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Figure 2-101.—Strap hangers from purlins. | Up
Steelworker Volume 02 - Building manual for how to work with steel | Next
Figure 2-103.—Duct installed to a built-up steel roof. |
degrees onto the flange of the beam or purlin. Again,
the standard 7 feet 10 inches maximum span required
between hangers applies. Also, the hanger screws
standard will apply. The hanger span may be shortened
to fit the job requirements.
For heavier or larger systems, an installation
similar to that shown in figure 2-102 maybe required.
This system is hung entirely on angle rails and the
straps are fabricated into one-piece units. This system
is by far the neatest looking and is normally used when
the duct system is exposed.
Installing a duct system under a built-up steel roof
(fig. 2-103) is accomplished by hanging the duct
system with all-thread bolts and 2-inch by 2-inch by
1/8-inch angles. The all-thread bolt protrudes through
the steel decking and is bolted from the top with a large
washer and bolt, which extends down alongside the
duct into the 2-inch by 2-inch angles which is also
bolted from under the angle. This system allows for
adjustment of height. Also notice that the all-the ad
bolt extends into the top flat of the apex of the steel
roof decking. This is required because connecting the
all-thread bolt to the bottom valley of the steel deck
will reduce the structural strength of the decking and
may also cause water leaks.
FIBER-GLASS DUCT SYSTEMS
Throughout the Naval Construction Force (NCF)
fiber-glass duct is becoming common on jobsites. It
has the advantage of added insulating value, ease of
fabrication and handling, as well as installation, and
making it useful where traffic and handling/abuse are
restricted.
DUCT CHARACTERISTICS
Fiber-glass ducts are manufactured of molded
fiber-glass sheets covered with a thin film coating of
aluminum, although thin vinyl or plastic coatings are
sometimes used. In the NCF, we are primarily
concerned with aluminum coated duct. Because it is
fabricated of glass fibers, it is inherently insulated;
therefore, it is used where insulation is a requirement.
Fiber-glass ducts can be molded into various
shapes for special applications. The desired shapes can
be ordered from the manufacturer’s stock In the NCF,
for all but special purposes, the duct is supplied in the
flat form of a board that has V grooves cut into the
inner surfaces to allow folding to fabricate rectangular
sections (fig. 2-104, view A). The ends of the board is
molded so when a rectangular/square duct is formed
two sections of the same size will fit together in a
shiplap joint (fig. 2-104, view C). This joint ensures a
tight connection coupled with a positive alignment.
Figure 2-102.—Duct system with strap hangers from angle rails transverse to purlti
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