IE50775B1 - Cantilever bracket - Google Patents

Abstract

A cantilever bracket intended for joining a pair of joists (30,31) at a point of contraflexure within the span of a building comprises a generally channel section sheet metal member having a base (13) and walls (11 and 12). An abutment (16) is bent upwardly from the base (13), being defined in the blank between a pair of cutouts (14, 15). The blank is of generally chevron shape and the cut-outs (14, 15) and the abutments (16) are at the concave edge. In use, a fixed joist has the free ends of the channel section secured to it so that the end of the joist (30) abuts against the abutment (16), which may be fastened by integral teeth (19) or nails. A second joist (31) is then dropped into the channel section so as to rest on the base (13) and is nailed in position. Use of a bracket is intended to reduce timber requirements and offers lateral restraint to the external walls of the building.

Description

This invention relates to a cantilever bracket for use in building.

In building, for example a house, the spacing of internal walls is irregular and some floor joists have to S' extend across a greater span than others. The crosssection of timber which needs to be used for a joist, particularly the depth of the joist is related to the span. In order to avoid unevenness in floor levels, all the joists are customarily selected to be of a depth io suitable for the greatest span between internal load bearing walls.

Since the span across a house is usually larger than the length of available joists, individual joist lengths are selected to extend across a single span from, for tS example, one of the external walls to an internal load bearing wall. Where the end of a joist reaches an internal wall, it is overlapped side by side with another joist, the two usually being nailed together.

It will be seen that considerable wastage of timber zo occurs in the procedure used at present, firstly because of the amount of overlap at internal walls, and secondly because excessively deep joists are used over most of the spans of the building.

Theoretically, a rigid beam supported only at its 25 ends has a bending moment which is greatest at the centre 50778 of its free span. If some intermediate point or points between the ends is or are also supported, the resultant bending moment at any point is altered and, at a plurality of positions along the beam, there will -be S’ created neutral points, known as points of contraflexure, at which the bending moment of the beam tends to zero.

It is an object of the present invention to provide a cantilever bracket enabling wastage of timber in the laying of floor joists to be reduced. /p According to the invention there is provided a cantilever bracket comprising a rigid generally channelshaped sheet metal member having a base and a pair of side walls, the base, or one or both of said side walls, being deformed inwardly of the channel to provide an is abutment extending in a plane generally at right angles to the base, each of the walls extending to each side of said plane and being adapted to be secured to respective joist end portions disposed at opposed sides of said abutment. io The plane of the abutment may coincide approximately with one end of the base.

The abutment may be provided with fastening means, for example one or more nail holes or fastening teeth, either stamped from the body or from the edge of the zS abutment.

The bracket may be formed from a generally chevronshaped blank such that the edges of the walls are inclined obliquely relative to the base.

A pair of cut-outs may be provided at spaced 34, positions on the concave edge of the chevron-shaped blank, the portion of the blank between the cut-outs forming said abutment and the base being defined by a pair of fold lines passing through said cut-outs.

The invention will now be described in more detail by way of example only with reference to the accompanying s drawings in which:FIGURE 1 is a plan view of a blank for forming a cantilever bracket embodying the invention; FIGURE 2 is a side elevational view of a cantilever bracket; FIGURE 3 is a perspective view of the bracket.

Referring firstly to Figure 1 of the drawings, there is illustrated a blank 10 of sheet metal having a generally chevron shape, which is intended to be pressed to form the cantilever bracket shown in Figures 2 and 3. is The blank has a pair of wall portions 11 and 12 which extend obliquely away from the axis of symmetry of the blank, the wall portions 11 and 12 meeting at a base portion 13· One end of the base portion 13 has a pair of cut-outs 14 and 15 extending inwardly from the concave io edge of the metal blank 10 which define a tongue 16, intended to form an abutment of the finished bracket. As shown, the tongue 16 is provided with a pair of triangular punched openings 17 and 18, the metal removed from these openings forming a pair of triangular teeth 19 isr and 20.

