How to design a 26m long column

[mosahed]

Hi there,

I'm designing the wall of a stadium and, due to the design of the roof, I need to implement free standing columns that are 26m tall. The columns can be restrained in one direction (let's say x), but not the other , since the space in the 'y' direction must be free. The columns will form the structural support for the cladding formation of an outer wall for the stadium.

Does anybody have any tips for how I could go about designing this, or know of any case studies I can refer to for the implementation of columns at such a length?

Many thanks.

 

[XR250]

Same as any other column. Check axial stress/buckling & bending interaction, deflection and connection to the structure and to the cladding.

 

[mosahed]

Sure, but universal columns and any standard columns for that matter are surely not appropriate for a column of such length, no?

Would I have to design a composite column to be able to develop stability and resistance to buckling?

 

[jwilki]

Are you on the design team to design a stadium with architects and engineers on board? It seems that there would be some pretty important visual requirements... Its just too hard to tell what you should or should not do, column design as an element is the easy part just "Check axial stress/buckling & bending interaction, deflection and connection to the structure and to the cladding."

 

[mosahed]

The visual appearance of the columns and wall cladding are not of importance at this moment in time of the conceptual design stage. I'm just trying to gather ideas on how to form the columns, given that they are 26m in length.

The columns / wall will be mostly hidden, it is the roof that will form the aesthetics of this structure.

 

[KootK]

Free standing as in cantilever? Some thoughts:

1) KL = 2 x 26 m = 170'. That's far. Real far.

2) Given what you've told us about the loads on the wall it may most closely resemble a column with distributed axial load. That's a bit more favorable of a condition than a tip loaded column. Timoshenko's book on elastic stability deals with this.

3) Given the ratio of wind load to axial load here, your column may really be a beam primarily.

4) If this is a steel column, it may well be a built up section. I'd consider a box section to increase lateral torsional stability. A precast column of some sort might do the trick. In either case, at that height, something trussed resembling a buttress might be ideal if there's space for that.

5) Steel or precast concrete, a splice or two may be required. That should be pretty standard stuff though (splice plates, CJP welds etc). If you have specific questions in this regard, let us know.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[mosahed]

Not exactly cantilevered, it has some restraint at the end of the column. I have the ability to restrain the column at as many points as I need in the 'x' direction, but it cannot be restrained in the 'y' direction, until at the very end of the column (at height=26m).

There will be a lightweight roof supported at the end of the column (well, at the end of various columns surrounding three of the four edges of the structure). This roof, by fault of design, will impose an outward horizontal force to the columns, which I maintain will be counteracted by tying the opposing columns to one another.

1) I'm not sure, given the restraints on the columns, that a k value of 2.0 is appropriate? Even if not, yes, very far.

3) I don't have exact loading from the roof yet, but I gather there will be sufficient loading for the 'column' to be considered a column. However, if not, that may be true.

4) Interesting, I haven't yet encountered a trussed column in design (still a relatively fresh graduate). We are trying to maintain a structure that is as light as possible, so perhaps a trussed steel member would be best.
What do you mean by the trussed column resembling a buttress?

Many thanks for your post, it has given me some good ideas to start with!

 

[hokie66]

Treat it as a beam-column, in other words a member subject to axial load as well as, probably uniaxial, bending. Probably one flange of your beam or truss will be adequately braced in the weak direction, and the other flange needs bracing as well. This is sometimes accomplished with horizontal trusses. Another solution is to use trusses with three chords.

 

[XR250]

Oh crap, did not see the free standing part - yea that's hard. :>

 

[KootK]

Consider posting some sketches of your framing plan and building section. We can be a good deal more helpful with better information in hand.

1) I'm not sure, given the restraints on the columns, that a k value of 2.0 is appropriate? Even if not, yes, very far.

Sounds more like K=1.0 now that I understand it better.

What do you mean by the trussed column resembling a buttress?

See the first pic below. Imagine some more webbing in there. This would be more suitable for the cantilever that I had envisioned. See the second pic below for something closer to your situation. There are really oodles of options for a built of column of course.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.