GB2065989A

GB2065989A - An Improved Cable Ladder

Info

Publication number: GB2065989A
Application number: GB8040889A
Authority: GB
Original assignee: BICC PLC
Current assignee: Balfour Beatty PLC
Priority date: 1979-12-20
Filing date: 1980-12-19
Publication date: 1981-07-01
Also published as: GB2065989B

Abstract

In a cable ladder, each stringer 21 and the ends of each rung 22 are so shaped that each end of a rung is in inter-engagement with and is permanently locked to one of the stringers without the use of separately formed securing means. Preferably, at each connection between an end of a rung 22 and a stringer 21, a part of the rung protrudes through an aperture in the stringer and is so deformed that the rung is permanently locked to the stringer. Each stringer 1 may have a surface that is inclined at an angle to the adjoining surface of the stringer and has, longitudinally spaced in this inclined surface, two transversely extending slots through which parts of the side walls of a channel-shaped rung 2 protrude, the protruding parts being deformed to lock the rung to the stringer (Figs 1- 6, not shown). <IMAGE>

Description

SPECIFICATION An Improved Cable Ladder This invention relates to ladder-like structures for supporting electric cables and/or service pipes, which structures comprise a pair of elongate side members (generally and hereinafter referred to as "stringers") and, extending transversely between and secured to the stringers at spaced positions along their lengths, a plurality of elongate support members (generally and hereinafter referred to as "rungs"). Such ladder-like structures may also include coupling components such as bends for supporting electric cables and/or service pipes as the direction and/or plane in which the extend gradually changes, tee-connectors and crossconnectors, all such coupling components having, as common features, at least one pair of stringers interconnected by mutually spaced transversely extending rungs.For convenience all such ladderlike structures and coupling components therefor will hereinafter be included in the generic expression "cable ladder".

In cable ladders of metal or metal alloy it is the general practice to secure the rungs to the stringers by a welding operation. In addition to being a time-consuming and hence expensive operation, where the stringers and rungs are zinccoated, a welding operation has the disadvantage that zinc coating in the vicinity of a weld is likely to be so damaged or destroyed that, unless the welded joint is subsequently coated with zinc, in the course of time, corrosion of a stringer and/or rung in the vicinity of a weld may occur and a corroded welded joint may eventually become an area of weakness.

It is an object of the present invention to provide an improved cable ladder which can be readily and inexpensively assembled and, when the cable ladder is of metal or metal alloy, in which risk of corrosion at the positions at which the stringers and rungs are secured together is substantially reduced.

According to the invention, in the improved cable ladder each stringer and the ends of each rung are so shaped that each end of a rung is in inter-engagement with and is permanently locked to one of the stringers without the use of separately formed securing means.

Preferably, at each connection between an end of a rung and one of the stringers, at least one part of the rung protrudes through an aperture in the stringer and said part of the rung and/or a part of the rung or stringer adjacent said part of the rung is or are so folded or otherwise so deformed that the rung is permanently locked to the stringer.

Where, as is preferred, each rung is of substantially channel-shaped cross-section, in a first preferred aspect of the invention, at at least one of said spaced positions along a stringer at which a rung is secured to the stringer, the stringer has a surface that is inclined at an angle to an adjoining surface of the stringer and has, longitudinally spaced in said inclined surface, two transversely extending slots through which parts of the side walls of the channel-shaped rung protrude, said protruding parts of the side walls of the rungs and/or the adjacent parts of the stringer being so deformed that the rung is permanently locked to the stringer. Preferably, the inclined surface on each stringer extends throughout the length of the stringer.

Preferably, each stringer is of substantially channel-shaped cross-section and is arranged with the flanges of the stringer pointing inwardly of the cable ladder but, in some cases, it may be of angle-shaped cross-section with one part of the angle pointing inwardly. The inclined surface on each stringer may be one surface of a longitudinally extending rib of inverted V-shaped transverse cross-section which extends throughout the length of an inwardly-pointing flange or part of the stringer. In one alternative embodiment, the inclined surface on each stringer may be the surface of a longitudinally extending part between the base of a channel-shaped stringer and one of its flanges or between parts of an angle-shaped stringer.

