80' unbraced steel columns

[DETstru]

I am proposing on a single story industrial project that will have 80' tall unbraced steel columns. The roof structure will be metal deck supported by joists and joist girders on 50' bays. Top of roof will be approximately 80' above top of slab. No mezzanines.

I want to get a sense of what these columns will be before I send my fee. I know I'll likely need to deal with splices and fairly large sections.

The joist girders will sit on top of column cap plates. I don't worry about eccentricity when you have a joist girder bearing on top of the usual HSS8x8 or 10x10 column since it's a small section. In this case, I'm wondering if it's warranted to assume some amount of eccentricity (with unbalanced loading situations) since the column sections will probably be 14x14 or larger and they're just so darn tall. The joist girder will still be on top of the column but maybe assume a few inches of eccentricity? See attached sketch.

Any opinions on whether I should assume some eccentricity for unbalanced load situations or thoughts on tall columns would be appreciated.

 

[DETstru]

Yes, the splice is due to shipping/rolling challenges.

I'd prefer the columns be one piece but I've never specified a member that long. I don't know how long they can make them at the mill or if shipping them to the fab shop/site at that length is easy to do.

Even if they can make them that long and ship them that long, whoever the fabricator/erector/contractor is may not want to deal with an 80' long column. I'm really not sure. If I get the project I'll definitely recommend getting a contractor/fabricator on board early to discuss the best way to build this.

 

[SlideRuleEra]

I don't know how long they can make them at the mill...

Well, if you are insistent on using HSS, you need to find out. After all, the internet is at your fingertips... I looked into it (at least from one manufacturer) and it took less than 5 minutes:

60 feet, max. But I also found out that you are not "stuck" with choosing from "wimpy" standard sizes or thicknesses... of course the cost goes up, up, up. Don't rule out W sections. Read this: Link

http://www.SlideRuleEra.net

http://www.VacuumTubeEra.net

 

[PMR06]

Could you contact a local power/telecom pole fabricator and see if they could help? I think I've seen monopoles that long without a splice?

 

[DETstru]

SRE/PMR06, thanks, great suggestions.

If I get the project this will be the first thing I tackle. I'm sure any fabricator I contact would love to get their hands on this project so they'd probably be willing to help me hash out the fabrication and constructability questions.

 

[SlideRuleEra]

Detstru - Check with "Atlas Tube" they are big-boy HSS manufacturer.

http://www.SlideRuleEra.net

http://www.VacuumTubeEra.net