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Re: Strength axis of plywood

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The strength axis of plywood (and OSB) is oriented in the stiffest, strongest
direction of the panel. Typically this is in the long (8 ft) direction of the
panel, or in the case of plywood, along the face grain direction. A few (rare)
cases exist where the strength axis may be in the short (4 ft) direction; for
plywood, this can occur in a "cross-face" panel, where the face grain is oriented
in the 4 ft direction.

Typically, floor and roof deck panels are installed with their strength axis
perpendicular to supports. For panelized roof deck components used in
nonresidential building construction, the strength axis may be oriented parallel
to supports. In this case, the stiffness and load capacity (vertical loading) of
panels is reduced from the normal orientation, but still adequate for many roof
deck loading conditions. For OSB, new "jumbo" panels (8 ft x 8 ft) are available,
which can be used for panelized roof decks with the panel strength axis
perpendicular to supports, maximizing stiffness and strength, and providing
improved dimensional stability in wet weather construction conditions.

Information on all of these options is available from APA; contact the Help Desk
through www.apawood.org.

John Rose/APA, Tacoma, WA

Patrick Rodgers wrote:

> Dear Jason,
>
> Plywood is most likely an odd number of plies but there is 4 ply plywood out
> there, and I believe 3 ply in addition to the 5 ply plywood.
>
> Patrick Rodgers
>
> Jason Emoto wrote:
>
> > From: "James Allen"
> >
> > What is the definition of the strength axis of a plywood panel?
> >
> > *********
> >
> > Plywood is built up of an odd number of laminations of veneer that are
> > "cross-laminated".  In other words, each alternating layer is oriented
> > perpendicular to its neighbors.  When the stress is parallel to the long
> > direction of the panel, there are more layers that are stressed parallel to
> > grain and they are located farther from the neutral axis.  Therefore, the
> > panel is stronger in this direction.
> >
> > Jason Emoto
>