drift for special concrete shear walls

[structural87]

Hello

I am designing a residential concrete building consisting of 8 floors with an important inherent torsion since the walls are placed on one of the edges.
The seismic design category is D and I am relying only on special concrete walls where i am hinging the columns at their top & bottom.
After I have amplified the torsion by the amplification factor found in ASCE (Dmax/(1.2Daverage))^2, the drift at the unsupported corner is going crazy and this is totally normal.
I was discussing with one colleague and he proposed to investigate the option that, only for ''somehow'' limiting the drift, remove the hinges from the columns only to check the drift.
Personally, I think that the chosen structural system should be consistent for checking the members design and for verifying drift and we can't mix between the 2.
I would like to take your opinion if the above option can be acceptable.
For information, i am using a response spectrum analysis and the eccentricities I have calculated are based on the ELF procedure.

 

[HTURKAK]

I am relying only on special concrete walls where i am hinging the columns at their top & bottom.

What is the reason that you did not design as dual system ?. The system would be composed of Special reinforced concrete shear walls and with SMF capable of resisting at least 25 % of the seismic forces ?
Can you post a floor plan with dimensions and walls and columns ?

 

[KootK]

What is the reason that you did not design as dual system ?

Dual systems require beams. The economics of residential towers in North America strongly encourage one to utilize beamless, flat plate slab systems in order to optimize formwork economy.

 

[KootK]

Personally, I think that the chosen structural system should be consistent for checking the members design and for verifying drift and we can't mix between the 2.

I agree. The drift requirement that you reference is a ULS requirement after all. As such, if one is to include the contribution of the columns in that, I feel that it would then be prudent to also:

1) Ensure that the columns are strong and ductile enough to survive the level of drift that they will be exposed to.

2) Evaluate things like cracking in the columns to ensure that their positive contribution is not over estimated.

To an extent, we already do #1 as part of routine design these days.

Considered in this way, I feel that such an approach starts to suggest performance based design methods which, of course, increase the analytical effort required substantially. No free lunch, right?

 

[structural87]

Thanks for your replies.

Dual systems require beams. The economics of residential towers in North America strongly encourage one to utilize beamless, flat plate slab systems in order to optimize formwork economy.

yes sir.

1) Ensure that the columns are strong and ductile enough to survive the level of drift that they will be exposed to.

yes deformation compatibility would be checked at the end once this drift would be controlled. By the way, this open up another question:
I check columns deformation while assigning drifts in both directions and then combine them to meet orthogonal directions (100%of main direction +30% of the perpendicular one). This is how we should do it in my opinion.
If the columns section is ok, then no need for special detailing. Otherwise, special detailing would be required.
Do you agree with the above approach ?

 

[structural87]

Considered in this way, I feel that such an approach starts to suggest performance based design methods which, of course, increase the analytical effort required substantially. No free lunch, right?

to be honest, I read about this method but never tried it. There is always a first time.