EP1135565B1 - Wooden trussed structural systems, such as frameworks, bridges, floors - Google Patents

Abstract

A wooden trussed structure includes beams which are constructed from at least three elementary planks, nailed together. The plank located in the central part is offset relatively to the ends of the lateral planks, so as to form thereat, tenons and/or mortises for inserting, at the junction forming a node, a panel-type reinforcement, positioned in the core, and wherein the shearing surfaces correspond to the lateral surfaces at each node. The panel includes a wooden structural element such as a micro-lath or plywood as a plate-type solid web.

Description

Technical area

Wood is a material widely used in construction, and with which it is possible to make a whole series of load-bearing systems with properties clean mechanics, and allowing to support all levels and all types of loads.

The different wooden load-bearing systems are posts and beams, triangulated systems, articulated systems, portal frames, beam grids, shells and elements functioning as plates.

Among all these structural systems, the triangulated system is the most universal, because it allows to take up very heavy loads, while being very simple to build. As an indication, the triangulated system is causing farm systems used in Europe and which have been developed since the ^12th century and are still used today.

The triangulated wooden systems are to be classified into two main families illustrated schematically by Figures 1 to 6 attached.

The first system, called “parallel frame system”, illustrated by Figures 1 to 3, is used for example for bridges or floor systems horizontal.

• d'une filière ou membrure supérieure (1),
• d'une filière ou membrure inférieure (2),
• de poteaux (3) et éventuellement de montants (M),
• de diagonales (4).

Such a system consists of:

• a die or upper chord (1),
• a lower die or chord (2),
• posts (3) and possibly uprights (M),
• diagonals (4).

The assembly thus produced rests on at least two supports (5). To reduce internal efforts, we can sometimes add support inside the system, but this is not always possible.

The “triangle-shaped” systems, as illustrated in FIGS. 4 to 6, are generally used to make roof structures and allow give the slope to the latter.

The elements involved in the realization of such systems are composed one or two crossbowmen (6), a tie (7), diagonals (8) and possibly one or more uprights (9).

Such assemblies rest on supports (5) arranged at each end the tie rod (7).

The invention relates to this technical sector and relates more particularly to the realization of a new type of load-bearing system both with parallel members in the shape of a triangle, which, while having mechanical characteristics high, reduce production costs and is easily adaptable depending on the characteristics desired for each particular application (load to be supported, system dimensions ...).

Previous techniques

One of the main problems that arises in connection with the realization both systems with parallel members and triangle-shaped systems, is that of being able to absorb the maximum effort flow which is located at the level of supports and generates maximum tensions and compressions in the linked bars on the first node by the different elements which transmit the forces on support.

Classically, the first node, in the case of frames, links, tie rods (7), crossbowmen (6) and diagonals (8), is made with wooden parts solid or glued laminated wood, depending on the section needs and the knot is made by means of metal fittings for systems with high inertia, or even sometimes simply glued for lower inertia floor systems.

Many proposals have been made for the realization of the knot assembly of triangulated wooden systems, whether they are with parallel members or in the shape of a triangle.

Among these solutions, we can cite the one that is the subject of document US-4,891,927 which proposes a reinforcement of the triangulation knot by an internal metal connector, provided with nails or pins which sink into the members made up of two layers. Such a solution is very expensive, because it requires a force and factory assembly of the knot, which eliminates the possibility of an artisanal assembly on the site itself, and which can be easily adapted according to the works to be carried out. Furthermore, it is not entirely satisfactory in that the strength of the knot is dependent on the section of the wood.
Document DE-39.10.027 proposes a solution with two-layer dies and a triangulation system with plank or compound diagonals positioned in the core. However, such a solution does not make it possible to reinforce the most stressed nodes.
Furthermore, it has been proposed for a very long time, as is apparent from document US-2,886,857, in order to reduce the costs of manufacturing triangulated systems, to produce the beams used in the production of such systems, not from solid wood of large section or relatively expensive glued wood, but by structures made up of boards nailed to each other to recompose larger sections from wood of small section, therefore economical.
Such a structure from nailed boards makes it possible to lower the cost prices and to recompose a large section without having the problems of solid wood such as deformations and cracks. Furthermore, with thin boards, for example of the order of 30 mm to 50 mm, it is possible to carry out an artificial drying under conventional conditions. In addition, the wood being nailed dry, there is no more deformation of the compound section.
The solution described in the aforementioned patent has, however, a certain number of drawbacks with regard to the strengthening of the knots and cannot be adapted equally to the two main families of triangulated wooden systems known as “parallel frame systems” and “ triangle shape ". First of all, this solution has boards in the central layer which are nailed between the two boards of the other members. This nailing tends to cause the central board to crack because the distance from the loaded edge, parallel to the fibers, is too small. This central plank core is therefore of poor performance in terms of its assembly.

