BE1019343A3 - BUILDING PRODUCT BASED ON BAMBOO OR HIGH PERFORMANCE WOOD AND METHOD OF MANUFACTURE - Google Patents

Abstract

Construction product of beam or column type, comprising boards of a fibrous material, arranged in layers (10,10 ', 10' ') thus forming a stack (1), characterized in that each layer comprises a succession of boards (101,101 ', 101' ') so as to produce abutments (102) in said stratum (10) and characterized in that for each group of two contiguous strata, the abutments of a stratum are arranged in an offset manner with respect to the abutments of the other stratum, such that the longitudinal distance between each abutment (102) of one stratum (10) and each abutment (102 ') of the other stratum (10') is greater than or equal to six times l 'thickness of said stratum. (Figure 1).

Description

HIGH-PERFORMANCE BAMBOO OR WOOD-BASED CONSTRUCTION PRODUCT AND METHOD OF MANUFACTURE

The present invention relates to a construction product, of the beam or column type, comprising several layers made from a material consisting essentially of bamboo and / or high performance wood. The present invention also relates to a method of manufacturing such a product.

The present invention aims to improve the known technology of laminated wood. This technology makes it possible to produce structural products of beam or column type construction from wooden planks. The boards are contiguous and stacked, incidentally put under pressure, thus forming a solidarized structure.

Products having a greater length than the length of the boards constituting the product are possible, thanks to the known technique of "finger jointing". The ends of the boards are provided with multiple notches (or toothing), made in the transverse direction according to the thickness of the board. The planks are then abutted and connected by gears. The planks connected at the abutment thus form a lamella (hereinafter called stratum) of the laminated product. They are then stacked and contiguous to form the final product, called "laminated".

The connection by multiple notches may be a weak point for the transmission of forces through said blade for woods with high mechanical strengths. In general, this fitting is accepted by certification bodies up to a flexural strength limit of about 30 MPa (determined by a 4-point bend test). The technique of "finger jointing" is validated when the break occurs in the wood. For this reason, medium performance wood types (eg C18, C20, C24 as defined in EN 338 "Structural timber, Strength classes") are used, with a characteristic bending stress of 30 MPa or less. Beyond this limit, the fracture is generally present in the abutment thus preventing the development of the mechanical advantages of the high-performance woods and consequently the obtaining of structural products based on glue-laminated wood more efficient.

[0005] Nevertheless, there are significantly more efficient wood species. In addition, it is known that the mechanical performance of certain materials made of natural fibers such as bamboo or rattan are generally much greater (typically more than twice) those of wood.

The present invention aims to provide a solution to this problem of the prior art by providing a building product, based on glue-laminated technology, having mechanical performance significantly higher than products made using laminated technology. glued from the prior art, and made from fibrous materials consisting essentially of natural fibers, such as high performance wood and bamboo. The present invention also aims to provide a method for the manufacture of such a construction product.

The present invention is therefore to provide a structural type of construction product, for applications as beam or column.

According to the present invention, a construction product and a method for the manufacture of such a product are described as recited in the appended claims.

According to a first aspect of the present invention, a construction product is provided comprising boards made from a fibrous material consisting essentially of natural fibers. The construction product is advantageously of the beam or column type.

[0010] Preferably, the material is (essentially) made of (fibers of) bamboo. Alternatively, the material is (essentially) made of wood, preferably of high performance wood. The material may consist of a mixture of bamboo and wood.

Preferably, said material has mechanical performance greater than or equal to type C35 woods as defined in EN 338 "Structure wood, strength classes". Preferably, the material has a characteristic axial tensile strength (according to EN 338) greater than or equal to 20 MPa, preferably greater than or equal to 25 MPa.

Preferably, the boards have a longitudinal shape with two ends, the boards therefore having a length greater than the width and the thickness. Preferably, the planks are of rectangular section, the planks thus having a greater width than the thickness.

The boards are arranged in layers, which are secured and arranged to form a stack. The construction product is characterized in that each stratum comprises (and preferably consists of) a succession of planks arranged in the longitudinal direction of said planks, so that the ends of successive planks face each other, thereby forming abutments in said stratum. The construction product is further characterized in that for each pair (group of two) of adjoining strata, the ends of one stratum are arranged offset from the abutments of the other stratum, so that the longitudinal distance between each abutment of one stratum and each abutment of the other stratum is greater than or equal to six times the thickness of said stratum.

This arrangement of the boards and abutments allows, in use, a transfer of the tensile stresses of a board to the subsequent board by bridging. The tensile stresses are taken up by shear stresses, which bypass the abutment. The effect is to cancel the tensile stresses at the abutment.

Using this arrangement of the boards, we obtain the advantage that it is no longer necessary to take into account the weakness of the abutments when sizing the product (the stack) in a structure. The tensile portions of the stack can therefore advantageously be dimensioned by using the characteristic axial tensile strength of the material of the boards, greater than or equal to 20 MPa, considering the portion of the tensile section reduced by a stratum (especially the transfer stratum). The compression portions of the stack may advantageously be dimensioned using the characteristic axial compressive strength by considering the entirety of the portion of the section in compression.

The sizing of products according to the present invention is preferably carried out according to the EUROCODES 5 standard.

The values of the characteristic resistors are preferably determined according to the standard EN 338.

Preferably, said offset of the abutments of a stratum is with respect to the abutments of two contiguous layers on either side. Thus, the abutments of each stratum are offset from said longitudinal distance with respect to the abutments of two contiguous strata on either side. Preferably, said offset of the abutments of a stratum is compared to the abutments of three adjacent layers on either side. Thus, the abutments of each stratum are offset from said longitudinal distance with respect to the abutments of three contiguous layers on either side.

[0019] Preferably, said longitudinal distance is greater than or equal to six times the thickness of said stratum.

Preferably, said boards are made of bamboo slats (lamellae compressed and glued). Preferably, the lamellae are essentially arranged in the longitudinal direction of the board and are essentially the same length as the board.

[0021] Preferably, the stack comprises layers having different thicknesses.

Preferably, the planks of at least one stratum of said stack are made from a material different from the material of the planks of another stratum.

Preferably, the stack comprises at most one abutment of any stratum in each transverse section perpendicular to the longitudinal axis of the stratum.

Preferably, the boards of the same layer are arranged without a physical or chemical connection between their ends. A coupling is advantageously not necessary thanks to the bridging of the stresses and, consequently, the cancellation of the tensile stresses at the abutment.

[0025] Preferably, said layers are secured with an adhesive material.

