Low noise engineered wood building elements

Abstract

The disclosed invention consists of a low noise engineered wood building element (1) with a length (L) a width (B) and a panel thickness (P), consisting of at least one solid wooden layer (10) or a wood laminate 5 with a given number n ≥ 2 of wood layer (10), showing improved noise control performance. This is reached through a plurality of single troughs (ABH) in form of trough-shaped indentations, recessed in the top surface (100), distributed over the top surface (100) of the panel (1), reaching within the panel thickness (P), with a maximum depth of 90% of the 10 panel thickness (P), each trough (ABH) has a circular, elliptical or rectangular diameter between 0.5m and 3m with necessarily defined spherical, ellipsoid or cuboid shaped profile, wherein the troughs (ABH) are filled between 50% and 100% of their profile with damping bulk material (2). 15 (Fig.1c)

Description

[0001] Low noise engineered wood building elements

[0002] TECHNICAL FIELD

[0003] The present invention describes a low noise engineered wood building element with a length a width and a panel thickness, consisting of at least one solid wooden layer or a wood laminate with a given number of wood layer, wherein a functional top surface is engineered.

[0004] STATE OF THE ART

[0005] Engineered wood building elements or wood construction elements such as cross-laminated timber or glued laminated timber panels and laminates formed from them are frequently used as floors and / or walls for the construction of wooden buildings due to their structural strength and relatively low weight. A major drawback, however, is their comparatively poor sound insulation performance, especially for impact sound in the low frequency range, when used as floors. In countries where builders and users have higher sound insulation requirements, such as Switzerland, Germany and Austria, the most common solution is to ballast the wooden floors with an additional layer, usually gravel or concrete, which doubles or even triples the mass of the base element. Each additional layer requires additional height (usually in the range of 90 mm and more) and the additional load of the ballast must be supported by the building structure.

[0006] The problem of poor soundproofing performance also occurs in solid wood floors, which continues to be and has been for years a troublesome problem that does not seem to be easily solvable.

[0007] The inventors became aware of a theory behind Acoustic Black Holes (ABH), which they wanted to use to improve impact sound. This theory behind ABH was published first for the one-dimensional case of a beam with a functional graded end in the late 1980s, Mironov, M. A. "Propagation of a flexural wave in a plate whose thickness decreases smoothly to zero in a finite interval.", Soviet Physics Acoustics-USSR. 1988; 34.3: 318-319.

[0008] Since then different designs of the ABHs were proposed and applied, Adrien Pelat, Frangois Gautier, Stephen C. Conlon, Fabio Semperlotti, "The acoustic black hole: A review of theory and applications.", Journal of Sound and Vibration. Volume 476, 2020. The most relevant developments are the two-dimensional ABHs (pits or indentations) in plate structures. The general principle remains for all designs and applications the same. Local gradual reduction of the thickness of the plate or beam material that follows a power law causing incident flexural waves to slow down, while their amplitude increases. For an ideal profile with an infinitessimaly thin end, the wavespeed in theory approaches zero and the wave is not reflected. In reality, for plates with ABHs tapering to a finite thickness, the effect also occurs to some extent due to damping of the waves in the ABH.

[0009] The challenge for the design of ABHs is the identification of proper geometrical design parameters and damping measures that are appropriate for the specific structure (dimensions and constitutive material) and frequency range of interest. The geometrical parameters are the coefficient and exponent of the power function that determine the gradient, the length or radius of the hole, the remaining residual thickness, as well as the location of the holes. The effect of wedge shaped ABHs in homogeneous materials can be analysed with analytical functions, whereas for circular types of ABHs the analysis is based on numerical simulations, i.e. using the Finite Element Method (FEM). For complex inhomogeneous materials, such as composite materials, e.g. carbon fiber reinforced polymers (CRFP), or even layered composite materials with orthotropic plies, like engineered wood products, basic FEM models for plate with acoustic black holes require a large number of degrees of freedom and the solution becomes computationally very costly as a result. For damping mechanisms of the ABHs, so far mainly viscoelastic damping layers or constraint-layer damping were considered.

[0010] ABHs for homogeneous materials, i.e. metal or fibre composite, were thoroughly investigated in academia. The only known industrial application so far is the vibration damping of turbine blades. For thick inhomogeneous or even layered complex composites materials like for engineered wood elements, there is no evidence of investigation on the performance of ABH for vibration reduction nor on the required design space of the geometrical parameters of the ABH for impact sound insulation.

