Civil Engineering Reference
In-Depth Information
Solution
Swell does not occur above FSP. Increasing the moisture content from 15% to 27%
causes swell. From the data given, Red Spruce swells 7.8% for a 27% change in
moisture content (from zero moisture content to FSP).
Percent swell
=
7.8/27
*
27
-
15
=
3.5
%
1
2
1
2
Change in dimension
=
250
*
3.5/100
=
8.7 mm
1
2
New dimension
=
258.7 mm
10.4
Wood Production
Trees are harvested in the fall or winter, because of their water content and
environmental concerns connected with fire hazard and other plant growth.
A vast industry has developed to harvest and process wood. Wood is har-
vested from forests as
logs
. They are transported to saw mills, where they are
cut into dimensional shapes to produce a variety of products for engineering
applications:
1.
Dimensional lumber
is wood from 50 mm to 125 mm (2 in. to 5 in.)
thick, sawn on all four sides. Common shapes include
and .
1
These sizes refer to the rough-sawn
dimensions of the lumber in inches. The rough-sawn lumber is sur-
faced to produce smooth surfaces; this removes 5 mm to 10 mm (1/4
in. to 3/8 in.) per side. For example, the actual dimensions of a
are 40 mm by 90 mm ( by ). Dimensional lumber is pro-
duced in lengths of 2.4 m to 7.2 m (8 ft. to 24 ft.) in 0.6 m (2 ft.) incre-
ments. Dimensional lumber is typically used for studs, sill and top
plates, joints, beams, rafters, trusses, and decking.
2.
Heavy timber
is wood sawn on all four sides; common shapes include
and larger. As with the case of dimensional lum-
ber, these sizes specify rough-sawn dimensions in inches. Surfacing
generally removes 10 mm (3/8 in.) per side. Heavy timbers are used
for heavy frame construction, landscaping, railroad ties, and marine
construction.
3.
Round stock
consists of posts and poles used for building poles, marine
piling, and utility poles.
4.
Engineered wood
consists of products manufactured by bonding together
wood strands, veneers, lumber, and other forms of wood fiber to produce
a larger and integral composite unit. These products are engineered and
2
*
4, 2
*
6,
2
*
8,
2
*
10, 2
*
12,
4
*
4
2
*
4
1
1
3
1
2
in.
2
in.
4
*
6, 6
*
6, 8
*
8,
1. The standards for dimensional lumber and heavy timber standards were implemented in
about 1970. When remodeling older structures, the dimension of the existing lumber must
be measured.
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