusively transferred by the welds into the web. The same applies to fillets welds that are typically used in case of light crane service to fasten the rail (flat material) to the top flange. For partial joint penetration, the welds of the aforementioned constructional details exhibit a weld root (w) in addition to the weld toes (t) as exemplified in Figure 1c for the rail weld. The stress distribution within the load-introduction region of the crane runway beam cannot be described by elementary strength theory (engineer's theory) anymore, as the cross sections of this region do not remain plane under loading. The web (and in approximation also the crane rail) are subjected to a plane multiaxial state of stress with several local stress components (  || ,  ⊥ ,  || ) that can be computed by advanced strength theory (theory of shells). The indices of the stress components refer to the longitudinal axis of the connecting weld. To illustrate the multiaxialstressing, Figure 2 shows a single-span crane runway beam with a concentrated force F at midspan. Figure 2c depicts the stress distribution of the beam’s web according to the theory of shells. Stress concentrations ("stress peaks") occur in the region of the load introduction. In the vincinity of the load introduction, the stresses  || and  || exceed the corresponding values (  ||global and  ||global ) that are predicted by engineer's theory. Additionally, a dominating stress component  ⊥ can be recognized. The portion of the stress components  || and  || , that is caused by global bending and global shear and that can be calculated by engineer's theory, are referred to as global stresses by EN 1993-6 (2006). The exceeding stress portion, that is not accounted forby engineer's theory, is denoted as local and caused by the load introduction. Under the assumption of an infinitively deep web, all web stresses are denoted as local since any global effect is suppressed. In addition to the stress concentration in Figure 2 resulting from the concentrated-load effect, the considered constructional details exhibit further stress-raising effects that are caused by the geometric notches of the weld toes and roots, materialinhomogeneity in the weld zones and residual stresses from welding. The sum of all theses stress raising effects describes the notch effect of the constructional details. In case of static load action, the "stress peaks", that are caused by the aforementioned effects, can be neglected in general, since they are dissolved by plastic deformation and stress redistribution. In case of cyclic load action (fatigue), the "stress peaks" occur repeatedly. Therefore, the cross-sectional spots with sharp notches – preferably the weld toes and roots of welded connections – are subjected to recurrent plastic deformations on a microscopic scale due to relocations in the metalstructure even if the crane runway beam behaves overall elastic. For high occurrence rates of the load action, the local plastifications might cause fatigue cracks.

Fig. 1. Crane supportingstructure: (a) cranerunwaybeam ofan overhead travellingcrane (schematic),(b)top flange of a welded crane runway beam (light crane service) subjected to top-running wheel load, (c) notches of a rail weld (fillet weld)