MXPA06004972A - High-strength concrete wall formwork - Google Patents

Abstract

The aim of the present invention is to increase the stiffness of built-in formwork during positioning thereof, and assist the work of civil engineers so that they can readily determine the contribution of horizontal reinforcements while reducing the production costs thereof. This aim is achieved by means of formwork comprising two mutually facing parallel shuttering walls (1, 1') provided with profile bars forming vertical wales (2, 2') and connected via at least one hinged connecting device for holding the shuttering walls (1, 1') either at a predetermined spacing to define a space for receiving a filler material such as concrete, or in a folded position for storage and transport. The connecting device is characterised in that it includes a first straight horizontal bar (3) parallel to the first shuttering wall (1) and extending through the wales (2) of said first wall (1), and a second straight horizontal bar (3') parallel to the second shuttering wall (1') and extending through the wales (2') of said second wall (1'), wherein said second bar (3') faces the first bar (3), a plurality of connecting bars (4) perpendicularly connect the two horizontal bars (3, 3'), and said connecting bars (4) are pivotable about said horizontal bars (3, 3').

Description

HEAVY DUTY FORM FOR CONCRETE WALL Description of the invention The present invention relates to a formwork intended for the manufacture of a concrete wall or a similar material. This formwork is constituted by two metallic shuttering walls provided with vertical tensioners and placed one opposite the other. Both are connected by a joining device that separates the walls creating a space between them destined to be filled with a material such as concrete. In order to ensure the solidity of the walls in buildings or other concrete constructions, it is foreseen to be able to arrange a supplementary vertical reinforcement inside the walls. A frequently used technique consists of using a formwork system in the form of lost or integrated formwork, that is, a formwork that subsists as if it were an integral part of the wall once the interior was filled with concrete. The documents EP0883719 and W002 / 38878 describe a formwork comprising an outer wall and an inner wall, these walls, called formwork walls, have vertical tensioners constituted by bars profiled generally in a U-shape. The formwork walls are connected by connecting devices each constituted by a rod bent substantially in REF: 172745 zigzag and articulated at the level of the tensioners. These devices maintain a certain space between the shuttering walls in which the concrete is poured. Document WO03 / 010397 describes the formwork according to the documents cited above, in which the elements of the reinforcement are inserted between the lateral sides of the U-profiles of two tensioners placed one opposite the other on each of the walls. Each member of the frame includes at least one vertical bar and at least two horizontal crossbars fitted to slide inside the profile of the tensioners. This element of the reinforcement is added after deploying the shuttering walls by sliding inside the tensioners that act as guide rails. The U-shape of these tensioners ensures the maintenance and stability of said reinforcement element while facilitating its insertion. The different elements of the formwork, such as the formwork walls, the joining devices and the tensioners, are prefabricated in a factory and subsequently assembled with the help of suitable fixings to form the formwork. Therefore, the latter manufactured in this way, leaves the factory in a folded shape thanks to the joints of the connecting elements of the tensioners, and then is deployed on the construction site at the time of being arranged in order to constitute a wall The aforementioned prior art formworks have excellent resistance to significant stresses due in particular to high intensity seismic shocks. However, since the zigzag shape of the joint elements between the walls does not correspond to the rectilinear reinforcements usually used, civil engineers are hardly able to accurately assess their contribution to the strength of the wall. The aim of the present invention is to increase the stiffness of the integrated formworks during their arrangement, to facilitate the work of civil engineers who can easily determine the contribution of the horizontal reinforcements, while reducing the costs of manufacturing them. This objective is achieved thanks to a concrete wall formwork comprising two parallel formwork walls placed one in front of the other and provided with profiled bars forming vertical tensioners and which are connected by means of at least one articulated joint device that allows or maintain the walls of formwork with a separation distance that defines a space intended to receive a filling material such as concrete, or folded for storage and transport, characterized in that the joining device includes a first horizontal rectilinear bar parallel to the first formwork wall and passing through the tensioners of said first wall, a second horizontal rectilinear bar parallel to the second shuttering