EP0717149B1 - Mixed structure of wood-concrete, especially for the construction of bridge decks - Google Patents

Abstract

The structure consists of lengthwise timber beams resting on supports, a concrete compression slab supported by the beams, and metal connectors between the beams and the concrete. Each of the connectors has a double bend, forming an upper vertical plate (13) which is embedded in the compression slab, and a lower vertical plate (20) fixed in a slot (21) in the upper surface of the beam. The intermediate section of the connector between the upper and lower plates lies horizontally and is fixed to the beam by bolts (17). The lower vertical plate is sealed into the beam slot by a product which has a good chemical compatibility with the timber, sufficient fluidity to impregnate the fibres, and a thixotropic property to prevent it from spreading where it is not required.

Description

The present invention, which of model tests and studies were carried out at ENPEPE-FORMEQUIP Geomaterials Laboratory, concerns the realization of mixed wood-concrete structures, especially for obtaining aprons of engineering structures such as bridges. Such structures include solid wood or laminated beams glued to their part lower and a concrete compression slab connected on the beams at their upper part.

It applies in particular, but not exclusively for the execution of small and average ranges for pedestrian traffic (walkways) and vehicles (bridges) and, more generally, for the crossing of breaches by static or dynamic loads (e.g. aqueducts) within the scopes defined above. She preferably, but not limited to, applies to isostatic spans.

The construction of mixed metal-concrete decks armed for bridges has become quite common in so-called "developed" countries, demonstrating the reliability and low cost of such works for average spans, compared to equivalent works made entirely of reinforced concrete.

However these metal-reinforced concrete structures result in a very high consumption of steel from frame (in metal beams) and reinforcement for reinforced concrete (in the upper slab). That constitutes an important obstacle for the construction of bridges in developing countries, in causing heavy foreign exchange expenses to procure the necessary quantities of steel.

The object of the present invention is to remedy to this disadvantage and it proposes for this purpose substitute, for metal beams, modes of known construction mentioned above, beams of wood of section defined according to the loads applied (may vary from solid wooden section solid in an I-section also in solid wood or a section of complex shape in glued laminate). She has also for object, thanks to a judicious choice of position of the neutral fiber of the composite section (at the border between wood and concrete), to decrease considerably the quantities of steel to be put in place to arm the compression slab.

We understand that such a substitution of wood metal would, in the developing countries development with natural wealth in wood, to alleviate the heavy foreign exchange expenses linked to the purchase of steel and thus enhance on site a national resource which would otherwise be exported with lower added value.

The combination of wood and concrete constitutes a very old process, although it stumbled on the quality of the connection between the wooden beams and the slab of concrete compression. Many systems provided so make this connection using nails sunk into the wood and whose head is buried in the concrete. Other systems provided for plates of connection made of sheets fixed on the two blanks of each beam, using nailing teeth horizontal obtained by cutting and folding some parts of their material.

These known connection systems, which have only used for building floors and low capacity gateways, are not designed to withstand all compression and shear generated in engineering structures.

We also know, by the French patent FR2611778 A, a wood-concrete collaboration floor in which a concrete slab is poured on beams of wood and connected to them by connector tubes metal with circular section which each fit on the one hand by sinking into a circular groove dug for this purpose in a beam and, on the other hand, in the slab when pouring concrete. In that case also, this type of connection seems better suited to low and medium intensity constraints. Another system, described in document DE673556 C and intended on building floors, includes stapling of two parts of a mixed structure using profiles Z or I type.

• des poutres de bois longitudinales reposant sur des appuis tels que des chevêtres,
• une dalle de compression en béton portée par les dites poutres, et
• des connecteurs métalliques, constitués de profilés en Z, assurant la liaison entre les poutres et la dalle de béton.

