Axial load level as a percentage of Buckling load?

[lukeme]

Dear forum members,

I would like to know the level of axial load of a column (or beam) in a concrete or steel frame at service conditions as a percentage of buckling load.(1%, 10%, 50% or what?) Any body has an idea?

Pls help. Thanks very much.

Luke

 

[SlideRuleEra]

Euler buckling direct calculations for a specific case are straight forward, for steel. Here is a link to use as a guide

http://physics.uwstout.edu/statstr/statics/Columns/colse61a.htm

Allowable column loads are given in Section 3 of AISC Manual of Steel Construction (ASD).

Then a comparison of the two values can be made.

It is unfortunate that the W10x29 size member used in the example at the link above is not modern size (with listed allowable concentric loads), but the principle can be applied to a listed member.

http://www.SlideRuleEra.net

 

[cap4000]

For an "idealized" steel column perfectly straight braced at the top and pinned at the bottom I beleive the safety factor to around 2. The AISC Manual Specs uses 12/23 when KL/r exceeds Cc as its reduction. You can easily compare each of the results. For a reinforced concrete column I have no idea as to the ACI built in safety factor.

 

[lukeme]

Thank you guys for your replies,

But I was just wondering about the ratio of the axial load present at that column (not the capacity of the column) to its buckling load.

Thanks so much for your input

 

[Ron]

lukeme...compute the buckling load using Euler's column buckling equation. Then divide your actual axial load by the critical load and that's the ratio you're looking for.

 

[rb1957]

that's a bit obvious (isn't it?) ...

i think lukeme is after a design guide line for a column allowable (as a percentage of the euler load)

i think it depends on your industry ... i'd be reasonably happy working to 50% to 80% of euler ... anything more i'd want a test. also airplanes are usually more sensitive to local column failures (crippling), and remember that euler critical loads are unreasonable for short columns (refer to euler-johnson)

good luck