EP0767282B1 - Collaborating metallic girder - Google Patents

Abstract

The beam is made by the cold assembly of two sheet metal profiles (6,9). The inner profile (9) is attached to two vertical side walls (6A,6B) of the outer one. This forms a horizontal transverse partition (12) with a cavity (8) above it which can be filled with concrete. The side walls of the cavity have elements which engage with the cast concrete. The cast concrete is formed either by the in-turned upper edges of the inner profile or by the fixings (10) which join the two profiles together. The profiles are joined so that the cavity formed between them has a depth which allows the concrete to perform essentially under compression while the beam is under load.

Description

The invention relates to a collaborating metal beam for the construction of buildings, i.e. a composite beam comprising a metal part and concrete part which work together to support a load.

The invention relates more particularly to the metal part of such a beam.

We can for example use this type of beam to support a floor in reinforced concrete, which can itself be of the "collaborating" type.

We then proceed by pouring a concrete slab on a ribbed sheet, which it serves as formwork and strong reinforcement.

After hardening of the concrete, the ribs of said sheet then provide mechanical collaboration between said sheet and hardened concrete.

To build the floor, you must be able to install the sheet metal panels of the floor on beams.

The beams form a network partially shown in Figure 1.

As the beam, steel beams 1 are usually used I-shaped hot sections

When we pour concrete, we pour at the same time on the sheets ribbed and on the upper faces 2 of the beams 1.

To ensure effective mechanical collaboration between the beams 1 and the concrete (not shown), beforehand, on these faces 2, concrete connectors (or "concrete connectors" 3), in the form of short rods; preferably, the end of these rods is prominent to ensure a better bonding of concrete.

Thanks to these concrete connectors 3, the poured concrete is not only secured to the ribbed sheets but also to the beams 1 themselves by through the concrete connectors 3 and the beams thus formed are said to be "Collaborating".

Concrete therefore reinforces the beams 1 by this collaborative effect and works there mainly in compression; the part of the slab in concrete which collaborates with the beam 1 is called "compression table".

According to this classic design of collaborating beam, the support that the beam brings to the floor is ensured both by the beam 1 in I and by the concrete slab of the floor itself (not shown).

• les connecteurs-béton 3 sont coûteux et leur pose est onéreuse ;
• sauf à rajouter des éléments de coffrages supplémentaires, il n'est pas possible de choisir l'épaisseur de la table de compression indépendamment de celle de la dalle, ni de faire varier cette épaisseur le long de la poutre - pour faire des poutres à profil d'épaisseur variable. Il n'est pas possible non plus d'obtenir à coup sûr une poutre dont les axes neutres présentent une position mécaniquement optimisée.
• sur un même chantier, il faut disposer d'autant de types de poutres à chaud qu'il y a de poutres de caractéristiques différentes à poser et à construire.

This method of constructing a collaborating floor on a collaborating hot beam has several drawbacks:

• the concrete connectors 3 are expensive and their installation is expensive;
• except adding additional formwork elements, it is not possible to choose the thickness of the compression table independently of that of the slab, or to vary this thickness along the beam - to make profile beams of variable thickness. It is also not possible to obtain without fail a beam whose neutral axes have a mechanically optimized position.
• on the same site, it is necessary to have as many types of hot beams as there are beams of different characteristics to lay and build.

Patent GB 2 189 525 describes a collaborating floor mounted on composite sheet-concrete beams.

The beams of this floor are made by assembling profiles of metal sheets, comprising approximately two side profiles parallel, U-shaped, the two openings of the U-shape facing each other and an internal sheet connecting the two lateral profiles by the lower leg of the U-shaped.

The assembly thus produced forms a cavity in the beam.

The upper legs of the U-shaped side profiles close partially the cavity from above, while leaving sufficient opening for pouring concrete into the cavity.

The depth of this cavity corresponds to the height of the beam, on its entire length.