The slots in the stringers of a cable ladder in accordance with the first preferred aspect of the invention can be formed by any convenient technique. When the slots are to be positioned at pre-arranged intervals along a stringer and the stringer is to be formed by roliing from sheet material, we prefer to punch the slots in the sheet material prior to rolling to the required crosssection. In other cases (e.g. where the spacing between slots in a stringer is to be determined on site or the stringer is extruded) saw cut or broached slots may be more convenient.

Deformation of the parts of a rung that protrude through the slots may be effected by means of a simple pliers-type crimping tool; for heavy duty work a hydraulically operated tool (similar for instance to those used for crimping large electric terminals) is suitable; in some cases a hammer and punch can be used. The precise shape of each deformed part is in no way critical; in some cases a deformed part may be split into two or more parts separately bent.

A cable ladder in accordance with the first preferred aspect of the invention has the important advantage that the ladder can be readily assembled on site by unskilled personnel to meet any specific requirement with a minimum of special equipment and without the use of separately formed securing means (such as rivets or bolts) that are liable to bye dropped under difficult conditions. Furthermore, since in a cable ladder in accordance with the first preferred aspect of the invention, the parts of the side walls of a rung are spaced from an end of the rung, the length of a rung is not critical and a rung can be cut from a long length, if desired on site, only a plain straight cut being necessary and tolerance on the position and angle of the cut not being critical.

In a second preferred aspect of the invention, at at least one of said spaced positions along a stringer at which a rung is secured to the stringer, a part of the rung of stringer is engaged between and permanently locked by at least two parts of the stringer or rung; preferably, these interengaging parts of the rung and stringer are clamped together by at least one over-lying lug or ear integral with the rung or stringer. Each stringer preferably, has, at each of a plurality of positions spaced along its length, at least one slot in which engages a tongue formed at an end of a rung, the tongue being fdlded against and clamped to a surface of the stringer by at least one over-lying lug or ear cut from and integral with the rung or stringer.The stringer preferably also has an aperture adjacent to but spaced from the or each slot; the tongue engaging in the slot preferably has an aperture which registers with the aperture in the stringer; and at least one lug or ear integral with the rung preferably passes through the apertures and is folded over to overlie the tongue and clamp it to a surface of the stringer. At each of a plurality of mutually spaced positions along each stringer, a single slot may extend lengthwise of the stringer and may be formed by punching or otherwise forming a substantially rectangular depression in the outwardly facing surface of the stringer to form on the inwardly facing surface of the stringer a similarly shaped protuberance having a longitudinally extending slot along its upper edge.

Where, as is preferred, each rung is of substantially channel-shaped cross-section, in the second preferred aspect of the invention at each end of the rung, the side walls of the channel are folded inwardly to form flanges which, when a tongue integral with the base of the channel engages in a lengthwise-extending slot in one of the stringers, bear against the inwardly facing surface of the stringer, each flange having an integral lug which passes through the aligned apertures in the stringer and rung and is folded back to overlie the tongue and clamp it against the outwardly facing surface of the stringer.

In all cases, preferably, the end faces of the rungs abut surfaces of the stringers.

The invention also includes a kit of parts for assembling a cable ladder substantially as hereinbefore described.

The invention its further illustrated by a description, by way of example, of three preferred forms of cable ladder with reference to the accompanying drawings, in which: Figure 1 its a fragmental pictorial view of the firstform of cable ladder; Figure 2 is a fragmental perspective view of a stringer and one of the rungs of the cable ladder shown in Figure 1:: Figure 3 is an enlarged view of detail of Figure 2; Figure 4 is a fragmental pictorial view of the second form of cable ladder; Figure 5 is a fragmental pictorial view of a stringer and one of the rungs of the cable ladder shown in Figure 4; Figure 6 is an enlarged view of detail of Figure 5; Figure 7 is a fragmental pictorial view of the third form of cable ladder; Figures 8 and 9, respectively, are fragmental perspective views of the stringer and one of the rungs of the cable ladder shown in Figure 7, and Figure 1 O(a) to (c) illustrate the stages of the method- of inter-engaging and interlocking an end of a rung with one of the stringers of the cable ladder shown in Figure 7 to 9.

