ADJUSTABLE JOIST

SOLIVE DE LONGUEUR REGLABLE

English Abstract

An adjustable length steel joist has been developed
which offers advantages in building construction compared to
the present open web joist of fixed length. The proposed
joist can be made in half lengths which can be joined
together at the construction site by means of a bolted
connection. This feature greatly facilitates building con-
struction and shipment. The joist which is constructed from
a tubular zig zag shaped web and two straight top and bottom
components made from sheet metal is light in weight and
easily assembled during manufacture.

Claims

Claims
1. An adjustable length steel joist having top and bottom
chords each made from two hat shaped sections approximately
half the joist length formed to nest and slide one end
inside the other which combined with a close fitting splice
member inside the inner chord provide a method of bolting
the two said chord pieces together end to end to form a
structural joint.
2. An adjustable length steel joist member as in 1 in
which the said splice member is in the form of a square
shaped hollow metal section instead of a solid rectangular
section as shown in fig 3.
3. An adjustable length steel joist chord member consist-
ing of a hat shaped configuration of four straight segments
and a shallow rounded segment forming the dome of the hat.
4. An adjustable length steel joist member in which the
web section consists of a hollow tube bent to approximately
60° within a confining die so that the sides which would
otherwise protrude and be pointed assume the flat surface
configuration similar to the opposite ends of a bow tie, and
the central cross section forming two opposing concave
segments or arcs said segments coming together at the mid
point of the arcs during the bending operation.
5. The use of resistance electric welding to join the
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central part of the web cross section described in claim 4
to the dome of the hat configuration of the chords.
6. The use of both arc welding and spot welding methods
for connecting the web and chord members described in claim
4.
7. A fixed length joist similar to that previously
described except each chord is made from a single length of
steel.
8. A fixed length joist as in 7 but containing a central
splice fitted and bolted inside the hats of the central part
of the joist chords for resistance against lateral forces.
- 5 -

Description

Purpose of the Invention
The purpose of the invention is to provide a light and
strong joist for building construction that may be adjusted
in length. A second purpose of the invention is to provide
a product that can be readily manufactured by either
resistance spot welding or arc welding methods of assembly.
Advantages
The sliding joint construction allows building to pro-
ceed without the necessity of custom length fabrication
prior to use. The joist may be fitted to length in the
field within reasonable variations in length of approxi-
mately 12 inches. A second advantage of the proposed design

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is in the method of assembly which is facilitated by a dome
shaped hat shape on the chord that approximately fits the
outside contour of the formed tube bend. This joint
facilitates both positioning of the web bend to the chord
and of spot welded connections.
A third advantage is the use of a splice component or
tongue inside the central joint which reinforces the chord
connection at the bolt locations. This feature increases
the shear strengthof the chord components and stabilizes the
joint against lateral forces.
Description
The proposed invention consists of the traditional
steel joist or truss configuration fabricated in two
lengths, figure 1, and joined in the centre by a formed
joint figure 2 by means of a bolted connection figures 2 and
3. The said connection allowing longitudinal adjustment by
means of equally spaced bolt holes, item 6 figure 2, through
the tong~ item 4 and chord members, items 1 and 2. The ends
of the chords are formed to nest one inside the other,
figures 2 and 3, which together with a splice piece item, 4
form the connection joining the two halves of each chord.
The web component is formed from round steel tubing by
bending it to the required angle inside a confining die
producing a strong outer surface at the corner elbow,
Figures 1, 3, 4 and 5, which tends to nest with the dome
contour of the hat shaped chord, items 10 and 11, figure 3
and 4. This connection facilitates positioning

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for assembly and of spot welding of the web to the chord
members, item 12, fig 4 and fig 5. This form of
connection may also be used of course, for a single length
joist structure.
With reference to the accompaning illustrations, Fig.
1, shows a slde view of a typical joist together with the
connecting joint for the two chords in the centre.
Figure 2 is an enlarged side view of the said connect-
ing joint showing the two chord members, items 1 and 2 the
bolting method, items 5 and 6, and the central tongue, item
4. Figure 3 is a cross sectional view through the connect-
ing joint at a bolt location. The illustration shows the
nesting of the chord half lengths, items 1 and 2, and the
splice piece, item 4. The configuration also shows the
cross section of the connection between the formed web
member, item 7, and the two ends of the chord, item 10, at
the bolted joint. The web and chord components are shown
joined by two arc welds, item 9. ~ A circular gap
between the dome shaped contour of the chord hat, item 10
and the web segment circular contour, item 11, provide a
ready means for positioning the web to the chord during
assembly and welding. Figure 4 illustrates a typical web to
chord connection at a spot welded joint showing the
collapsed gap, item 8, Fig 3, and a weld nugget, item 12.
Fig 5 is a partially oblique view of section C-C, Fig 4,
showing a longitudinal cross section of the spot welded
joint. The circular arch, item 13, at the inside of the

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corner joint is formed during the said web bending operation
and provides clearance for the top spot welding electrode.

Representative Drawing