Then, the fact of having a succession of planks in central core makes it possible to create inertia by spacing the external members, but this planked core being discontinuous transversely, it cannot take again neither the bending moment nor the local shearing generated by the two internal beams, for example the compressed diagonal and the stretched upright. It therefore does not strengthen the knot in relation to bending and local shears which are important mechanical components of the knot system.
Finally, this central core is forced to fill all the space between the external members, since it only has rigidity on one axis, its longitudinal axis. This core therefore constitutes a global zone between the external members, and does not allow local reinforcement, adjusted for a single connecting node. It does not allow the optimization of the node, neither in performance (fragility in nailing), nor in economy of material (full area, compared to local area).
We know from documents CH- 467.402 and FR- 2.303.128 a truss of the triangle-shaped type, comprising massive beams (crossbowmen, tie rods and diagonals) and a reinforcing element in the form of a plate made of plywood or aluminum placed at the junction zones.
We know from document FR-1,541,776 a system with triangulated wooden structures, with triangular-shaped frames, for the production of frames, consisting of beams constructed from three elementary blades, a central blade and two blades side. glued to each other, the elementary blades constituting each beam can be of the same thickness.

Statement of the invention

However, it was found, and this is the subject of the present invention, that it was possible to build structural systems with both parallel members and triangle shape of the type illustrated by Figures 1 to 6, the different elements of which - dies, diagonals, posts, tie rods, uprights, crossbowmen, - which, in the rest of the description, will be designated by the common expression "beam", allow, to simple way, to reinforce the junction nodes between these elements, each beam being constructed from boards nailed together to compose larger sections.

In general, a system with triangulated wooden structures, with frames parallel or triangle-shaped, for the production of frames, bridges and floors, consists of beams forming between them junction zones and being constructed at from at least three boards, a central board forming a core and at least two side planks, all planks having the same thickness and being nailed to each other.

According to the invention, the system is characterized in that the board center is offset from the ends of the two side boards, so that form mortises at this level, which include, at the level of the junction zones between the beams, a reinforcement panel positioned in the core, the shear surfaces of the reinforcement panel corresponding to the lateral surfaces of the two boards lateral at each junction zone, said reinforcing panel being in microlame or plywood.

Such a solution makes it possible to withstand greater efforts, the panels interfaced at the junction zones (knot) increasing the studding zones.

Furthermore, the solution according to the invention also makes it possible to reduce the bending moments in the joint since the reinforcement itself absorbs the bending since the “plate” type reinforcement has a very high rigidity since he works in both directions of his plan. Such reinforcement allows resume the shear forces of the internal beams, such as for example the shear between a compressed diagonal and a tensioned beam, at the level of the node, by mechanically relieving the external beam accordingly.

This reinforcement can be more or less isotropic depending on the forces to be resume.

As indicated above, the beams involved in the realization of a system according to the invention will consist of at least three layers, the reinforcements being therefore positioned at the level of the central layer, which allows a double shearing of the through nails relative to the reinforcement which would be exposed to outside the system, as is often the case.

According to a particular embodiment which will emerge from the following description, in particular in the case of a system with parallel members, the two end posts will also consist of three layers nailed together, the central layer not being constituted by a board, but by a wooden structural element of the microlame type extending beyond the ends of the two lateral boards as well as towards the inside of the structure in order to form tenons capable of receiving the mortises of the other beams of the system.
In addition to beams comprising three elementary layers, it can also be envisaged to produce beams with five or more layers, the reinforcement can either be positioned only in the central position, or can be doubled and then being positioned in the layers (two) and (four).
In other words, in such a case, the structural system according to the invention is characterized in that the number of boards used in the constitution of each layer is odd and is greater than three, five for example, a reinforcement being positioned at each node in the even layers.

The ribs or reinforcing plates are arranged at least at the support zones where the forces are maximum. Possibly, the internal forces being lower in the uprights and diagonals, the assemblies of the triangulated system can possibly be carried out conventionally by a simple assembly of the “tenon / mortise” type, the tenon being formed by the offset towards the outside of the board. central, and the mortise by the spacing between two elementary boards constituting the central board.
It is however advantageous to also reinforce these zones by fitting a reinforcing plate at this level making it possible to directly absorb the shear between the compressed diagonal and the tensioned post or vice versa.

