FR2631882A1 - Method for manufacturing structural elements made from bonded plywood which has been reinforced by incorporating a reinforcing material and reinforcing strip which can be used to implement it - Google Patents

Abstract

The present invention relates to a method for manufacturing structural elements made from bonded plywood consisting of a stack of strips bonded together. According to this method, there is incorporated, at the level of the strips 7 to 10 of the structure subjected to tensile stresses, at least one reinforcing material 15 which has a high tensile strength associated with the strips 7 to 10 of the structure by means of a binder giving the linking surface sufficient shear strength to transmit the tensile stresses between the said reinforcing material 15 and the said strips 7 to 10. Application to structures made from bonded ply.

Description

Method for manufacturing structural elements of glued laminated wood reinforced by incorporation of a reinforcing material and reinforcing strip usable for its implementation.

The present invention relates to a method of manufacturing structural elements of glued laminated wood having the aim of improving the mechanical resistance of such a structure, as well as a reinforcing blade with high tensile strength intended to be used in such a structure.

In general, glued laminated wood structures are in the form of beams or arches. They are made by stacking on top of each other either flat or by shaping them on a hanger at the curvature of the arc, glued blades, then tightening said blades until drying by means of clamps or porous. In very long structures, the elementary blades, with the exception of the outermost blades, are placed end to end with joints offset lengthwise to transmit stresses to the right of said joint, by the adjacent blades. of tension developed in the blades separated by the joint. In the external blades of the structure, the cut-outs of the elementary blades are, to ensure the same transfer, made in bevel, the stresses of tension being transmitted by the adhesive between the two bevels blades. To obtain with such a structure a beam or an arc having a high mechanical resistance it is necessary that the blades are made in a healthy wood, having a humidity lower than 15 X and which are cut according to the straight grain of the wood with a minimum knots and other defects that reduce the tensile strength.

Currently, in particular to meet the standards of mechanical resistance, the blades used in glued laminated structures are made of imported wood, more particularly in wood from the Nordic countries. In fact, this type of wood which has grown more slowly has better mechanical resistance than the Scots pines or maritime pines found in France.

The present invention therefore aims to provide a new method of manufacturing a glued laminated wood structure such as straight beams or arched beams, which allows the use of softwood products produced in France while obtaining a resistance structure mechanical equivalent or superior to imported wooden structures with identical wood sections.

The present invention also aims to provide a method of manufacturing a glued laminated wood structure having improved mechanical strength which does not cause significant modifications in the steps of the method of manufacturing glued laminated wood structures currently used.

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The present invention also aims to provide a new blade intended to be incorporated into a glued laminated wood structure to increase the mechanical resistance, in particular the resistance to bending.

Consequently, the subject of the present invention is a process for manufacturing structural elements of glued laminated wood constituted by a stack of glued strips, characterized in that there is incorporated, at the level of the strips of the structure subjected to tension stresses, at least one reinforcement material with high tensile strength associated with the structure blades by a binder ensuring a shear strength of the bonding surface sufficient to transmit the tension stresses between said reinforcement material and said blades .

The incorporation of a reinforcing material at the level of the blades subjected to tension constraints makes it possible to improve the mechanical resistance to bending of the glued laminated wood structure as a whole.

Different embodiments can be used to incorporate the reinforcement material with high tensile strength into the structure. According to a first embodiment, a reinforcement material with high tensile strength coated in a binder ensuring the connection between said material and the wood constituting the boards, is incorporated between two wooden boards of the structure during stacking during the manufacturing of the glued laminated wood structure.

According to another preferred embodiment, the reinforcing material is incorporated into a wooden blade or other solid material which can be dissipated with the wood of the blades, so as to produce a reinforced blade incorporated in the stack during the manufacture of the structure in glued laminated wood. In this case, independent reinforced blades are produced separately which are then used like the other blades during the manufacture of the glued laminated wood structure.

The present invention also relates to a reinforcing strip for a structure of glued laminated wood, characterized in that it is constituted by a sandwich structure comprising at least two wooden strips, with between two adjacent strips a reinforcing material, l 'assembly being secured by a binder.

