Field of the invention

The present invention relates to the domain of formworks used for building a wall or a slab in concrete or similar material. More particularly, it relates to the formwork walls or formwork panels which form the formwork itself. A panel includes a latticed metallic sheet extending on vertical bars called stiffeners that are spaced at predefined intervals and fixed to the metallic latticed sheet.

In the case of a wall or a partition, the formwork is formed by vertically arranged parallel panels facing one another. They are usually linked together by a connection device creating a space intended to be filled with a material such as concrete.

Such a formwork system is generally used as a lost or integrated formwork, i.e., it subsists as a part integrated to the wall after having poured concrete into the space separating the two panels.

Technical background

The document WO2005042864 describes a high resistance formwork for concrete wall including two parallel formwork walls placed facing one another and provided with profiled bars forming vertical stiffeners. The walls are connected by an articulated connection device allowing maintaining between the formwork walls a distance defining a space that is intended to receive a filling material such as concrete. The articulation of the connecting device allows folding the formwork for its storage and transportation. The connection device includes a pair of horizontal rectilinear bars parallel to the formwork walls. The bars placed facing one another pass through the stiffeners of the respective formwork walls. The connection device also includes a plurality of connection bars linking perpendicularly the two horizontal bars about which they are articulated.

The formwork with its two formwork walls provided with stiffeners and assembled with the connection devices is prefabricated at factory. It is transported to the building site in the folded form thanks to the articulations of the connection elements on the stiffeners. The advantage of such a formwork is its handiness and its rapidity of mounting on the building site with a minimum of tools and labor. In order to minimize the construction global costs and to assure a high quality of the erected walls, each step of the production of the formwork has to be optimized as well in rapidity of execution as in reliability of the components or finished product. An important component is here the formwork wall or the formwork panel conceived to resist the deformations due to the pressure and the weight of the concrete poured into the formwork formed by these panels.

The document FR2712016 describes a process of manufacturing formwork walls comprising an expanded metal plate provided with V-shaped parallel ribs. This latticed plate is fixed to a plurality of stiffeners spaced at regular intervals and arranged perpendicular to the ribs of the plate. The process includes an operation of clamping the stiffeners on the plate wherein a first step consists of cutting strips by stamping on one of the stiffeners faces. During a second step, these strips are bent on the ribs of the plate after their passage through the lattice on each side of the ribs.

The document FR2497857 describes a prefabricated panel comprising a framing formed by profiled stiffeners covered by a metallic latticed sheet and at least one layer of coating material such as concrete. The stiffeners are provided with strips coming from one of the faces of the profile, passing through the latticed sheet for being bent on the external face of the latticed sheet in order to attach it to the stiffeners.

The document WO2007/079989 describes a formwork panel for walls or concrete slabs comprising a latticed metallic sheet on the one hand reinforced by a plurality of stiffeners formed by rigid profiled metallic bars integral with one face of said sheet arranged in parallel one to another and spaced at predefined intervals, and on the other hand by ribs integral with the lattice of the sheet. These ribs are spaced at predefined intervals and cross the stiffeners preferably at right angles. The latticed sheet is fixed on the stiffeners by means of a crimping carried out on at least one intersection between the ribs and the stiffeners. The crimping is achieved so that at least one strip that comes from the metal of the rib holds the stiffener by passing through a corresponding orifice in said stiffener. The strip is bent down against the internal face of the stiffener around the edge of the orifice so as to lean the latticed sheet against the stiffener. According to a practical example of manufacturing, the orifice is stamped in the form of a rectangle in order to create strips at the same time in the metal of the ribs and on that of the stiffener attached to the two opposite smaller sides of the rectangle. The strips directed towards the internal face of the stiffener profile are then bent down against this face in a zone adjacent to the smaller sides of the rectangle.

