Abstract
The invention relates to a functional panel for receiving surface loads comprising a plurality of veneer layers that are arranged one on top of another and are connected together in a materially bonded manner, wherein a part of these veneer layers has an A-fibre direction, and another part of these veneer layers has a B-fibre direction oriented at more or less 90° to the A-fibre direction. The functional panel has a central plane defined substantially in the middle of the functional panel in the in the thickness direction. The cumulative thickness of the veneer layers with the A-fibre direction differs from the cumulative thickness of the veneer layers with the B-fibre direction on a first side of the central plane, and the cumulative thickness of the veneer layers with the A-fibre direction differs from the cumulative thickness of the veneer layers with the B-fibre direction on the second side located on the opposite from the first side of the central plane. As a result, the functional panel has an asymmetric structure in its thickness direction. The invention also relates to the use of a functional panel as a formwork shell for the formwork of a building part, and a method for producing the formwork of a building part with at least one functional panel.
Claims
1. A functional panel (1) for receiving surface loads comprising: a plurality of veneer layers (A, B) connected together in a materially bonded manner that are arranged one on top of another, wherein a part of these veneer layers (A) has an A-fibre direction and another part of these veneer layers (B) has a B-fibre direction oriented at more or less 90° to the A-fibre direction, and the functional panel (1) has a central plane (ME) defined substantially in the middle of the functional panel (1) in the in the thickness direction, wherein the cumulative thickness of the veneer layers (A) with the A-fibre direction differs from the cumulative thickness of the veneer layers (B) with the B-fibre direction on a first side of the central plane (ME) and the cumulative thickness of the veneer layers (A) with the A-fibre direction differs from the cumulative thickness of the veneer layers (B) with the B-fibre direction on the second side located opposite of the first side of the central plane (ME); and wherein the ratio of the cumulative thicknesses of the veneer layers (A) with the A-fibre direction to the cumulative thicknesses of the veneer layers (B) with the B-fibre direction on the first side of the central plane (ME) differs from the ratio of the cumulative thicknesses of the veneer layers (A) with the A-fibre direction to the cumulative thicknesses of the veneer layers (B) with the B-fibre direction on the second side of the central plane (ME) so that the functional panel (1) has an asymmetric structure in its thickness direction, wherein a first surface of the functional panel (1) is configured as a pressure side (2) provided for receiving pressure forces as a load, and the surface of the functional panel (1) located opposite of the pressure side (2) is configured as a tension side (3) wherein, in particular, the tension side (3) is not provided for receiving a load, and the cover layer the of functional panel (1) on the pressure side (2) is formed by a veneer layer (A) with the A-fibre direction, and the ratio of the cumulative thicknesses of the veneer layers (A) with the A-fibre direction to the cumulative thicknesses of the veneer layers (B) with the B-fibre direction on the first side of the central plane (ME) oriented in the direction of the pressure side (2) is larger than the ratio of the cumulative thicknesses of the veneer layers (A) with the A-fibre direction to the cumulative thicknesses of the veneer layers (B) with the B-fibre direction on the second side of the central plane (ME) oriented in the direction of the tension side (3), wherein, on the first side of the central plane (ME) oriented in the direction of the pressure side (2), the cumulative thickness of the veneer layers (A) with the A-fibre direction is larger than the cumulative thickness of the veneer layers (B) with the B-fibre direction.
2. The functional panel (1) according to claim 1, characterised in that, on the second side of the central plane (ME) oriented in the direction of the tension side (3), the cumulative thickness of the veneer layers (A) with the A-fibre direction is smaller than the cumulative thickness of the veneer layers (B) with the B-fibre direction.
3. The functional panel (1) according to one of the preceding claims, characterised in that the number of the veneer layers (A, B) is at least 5, preferably at least 6, and/or in that the number of the veneer layers (A, B) is maximally 20, preferably maximally 12, particularly preferred maximally 10.
