SPColumn - ACI318 Second order Analysis .. 1

[BOCH]

Good morning guys,

I was checking a column versus buckling using SPColumn software and following ACI318 chapter 10 recomendations for moment magnification procedure .. After the analysis on SPColumn, i have received a message stating the following "Magnified (second-order) moment exceeds 1.4 times first-order moment. Revise column!" .. This is stated in chapter 10.10.2.1 ..

What is the solution of such situation ?

To check this column, i have extracted the forces applied to this column after doing a PDelta analysis in Etabs;
Could this condition be neglected if a non-linear PDelta analysis is done ?

Thank you ..

 

[KootK]

Could this condition be neglected if a non-linear PDelta analysis is done

I wouldn't say neglected but, most likely, remedied. I'm guessing that your KL value is too high and you've got SPColumn magnifying big P-delta moments that you've already magnified in ETABS.

What's your floor to floor height?

What are you and SPColumn using for KL?

Are the columns part of a moment frame system or do they just ride along with your shear walls?




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.

 

[BOCH]

Thank you KootK for your reply ..
Well the KL values is equal to 1*6.6 m (quite high) and the lateral resisting system is a shear walls system not frame system ..

 

[KootK]

So K=1 and your floor to floor height is 6.6 m? It may be that your column is just toO slender. What are its dimensions?

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.

 

[BOCH]

The column is 360x500 mm and it is not possible to increase the dimension ..
My point is that am i magnifiying twice the moment, once in etabs and twice in SPcolumn ?

 

[KootK]

For a K=1, non-sway column, SPColumn will only be amplifying your moments for P-Small-Delta effects, which is appropriate.

It's interesting to note that the commentary to the ACI section that you referenced only mentions P-Big-Delta effects, even though the clause itself just references general second order effects.

Since this is a non-sway column, can you justify a K value less than one?

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.

 

[Trenno]

What frames into the column at the top and bottom? Beams? If so, you may be able to justify a smaller K value.

 

[chekre]

this message is to ignored since the purpose of this clause in ACI318 does apply to a story not to a single element. If the second order moments are greater than 1.4 times the 1st order, then your story is very sway and your structure needs more bracing versus lateral loading.

 

[BOCH]

Thanks Chekre for your reply, this is what i thought, but i couldn't find this statement clearly in the code ACI318 .. could specify where did you find this because 10.10.2.1 is not very clear regarding this point, it doesn't tell you if this condition is for story check or elements check ..