Elle se caractérise en ce que les dits profilés en Z présentent chacun la forme d'une double cornière inversée dont l'aile verticale supérieure est noyée dans la dalle de compression, dont l'aile verticale inférieure est fixée dans une fente de la semelle supérieure de la poutre, et dont la partie intermédiaire horizontale est fixée sur la poutre, par exemple par des boulons ou tirefonds engagés dans des trous ménagés dans la poutre.According to the present invention, the mixed wood-concrete structure, intended in particular for the production of decks for engineering structures such as bridges, is of the type which comprises:

• longitudinal wooden beams resting on supports such as trimmers,
• a concrete compression slab carried by said beams, and
• metal connectors, made up of Z-sections, ensuring the connection between the beams and the concrete slab.

It is characterized in that the said Z-shaped profiles each have the shape of a double inverted angle iron whose upper vertical wing is embedded in the compression slab, whose lower vertical wing is fixed in a slot in the upper sole of the beam, and the horizontal intermediate part of which is fixed to the beam, for example by bolts or lag bolts engaged in holes made in the beam.

Advantageously the connector, which can be consisting of a folded sheet or obtained by welding two standard angles in head-to-tail position, has an opening on its upper vertical wing for the passage of a longitudinal streak intended to be drowned in concrete.

• une bonne compatibilité chimique avec le bois,
• fluidité suffisante pour imprégner les fibres de bois afin de reprendre correctement les efforts de cisaillement,
• thixotropie permettant de ne pas diffuser à l'excès le produit dans des zones où il ne serait pas utile.

The seals of the lower flange of the connector in the slot in the wood and of the bolts or lag bolts in the beam are produced using a product having the following characteristics:

• good chemical compatibility with wood,
• sufficient fluidity to impregnate the wood fibers in order to correctly take up the shearing forces,
• thixotropy allowing not to excessively diffuse the product in areas where it would not be useful.

We understand that the connector according to the invention is perfectly suited to the execution of decks with a mixed wood-concrete structure. Indeed its upper part works exactly as in mixed metal / concrete decks in which the connector is embedded in the compressed part of the transmitting concrete a compression which dimensions it (it also prevents, thanks to the thread passing through all connectors in a row, lifting the slab). Of even its lower part pressed into a slot in the beam transmits in the best possible conditions wood compression within the limits of constraints admissible of it (defined by calculation). The mobilization of efforts is ensured by filling of the slit using the product defined above.

The connector is temporarily fixed on the wood by a point and the efforts of tearing off connector-wood are taken up by constituted bolts a rod inserted in a pilot hole and sealed with product defined above in order to reconstitute the material around the stem, and a head opposing the uprising.

The shear force on the section transverse of the lower wing of the double angle reversed dimensions the thickness of this wing. Finally the bending force on the upper part of the connector dimensions the thickness of the upper wing.

The set of connectors thus defined according to the invention is able to resist all efforts generated by the cutting forces known in the engineering structures including fatigue efforts.

Note that the lower part of the connector is pressed into the upper sole of the wooden beam on a relatively small part of the total height of said sole. However, given the position of the neutral axis, this area is very weak stretched, which means that the few fibers of the wood intercepted by the bottom of the connector are without affecting the holding of the whole structure.

It should also be noted that the weak dimensions of the connector compared to those of the wooden beam upper sole make this connector is very far from atmospheric air as much on the concrete side than on the wood side. This characteristic effectively protects the connector against possible fire risks as well as against corrosion, protection which can be further improved by galvanizing and / or whitewashing with resin.

• de constituer d'une part un coffrage perdu participant ou non pour la dalle de compression en béton située au-dessus. Cette voûte est réalisée à l'aide de trois files de parpaings (deux files de rive et une file de clef) dont la flèche et l'épaisseur sont déterminées par la nécessité d'être entièrement comprimée sous l'effet du béton liquide de la dalle de compression.
• de transmettre directement, grâce à l'effet de voûte créé, les efforts des charges statiques et dynamiques de la chaussée aux poutres de bois et d'éviter ainsi la création de moments de flexion transversaux importants qui auraient imposé l'augmentation sensible des quantités d'acier dans la dalle, réduisant d'autant l'intérêt du procédé.