wall and passing through the tensioners of said second wall, said second bar being located in front of the first bar, and a plurality of connecting rods connecting in a perpendicular manner the two horizontal bars, said connecting rods being hinged around of said horizontal bars. The vertical and horizontal notions are relative since the shuttering assembly can rotate at an angle of 90 °. Thus, the vertical elements initially become horizontal and vice versa. In practice, during the construction of a wall, the formwork is placed on a substantially horizontal surface (floor or paving slab) so that the tensioners are arranged vertically. According to a preferred embodiment, the tensioners are constituted by U-shaped profile bars whose opening is directed towards the interior of the formwork. These tensioners, fixed on the shuttering walls at substantially regular intervals, are perforated by lateral holes of a sufficient diameter to ensure the free passage of a horizontal rectilinear bar. The connecting rods are preferably arranged between the lateral sides of the U forming the tensioners in order to limit their movement along the horizontal bars and maintain a constant interval between them corresponding to the interval between the tensioners. The horizontal bars are also distributed at substantially regular intervals over the height of the shuttering walls. This configuration makes it possible to arrange tie bars at regular intervals both in the direction of the height and in the direction of the length of the formwork. This arrangement ensures a uniform separation between the formwork walls during the pouring of the concrete. The joints of the tie bars around the horizontal bars allow folding the walls of formwork one over the other during storage and transport from the factory to the work site. The main advantage of the joining device according to the invention with respect to the zigzag device of the prior art is that it allows the use of bars with a larger section. In this way, since the horizontal bars parallel to the shuttering walls are rectilinear, it is possible to increase their diameter without major drawbacks in terms of manufacturing, unlike what happens with the joining device formed by a zigzag bar. In this case, how much more important is the section of a bar, the more consequential are the means used to bend and arrange the bar, which reach a high cost. In this way, by suppressing the folding operations of the bars of the joining device, the manufacturing costs are reduced. The arrangement of the bars of the connecting device according to the invention is also easier, since they are arranged by sliding through the holes previously drilled in the tensioners with a suitable diameter. You can also increase the section of the tie bars in proportion to the horizontal bars. In this way, thanks to the possibilities of using large section bars, the joining device becomes more rigid, which allows an easier arrangement of the formwork in place, a better alignment and, consequently, the possibility of reducing the thickness of the plaster layer. The latter consists of a mortar coating applied to the external faces of the formwork walls once the concrete has been poured into the interior of the formwork. Thanks to the greater rigidity, a better surface regularity of the formwork walls can be obtained, which makes possible the distribution of a coating of a regular thickness over the entire surface of the walls without having to compensate the deformations. Another advantage of the structure of the formwork according to the invention is that it allows an easier introduction of a floating reinforcement between the two walls of formwork in the intervals separating the connecting rods. This reinforcement composed of at least two vertical bars connected by transverse bars slides in the intervals from the upper part of the formwork when this is arranged in the location where the wall is to be built before the pouring of the concrete. According to a variant, the reinforcement can be fixed on the upper part of the formwork in order to maintain its position while filling the formwork with concrete. In addition, filler tests have shown that the formwork according to the invention can reduce the risks of concrete segregation. The presence of obstacles during the pouring of concrete, which serve as filters, slowing the fall of concrete and decreasing the risks of segregation. The obstacles during the pouring of the concrete between the two shuttering walls 30 are of the same type in the structure according to the invention as in which it uses a zigzag joining device. In both cases, the elements of the joining device, which traverse the space between the walls, form various obstacles during the pouring of the concrete. The invention will be better understood thanks to the following detailed description, which refers to the appended figures indicated by way of example in no case limitative, in which: - Figure 1 illustrates a perspective view of the formwork according to the invention. - figure 2 illustrates a top view of the formwork of figure 1. - figure 2a illustrates a portion of the formwork of figure 2 when it is folded. - Figure 3 illustrates a top view