4. The functional panel (1) according to one of the preceding claims, characterised in that the thicknesses of the veneer layers (A, B) are identical, or in that the thicknesses of the veneer layers (A, B) have a tolerance range, wherein the tolerance range is maximally +/-20% of the nominal thickness, preferably +/- 10% of the nominal thickness, particularly preferred +/- 5% of the nominal thickness.
5. The functional panel (1) according to one of the preceding claims, characterised in that the functional panel (1) has a first load direction (R1) which extends parallel to the fibre direction of the cover layer on the pressure side (2) and parallel to the surface of the functional panel (1) forming the pressure side (2), and the functional panel (1) has a second load direction (R2) oriented at right angles to the first load direction (R1), and in that the bending strength and/or the bending modulus of elasticity of the functional panel (1) along the first load direction (R1) differs from the bending strength and/or the bending modulus of elasticity of the functional panel (1) along the second load direction (R2) by a maximum of 30%, preferably by a maximum of 20%, particularly preferred by a maximum of 10%.
6. The functional panel (1) according to one of the preceding claims, characterised in that a coating (5a, 5b) is applied to the cover layer formed by at least one veneer layer (A, B), wherein the coating (5a, 5b) is made of a material different from the veneer layers (A, B).
7. The functional panel (1) according to claim 6, characterised in that, on the pressure side (2), a coating (5a) is applied which is made of a thermoplastic, particularly of polypropylene, and/or in that, on the tension side (3), a coating (5b) is applied which is made of a thermosetting plastic, particularly of a phenolic material.
8. The functional panel (1) according to one of the claims 6 or 7, characterised in that the bending strength and/or the bending modulus of elasticity of the coating (5a, 5b) are substantially identical along the first load direction (R1) and along the second load direction (R2).
9. The functional panel (1) according to one of the claims 6 to 8, characterised in that the bending strength and/or the bending modulus of elasticity of the coating (5a) are smaller than the bending strength and/or the bending modulus of elasticity of a veneer layer along the fibre direction, and the bending strength and/or the bending modulus of elasticity of the coating (5a) are larger than the bending strength and/or the bending modulus of elasticity of a veneer layer transverse to the fibre direction, and/or the bending strength and/or the bending modulus of elasticity of the coating (5b) on the tension side (3) are smaller than the bending strength and/or the bending modulus of elasticity of a veneer layer along the fibre direction and the bending strength and/or the bending modulus of elasticity of the coating (5a) are larger than the bending strength and/or the bending modulus of elasticity of a veneer layer transverse to the fibre direction.
10. The functional panel (1) according to one of the claims 6 to 9, characterised in that the thicknesses of the coatings (5a, 5b) are part of the thickness the functional panel (1) and are therefore also taken into account in the definition of the position of the central plane (ME).
11. Use of a functional panel (1) according to one of the preceding claims as a formwork shell for the formwork of a building part.
12. The use according to claim 11, characterised in that the pressure side (2) of the functional panel (1) used as a formwork shell faces the material, particularly the concrete material, of the building part to be erected.
13. The use according to claim 11 or 12, characterised in that the functional panel (1) used as a formwork shell is fastened to a formwork support (6) on its tension side (3).
14. A method for producing a functional panel (1) according to one of the claims 6 to 10, comprising the steps of A) connecting the veneer layers (A, B) in a materially bonded manner, B) applying the coatings (5a, 5b) to the cover layers of the connected veneer layers (A, B).
15. A method for producing the formwork of a building part, wherein at least one functional panel (1) according to one of the claims 1 to 10 is used as a formwork shell, comprising the steps of I) setting up and positioning a formwork support (6), II) attaching at least one formwork shell formed by a functional panel (1), wherein the pressure side (2) is oriented towards the building part to be erected, and the tension side (3) is oriented towards the formwork support (6), and wherein the orientation of the formwork shell is variable about a position axis (PA) oriented towards the pressure side (2) in the normal direction (N) since the mechanical properties of the functional panel (1), particularly its bending strength and/or its bending modulus of elasticity, are identical in all load directions orthogonal to the position axis (PA) or deviate from each other by a maximum of 30%, preferably by a maximum of 20%, particularly preferred by a maximum of 10%.
