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plywood diaphragm deflection calculation

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Title: plywood diaphragm deflection calculation

You might want to review the ASD/LRFD Wind Seismic Supplement online at:

It has the most recent deflection equations for shearwalls and diaphragms.



John "Buddy" Showalter, P.E.
Director, Technical Media
AF&PA/American Wood Council
1111 19th Street, NW, Suite 800
Washington, DC 20036
P: 202-463-2769
F: 202-463-2791

The American Wood Council (AWC) is the wood products division of the American Forest & Paper Association (AF&PA). AWC develops internationally recognized standards for wood design and construction. Its efforts with building codes and standards, engineering and research, and technology transfer ensure proper application for engineered and traditional wood products.

>The guidance provided herein is not a formal interpretation of any AF&PA standard.  Interpretations of AF&PA standards are only available through a formal process outlined in AF&PA's standards development procedures.


Subject: plywood diaphragm deflection calculation
From: "Bruce Holcomb" <bholcomb(--nospam--at)>
To: <seaint(--nospam--at)>
I submitted this yesterday, but got a message that it was undeliverable, =
so I am trying again. I am basically asking what values to use for "G*t-=
sub-v" in calculating wood diaphragm deflection.
In calculating the deflection of a plywood diaphragm, you use the terms "=
G" (shear modulus) and "t-sub-v" (effective thickness for shear).=A0 I ha=
ve the 2001 NDS including the Supplements book for Structural Lumber, Str=
uctural Glulam Timber, Timber Poles & Piles, Wood Structural Panels and S=
hear Walls & Diphragms.=A0 On p SP-17 of the Wood Structural Panels secti=
on, Table 3.4 has values listed for the "Rigidity through the thickness",=
"G*t-sub-v".=A0 Are these the values to use for calculating the diaphrag=
m deflection?=A0=20
The reason I ask is when I compare with the "Plywood Design Specification=
" from APA, I find values for G and t-sub-v separately.=A0 I am checking =
three thicknesses: the first is 15/32" & 1/2" vs. 32/16 span rating, the =
second is 19/32" & 5/8" vs. 40/20 span rating and the third is 23/32" & 3=
/4" vs. 48/24 span rating.=A0 I am using "APA Rated Sheathing"; unsanded =
panels.=A0 I get approximately the same G*t-sub-v for the first and secon=
d, but not even close for the third thickness.=A0 Any advice? =A0
I am using "species group 1 for face ply" giving me G=3D90,000 psi and an=
d effective thickness of 0.298", 0.315" and 0.445" (corresponding to my 3=
checks above). =A0=A0
What am I missing?
Bruce D. Holcomb, PE
Butler, Rosenbury & Partners
300 S. Jefferson, Suite 505
Springfield, MO 65806
ph. 417-865-6100
fax 417-865-6102
Architecture, Engineering, Interior Design, Planning & Development
Your Vision.=A0 Our Focus.