of a variant of the formwork where the tensioners are placed in staggered fashion. - Figure 3a illustrates a portion of the formwork of the figure 3 when it is folded. Figure 4 shows different variants of reinforcements introduced into the shuttering intervals. Figure 5 illustrates a cross section of the formwork of Figure 4 showing one of the armor variants. - Figure 6 illustrates a top view of a variant of the formwork including an insulating wall. Figure 7a illustrates a variant of an embodiment of the connecting rods with the ends wrapped around the horizontal bars, the tensioners of a formwork wall facing those of the other wall. 7b illustrates the variant of the connecting rods of FIG. 7a with the staggered tensioners. Figure 8a shows a top view of a first variant of joining between two formwork panels using a vertical bar with U-bars. Figure 8b shows the variant of figure 8a seen according to a cut between the shuttering walls. Figure 9a shows a top view of a second variant of joining between two formwork panels using flexible curved rods and two vertical armor bars. - Figure 9b shows the variant of figure 9a seen according to a cut between the shuttering walls. Figure 10 shows a top view of a third variant of joining between two formwork panels using flexible bends folded in U and a vertical reinforcement bar. Figure 1 shows a portion of a formwork for a concrete wall comprising two parallel formwork walls (1, 1") placed one in front of the other, each wall (1, 1 ') is provided with vertical bars profiled in U whose opening is directed towards the inside of the formwork, these are preferably separated at regular intervals along the entire length of the walls These bars called tensioners (2, 2 ') contribute to the stability of the formwork walls (1, 1') , which are generally constituted by relatively flexible lattice metal panels The tensioners (2, 2 ') are fixed to the grid of the shuttering walls (1, 1') by means of a welding, by means of a fixation on pins or with a ligature By means of metallic threads, the formwork walls (1, 1 ') include horizontal ribs distributed at more or less regular intervals above the height, these ribs serve to make the walls more rigid. (1, V) preventing them from deforming with the thrust of the concrete, especially in cases where the intervals between the vertical tensioners (2, 2 ') are large. The meshes of the grid of the shuttering walls (1, 1 ') have a size adapted for the passage of the finest particles of the concrete of the filling. This fine concrete that comes out of the formwork serves for the final wall covering, since it facilitates the application of a mortar plaster (on the outside) or plaster (on the inside of the building). The formwork walls (1, 1 ') are maintained in parallel at a certain distance thanks to the connecting devices distributed over the entire height of the walls. These devices are each constituted by a pair of horizontal rectilinear parallel bars 3, 3"placed opposite each other and connected by a plurality of perpendicular junction bars (4), whose length is substantially equal to the distance separating them. formwork walls (1, 1 ') - The horizontal bars (3, 31) are integral with the formwork walls (1, 1') with which they are maintained thanks to the tensioners (2, 2 '). perforated by holes in the lateral sides of the U-profile with a diameter greater than that of the horizontal bar (3, 3 '). These holes are arranged one opposite the other on each side and in front of the two holes on the sides of the tensioners neighbors, so that a free sliding of the horizontal bar (3, 3 ') is achieved on traversing each tensioner (2, 2') of the formwork wall (1, 1 '). The connecting rods (4) are perforated with a hole in each end that allows the free passage of the horizontal bar (3, 3 ') - This fixing of the connecting rods (4) allows its articulation around the horizontal bars ( 3, 3 ') thanks to which the shuttering walls (1, 1') can be folded against one another during storage or transport. These connecting bars (4) are preferably arranged between the lateral sides of the U forming the tensioners (2, 2 ') in order to prevent their displacement along the horizontal bars (3, 3'), either during the arrangement of the formwork or during the pouring of the concrete. According to a first variant represented by FIG. 2, which is a top view of the shuttering of FIG. 1, the tensioners (2, 2 ') of the shuttering walls (1, 1') are located one opposite the other. The connecting bars (4) are placed between the lateral sides of the U of two opposite tensioners (2, 2 ') and are articulated around the horizontal bar portion (3, 3') between these sides. According to a second variant shown in FIG. 3, the tensioners (2, 2 ') of a shuttering wall (1, 1') are arranged alternately with respect to the tensioners of the opposite wall. In this configuration, only one of the ends of the connecting rod (4) is articulated between the lateral sides of the U of a tensioner (2, 2 ') while the other end is articulated around a portion of the horizontal bar (3, 3 ') located between two tensioners (4). This variant allows to reduce the width Ll of the formwork when it is folded. Indeed, once the formwork has been folded, two