Tests made with formwork made up of latticed panels that are crimped according to the above method have shown that under a high pressure exerted by the concrete poured between the two panels, the strips of the ribs bent down can straighten up and pass through the orifice of the stiffener. This loosening of the crimping leads to a local detachment of the latticed sheet from the stiffener and causes undesirable swells of the external surface of the formwork filled with concrete. The detachment of the latticed sheet can also spread to the whole formwork wall if it is not detected in time at the moment of pouring the concrete. This phenomenon is more accentuated when the quality, the thickness and the hardness of the steel used for the production of the lattice are insufficient.

When the strips are bent on the external face of the walls as in the clamping of the stiffeners to the lattice described in the document FR2712016, the pressure of the concrete can also involve a straightening of the strips. These strips, when brought out of the meshes of the lattice, cause the disconnection of the formwork wall and deformations on the surface of the built wall. The hooking of the formwork wall to the stiffeners as disclosed in the document FR2497857 also presents a similar drawback of straightening of the hook under the pressure of the concrete.

A fastening with screws or others fixation means adds supplementary pieces to the panel, which is not desirable when the manufacturing has to be rationalized and automated at the most, particularly for mass production.

In relation to the spot welding, the crimping of the lattice to the stiffeners presents some important advantages, namely:

- the crimping can be carried out with an automated tooling equipment, independently of external conditions and without alteration of the steel surface treatment which is generally galvanized. - eventual fastening deficiencies due to the crimping are visible immediately and can be corrected before the formwork leaves the factory.

- the crimping does not degrade the steel surface treatment as would do the welding by oxidation of the fastening points of the latticed sheet thus causing damage to the lifetime of the wall built with the integrated formwork.

- the crimping does not require a particularly clean environment free of dusts involving onerous manufacturing conditions to be put in place and to be respected.

Brief description of the invention

The aim of the present invention is to notably improve the strength of the crimping of the prior art by maintaining the advantages specific to the crimping in relation to the fastening of the lattice by welding and other means of attachment. Moreover, the crimping allows reducing production costs and rationalizing the mass production of the formwork panels at the factory by ensuring a maximum resistance of the walls built with this kind of formwork.

This aim is achieved by a panel for formwork of concrete walls or slabs comprising a latticed metallic sheet reinforced on the one hand, by a plurality of stiffeners formed by profiled rigid metallic bars arranged in parallel one to another and spaced at predefined intervals, and on the other hand by ribs integrated to the lattice of the sheet spaced at predefined intervals and crossing the stiffeners, the latticed sheet being fixed on the stiffeners by means of a crimping carried out on at least one intersection between a rib and a stiffener so that at least one part of the metal of the rib, forming a strip having one end attached to the rib and one free end, holds the stiffener by passing through an orifice in said stiffener, the orifice having a shape corresponding to the shape of the strip, said panel is characterized in that the strip includes, close to the end attached to the rib, a first part of smaller width than the width of a second part close to the free end, the outline of the two parts forming at their junction at least one step at a predetermined distance from one of the ends of the strip, said step forming a abutment preventing the disengagement of the strip out from the corresponding orifice under the effect of pressure forces exerted on the latticed metallic sheet. In practice, at construction of a wall, the formwork is placed on a substantially horizontal surface (ground or floor slab) so that the stiffeners of the panels are arranged in the vertical direction. The ribs of the latticed sheet cross perpendicularly the stiffeners and are thus horizontally arranged and preferably at regular intervals on the whole height of the panel. The notions of vertical and of horizontal are relative because the whole formwork can be turned according to a 90° angle. Thus the originally vertical elements become horizontal and vice versa.

A panel can be used as a simple wall and placed either vertically against a wall to form a simple formwork, or horizontally for production of slabs.

In the case of a wall or a partition, the formwork is formed by two panels arranged vertically and in parallel facing each other. They can be connected by a connection device creating a space intended to be filled with a material such as concrete. A panel can be vertically arranged against a wall to form a simple formwork. It can also serve as a base for the construction of different civil engineering works such as a floor or a roof slab, poles, girders, pillars, etc.

