Overturning Force Calculation

As per SDPWS 4.3.6.1.2 Eqn. 4.3-8 , the overturning component of the hold-down force is calculated by

F = vh = Vh/ L

where

• V is the ASD-factored shear force on the wall segment,
• h is the height of the wall. In the Hold-down settings, you can decide whether the height includes the height of the diaphragm floor joist as well. The SDPWS equation indicates that this distance is not included, but this creates gaps in the static analysis of multi-level structure.

Refer to the discussion in the Holddown forces topic for wall heights at gable ends.

• L is the length of the wall between chords. In the Hold-down settings, you can decide whether the length includes the distance between hold-downs and wall ends. SDPWS does not subtract this distance, however engineering mechanics, particularly when there is only one shear wall on a line, require that it be subtracted.

If the hold-down offset is not subtracted, it is still used to prevent the incorrect addition of compression hold-down forces with tension ones on adjacent walls, and to allow for a more accurate presentation of your design.

Perforated Shear Walls

For perforated shear walls, the calculation from SDPWS Eqn. 4.3-8 in 4.3.6.1 is

F = Vh/ C_OSL_i

where C_O is the perforation factor and SL_i is the sum of the shear wall segments, adjusting for narrow segments as per 4.3.4.3.

Note that this provision also indicates that the wall height is to be used and the hold down offset is not to be subtracted, but these can be over-ridden by the Hold-down settings,.