tensioners (2, 2 ') are placed side by side on the horizontal bars (3, 3') (figure 3a) instead of overlapping one on top of the other as in the first variant, see figure 2a. The difference in width (L1-L2) of the folded form corresponds to the distance D that separates a horizontal bar (3, 3 ') from the edge of the lateral sides of a tensioner (2, 2'), as illustrated in FIG. Figure 3a. This distance D depends on the dimensions of the tensioners (2, 2 '), the section of the horizontal bars (3, 3') as well as the position of the hole in the lateral sides of the tensioners (2, 2 ') for the passage of said bars. This benefit in the width can present an advantage during the storage or the transport of a large number of stacked formworks due to the reduction of the necessary space. Figure 4 shows several possibilities (a, b, c, d) of metal reinforcements (5) that are placed from the top inside the formwork in the spaces delimited by the tie bars (4) and the walls of formwork (eleven' ) . These reinforcements (5) are installed on site, when the formwork deployed in the location where the wall to be created is placed and before the concrete pouring operation between the formwork walls (1, 1) is placed. '). They are intended to be completely submerged in the concrete and serve to reinforce the wall. The continuous spaces from the top to the bottom of the formwork allow to easily enter different types of reinforcement (5) of height substantially equal to that of the formwork. The examples illustrated in figure 4 are not exhaustive, other reinforcement structures (5) are also possible that include a variable number of vertical bars (7) and / or horizontal bars (6) arranged in different ways provided their dimensions are adapted to the spaces between the shuttering walls (1, 1 ') • The variant (a) of the reinforcement (5) of figure 4 includes two vertical bars (7) connected by a plurality of horizontal bars (6). This armature (5) of floating type is arranged in a central area of the space between the shuttering walls (1, 1 '). It is held temporarily by means of a fixing device during the pouring of the concrete in order to prevent its displacement. The variant (b) comprising four vertical bars (7) connected through horizontal bars (6) offers better stability. The variants (c) and (d) are distinguished from the previous ones by the presence of a fastening device in the form of hooks (8) that allow to maintain said bars in place during the pouring of the concrete without the need of resorting to a device of temporary fixation. The fixing is made on the top and accessible part of the formwork, either on the connecting rods (4) (variant c), or on the horizontal rods (3, 31) (variant d) of the last joining device. The hooks (8) can be replaced by a fixation or a wire tie. Figure 5 illustrates a cross section according to the axis A-A of the formwork of figure 4 showing the variant (d) of the reinforcement (5) attached to the horizontal bars (3, 3 ') and that extends over the entire height of the formwork. Figure 6 shows another variant of the formwork including an insulating panel (9), for example of expanded polystyrene, between one of the formwork walls (1, 1 ') and the corresponding tensioners (2, 2'). The use of this type of formwork no longer requires the additional addition of insulating panels when the construction of the wall is completed, which also contributes to the reduction of construction costs. This insulating panel (9), which extends over the entire surface of the formwork wall (1, 1 '), is fixed to the back of the tensioners (2, 2') by means of screws or fixings (10) passing through the panel (9) thus maintaining the shuttering wall (1, 1 ') against the tensioners (2, 2'). The formwork wall (1, 1 '), which is thus located on the external face of the insulating panel (9), is covered with fine concrete once the space between the insulating panel (9) and the second formwork wall (1, 1') is filled. ). Reinforcements (5) can be inserted in the space between the connecting rods (4), in the same way as in the formwork configuration without insulating panel, as illustrated in figures 4 and 5. Figure 7a shows a example of embodiment of a connecting rod (4) constituted by a steel bar for example, whose ends (12, 12 ') are curved so that they wrap around the horizontal bars (3, 3 '). This embodiment, which represents an alternative to the bars (4) drilled with a hole in each end that serves as a passage for the horizontal bars and that constitutes the articulation around them, can obviously be applied to the examples of formwork described above and illustrated in figures 1 to 6. In order to prevent the displacement of the tie bar (4) along the horizontal bars, at least one of its ends (12, 12 ') is wound around the portion of horizontal bar (3, 3 ') which is located between the lateral sides of the U formed by the tensioners (4, 4') of one or another formwork wall (1, 1 '). In the field of formwork reinforcement, folding or bending of steel bars to their perforation is preferred. In fact, a bar with limbs formed as in figures 7a and 7b will have a greater resistance and directly proportional to its section than a similar bar perforated with through holes.

