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For the primary side of the wall, some information can be set to "unknown" , in which case the program will search for a suitable design. If different materials are selected for either side, all information for the other side must be known. If "Both Sides Same" is selected, then the unknowns apply to both sides.
The primary side is the one in which structural plywood or fiberboard materials are selected. If both sides have structural materials, then the exterior side of perimeter walls, or Side 1 of interior partitions, is considered the primary side of the wall.
Any of the following values can be set to unknown.
Sheathing thickness: Controls shear capacity, deflections, and out-of-plane sheathing capacity for wind loads
Fastener size: Controls shear capacity, deflections, and nail withdrawal capacity for wind loads
Fastener edge spacing: Controls shear capacity, deflections, and can determine withdrawal wind load on nails
Fastener field spacing: Usually determines withdrawal wind load on nails; also affects unblocked shear wall factor for shear capacity and deflections
Stud spacing: Controls out-of-plane sheathing capacity for wind loads; determines withdrawal wind load on nails; affects unblocked shear wall factor for shear wall capacity and deflections
Solving for Unknowns
The program assumes initial values for each unknown material parameter. The initial values represent the most economic design rather than the strongest, so stud spacing and nail spacing are at their maximum while sheathing thickness and nail size are at their minimum.
The factored shear wall capacity per lineal distance is evaluated and compared to the factored unit shear force on the design case being considered. For C&C wind design, the factored nail capacity in withdrawal is compared to the factored suction wind force tributary to that nail and the factored strength in bending of the plywood panel between studs to the out-of-plane wind force, whether it be from suction or wind bearing on the wall. If the wall satisfies all these criteria, it is selected as the design wall for the design case.
If it doesn't, the unknown parameters are incremented in a hierarchical search for a passing design. The selection of one parameter may update the available choices for subsidiary parameters, for example, incrementing to a new sheathing thickness will update the nail sizes that are cycled through.
When a combination of materials that passes is first encountered, it is chosen as the design wall for that design case. If a design is not found, the program determines the strongest possible design, outputs the results for that wall, and warns of the failure.