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RE: Wood: Stronger lateral design measures vs. improved construction

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Ara, I breezed through your post only because of lack of time to 
consider fully your remarks. I am therefore responding to some 
gut reactions.
In most new residential construction with interior partitions 
(non-load bearing) and roof trusses - it would be rare to find a 
wall with a truss directly above it unless designed specifically 
for drag. In which case the wall would be considered a shear 
wall rather than a non-bearing partition and would be connected 
to an adequate foundation.
Next, when does a non bearing wall suddenly separate at it's 
middle and through half of it's weight into a roof diaphragm. 
I've notice lately that even metal stud shearwalls are designed 
and held in place with powdered nails. My point is that unless 
the wall comes free from it's connection to the slab then the 
wall will act with the total envelope rather than independently 
- providing no more or less weight to the roof diaphragm.

What are we really trying to accomplish? We are trying to 
prevent the mass of the roof and floor from sliding away from 
the building. I can agree with you in a multi-story structure 
that the walls are connected to the floor diaphragm from that 
level and possibly to the level below by nature that non-bearing 
walls rarely have the 1/2" clearance that is detailed into their 
connection for allowable movement and that contractors make a 
more positive connection.

Next, Assume that the interior wall is toenailed to the bottom 
chord of the truss. In lateral motion, I would be hard pressed 
to believe that the wall is contributing to the action of the 
roof diaphragm, but rather that the deflection of the bottom 
chord is sufficient to dampen the motion of the non-bearing 
partition with very little load transferring into the diaphragm.

Even after Northridge, the majority of damage to non-anchored 
interior walls was that they moved away from their connection by 
an inch or two, but that none of them could be accounted as a 
contributing factor in the damage to the shear elements that 
attempted to control the motion of the roof and floor.

I believe that we consider the lateral load of the shearwall 
since it is positively tied to the diaphragms and therefore do 
contribute to the motion of the diaphragm.

Finally, if you must consider the weight of non-bearing 
partitions into the lateral load to the diaphragm, then you 
should consider the non-bearing walls as having some restraint 
against the movement of the diaphragm by nature of their 
connections to the diaphragm or slab below and the minimal 
amount of capacity that the gypsum yields. If they don't 
restrain, how can they contribute?