Kl/r Ratio of The Steel Column ????

[TekEngr]

I am designing a steel shed in SAP2000 (Sizes 29.5mx43.2mx9m) shed have 2 span so intermediate column length is 10 m and for this column Sap is giving me warning that the column Kl/r is increasing by 200 (actual ratio coming 256) so my question is that can I ignore this warning if not then how I can fix this problem any economical solution however stress ratio of this column is 75% so I don’t want to increase the column section any other reasonable solution regarding this.
Waiting for your valuable reply thanks in advance

 

[KootK]

I'd increase the size of the column. The economic impact will be minor. And your 75% may not be a great representation of the capacity of your slender column that will be rather sensitive to accidental eccentricities and imperfections. Other options might include fixing the top and/or bottom of the columns to reduce the effective length. You could also brace the column part way down with braces back to the roof (tree column-ish). I'd expect all of thes option s to be more expensive than just increasing the column size however.

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.

 

[TekEngr]

I tried to solve this problem by changing the section as you suggested above, I tried the section
UB 610x229x140 still the warning appears and before I was using the section UB457x191x67 this much different does not solve my problem, still if I go with this option my boss will kill me
I cannot provide bracing because of the block wall between the steel columns, by using the block wall I can reduce unbraced length of the column by providing some connection through angels or plates????

 

[vhengr]

Try UC sections.

Cheers! -VH

 

[KootK]

Connection to the wall may indeed work. But so should selecting a suitable column. As suggested above, a designated column section may be the way to go. I'd check kL/r by hand before selecting a new colun in your software package to ensure that slenderness works.

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.

 

[BAretired]

Sounds like a hollow steel column would be the way to go. HSS 152 x 152 x 4.8 weighs only 21.7 kg/m and satisfies the L/r requirement.

BA

 

[BUGGAR]

"so my question is that can I ignore this warning"

Ignore it and you can then follow up in the Engineering Failures forum. Why do you think this limit is required?

 

[delagina]

there should be kl/r "200" value that you can change to another number. I don't think this is a requirement but "preferable" per AISC.

 

[jayrod12]

I believe when it comes to compression members, there's no leeway. Tension members they have leeway in the 300 number if the attached components can handle the possible additional deformation.

 

[tstructural]

KL/r can exceed 200. Per AISC Spec Section E2 - 'it isn't preferred' but it does not state that you cannot exceed the 200 limit. I believe the old ASD code did maintain that you CAN NOT exceed 200.

 

[Archie264]

Well, be that as it may it's no an envelope I'd care to push as buckling occurs suddenly, without warning.

 

[Trenno]

What's the buckling load factor?

 

[BAretired]

UB 610x229x140 is the wrong shape to be using because of its low r[sub]y[/sub] value. Use an HSS instead.

Also, if applicable, you may wish to consider the possibility of forklift trucks colliding with the column.

BA