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The program implements the provisions in SDPWS 4.3.3.2 for unblocked wood structural panel sheathing. You can specify that only one side of a wall is blocked; that is, the sheathing is nailed to the blocking on that side, but not on the other.
Limitations
Wood structural panels correspond to Structural I, Structural Sheathing and Plywood siding materials. Fiberboard must be blocked. The factor is not relevant to Lumber sheathing or gypsum-based materials.
Structural sheathing with gypsum underneath cannot be unblocked, as SDWPS 4.3.3.2. refers to Table 4.3A only, not to table 4.3B for gypsum underlay.
Unblocked is unavailable for walls greater than 16’ in height. A wall changed to that height will cause an unblocked wall to change to be blocked.
Cub Factor and Shear Wall Capacity
The program determines Cub factors from Table 4.3.3.2 based on the based on stud spacing and intermediate (field) nail spacing on that each side ot the wall. As per Equation 4.3-2, it applies this factor to the capacity of sheathing on a wall with 24" stud spacing and 6" edge nail spacing, regardless of the actual stud and nail spacing.
The Cub factor is applied for the stud spacing choices of 12, 16, 19.2" and 24”. 19.2" corresponds to 20" in the table.
For values of intermediate nail spacing between 6 and 12”, the factor for 12” spacing is used, in other words, the program does not interpolate Table 4.3.3.2. The table value for 6" nail spacing is used for all input nail spacings, i.e. for those less than 6" as well as 6".
The Cub factor is given below
Field Nail Spacing |
Stud Spacing |
|||
12" |
16" |
20" |
24" |
|
6 |
1.0 |
0.8 |
0.6 |
0.5 |
12 |
0.8 |
0.6 |
0.5 |
0.4 |
Output
The Sheathing Materials table indicates whether each side of the wall is blocked.
Shear Results
The program shows the Unblocked Factor in the Shear Results table in the wall row in the column Cub/Asp.
Deflection Table
The unit shear force v shown in the Deflection Table is v divided by Cub. The force Vn per fastener has not been divided by Cub.