EP0298838B1 - Wall frame post to avoid the collapse of the insulating panels of this wall - Google Patents

Abstract

Elongate structural element made from laminated metal and intended to be used as a component of a wall frame determining a cavity for receiving insulating panels made of glass fibres of the type having easily separable layers, the said element (12) forming a U shape in cross-section defining a web (18) and two flanges (20) connecting the said web and having a width at least one quarter of that of the said web, the said element being employed as a post, the said post having sections cut out from the said web, which sections are longitudinally spaced apart and each one defining an elongate branch (36, 38) ending in a free point (46) and having free longitudinal edges and an internal end integral with the said web in a line of flexure (42), the said branch being able to flex between a non-operative position coplanar with the said web and an operative position generally orthogonal to the said web so as to engage and to retain an insulating panel, the said branch, when it is in its operative position, being inclined downwards and transversely towards one of the said flanges, and at least one of the said longitudinal edges being inclined relatively to the plane of the said web. <IMAGE>

Description

The present invention relates to constructions of wall frames for buildings and, more specifically, to wall frame uprights provided with innovative means making it possible to support and retain the insulating panels of glass fibers between the uprights.

In the construction industry, it is now well known to add insulating materials to the interior walls of an office, a ceiling, a storage space, a basement or the exterior wall of a building. 'a building. Such building materials can be installed for their sound insulation characteristics: this is usually the case for offices in multi-storey office buildings of the first category, also called category "A", for the purpose of provide the minimum discretion reasonably necessary to tenants; and / or such insulating materials can be used for their thermal barrier properties: this insulation is necessary for all the exterior walls of buildings located in countries with cold climates, as well as in countries with warm climates where cooling is desired. .

These insulating materials are installed between the vertical uprights forming the frame of the wall. Flexible glass fiber insulation boards are often used. Such insulating panels can be compressed and consist of easily separable layers. In the past, such panels were glued to one or two sheets of paper which served as means for securing the insulating panels in place. However, for fire safety reasons, the recovery of paper is no longer allowed.

It is well known that fiberglass panels, if not properly secured in place, will tend to collapse, that is to say to descend from their original position in the cavity of the wall in which they are embedded; this is all the more true as the insulating panels are thick.

There are many reasons why flexible insulation panels sag in their wall cavity. Among these, we find the contingencies of the construction working conditions, the vibrations, the humidity and the water absorbed during natural atmospheric conditions and the vagaries of the trade, the use of inadequate support members. , and many other conditions in the field where products subject to friction adjustment cannot meet the required performance criteria.

Of course, the collapse of these materials means the unacceptable loss of sound or thermal insulation to the exposed regions.

Various attempts have been made in the art. Overall, such improvements include either bonding the insulating panels to a bearing surface, or attaching metal strips transversely and vertically spaced as bodies to be added to the wall frame, the strips being provided with sharpened members or branches intended to be inserted into the insulating panels, so as to support the panels more firmly in position.

Gluing or installing crossbands to add requires additional labor and inspection. In addition, it was discovered that the tapes did not retain the insulation boards properly.

Furthermore, from US-A-3196499, there is already known an elongated structural member made of sheet metal and intended to be used as a component of a wall frame determining a cavity for receiving insulating panels, said member forming a U in section defining a core and two legs connected by said core, said member being used as an upright and said upright having cutouts made in said core and longitudinally spaced apart others, each of said cutouts defining an elongated branch terminated by a free point and having free longitudinal edges and an inner end integral with said core along a fold line, each branch being foldable between an inoperative position coplanar with said core and an operating position for which the plane of said branch is at least substantially orthogonal to said core.

However, such a member does not solve the problem of sagging flexible insulating panels.

The object of the invention is therefore the use of improved means for supporting and retaining flexible insulating panels in constructions of building walls, using members of the above type.

A corollary object of the present invention is that the support and the retention characteristics of the insulating panels are very long-lasting and very effective.

Other objects of the invention consist in that the means listed above are economical in manufacturing costs, solid in construction, and that they are easier and safer to install.

Taking into account the aims of the present invention listed above, vertical uprights are proposed for supporting and retaining insulating panels in a wall structure.

To this end, according to the invention, the elongated structural member of the type described above is characterized in that the width of said legs is at least equal to a quarter of that of said core and in that, in the operating position of said branch, the plane of the latter is oblique with respect to the longitudinal axis of said member, and, in its plane, said branch is inclined towards one of said legs, at least one of said longitudinal edges of said branch being inclined relative to the plane of said soul.

