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RE: Skewed (45 degree) shearwalls

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RE: Skewed (45 degree) shearwalls

No straps around corners. 
It may not hurt and the cost is low so go ahead.
The top plates must overlap.  Or use metal plate on top of topplate.
Detail a wedged cross section for one or both of the facing or 
meeting corner studs.

If the corner has the weight of a stone fire place, I would rather 
rely on additional straps that would attach directly to the body of 
the fire place. It is conceivable that there may be a short top plate 
of no use between the corner and the edge of fire place. I would 
consider straps on diagonal blocking directing the pulling-out 
tension directly into the body of the diaphragm.

The diaphragm shear may need more nailing to match a shear in 
the diagonal wall. A triangular section of diaphragm at the 
diagonal wall with interior edges perpendicular to framing could 
be considered. The triangle body having heavier diaphragm nailing 
and having the interior edges of the triangle collecting the 
diaphragm load or capacity further inside the building.

If corners are not shear walls, then the triangular element is not 
needed.

If a rigid diaphragm is considered.

If the corners are of shear walls. The principle axis of the whole 
diaphragm may be skewed. The maximum shears will be with a 
force skewed to the direction of framing.  The principle axis is not 
rotated, when the skewed shear walls have equal and opposite 
skewed shear walls, balancing the affects of rotating the principle 
axis. Get the Dennis Wish Program.

For flexible diaphragms. 

If the diagonal shear wall is larger and stiffer than the walls 
perpendicular to the shear wall line being considered, then as the 
load is added the skewed wall will have an additional tilt. This 
makes the diagonal wall very flexible and not rigid enough to 
collect its tributary shear due to its other wise assumed relative 
stiffness. I am not talking about the already reduced stiffness based 
only on the 45 degree component. 

With out correctly knowing the true stiffness it is best to design the 
diagonal wall with out considering other inline walls, and design 
the other inline walls with out sharing the load with the diagonal 
wall.

David Merrick, SE
MerrickGroup(--nospam--at)compuserve.com