The preferred configuration shown in FIG. 7b is distinguished by the fact that the tensioners (2, 2 ') of a shuttering wall (1, 1') are located staggered with respect to those of the opposite wall, in such a way that that the connecting rods (4) can be arranged perpendicular to the horizontal bars (3, 3 ') with one of their ends (12, 12') within the profile of the corresponding tensioners (2, 2 '). The advantage of this arrangement is to be able to reduce the width of the formwork, once folded, in a manner analogous to the variant illustrated by figures 3 and 3a, while ensuring a good stability of the formwork when the latter is deployed in the work . In general, a concrete wall is constructed with a formwork consisting of several shuttering panels joined together. Figures 8a (seen from the top of the formwork) and 8b (cut between the formwork walls according to the axis A-A) show a first variant of union between two formwork panels a and b. The continuity of the horizontal bars (3, 3 ') between two contiguous panels (a, b) is ensured by the arrangement on the site, at the junction of the panels (a, b), of a set consisting of a vertical bar (14) on which are welded inverted U bars (13) located with the same separation distance as the horizontal bars (3, 3 ') of the panels (a, b). This assembly (13, 14) is introduced from the top at the point of attachment of the panels (a, b) and subsequently rotates on itself 90 ° so that the U-bars (13) rest on the latter connecting rods (4) at the point of attachment of each panel (a, b) at the same time that said panels remain fixed with respect to each other. Figures 9a (seen from the top of the formwork) and 9b (cut between the formwork walls according to the axis B-B) show a second variant of joining between adjacent panels (a, b). This consists of using flexible steel bars (15) in the form of a loop that are inserted between the shuttering walls at the level of the horizontal bars (3, 3 ') and placed on the last joining bars (4) in the junction point of the panels (a, b). In order to keep these curved bars in place (15), a vertical reinforcement bar (16, 16 ') is introduced by the upper part towards the interior of the space situated between a joining bar (4) near the junction point and the curvature (15') of the formed loop by the bar (15) on each of the two panels (a, b). These armor bars (16, 16 ') thus enter the curved part (15') of the loop (15) at the level of each connecting rod (4) located one on top of the other near the junction point of the two panels ( a, b) of formwork, as illustrated in Figure 9b. The loop-shaped bars (15) are preferably placed on the work site once a first formwork panel has been deployed (a), inserting them between the formwork walls (1, 1 ') on one of the vertical sides at the level of the tie bars (4), so that they protrude from the panel (a). A second panel (b) is then deployed and placed in the extension of the first one introducing the parts of the looped bars (15) protruding from the first panel (a) between the formwork walls (1, 1 ') of the second panel at the level of the tie bars (4). The vertical reinforcement bars (16, 16 ') are placed from the top of the panels (a, b) to complete the joining operation of the two panels (a, b). Figure 10 shows a third variant of connection between two formwork panels a and b, according to which these are connected by means of flexible steel bars bent in U (17). The curved part (17 ') of the U penetrates between the two formwork walls (1, 1') of the first panel (a) at the level of the tie bars (4) and the branches of the U (17") they penetrate between the formwork walls (1, 1 ') of the second panel (b) .These U-bars (17) are preferably introduced, in the factory, between the formwork walls (1, 1') on a vertical side of the panels and joined, for example by means of a wire (18), to the connecting rods (4) in order to be supported when the panel is folded for storage and transport. They are made on the last junction bars (4) of the panel, but are preferably made on the inner junction bars near the last ones for reasons of stability of the union.In the work, a first panel (a) is deployed and place the U-shaped bars (17) on the tie bars (4), the branches of the U (17") are released in order to pass the vertical side of the panel (a). The second panel (b) is located in the extension of the second, so that the branches of the U (17") protruding from the first panel (a) penetrate between the formwork walls (1, 1 ') of this second panel (b) These branches (17") are placed on the last junction bars (4) near the vertical side of the second panel (b). In the same way as in the previous variant, a vertical reinforcement bar (16) is introduced from the upper part of the first panel (a) in the space between the curved part of the U (17 ') of the flexible bars ( 17) and the connecting bars (4). It is noted that in relation to this date the best method known by the applicant to carry out the aforementioned invention, is that which is clear from the present description of the invention.