According to a feature of the invention, in order to make the realization easier by an unskilled workforce and to minimize the quantities of steel for reinforced concrete, precast concrete elements using the shape of a vault are used and supported by notches made on the edge of the wooden beams. These vaults have two purposes:

• to constitute on the one hand a lost formwork participating or not for the concrete compression slab situated above. This vault is made using three rows of concrete blocks (two shore rows and a row of keys) whose deflection and thickness are determined by the need to be fully compressed under the effect of the liquid concrete of the compression slab.
• to transmit directly, thanks to the vault effect created, the forces of static and dynamic loads from the roadway to the wooden beams and thus avoid the creation of significant transverse bending moments which would have required the appreciable increase in the quantities of steel in the slab, thereby reducing the interest of the process.

All the elements to be put in place are light enough to be handled manually or using hoists.

The longitudinal wooden beams are normally braced at a rate defined by the calculation. These spacers are in principle made up a steel tube taking up the shears crossing a wooden concrete element which takes up the compressions and a FE 500 steel clamping rod or hard steel - (depending on the efforts concerned) - which resumes pull-ups. The wooden beams rest on headers constituting supports.

Finally to make execution easier again, prefabricated elements placed on the bank of the deck on a side notch of the edge beams both serve as vertical lost formwork for the compression slab and the overlying sidewalk but also of protection against the flow of water the along the edge beams and decorative facing.

The invention as defined can be implemented implemented both in developing countries development for its maximum use of local resources and the simplicity of its execution, and in industrial countries that wish to develop the wood industry at reasonable costs thanks to low consumption of labor on site properly said.

la figure 1 est une vue en coupe verticale transversale d'un tablier de pont selon la présente invention ;

la figure 2 est à plus grande échelle, une vue en perspective d'un connecteur utilisé selon la présente invention ; et

la figure 3 représente en perspective une voûte type en parpaings préfabriqués.

To clearly understand the invention, a preferred embodiment will be described below, by way of example, with reference to the appended schematic drawing in which:

Figure 1 is a cross-sectional vertical view of a bridge deck according to the present invention;

Figure 2 is on a larger scale, a perspective view of a connector used according to the present invention; and

Figure 3 shows in perspective a typical vault in precast concrete blocks.

Referring to Figure 1 there is shown a bridge deck produced according to the invention, which comprises wooden beams 1 which can be solid or laminated glued. In the example shown, the beams are section in I and consist of several elements superimposed assembled together. They could however be rectangular.

Beams 1 extend in the direction longitudinal of the bridge between piers and abutments, and they are braced using a set made of 2 steel tubes passing through butons wood 3, the whole being tightened by pre-stressed rods 4.

At their upper part, the beams 1 are notched by notches 5, intended to receive prefabricated concrete vaults 6 which are arranged in arch shape and serve to form the space included between the beams 1. The outer notches 5 of the edge beams allow to support cornices prefabricated 7 which have as their object, in addition to their role decorative and protective beams, formwork vertically the concrete slab 8 of the deck as well as the overlying sidewalk 9.

Beams 1 and prefabricated concrete blocks 6 serve as formwork for pouring the concrete slab 8, which is simply armed with a double layer of trellis welded to resist some conditions to limits, and not at the transverse moments which are eliminated thanks to the arch effect created by the concrete blocks 6.

Connectors 12 in the form of a double angle connect the wooden beams 1 to the concrete slab 8 in opposing the sliding forces between these elements. A sealing layer 10 and a wearing layer 11 cover the concrete slab 8.

As can be seen more particularly in the Figure 2, the connector 12 consists of a sheet folded about 8mm thick S-shaped without upper and lower bars produced by folding or by welding two angles together. The amount upper 13 has dimensions of the order of 10cm x 10 cm. It is drilled with a hole 14 allowing the introduction of a round strip of about 12mm.

