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Sheathing on both sides of the wall resists in-plane shear line shear line forces from wind and seismic loads that were transferred from the diaphragm above the wall to the wall. For seismic design, this is the only design criterion.
For wind design, exterior sheathing also resists out-of-plane wind component and cladding (C&C) wind loads from wind pressures perpendicular to perimeter walls. C&C design is for plywood bending between wall studs and for nail withdrawal. Wall studs and other framing members are not checked for out-of-plane loading.
If the exterior sheathing materials have no resistance to C&C loads, or no material at all is specified on the exterior side of an exterior wall, the program notifies you that it is unable to perform C&C design for that wall.
Combined Shear and C&C Design
If both Component and Cladding (C&C) loads and shear loads are present, minimum thickness, nails spacing, and nail size are determined by considering the strength required to resist lateral shear and the strength required to resist out-of-plane wind loads. Since the forces are independent, the larger of the two thicknesses or nail sizes and smaller of the nail spacings will control the design.
Where withdrawal loads are excessive a larger nail size will be used than is listed in the shear capacity tables, but the shear capacity is based on the capacity of the largest nail size listed in the tables for shear design.
Wall Groups and Design Cases
In determining the worst-case design of wind vs. seismic, and in determining the critical wall within a group, the program considers wind shear, nail withdrawal, and C&C sheathing design. On rare occasions the procedure can choose as the critical wall one that is less strong than another wall on the structure for nail withdrawal. This is because thicker sheathing, which is optimal for out of plane sheathing strength and for shear design, makes for weaker nail withdrawal strength due to reduced penetration. So when determining the strongest wall, one wall may be stronger for out-of-plane bending design and for shear but another may be stronger for nail withdrawal. In such a case, the program uses the wall thicker sheathing. It is extremely rare for the wall to fail for nail withdrawal as a result
Factors
The out-of-plane bending capacity from Table 3.2.1 is divided by the 1.6 wind capacity reduction factors from ASCE 7 3.2.1,. For shear strength, the value from table 4.3A is divided by the 2.0 wind capacity reduction factor from ASCE 7 4.3.3. The program also applies 1.6 wind load duration factors from NDS for nail withdrawal and out-of-plane bending, and wet service and temperature factors for nail withdrawal.
Non-shear walls
Non-shear walls on perimeter walls are designed for wind C&C loads only.