The reinforcing material used, either between the strips of the glued laminated structure, or incorporated into the reinforcing strip, can consist of mineral or organic fibers such as glass fibers, carbon fibers, poly fibers ter, aramid fibers such as those sold by Dupont de
Nemours under the brand name "Kevlar", etc.

These fibers can be incorporated between the stacking boards or in the reinforcing board in different ways. According to a first embodiment, the fibers are incorporated in the form of a woven or non-woven fabric joined by a binder with the surfaces of the adjacent blades. According to another embodiment, the fibers are used in the form of a sheet soaked in binder which ensures the connection between the fibers and the connection of the sheet with the adjacent surfaces of the blades or lamellae. According to another embodiment, the fibers are incorporated by mixing short fibers with a material capable of being molded or extruded in the form of a blade such as a mixture of a binder with various fillers, in particular particles of wood or a plastic material compatible with the binder of the glued laminated structure. According to a third embodiment, the fibers are incorporated in the form of long fibers or in the form of continuous elements such as wires, cables and strips positioned in the lengthwise direction of the blades, in particular between two blades of the structure, said blades possibly having their facing surfaces grooved to receive the reinforcing material.

On the other hand, the binder used is chosen from casein adhesives or synthetic resin adhesives, such as urea-formaldehyde adhesives. This binder must provide a superficial bond with the reinforcing material and the wood of the blades or lamellae sufficient to ensure the transmission of the tension stresses between the reinforcing material and the adjacent wooden blades or lamellae.

Other characteristics and advantages of the present invention will appear on reading the description of various embodiments of glued laminated beams made below with reference to the attached drawings in which:
Figure 1 is a perspective view with cutaway
partial of a first embodiment of a beam in
glued laminate according to the present invention; the Figu
res 2 and 3 are similar views for two other modes
of achievement.

it is obvious to a person skilled in the art that the dimensions and dimension ratios of the various blades and reinforcing materials have not been observed to facilitate illustration.

As shown in Figure 1, the glued laminated wood structure obtained, namely a straight beam, is constituted by a stack over a height corresponding to the thickness of six blades, blades 1 to 10. In the embodiment shown and-in known manner, the groove 11 between the two elementary blades 1 and 2 abutted to constitute the upper blade of the stack, is constituted by a bevel so that the mechanical stresses are transmitted by the binder applied to the two fingerprint surfaces, while the strips 4 and 5 which are at an intermediate level of the stack are joined by an end-to-end joint, the longitudinal stresses exerted in the elementary strips 4 and 5 being transmitted by the adhesive bonding of the blades to the upper and lower blades 3 and 6 which overlap the joint.

According to the present invention, between the lower blade formed by two elementary blades 9 and 10 joined by a bevel cut 13 and the blades 7 and 8 joined by a butt joint 14 forming the immediately upper layer of the stack, is incorporated a reinforcing material which, in this embodiment, is- constituted by cables 15 housed in grooves 16 made in the facing faces of the blades 7 to 10. The cables are secured to the wall of the grooves 16 by a binder which is the same as that ensuring the bonding of the stacking boards.

The cables can be made of a wide variety of fibers and they preferably have a stranded structure to prevent any slippage of the cable relative to its binder sheath and to the wall of the groove under the effect of the differences in elongation which may appear under the action of longitudinal stresses exerted in the blades and in the cable. The junctions between unitary blades by bevel or end-to-end cutting according to the conventional technique avoids any local concentration of tension stresses in the reinforcement cables in line with the connections between the blades.

In the embodiment of Figure 2 the same references are used to designate the same elements or equivalent elements. In this embodiment, the reinforcing material consists of a strip of canvas 17 or other similar material which is incorporated with the binder with which it is impregnated, during the manufacture of the glued laminated wood beam, between the lower blades 7 -8 and 9-10. The binder used can also be the binder usually used for gluing the blades or a specific binder whose resistance is greater than that of wood but does not cause tearing in the wood.

According to another embodiment shown in FIG. 3, instead of interposing the reinforcing material between two thicknesses of blades, a reinforced blade such as the blade 18 in FIG. 3 is used in the glued laminated wood structure. This blade 18 is preferably used as a lower blade, namely in the stretched part of the beam. On this blade 18 are stacked in the usual way the glued blades 1 to 8. As in the embodiment of Figure 1, the blades, including the blade 18, are stacked at a height corresponding to the thickness of six blades .

