Eccentrically Loaded Post

[wawa_10]

Please see the attachment. Have a eccentrically loaded round tube post that is inserted into another post. Trying to ensure the posts won't buckle or yield and want to make sure I am approaching this problem correctly. Approach is to use secant formula for top post, but I don't know how to find max stress in second post.

 

[Harbringer]

Your second "post" will have a couple applied to the top, arm will depend on the fit-up between tubes. You need fixity at the bottom of the second tube to achieve stability, so I would also consider it free-fixed. The real problem you have will be analyzing the second post for local buckling due to this couple that you are creating.

From your drawing the connection of the top tube into the bottom tube is not clear.

As far as checking the columns themselves that's a pretty straight forward application of whichever steel design code your subject to.

I'd look at a different solution, this is goofy for anything other than nominal loads. Having a hinge in a column is almost always a bad idea.

 

[rb1957]

your sketches are very unclear to me !

1) the outer post only contacts the inner post (before load is applied) at some flange (ring?) welded to the base ? So under load it'll pivot and contact the inner post and transfer load on an elastic support.

2) you haven't drawn a FBD.

Are these interview questions ?

another day in paradise, or is paradise one day closer ?

 

[wawa_10]

See attached. I made a very basic 3D model to hopefully make it clear. You are correct, the welded flange simply rests on top of the receiving post, not fastened in any way. Assume the receiving post is fixed-fixed. My plan is to resolve the forces into a force and couple acting at top of receiving post and then check yielding with secant formula. Not sure how to check for local buckling (also tubes are aluminum). Don't worry, this isn't for a building/bridge type structure, I know its goofy.

 

[rb1957]

ok, that's much clearer. so what's the question ? the 2nd post sees compression and bending.

it would work much better if the upper post had a bearing (an circular plate welded to the lower end) so the upper post wouldn't rattle about in the lower post.

another day in paradise, or is paradise one day closer ?