Below the yield strength of crane girder steel, the girder will spring back to its original shape after unloading. The girder camber of overhead crane is shown just like the following diagram:
However when the loads exceed the yield strength by more than about 10%, the girder camber will lose. Then when it is loaded again with the loads ≤ rated capacity, it will deflect the normal incremental amount and the stress will be at the normal level except that the starting point for the deflection increment will be at a lower elevation due to the lost camber. The girder camber will be lost each time the girder is loaded past the yield strength and the permanent deformation is produced, shown in the following diagram:
Normal crane camber deflection vs. Permanent deformed crane camber. In severe conditions, overhead crane girder may have a “kink” around the center of crane span.
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