Jib crane

[Zambo]

I have a jib crane of capacity 5 tonne, max lifting radius 6m. The jib crane can swing 180 degress using an electric motor. The crane is mounted on the face of a flange of a column. The jib crane column is restrained against the building column by 75 x 75mm steel angle supports.

When the jib crane is acting at 90 degrees to the building frame the deflection of the column is almost zero. When the jib crane under full load is swung 90 degrees until it is parallel with the building frame the pull and thrust from the mounting plates is acting against the minor axis of the column.

The measured deflection of the flange which the crane is mounted on is about 7mm when at the most severe angle and while carrying full load. How can I determine if this deflection is acceptable?

 

[hokie66]

Sounds like the flange carrying the jib crane should have been stiffened. Now that it is built this way, and you have fully loaded the flange, if it returns to vertical, at least you haven't stressed it to yield. The 7mm deflection, what length is that over? And is that the differential from top to bottom mounting point of the jib? So say 3.5 mm each side of the vertical axis? How much jib deflection results? I would start by doing a simple bending stress check with the push-pull loads resisted only by the one flange. If the stress is low, no problem. If high, considering your normal stresses for crane loading with the grade of steel in question, then stiffening will be required.