Preferably, slight asperities are formed on the longitudinal surfaces of bonding strata. Contrary to the recommendations of the prior art of planing these surfaces, the increased roughness allows, for some species of wood and bamboo, a better capacity shear strength of the bonding joint. The asperities are preferably at a characteristic interdistance between 0.05 mm and 10 mm.

Alternatively, the longitudinal bonding surfaces of the boards are provided with notches. The notches are preferably oriented in the longitudinal direction of the boards. Alternatively, they may be oriented in a direction perpendicular to the longitudinal direction. The notches thus created advantageously make it possible to improve the shear strength of the longitudinal seam joints between two layers. This surface treatment simultaneously causes an increase in the bonding surface, a better mechanical adhesion of the adhesive agent and a rupture plane comprising in part the bonding joint and for other part the base material.

Preferably, the construction product according to the present invention further comprises a set of lamellate-glued strata. Said assembly is secured to 11 stack.

Preferably, the transverse direction along the width of the strata of said set is perpendicular to the transverse direction along the width of the strata of the stack and the longitudinal direction of the strata of said set is parallel to the longitudinal direction of the strata of the stack.

Preferably, the construction product according to the present invention has a cross section of form I or T, wherein said stack constitutes at least a rectangular portion.

According to a second aspect of the present invention, a construction product is provided comprising boards made from a fibrous material consisting essentially of natural fibers. The construction product is advantageously of the beam or column type.

Preferably, the boards have a longitudinal shape with two ends, thus having a length greater than the width and the thickness. Preferably, the planks are of rectangular section, the planks thus having a width greater than 11 thickness.

[0033] Preferably, said material has mechanical performance greater than or equal to type C35 woods as defined in EN 338 "Structural wood, strength classes". Preferably, the material has a characteristic axial tensile strength (according to EN 338) greater than or equal to 20 MPa, preferably greater than or equal to 25 MPa.

The boards are arranged in succession in the longitudinal direction of said boards, so that the ends of successive planks face each other, thus achieving abutments. Such a succession of boards will be referred to as the stratum. Several layers can be superimposed to form a stack. The product according to this second aspect of the invention therefore comprises at least one layer of planks arranged in succession.

The construction product is characterized in that the boards of the same stratum are preferably secured by mechanical connection constituted by multiple notches. Multiple nicks are provided on the ends of the boards.

The ends of the boards are preferably oriented in a plane, said orientation, which can be oriented according to one of the following orientations or any possible combination of the following orientations.

Preferably, the plane of orientation of the ends of the boards is parallel to the direction (axis) transverse of the board following the thickness.

By considering a first reference plane parallel to the transverse axis along the thickness of the board and parallel to the longitudinal axis of the board, preferably, the plane of orientation of the ends of the boards is oblique to the first. reference plane at an angle between 10 ° and 80 °, preferably between 20 ° and 70 °. This angle refers to the angle measured in a plane perpendicular to the intersection of the plane of orientation with the first reference plane.

Preferably, the plane of orientation of the ends of the boards is parallel to the direction (axis) transverse of the board following the width.

By considering a second reference plane parallel to the transverse axis along the width of the board and parallel to the longitudinal axis of the board, preferably, the plane of orientation of the ends of the boards is oblique to the second plane reference at an angle between 10 ° and 80 °, preferably between 20 ° and 70 °. This angle refers to the angle measured in a plane perpendicular to the intersection of the plane of orientation with the second reference plane.

Preferably, the multiple notches are parallel to the intersection of the plane of orientation of the board ends with the first reference plane. Alternatively, the multiple notches are parallel to the intersection of the plane of orientation of the board ends with the second reference plane.

Preferably, the stack comprises a first group of board ends oriented in a first plane of orientation and a second group of board ends oriented in a second plane of orientation. The two orientation planes are oblique to the first or second reference plane at an angle of equal magnitude, but in the opposite direction. Preferably the same board may comprise one end of the first group and one end of the second group. Alternatively, the layers of the stack comprise alternately ends of the first group and ends of the second group.

According to a third aspect of the present invention, a construction product is provided according to the first aspect of the present invention and comprising in combination one or more elements of the construction product according to the second aspect of the present invention. Alternatively, a construction product is provided according to the second aspect of the present invention and comprising in combination one or more elements of the construction product according to the first aspect of the present invention. Since the mechanical connections between successive boards according to the present invention allow a greater transfer of the traction forces directly through abutments, the minimum offset distance of the abutments of adjoining layers may advantageously be chosen to be less than six times the thickness of the board. . The minimum offset distance is preferably three times the board thickness, or preferably four times the board thickness.

According to a fourth aspect of the present invention, a method for the manufacture of a construction product is provided. In a first step of the method, planks of a fibrous material consisting essentially of natural fibers, such as bamboo or wood, are provided. The material has a characteristic tensile strength greater than or equal to 20 MPa (according to EN 338). Then, a minimum length Lv transfer tensile forces of a board to the next board by bridging is determined. This transfer of tensile forces is achieved by resuming the tensile stresses by shear stresses. Successively, a minimum offset value corresponding to the maximum between Lv and six times the thickness of the boards is determined. Hereinafter, a stratum is made by placing several of said boards in succession in the longitudinal direction, so as to present the ends of successive planks face to face, thus forming abutments. Finally, several of said layers are arranged and secured so as to form a stack intended to constitute at least a portion of the construction product. The arrangement of the boards is such that, for each pair of adjoining strata, the longitudinal distance between each butt of planks of one stratum and each abutment of planks of the other stratum is greater than or equal to the said minimum value of offset.

Preferably, the minimum length Lv is determined according to the equation:

with: ft the value of the characteristic axial tensile strength of the board material, - h the thickness of the board, - kSh a coefficient of nonuniformity of the shear stresses, having a value between 0.5 and 1, tv shear stress initially present in the transfer plane, as calculated by the material resistance theory for the board material and fv the value of the characteristic shear strength of the board material.

Preferably, the layers are formed by arranging the boards without physical or chemical connection between their ends.

Alternatively, the ends of the boards are provided with multiple notches as mentioned in the second aspect of the present invention.

Brief description of the figures

FIG. 1 represents a beam according to an example of an embodiment of the present invention, in side and front view (B-B). The strata and the layout of the planks are visible.

FIG. 2 represents an example of an embodiment of an assembly diagram of a beam according to the present invention. The beam is shown in side view.

FIGS. 3A-E show five configurations of ends (abouts) of plank with multiple notches made in the direction of the thickness (h) or in the direction of the width (w) of the planks, to allow the abutment or the connection between two successive boards.

Figures 4A and B respectively show an example of notched longitudinal sides of board (or block) with the notches oriented in the longitudinal direction or perpendicular to this direction.