Thus, said branches have a double inclination and, thanks to this feature, said insulating panels are blocked in the horizontal direction under the action of their own weight, while, in the longitudinal direction, each branch can penetrate through several separable layers said panels.

Preferably, the longitudinal axis of said branch is oblique to the longitudinal axis of said member when said branch is in the inoperative position. Advantageously, said fold line is oblique to the longitudinal axis of said member. Advantageously, only one of said longitudinal edges of each branch is provided with barbs spaced from each other and oriented towards said fold line, said longitudinal edge being that which is directed towards said core. Preferably, it is expected that each branch has a longitudinal reinforcement ridge. Also, it is desirable that said branches are arranged in pairs and are oriented in directions opposite to said core when they are in the operating position, in order to impale said insulating panels on either side of said upright.

The invention also relates to a wall structure comprising, in combination, at least three parallel uprights substantially spaced apart in the upright position, a horizontal ceiling joist extending transversely and above the upper ends of said uprights and connecting them, said uprights being made of sheet metal, each upright forming a U in section defining a core and two legs connecting said core, the cores of the uprights being arranged in parallel planes substantially at right angles to the general plane of the wall structure, wall panels being fixed to the legs of said uprights on at least one side of said uprights, glass fiber insulating panels made up of layers easily separable occupying the space between said uprights, said insulating panels extending on opposite faces of the core of at least one of said uprights, and characterized in that said uprights consist of the structural member specified above , so that said branches of said members impale said insulating panels through at least some of said s separable layers, and a section of said insulating panels which are above said branches tends to be displaced by said branches inclined transversely towards said wall panels.

Preferably, said structure further comprises a horizontal beam made of sheet metal, transverse to said uprights and roughly forming a U in section, defining a base wall and side walls so as to constitute a groove and also at least a rim facing outwards along the longitudinal edge of a side wall, said rim abutting against a leg of said uprights and fixed thereto, said rim having elongated branches spaced apart longitudinally, each branch having a point free, free longitudinal edges integral with said flange by a fold line, said branch being able to be folded along said fold line between an inoperative position coplanar with said flange and an operating position transverse to said rim and oriented on the other side of said base wall, the longitudinal axis of said branch being generally parallel to the longitudinal axis of said rim when said branch is in inoperative position, said fold line being inclined relative to said longitudinal axis of said branch in a direction oriented towards said tip, said branch, when in the operating position, impaling and anchoring an insulating panel which is opposite and oriented upwards in said insulating panel, its most longitudinal edge high being provided with a barb oriented towards said fold line. Such a structure comprising uprights spaced parallel in a standing position, a horizontal ceiling joist on the upper ends of said uprights and connecting them, and glass fiber insulating panels occupying the space between said uprights, may further include anchor plates for attaching the top of said insulating panels to said ceiling joist, each anchor plate being made of sheet metal and having a pair of elongated branches, each having a free point, free longitudinal edges integral with said plate by a fold line, the fold lines of the two branches converging towards each other, each branch having barbs oriented towards said fold line, said barbs protruding only from the longitudinal edges of the two branches which face each other, said branches being able to be folded along their respective fold lines between an inoperative position coplanar with said anchor plate and an operating position transverse to said anchor plate to be inserted into said insulating panels, said anchor plates being intended to be fixed to said ceiling joist with said branches under it.

Note that document US-A-4512130 describes an anchor plate capable of retaining a pair of panels made of insulating fibers and joining end to end. end, said plate being of sheet metal and having elongated branches each having a free point, free longitudinal edges and integral with said plate by a fold line, said branches being able to be folded along their respective fold line in order to allow a relative movement of the branches between a first inoperative position coplanar with said plate and a second operating position, transverse to said plate.

According to another feature of the invention, the anchor plate capable of retaining a pair of panels made of insulating fibers and joining end to end, said anchor plate being made of sheet metal and having elongated branches, each having a free tip, free longitudinal edges integral with said plate by a fold line, said branches being able to be folded along their respective fold lines in order to allow relative movement of the branches between a first inoperative position, coplanar with said anchor plate, and a second operating position, transverse to said anchor plate, is characterized in that said anchor plate comprises two pairs of such elongated branches and in that the fold lines of each pair of branches converge towards each other, each branch having barbs along its longitudinal edge which is closest to the other branch of the pair, the other longitudinal edge of each branch being devoid of barb, the branches of one of the pairs being inserted in an insulating panel, and the branches of the other pair being inserted in another insulating panel.