Description
[0034] In the Figures, embodiments of the invention are schematically illustrated. Here,
[0035] FIG. 1 shows a schematic perspective view of an embodiment of a functional panel according to the invention,
[0036] FIG. 2 shows a schematic cross sectional view of an embodiment of a functional panel according to the invention,
[0037] FIG. 3 shows a schematic perspective view of a formwork including an embodiment of a functional panel according to the invention in the process of being assembled.
[0038] In the Figures, identical elements are designated by the same reference numerals. In principle, the described properties of an element described with reference to a Figure also apply to the other Figures. Indications of directions such as above or below relate to the described Figure and are to be contextually applied to the other Figures.
[0039] FIG. 1 shows a schematic perspective view of an embodiment of a functional panel 1 according to the invention. In FIG. 1, a section of a multi-layer functional panel 1 can be seen. The dimensions in the length and width of the functional panel 1 may, of course, vary, so that the illustrated section only serves the exemplary description of the functional panel 1. The illustrated functional panel 1 consists of a total of six veneer layers A, B made of a naturally renewable material. In the illustrated embodiment, the veneer layers A, B are made of veneer wood. The veneer wood may be made of hard wood or soft wood. Suitable veneer wood types are, for example, poplar, birch, or beech. The veneer layers A, B are arranged on top of each other and firmly connected to each other in a materially bonded manner. The fibre directions of the veneer layers A, B are partly different from each other. The cover layer disposed on top is formed by a veneer layer A the fibres of which extend along an A-fibre direction extending from the right to the left in FIG. 1. The veneer layer B disposed directly below the cover layer has a B-fibre direction oriented at 90° to the A-fibre direction which extends from the front to the back in FIG. 1. For a better understanding, the illustrated cut fibres are represented by dots in the veneer layers B with the B-fibre direction on the side of the functional panel 1 facing forwards in FIG. 1. Based on these dots, it can be discerned whether a veneer layer A, B is a veneer layer A with the A-fibre direction or a veneer layer B with the B-fibre direction. The central plane ME conceptually divides the functional panel 1 into in an upper and a lower half. The central plane ME extends parallel to the surfaces of the veneer layers A, B. The illustrated embodiment of a functional panel comprises a total of six veneer layers A, B all having the same thickness. The central plane ME is located in the middle of the functional panel 1 between the three upper veneer layers A, B and the three lower veneer layers A, B. The surface or side facing upwards in FIG. 1 is the pressure side 2 provided for applying a surface load. The surface of the functional panel 1 located opposite of the pressure side 2 is the tension side 3. In the illustrated embodiment, the cover layers on the pressure side 2 and on the tension side 3 are formed by veneer layers A with the A-fibre direction. The two cover layers thus have the same fibre direction here. However, it is also feasible that the cover layers on the tension side 3 and the pressure side 2 have different fibre directions. The functional panel 1 has an asymmetric structure in the thickness direction. The thickness direction of the functional panel 1 extends from the top to the bottom in FIG. 1, from the tension side 2 to the pressure side 3 or vice versa. The sequence of the veneer layers A, B in the thickness direction is irregular: starting from the top, the cover layer on the tension side 2 is formed by a veneer layer A with the A-fibre direction. Adjacent to and below it, a veneer layer B with the B-fibre direction is disposed, which in turn is followed by a veneer layer A with the A-fibre direction. On the first half of the functional panel 1 extending from the central plane ME to the pressure side 2, thus, two veneer layers A and only one veneer layer B having the same thickness are disposed. In this first half, therefore, the cumulative thickness of the veneer layers A is larger than the cumulative thickness of the veneer layers B. In addition, the thickness proportion of the veneer layers A is larger in the ratio to the thickness proportion of the veneer layers B. The ratio of the cumulative thicknesses of the veneer layers A to the veneer layers B is 2 to 1 in the