An alternative form of cut-out is indicated at 21 in dotted lines. The cut-outs 21 are formed during the process of blanking out the blank 10 from a strip of sheet metal and may be arranged to extend slightly beyond jo the edge 23, so that portions of these cut-outs 21 then form notches 22 in the opposite edge 24 of the base portion 13 of the blank.

During the formation of the blank, a number of fastening holes are provided through each of the wall portions 11 and 12, the holes being arranged in distinct groups 25 and 26. The reason for this layout will-be s described later.

The extreme ends of the wall portions 11 and 12 are truncated at 27. Although this is not necessary for structural reasons, the truncated corners 27 assist in feeding the strip of sheet metal through the apparatus by ie> forming a marker.

The blank 10 is formed by folding about a pair of fold lines lying within the regions 28 and 29 which coincide with the position of the cut-outs 14 and 15 or 21 and 22. The broader cut-outs 21 and 22 may be used if ts it is necessary to provide a wide range of widths for the base portion 13 defined between the fold lines.

When the blank has been formed by pressing, it takes the shape shown in Figures 2 and 3 of the drawings. The base portion 13 extends perpendicularly between the wall io portions 11 and 12. The tongue 1b is pressed upwardly so as to extend at right angles to the base and to define an abutment at the end of the base. In an alternative embodiment (not shown) a similar abutment could be provided by pressing inwardly a portion of one or both of zb the walls 11 and 12, provided that the abutment extended at right angles to’the base 13· The cantilever bracket then takes a generally channel shape with a pair of parallel side walls 11 and 12 separated by a base 13 at right angles to the walls.

The walls, as seen particularly in Figure 2, extend obliquely from the base.

The bracket is intended to be used to secure together a pair of joists shown in outline at 30 and 31 in Figure 2 of the drawings.

This connection is made at a point of contraflexure, s' spaced from an intermediate support such as a load bearing internal wall. The joist 30 extends from the intermediate load bearing wall (not shown) to the point of contraflexure, where it has the cantilever bracket secured to it. It will be seen from the drawings that no /0 trimming of the underside of the joist 30 is required. The cantilever bracket is presented to the end of the joist and nailed in place. It may be of assistance to provide the integral teeth 19 and 20 which can be hammered into the end of the joist or alternatively, one ;s or two nail holes may be provided in the tongue 16 which forms an abutment against the end of the joist 30. Because this abutting tongue 16 is at right angles to the base portion 13 of the bracket, the second joist 31 will automatically be aligned with the joist 30. However, io before the joist 31 is presented to the bracket, a firm fixing is made between the walls 11 and 12 of the bracket and the joist 30, by means of the nail holes shown in the group 26. These nail holes are spaced from the end of the joist 30 as defined by the abutment tongue 16, by a zs distance which complies with the relevant standards for attachment to timber joists. In this way, the fixings are sufficiently spaced from the end of the joist to avoid splitting the wood substantially. Screws can, if desired, be used instead of nails.

As an alternative, or in addition to the nail holes, a pair of larger bolt-reoeiving holes (not shown) can be provided for use in securing the bracket to the timber.' The second joist 31 is then presented to the cantilever bracket by being dropped downwardly in abutment 80775 with the tongue 16 onto the base 13 which holds the joist 31 in alignment with the joist 30. The joist 31 can then be nailed in place using the group of nail holes 25. These again are spaced according.to the relevant standard s from the free end of the joist 31 to avoid splitting the wood.

The bracket is nailed securely to the joists by the fastening means 25 and 26 in order to provide lateral restraint.

Within any building structure, it is extremely desirable that the upright load bearing walls are restrained against lateral movement relative to each other under for example storm conditions, ground movements or other unusual stresses. At the external walls of fy the building, the joists will be secured in suoh a manner that they are keyed into the structure of the wall, either by being directly built in or by being supported by a joist hanger or bracket keyed into the wall.