• La figure 1 représente une vue en perspective partielle d'une structure de mur, construite en respectant les leçons de l'invention, et avec les branches en position opérante déployée prêtes à empaler les panneaux isolants lesquels seront ainsi supportés et retenus dans le mur pour éviter leur affaissement;
• La figure 2 est une coupe longitudinale partielle et agrandie d'un montant et de la poutrelle transversale de la figure 1;
• La figure 3 est la vue de la figure 2, mais pour une autre réalisation de la poutrelle transversale;
• La figure 4 est une vue partielle d'une solive de plafond et d'un montant interreliés, le montant étant en élévation et la solive en coupe, et avec les branches du montant dans leur position inopérante;
• La figure 5 est une coupe longitudinale partielle d'un montant et d'une solive de plafond avec les branches de montant en position opérante déployée;
• La figure 6 est une vue en plan de dessous d'une solive de plafond et de montants associés en coupe, comprenant des panneaux isolants qui sont illustrés comme étant supportés par les branches du montant lorsqu'en position opérante déployée;
• La figure 7 est une élévation partielle d'un montant dont les branches sont en position opérante, et montrant également en coupe un panneau de mur fixé à une patte de côté du montant;
• La figure 8 est une élévation d'une plaque d'ancrage avec les branches en position opérante pliée;
• La figure 9 est une coupe selon la ligne 9-9 de la figure 8 et avec les branches insérées dans deux panneaux isolants au niveau de leur joint bout-à-bout;
• La figure 10 est une élévation d'une plaque d'ancrage modifiée pour fixer le dessus d'un panneau isolant à une solive de plafond; et
• La figure 11 est une coupe transversale d'une solive de plafond avec la plaque d'ancrage de la figure 10 fixée à celle-ci.

The elongated structural member, according to the invention, made of sheet metal and intended to be used as a component of a wall frame defining a cavity for receiving insulating panels, said member forming a U in section defining a core and two legs connected by said core, said member being used as an upright and said upright having cutouts made in said core and spaced apart longitudinally from each other, each of said cutouts defining an elongated branch terminated by a free point and having free longitudinal edges and an inner end integral with said core along a fold line, each branch being foldable between an inoperative position coplanar with said core and an operating position for which the plane of said branch is at least substantially orthogonal to said core, may comprise in operating position said branches , branches arranged on one side of said core and other branches arranged on the other side of this core.

• FIG. 1 represents a partial perspective view of a wall structure, constructed respecting the lessons of the invention, and with the branches in the deployed operating position ready to impale the insulating panels which will thus be supported and retained in the wall for avoid their collapse;
• Figure 2 is a partial and enlarged longitudinal section of an upright and the transverse beam of Figure 1;
• Figure 3 is the view of Figure 2, but for another embodiment of the transverse beam;
• Figure 4 is a partial view of a ceiling joist and an upright interconnected, the upright being in elevation and the joist in section, and with the branches of the upright in their inoperative position;
• FIG. 5 is a partial longitudinal section of an upright and of a ceiling joist with the upright branches in the deployed operating position;
• Figure 6 is a bottom plan view of a ceiling joist and associated uprights in section, comprising insulating panels which are illustrated as being supported by the legs of the upright when in the deployed operating position;
• Figure 7 is a partial elevation of an upright whose branches are in the operating position, and also showing in section a wall panel attached to a side tab of the upright;
• Figure 8 is an elevation of an anchor plate with the legs in the folded operative position;
• Figure 9 is a section along line 9-9 of Figure 8 and with the branches inserted in two insulating panels at their butt joint;
• Figure 10 is an elevation of a modified anchor plate for securing the top of an insulating panel to a ceiling joist; and
• Figure 11 is a cross section of a ceiling joist with the anchor plate of Figure 10 attached thereto.