To build the floor, concrete is poured at the same time on the collaborating sheets of the floor and in the cavities of the beams.

• à une charge de béton liquide très importante au moment de la coulée, que la partie métallique de la poutre n'est forcément capable de soutenir sans fléchir, ce qui rend nécessaire la pose de soutènements provisoires de la poutre elle-même.
• à des poutres pesant très lourd qui nécessitent des superstructures de bâtiment sur-dimensionnées.

In this process of construction of a floor collaborating on a composite beam offering an internal cavity, the thickness of concrete poured into the beam necessarily corresponds to the height of the beam, which leads to:

• at a very high load of liquid concrete at the time of casting, which the metal part of the beam is not necessarily capable of supporting without bending, which makes it necessary to install temporary supports for the beam itself.
• very heavy beams that require oversized building superstructures.

In this configuration, it is also not possible to obtain suddenly on a beam whose neutral axes have a position mechanically optimized.

Patent DE 216 531 also describes a composite sheet-concrete beam.

The metal part of the beam here offers an internal cavity whose depth, variable along the beam, is less than the height of the beam: in fact, the sheet forming the bottom of the cavity and joining the two walls lateral, forms an arch whose high point corresponds approximately to the middle of the beam.

The concrete poured into this composite beam then forms an arch.

The metal formwork of the concrete and the concrete arch then serve set of support means.

On the beams described in these two documents (GB 2 189 525 and DE 216 531), there is no means of sheet-concrete collaboration (this is why we speaks of composite beams).

The absence of sheet-concrete collaboration means in the document DE 216,531 may affect the integrity (and sustainability) of the beam if the thickness of the concrete arch is insufficient; conversely, for a thickness higher concrete, we find the disadvantages of weight cited previously.

In document GB 2 189 525, the upper legs of the shapes in U lateral profiles, which partially close the cavity, do not exert collaborating function, this function being useless here to maintain the integrity of beam.

Indeed, the concrete part, extending over the entire height of the beam, works as much in traction (lower part) as in compression (part superior) and no force is exerted to separate the concrete part of its formwork.

The object of the invention is to avoid the abovementioned drawbacks, in particular of offer an economical type of collaborative beam, easy to assemble, easy to mount, easy to access features optimal mechanical (especially for the position of the neutral axes).

• des rebords supérieurs dudit profilé interne, lesdits rebords pénétrant vers l'intérieur de la cavité
• et/ou des moyens d'assemblage dudit profilé interne avec lesdites parois latérales qui font saillie vers l'intérieur de la cavité,

et en ce que la fixation dudit profilé interne sur lesdites parois latérales est adaptée pour obtenir une profondeur de cavité permettant au béton coulé dans ladite cavité de travailler essentiellement en compression lorsque ladite poutre est en charge.The subject of the invention is a collaborating metal beam intended to support a load, in particular a building floor, produced by assembling cold sections of metal sheets, comprising at least two vertical side walls made of approximately parallel sheet metal and an internal section fixed on the two said side walls for connecting them together, said side walls and said internal profile being configured to constitute a cavity in the upper part of said beam, the depth of which extends, from bottom to top, from a bottom of cavity formed by said internal profile up to an opening formed between upper edges of said side walls, said cavity being intended to receive concrete poured through said opening characterized in that the walls of said cavity are provided with means for collaborating with concrete who understand :

• upper edges of said internal profile, said edges penetrating towards the inside of the cavity
• and / or means for assembling said internal profile with said side walls which project towards the inside of the cavity,

and in that the fixing of said internal profile to said side walls is adapted to obtain a depth of cavity allowing the concrete poured into said cavity to work essentially in compression when said beam is loaded.

The invention also relates to the metal beam according to the invention containing concrete in said cavity.

Said cavity therefore forms a formwork for the concrete.

After pouring and setting the concrete, the beam includes a lower part purely metallic intended to work essentially in traction and a upper part, mainly of concrete, intended for working essentially in compression and called "compression table".

