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ETABS- Concrete Wall Pier Large Torsion Output

ETABS- Concrete Wall Pier Large Torsion Output

ETABS- Concrete Wall Pier Large Torsion Output

(OP)
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!

RE: ETABS- Concrete Wall Pier Large Torsion Output

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 - www.re-tug.com

RE: ETABS- Concrete Wall Pier Large Torsion Output

(OP)
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.

RE: ETABS- Concrete Wall Pier Large Torsion Output

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 - www.re-tug.com

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