The metal frame 10 of the wall of a building, shown in partial view in FIG. 1, conventionally consists, among other things, of a plurality of wall uprights 12, arranged in a parallel and spaced manner. Ceiling joists 14 are provided to connect the upper ends of a number of uprights 12, and also transverse beams 16 and / or 16 ′ can connect the side edges of the intermediate sections of the uprights 12. Floor joists ( not shown) are also provided, and are similar to ceiling joists; the joists receive the lower ends of the uprights 12. Dry wall panels W (fig. 7) are fixed on one or two sides of the wall frame 10 to complete the wall. Each element 12, 14, 16, 16 ′ is made of sheet metal and roughly forms a U in section, to form grooves. The upright 12 is only slightly smaller than the joist 14, so as to fit into the groove thereof. The uprights 12 define a section of conventional shape defining a core 18 and two side tabs 20, each of these being provided with a narrow flange 22 facing inwards. The width of each tab 20 is at least a quarter of the width of the core 18.

Each beam 16, 16 ′ is formed by a base wall 24 and two side walls 26. Each of the two side walls 26 of each transverse beam 16 defines a flange 28 facing outwards. The beams 16 ′ are used for sound insulation purposes, and their side edge 26 opposite the flange 28 is perforated.

When the beams 16 or 16 ′ are not used, the dry wall panels W, normally plaster panels (fig. 7) are fixed directly to the side legs 20 of the uprights 12. If the beams 16 or 16 ′ are used , the wall panels W are fixed to the wall wall 24 of these beams.

The uprights 12 and the ceiling joists 14 are intended to be engaged by conventional insulating panels B, which occupy the space between the uprights 12 and between the dry wall panels W. The panels B are rectangular and are made of fibers of glass whose fibers are generally oriented in the main plane of the insulating panel and thus form easily separable layers.

The side walls 30 of the ceiling joists 14 are connected by screws 32 to the two lugs 20 of the uprights 12, while the flanges 28 facing outwards of each transverse groove member 16 or 16 ′ are connected by screws 34 to one of the legs 28 corresponding to each upright 12. Conventionally, the threaded body of the screws 32, 34 which extend on the side of the grooves of the uprights 12, impaling the insulating panels B, into which they are inserted; but this is not enough to prevent sagging of the B panels.

According to the specific features of the invention, the members made of sheet metal 12, 16, 16 ′ (which are conventional as such) include branches partially cut spaced longitudinally along the sheet metal member.

As shown in Figure 1, pairs of branches 36, 38 are arranged at spaced intervals along the core of the uprights 12. The branches of each pair are spaced and parallel and are oriented upwards. Each branch 36, 38 is made by partially cutting the core 18 so as to create an opening 40, each branch being integrally connected to the core 18 along the fold line 42.

Until they are used, the branches 36, 38 are left coplanar with the core 18, in order to avoid bodily injury when handling the uprights 12. However, when the uprights 12 are installed, the branches 36, 38 of each pair are selectively folded along their fold lines 42, in opposite directions, in an operating position generally at right angles to the core 18, the uppermost branch 36 preferably extending from the side opposite to the side legs 20, the lower legs extending between the side legs 20 (fig. 5). In such a position, the two branches 36, 38 can impale a pair of opposite insulating panels B, which are installed between the uprights 12, leaning against their cores 18 (fig. 6).

As clearly shown, not only the longitudinal axis of each elongated branch 36, 38 is inclined relative to the longitudinal axis of the upright 12, but also the fold line 42 is inclined relative to said longitudinal axis of the upright and also relative to to said longitudinal axis of the branch. Therefore, when the branches are bent towards their operating position, not only do they pass through several layers of fibers of glass insulating panels, but in addition the plane of the branches is inclined relative to the vertical. Only their longitudinal upper edge is provided with a plurality of barbs 44 facing inwards, and they have a beveled point 46. It has been discovered that with this arrangement, the anchoring of the insulating panels B of glass fibers is very effective and that the engagement of the branches in the insulating panel is also facilitated. These panels only have to be pushed against the branches. When it is released, the insulating panel tends to slide down along the branch 36 or 38 inclined transversely, until it abuts on a side tab 20 of the upright 12 or against a panel W wall fixed to the side leg or to a 16 or 16 ′ beam. Each branch 36, 38 is preferably provided with a longitudinal reinforcing rib 48.

