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RE: 3x6 T&G diaphragm capacity

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The shear capacity for *thin* sheathing perpendicular to beams is the "couple" formed by the two nails.  Three inch thick sheathing may have different numbers if the sheathing boards are nailed together.  For more information, see Western Wood Products Association's "Western Woods Use Book".
Sheathing shear capacity:
Diaphragm shear capacity =
nail shear X nail spacing X # sheathing boards per foot / beam spacing
v = V*s/(w*b)
V = Nail shear capacity (lb.)
s = Nail spacing (in.)
w = board (sheathing) width (in.)
b = beam spacing (ft.)
v = shear in lb/ft
The answer is usually a pretty low number.

Jason W. Kilgore, P.E.
Project Engineer
Leigh & O'Kane, L.L.C.
(816) 444-3144

 -----Original Message-----
From: Mark Baker [mailto:shake4bake(--nospam--at)]
Sent: Tuesday, March 19, 2002 11:32 AM
To: seaint(--nospam--at)
Subject: 3x6 T&G diaphragm capacity

Anybody know or can refer me to a reference for diaphragm capacity on the following roof construction:
6x16 @ 10' o.c.
3x6 T&G sheathing (Western Red Cedar) with (2) 50d per board to each 6x16.
Constructed in 1966