EP0280228B1 - Combined wood and concrete floor - Google Patents

Abstract

A concrete slab (8) is cast over wooden beams (2) and is connected to the beams by metal connector tubes (14) of circular section, each of which is embedded at one end by being forced into a circular groove provided for the purpose in a beam and at its other end in the slab by virtue of the concrete being cast thereover. The invention is applicable to building or converting buildings and also to works such as gangways and bridges.

Description

The present invention relates to the production or reinforcement of floors formed on wooden beams. It applies in particular when such beams can be brought to the site of an existing construction to renovate, transform, or consolidate, such constructions can be for example residential buildings, workshops, walkways or bridges.

The principle of the wood-concrete collaboration floor is known. Its resistant profile is a T-profile, the lower part of which is a wooden beam and the upper part of a concrete slab, generally of compression. This slab was cast on a formwork lost or not, placed on the beams or between them.

The collaboration between wood and concrete is ensured by metal connectors whose rigidity and embedding in wood and concrete prevent any relative displacement of the constituents in the direction of the span, that is to say in the direction longitudinal of the beams. The distribution of connectors is similar to that of stirrups in a reinforced concrete beam.

A distribution trellis made of steel and embedded in the concrete ensures the resistance of the slab to punctures and transverse bending.

As regards the resistance of the materials, the composite beams formed by this T-shaped profile are most often simply supported on their ends. This case is the simplest and will be considered below by way of example, it being understood that, if the beams are locally embedded or bear on intermediate supports, the forces are locally reversed. In this simple case the composite beams work in simple bending. Their neutral fiber is preferably located in the vicinity of the lost formwork, the dimensions of the wood and the concrete being chosen accordingly. The concrete works in compression, the wood in tension, in the longitudinal direction, and the connectors support the internal shearing forces which are exerted between wood and concrete in the same direction.

In a first known floor of this type, the connectors are formed by vertical nails partially driven into the upper faces of the joists through the formwork before the slab is poured. The head and the upper part of each of these nails is embedded in the concrete during this pouring. Such a floor is described in an article by Godycki et al. "Verbunddecke aus Holzrippen und Betonplatte" (Bauingenieur 59 (1984) 477-483, Springer-Verlag, German Federal Republic). Such connectors have the disadvantage that their middle and lower sections flex easily under the internal longitudinal forces mentioned above. They then tilt in the wood. This bending of the connectors results in deformation of the floor and a reduction in its resistance.

In a second known floor, the connectors are also metallic and they are rigid. They are formed by connection plates made of sheet metal and extending vertically and longitudinally in contact with the two sides of each beam. Pointed transverse horizontal nailing teeth can be formed by cutting and bending horizontally certain areas of each such plate. They penetrate into the side of the beams to fix the plate during an operation which can be called "nailing". This operation can however also be carried out using ordinary horizontal transverse nails passing through the plate. The upper part of the plate protrudes above the beam and is cut to form pointed vertical connection teeth which pass through the formwork when it is placed on these beams and which are then embedded in the concrete of the slab.

Such a second floor is mentioned without being precisely described in the European patent document EP-A1-0104629 (Poutanen, Tuomo Tapani).