Figures 5A and B show an implementation of the stack according to the present invention in two different orientations.

FIG. 6 represents a construction product having a section of form I. The product consists of stacks of planks of planks made in a horizontal direction.

Detailed description of the invention

The basic raw material of the construction product of the present invention is preferably bamboo. Alternatively, the basic raw material can be rattan.

The basic raw material of the construction product of the present invention can be high performance wood.

By high performance is meant a material having mechanical performance greater than or equal to type C35 woods as defined in EN 338 "Structural wood, strength classes". The materials mentioned above are fibrous materials, consisting essentially of natural fibers.

The bamboo planks are preferably formed of bamboo slats arranged parallel to the longitudinal direction of the board. Preferably, therefore, the axial orientation of the lamellae substantially coincides with the longitudinal axis of the board. The slats preferably (all) have a length equal to the length of the board. This allows to better exploit the mechanical performance of bamboo.

The bamboo planks preferably have a density of between 600 kg / m 3 and 13 00 kg / m 3, preferably between 1000 kg / m 3 and 1300 kg / m 3, preferably between 1050 kg / m 3 and 1300 kg. / m3.

Alternatively, high performance wooden planks may be used in the construction product according to the present invention. These high performance woods can be class C35, C40, C45, C50 and higher. They can be class (hardwood) D35, D40, D50, D60, D70 and higher. Classes are defined in EN 338 "Structural wood, Classes of resistance".

According to a first aspect of the present invention, a construction product is provided. The construction product is used more for structural applications, such as beam or column. In the remainder of the description, said construction product will be designated by the term "beam".

The construction product comprises several boards made from one or more of the materials described above (bamboo and / or high performance wood).

In the present invention, the term "board" refers to a material that exhibits essentially uniform and continuous mechanical characteristics throughout the material.

Preferably, the boards are of longitudinal shape, thus having a length greater than the width and the thickness. Preferably, the width is greater than the thickness (the boards have a rectangular section). The boards preferably have a length of between 1 m and 12 m, preferably between 1.5 m and 12 m, preferably between 2.5 m and 12 m.

[0064] Preferably, the thickness of the boards is between 5 mm and 150 mm, preferably between 10 mm and 100 mm, preferably between 20 mm and 70 mm.

[0065] Preferably, the width of the boards is between 5 cm and 50 cm, preferably between 10 cm and 30 cm, preferably between 13 cm and 25 cm.

The arrangement of the boards in the beam is described with the help of Figure 1. Said boards 101 are arranged in several layers 10 and secured, thus forming a stack 1 (shown in side view and in front view, section BB ). The stratum 10 has a width corresponding to the width of a board 101 and a thickness corresponding to the thickness of a board 101. The stack 1 consists of a single row of strata 10, 10 '. The layers may be assembled by known techniques, advantageously by gluing. They can alternatively, or additionally be secured by mechanical means of assembly, rod type, such as screws, nails, lag screws or the like.

According to the present invention, each layer 10 comprises several boards 101, 101 ', 101' 1 arranged end to end, in the longitudinal direction of the boards. In each stratum 10, the boards are arranged one after the other, with their ends (their abutments) facing each other.

In order to be able to make the most of the superior performance of these high performance materials in the beam, the arrangement of the boards in the strata of the stack is such that, as will be described, the constraints can circumvent the point. weakness formed by the abutment 102 of two successive boards in the same stratum.

According to one aspect of the present invention, the strata subjected to tensile stresses do not transmit these forces from one board 101 to the other 101 'directly by the abutment 102, but bypassing it. These tensile forces in the plate 101 generate shear stresses in the interface 19 between two layers 10 and 10 '. This shear is compensated by one. additional tensile force taken up in the stratum 10 '. Beyond the abutment, this force again crosses the interface 19 by shearing to generate a tensile force in the board 101 '. And vice versa. This effect is represented by the arrows in Figure 1.

This principle is useful especially for the strata subject, in use, to tensile stresses. In strata subjected, in use, to compressive forces, the problem in principle does not arise. In the latter case, the compression forces can be transmitted directly through the abutment between two successive boards.

The resumption of tensile forces by shearing forces can be done only if the ends (abouts) of planks and corresponding abutments present in the contiguous strata are offset from the stratum in which l It is desired that abutment 102 be bypassed. This condition can be achieved by an offset arrangement of the boards in the longitudinal direction and this for one or more contiguous (adjacent) strata.

The offset of the boards in a stratum with respect to the arrangement of the boards in the adjacent strata preferably takes into account the length necessary to ensure that the recovery of tensile stresses by shear stresses can take place.

The minimum lag length Lv could be determined as follows. Consider the tensile state tensile strength Rt in a stratum 10:

with: - ft the value of the tensile strength (stress limit) of the material of the board and - Ap the cross-section of a board (stratum), Ap being equal to the thickness (height) h of the board multiplied by the width w of the board.

This tensile strength Rt in transit to the bridging layer 10 'generates a shear stress rtr such that:

with: - Av the minimum transfer surface of the shear forces being equal to the width w of the board multiplied by the minimum transfer length Lv and - ksh a coefficient making it possible to take into account the non-uniformity of the shear stresses. Preferably, k3h = 0.5. Depending on the type of glue, the state of the board surface and the type of material, ksh can have a value between 0.5 and 1.

This shear stress rtr is added to the shear stress rv initially present at this location. tv can be calculated according to the theory of resistance of materials and considering the beam as entirely homogeneous (without strata or butts).

Therefore, the determination of Lv must satisfy the following equation: with:

- fv the value of the shear strength (stress limit) of the material of the board.

The values ft and fv are preferably determined according to ISO 8375 "Glulam structure - Test methods for the determination of certain physical and mechanical properties" (2009-02-01). The value fv can be determined according to ISO 3347 "Determination of shear stress in parallel shear with fibers" (1975-01-15).

Two examples of calculation of Lv follow. Both examples consider an isostatic beam of length L, width w and thickness (height) h, loaded with a load P in the middle of the beam (L / 2). The boards have a length 1, a width w and a thickness h.

As demonstrated by the theory of the resistance of materials, the general equation of shear stresses τ <Z) in the case of a rectangular section beam is expressed as (z is the axis in the transverse direction following the thickness, z = 0 in the middle of the thickness):

By this equation we thus find a minimum for T (Z = H / 2) = 0 and a maximum for the neutral fiber τ (ζ = 0) = 3

Vz / (2wH).

We seek Lv for the planks of the strata subjected to the most important tensile stresses, in particular the lowest stratum. We seek to identify τν which is the shear stress for z = v with v being the distance from the neutral fiber to the fiber taking up the transfer of forces: v = H / 2 - h. By replacing this term in the equation τ (z) we obtain:

or

We can then replace V2 by -P / 2 that we have found previously:

Since then we know the value of τν.