For a given support application (for example: span between supports, weight and nature of the floor to be supported, maximum floor load), we can define, in a manner known in itself, the characteristics mechanically optimal of a beam.

• de dimensionner l'assemblage de la poutre pour obtenir la position mécaniquement optimale des axes neutres,
• de choisir l'épaisseur de la table de compression en adaptant la profondeur de la cavité, c'est à dire en adaptant la hauteur de fixation du profilé interne sur les parois latérales au moment de l'assemblage de la poutre.

With the type of beam that the invention proposes, it is then very easy to obtain a collaborating beam that is both light and adapted to these characteristics, in particular thanks to the possibility:

• to size the beam assembly to obtain the mechanically optimal position of the neutral axes,
• to choose the thickness of the compression table by adapting the depth of the cavity, that is to say by adapting the fixing height of the internal profile on the side walls when assembling the beam.

The means of collaboration with the concrete with which the walls of the cavity guarantees the maintenance of the integrity of the beam and prevents concrete to come out of its formwork, especially in cases of small thicknesses of the compression table.

On the same site, from the same profiles, we can therefore carry out beams with very different characteristics.

If the beams are intended to support collaborating floors, we can proceed as in the prior art, in particular by pouring in a single operation the concrete in the beam and the concrete on collaborating sheets of the floor.

In this case, the characteristics of the collaborating beam according to the invention can be determined regardless of the thickness of the concrete slab of the floor, without adding formwork elements additional.

Conversely, it is also possible to make the beams entirely regardless of the floor itself, so do not pour concrete, in a first, that in the beams.

It is also possible to produce, from the beams according to the invention, prefabricated collaborating beams, usable for example to support prefabricated floors.

An advantage of the invention lies in the ease of assembly of the beam directly on the construction site from cold sections in sheet metal cut to the required dimensions.

The profiles are assembled, for example using self-tapping screws, nails or rivets.

Another advantage is to simplify site supplies; where it should have been, using hot profiled beams, to supply in beams of different characteristics (height, thickness of steel), the same cold sections can be used for beams with very characteristic different.

• par des rebords supérieurs dudit profilé interne, ces rebords pénétrant vers l'intérieur de la cavité.
• par des moyens d'assemblage dudit profilé interne avec lesdites parois latérales qui font saillie vers l'intérieur de ladite cavité.

According to additional characteristics of the invention, the beam-concrete collaboration can be ensured in the following manner:

• by upper edges of said internal profile, these edges penetrating towards the inside of the cavity.
• by means of assembly of said internal profile with said side walls which project towards the inside of said cavity.

These assembly means can be for example screws, nails or rivets which protrude towards the interior of the cavity and, therefore lying embedded in concrete after casting, also serve as means of collaboration.

Advantageously, this therefore eliminates any costly installation operation of "concrete connectors".

According to a preferred arrangement of the invention, said internal profile is U-shaped or Σ-shaped with the opening facing up; the walls side of the beam are then integral with the legs of the U or Σ.

According to a particular provision of the invention, said internal profile has a suitable shape, particularly curved, to vary the depth of said cavity along the beam.

It then becomes possible and easy, according to the invention, to obtain beams with compression table of variable thickness along the beam, whose profile is adapted to the distribution of the efforts to be taken care of.

The invention also makes it possible to solve a problem posed by generally the superposition of several beam networks, illustrated here as following.

We know that for a collaborating floor, the maximum admissible range is around 4 m.

To support this type of floor, it is therefore necessary to have a network of beams distant from each other at most 4 m.

Figure 1 presents a case where the main beams 4 of a network existing are more than 4 m apart.

Before building the floor, it is then advisable to build a network of secondary beams 1, denser, on the network of main beams 4.

This solution, which involves two superimposed beam networks, considerably increases the overall thickness of beams + floor.