first half. On the second half extending from the central plane ME to the tension side 3, adjacent to the central plane ME, two veneer layers B are disposed adjacent to each other. The lower end of the second half is formed by the cover layer formed by a veneer layer A. The cumulative thickness of the veneer layers A is therefore smaller than the cumulative thickness of the veneer layers B on the second side of the central plane ME. The cumulative thicknesses on the second side are therefore exactly the reverse of the cumulative thicknesses on the first side. On the second side, the thickness proportion of the veneer layers A is, in contrast to the first half, smaller than the thickness proportion of the veneer layers B. The ratio of the cumulative thicknesses of the veneer layers A to the veneer layers B is 1 to 2 in the second half. In the second half of the functional panel 1 facing the tension side 3, the thickness proportion of the veneer layers B is therefore larger than the thickness proportion of the veneer layers B in the first half facing the pressure side 2. When a surface load is applied to the pressure side 2 the veneer layers A, B disposed below the central plane ME are subjected to tension. The load or the elongation is the smallest directly adjacent to the central plane and the largest on the surface of the tension side 3. Here, the cover layer on the tension side 3 bears the highest load and, in the reverse conclusion, provides the largest and most effective share in the resistance against the bending load. The cover layer has an A-fibre direction. In a wood material, the mechanical rigidity is considerably larger parallel to the fibre direction than transverse to the fibre direction. The cover layer on the tension side 3 therefore has a high tensile strength in a direction extending from the right to the left in FIG. 1, parallel to the A-fibre direction. On the pressure side 2 of the functional panel, two load directions R1 and R2 represented by two arrows are illustrated. The load direction R2 extends parallel to the A-fibre direction. When a line load parallel to the load direction R2 is applied, in other words, when a bending load is applied along the load direction R2 the cover layer facing downwards which has an A-fibre direction has a high bending strength and a high bending modulus of elasticity. When a bending load along the other load direction R1 located orthogonal to the load direction R2 is applied the bending strength and the bending modulus of elasticity of the cover layer facing downwards are considerably smaller. Without other veneer layers, the cover layer on the tension side 3 would therefore exhibit an anisotropic mechanical behaviour, with strengths against a bending load in the load direction R2 and weaknesses against a bending load in the load direction R1. To compensate this anisotropy, the thickness proportion of the veneer layers B is selected so that it is larger in the second half of the functional panel 1 facing downwards. These veneer layers B are located further inwards, i.e., closer to the neutral fibre extending in the central plane ME so that the influence of these veneer layers B against a bending load decreases with increasing proximity to the central plane. This influence of the distance from the neutral fibre is compensated by the thickness proportion of the veneer layers B being significantly higher than the proportion of the veneer layers A. In this way, the bending strength and the bending modulus of elasticity of the entire functional panel 1 against a bending load in the load direction R1 are improved and increased. As a result of this asymmetric thickness structure, the functional panel 1 has an almost identical bending strength and identical bending modulus of elasticity in the two load directions R1 and R2. Despite its structure of naturally renewable wooden materials, the illustrated functional panel 1 exhibits an almost isotropic mechanical behaviour when exposed to a surface load applied to the pressure side 2. When a surface load is applied to the pressure side 2 the functional panel 1 therefore bends to a comparable extent parallel to the load direction R1 as compared to a direction parallel to the load direction R2. In the ideal case, the bending strength and the bending modulus of elasticity are identical along the load directions R1 and R2. However, in reality these mechanical characteristics slightly deviate from each other. Here, such a slight deviation means, for example, a deviation of maximally 20 %, preferably of maximally 10 %, particularly preferred of maximally 5 % from each other.
