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These settings affect the generation of hold-down and compression forces from shear forces on shear wall segments.
Hold-down offset
Here you specify the value of the hold-down offset, that is, the distance between the end of a wall segment and where the hold-down force is situated or the force at the compression end is assumed to act.
These offsets are used to calculate the moment arm used for overturning calculations and for the calculation of shear wall deflection due to the rotation caused by vertical displacement of the hold-down device.
If Calculate for each standard shear wall segment is selected, this input applies only to walls of the type Proprietary/non wood and the program calculates the hold-down and compression force offsets for each standard wood shear wall segment in the structure.
If a value is entered or calculated that is greater than or equal to ½ a shear wall segment length, the program reverts to the original default value of 1.5”, for that segment only. It issues no warning in this case, it is evident only by the placement of the hold-down in elevation view and its position as listed in the Hold-down Design table.
Calculate for Each Standard Shear Wall Segment
If this check box is selected, then the hold-down offset is calculated for each segment on a standard wood shear wall, separately for the tension end and the compression end. For Proprietary/non-wood shear walls, the input hold-down offset is always used.
The distance at the tension end is the width of the end studs as entered in Wall or Opening input view, plus the hold-down anchor bolt center line offset, which comes from the hold-down database for the selected hold-down.
The distance at the compression end is one-half the width of the end studs, i.e. the center of the end stud pack.
Note that O86 11.6.4.1 requires that you use the centre of the end studs as your hold-down offset for moment arm calculations at both ends, however using the location of the hold-down anchor bolt is more accurate and slightly conservative when compared to the centre of the wall studs.
When anchorages are used instead of hold-downs, the location is the end of the wall studs plus 2", which is sufficient space to comfortably place a 3" x 3" washer. In addition, when calculating the moment arm, the program imposes a 300 mm minimum on the total offset from both ends of the wall, to comply with O86 11.6.4.1.