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Concrete Column Cm factor

Concrete Column Cm factor

Concrete Column Cm factor

(OP)
If I have a concrete column (non-sway) that I am checking for axial load only (no moments- M1 = 0, M2 = 0) but is tall enough to warrant the slenderness check, what would the Cm factor be? Would it be 0.6 or 1.0?

RE: Concrete Column Cm factor

You will have moments.... based on the M2,minimum equations. Based on those code provisions, you can probably extrapolate it out so that M1/M2 = 0 and you'd have a Cm of 0.6.

Personally, I'd probably use a Cm of 1.0. But, I think that M2 minimum equation woudl allow you to justify a Cm of 0.6.

RE: Concrete Column Cm factor

You forgot to account for minimum moment caused by excentricity prescribed by code.

M2 need to be at least Cm*M2_Min !

RE: Concrete Column Cm factor

Sorry for double answering..... I didn't saw the first anwser of JoshPlum !

RE: Concrete Column Cm factor

Personnaly I use Cm=1.0 because the column subjected only to minimum moment will be in single curvature.

The ration M1/M2 = 1.0 where M1=M2=M_Min is discutable because of the slab dead load cause slab bending that can reduce the M1/M2 ratio...

To be safe I use Cm=1 & M1/M2 = 1.0 for minimum moment ..but I know that not all engineer aggree with me - they find that too much conservative !

RE: Concrete Column Cm factor

(OP)
Thanks everyone for your response. I knew about the minimum moment and was accounting for that in the design. It sounds like Cm = 1 is the way to go.

RE: Concrete Column Cm factor

Cm accounts for reverse curvatures of columns to your benefit to account for end moments with same sign.

Since, analysis doesn't give you end moments except for code required minimum, I believe, you cannot take advantage of Cm being less than 1.

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