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Re: horiz. diaph. blk'g.

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The traditional approach is to apply blocking flatwise and adjust lateral load for sheathing nails based on actual vs. required nail penetration (or refigure based on EYM in 1997 NDS).  But APA has a recent report (APA Report T98-22) which shows nail penetration based on NDS EYM methodology can be reduced to 1.5" for 10d common nails, and 1.375" for 8d common nails.  This provision will be included in 2000 IBC for shear wall and diaphragm tables. The 10d common short (diaphragm) nails (0.148" dia. x 2-1/8" long) will provide the needed penetration with 15/32" and 19/32" wood structural panel sheathing; actually, a 0.148" dia. x 2" nail would work better with 15/32" sheathing.
A caution, though - if you get a lot of nails in 2x flat blocking, you may split the blocking. It might be better to use 15 ga. or 14 ga. staples into 2x flat blocking; or if nails are used, change to 3x or 4x blocking.
John Rose/APA, Tacoma, WA

Mark Baker wrote:

If 2x4 blocking, laid flat is used for blocking in a horiz. diaph., what reduction in shear capacity should be applied? If there is such a reduction, does it correspond to a shorter (10dx1.5") nail, nailed into the 1.5" block dimension or the normal 10dx3" nail? Or, is blocking laid flat simply out of the question? Mark