At any intermediate positions where the joists are io secured together by means of the cantilever bracket shown, any tensile or compressive force on one joist is transmitted to the other so that the joists provide a continuous lateral restraint across the building.

Various modifications can be made to the cantilever as bracket shown, for·example by making the integral teeth 19 and 20 extend from the edge 23 of the abutment tongue 16 or by pressing upwardly the central region of the base portion 13 to avoid the crushing of the side edges of a joist held in the bracket. As referred to above, the positions of the fold lines will be within the regions 28 and 29 so that the same blank, can be used to accommodate a range of widths of joist.

The shape of the blank shown in Figure 1 is chosen for economy of metal but it will be appreciated that the blank could be generally rectangular in shape with the wall portions 11 and 12 being substantially wider than S illustrated. This would enable the fixings 25 and 26 to be spaced from each other in the manner shown in the drawings, but being disposed adjacent diametrically opposed corners of generally rectangular side walls. The inclined side walls shown in the drawings may be advanic tageous in inserting the second joist 31 but it would be feasible to construct the bracket without the inclined edges 32 and 33 on the walls although this would involve use of more metal to produce the bracket.

In use, the calculation of the points of contrazS flexure predicted for a continuous joist is firstly made and the joist sections are then cut to size so as to extend from the supporting walls, to these points. In each case, the joist 30 will be cantilevered from a supporting wall and the joist 31 will be subsequently it? fitted.

It will be seen that there is no overlap between the joists 30 and 31, thereby saving a considerable amount of timber, typically of the order of 50 cm in length. Additionally, considering the largest gap which has to be is bridged by a joist in an individual building, part of this gap will be occupied by a cantilevered section extending from a supporting wall to a point of contraflexure so that the remaining part of the joist only bridges the remaining part of the gap. In contrast, by the conventional joist laying method, a single joist is required to bridge the entire gap between the internal supporting wall and the external wall, which means that the joist needs to be relatively deep in order to resist the bending moment exerted on it over that span. With part of the span occupied by the cantilevered joist ’ 50775 portion 30, the depth required for the joists is reduced. In previous building practice, all the joists were chosen to be of a suitable depth to support the bending moment across the largest span of a building and hence S considerable savings can be made if the depths of the joists can be reduced overall by use of cantilever brackets at appropriate positions. Taken in combination with the savings in the length of the joists because of the absence of overlaps, considerable economy can be made lo in the use of timber without harming the structural properties and while providing good lateral restraint.

Claims (10)

CLAIMS:

1. A cantilever bracket comprising a rigid generally channel-shaped sheet metal member having a base and. a pair of side walls, the base, or one or both of said side walls, being deformed inwardly of the channel to provide S an abutment extending in a plane generally at right angles to the base, each of the walls extending to each side of said plane and being adapted to be secured to respective joist end portions disposed at opposed sides of said abutment. /o 2. A cantilever bracket according to Claim 1 wherein the plane of the abutment coincides approximately with one end of the base.

2.S claim and formed from a generally chevron-shaped blank such that the edges of the walls are inclined obliquely relative to the base. 50778

3. A cantilever bracket according to any preceding claim wherein the abutment is provided with fastening is· means.

4. A cantilever bracket according to Claim 3 wherein the fastening means comprise teeth pressed from the metal of the abutment. 5. The base being defined by a pair of fold lines passing through said cut-outs.

5. A cantilever bracket according to Claim 3 wherein Id the fastening means comprise teeth formed from the edge of the abutment.

6. A cantilever'bracket according to Claim 3 wherein the fastening means comprise nail holes.

7. A cantilever bracket according to any preceding

8. A cantilever bracket according to Claim 7 wherein a pair of cut-outs are provided at spaced positions on the concave edge of the oAevron-shaped blank, the portion of the blank between the cut-outs forming said abutment and

9. A cantilever bracket substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings. It

10. A blank for forming a cantilever bracket substantially as hereinbefore described with reference to and as illustrated in Figure 1 of the accompanying drawings.