As shown in Figures 1 and 3, the branches 54 are made by puncturing each flange facing outward 28 of the transverse beam 16 at spaced intervals along the beam. An opening 52 is thus defined, which corresponds to the shape of a single branch 54. The branch 54 is substantially rectangular, with a short bevelled point 56 and a pin 58 on its edge opposite the side wall 26 of the beam 16 opposite. The inner edge of the branch 54 is integral with the flange 28, and constitutes a fold line 55 at the level of which the branch can be folded from a first position, while it is coplanar with the flange 28, up to a second position oriented towards the outside of the rim 28 and inclined by about 30 degrees from the axis orthogonal to the rim 28 on the outside of the plane passing through the opposite side wall 26, and parallel to the base wall 24, and also intended to impale the insulating panels B. As shown in FIG. 2, the two branches 54 are tilted upwards, so that sagging panels would tend to slide down along the branch to lean on the rim 28. In the transverse beams (Figure 3), which have only one rim longitudinal 28 turns outwards, there is only a single series of branches 54 inclined upwards. The longitudinal axis of the branch 54 is parallel to the longitudinal axis of the rim 28 because the rim 28 is narrow, but its fold line 55 is inclined upwards towards the point 56 relative to the longitudinal axis of the branch 54.

In Figures 8-9, an anchor plate is shown with a modified arrangement of the legs. These branches 76, 78 are cut from a quadrangular plate 80 in order to constitute a corresponding opening 82, 82 ′, respectively.

Their fold line 86 is at right angles to their longitudinal axis. Each branch has barbs 88 along a longitudinal edge only. The barbs 88 of the pair of branches 76 face each other and the branches 76 diverge from each other from their fold line 86. The same is true for the pair of branches 78.

When the branches 76, 78 are folded up to their operating position (FIG. 8), the plate 80 is pressed against the two panels B through their joint C, with the branches inserted in the insulating panels. The plate 80 can be arranged in any orientation; in all cases, these branches, with their highest barbs 88, diverge downward and transversely, so as to exert a slight tension in the insulating panel under the weight of the upper insulating panel. Therefore, the butt joint C is sealed and also the two insulating panels are kept coplanar.

The plate 80 may have holes 90 at the four corners, the two highest holes being used to fix the plates by screws to the side wall 24 of the ceiling joist 14, as shown in FIG. 11, and thus to retain the insulating panels in said joist. For this latter purpose, a plate 80a (fig. 10) can be used, which has only a pair of branches 78a corresponding to the branches 78 of FIG. 8, and which is fixed to the side wall 24 of the ceiling joist 14 (Fig. 11) for example by means of metal screws 92 passing through the orifices 90. Obviously, the anchor plates 80 or 80a can be fixed to a wooden ceiling joist instead of the joist 14 made of metal leaf. The branches 78a have a longitudinal rib 94 for reinforcement. The branches 76 and 78 can be reinforced in the same way.

Claims (11)

1. Structural, sheet metal elongated member adapted to be used as a component of a wall frame defining a cavity for receiving insulating batts (B), said member (12) of U-shape cross-section defining a web (18) and two legs (20) interconnected by said web, said member being used as an upright stud and said stud having longitudinally-spaced struck-out portions made in said web, each struck-out portion defining an elongated prong (36, 38) having a free tip (46) and free longitudinal edges and an inner end integrally-connected to said web at a bending line (42), each prong being bendable between an inoperative position co-planar with said web (18) and an operative position in which the plane of said prong is at least substantially normal to said web,
characterized in that the width of said legs (20) is at least equal to one fourth that of said web (18), and in that, in the operative position of said prong (36, 38), the plane thereof is oblique relative to the longitudinal axis of said member, and, in its plane, said prong is inclined towards one of said legs (20), at least one of said longitudinal edges of said prong being inclined relative to the plane of said web.

2. Structural member according to claim 1, characterized in that the longitudinal axis of said prong (36, 38) is oblique relative to the longitudinal axis of said member when said prong is in inoperative position.

3. Structural member according to claim 2, characterized in that said bending line (42) is oblique relative to the longitudinal axis of said member.

4. Structural member according to one of claims 1, 2 or 3, characterized in that only one of said longitudinal edges of each prong (36, 38) is provided with barbs (44) spaced from each other and oriented towards said bending line, said one longitudinal edge being the one oriented toward said web.

5. Structural member according to one of claims 1 to 4, characterized in that each prong (36, 38) includes a longitudinal reinforcing rib (48).

6. Structural member according to one of claims 1 to 5, characterized in that said prongs (36, 38) are arranged in pairs and extend in opposite directions from said web when in operative position, to thereby impale said insulating batts (B) on opposite sides of said stud.