We can therefore identify the minimum length Lv in this situation from the general equation for which all the other terms are known:

and deduce 11 equation for Lv:

Example 1:

Take the case of a high performance material: ft = 80 N / mm2 fv = 20 N / mm2 with boards 5 mm thick, a kSh = 0.5, a beam: L = 15 mw = 125 mm H = 600 mm, and a load P = 100 kN.

Since then:

So :

corresponding to 40/5 = 8 times the thickness of the board.

Example 2:

Take case 2 of a high performance wood C40: ft = 24 N / mm2 fy = 3.8 N / mm2 with planks 40 mm thick, a ksh = 0.5, a beam L = 15 mw = 125 mm H = 600 mm, and a load P = 100 kN.

Since then:

So :

corresponding to 1800/40 = 45 times the thickness of the board.

It is understood that Lv is the minimum offset distance and that, depending on the situation, one can choose a value greater than that calculated.

In cases where the value of Lv results to be less than six times the thickness of the board, it is preferable to use this last value as the minimum distance of shift.

Lv is also dependent on the non-uniform distribution of shear stresses on this transfer length. The coefficient ksh takes into account this phenomenon which is, among other things, a function of the type of glue used, the constituent material, the roughness of the bonding surfaces, etc.

As the offset is only required so that the constraints can bypass the abutment of two boards, it is obvious that, advantageously, a 1 shift condition applies only for the strata immediately adjacent to the stratum of the stratum. abutment considered.

Thus, in the stack 1, the abutments 102 'of the planks in a stratum 10' are offset in the longitudinal direction of the stratum with respect to the abutments 102 of the planks of the stratum 10 immediately contiguous by a greater distance or equal to Lv or six times the thickness of the boards.

The offset indicated above advantageously applies only to the portion of the stack of layers provided, in use, to be put in tension, because the compression strata can always transfer the forces directly through the abutment, for example because the ends (abouts) of the boards touch. Said offset may advantageously be applied to the entire stack.

Preferably, for each stratum of the stack, the distance (measured in the longitudinal direction of the board) between each abutment of two planks in said stratum and the abutments located in the stratum (s) immediately contiguous ( s) at said stratum is at least six times the thickness h of said stratum.

[0090] Preferably, the abutments of the boards (102) in each pair of adjoining layers one to 1! other of the stack, are offset by a distance of at least 8 times the thickness (height) of board, preferably at least 10 times the thickness, preferably at least 12 times the thickness thickness of the boards.

Preferably, for each stratum (10 '') of the stack, the abutments are arranged in a staggered manner along the longitudinal direction of the stratum with respect to the abutments of two adjacent strata on either side (in particular and 10 'on the one hand and 10' '' and 101V on the other hand), the offset being a distance of at least six times the thickness h of the stratum, preferably at least 8 times the thickness of the layer, preferably at least 10 times the thickness, preferably at least 12 times the thickness.

Preferably, for each stratum of the stack, the abutments are arranged in a staggered manner along the longitudinal direction of the stratum with respect to the abutments of three adjacent strata on either side, the offset being from a distance at least six times the thickness h of the layer, preferably at least 8 times the thickness of the layer, preferably at least 10 times the thickness, preferably at least 12 times the thickness of the layer, 'thickness.

By considering the shift over several strata, the shear stresses taking up the tensile stresses can advantageously be distributed over several strata. It is considered that the effects of the resumption of tensile stresses by shear stresses become negligible beyond three strata (of the same thickness).

[0094] Preferably, the abutments in each pair of adjacent layers are spaced apart in the longitudinal direction by at least 150 mm, preferably by at least 200 mm, preferably by at least 240 mm. mm.

As an example, a method of assembling the strata is described, as shown in Figure 2, and which takes into account the offset constraints of the boards (and therefore abutments) indicated above.

A first layer 11 is formed from a board 108 of length L and arranging the successive boards behind it in the longitudinal direction. A second layer 12 is formed above the first layer 11 from a first half-cut board of length L and successively arranging boards of length L. An offset of% L is thus achieved with respect to the boards of the first stratum 11.

The third layer 13 is formed from a board cut to a quarter length L and successively arranging boards of length L. An offset of% L is thus reached relative to the boards of the first layer 11 and % L relative to the planks of the second stratum 12.

The fourth layer 14 is formed from a board cut to three quarters length L and successively arranging boards of length L. An offset of% L is thus achieved relative to the boards of the first layer 11, of KL with respect to the planks of the second stratum 12 and ^ L with respect to the planks of the third stratum 13.

The strata 11-14 are stacked and secured, for example contiguous, performing a first stack. By having several stacks identical to this first stack, a larger stack can be achieved. This last stack can constitute a part of the beam, or even the entire beam.

However, it is preferable to shift each repetition (each stack of four layers 11-14) by a certain distance in order to avoid any coincidence of abutments 102 at the same longitudinal position of the beam.

Preferably, the board abutments in the stack are all offset with respect to each other, in the longitudinal direction of the strata (of the stack). This offset of all the abutments in the stack is preferably made so that each cross-sectional section of the stack comprises at most one butt of two boards. Thus, at each position along the beam preferably there is preferably a butt of planks. Considering the entirety of the strata of the stack, the abutments 102 of planks are therefore all at different (distinct) positions along the stack.

Preferably, the length of the boards is at least 24 times the height (thickness), preferably at least 36 times the height, preferably at least 48 times the height. This length refers to the nominal length of the boards, regardless of the boards at the longitudinal ends of the beam.

The stack (the strata) as indicated above preferably forms the outer part of the construction product (the beam), intended to take the most important tensile forces during the use of the construction product.

Said stack preferably consists of a minimum of 4 layers of planks, preferably at least 8 plies, preferably at least 12 layers of planks.

Advantageously, said stack constitutes at least 20% of the total cross section of the construction product, preferably at least 50% of said cross section and preferably at least 70% of said cross section. This percentage depends on the mechanical performance of the high performance woods and / or bamboo.

Advantageously, different layers have a different thickness. At least one layer, and preferably at least the outermost layer, may have a smaller thickness than the other layers (located inside the beam). Preferably, at least the four outermost layers (with respect to the entirety of the construction product) have a smaller thickness than the other layers. Such an arrangement has the advantage of maximizing shear transfer.

According to the present invention, it is therefore not necessary for there to be a connection between said boards 101, 101 'at the abutment. The abutment 102 is therefore preferably a seamless arrangement. In this case, the abutments (ends) of two successive boards in a stratum are preferably arranged facing each other against (in contact with) the other.

