Hold-down Forces Under Gable Ends

Important Note – These are descriptions to changes implemented in WoodWorks Shearwalls for version 10.0 and may not reflect current behavior

The program now allows you to choose whether the longer moment arm to the sloping roof, or the moment arm to the ceiling, is used for upper level hold-down calculations at the gable end. We also fixed a problem with the calculation of the longer moment arm when there were openings beneath a gable end.

Hold-down Moment Arm at Gable End
Starting with version 9.2, the program calculated the hold-down forces at gable ends by using the average height of the wall extending to the roof at gable ends for the overturning moment arm ( see Shearwalls Help topic Hold-down Forces for an explanation). Part of the motivation for this was NDS 14.3.1.1 (2), which said this height should be used as the shearwall height, however, this clause has been removed along with all other NDS clauses.
Some users believe that the ceiling acts as a diaphragm at gable ends, even distributing the load from the roof to the shearwalls. For this reason, we have enabled you to model the building such that the diaphragm height at the gable end is the height of the wall to the low point of the eave.
1. Input
  In the Block input of the Structure Input View, a checkbox has been added saying

Ceiling acts as upper level diaphragm

This check box is unchecked by default. When checked, the roof associated with that bloc is considered to have a ceiling diaphragm that transmits all of the lateral force to the shearlines.

Hold-down design
When calculating hold-down forces, if a wall has a roof above it from a block that has a ceiling that acts as a diaphragm, the moment arm used in the calculation is the wall height as entered by the user, plus the ceiling height if there is one if the Hold-down setting to include the floor/ceiling is checked.

Hold-down Forces at Openings under Gable End (Bug 2650)
The hold-down force calculated for each segment between openings at a gable end was using the average height of the gable end at the first segment in the direction of force as the moment arm. It now uses the average height of the gable end at the segment in question.