BRIDGE REPAIR/REHABILITATION FEASIBILITY STUDY

6 U.S. DEPT. OF AGRICULTURE HANDBOOK NO. 207
nal specific gravity. True specific gravity is to the moisture content in question. Thus, by
generally based on the volume and weight of wood quoting the nominal specific gravity based oh
in either the air-dry or the green condition. Nom-
green volume and ovendry weight, the reader is
inal specific gravities are usually based on volumes able to compute the true specific gravity for wood
when green and weights when ovendry. This at any moisture content.
specific gravity is based on conditions that could The weight of wood per cubic foot is determined
never occur simultaneously. However, true by multiplying true specific gravities by 62.4, or
specific gravity can be calculated from nominal by multiplying nominal specific gravities by the
specific gravity with perfect accuracy for wood product of 62.4 times the sum of one plus the
of any moisture content above the fiber saturation moisture content, of the specimen at the time of
point, (green timber), and with fair accuracy be-
test. The weight per cubic foot for each timber
tween the fiber saturation point and air-dry by when air dry at about 12 percent moisture content
simply increasing it by a percentage corresponding and when green is given in table 2.
TABLE 2.— Specific gravity and weight of Caribbean timbers
Specific gravity based
on—
Weight per cubic
foot
Trade name
Scientific name
Green
volume and
ovendry
weight
Air-dry
volume and
weight
Green
Air dry