AD.2007-09.2.2 Load & Definition
A new feature has been added to include horizontal torsion for rigid floor diaphragms in the equivalent static seismic analysis. This torsion —referred to as the natural torsion— accounts for the static eccentricity which is the difference between center of mass and center of rigidity of a rigid floor diaphragm, to be used to multiply the UBC, IBC, 1893, etc.
Refer to TR.32.12.2 Generation of Seismic Loads for additional details.
Adding Natural Torsion factor to a static seismic load
The natural torsion factor is specified along with the accidental torsion factor.
- Add a Seismic Load definition to your model.
- Add a Load Case with the Loading Type of Seismic to your model.
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Select the seismic load case in the Load & Definition dialog and click Add.
The Add New: Load Items dialog opens.
- Select the Seismic Loads tab.
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Set the option to use the Multiplying factor for Natural Torsion Moment and type a value (less than or equal to one).
- Select the direction and specify the accidental torsion option as necessary.
- Click Add.