[0040] FIG. 2 shows a schematic cross sectional view of an embodiment of a functional panel 1 according to the invention. In contrast to the embodiment of a functional panel 1 illustrated in FIG. 1, the embodiment of a functional panel 1 in FIG. 2 has a coating 5a, 5b on both sides. The functional panel 1 in FIG. 2 also comprises six veneer layers A, B of veneer wood the arrangement of which on top of each other is identical to the embodiment in FIG. 1. On the pressure side 2 of the functional panel 1 facing upwards in FIG. 2, a coating 5a is applied to the veneer layer A forming the cover layer. Here, the thickness of the coating 5a is about as large as the thickness of the veneer layers A, B. Here, the coating 5b applied to the tension side 3 is substantially thinner than the thickness of the veneer layers A, B. The coatings 5a and 5b are made of different materials. The thicker coating 5a on the pressure side 2 is made of polypropylene here, the thinner coating on the tension side 3 is made of phenol here. The thicker coating 5a made of polypropylene on the pressure side has isotropic mechanical properties when exposed to bending loads in different load directions, particularly in the two load directions R1 and R2 extending orthogonal to each other. In the illustration in FIG. 2, the load direction R2 extends from the left to the right, the load direction R1 extends into the drawing plane. By subsequently applying the coating 5a to the veneer layers A, B, therefore, no anisotropic mechanical behaviour of the entire functional panel 1 will occur. However, due to its larger thickness, the coating 5a significantly contributes to the overall bending strength and to the overall modulus of elasticity of the functional panel 1. The directionally independent rigidity of the coating 5a adds up to the rigidity obtained by the interaction of the six veneer layers A, B. By applying the coating 5a to the pressure side 2, the bending strength and the bending modulus of elasticity of the functional panel are uniformly increased here. The coating 5b applied to the tension side 3 and made of phenol is so thin that its rigidity has no significant influence on the mechanical properties the entire functional panel 1. Like the coating 5a, the coating 5b exhibits a directionally independent, isotropic mechanical behaviour. The coating 5b applied to the tension side is not provided to increase the bending strength and the bending modulus of elasticity, but only serves to protect the veneer layers A, B from environmental influences. In FIG. 2 as well, the central plane ME conceptually dividing the functional panel 1 in two halves in the thickness direction is illustrated. Here, the central plane ME is indicated so as if the two coatings 5a and 5b did not exist. The central plane ME is indicated exactly between the three upper veneer layers A, B and the three lower veneer layers A, B, the thickness of all veneer layers A, B being identical here. On the left of the functional panel 1, the distance E from the central plane is represented by an arrow starting from the central plane ME. The larger this distance E from the central plane in direction of the tension side 3 is, the larger is the influence of the layer disposed there on the bending strength and the bending modulus of elasticity of the entire functional panel 1. In FIG. 2, it can be clearly seen that the cover layer on the tension side 3 formed by a veneer layer A has the largest distance E from the central plane ME and therefore the largest influence on the mechanical rigidity of the functional panel 1. The two veneer layers B located between the central plane ME and the veneer layer A forming the cover layer have a smaller distance E to the central plane and therefore have a smaller influence on the mechanical rigidity of the functional panel 1. Due to this smaller influence of these inner layers, the overall thickness of the veneer layers B on the side of the central plane facing downwards is twice as large as the overall thickness of the veneer layer A. By increasing the thickness proportion of the veneer layers B for compensating the smaller distance E to the central plane ME, directionally independent, isotropic mechanical properties of the entire functional panel 1 are obtained. In FIG. 2, a second central plane ME‘ located above the central plane ME is indicated. In this second central plane ME‘, the thicknesses of the coatings 5a and 5b are taken into account. Since the thickness of the coating 5a is larger than the thickness of the coating 5b the dimensional centre of the entire functional panel 1 in the thickness direction in which the central plane ME‘ is defined is located further upwards than in the case in which no coating 5a, 5b is applied. It can be clearly seen in FIG. 2 that the central plane ME‘ in which, in case of a bending load on the coated functional panel 1, the neutral fibre extends is located further up than in a non-coated functional panel 1. With the thicker coating 5a on the pressure side 2, therefore, the neutral fibre moves upwards in case of a bending load so that a part of the veneer layer A through which the central plane ME‘ extends is subjected to tension. Without the coating 5a, 5b, this veneer layer would be located above the central plane ME and would, in the event of a deflection, be exclusively subjected to pressure. When coatings 5a and 5b having different thicknesses are applied to the two sides of the veneer layers A, B, therefore, the neutral fibre moves upwards in case of a bending load which in turn has to be taken into consideration in the design of the asymmetric thickness structure of the entirety of the veneer layers A, B.