• 1° Si, pour l'opération de clouage précédemment mentionnée, on utilise des dents de clouage préalablement formées par découpage et pliage de certaines zones de la plaque, cette opération nécessite l'utilisation d'une presse capable d'exercer un effort important.
  S'il s'agit d'une construction neuve elle peut être assez aisément effectuée à l'aide d'une grosse presse disposée à demeure dans un atelier. Mais le stockage et la manutention des poutres deviennent délicats après cette opération notamment en raison de la faible raideur des dents de connexion et des plaques dans le sens transversal. Si au contraire on utilise des poutres qui sont déjà en place, il est généralement difficile de mettre en oeuvre une telle grosse presse au contact de ces poutres. Si enfin l'opération de clouage est réalisée à l'aide de clous ordinaires, ces clous peuvent fléchir dans le bois.
• 2° Les dents de connexion forment des groupes au sein de chacun desquels elles se succèdent longitudinalement à petit intervalle. Lors du coulage de la dalle les granulats du béton s'insérent difficilement entre deux dents successives ce qui affaiblit le béton dans une zone où il est fortement sollicité par le connecteur.
• 3° La liaison entre la plaque et la poutre ne peut être parfaitement rigide. En effet si les dents de clouage sont formées à la fabrication du connecteur dans des plans verticaux transversaux par pliage de la tôle autour d'une ligne de pliage verticale, les efforts longitudinaux en service peuvent les faire facilement plier autour de cette ligne. Si ces dents sont formées dans des plans horizontaux par pliage autour de lignes horizontales longitudinales, ces dents ne présentant qu'une surface d'appui très petite sur le bois dans le sens longitudinal, cette surface correspondant à l'épaisseur de la tôle, et il en résulte que les efforts longitudinaux appliqués en service peuvent facilement pousser ces dents à travers le bois.
• 4° Si on n'accepte pas que le coffrage de la dalle soit percé par les dents de connexion lors de la mise en place de ce coffrage, et si on préfére alors constituer le coffrage par des plaques de coffrage posées chacune sur les bords de deux poutres adjacentes, la présence des plaques de connexion qui sont clouées sur les flancs des poutres et qui débordent localement au dessus de celle-ci est gênante pour poser les plaques de coffrage sur les poutres.
• 5° La partie inférieure des plaques reste apparente, ce qui nuit à l'homogénéité esthétique du bois.
• 6° Les plaques étant apparentes et pénétrant dans les flancs des poutres, la connection est exposée aux élévations de températures produites par un incendie. Elle présente donc un degré de sécurité qui n'est pas satisfaisant.

This second known floor has the particular advantage that the shape of the connectors gives each of them a great overall stiffness vis-à-vis the bending forces formed by the longitudinal internal forces previously mentioned. But he presents various disadvantages among those which will be indicated.

• 1 ° If, for the above-mentioned nailing operation, nailing teeth previously formed by cutting and bending certain areas of the plate are used, this operation requires the use of a press capable of exerting a large force.
  If it is a new construction, it can be fairly easily carried out using a large press permanently installed in a workshop. However, the storage and handling of the beams becomes delicate after this operation, in particular because of the low stiffness of the connection teeth and of the plates in the transverse direction. If on the contrary one uses beams which are already in place, it is generally difficult to implement such a large press in contact with these beams. If finally the nailing operation is carried out using ordinary nails, these nails can bend in the wood.
• 2 ° The connecting teeth form groups within each of which they succeed longitudinally at small intervals. When pouring the slab, the concrete aggregates are difficult to insert between two successive teeth, which weakens the concrete in an area where it is highly stressed by the connector.
• 3 ° The connection between the plate and the beam cannot be perfectly rigid. Indeed, if the nailing teeth are formed during the manufacture of the connector in transverse vertical planes by folding the sheet around a vertical fold line, the longitudinal forces in service can easily make them fold around this line. If these teeth are formed in horizontal planes by folding around longitudinal horizontal lines, these teeth having only a very small bearing surface on the wood in the longitudinal direction, this surface corresponding to the thickness of the sheet, and as a result, the longitudinal forces applied in service can easily push these teeth through the wood.
• 4 ° If we do not accept that the formwork of the slab is pierced by the connection teeth during the installation of this formwork, and if we then prefer to form the formwork by formwork plates each placed on the edges of two adjacent beams, the presence of the connection plates which are nailed to the sides of the beams and which protrude locally above it is inconvenient for placing the formwork plates on the beams.
• 5 ° The lower part of the plates remains visible, which harms the aesthetic homogeneity of the wood.
• 6 ° The plates being visible and penetrating into the sides of the beams, the connection is exposed to the temperature increases produced by a fire. It therefore has a degree of security which is not satisfactory.

The object of the present invention is to economically produce a wood-concrete collaboration floor of increased strength. It aims more particularly to produce connectors and to put them into service in such a floor in a simple and effective manner which avoids the drawbacks indicated above.

