Fatigue strength of wheel load introduction above interrupted rail welds

Flat and square rails are fastened to the upper chords of crane girders by interrupted rail welds (fillet welds), a method that has been used for many decades in light to medium-heavy crane operations. Interrupted rail welds are a common design variant. By avoiding continuous rail welds, the production time and material usage are reduced on the one hand, and on the other hand the welding distortion of the beam and thus the straightening effort is reduced. Although interrupted rail welds are mentioned in reference books, their design and execution are not in themselves regulated by the applicable steel construction standard (DIN EN 1993-6). Since crane runway girders are subjected to cyclic loading, DIN EN 1993-6 in conjunction with DIN EN 1993-1-9 requires fatigue verifications to be carried out also for the design details of the rail fastening. In practice, this raises three design questions for which no answers have yet been found:

1. How distinct is the contact between the crane rail and the top flange? Can the applied force possibly also be transferred via this contact instead of exclusively via the weld seams?
   In contrast to continuous rail welds, the contact between the crane rail and the top flange can be determined by a non-destructive testing method for interrupted rail welds. In the case that contact can be ensured, it would be uneconomical to dimension the transmission of forces exclusively via the welds (large weld thicknesses). Corresponding production monitoring and tolerances would have to be created for the design taking the contact into account.
2. In which notch case according to DIN EN 1993-1-9 can this detail be classified?
   In the area of the rail fastening, the crane girder experiences a multiaxial stress consisting of global longitudinal stresses (σ||) and shear stresses (τ||global) due to girder bending, as well as local transverse compressive stresses (σ⊥) and shear stresses (τ|| local) due to wheel load introduction. For the evaluation of these multiaxial stresses within the framework of a nominal stress analysis, a corresponding notch case classification according to DIN EN 1993-1-9 is required for each stress type (σ⊥, σ||, τ||). The notch cases used so far do not correctly reflect the notch effect in interrupted rail welds. It is known from previous studies of the research institute that these notch cases are too conservative, also in comparison with the former national design practice DIN 4132.
3. How do the different stress states overlap in contrast to the continuous weld?
   In addition to the stress components σ⊥ and τ||, which also occur in continuous welds, the longitudinal stress σ|| in interrupted welds leads to failure in the base material. However, it is still unclear whether it is possible to consider these stresses individually or whether they superimpose on each other.

University of Stuttgart
Institute of Structural Design
Prof. Dr.-Ing. Ulrike Kuhlmann, Wigand Knecht

RWTH Aachen University
Chair for Steel and Lightweight Metal Construction
Prof. Dr.-Ing. Markus Feldmann

FOSTA e.V. / AIF

01.10.2020 - 30.06.2021