ETABS- Concrete Wall Pier Large Torsion Output

[Kate_16]

Hello!
I am working on a concrete podium building 1 story of concrete podium slab over concrete shear walls with 5 stories of CFS shear wall system above.
The building is very narrow, so we have extreme torsional irregularity. Using MRSA for shear wall design

I am using ETABS to get the lateral output for the shear wall design. Wall boundaries are pinned at the base and connected to the modeled slab at the top. When I output the wall pier forces, there are very high torsion forces in the top of pier output.

What could be causing this? How to account for this in design properly? I am using Sconcrete to design the walls themselves- inputting the load output from ETABS.

Thanks!

 

[sticksandtriangles]

Can you throw some real numbers at us to see the magnitude of this torsion? Are we talking 5 kip*ft or 500 kip*ft?

Generally you do not design for torsion in concrete shear walls as the torsion is typically negligible.
You could fake this to not develop torsion by only a a restraint in plane with the wall at the base, but this will mask a potential modelling problem.



S&T -

http://www.re-tug.com

 

[Kate_16]

Thanks for the quick reply @sticksandtriangles !

For most of the walls the torsion load is somewhere between 0-50 kft at the bottom of the pier output, with a couple outliers at around 125 kft. For the top of wall pier output however most are around 0-80 kft (most closer to 0 still) and a couple above 100, two that are in the 300 and 400 kft range. The max is 489 kft for a 25 ft wall.
I am having trouble understanding how this load is happening and why it would be higher at the top of the wall pier vs the bottom.

 

[sticksandtriangles]

Can you give us some photos of the deformed shape and the wall pier results? Hard to trouble shoot without more info.

Which wall is getting the 489 kip*ft? How do these MRSA results compare to an ELF type result? Do both produce large torsion in the wall piers?

S&T -

http://www.re-tug.com