• des poutres de bois s'étendant selon une direction longitudinale et se succèdant selon une direction transversale dans un plan de poutraison sensiblement horizontal, ces poutres reposant sur des appuis pour supporter le plancher, chacune d'elles présentant une face supérieure, une face inférieure et deux flancs latéraux,
• une dalle de béton formée sur ces poutres pour constituer la surface du plancher et participer à la résistance de celui-ci,
• et des connecteurs encastrés chacun d'une part par un tronçon inférieur dans l'une de ces poutres d'autre part par un tronçon supérieur dans cette dalle, ces connecteurs présentant une raideur leur permettant, sans déformation sensible, de transmettre, entre le béton de ladite dalle et le bois desdites poutres, les efforts longitudinaux internes qui résultent des charges de flexion appliquées au plancher.

The floor according to the invention comprises certain elements which are analogous to elements of the known floor with rigid metal connectors previously described. Those are

• wooden beams extending in a longitudinal direction and succeeding each other in a transverse direction in a substantially horizontal beam plane, these beams resting on supports for supporting the floor, each of them having an upper face, a lower face and two lateral sides,
• a concrete slab formed on these beams to constitute the surface of the floor and participate in the resistance of the latter,
• and connectors each embedded on the one hand by a lower section in one of these beams on the other hand by an upper section in this slab, these connectors having a stiffness allowing them, without significant deformation, to transmit, between the concrete of said slab and the wood of said beams, the internal longitudinal forces which result from the bending loads applied to the floor.

Compared to this floor known from document CH A 223 498, the floor according to the invention is characterized by the fact that each of said connectors has the form of a tube, said lower section of this tube occupying a housing hollowed out in the wood of the upper face of a so-called beam so that this section constitutes, with respect to said internal longitudinal forces, an extended bearing surface of this tube on the wall of this housing and that the stiffness of this tube distributes these forces over this entire bearing surface. This tube will hereinafter be called connector tube.

• Ledit logement et ledit tronçon inférieur dudit tube connecteur sont réalisés de manière que la paroi extérieure de ce tronçon soit en appui permanent sur sensiblement toute sa surface contre la paroi de ce logement.
• Ce logement est réalisé sous la forme d'une rainure laissant subsister un noyau du bois de ladite poutre.
• Le diamètre dudit tube connecteur est suffisant pour permettre au béton de pénétrer sans ségrégation sensible dans l'espace intérieur audit tronçon supérieur de ce tube lors du coulage de ladite dalle de béton, de manière à renforcer l'encastrement de ce tronçon dans cette dalle après durcissement du béton.
• Ledit tube connecteur est constitué d'un matériau présentant une résistance mécanique supérieure et/ou plus homogène que celles du bois desdites poutres et du béton de ladite dalle.
• Ledit tube connecteur présente des génératrices verticales et une section circulaire de manière à en permettre une fabrication simple et à permettre une réalisation facile de son logement dans ladite poutre de bois.
• Son diamètre est compris entre 30 et 130mm et de préférence entre 40 et 100mm environ.
• Sa hauteur est comprise entre 6 et 15cm et de préférence entre 8 et 12cm environ.
• Ledit tronçon inférieur dudut tube connecteur pénétre dans la face supérieure de ladite poutre de bois sur une fraction inférieure à la moitié de la hauteur de cette poutre.
• Il présente un diamètre inférieur à la largeur de cette poutre selon ladite direction transversale, et son dit tronçon inférieur reste à distance des flancs de cette de manière à être protégé contre la chaleur et/ou la corrosion par une épaisseur de bois à partir de ces flancs. Cette dernière disposition permet par ailleurs de poser entre les poutres des plaques de coffrage rectangulaires qui s'appuient sur les bords de ces poutres.

