ASCE7 - Torisional Irregularity Question

[CURVEB]

Referencing ASCE7-10:
When calculating torsional irregularity per table 12.3-1, is it necessary to calculate the drift for the entire structure or each individual story? The example situation is one where a shear wall stops one level below the top of the building (call the top level "roof"). At the roof, a torsional irregularity is created by the removal of this wall (if you consider only that one story), however, every level below has adequate stiffness and distribution of shear walls such that torsion is minimized. Since there is a torsional irregularity at the roof must you define the entire structure as having a type 1a or 1b irregularity?

Alternatively is it appropriate to simply compute the maximum total drift at each end of the structure and use that to determine torsional irregularity?

See attached for an example building where this might occur.

 

[HTURKAK]

If torsional irregularity exists at any level of a building for loads acting in any of the orthogonal directions,the entire structure is torsionally irregular.

 

[EDub24]

You have to check each story individually and in both orthogonal directions to determine the torsional irregularity of the structure. In your case the structure would classify as torsionally irregular because of the roof level.

With that said, if all other stories are fine you can consider removing the shear wall at the opposite side of the building at the roof level to make it more balanced. That might help.

 

[CURVEB]

Thanks.