Preferably, the joining of the layers in the stack is performed with means having a greater resistance than the shear strength of the material of the boards. For this purpose, the bonding is preferably carried out with an adhesive agent, such as a urea-formaldehyde, for example melamine-urea-formaldehyde. Alternatively, the adhesive agent may be a polyurethane, for example a mono- or bi-component polyurethane. The adhesive agent may be of the resin type, for example an epoxy resin, for example a mono- or bi-component epoxy resin. In addition, a securing with mechanical means (rod type) may be practiced near the abutments in areas intended to be subject, in use, to tensile forces. The stems (screws, nails, etc.) around the abutments can improve the recovery of traction forces perpendicular to the fibers (wood, bamboo).

The prior art recommends the planing of the longitudinal gluing surfaces of the boards.

According to the invention, a different surface treatment can be achieved for certain species of wood and bamboo to shape slight asperities. The creation of a certain roughness advantageously makes it possible to improve the resistance capacity of the shear planes of the longitudinal bonding joints between two layers. This surface treatment simultaneously causes an increase in the bonding surface and a better mechanical adhesion of the adhesive agent.

Preferably, these asperities are mechanically shaped. For example, these asperities are equivalent to the marking developed on the surface by the cutting in the longitudinal direction of a board using a circular saw. Preferably, this marking has a characteristic interdistance of less than or equal to 10 mm, preferably less than or equal to 5 mm, preferably less than or equal to 1 mm. The marking preferably has a characteristic interdistance of greater than or equal to 0.05 mm, preferably greater than or equal to 0.1 mm.

Alternatively, a different surface treatment is carried out for certain species of wood and bamboo for shaping notched planes in the longitudinal direction (701, Fig. 4A) or perpendicularly (801, Fig 4B) to this direction. These notches thus created advantageously make it possible to improve the shear strength of the longitudinal gluing joints between two layers. This surface treatment simultaneously causes an increase in the bonding surface, a better mechanical adhesion of the adhesive agent and a rupture plane comprising in part the bonding joint and for other part the base material.

The notches are preferably at an interdistance less than or equal to 500 mm, preferably less than or equal to 250 mm, preferably less than or equal to 100 mm. The interdistance of the notches is preferably greater than or equal to 10 mm, preferably greater than or equal to 25 mm.

Advantageously, on either side of the abutments, preferably abutments of the outermost stratum, provided, in use, to take up the most important tensile forces, the mechanical fastening means (rod type) are here. These means advantageously increase the bonding force with the adjacent layers.

According to the EUROCODES, the dimensioning of the ultimate limit state beam (ELU) can be carried out for the case of a stack in which each abutment is shifted relative to the others. The useful section considered for the bending verification can be approximated as being equal to the total section of the beam minus the section of a stratum. The shear verification of the adhesive agent strength must take into account the stress increase due to the "bridging" of forces in addition to that initially present in the case of a homogeneous beam. The shearing of the stratum which transfers the tensile forces of the board 101 to 101 'must likewise take into account a stress increase due to the "bridging" in addition. to the shear stress initially present in this stratum.

The sizing following the EUROCODES at the service limit states (ELS) is not affected. The total of the section of the stack can be considered. Indeed, bending deformation is equivalent to the integration of an infinity of small deformations, on which the abutments are only minor damage. This aspect of sizing (ELS) is one of the basic principles of the invention. In the case of beams, it is generally this criterion (ELS) that is dimensioning and not the ELUs. Therefore, the invention does not cause damage to the design compared to a perfectly homogeneous beam.

According to a second aspect of the present invention, a construction product is provided, comprising several boards made from one or more of the materials indicated above (bamboo, high performance wood, rattan). The boards are arranged in succession in the longitudinal direction of said boards, so that the ends of successive planks face each other, thus achieving abutments. Such a succession of planks forms a single layer of planks. Several layers can be superimposed to form a stack.

According to the present aspect of the invention, the abutment comprises a connection between the planks. At the level of the abutment, the planks are connected by multiple cuts. The cuts are formed in the two ends (butts) which are butted. Figs. 3A-E show different types of multiple notch abutments considered by the present invention. In said figures, the orientation of the boards is indicated by the longitudinal axes (1), transverse to the width (w) and transverse to the thickness (h).

According to a first embodiment, the notches, in the form of teeth 21, are made (for example, by milling) in the ends of the boards which form a plane parallel to the transverse directions according to the thickness (h) and following the width (w) of the board 201, as shown in Figure 3A. This form is known in the manufacture of reconstituted wood.

FIG. 3B shows an alternative embodiment, in which the ends 32 of the board 301 are cut by a plane parallel to the transverse direction according to the thickness (h) and countersunk (for producing the notches 31). in this plane along the direction defined by the intersection of this plane with a plane perpendicular to the transverse direction along the width (w) of the board.

Preferably, the end (the end) 32 thus milled of the board 301 is oriented at an angle α between 10 ° and 80 ° with respect to the longitudinal axis (1) of the board 301, preferably at an angle between 15 ° and 80 °, preferably at an angle between 15 ° and 60 °.

In Figure 3C is shown an abutment shape alternative to those of the previous figures. Preferably, the ends 42 of the board 401 are cut by a plane parallel to the transverse direction along the width (w) and countersunk (for producing the notches 41) in this plane in the direction defined by the intersection of this plane with a plane perpendicular to the transverse direction along the width (w) of the board.

Preferably, the end (abutment) 42 thus milled from the board 4 01 is oriented at an angle β between 10 ° and 80 ° with respect to the longitudinal axis (1) of the board, preferably an angle between 15 ° and 80 °, preferably between 15 ° and 60 °.

In Figure 3D is shown an abutment shape alternative to those of the previous figures. Preferably, the ends 52 of the board 501 are cut by a plane parallel to the transverse direction along the thickness (h) and milled (for making the notches 51) in this plane in the direction defined by the intersection of this plane with a plane perpendicular to the transverse direction according to the thickness (h) of the board.

Preferably, the end (the end) 52 thus milled of the board 501 is oriented at an angle α between 10 ° and 80 ° with respect to the longitudinal axis (1) of the board 301, preferably at an angle between 15 ° and 80 °, preferably at an angle between 15 ° and 50 °.

In Figure 3E is shown an abutment shape alternative to those of the previous figures. Preferably, the ends 62 of the board 601 are cut by a plane parallel to the transverse direction along the width (w) and countersunk (for producing the notches 61) in this plane in the direction defined by the intersection of this plane with a plane perpendicular to the transverse direction according to the thickness (h) of the board.

