4. DEFINITIONS (*Recommendation. After all the definitions are agreed upon this
section should be put into alphabetical order.)
4.1 Plywood: An engineered structural material consisting of veneer/plies of wood at
different thicknesses glued or bonded together with the wood grain of adjacent layers
arranged at right angles or parallel to each other. Depending on the desired properties in
container plywood panels, up to 3 plies in specific locations all run in the same
longitudinal direction, for special increased strength reasons. Also, see lay-up
configuration definition below.
OSB – Oriented Strand Board (OSB) is an engineered panel typically comprised of a core
of wood strands oriented for directional properties along the length of the panel and with
wood veneers adhered to the top and bottom of the OSB core.
Bamboo – Engineered panel comprised solely of bamboo or a hybrid combination of
bamboo and wood veneers where the bamboo is oriented for directional properties along
the length of the panel.
4.2 Internal Forces: When any structural member is supported on an approximate 300-
350 mm (11.8” – 13.8”) span and experiences a vertical load, such as a rolling fork truck
wheel, it experiences both vertical and horizontal induced forces. The vertical forces are
maximum on the member’s top and bottom surface. The top surface is loaded in a
compression mode, while the bottom surface is loaded in a tension mode. These forces
are zero at the center of the thickness. The horizontal forces are maximum at the center
of the member’s thickness, and are zero at the top and bottom surfaces. In wood, these
horizontal forces create the potential for a sliding motion between the upper and lower
portions of the member.
4.3 Internal forces, Wood Plank in container floor: When a hardwood plank is
subjected to vertical loads, such as a rolling fork truck wheel, and is used in container
flooring that is supported on approx 300-350 mm spans, the plank experiences both
vertical and horizontal internal forces. Common oak and Apitong/Keruing planks
generally are stronger in resisting horizontal internal, shear forces, and thus fail from
vertical overloading (in bending), which usually results in splits on their lower exterior
surface.
4.4 Internal forces, Plywood panels in container floor: When a plywood panel is
subjected to vertical loads, such as a rolling fork truck wheel, in container flooring that is
supported on approx 300-350 mm spans, the panel experiences both vertical and
horizontal internal forces. Traditional Apitong/Keruing panels generally are stronger in
resisting the internal vertical forces, and thus fail from horizontal shear overloading. This
failure usually results in splits/separations within the interior “middlemost” transverse
layers. These failures occur between, or within, a veneer/ply as fibers rolling over each
other. This is referred to as a rolling shear failure.
4.5 Rolling Shear Failure: When veneers/plies in a plywood panel are loaded
ACROSS/at right angles to the grain, a sufficient load can become more than their natural
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shear strength. This overload then causes grains to rip free of each other, and begin to roll
over each other, in what is known as a rolling shear failure.
4.6 Delamination: A true delamination is when the adhesive bond fails in a panel, and
adjacent veneer, plies, or strands are no longer permanently joined to one another.
Because panels are often made from the same batches of glue, multi veneer/plies/strands
and multi panels often reveal true delamination.
4.7 Separation: When a panel fails due to overload, veneers/plies pull apart/separate; in
these cases, because horizontal stresses are highest at the center of the panel thickness,
the first failure (a rolling shear failure) usually occurs in a transverse layer above or
below the core of the panel’s thickness. Sometimes secondary failures occur at approx ½
thickness of the remaining thicknesses. After shear failures, extreme loads can also cause
splitting/bending failures of outermost longitudinal plies.
Note: Continuous overloading/fork truck travel can result in “rubbing” internal friction
forces between adjacent, previously separated veneers/plies. This may result in a smooth
appearance at the location of the adhesive bond. This “smoothing” should not be
confused with a “true delamination”.
4.8 High Impact Over Small Area: A high impact can cause another type of failure. If a
heavy impact occurs over a small area, it can cause simultaneous multi ply rolling shear
failures through the thickness, and also a bending failure of outermost longitudinal plies
4.9 Wood/fiber failure: In testing when solid wood is overloaded in bending, it will
usually fail/crack through its thickness, similar to a tree branch broken over one’s knee.
When panels (i.e. plywood, OSB or Bamboo) are tested according to the test procedures
in this bulletin, they generally fail in rolling shear, separating within inner veneers/plies
or core. As long as the adhesive bond is good, fibers will remain attached to the adhesive.
This is considered wood/fiber failure within a plywood panel.
4.10 Decay: Decay is deterioration of wood as a result of fungal attack. The typical
appearance of decayed wood includes splitting across the grain, soft and punky, stringy,
or crumbly. The presence of wood decay can result in significant reductions in strength.
Decay must NOT exist in wood to be used for panels, as it has no strength and, under
some conditions, may continue to spread into surrounding good wood.
4.11 Decay resistance: The resistance of a wood species or panel treated with a wood
preservative to stop/retard wood decay.
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4.12 Plywood layup: Layups are the ply directions of each layer in a panel, and these are
transverse (at right angle to panel length) and longitudinal (parallel to panel length).
Traverse plies maintain panel dimensional stability (minimize length and width
dimensional changes from moisture changes, frequently noted in planks), and allow
smaller pieces to be used in these layers to best use varying log trimmings; Longitudinal
plies resist bending and shear forces, but must be used full length for attaining panel
strength. Lay-up is a part of the “engineered” feature of the panel to meet specific service
requirements.
4.13 Density: The weight of a sample divided by its volume. Density is expressed in
kilograms per cubic meter (KCM), pounds per cubic foot (PCF), etc.
4.14 Specific gravity: The ratio of the oven dry weight of wood to an equal volume of
water. Specific gravity is a unit-less value. This value is most often used in industry
testing procedures for comparative purposes for wood strength and is cited in wood
science textbooks. As the specific gravity increases, strength generally increases. As the
specific gravity decreases, strength generally decreases. Specific gravity is typically
determined with the oven dry weight, or zero moisture content, and oven dry volume of a
tested sample.
4.15 Marine Grade Plywood: Plywood manufactured to the highest standards and
longest service life. Panels of this grade can be permanently exposed to moisture or
elevated moisture conditions.
4.16 Moisture Content: The amount of water in wood usually expressed as a percentage
of the weight of the oven-dry wood. Moisture content is sensitive to changes in the
surrounding environment. As the surrounding relative humidity increase, the wood
moisture content will also increase, and as the surrounding relative humidity decreases
the wood moisture content will also decrease.
IICL TB 001 was prepared under the supervision of the IICL Technology Committee.
1120 Connect icut AVE NW, Sui te 440, Washington, DC 20036-3946 USA
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