Referring to Figures 1 to 3, the first form of cable ladder comprises two steel stringers 1 of substantially channel-shaped cross-section arranged substantially parallel to one another with the flanges of the stringers pointing inwardly and, extending transversely between and secured to the stringers at spaced positions along their lengths, a plurality of steel rungs 2 each of channel-shaped cross-section. Each stringer 1 has formed in one flange 3 a longitudinally extending rib 4 of inverted V-shaped cross-section, one surface 5 of the rib being inclined at an obtuse angle to the adjoining surface of the flange 3.

Each rib 4 has at each of a plurality of longitudinally spaced positions along its length a pair of longitudinally spaced, transversely extending slots 6 through which parts 8 of the side walls 7 of a rung 2 protrude and are distorted, as shown in Figures 2 and 3, using a plier-like crimping tool, to lock the rung permanently and rigidly to the stringer. The degree of crimping will determine the rigidity of the joint.

Referring to Figures 4 to 6, the second form of cable ladder comprises two steel stringers 11 of substantially channel-shaped cross-section arranged substantially parallel to one another with the flanges of the stringers pointing inwardly and, extending transversely between and secured to the stringers at spaced positions along their lengths, a plurality of steel rungs 12 each of channel-shaped cross-section. Each stringer 11 includes a base 1 3 and a flange 14 interconnected by a longitudinally extending part 1 5 whose surfaces are inclined at an obtuse angle to the flange 14.The longitudinally extending part 1 5 of each stringer 11 has in its outwardly facing surface at each of a plurality of longitudinally spaced positions along its length a pair of longitudinally spaced depressions 1 9 in each of which is a transversely extending slot 1 6. End parts 18 of the side walls 17 of a rung 12 protrude through a pair of slots 1 6 and are folded, as shown in Figures 5 and 6, to lie in the depressions 1 9 and to lock the rung permanently to the stringer. The end faces of the rungs 12 abut the bases of the channel-shaped stringers 11.

Referring to Figures 7 to 10, the third form of cable ladder comprises two steel stringers 21 channel-shaped cross-section arranged substantially parallel to one another with the flanges of the stringers pointing outwardly and, extending transversely between and secured to the stringers at spaced positions along their lengths, a plurality of steel rungs 22 each of channel-shaped cross-section. Each stringer 21 has, at each of a plurality of positions along its length, a single lengthwise-extending slot 23 formed by punching a substantially rectangular depression 24 in the outwardly facing surface of the stringer to form on the inwardly facing surface of the stringer, a similarly shaped protuberance 25 with the slot 23 running along its upper marginal edge. Below the slot 23 is a rectangular aperture 26. At each end of each rung 22, the base 27 is folded through 90 to form a tongue 28 having a rectangular aperture 29 of the same shape and size as the apertures 26 in the stringers 21. Each end of the side walls 30 of the rung 22 are folded inwardly through 90 to form flanges 31 having integral lugs 32 extending from their end edges.

In assembling a stringer 21 and rung 22, the tongue 28 at one end of the rung is inserted into a slot 23 in the stringer so that the wall of the stringer is engaged between the tongue 28 and the flanges 31 and the rectangular apertures 26 and 29 are in alignment. The lugs 32 are folded outwardly through the aligned apertures 26 and 29 and over the tongue 28 to clamp it against the outwardly facing surface of the stringer.

Claims

1. A cable ladder comprising a pair of stringers and, extending transversely between and secured to the stringers at spaced positions along their lengths, a plurality of rungs, wherein each stringer and the ends of each ring are so shaped that each end of a rung is in inter-engagement with and is permanently locked to one of the stringers without the use of separately formed securing means.

2. A cable ladder comprising a pair of stringers and, extending transversely between and secured to the stringers at spaced positions along their lengths, a plurality of rungs, wherein, at each connection between an end of a rung and one of the stringers, at least one part of the rung protrudes through an aperture in the stringer and said part of the rung and/or a part of the rung or stringer adjacent said part of the rung is or are so folded or otherwise so deformed that the rung is permanently locked to the stringer.