Preferably, the end (the end) 62 thus milled of the board 601 is oriented at an angle β between 10 ° and 80 ° relative to the longitudinal axis (1) of the board, preferably an angle of between 15 ° and 80 °, preferably between 15 ° and 60 °.

Finally, below is presented an alternative form of abutment to the previous figures. Preferably, the ends of the board are cut by a plane neither parallel nor perpendicular to the transverse directions following the width (w) and the thickness (h) and milled (for making the notches) in this plane in the defined direction by the intersection of this plane with a plane perpendicular to the transverse direction along the thickness of the board (h) or with a plane perpendicular to the transverse direction along the width (w) of the board.

These new abutment shapes develop bonding surfaces up to more than twice as much (depending on a and β) than that of FIG. 3A. They therefore allow a greater transfer of the forces directly through the connection of the abutment, before rupture. In addition, the transfer of forces is not concentrated in a single cross section (perpendicular to the transverse axis of the board). Such an embodiment can reduce the risk of rupture. For example, in the case of compressed and glued bamboo planks, the new abutments can withstand 4-point flexure failure up to more than 100 MPa.

The main aspect of the novelty of these abutments lies in the increase of the bonding surface not by the improvement of the profile of the multiple notches (depth, width, etc.) widely explored in the prior art but by the increase of the surface of the plane in which these cuts are milled.

The abutments arranged in oblique planes can be presented in the stack alternately at a first angle and at the opposite angle. For example, the abutments in a first stratum are oriented at an angle to the longitudinal axis and the abutments in the adjoining stratum are oriented at the opposite angle.

[0132] The abutments with multiple notches presented above make it possible to valorize up to 100% of the mechanical performances of the fibrous materials considered in the present invention. In some cases, during 4-point bending tests on these materials, the fracture no longer occurs in the bonding joint but in the material itself. This can make an offset of the abutments in the different optional strata. The construction element thus produced could be considered as perfectly homogeneous with the image of the prior art of the reconstituted wood beams.

According to a third aspect of the present invention, the elements of the first aspect and second aspect of the present invention are advantageously combined to achieve a building product with improved mechanical performance. In particular, the abutment without connection between the boards in the stack according to the first aspect of the invention is advantageously replaced by a multiple cut fitting abutment according to the second aspect of the invention.

The construction products according to the different aspects of the invention may comprise, in addition to the stack described, one or more layers of another material.

As shown in FIG. 5A, in the construction products according to the various aspects of the invention, the stack of boards, abutments without or with a connection, can be used, in use, as a stack 5 in which the transverse direction along the width (w) of the planks is parallel to a horizontal axis. The strata 55 of the stack 5 are one above the other. Interfaces between adjacent layers form horizontal planes.

Alternatively, as shown in FIG. 5B, in the construction products according to the various aspects of the invention, the stack of boards, abutments without or with a connection, can be used, as a stack 6, in use. where the transverse direction along the width (w) of the planks is perpendicular to a horizontal axis. The layers 65 of the stack 6 are next to one another. Interfaces between adjacent layers form vertical planes. This configuration makes it possible to distribute the tensile stresses of the same amplitude (lying in the same horizontal section) on all the strata of the stack. At the abutments, the tensile stresses are transferred by shear stresses, which bypass the abutment by the side (instead of bypassing the abutment from the top / bottom as in the configuration of Figure 5A). In this configuration, the offset considerations for the no-join abutments mentioned above remain valid.

The stack may constitute only a part of the construction product, preferably an outside part of said product, as for example it is the case for the stack 6 of FIG. 5B, constituting the lower part of the product 7. The other part (or the other parts) of the construction product may be constituted by a stack of laminated-glued layers as known from the prior art.

The construction product can therefore comprise several stacks of layers. The strata in the different stacks may have a different orientation, as shown in Figure 5B. Stack assemblies as described in EP 0575268 are also contemplated.

In addition, products having different cross-sectional cutting shapes can be made, for example beams with a cross section of Form I or T, as shown in FIGS. 5B and 6. FIG. a structural product of form I, consisting of several horizontal stacks 8, 9.

According to an additional aspect of the invention, an advantageous method of manufacturing boards is provided from bamboo slats. The method comprises the following steps: - soaking bamboo slats in a bath of an adhesive liquid in order to obtain coated slats, - arranging the coated slats in a mold, - compressing the slats coated in the mold to a pressure between 250 and 700 bar, harden the adhesive liquid around the slats coated in the mold by maintaining said pressure to obtain a material consisting essentially of compressed bamboo. The material may be in the form of a board.

Preferably, the mold is such that it provides a block of compressed and glued bamboo slats. Preferably, the boards are obtained by cutting the length of the block.

[0142] Preferably, the bamboo slats all have essentially the same length. Preferably, the boards and / or the block are essentially the length of said bamboo strips.

[0143] Bamboo belongs to the family of children, namely Poaceae, sub-family of Bambusoideae. This subfamily gathers between 1100 and 1500 species divided between 60 and 90 different kinds of bamboos.

The rhizome is the root system of bamboo, which includes nodes. Around these nodes grow roots and buds. Some buds will grow and come out of the ground as spears wrapped in a protective sheath. As they develop, they form culms (canes), usually hollow and made up of nodes and internodes. The stubble unfolds like a telescopic rod. Some species have stubble up to 35 m tall and 25-5 cm in diameter.

The internodes comprise vascular bundles and fibers oriented axially, vertically and parallel to each other. Most beams traverse the nodes directly to join the next entrenœud. However, some vascular bundles deviate from their trajectory at the node's height. As a result, the presence of shorter fibers at the node is probably the cause of a significantly lower mechanical performance of the nodes relative to the internodes.

From this raw material, the stubble (the cane) is harvested and cut to the desired length, generally between 1.5 m and 3.5 m, then laminated by splitting or sawing, typically radially.

The lamellae thus obtained still include the inner part (the marrow), too little resistant and the epidermis (outer skin). A planing process removes these two parts.

The planing can be practiced on both sides (external and internal). It can be practiced on the four sides of a coverslip.

Alternatively and advantageously to the planing, the removal of the epidermis and the marrow is preferably practiced mechanically by sanding, preferably with a brush combining a rotary movement. Preferably, the brush is provided with metal (for example steel) and / or synthetic son and / or abrasive sheets (for example sandpaper). The use of a brush makes it possible to follow the curvature of the slats and thus to reduce the losses.

In addition, the brushing makes it possible not to touch the nodes. Although having weak fracture and tensile characteristics, the knots can offer better resistance under certain other stresses, probably due to the presence of fibers that take a different orientation than the longitudinal orientation.

The sanding with a brush makes it possible to preserve the most dense layer of fibers located directly below the epidermis.

