Combining Types of Shear Walls

During our outing to the field you viewed several different types of shear walls. Let's review before we move on.

The Typical Wall Framing
From the basic forces...

The Plywood Sheathed Wall
The addition of sheathing, placement of hold-downs and compression posts completes the wall.

The Straight Sheathed Wall
Each nail at the top of each board resists a portion of the total lateral load. The force is transferred through the board to the bottom nails where the same force is resisted but in the opposite direction. To complete the diagram, opposing vertical forces are applied at the stud centerlines.

Example Calculation:

• One 8d common nail can resist 78 pounds lateral load.
• Separation between nails vertically = 6 inches.
• Separation between nails horizontally = 16 inches.
• Vertical load = (6/16) * (Horizontal load)
• 78 = SQRT( SQR( Horizontal load ) + SQR( (6/16)*Horizontal load ) )
• Horizontal load = 73 pounds.
• Allowable load per foot = (12/16)*73 = 54 pounds.

The Cement Plaster (Stucco) Wall - Step One
Note the different style of bolts according to purpose.  Although not stressed in previous diagrams, this is an important consideration in shear wall design.

The Cement Plaster (Stucco) Wall - Step Two
By going a bit further with the description of forces in shear walls we can see why cement plaster - though a stronger material - has such a low Code shear value.

The Cement Plaster (Stucco) Wall - Step Three
Although strong, cement (and concrete) are brittle materials that, for the most part, lack the ability to resist tension forces.  That is the purpose for the embedded wire mesh.

Each of these walls has a different way of resisting lateral loads. Under similar loading they will all deflect differently. As a result, the combination of distinctly different lateral force-resisting walls along one wall line is not permitted. Walls in line must work together in similar ways to effectively resist lateral loads.