Using DL to resist overturning on wood shear wall? 2

[abusementpark]

When you are calculating the overturning hold-down forces on a wood shear wall segment, do you treat the entire wall segment as a rigid body and reduce the hold-down forces based on the dead load (self-weight or from floor above) across the entire wall segment?

I always do this for a masonry or concrete shear wall since the wall is truly one integral rigid body. However, a wood wall is an assembly of vertical studs, blocking, and sheathing. I have questions on whether or not dead load on a wall stud in the middle of a long wall segment is truly capable of reducing the overturing uplift forces of the chord studs at the end of the wall segment. However, I haven't really seen a discussion of this issue. In Breyer's wood book, he indicates that you should reduce the forces due to the dead load, but without any discussion of my questions above.

Thoughts? TIA.

 

[hawkaz]

See the SEAoC 2006 IBC Structural/Seismic Design Manual (volume 2). They use the DL (times the factors Slomobile indicated above) to resist overturning.

Unless I am mistaken, I don't remember many properly constructed plywood shear wall buildings having structural failure issues at Northridge or Loma Prieta. Many multiple story wood buildings that had issues were sitting on top of concrete parking levels. These parking levels pancaked, but the wood above maintained its integrity for the most part (although at a lower level than it was constructed at). I heard of emergency workers driving past buildings multiple times before they realized that what was originally 3 stories of wood on a parking level was now 3 stories of wood on rubble.

If there is a valid reason to change the codes, I'm all for it, but let's not change codes just for the sake of change (or to sell books).