Alternatively, the shrinkage can be practiced chemically by dipping in an acid or base bath, for example HCl or NaOH.

Chemical shrinkage, if adapted to the type and dimensions of bamboo slats, can lead to the same advantages as mechanical shrinkage (sanding).

The described shrinkage thus makes it possible to preserve the most interesting parts from the point of view of mechanical performance, such as knots and fibers directly below the epidermis. This removal allows better preservation of the material with yields greater than or equal to 90% on the original section of the coverslip.

Advantageously, the bamboo strips after removal are preferably used raw, that is to say without retrenchment to arrive at a rectangular section. Calibration of the slats in rectangular section is therefore preferably not practiced.

. The planed slats obtained according to the present invention typically have a section between 3 and 25 mm in height (thickness) and between 10 and 40 mm in width.

The planed lamellae preferably have the same length.

In a next step of the process, the planed lamellae are subjected to a treatment aimed at increasing resistance to insects and fungi. Homogenization treatment of the color can also be practiced. The treatment provides for example a dipping of the lamellae in an aqueous solution of water-soluble agent. The agent may be one of the following components or a combination thereof: formalin, copper sulfate, phenol, sodium chlorophenate, boric acid and hydrogen peroxide. This soaking eliminates traces of sugar and reduces the risk of attacks of insects and fungi. Alternatively or in combination, an autoclave heat treatment may be provided, for example at a temperature between 100 ° C and 200 ° C and at a pressure between 3 and 10 bar. These treatments can simultaneously improve the homogenization of the color of the lamellae.

For use in the rest of the process, the slats should have a water content preferably less than 12% (by weight). The previously described treatments generally increase the water content of the lamellae by around 80%. Slat drying is therefore preferably envisaged to reduce the water content to acceptable values, preferably less than or equal to 12%. The drying can be carried out in an oven, for example at a temperature of 70-80 ° C for 4 hours. It can be practiced by arranging the slats under the action of the air and the sun (natural drying).

The storage is preferably carried out in temperate rooms.

A step in the process is the coating of the bamboo strips with an adhesive material. This step preferably provides for soaking the slats in a bath of an adhesive liquid, preferably a urea-formaldehyde, for example melamine-urea-formaldehyde. Alternatively, the adhesive may be a polyurethane, for example a mono- or bi-component polyurethane. The adhesive agent may be of the resin type, for example an epoxy resin, for example a mono- or bi-component epoxy resin. The slats can be arranged in a cage and the cage is immersed in the bath of adhesive. The soaking time depends on the dimensions of the cage and is typically between 10 and 60 minutes. By leaving the cage, the excess adhesive is allowed to flow.

The adhesive-coated strips are preferably dried in order to lower their water content. Drying can be done in an oven (autoclave or preferably continuous tunnel). Preferably, the water content is reduced to a range of 5% to 20%, preferably 10% to 15% (by weight).

In a subsequent step of the method, the lamellae are compressed. The coated strips are arranged in a mold. The mold may be a formwork that is insertable into a press. The mold is preferably of prismatic shape with a rectangular section. The length of the mold and that of the coated lamellae preferably correspond (the mold may be slightly longer to facilitate the insertion and arrangement of the lamellae).

Alternatively to a mold comprising perfectly flat inner faces, some of them may be designed so as to have asperities and / or notches so that, when pressing the bamboo strips in this other type of mold these shapes are printed directly on the longitudinal faces (opposite the said mold faces) of blocks or boards molded with bamboo slats.

The slats are arranged parallel in the mold. The longitudinal orientation is therefore the same for all the lamellae in the mold. However, the transverse orientation of the lamellae can be random (random arrangement).

The mold is then pressurized. The coated slats are compressed to a pressure between 250 bar and 700 bar, preferably between 350 and 700 bar, preferably between 450 and 600 bar.

The slats are held in the mold at the aforementioned pressure for a time to eliminate the vacuum between the slats, thus producing a homogeneous material. The polymerization is preferably carried out at high temperature, for example in an oven, preferably at a temperature between 80 ° C and 200 ° C, preferably between 100 ° C and 150 ° C. The polymerization time of the adhesive is a function of the dimensions (thickness) of the material, since the heat must penetrate to the core of the material.

According to a preferred embodiment, the mold, filled with the coated strips, is pressurized. The pressurization may be continuous or discontinuous depending on the desired compaction. Arrived at the predetermined pressure, the formwork of the mold is blocked and the pressure on the mold is released. The formwork, however, allows to maintain the deformation on the slats. Then, the mold is transferred to an oven, where the polymerization of the adhesive is obtained.

After polymerization, the mold is cooled, preferably rapidly, which facilitates the demolding of the material.

Depending on the type of adhesive, the polymerization may occur by action of moisture, as for example for some polyurethanes.

With high pressure, a homogeneous material is obtained, wherein the slats form a coherent mass and preferably without vacuum. The density of the material is preferably between 1000 and 1300 kg / m3. Density is also a function of the bamboo species. A failure test of the 4-point flexural material as defined in ISO 8375 "Timber structures - Glulam timber Test methods for the determination of certain physical and mechanical properties" preferably gives a higher rupture limit or equal to 70 MPa, preferably greater than or equal to 100 MPa, preferably greater than or equal to 120 MPa.

The method as indicated above allows to obtain directly boards. Alternatively, a "block" of larger dimensions is obtained as material exiting the mold. This block can be cut lengthwise to obtain boards. The ends of the block possibly being irregular, they are preferably equalized before the block is cut into boards. After cutting the ends, one obtains bamboo slats compressed in the block preferably having all the same length.

The boards thus obtained preferably form the basic element of the construction product according to the present invention (from the first to the third aspect). This bamboo material can achieve technical performance that is significantly higher than that of the best wood species (high performance wood).

