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All hold-down and compression forces on upper floors are transferred directly to the levels below. If hold-down or compression forces from above come in at a hold-down location on the floor below, then the hold-down values from the two levels are added. A tolerance of 5.5" is applied so that forces on hold-downs on an upper level within that distance in plan of a hold-down on a lower level will accumulate.
Shear line force for Overturning Calculation
The shear line force used to determine the overturning moment is the vertically accumulated shear line force V. Thus the overturning component is accumulated twice – as a shear line force and as a hold-down force. This seeming duplication is an indirect way of accounting for the increased moment arm of upper story shear line forces in the calculation of lower story overturning moments.
This assumption creates forces that are statically balanced if all full height sheathing segments on different floors line up with each other. Otherwise, this method can create a conservative design, with a greater total hold-down force reported than exists in reality. This is partly because some resisting dead load is neglected, and partly because of the indirect method of accounting for increasing moment arm. However, a more rigorous analysis would be unnecessarily complex and difficult to check.
Vertical Force-transfer Elements
If hold-down or compression forces on the level above do not line up with a hold-down location on the level below, to within the tolerance of 5.5", it is assumed that a vertical force transfer element is present in the lower wall or space between walls to transfer the force down. These are shown in Elevation view and in the Hold-down Design output table as "vertical elements".
You cannot specify these vertical elements in Shearwalls; it is your responsibility to design them. You can create a column or built-up wall stud in the WoodWorks Sizer program and enter the dead, wind and/or earthquake axial loads on the member. Please note that the forces shown in Shearwalls are factored, and Sizer expects unfactored loads, so you need to divide out the load combination factors, shown in the legend in Elevation view, before entering the loads in Sizer. Designing these elements in Sizer will also allow you to add occupancy live loads.