The ribs are profiled V-shaped or U-shaped elongated parts of full metal integral with the lattice of the sheet serving to stiffen the lattice in the same way than stiffeners. The latticed sheet is preferably fixed to each intersection of a rib with a stiffener in order to minimize the deformations caused by the weight of the concrete poured into the formwork using these panels. This fastening is carried out by a crimping in which at least one strip of the metal of the rib is cut by stamping and then bent in a corresponding orifice of the stiffener.

At the place where the width of the strip changes, the step forms an abutment that prevents the strip getting out from the orifice under the effect of pressure forces exerted by the concrete on the lattice. This abutment leans against the stiffener on a side of the narrow part of the corresponding orifice.

A preferred shape of the strip includes two steps forming two symmetrical abutments placed facing each other. These abutments lean against the stiffener on each side of the narrow part of the orifice under the effect of the pressure forces on the latticed sheet. Brief description of the drawings

The invention will be better understood thanks to the following detailed description with reference to the enclosed drawings, which are given as non-limitative examples, namely:

- Figure 1 represents a crimping according to the invention at an intersection between a stiffener and a rib of the latticed sheet.

- Figure 2a shows a schematic view of the crimping strips straightened on each side of the orifice.

- Figure 2b shows the strips of figure 2a bent down on each side of the orifice.

- Figure 2c shows the position of the strips and the effect of the abutments when a pressure is exerted on the latticed sheet.

- Figure 2d shows an example of bent down opposite strips each one including a step arranged in quincunx with respect to one another.

- Figure 3a represents a front view of the end of a stamp for cutting the strips and forming the orifice through which the strips pass for achieving the crimping.

- Figure 3b shows a top view of the end of the stamp of figure 3a

- Figure 3c shows an orifice as it would be machined in a fixed support with an outline corresponding to the one of a section of the stamp.

- Figure 4 schematically shows on a cross section view of a stiffener the step of bending down the stamped strips against the internal face of a stiffener.

- Figure 5 schematically shows the result obtained after bending down the strips against the internal face of the stiffener.

- Figure 6 schematically shows an embodiment of the crimping in which the orifice includes a strip on only one side. Strips are alternatively retained on each side of the orifices stamped along a rib. Detailed description

A formwork panel (1 ) includes a latticed metallic sheet (2) extending on a plurality of stiffeners (3) arranged in parallel with respect to one another preferably at regular intervals. The latticed sheet (2) includes a plurality of parallel ribs (4) crossing the stiffeners (3), preferably perpendicularly, and also arranged at regular intervals on the surface of the sheet (2). The latticed sheet (2) is preferably crimped at each intersection between the ribs (4) and the stiffeners (3) in order to reduce to a minimum the deformations due to the pressure of the concrete and to ensure an optimal fastening.

The stiffeners (3) are made with profiled steel bars generally U-shaped as shown by the section views of figure 4 and 5. The latticed sheet (2) is applied against the lower faces of the U-shaped profiles and maintained by the ribs (4) at each intersection with these profiles. According to one preferred embodiment, the ribs (4) are also U- shaped profiled with the flat lower part placed on the stiffeners (3).

The lattice (2) is made according to a known process, by stretching or spreading a steel sheet punched by means of a plurality of blades. The ribs (4) are formed by embossing the sheet at predefined intervals before spreading. The ribs (4) thus form integral parts of the latticed sheet (2) without being added on the lattice as supplementary pieces. According to a practical example, the width of the U of the ribs (4) is of 1.5 to 2.5 cm with a width of the U of the stiffeners (3) of about 5 cm.

The profile of the ribs (4) can have a different shape without flat part applied against the stiffener as for example in the shape of a V where the line is placed on the stiffener (3). In this case, the crimping operation locally deforms the rib (4) in order to make it flat near the strips (6). This deformation is judged acceptable both for the solidity of the crimping and of the surface planahty of the panel where the concrete coating compensates the irregularities.