Claims (30)

1. Beam or column type construction product comprising longitudinal planks (101, 101 ', 101' ') made from a fibrous material consisting essentially of natural fibers, such as bamboo or wood, said material having a characteristic axial tensile strength greater than or equal to 20 MPa, the boards being arranged in layers (10, 10 '), said layers being secured and arranged so as to form a stack (1, 2, 5, 6), characterized in that: each stratum (10, 10 ') comprises a succession of planks (101, 101', 101 '') arranged in the longitudinal direction of said planks, so that the ends of successive planks face each other, thereby making abutments (102) in said stratum, and - for each pair of contiguous strata (10, 10 '), the abutments (102) of a stratum (10) are arranged offset from the abutments of the stratum (10). other stratum (10 '), such that the longitudinal distance between each butt of one stratum (10) and each abutment of the other stratum (10') is greater than or equal to six times the thickness of said stratum (10) , the arrangement of the boards and abutments allowing, in use, to transfer the tensile stresses of a board to the successive board by shear stresses bypassing the abutment (102). 2. Product according to claim 1, wherein said offset of the abutments (102) of a stratum (10) is with respect to the abutments (102 ') of two contiguous layers on either side. '3. A product according to claim 2, wherein said offset of the abutments (102) of a stratum (10) is in relation to the abutments (102 ') of three adjoining strata on either side. 4. Product according to any one of the preceding claims, wherein said boards (101, 101 ', 101' ') consist of compressed and glued bamboo slats being essentially arranged in the longitudinal direction of the board and having essentially the same length as the board. 5. Product according to any one of the preceding claims, the stack comprising strata having different thicknesses. 6. Product according to any one of the preceding claims, wherein the boards of at least one layer of said stack are made from a material different from the material of the boards of another layer. 7. A product according to any one of the preceding claims, wherein at most one abutment (102, 102 ') of any stratum is present in the stack (1) in each cross section perpendicular to the longitudinal axis of the stratum (10). 8. Product according to any one of the preceding claims, wherein the boards (101, 101 ', 101' ') of the same layer (10) are arranged without a physical or chemical connection between their ends. 9. Product according to any one of claims 1 to 8, wherein the planks (201, 301, 401, 501) of the same stratum are secured by mechanical connection constituted by multiple notches (21, 31). , 41, 51, 61) present in the ends of the boards. 10. The product of claim 9, wherein the ends of the boards (32, 52) are oriented in a plane of orientation parallel to the transverse direction of the board following the thickness. 11. The product of claim 9 or 10, wherein, considering a first reference plane parallel to the transverse axis along the thickness of the board and parallel to the longitudinal axis of the board, the ends of the boards (32). , 52) are oriented in an oblique orientation plane at the first reference plane at an angle between 10 ° and 80 °. 12. Product according to claim 9 or 10, wherein the ends of the boards (42, 62) are oriented in a plane of orientation parallel to the transverse direction of the board along the width. 13. The product of claim 9 or 12, wherein, considering a second reference plane parallel to the transverse axis along the width of the board and parallel to the longitudinal axis of the board, the ends of the boards (42, 62) are oriented in an oblique orientation plane to the longitudinal axis of the board at an angle between 10 ° and 80 °. The product of claim 9 comprising the combination of the features of claims 11 and 13. A product according to any one of claims 10 to 14, wherein the multiple notches (31, 41) are parallel to the intersection of the plane of the board ends (32, 42) with a plane including the longitudinal axis of the board and parallel to the transverse axis following the thickness. The product of any one of claims 10 to 14, wherein the multiple notches (51, 61) are parallel to the intersection of the plane of the board ends (52, 62) with a plane comprising the longitudinal axis of the board and parallel to the transverse axis along the width. 17. Product according to any one of the preceding claims, wherein said layers are secured by means of an adhesive material and the longitudinal surfaces of bonding boards are provided with asperities, the asperities having a characteristic interdistance included between 0.05 mm and 10 mm. 18. Product according to any one of claims 1 to 17, wherein said layers are secured with an adhesive material and the longitudinal bonding surfaces (701, 801) of the boards are provided with notches. 19. Product according to claim 18, said notches being oriented in the longitudinal direction of the boards or perpendicular to this direction. 20. Product (7) according to any one of the preceding claims, further comprising a set of lamellate-bonded layers, said assembly being secured to the stack (6) so that the transverse orientation along the width of the strata of said sst set perpendicular to the transverse orientation according to the width of the strata of the stack, the longitudinal orientations of said set and the stack being parallel. 21. Product (7) according to any one of the preceding claims, having a cross section of the form I or T, wherein cross section said smpilage (6) constitutes at least a rectangular portion. 22. Use of the product according to one juelconque of the preceding claims in a structure, to take structural loads in said structure, wherein use at least a portion of the stack of the product is designed to take tensile forces, said part comprising at least one abutment and being dimensioned according to the EUROCODES 5 standard using as the axial tensile strength, the axial tensile strength characteristic of the fibrous material and as section, the section of said reduced portion of the section of a stratum. 23. Use of the product according to any one of claims 1 to 21 in a structure, to take structural loads in said structure, wherein use at least a portion of the product stack is designed to take compression efforts, said portion comprising at least one abutment and being dimensioned according to the EUROCODES 5 standard by using a characteristic resistance to the axial compression of the fibrous material. 24. A method of manufacturing a construction product of the beam or column type, comprising the following steps: - providing boards of a fibrous material consisting essentially of natural fibers, such as bamboo or wood, said material having a resistance axial tensile characteristic greater than or equal to 20 MPa, - determining a minimum length Lv of transfer of the tensile forces of a board to the subsequent board by bridging, by taking up the tensile stresses by shear stresses, - determine a minimum value of offset corresponding to the maximum between Lv and six times the thickness of the boards, - forming a layer by placing several of said boards successively in the longitudinal direction, so as to present the ends of successive boards face to face, thus forming abutments - arrange and secure several of said layers so as to form a stack constituting at least a part of the construction product, the arrangement of the planks being such that for each pair of adjoining plies (10, 10 ') the longitudinal distance between each abutment of planks of a ply and each board butting, the other stratum is greater than or equal to said minimum offset value. 25. The method of claim 24, wherein the minimum length Lv is determined according to the equation:

with: ft the value of the characteristic axial tensile strength of the board material, - h the thickness of the board, - kSh a coefficient of nonuniformity of the shear stresses, having a value between 0.5 and 1, - tv shear stress initially present in the transfer plane, as calculated by the material resistance theory for the board material and fv the value of the characteristic shear resistance of the board material. 26. The method of claim 24 or 25, wherein the layers are formed by arranging the boards without physical or chemical connection between their ends. 27. The method of claim 24 or 25, comprising providing the ends of the multi-notch boards oriented parallel to the transverse direction along the width or thickness of the board and connecting the successively arranged boards in a gear stratum of said multiple notches. . 28. The method of claim 27, comprising cutting the ends of the boards in a plane parallel to the transverse direction along the thickness of the board and oblique to the longitudinal axis of the board at an angle of between 10 ° and 80 °. ° and provide said multiple notches in this plane. 29. The method of claim 27, comprising cutting the ends of the boards in a plane parallel to the transverse direction along the width of the board and oblique to the longitudinal axis of the board at an angle between 10 ° and 8 0 °, and providing said multiple notches in this plane. 30. The method of claim 28 or 29, comprising arranging the boards in each pair of adjacent layers with the ends of the boards oriented in reverse.