CA2163272A1

CA2163272A1 - Adjustable joist

Info

Publication number: CA2163272A1
Application number: CA 2163272
Authority: CA
Inventors: Gordon Ashton Webster
Original assignee: Individual
Current assignee: Individual
Priority date: 1995-11-20
Filing date: 1995-11-20
Publication date: 1997-05-21

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.

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 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 - 216327~
.~
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 216327~ -... ; 3a corner joint is formed during the said web bending operation and provides clearance for the top spot welding electrode.

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 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.