Calculation of sway and non-sway for K value

[h-badawy]

Dear experts,

In order to calculate(K) for design columns , i have to know first type of building (sway or non-sway) and as per the etabs manual design software takes k=1 as a default , and he gives an option to the user to change the value as per section 10.10.1 ACI318-08 , so shall i calculate sway and non-sway manual by calculating Q-index and put values of K for each columns ?

Thank you for help

Thank you

 

[JoshPlumSE]

Two ways to determine whether a frame is sway or non-sway as I see it:
Per ACI 318-14 section 6.6.4.3:
a) The increase in column end moments due to 2nd order effects is less than or equal to 5% (in which case it's considered a non-sway frame).
b) The Q value doesn't exceed 0.05.


It's really two sides of the same coin. It's just two different ways of calculating / estimating the ratio of 2nd order deflection / 2st order deflection.

 

[h-badawy]

Тнαηкs Josh and appreciated your response but actually i concern about the value of (k) in case of sway (non-braced) building , is it calculated/considered automatically in Etabs when we run the P-delta effect by increasing or i have to check manually by either two methods u mentioned above And get (K) from chart ACI318-08 chapter10 and assign for each column .

For non-sway it is already conservative K=1 by software default , the main problem if the building is non-sway so maybe the value of k is more than 1 and I am sure many engineers did not concentrate on this point and keep the value same.

Thank you

 

[h-badawy]

Updated
For non-sway it is already conservative K=1 by software default , the main problem if the building is sway so maybe the value of k is more than 1 and I am sure many engineers did not concentrate on this point and keep the value same.

Thank you

 

[JoshPlumSE]

For calculation of K values, there is an "alignment chart". See Figure 6.2.5 of ACI 318-14.

That chart using the following to values:

Sum (EI/L)_columns / Sum (EI/L)_Beams.

You do this for each floor span of the column.... then using the alignment chart to come up with the K factor for the column. That being said, the standard values are the following (for sway frames):
Fixed - Fixed: K = 1.2
Pinned-pinned: K = 2.0
Fixed - Free: K 2.1

If you enter the value for K as 0 in ETABS, I believe that means that the program will automatically calculated it based on the procedure described using the alignment charts. Though I have to admit, I'm more familiar with the way this is done for steel design.

 

[h-badawy]

Yes this part in the concrete is very close to the steel but i think etabs can not calculate the value of K even if you put value =0 , anyhow i will try to make experimental model and see what is the result when k=0 .

Thank you