At the junction zones, the reinforcement or rib is fixed over its entire perimeter to other beams (tie rods, rafters, uprights or diagonals) by simple nailing, which is the most economical solution and which presents as advantage of being semi-rigid allowing the entire plate to be stressed, after deformation of the edge connectors.

Brief description of the drawings

• les figures 1 à 3 et 4 à 6 illustrent, comme dit précédemment, la structure générale d'une part des systèmes à membrures parallèles et d'autre part en forme de triangle réalisables conformément à l'invention ;
• la figure 7 est une vue schématique en élévation d'un système à membrures parallèles réalisé conformément à l'invention ;
• la figure 8 est une vue détaillée en perspective éclatée de la zone cerclée de la figure 7 montrant la réalisation des noeuds d'assemblage au niveau de l'appui ;
• la figure 9 est une vue schématique en perspective montrant une charpente réalisée conformément à l'invention avec clouage des différents éléments entre eux ;
• la figure 10 est une vue éclatée, en perspective, de la réalisation des noeuds au niveau de la zone d'appui extrême et du montant central avec le tirant et la diagonale de la charpente.

The invention and the advantages which it brings will however be better understood thanks to the following description which is illustrated by the appended diagrams in which:

• Figures 1 to 3 and 4 to 6 illustrate, as said above, the general structure on the one hand of the systems with parallel members and on the other hand in the form of a triangle achievable in accordance with the invention;
• Figure 7 is a schematic elevational view of a system with parallel members made according to the invention;
• Figure 8 is a detailed exploded perspective view of the circled area of Figure 7 showing the production of the assembly nodes at the support;
• Figure 9 is a schematic perspective view showing a frame produced according to the invention with nailing of the various elements together;
• Figure 10 is an exploded perspective view of the realization of the nodes at the extreme support area and the central upright with the tie and the diagonal of the frame.

Way of realizing the invention

To make these structures, the elementary planks entering the constitution of each beam are massive planks whose section is generally between 10 and 30 cm in width for 3 to 8 cm in thickness.

For structures that can represent a very high resistance, individual boards can be recomposed into larger sections.

The length of said boards can be variable and depends on the systems to achieve and will for example be between four to eight meters.

The following concrete examples of implementation will help better understand the invention.

Realization of a system with parallel members

Such a system is of the type shown in FIG. 1.

To make a system according to the invention, illustrated by FIGS. 7 and 8, all of the beams entering into its constitution, namely the channels or frames (1) and (2), posts (3), diagonals (4) and intermediate posts (M) in the system have the following structure.

Concerning the horizontal channels or members (1) and (2) as well as the diagonals (4) and the uprights (M) (uprights not shown in Figure 8), each beam consists of three elementary planks (10,11,12). The board intermediate (10) is offset from the ends of the side boards (11,12), and this, in this case, from a distance of about 50 cm thus allowing to provide at each end a recess forming a mortise (13).

The diagonals (4) are made in a similar way from three boards and also have a mortise at their end.

The internal uprights (M) are made in a similar way.

The post (3) consists of two external planks (14) between which is inserted, over its entire length, a third board (15), intended to constitute the reinforcement of the panel type positioned in the core and which is formed by a microlame type structural panel having a thickness of 4 cm, the external boards (14) also having a thickness of 4 cm.

This panel (15) projects at each end relative to the boards lateral (14,15) and forms a tenon having a height of 20 cm corresponding therefore the width of the boards (10,11,12) constituting the dies, and a length of 50 cm corresponding to the length of the mortise (13) provided at the ends of the beams constituting the dies.

The association of the different elements between them is carried out by nailing.

If in the example illustrated, the reinforcing plate (15) extends over the entire system surface at each end at the supports (5), it could possibly consider making reinforcing plates only at each of the ends, the central part of the post (3) then being constituted by an additional board, set back from the ends of the boards side.

Regarding the nodes (17) formed at the junction zones internal, dies, uprights, diagonals, the connection is also made by inserting, at the junction zones, additional plates.

Each of the elements therefore comprises at the junction zone a mortise intended to receive the reinforcing element.