[0041] FIG. 3 shows a schematic perspective view of a formwork including an embodiment of a functional panel 1 according to the invention in the process of being assembled. In FIG. 3, the use of a functional panel 1 as a formwork shell of a formwork for the erection of a building part is schematically illustrated. A functional panel 1 is well suited as a formwork shell since it exhibits a mechanically isotropic behaviour when loaded with a surface load. A formwork is erected to be capable of producing a building part, for example a wall or a ceiling, by casting. The formwork has the function to accommodate the initially liquid material, particularly a concrete material, in a shaping manner. After the material has hardened, the formwork will be removed again, and the building part remains as a negative mould of the interior of the formwork. For erecting a formwork, first a formwork support 6 is assembled and positioned in accordance with the specifications of the building part. In FIG. 3, only a small section of the formwork is illustrated which has a rectangular formwork support 6 having the shape of a frame here. For erecting the building part, further formwork supports 6 are assembled which, however, are not illustrated for the sake of clarity. The formwork support 6 is composed of metal pipes having a rectangular cross section here. In the illustrated case, a formwork for a building wall is assembled. The formwork support 6 is therefore oriented so as to extend vertically. After the assembly of the formwork support 6, the formwork shell is fastened on the formwork support 6. A part of this formwork shell is formed by a functional panel 1 here. Starting from the illustrated state, further functional panels 1 can be attached to the formwork support 6 as further parts of the formwork shell. The functional panel 1 is fastened to the formwork support 6 on its tension side 3. The pressure side 2 of the functional panel 1 faces away from the formwork support 6 and is oriented towards the section into which, later, the liquid concrete material is filled. After the concrete material was poured in, it abuts on the pressure side 2 of the functional panel 1 and will then generate a surface load acting on the functional panel 1. Orthogonally pointing away from the surface of the pressure side 2, the normal direction N to the pressure side 2 is indicated. Parallel to this normal direction N, a position axis PA extends. Such a position axis PA can be located in any position on the pressure side 2. The position axis PA is an imaginary, geometrical assist feature serving to describe the orientation of the functional panel 1 relative to the formwork support 6. When known plywood panels are used as a formwork shell, the rotational orientation of these plywood panels about a position axis PA has to be precisely observed. Since known plywood panels have different bending strengths in different load directions it always has to be ensured that, for example, such panels are positioned so that the mechanically more resilient load direction extends along the longer dimension of the panel. A known plywood panel could, in the application illustrated in FIG. 3, only be used as a formwork shell instead of the functional panel 1 if its higher load direction extended along the longest dimension of the panel extending from front right to back left. A known plywood panel in which the highest load direction extends parallel to the shorter side of the panel could not reasonably be used for this application. A functional panel 1 according to the invention is advantageous in that it can be attached to the formwork support 6 in any rotational orientation relative to the position axis PA and in that it always has the same or at least very similar mechanical properties such as the bending strength and the bending modulus of elasticity in any of these rotational orientations. These different rotational orientations are represented by the curved double arrow on the base of the depicted position axis PA. The functional panel 1 illustrated in FIG. 3 could therefore also be attached to the formwork support 6 upright, i.e., with its longest dimension extending in the vertical direction. The mechanical behaviour of the functional panel 1 exposed to a surface load generated by the cast concrete material would not change thereby. A functional panel 1 according to the invention can therefore be used as a formwork shell in a much more variable way than known plywood panels. Starting from the state illustrated in FIG. 3, other functional panels in any rotational orientation could be fastened to the formwork support 6 adjacent to the functional panel 1 already attached until the entire face of the formwork support 6 is provided with a formwork shell.