However, a large thickness is often annoying, especially for architects, who generally want to build the maximum number of floors in the minimum height.

To avoid this drawback, we can then proceed as shown in Figure 2, fixing for example by angles 5 the end of the beams side (beams 1) on the side of the main beams 4.

But this method of fixing the secondary beams on the beams main ones is expensive.

The object of the invention is also a beam of the secondary beam type which avoids the aforementioned drawbacks.

The invention therefore also relates to the beam according to the invention previously described, characterized in that it is furthermore provided with means to collaborate with a support, in particular on a main beam, adapted to rest said internal profile directly on said support.

• lesdits moyens comprennent, à au moins une extrémité de la poutre, un dépassement longitudinal dudit profilé interne par rapport auxdites parois latérales, ledit dépassement étant destiné à reposer directement sur ledit support, notamment une poutre principale.
• lesdits moyens comprennent une échancrure pratiquée dans la partie inférieure des dites parois latérales, ladite échancrure étant adaptée pour permettre audit profilé interne de reposer à cet endroit directement sur ledit support, notamment une poutre principale.

According to additional features of the invention,

• said means comprise, at at least one end of the beam, a longitudinal projection of said internal profile relative to said side walls, said projection being intended to rest directly on said support, in particular a main beam.
• said means comprise a notch formed in the lower part of said side walls, said notch being adapted to allow said internal profile to rest at this location directly on said support, in particular a main beam.

This notch can also be made at the end of the beam, or any place where it is a question of resting the beam on a support.

• la figure 1 est une vue en perspective de deux réseaux superposés de poutres pour supporter un plancher, les poutres supérieures étant dotées de connecteurs-béton selon l'art antérieur.
• la figure 2 est une vue en perspective d'un mode de fixation selon l'art antérieur d'une poutre secondaire sur une poutre principale.
• les figures 3A, 3B, 3C, 3D sont des vues respectivement en perspective, de dessus, d'extrémité et de côté d'une poutre selon l'invention.
• la figure 4 est une vue de côté d'une poutre selon l'invention présentant une cavité de profondeur variable dans le sens de la longueur.
• les figures 5 à 12 sont des vues d'extrémité de poutres selon d'autres variantes de l'invention ; la partie hachurée de la figure 11 représente en outre une coupe d'un plancher en béton collaborant supporté par la poutre.
• les figures 13A, 13B, 13C sont des vues respectivement en perspective, de dessus et d'extrémité d'une poutre selon l'invention dotée de moyens pour faire reposer l'extrémité de la poutre sur un support, ici un dépassement longitudinal du profilé interne.
• la figure 14 décrit comment la poutre de la figure 10 peut être posée à une extrémité sur une poutre principale.
• la figure 15 représente une variante des moyens de support de la poutre selon l'invention, ici une échancrure pratiquée dans la partie inférieure des parois latérales, et la mise en oeuvre de cette variante.

The invention will be better understood on reading the description which follows, given by way of example, and with reference to the appended figures in which:

• Figure 1 is a perspective view of two superimposed networks of beams for supporting a floor, the upper beams being provided with concrete connectors according to the prior art.
• Figure 2 is a perspective view of a method of fixing according to the prior art of a secondary beam on a main beam.
• FIGS. 3A, 3B, 3C, 3D are respectively perspective, top, end and side views of a beam according to the invention.
• Figure 4 is a side view of a beam according to the invention having a cavity of variable depth in the lengthwise direction.
• Figures 5 to 12 are end views of beams according to other variants of the invention; the cross-hatched part of FIG. 11 also represents a section of a collaborating concrete floor supported by the beam.
• FIGS. 13A, 13B, 13C are respectively perspective, top and end views of a beam according to the invention provided with means for resting the end of the beam on a support, here a longitudinal projection of the profile internal.
• Figure 14 describes how the beam of Figure 10 can be placed at one end on a main beam.
• FIG. 15 represents a variant of the support means of the beam according to the invention, here a notch formed in the lower part of the side walls, and the implementation of this variant.