According to the invention, the following preferred arrangements can also be adopted, at least in certain cases:

• Said housing and said lower section of said connector tube are made so that the outer wall of this section is in permanent support over substantially its entire surface against the wall of this housing.
• This housing is produced in the form of a groove leaving a core of the wood of said beam.
• The diameter of said connector tube is sufficient to allow the concrete to penetrate without appreciable segregation into the interior space of said upper section of this tube during the pouring of said concrete slab, so as to reinforce the embedding of this section in this slab after hardening of concrete.
• Said connector tube is made of a material having a higher and / or more homogeneous mechanical resistance than that of the wood of said beams and the concrete of said slab.
• Said connector tube has vertical generators and a circular section so as to allow simple manufacture and to allow easy production of its housing in said wooden beam.
• Its diameter is between 30 and 130mm and preferably between 40 and 100mm approximately.
• Its height is between 6 and 15cm and preferably between 8 and 12cm approximately.
• Said lower section of said connector tube penetrates into the upper face of said wooden beam over a fraction less than half the height of this beam.
• It has a diameter less than the width of this beam in said transverse direction, and its said lower section remains at a distance from the sides so as to be protected against heat and / or corrosion by a thickness of wood from these sides. This latter arrangement also makes it possible to lay rectangular beams between the beams which rest on the edges of these beams.

When producing such a floor, said beams are placed in said longitudinal direction which is horizontal. One obtains said connector tubes which are for example metallic. Their lower sections are driven into grooves provided for this purpose in the upper faces of the beams, their axes being vertical. Their upper sections are then embedded in the concrete when the slab is poured. Their role is to prevent the relative horizontal displacement of the wooden beams and the concrete slab when the floor is subjected to bending forces. Their effectiveness is ensured by the fact that, embedded in the concrete, they keep in their upper sections a constant position and orientation imposed by the rigidity of the concrete and that their tubular shape provides them with sufficient inherent rigidity on the one hand not to deform in their median section located in the vicinity of the wood-concrete interface and on the other hand do not create a wedge effect in their connection with the wood. They then apply a constraint on the latter which is distributed as uniformly as possible over the entire depth of their homes. Furthermore, the tubular shape of the connector and its vertical arrangement allow the desirable resistance of the floor to bending to be obtained with a number of connectors and a quantity of metal that is less than would be necessary with other methods.

With the aid of the attached diagrammatic figures, a description will be given more particularly below, by way of nonlimiting example, how the present invention can be implemented within the framework of the description which has been given thereof. above. When the same element is represented in several figures, it is designated therein by the same reference sign.

The mode of implementation described includes the arrangements mentioned above as preferred according to the present invention. It should be understood that the items mentioned may be replaced by other elements ensuring the same technical functions.

Figure 1 shows a view of a floor according to the invention in partial section through a longitudinal vertical plane.

FIG. 2 represents a partial view of the same floor in section through a transverse vertical plane II-II of FIG. 1.

FIG. 3 represents a perspective view of a connector tube of this floor, before the incorporation of this connector tube into this floor.

According to Figures 1 and 2 the floor given by way of example comprises wooden beams or joists such as 2 which can be solid or laminated, and which extend longitudinally as well as their fibers. A lost formwork 4 of known type rests on these beams. A layer of sound and thermal insulation 6 is placed on this formwork, it being understood that this layer can be omitted without loss of the specific advantages of the present invention. A concrete slab 8 is poured on this layer. It is reinforced in a known manner by a metallic distribution trellis which comprises transverse reinforcements such as 10 and longitudinal reinforcements such as 12. The center line between beams can be from 0.6 to 1.2 m approximately, for example 0 , 7m.

Connector tubes 14 extend vertically and each have a lower section 14B embedded in a beam 2, and an upper section 14A embedded in the slab 8, for example 2 cm from the upper face thereof. The trellis 10, 12 is placed on these connector tubes which makes it possible to maintain its altitude before and during the pouring of this slab. Such connector tubes could also have a non-embedded intermediate section at the level of the formwork 4 and of the insulation layer 6.

The formwork 4 and the insulation layer 6 have been drilled with holes 5 which are wider than the connector tubes so that, when the slab is poured, the concrete fills them without segregation on either side of the walls of the connectors 14. The diameter of each hole in the formwork 4 is however sufficiently limited so that the edge of the latter rests on the beam 2 all around the hole.

The connector tubes 14 have a circular section of 40 to 100 mm in diameter depending on the span of the beams and a height of 8 to 12 cm. The thickness of the sheet which constitutes them is for example 2mm.

