Insights into the occurrence of transverse bending stresses in web plates of crane runway girders

Crane runway girders are installed in industrial buildings to carry heavy loads from crane operation. The wheels of the bridge crane introduce concentrated forces in the crane runway girder via the rails. This leads to local vertical stresses in the web plates of the crane runway girders in addition to the global bending stresses. The local stresses at the top of the web usually become crucial for the fatigue design of the girder. The potential eccentricity of vertical wheel loads as well as additional horizontal forces from operation of the crane can lead to torsional rotations of the rail and the top flange and subsequently to transverse bending of the web plate of the crane runway girder. In the current design model of EN 1993-6, the rotation at the top of the web plate is described by assuming the rail and the top flange of the girder acting as a bar under torsion, supported continuously by the bending stiffness of the web. Within this paper the existing model for the rotations is improved and it is shown that these modifications lead to more accuracy in comparison with numerical finite element calculations. It is also shown that the current simplified procedure for calculating the resulting stresses in the web is not able to adequately describe the real stresses for all practical cases. It is found that the quality of the stress predictions can significantly be improved by considering the web as a simply supported plate with the previously identified rotations on its top edge.