We will now describe examples of implementation and use of beams according to the invention, without limitation.

The beam is made by assembling cold sections of sheets metal.

The assembly of the profiles which form the beam according to the invention is designed to provide a cavity all along the upper part of the beam intended to receive concrete through an opening in the face higher.

The cavity is equipped with means of collaboration with concrete, such as edges of profiles, cap screws or bosses projecting towards inside the cavity.

Reference is made, for example, to FIGS. 3A to 3D.

• un profilé dit "externe" 6 de section générale parallélépipédique présentant une forme de U avec des rebords supérieurs 7A, 7B rentrant l'un vers l'autre sans se rejoindre : on a donc essentiellement une paroi inférieure et deux parois latérales 6A, 6B approximativement parallèles.

Here we have two types of cold sections, generally made of steel:

• a so-called "external" section 6 of generally parallelepipedal section having a U shape with upper edges 7A, 7B returning towards one another without joining: there is therefore essentially a bottom wall and two side walls 6A, 6B approximately parallel.

• un profilé dit "interne" 9, en forme de U, dont la largeur est adaptée pour être inséré dans le profilé externe 6 et pour joindre les deux parois latérales 6A, 6B du profilé externe 6.

On the upper part, the distance between the flanges 7A, 7B provides an opening 8 towards the inside of the external profile.

• a so-called "internal" section 9, U-shaped, the width of which is adapted to be inserted into the external section 6 and to join the two side walls 6A, 6B of the external section 6.

As shown in Figures 5, 6 and 7, the internal profile 9 includes preferably re-entrant upper edges 10A, 10B.

The two sections 6, 9 are cut to the required length of the beams

The internal profile 9 is inserted into the external profile 6 as indicated in Figures 3A and 3C, preferably pointing the U shape of the internal profile 9.

According to the invention, the height position for fixing the internal profile 9 in the external profile 6 determines the depth of an internal cavity 12, therefore the thickness of the beam compression table.

The desired thickness is determined in a manner known per se of the beam compression table, in particular depending on the stresses which the beam must be able to withstand and depending on the desired position of the neutral axes of the beam.

We choose a thickness small enough to limit the weight of the beam after pouring concrete.

The two sections 6 and 9 are made integral, by a known method of fixing in itself, for example by rivets 10.

As shown in Figure 5, is used for the assembly of screws 11 which project towards the inside of the beam to contribute to the attachment of the concrete.

One can in particular use self-tapping screws.

It is advantageous to assemble the beam on the site itself construction.

A beam is thus obtained which has a cavity in its upper part. internal 12 open on the upper face of the beam through the opening 8.

This cavity 12 is intended to receive concrete with its reinforcements, for which it will serve as formwork.

Concrete is poured into cavity 12.

When the beam is in service, the hardened concrete (not shown) in the cavity 12 will work mainly in compression and will therefore constitute the compression table.

The formwork formed by the cavity 12 then collaborates with the concrete.

According to the invention, the cavity 12 includes collaboration means concrete beam.

The means of collaboration of the beam with the concrete include here the reentrant upper edges 7A, 7B of the external profile 6 (FIGS. 3A to 3C, 5 and 6), and / or the flanges 10A, 10B of the internal profile 9 (FIGS. 5 to 7) and / or the screws 11 which project towards the inside of the beam (FIGS. 5 and 7).

The beam-concrete collaboration means may include bosses made in the side walls 6A, 6B of the external profile, or in the internal profile 9.

Advantageously, the collaborating beam obtained is therefore economical (no installation of concrete connectors), easy to assemble and assemble.

Advantageously, the type of beam according to the invention makes it possible to reconcile lightness and optimal mechanical characteristics in a large number of configurations from the same cold profiles.

From the same profiles 6, 9, it is possible to make several types beams on the same site, by varying the fixing height of the internal profile 9 in the external profile 6.