They are embedded in the wood by forced insertion into a circular groove 15 which constitutes said housing and which has been previously dug into the beam by means of a tool of the hole saw type. The depth of the groove 15 is for example 4 cm.

The outside and inside diameters of this tool are for example chosen exactly equal to those of the connector tubes, which then requires the application of a moderate vertical force to drive these tubes.

Under these conditions the use of an adhesive to bond the connector to the wood generally appears unnecessary.

The connector tubes are made of structural steel. They could be made of other materials with high and homogeneous mechanical resistance, such as resins reinforced with glass fibers, for example.

They are embedded in the concrete of the slab by pouring this concrete which spreads outside and inside the tube. This embedding in the concrete being a perfect embedding, and the rigidity of the tubes being very great, they create practically no wedge effect in the wood, that is to say that the shearing forces at the level of the wood bond- concrete is transmitted as a uniform lateral pressure of the metal on the wood.

A vertical slip between the concrete slab and the connector could occur for example in the presence of high frequency alternating loads. It is prevented by simply leaving the saw burrs of the tubes on the upper edge for example. It could also be by welding the reinforcements.

As a variant, it should be understood that the cylindrical connector tubes of circular section could be produced in the form of tubes split along a generator so as to be able to easily adapt to housings of slightly different diameters.

Claims (10)

1. A combined wood and concrete floor comprising:

   - wooden beams (2) extending along a longitudinal direction and following one another in a transverse direction in a substantially horizontal beam plane, said beams resting on supports for supporting the floor, each beam having a top face, a bottom face, and two side faces;

   - a slab of concrete (8) formed on said beams in order to constitute the floor surface and to contribute to the strength of the floor; and

   - connectors each having a bottom length received in one of the beams and a top length (14A) received in said slab, said connectors being sufficiently stiff to transmit the internal longitudinal forces which result from bending loads applied to the floor between the concrete of said slab and the wood of said beams without said connectors suffering significant deformations;

   - said floor being characterized in that each of said connectors is in the form of a tube (14), with the bottom length (14B) of said tube occupying a housing (15) hollowed out in the wood from the top face of one of said beams (2) such that said length constitutes an extended bearing surface for said tube to bear against the wall of said housing in response to said internal longitudinal forces, and that the stiffness of said tube spreads said forces over all of said bearing surface, said tube being a "connector" tube.
2. A floor according to claim 1, characterized in that said housing (15) and said bottom length (14B) of said connector tube (14) are made in such a manner that the outer wall of said length is permanently applied with substantially all of its surface against the wall of said housing.
3. A floor according to claim 1, characterized in that said connector tube (14) and said housing (15) have a section which is circular in shape so as to facilitate fabrication of said tube and said housing.
4. A floor according to claim 3, characterized in that said housing is made in the form of a groove (15) leaving a core of wood of said beam in place.
5. A floor according to claim 1, characterized in that the diameter of said connector tube (14) is sufficient to enable the concrete to penetrate without significant segregation into the inside space of the top length (14A) of said tube while said concrete slab (8) is being cast, thereby reinforcing the embedding of said length in said slab after the concrete has set.
6. A floor according to claim 1, characterized in that said connector tube (14) is made of a material having mechanical strength which is greater and/or more uniform than the mechanical strength of the wood from which said beams (2) are made, and of the concrete from which said slab (8) is made.
7. A floor according to claim 3, characterized in that the diameter of said connector tube (14) lies between about 30 mm and about 130 mm.
8. A floor according to claim 1, characterized in that the height of said connector tube (14) lies between about 6 cm and about 15 cm.
9. A floor according to claim 1, characterized in that said bottom length (14B) of the connector tube (14) penetrates into the top face of said wooden beam (2) over a fraction of the height of said beam which is less than one half.
10. A floor according to claim 1, characterized in that said connector tube (14) has a diameter which is less than the width of said wooden beam (2) in said transverse direction, and its bottom length (14B) remains at a distance from the sides of said beam so as to be protected against heat and/or corrosion by a thickness of wood extending up to said sides.

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