Portal Frame with crane runway girder

[oranda]

Fatique check is required when designing heavy duty crane runway girder. What about the main portal frame structure? The portal frame members and their connections would also undergo repetitive loading as the crane travels back and forth. Is it necessary to check the portal structure for fatique?

 

[RockEngineer]

I would check it for fatigue. It is receiving an changing load like any building. You need to determine how much of a stress reversal the portal frame members get. The runway girder members get a reversal of stress as the crane goes from one bay to another but it is not a full reversal where it goes from tension to an equal compression. It goes from tension to a smaller compression or even a small tension for your fatigue range.

Look at your building. Can the loads which rack the frames come from any direction? Determine the fatigue range for your frames and then apply the criteria for your building members

 

[phdunn]

If the portal is designed to not see vertical load, I do not think that fatigue is a concern. The loading is from longitudinal loading and most likely limited by the bumper force. The American Institute of Steel Technologies (formerly American Iron and Steel Engineers) guide number 13 may help you in this matter.

 

[dbuzz]

The elements providing support to a crane runway girder can be susceptible to low-cycle high-strain fatigue.

Unlike connections in normal structures, where forces and displacements reach their maximum value perhaps a few times in the structure's life, the elements supporting a crane runway girder are repeatadly subjected to near-maximum value forces, translations and rotations.

These elements should be detailed to prevent them undergoing a large amount of bending or stretching in service.

 

[Lutfi]

I do not see a load reversal in the crane runway support bracket or the column due to heavy duty crane. Of course I am assuming that the crane runway will be supported on a rigidly connected bracket to the frame column. Please correct me if I am wrong.

My concern would be the connection of the bracket to the rigid frame column more than the column itself. I recall my college professors and experience tell us all that most failure occurs at the connections.

Having said that, I would determine the number of cycles and the approximate the welded connection and then compute the allowable stress based on AISC ASD or LRFD.

Regards

 

[sdz]

The Australian codes for crane loading (AS1418) specify the classification of the supporting structure according to load and repetitions. In many cases fatigue analysis is not required but for high loads and/or repetitions it will be.

So, in general, fatigue design of portal frames with cranes is required unless exempted by the code.