Furthermore, access to these optimal mechanical characteristics is easy to obtain, in particular by adapting the fixing of the internal profile 9 in the external profile 6 (in order to obtain the required cavity depth 12).

While we choose the most compression table thickness low possible to limit weight, advantageously avoids any risk of see the concrete escape from its formwork (when the beam is loaded) thanks to the means of concrete-sheet collaboration in the cavity.

It is also possible to obtain a beam with a compression table of variable thickness along the beam, using an internal profile configured for this purpose: Figure 4 shows a beam with an internal curved profile 9 to the top.

The beams according to the invention are advantageously used in construction to support floors.

In the case where the beam is used to support a collaborating floor, we can proceed as follows.

Before pouring concrete into the beam, a network of floor support beams.

Between the beams, ribbed sheets are placed, adapted to the construction of collaborating floors.

The sheets rest at their ends on the upper edges 7A, 7B beams without covering or masking the opening 8 towards the interior of the cavity 12 to fill with concrete of each beam.

If necessary, fittings and reinforcing gratings are available, including in the cavity 12.

Concrete is then poured both into the beams and onto the sheets.

After the concrete has dried, a collaborating floor is then obtained supported by the collaborating beams according to the invention.

• la figure 7 décrit une poutre identique à la poutre précédemment décrite à la différence près que le profilé externe 9 présente des rebords sortants-donc non collaborants ; cette disposition facilite l'insertion du profilé interne dans le profilé externe.
• la figure 8 décrit une poutre réalisée par l'assemblage de quatre profilés également plus facilement assemblables : deux profilés en L renversé pour les parois latérales, la base du L servant de rebord supérieur, reliés par deux profilés en U, l'un 9 interne, l'autre 13 à la base de la poutre.
• Les figures 9 et 10 décrivent une poutre réalisée à partir de deux profilés en S, 14A et 14B , reliés par un profilé interne 9 en U.

Without departing from the present invention, other types of profiles can be used to make a beam according to the invention:

• Figure 7 describes a beam identical to the previously described beam with the difference that the external profile 9 has outgoing edges-therefore not collaborating; this arrangement facilitates the insertion of the internal profile into the external profile.
• FIG. 8 describes a beam produced by the assembly of four profiles which are also more easily assembled: two L-shaped profiles inverted for the side walls, the base of the L serving as an upper edge, connected by two U-shaped profiles, one internal 9 , the other 13 at the base of the beam.
• Figures 9 and 10 describe a beam made from two S-sections, 14A and 14B, connected by an internal section 9 in U.

• La figure 11 représente une variante de la poutre de la figure 9, où un profilé supplémentaire en U a été rajouté sur la face inférieure de la poutre pour renforcer la poutre dans la partie soumise à des contraintes en traction et pour empêcher un flambage des parois latérales.

The ends 15 of the S-shapes are slightly folded back on themselves, in order to hang elements, in particular ceiling construction elements, on the lower part of the beam.

• FIG. 11 represents a variant of the beam of FIG. 9, where an additional U-shaped profile has been added on the underside of the beam to reinforce the beam in the part subjected to tensile stresses and to prevent buckling of the walls side.

• La figure 12 représente une variante de la poutre de la figure 11, où les deux profilés en forme de U sont remplacés par des profilés 9' en forme de Σ.

FIG. 11 also partially shows: ribbed sheets 16 bearing on the upper flanges 7A, 7B of the beam, leaving the opening 8 accessible in the beam; and, in the hatched area, concrete 17 filling the cavity of the beam and covering the sheets 16 to form a working floor.

• Figure 12 shows a variant of the beam of Figure 11, where the two U-shaped profiles are replaced by profiles 9 'in the form of Σ.

We will now describe the fixing advantages of the beam according to the invention, in particular for the production of secondary networks of beams.

Advantageously, the beam is made to rest on a support by through the internal profile itself.

