Stiffness & Drift for Cantilever Columns
Stiffness & Drift for Cantilever Columns
(OP)
When designing a cantilevered column (steel) is the base assumed to be fixed for drift calculations? Is there any consideration for rotation or rocking of the footing? This will be supporting an overhead crane runway - I am worried that the assumption of fixity at the base is underestimating the drift too much... but any guidance on how much that is?






RE: Stiffness & Drift for Cantilever Columns
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RE: Stiffness & Drift for Cantilever Columns
RE: Stiffness & Drift for Cantilever Columns
Its outlined procedure can be used iteratively to determine the proper spring constant to use. It required an estimate of footing and baseplate, and redesign of those for the moments, and messing with the model until applied P & M can match a FEM model by adjustment of the spring constant.
RE: Stiffness & Drift for Cantilever Columns
RE: Stiffness & Drift for Cantilever Columns
There are two phases to the job, phase 2 is that it someday gets enclosed. So in the current scheme (phase 1) there is very little wind/seismic load, the lateral from the crane will control. This brings up another question which is can I design the horizontal catwalk on the one side to take 100% of the crane lateral load? Maybe I'd do that but still design the cantilever for 50% of the load as a belts & suspenders... thoughts?
RE: Stiffness & Drift for Cantilever Columns
RE: Stiffness & Drift for Cantilever Columns
It also appears from your description, that column A-2 is the cantilever column. Again, in my opinion, this is just another reason to "skip" this column all together. If that is not possible, I would probably design the column as a A frame installing another footing to the north of line A and not rely on the column cantilevering up from the footing. Just something I would not be comfortable with.
Just my $0.02
RE: Stiffness & Drift for Cantilever Columns
If using two 60ft. span runways beams and only one has a horizontal truss can lateral crane loads be distributed based on stiffness, i.e. most of it will go to the truss? If not then I need to add another lateral element along line A.
RE: Stiffness & Drift for Cantilever Columns
You will get some differential deflection due to the position of the picked load on the crane..... but that's not my problem and there is nothing I can do about that. I just do the best I can with the problems I have control over, and in this instance I made all of the columns align to give me equal span crane girders on each side of the building.