calculation of sway and non sway column in Etabs

[CHAKKOUR]

Hi guys,

Etabs doent calculate the Q proposed by the ACI to determine a floor if its sway or non sway. I took an example of a one single column fixed at the base, length = 8m and i run the calculation. In the summary, k = 1 which its wrong.
In addition to that, i think that there is a bug in the delta s because, in the same example, i changed the k to k = 2 and i took a look to the new straining actions. The calculation of delta ns (moment magnification factor for the non sway) has changed and the delta s hasnt which is wrong.

Any help would be greatful. Try to take the same example and u'll see.
Many thanks

 

[saeedHR]

hi
Etabs has an approach which you can see in it's help and tutorial. based on that it is assumed that you have run a P-Delta analysis. therefore K is always considered as 1 as well as delta s.
Hope helps

 

[CHAKKOUR]

Thanks SaeedHR. But how can i check if a story is sway or non sway(in etabs without calculating the Q) ?? And why in the overwtites, etabs gives u the chance to change its K if he wont take into account?? Thanks

 

[saeedHR]

1. As long as you run a P-delta analysis you don't need to be worry about if it is sway or non-sway since if it is nonsway then according to ACI-318 10.12 we have k=1 and Mc=Delta ns *M2
which is completely the same as etabs.
if it is sway according to 10.13.4 the magnified delta s*Ms is the same as end moment Ms and if you go back to 10.13.3
M2 = M2ns+M2s.
so when you have M2 you will have Mc=Delta ns * M2 which is the same as for nonsway frames.

2. If you don't want to run a p-delta analysis you have the chance to use other ACI clauses and determine K and delta s

Hope it is usefull

 

[CHAKKOUR]

Thanks a lot. Another question, when do u have a transfer beam supporting a column carrying many floors, can we release the edges of the beam so it wont transmit the shear and the moment to the column supporting the transfer beam ??

 

[saeedHR]

I don't understant. but for sure you can't release the shear. foir moment it depends on the type of structure. steel or concrete

 

[slickdeals]

an we release the edges of the beam so it wont transmit the shear and the moment to the column supporting the transfer beam ??

Of course you can. Only if you have the Lord Almighty holding the transfer beam with a cable from above.

You can release moment, but you cannot release shear. The beam will be unsupported then.