It suffices for example to provide, when cutting the profiles 6, 9, a length of the internal profile 9 greater than that of the external profile 6, of so that after assembly, the internal profile 9 exceeds at least one end 18 relative to the end of the external profile 6, as shown in Figures 13A, 13B and 13C.

In this way, the end of the beam can be rested according to the invention via the protruding end 18 of the internal profile 9, as shown in Figure 14; the beam according to the invention is supported here by a main beam 4 identical to that of FIG. 1.

Thanks to this arrangement made possible by the very structure of the beam according to the invention, it is possible to limit the overall thickness of the floors even when it is necessary to mount several superimposed networks of beams to support a floor, and while maintaining ease of assembly by simply placing beams on top of each other; it is no longer useful, then, to use complex and expensive fastening systems, as in the art anterior (Figure 2).

Other variants concerning the beam support means according to the invention offer the same advantages, such as that shown in the FIG. 15, where a notch 19 has been made in the side walls 6A, 6B, here at the end of the beam, to also allow the beam through the internal profile, in particular to also limit the overall thickness of a floor.

Claims (8)

1. Metal girder intended to support a load, particularly a floor of a building, produced by the cold assembly of sheet metal profiles (6, 9) comprising at least two sheet metal vertical side walls (6A, 6B) which are approximately parallel, and an internal profile (9) fixed to the two said side walls (6A, 6B) to join them together, the said side walls (6A, 6B) and the said internal profile (9) being configured to constitute a cavity (12) in the upper part of the said girder, the depth of which extends, from the bottom upwards, from a cavity bottom consisting of the said internal profile (9) as far as an opening (8) formed between upper rims of the said side walls (6A, 6B), the said cavity (12) being intended to receive concrete poured through the said opening (8), characterized in that:

   the walls of the said cavity (12) are provided with means for cooperating with the concrete which means comprise:

   upper rims of the said internal profile (10A, 10B), the said rims protruding towards the inside of the cavity (12),

   and/or means of assembling the said internal profile (9) with the said side walls (6A, 6B) which project towards the inside of the cavity (12),

   and in that the fixing of the said internal profile (9) to the said side walls (6A, 6B) is designed to obtain a depth of cavity (12) that allows the concrete poured into the said cavity to work essentially in compression when the said girder is under load.
2. Girder according to Claim 1, characterized in that the said internal profile (9) is in the shape of a U or Σ and is fixed to the two said side walls (6A, 6B) in such a way as to have an opening of the said U or Σ shape facing upwards.
3. Girder according to any one of the preceding claims, characterized in that the said internal profile (9) has a special shape, particularly is bent along its length, so as to cause the depth of the said cavity (12) to vary along the length of the girder.
4. Girder according to any one of the preceding claims, characterized in that it is provided with means for cooperating with a support, particularly on another girder (4), which means are designed to cause the said internal profile (9) to rest directly on the said support.
5. Girder according to Claim 4, characterized in that the said means comprise, at least at one end of the said girder, a longitudinal overhang (18) of the said internal profile (9) with respect to the said side walls (6A, 6B), the said overhang (18) being intended to rest directly on the said support, particularly a main girder (4).
6. Girder according to Claim 4, characterized in that the said means comprise a cut-out (19) in the lower part of the said side walls (6A-6B), the said cut-out (19) being designed to allow the said internal profile (9) to rest, at this point, directly on the said support, particularly a main girder (4).
7. Girder according to any one of the preceding claims, characterized in that the said cavity (12) contains concrete, forming a compression table when the said girder is under load.
8. Method of constructing a floor of a building supported by at least one girder according to any one of the preceding claims, characterized in that, with the said floor being of the collaborating or compositely-acting type, comprising metal sheets which act as form work for the collaborating concrete, the concrete is poured simultaneously into the cavity (12) of the said girder and over the said metal sheets that act as form work for the floor.

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