Figure 1 shows an enlarged view of a preferred example of crimping according to the invention at the intersection of a rib (4) and a stiffener (3) seen from its internal face at the bottom of the U profile. The rib crossing perpendicularly the stiffener leans on the external face of the U profile. The stiffener (3) and the rib (4) have an orifice (5) through which strips (6, 6') pass; the strips come from a stamping performed in a same time in the rib (4) and in the stiffener (3). The strips (6, 6') are bent, for example, on two opposite edges of the orifice (8) towards the inner face of the U- shaped profile as shown in figure 2a, the strips (6) coming out from the rib (4) passing through the orifice (5). Each of them has a part of a given width (5.6 mm according to a practical example) whose end is attached to the rib (4), respectively to the stiffener (3) and a larger part (8 mm for example) having a free end.

The outline of the junction of the narrow part and the larger part of a strip (6, 6') form two symmetrical abutments (7, 7') preferably placed facing each other. These abutments (7, T) have an outline preferably forming a right angle and are located at a predetermined distance from one of the ends of the strip (6, 6'), for example at about 5 mm from the free end of the strip (6, 6'). Each abutment (7, 7'), having 1 .2 mm width in the example, has a function of locking the strip (6) coming out from the rib (4) once bent on the edge (8) of the orifice (5). In fact, the width of the orifice (5) close to the attached end of the strip (6) is smaller than the width of said orifice (5) close to its center. This width difference forming the abutments (7) allows preventing the strips (6) coming from the rib (4) getting out of the orifice (5) by pressure on the latticed sheet (2).

It should be noted that other forms of orifice and corresponding strips whose outline include one or more steps forming one or more abutments arranged in a symmetrical or asymmetrical way are also possible as long as their locking function is maintained.

Figure 2a shows a first option of the crimping in which the respective strips (6, 6') coming out from the stiffener (3) and the rib (4) are bent substantially at a right angle relative to the plane of the orifice (5). A crimping of this type presents a clearance equivalent to the distance separating the attached end of the strip (6) and the abutments (7) (about 5 mm according to the example). An internal pressure P derived from filling concrete on the latticed sheet (2) will make the sheet (2) advance with respect to the stiffeners (3) by leaving a space equivalent to the clearance between the stiffeners (3) and the ribs (4). This movement remains limited to the clearance thanks to the abutments (7) of the strips (6) which prevent the disengagement of them out from their corresponding orifices (5). When the distance between the attached end of the strip and the abutments corresponds to the thickness of the metal of the stiffener, the clearance is reduced to a minimum. According to a second option the strips (6, 6') are bent down against the internal face of the stiffener (3) at the bottom of the U-shaped profile by means of a suitable tool. Figure 2b shows a crimping in which the two strips (6, 6') of the stiffener (3) and of the rib (4) are symmetrically bent along their ends attached to the edge (8) of the orifice (5) in order to be applied against the face of the stiffener (3) on two opposite sides of the orifice (5) (arrows R). This kind of crimping offers a better holding of the lattice (2) on the stiffeners (3) as it leaves no clearance between the rib (4) and the stiffeners (3) as presented in the first option.

Figure 2c shows the behavior of a crimping (6, 6'), whose strips are bent down as represented in figure 2b when pressure forces P are exerted on the latticed sheet (2).

The pressure P causes the straightening of the strips (6) coming out from the ribs (4) in order to form an angle of about 90 degrees with the plane of the orifice (5) or that of the internal face of the profile of the stiffener (3), the strips (6') coming out from the stiffener (3) remaining bent down. The abutments (7) lean on the internal face of the stiffener (3) on the edge (8) of the narrow part of the orifice (5) by preventing the strip

(6) getting out. As in the option of figure 2a, the latticed sheet (2) or more precisely the rib (4) moves away from the stiffener (3) at a distance that corresponds at maximum to the length of the narrow part of the strip (6). The lattice (2) disconnecting problem specific to the crimping with strips having a constant width on their whole length as described in the document WO2007/079989 is thus solved thanks to the abutments (7) serving as locking mechanism.

