(4) Chord member is a member which
accompanies the air compressor. They should be
forms part of either the top of bottom chord.
bored perpendicular to the face of the timber. After
the holes have been bored, the truss is dismantled and
(5) Web member is a member which
the nails with drawn. The assembling of a truss after
lies between the top and bottom chords. If it is
it has been cut and bored is simple. In most cases,
vertical and at the centerline, it is also called a
timber connectors are used where the different
hanger.
members of the truss join. The truss is again
assembled as it was for boring holes, with the timber
(6) Joint is any point in a truss where
connectors in place. The bolts are then placed in the
two or more members meet and is sometimes called a
holes and tightened, a washer being placed at the
"panel point."
head and nut ends of each bolt. Straight and sound
(7) Panel length is the distance
timber should be used in trusses to avoid weak
between any two consecutive joint centers in either
places.
the top or bottom chords.
2-10. PURLINS
(8) Pitch is the ratio of the height of
Purlins are roof members that run at right angles
truss to the span length.
to the rafters or rafter trusses. They are used in roof
(9) Height of truss is the vertical
construction where corrugated sheet metal is used
distance at midspan from the joint center at the ridge
without sheathing, or to support the sheathing when
of a pitched truss, or from the centerline of the top
roofs are framed with high-capacity trusses set on
chord of a flat truss to the centerline of the bottom
wide centers. In small roots, short purlins are
chord.
inserted between the rafters and toenailed through the
rafters (fig. 3-2, lesson 3). In small buildings, such as
(10) Span length is the horizontal
barracks, mess halls, and small warehouses, 2 x 4's
distance between the joint centers of the two joints
are used for purlins, with the narrow side up. In
located at the extreme ends of the truss.
large-building construction, the purlins are
d. Use. Timber trusses are used for large
continuous members which rest on the trusses and
spans to provide wide unobstructed floor space for
support the sheathing.
such large buildings as shops and hangars. The
2-11. LIGHT
THEATER-OF-OPERATIONS
Howe and Fink trusses are the ones most commonly
TYPE FRAMING
used.
a. Plates, corners, and T-posts. TO type
e. Truss layout and construction (fig. 2-
framing is characterized by simplicity and by
23). The first task is to get the material to a level
economy in the use of lumber. Single rather than
spot of ground where workbenches will be
double top plates are used. Most TO buildings have
approximately level. Obtain from the blueprints the
no inside wall finish, and partitions, when used, are
necessary measurements of all pieces that are to be
finished on one side only. Consequently, corners are
used in the truss. Lay out the length on the different
formed by simply nailing end studs together as
sizes of timber and cut them. Care must be taken that
shown in 4, figure 2-1 and figure 24. T-posts are
the lengths are cut accurately. After all the lengths of
omitted as shown in A in 1, figure 2-3.
different sizes of material for a truss have been cut,
lay the pieces in their correct position to form a truss
b. Girts.
TO type framing is also
and nail them together temporarily. After the truss is
characterized by widely spaced studs (spacings as
assembled in this manner, lay out the location of all
wide as 8 feet OC are common) and the use of girts
holes to be bored, then recheck the measurements to
(fig. 2-24). Girts are horizontal members placed
be sure that they are correct. After this is done, bore
between studs halfway between the
the holes to the size called for on the print. They may
be bored with a brace and bit, an electric drill, or with
the woodborer which is part of a set which
2-18
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