Possibly, the assembly could be carried out without reinforcing element and the ends of the uprights (M) and diagonals (4) will have the shape of a tenon formed by the offset towards the outside of the central board while the dies or members (1,2) will have, along their length, mortises obtained in producing the internal board (10) by means of elementary boards spaced apart each other of a length corresponding to the tenon of the ends.

Construction of a framework

Such an embodiment according to the invention is illustrated by the FIGS. 9 and 10 and corresponds to the general structure which is the subject of FIG. 4, it being understood that structures of the type illustrated by figures 5 and 6.

This structure is also produced from boards having a cross section 20 cm x 4 cm.

In this example, all of the junction areas between the rafters (6), the tie rod (7), the diagonals (8) and the upright (9) have reinforcement designated by the same reference (20).

As illustrated above, all of the beams entering the constitution of such a system, consists of three elementary boards (21,22,23) nailed together. The central plate (21) is, at the ends, set back from the ends of the side boards, so forming at this level a mortise (24) capable of receiving a reinforcing element.

At the junction between the ends of the tie rod (7) and the crossbowman (6), the reinforcement insert (20) is triangular in shape, the base of which has a length of 700 mm and a height of 400 mm.

At the node formed by the diagonals (8), the uprights (9) and the drawing (7), mortises are provided at each end of the diagonals (8) and uprights (9), and this by offset of the inner layer relative to the ends of the side boards, the mortise in the tie rod (7) being, in turn, obtained by making the central board from elementary boards spaced from each other other.

As before, the connection between the different constituents is obtained by nailing and reinforcements (20) of the nodes whose junction is made from a panel consisting of a wooden structural element of the type microblades having a thickness of 4 cm.

• possibilité de réalisation sur le site même,
• possibilité de recomposer une section importante, et ce de manière très économique,
• possibilité de mettre de la matière (panneau), seulement pour permettre le clouage nécessaire et la reprise du moment de flexion localisé ainsi que le cisaillement des poutres internes arrivant dans le noeud, par exemple le cisaillement généré d'une diagonale comprimée et un poteau tendu ou inversement.

Such systems with a triangulated structure have many advantages over previous solutions, namely:

• possibility of realization on the same site,
• possibility to redial a large section, and this very economically,
• possibility of putting material (panel), only to allow the necessary nailing and the resumption of the localized bending moment as well as the shearing of the internal beams arriving in the knot, for example the shearing generated by a compressed diagonal and a tensioned post Or vice versa.

Furthermore, the fact of making such a structure from planks nailed to form the various beams entering the system, allows make tenons and mortises by simply shifting a layer relative to the other.

In addition, the reinforcement panels positioned in the core of each beam, make it possible to increase the surface of the nailing zones reinforcing the structure. Such an interfaced panel also regulates the bending moments in the articulation on the dies in the case of a system with parallel members or triangulated since the reinforcement itself absorbs bending; it thus absorbs the shear between the internal beams arriving in the node by relieving mechanically the external beam.

Claims (4)

1. A system for trussed wooden structures, with parallel members or in the shape of a triangle, for producing frameworks, bridges, floors, consisting of beams (1, 2, 3, 4, 6, 7, 8, 9) made up of at least three planks (10, 11, 12, 21, 22, 23), a central plank forming a web (10, 21) and at least two lateral planks (11, 12, 22, 23) being of the same thickness and nailed together, characterized in that:

   the central plank (10, 21) is offset with respect to the ends of the two lateral planks (11, 12, 22, 23), this being in such a way as to form, at this point, mortises (13, 24) which include, at the junction zones between the beams (1, 2, 3, 4, 6, 7, 8, 9), a reinforcement panel (15, 20), which is positioned in the web, the shear surfaces of the reinforcement panel (15, 20) corresponding to the lateral surfaces of the two lateral planks (11, 12, 22, 23) at each junction zones, said reinforcement panel being made up of a structural wooden element of the "thin strip" or "ply" type.
2. The structural system as claimed in claim 1, characterized in that the central plank (10, 21) consists of elemental planks placed end to end or spaced apart so as to form a mortise capable of accommodating a reinforcement of the "panel" type.
3. The structural system as claimed in one of claims 1 and 2, characterized in that the number of planks involved in making up each beam is an odd number and is greater than three, a reinforcement being positioned at each node in the even-numbered layers.
4. The structural system as claimed in one of the preceeding claims, characterized in that the reinforcing plate consisting of a structural wooden panel constitutes the central plank (15) of the beams that make up the posts (3) of a trussed structure with parallel members.

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