Crane runway girders

As a specific structural steel element, located at the interface between the primary structure and the handling equipment, the crane runway girder alone concentrates many of the problems encountered in the design and calculation of steel structures.

In fact, we are dealing here with stresses due to moving loads, non-uniform torsion, dynamic actions, specific local effects and fatigue risks, all of which are subjects of technical analysis that are rarely present simultaneously on the same element.

A running girder can be used for a simple suspended hoist in a car maintenance workshop, or for an overhead travelling crane in a steel plant, operating day and night without interruption and carrying several hundred tons. There is, of course, a big difference in design between these two extreme configurations.

So, to make the right design choice, you need to know about the different types of overhead travelling crane used, their movements, and the various parameters that characterize them.

Once this first stage has been completed, it is then possible to match the bearing beams to the various configurations, which are accompanied by specific qualitative measurements, the level of which increases with the importance of the various parameters:

• bridge span ;

• span of rolling beams ;

• the characteristics and intensity of the load to be lifted ;

• the number of handling cycles expected over the lifetime of the rolling beams.

Long designed and dimensioned according to a patchwork of heterogeneous standards and recommendations, rolling beams have for some years now been governed by a single calculation code, in harmony with the code used to design lifting and handling equipment.

The calculation methods employed use the stresses determined by traditional strength of materials, i.e. the classical six-component force torsorsors. In many cases, however, it is necessary to use the theory of bent torsion (or Vlassov torsion).

For beams subjected to heavy loads and intensive use in terms of handling cycles, fatigue testing becomes the most important factor when compared with traditional strength and deformation limits.

Appropriate structural measures can then be taken to limit impact and stress concentrations in welded or bolted assemblies.