3. A cable ladder comprising a pair of stringers and, extending transversely between and secured to the stringers at spaced positions along their lengths, a plurality of rungs each of substantially channel-shaped cross-section, wherein, at at least one of said spaced positions along a stringer at which a rung is secured to the stringer, the stringer has a surface that is inclined at an angle to an adjoining surface of the stringer and has, longitudinally spaced in said inclined surface, two transversely extending slots through which parts of the side walls of the channel-shaped rung protrude, said protruding parts of the side walls of the rung and/or the adjacent parts of the stringer being so deformed that the rung is permanently locked to the stringer.

4. A cable ladder as claimed in Claim 3, wherein the inclined surface on each stringer extends throughout the length of the stringer.

5. A cable ladder as claimed in Claim 3 or 4, wherein each stringer is of substantially channelshaped cross-section and is arranged with the flanges of stringer pointing inwardly of the cable ladder.

6. A cable ladder as claimed in Claim 3 or 4, wherein each stringer is of angle-shaped crosssection with one part of the angle pointing inwardly.

7. A cable ladder as claimed in Claim 5 or 6, wherein the inclined surface on each stringer is one surface of a longitudinally extending rib of inverted V-shaped transverse cross-section which extends throughout the length of an inwardly pointing flange or part of the stringer, and wherein said parts of the side walls of the rung protruding through said slots are spaced from the neighbouring extreme end of the rung.

8. A cable ladder as claimed in Claim 5 or 6, wherein the inclined surface on each stringer is the surface of a longitudinally extending part between the base of a channel-shaped stringer and one of its flanges or between the parts of an angle-shaped stringer.

9. A cable ladder comprising a pair of stringers and, extending transversely between and secured to the stringers at spaced positions along their lengths, a plurality of rungs, wherein, at at least one of said spaced positions along a stringer at which a rung is secured to the stringer, a part of the rung or stringer is engaged between and permanently locked by at least two parts of the stringer or rung.

1 0. A cable ladder as claimed in Claim 9, wherein the inter-engaging parts of the rung and stringer are clamped together by at least one overlying lug or ear integral with the rung or stringer.

11. A cable ladder as claimed in Claim 10, wherein each stringer has at each of a plurality of positions spaced along its length at least one slot in which engages a tongue formed at an end of a rung, the tongue being folded against and clamped to a surface of the stringer by at least one overlying lug or ear cut from and integral with the rung or stringer.

12. A cable ladder as claimed in Claim 11, wherein the stringer also has an aperture adjacent to but spaced from the or each slot; the tongue engaging in the slot has an aperture which registers with the aperture in the stringer; and at least one lug or ear integral with the rung passes through the apertures and is folded over to overlie the tongue and clamp it to a surface of the stringer.

13. A cable ladder as claimed in Claim 12, wherein, at each of the plurality of mutually spaced positions along each stringer, a single slot extends lengthwise of the stringer and is formed by punching or otherwise forming a substantially rectangular depression in the outwardly facing surface of the stringer to form on the inwardly facing surface of the stringer a similarly shaped protuberance having a longitudinally extending slot along its upper edge.

14. A cable ladder as claimed in Claim 13, in which each rung is of substantially channelshaped cross-section, wherein at each end of the rung, the side walls of the channel are folded inwardly to form flanges which, when a tongue integral with the base of the channel engages in a lengthwise-extending slot in one of the stringers, bear against the inwardly facing surface of the stringer, each flange having an integral lug which passes through the aligned apertures in the stringer and rung and is folded back to overlie the tongue and clamp it against the outwardly facing surface of the stringer.

1 5. A cable ladder as claimed in any one of the preceding Claims, wherein the end faces of the rungs abut surfaces of the stringers.

1 6. A cable ladder substantially as hereinbefore described with reference to and as shown in Figures 1 to 3 ofthe accompanying drawings.

1 7. A cable ladder substantially as hereinbefore described with reference to and as shown in Figures 4 to 6 of the accompanying drawings.

1 8. A cable ladder substantially as hereinbefore described with reference to and as shown in Figure 7 to 10 of the accompanying drawings.

19. A kit of parts for assembling a cable ladder as claimed in any one of the preceding Claims.