The construction of the reinforced blade 18 will now be explained.

This reinforced blade 18 is obtained by sawing in the direction of length a conventional blade so as to obtain strips 18a and 18b. A reinforcing material 19 associated with a binder is interposed between the two strips 18a and 18b and the assembly is kept under pressure until the binder sets. When the elementary lamellae 18a-18b must be butted to obtain a blade 18 of desired length, the joints 20 are of the bevelled edge type as for the upper and lower blades of a glued laminated beam.

In accordance with the present invention, the reinforcing material 19 of the reinforced blade 18 can consist of mineral or organic fibers such as glass fibers, carbon fibers, polyester fibers, aramid fibers sold under the brand. "Kevlår". On the other hand, the binder is chosen from casein adhesives or adhesives with synthetic resins such as urea formaldehyde adhesives.

The fibers constituting the reinforcing material 19 can be incorporated between the lamellae 18a-18b in different ways. They can be in the form of long fibers positioned lengthwise of the blade 18 and embedded in the layer of binder interposed between the strips 18a and 18b. They can also be in the form of a mixture of short fibers associated with the binder. In this case, the mixture is sprayed onto the upper surface of the strip 18a, then the strip 18b is superimposed and the assembly is tightened until complete drying. The fibers can also be in the form of a fabric in a manner analogous to the case of FIG. 2, the fabric coated with binder being interposed between the lamellae 18a and 18b.

One can also consider mixtures of short or long fibers and fabric.

Claims (10)

Claims 1. A method of manufacturing structural elements of glued laminated wood consisting of a stack of glued strips, characterized in that there is incorporated, at the level of the strips (7 to 10) of the structure subjected to tension stresses, less a reinforcement material (15) with high tensile strength associated with the blades (7 to 10) of the structure by a binder ensuring a shear strength of the bonding surface sufficient to transmit the stresses of tension between said reinforcement material (15) and said blades (7 to 10). 2. Method according to claim 1, characterized in that the reinforcing material (15,17) with high tensile strength coated in a binder ensuring the connection between said material and the wood constituting the blades (7 to 10), is incorporated between two wooden slats of the structure during stacking during the manufacture of the glued laminated wood structure. 3. Method according to claim 1, characterized in that the reinforcing material (19) is incorporated in a wooden blade (18) or other material which can be joined to the wood of the blades, so as to produce a reinforced blade (18) incorporated in the stack during the manufacture of the glued laminated timber structure. 4. Reinforcement blade for implementing the method according to re vendication 3, characterized in that it is constituted by a sandwich structure comprising at least two wooden strips (18a-18b), with between two adjacent strips a reinforcing material (19), the assembly being secured by a binder. 5. Method according to any one of claims 1 to 4, characterized in that the reinforcing material consists of mineral or organic fibers such as glass fibers, carbon fibers, polyester fibers, aramid fibers sold under the brand name "Kevlar". 6. Method according to claim 5, characterized in that the fibers are incorporated in the form of a woven or nonwoven fabric (17). 7. Method according to claim 5, characterized in that the fibers are used in the form of a sheet soaked in binder which ensures the connection between the fibers and the connection of the sheet with the adjacent surfaces of the strips (7 to 10 ) or lamellae (18a-18b>. 8. Method according to claim 5, characterized in that the fibers are incorporated by mixing short fibers with a material capable of being molded or extruded in the form of a blade such as a mixture of a binder with various fillers, in particular particles of wood or plastic compatible with the binder of the glued laminated structure. 9. Method according to claim 5, characterized in that the fibers are incorporated in the form of long fibers or in the form of continuous elements such as son, cables (15) and strips positioned in the lengthwise direction of the blades (1 to 10) in particular between two blades (7-8, 9-10) of the structure, said blades optionally having their grooved facing surfaces (16) for receiving the reinforcing material. 10. Method according to any one of claims 1 to 4 and 6 to 9, characterized in that the binder used is chosen from casein adhesives or synthetic resin adhesives, such as urea-based adhesives. formalin.