Claims (15)

1. CLAIMS Having described the invention as above, the content of the following claims is claimed as property. 1. A formwork for concrete wall comprising two parallel formwork walls, placed one in front of the other, provided with profiled bars forming vertical tensioners and connected by at least one articulated joint device that allows or maintain the walls of formwork with a separation distance defining a space intended to receive a filling material such as concrete, or folded for storage and transport, characterized in that the joining device includes a first rectilinear horizontal bar parallel to the first formwork wall and passing through the tensioners of said first wall, a second horizontal bar rectilinear parallel to the second formwork wall and passing through the tensioners of said second wall, said second bar being located opposite the first bar, and a plurality of tie bars that they connect in a perpendicular way the two horizontal bars, said connection bars being articulated around said horizontal bars. The formwork according to claim 1, characterized in that the tensioners of the shuttering walls which face each other generally have a U-shape and are located opposite one another, and because the connecting rods are placed between the lateral sides of the U-profile of two opposite tensioners and articulated around the horizontal bar portion lying between these sides. 3. The formwork according to claim 1, characterized in that the tensioners of a shuttering wall are located in an alternating manner with respect to those of the opposite wall, and by the fact that one of the ends of a connecting rod it is articulated between the lateral sides of the U-shaped profile of a tensioner while the other end is articulated around a portion of the opposite horizontal bar located between two tensioners. The shuttering according to claims 1 to 3, characterized in that the shuttering of the shuttering walls are spaced at substantially regular intervals over the length of the shuttering walls. The formwork according to claims 1 to 4, characterized in that the horizontal bars are spaced at substantially regular intervals above the height of the shuttering walls. The formwork according to claims 1 to 5, characterized in that the tensioners have passing holes on each side side of the U-profile, said holes are placed one opposite the other on each side and in front of the holes of the sides. lateral sides of the neighboring tensioners, in such a way that a horizontal bar can freely slide through each tensioner of the formwork wall. The shuttering according to claims 1 to 6, characterized in that the connecting rods have a hole in each end through which the horizontal bar freely passes, thus forming the articulation of said joint bar around said horizontal bar . The shuttering according to claims 1 to 6, characterized in that the connecting rods have bent ends that wrap around the horizontal bars. The formwork according to claim 8, characterized in that at least one of the ends of the connecting rods is wrapped around the horizontal bar portion lying between the lateral sides of the U formed by the tensioners in a another of the formwork walls. The shuttering according to claims 1 to 9, characterized in that the connecting rods are arranged at substantially regular intervals both in the longitudinal direction and in the direction of the height of the shuttering walls. 11. The formwork according to claims 1 to 10, characterized in that the dimensions of the tensioners, the section of the horizontal bars and / or the section of the connecting rods are adapted according to the demands of resistance to the stresses that the wall constructed with said formwork must satisfy. The shuttering according to claims 1 to 11, characterized in that it includes a reinforcement arranged in the spaces delimited by the connecting rods and the shuttering walls, said reinforcement includes at least two vertical bars of height substantially equal to that of the shuttering and a plurality of horizontal bars connecting the two vertical bars. The shuttering according to claim 12, characterized in that the reinforcement, of floating type, is located in a central area of the space it occupies between the shuttering walls and the connecting rods. The formwork according to claims 12 and 13, characterized in that the reinforcement (5) is maintained, by means of a fixing device in the form of hooks or fixings, or above the horizontal bars or above the bars of union of the last joining device of the upper part of the formwork. 15. The formwork according to claims 1 to 14, characterized in that it comprises an insulating panel located between the tensioners and one of the shuttering walls, said insulating panel, which extends over the entire surface of the shuttering wall, is fixed to the back of the tensioners by means of screws or fixings that, when crossing the panel, maintain the wall of formwork against the tensioners. SUMMARY OF THE INVENTION The objective of the present invention is to increase the rigidity of the integrated formwork during its disposal, to facilitate the work of civil engineers who can easily determine the contribution of horizontal reinforcements, while reducing manufacturing costs thereof. This objective is achieved by means of a formwork comprising two formwork walls (1, V), parallel placed one in front of the other, provided with profiled bars forming vertical tensioners (2, 2 '), and which are connected by at least an articulated joint device that allows either to maintain the shuttering walls (1, 1 ') with a separation distance defining a space intended to receive a filling material such as concrete, or folded for storage and transport. The joining device is characterized in that it comprises a first horizontal bar (3) rectilinear parallel to the first formwork wall (1) and passing through the tensioners (2) of said first wall (1), a second horizontal bar (3 ') rectilinear parallel to the second shuttering wall (1') and passing through the tensioners (2 ') of said second wall (1'), said second bar (3 ') being located opposite the first bar (3') ), and a plurality of tie bars (4) that connect perpendicularly the two horizontal bars (3, 3 '), said tie bars (4) being articulated around said horizontal bars (3, 3').