The example of figure 2d shows the strips having each a step serving as an abutment. The quincunx arrangement of the steps prevents a torsion effect of the rib at the crimping level under the effect of pressure forces. The asymmetrical shape of the orifice (5) corresponds to the shape of each of the strips. The preferred arrangement of the crimping corresponds to the one comprising symmetrical strips with two steps forming two abutments facing each other as represented by figures 1 , 2a, 2b and 2c.

The advantage of the crimping is that it can be carried out quickly with a suitable tool machine allowing, in a first time, stamping the ribs (4) and the stiffener (3) and, in a second time, bending respectively the strips (6) of the rib (4) and the strips (6') of the stiffener (3) into the orifice (5) of the stiffener (3). In order to preserve a precise alignment of the strips (6) with the corresponding openings (5), the operations of stamping and bending down the strips (6, 6') are carried out simultaneously when the ribs (4) and the stiffeners (3) are maintained in their definitive position on the machine.

According to an embodiment, the orifices (5) of the stiffeners (3) can be stamped during a preliminary step. In this case, only the strips (6) coming out from the ribs are bent towards the internal face of the profile of the stiffener (3) during crimping. This embodiment requires a previous positioning of the stiffeners (3) and a precise alignment of the orifices (5) with respect to the ribs (4) of the lattice (2) in order to stamp and bend down the strips (6) in optimal conditions.

The invention also concerns a tooling for crimping a plurality of stiffeners (3) to a latticed sheet (2) including a plurality of ribs (4) forming a formwork panel (1 ). The tooling comprises a stamp (9) and a support (14) suitable to form an orifice (5) and two strips (6) at an intersection between a rib (4) and a stiffener (3). The strips have a first part with one end attached to the rib (4) and one free end. The tooling is characterized in that the end of the stamp (9) forms a symmetrical point with a central line (12) and two pairs of lateral lines (13) inclined and perpendicular to the central line (12) and in that the section includes a central part that is wider than the width of the parts placed on both sides of the central part. The stamp (9) and the support (14) are able to create two symmetrical opposite strips (6) including, close to the end attached to the rib (4), a first part of smaller width than the width of a second part close to the free end. The outline of the two parts forms at their junction two abutments (7) placed facing each other at a predetermined distance from one of the ends of the strip (6).

The stamping of the strips (6, 6') and the orifice (5) as illustrated by figures 2a to 2c is carried out with a tooling comprising a stamp (9) and a support (14) as represented by figures 3a to 3c. The section of the stamp (9) has a shape that corresponds to that of the orifice (5) with the part that is close to the center being wider than the parts placed on both sides of said center. The end forms a point with a central sharp line (12) allowing creating the free ends of each strip (6, 6'). The cutting of the remainder outline of the strips (6) with the abutments (7) is carried out by means of two pairs of side sharp lines (13) perpendicularly inclined on each side of the central line (12). Figure 3b shows a top view of the point of the stamp (9) with the central line (12) passing through the wide part of the section. During crimping operation, the stamp (9) firstly passes through the metal of the rib (4) then through that of the stiffener (3) so that it cuts in a single operation the strips (6, 6') and the orifice (5) at the same time in the rib (4) and in the stiffener (3).

The support (14) disclosed in figure 3c, including a window (15) similar to the orifice (5) created by the stamp (9), is placed against the internal face of the stiffener (3) facing the stamp (9) in order to make it slide after having formed the strips (6, 6') in the metal of the rib (4) and of the stiffener (4). Moreover, the window (15) of the support (14) has a depth that is sized so as to place the strips (6, 6') perpendicularly to the plane of the window (15). In order to obtain a more tightened crimping, the strips (6, 6') are then bent down against the internal face of the profile of the stiffener (3) with a suitable tool after withdrawal of the stamp (9) and the support (14).