The horizontal part 15, which in the structure is fixed on the upper face of the beam wood, has dimensions of the order of 10cm x 10 cm. She is drilled with four main holes 16 intended for the passage of rods 17 for fixing the connector on the wooden beam. The stems are sealed with a sealant in pre-drilled holes 18 in wooden beams. They have a head opposing the breakout efforts of the connector.

A central hole 19 allows the introduction of a connector positioning and fixing tip.

The lower upright 20 has dimensions of the order of 10cm x 3.5cm.

It is inserted into a slot 21 made in the wood with a router and sealed with a sealant.

As seen in Figure 3, the vault in prefabricated concrete blocks are made using two shore lines 22 and a key line 23 extending slightly beyond the beam in order to form the ends 24 of the apron projecting from the beams wood.

It will be understood that the above description has was given as an example, without character limiting, and that additions or modifications could be made.

We will understand in particular that we have described the invention as applying to the realization of a bridge deck but that she might as well apply to the realization of building floors.

Claims (10)

1. Composite wood - concrete structure aimed at bridges construction including:

   longitudinal wood beams (1) lying on bearings.

   compression concrete slab (8) supported by the above mentionned beams (1), and

   metallic connecting devices (12) securing the connection between the so called beams (1) and the concrete slab (8),

   characterized in the so called connecting devices (12) appearing in the shape of a double inverted angle whose top flange (13) is embedded in the compression slab (8), whose bottom flange (20) is fixed inside a slot (21) grooved in the top sole of the beam (1) and whose intermediate horizontal part (15) is fitted to the beam (1).
2. Composite wood - concrete structure according to claim 1 characterized in the fitting of the horizontal part (15) of the connecting device (12) to the beam (1) being carried out by rods (17) placed in holes (18) drilled in the beam (1).
3. Composite wood - concrete structure according to claim 2 characterized by the sealing of the bottom flange (20) in the slot (21) and of the rods (17) in the holes (18), this sealing being achieved by means of a chemical produce with the following characteristics:

   good chemical compatibility with timber

   Sufficient fluidity insuring a proper impregnation of timber fibres in order to correctly resist shear stresses

   good thixotropic quality so as to prevent the produce to spread in areas where it would be of no use.
4. Composite wood - concrete structure according to any of the Claims 1 to 3, characterized in the top flange (13) of the connecting device (12) being connected to the concrete in order to resist the uprising of the concrete slab (8) using-by instance - an opening (14) through which a longitudinal renforcement bar can be pulled and eventually embedded in the concrete slab (8).
5. Composite wood - concrete structure according to any of the claims 1 to 4, characterized in the connecting device (12) being made of bended steel sheet.
6. Composite wood - concrete structure according to any of the claims 1 to 4, characterized in the connecting device (12) being made of two welded inverted angles.
7. Composite wood - concrete structure according to any of the previous claims, characterized by the placing between beams (1) of vaults made of precast concrete elements (6) constituting a lost formwork to the concrete slab (8) and transferring to beams (1) the efforts coming from the static and dynamic road loads thanks to a clever combination between the thickness of the precast elements (6) and the rise of the vaults enabling a consistant reduction of steel reinforcement in the concrete slab.
8. Composite wood - concrete structure according to claim 7, characterized in the grooving of the top sole of beams (1) on each side in order to fit (5) in the so called precast elements (6) constituting the vaults.
9. Composite wood - concrete structure according to claim 8, characterized in that external grooves (5) in side beams (1) fit in precast edge beams (7).
10. Composite wood - concrete structure according to any of the claims 7 to 9, characterized in that the vaults constituted of precast elements (6) are arranged in two side files and one key file stretching slightly further beyond the beams (1) length in order to form the ends of the deck slab (24) which protrudes beyond the timber beams (1).

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