tapered Column design

[Hasan_123]

I need to design this inverted tapered column with narrow section at the bottom. Since I am a recent graduate, I don't have much experience. Pls guide me to design this. TIA

 

[JoshPlumSE]

There is a design guide that AISC has for Tapered members. This is a pretty good place to start. I've actually only read the 1st edition. It appears there's a newer edition now.

Design Guide 25: Frame Design Using Nonprismatic Members (Second Ed.) | American Institute of Steel Construction

www.aisc.org

In the 1st edition, there are some benchmark problems in Appendix C. There is an example and citation for the "Method of Successive Approximations" for the elastic buckling value of a stepped or tapered column. If that appendix still exists in the 2nd edition (and it should) then this would give a good method for calculating the axial capacity of such a member.

 

[271828]

What material is this?

What are the boundary conditions and loading?

 

[Hasan_123]

What material is this?

What are the boundary conditions and loading?

The whole thing is concrete with a metal cover at the top portion

 

[Lomarandil]

Looks like a pretty standard column, just happens to have a bunch of eccentric dead load on one side. Design as though 9" wide.

Now detailing -- there's a little bit of detailing attention required here, particularly if the column receives any external load. But that's tomorrow's thread.

 

[JoshPlumSE]

I didn't realize the stepped member was a concrete column. Technically, the method of successive approximations is still valid for the calculation of elastic buckling. Though it would likely be a less straightforward incorporation for concrete code checks.

I think for concrete, the most important thing will be how the reinforcement transition works at this stepped area / transition. Honestly, it seems weird that (for concrete) a member would be stepped like this.... I feel like it would be more common to see a tapered depth in that are rather than an abrupt change in depth

 

[BAretired]

There is a hand method developed by Nathan Newmark, which I attach below. See p. 22 and 23 for stepped and tapered columns.