Figure 4 shows a schematic shape of a stamping tool (9) allowing to carry out an orifice (5) at the same time through the rib (4) and through the stiffener (3) by forming strips that are opposite with respect to one another, each one having one end attached to the edge (8) of two opposite sides of the orifice (5) and one free end.

During a second facultative step, the strips (6, 6') directed towards the internal face of the profile of the stiffener (3) are bent against this face by means of a bending tool (16) from the lower face of the panel (1 ). A supporting part of the stamp not represented and intervening after the withdrawal of the stamp leans on the rib (4) on a zone near the orifice (5) in order to maintain the assembling of the rib (4) and stiffener (3) when the bending tool (16) bents the strips (6, 6'). This tool (16) includes an end with a shape dimensioned and adapted so as to bend down the strips (6, 6') against the internal face of the stiffener (3) as shown in figure 5.

According to an embodiment, the end of this bending tool (16) can extend during its advance in order to make the strips (6, 6') completely flat against the stiffener (3).

It should be noted that the crimping according to the invention can be carried out with a single strip (6, 6') when for instance the width of the U of the stiffener is insufficient to contain two symmetrical opposite strips (6, 6') and bent down on both sides of the orifice (5). In this case, the outline of the orifice (5) corresponds to the outline of a strip (6) with two parts of different width as represented by figures 1 , 2a, 2b and 2c by considering only the left or right half of the symmetry axis A. The stamp (9) also adapted to form only one strip includes an asymmetrical point whose shape corresponds to the left half or to the right half relatively to the symmetry axis A of the point represented by figures 3a and 3b. The window (15) of the support (14) obviously has a shape that corresponds to that of the halves relatively to the axis A of the shape shown by figure 3c.

Figure 6 shows a crimping example with one single strip (6, 6') per orifice (5). In order to avoid the disconnecting of the latticed sheet (2) by a shifting movement of the stiffeners (3), the stamping of the strips (6, 6') is carried out so that they are alternatively retained on the right and left sides of the orifices (5) aligned along a same rib (4). Moreover, the strips (6, 6') can also be alternatively attached on the right and left sides of each orifice (5) along each stiffener (3). They present thus a quincunx arrangement on all the intersections between the ribs (4) and the stiffeners (3) of the panel (1 ).

The manufacturing of a panel (1 ) is carried out by a machine on which the latticed sheet (2) is temporarily maintained flat on the stiffeners (3) by means of clamping devices.

The steps of stamping and bending the strips (6, 6') are carried out generally simultaneously on a plurality of intersections between at least one rib (4) and some stiffeners (3) by a plurality of stamping (9) and bending (16) tools. These tools aligned on at least one support parallel to the ribs (4) and arranged facing said intersections move forward according to the interval between the ribs (4) in order to crimp the latticed sheet (2) at each intersection of the ribs (4) with the stiffeners (3).

The present invention also relates to a formwork comprising two panels (1 ), as described above, placed facing each other and connected by connection elements that are articulated to the panels through the stiffeners (3). These connection elements allow either maintaining a space between the panels (1 ) intended to receive concrete or a similar material, or folding together the panels for storage and transportation. The wall erected with an integrated formwork as described above also constitutes an object of the present invention. The space between the two panels (1 ) is filled with concrete or a similar material.

A slab in concrete made with a panel (1 ) described above is also an object of the present invention. The slab is manufactured by placing the panel (1 ) generally horizontally with the face including the stiffeners (3) directed upwards. Reinforcement frameworks are generally placed on the stiffeners before pouring on this face a preferably uniform concrete layer covering the stiffeners (3) and the frameworks. The quantity of the frameworks and the thickness of the concrete layer are determined according to the bearing surface of the slab, loads, quality of the concrete, etc.