7. Wall structure comprising, in combination, at least three upright, parallel, substantially spaced studs (12), a horizontal ceiling joist (14) extending transversely and over the top ends of said studs and interconnecting the same, said studs being made from sheet metal, each stud of U-shape cross-section defining a web (18) and two legs (20) interconnected by said web, the webs of the studs being disposed in parallel planes substantially normal to the general plane of the wall structure, wall panels (W) fixed to the legs of said studs on at least one side of said studs, glass-fiber insulation batts (B) made from easily separable layers filling the space between said studs, said insulating batts extending on opposite faces of the web of at least one of said studs,
characterized in that said studs (12) are made from the structural member specified in any of claims 1 to 6, such that said prongs (36, 38) of said members impale said insulating batts (B) through at least some of said separable layers, and a portion of said insulating batts overlying said prongs has a tendency to be displaced by said transversely-inclined prongs towards said wall panels.

8. Wall structure according to claim 7, characterized in that it further includes a sheet metal, horizontal beam (16) extending transversely to said studs (12) and of substantially cross-sectionally U-shape to define a base wall and side walls to form a channel and also at least one out-turned flange (28) along the longitudinal edge of one side wall, said flange (28) abutting against and being fixedly secured to a leg of said studs, said flange being provided with longitudinally spaced elongated prongs (54), each prong (54) having a free tip (56), free longitudinal edges and being integrally connected to said flange by a bending line (55), said prong being bendable about said bending line between an inoperative position coplanar to said flange and an operative position transverse to said flange and oriented away from said base wall, the longitudinal axis of said prong being generally parallel to the longitudinal axis of said flange when said prong is in inoperative position, said bending line being inclined relative to said prong longitudinal axis in a direction towards said tip, said prong, when in operative position, impaling and anchoring a registering insulating batt (B) and being upwardly directed within said insulating batt, the upper one of its longitudinal edges being provided with a barb (58) directed towards said bending line.

9. Wall structure according to claim 7 or 8, including spaced upright, parallel studs (12), a horizontal ceiling joist (14) on the top ends of said studs and interconnecting the same, and glass fiber insulating batts (B) filling the space between said studs,
characterized in that anchor plates (80) are further provided to secure the top of said insulating batts to said ceiling joist, each anchor plate ((80) being made from sheet metal and having a pair of elongated prongs (76, 78), each having a free tip, free longitudinal edges and being integrally connected to said plate at a bending line (86), the bending lines of the two prongs converging towards each other, each prong having barbs (88) directed towards said bending line, said barbs protruding only from the longitudinal edges of the two prongs which face each other, said prongs (76, 78) being bendable about their respective bending lines between an inoperative position coplanar to said anchor plate and an operative position transverse to said anchor plate to be inserted into said insulating batts, said anchor plates being adapted to be secured to said ceiling joist with said prongs below the latter.

10. Anchoring plate (80) destined to retain a pair of panels (B) made from insulating fibers and endwisely joining to each other, said anchoring plate being made from sheet metal and having elongated prongs (76, 78) each having a free tip, free longitudinal edges integral to said plate by a bending line, said prongs being bendable along their respective bending lines so as to allow relative movement of the prongs between a first inoperative position, coplanar to said anchoring plate, and a second operative position, transverse to said anchoring plate,
characterized in that said anchoring plate (80) comprises two pairs of such elongated prongs (76, 78) and in that the bending lines (86) of each pair of prongs converge towards each other, each prong having barbs (88) along its longitudinal edge which is the nearest to the other prong of the pair, the other longitudinal edge of each prong lacking any barb, the prongs of one of said pairs being inserted into an insulating panel, and the prongs of the other pair being inserted into another insulating panel.

11. Elongated, sheet metal, structural member designed to be used as a wall frame component defining a cavity to receive insulating panels, said member (12) being cross-sectionally U-shape defining a web (18) and two legs (20) connected to said web, said member being used as a stud and said stud having struck-out portions made in said web and longitudinally spaced from each other, each of said struck-out portions defining an elongated prong (36, 38) having an endwise free tip and also having free longitudinal edges and an inner end integral to said web along a bending line (42), each prong being bendable between an inoperative position coplanar to said web and an operative position in which the plane of said prong is at least substantially normal to said web,
characterized in that it comprises, in the operative position of said prongs, prongs (36) located on one side of said web and other prongs (38) located on the opposite side of said web.

Images