[0011] Engineered wood building elements for example for floors need additional measures to achieve an acceptable impact sound insulation. In the closest prior art, Vallely, S., & Schoenwald, S. (2023). "An efficient analytical method to obtain the homogenised frequency independent elastic material properties of cross-laminated timber elements", Journal of Sound and Vibration, 546, 117424 (24 pp.), the inventors started to define basics of ABHs in engineered wood building elements. It focusses on the initial step of the developed computational efficient numerical method. The described analytical method is applicable to obtain the elastic material properties of layered composite materials in general, which is input data for further calculations. Cross- Laminated Timber (CLT) is a wood laminate composed of bonded layers of timber planks (laminae / plies) where each lamina / ply is typically orientated perpendicular with respect to the previous layer. This engineered timber product as example for an engineered wood building element, has several environmental, economic, and structural advantages over traditional building materials, showing promise in the construction industry as a versatile standalone structural element. For example, CLT is a renewable, sustainable, and environmentally friendly building element that has a high stiffness-to-mass-density ratio relative to concrete and is well suited for pre-fabrication, allowing for bespoke designs and a greatly simplified on-site construction process. However, CLT's high stiffness-to-mass-density ratio is also a disadvantage, resulting in less than optimal noise and vibration isolation performance.

[0012] Current measures significantly increase the weight and thickness of these floor elements. This requires stronger and more expensive building elements in the lower stories to support the additional loads and also increases the building height.

[0013] However, thin and lightweight wood-based engineered building elements could not be achieved with sufficient noise control performance in series products.

[0014] DESCRIPTION OF THE INVENTION

[0015] The object of the present invention is to create improved noise control performance of engineered wood building elements, simple and inexpensive. The new concept results in low noise engineered wood building elements, made of wood-based materials, for example solid wood or wood laminates, which will be used by planners and finally bought by building contractors and building owners. It allows for the design and production of lighter thinner floors than prior art known solutions.

[0016] Such low noise engineered wood building elements can be adapted for any dimensions of timber construction, what makes them very appealing from a design and economical perspective. Lightweight thinner floors allow for slenderer and cheaper supports at the lower floors, as well as potentially a higher number of building stories or a bigger room height for a given maximum building height.

[0017] Glued engineered wood elements with ABHs have better impact and airborne sound insulation performance than plain- engineered wood elements allowing for thinner and more lightweight constructions than the state of the art. This gives the possibility for more flexible building designs and better use of building volume, as well as brings cost reduction, saving in materials and resources.

[0018] BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Further understanding of various aspects of the invention can be obtained by reference to the following detailed description in conjunction with the associated drawings, which are described briefly below.

[0020] It should be noted that in the differently described embodiments, the same parts are provided with the same reference symbols or the same component names, the disclosures contained in the entire description being able to be applied analogously to the same parts with the same reference symbols or the same component symbols.

[0021] A preferred exemplary embodiment of the subject matter of the invention is described below in conjunction with the attached drawings.

[0022] FIG. la shows a schematic perspective view of one engineered wood building element with a multiplicity of acoustic black holes, while

[0023] FIG. lb shows a partial view of the three layer-panel according to FIG. la, with empty acoustic black hole, while

[0024] FIG. lc shows a schematic perspective view of a single-layer solid wood panel with filled acoustic black holes. FIG. 2a shows a standard impact sound level vs. frequency diagram of 200 mm engineered wood floor with and without 4 filled ABHs, while

[0025] FIG. 2b shows a sound reduction index vs. frequency diagram of the 200 mm engineered wood floor with 4 filled ABHs and without ABHs.

[0026] FIG. 3a and 3b are showing schematic diagrams of numerical analysis of two panels with different ABH layouts and their different vibrational behaviours, which formed part of the development.

[0027] FIG. 4 shows a table of various arrangements of the Acoustic Black Holes (ABHs) in cross-laminated timber panels with resulting f_0 is the cut-on nascent frequency of the ABH effect.

[0028] DESCRIPTION

[0029] We produced different engineered wood building elements 1 that use the technology of Acoustic Black Holes (ABH), which are marked in the figures and in the application such ABHs are filled with a damping bulk material 2 for optimized noise reduction, as indicated in Figure lc.

[0030] An engineered wood building element 1 with n greater than or equal to one layer 10, is selected as the basis in Figures la to lc. As an example, a three-layer wood panel 1 (n = 3) with wood layers 10 arranged in parallel, glued together in parallel to form a multi-ply cross laminated timber, is shown here.

[0031] Independent from the number of layers n and the orientation of each wood element of the stack, the engineered wood building element 1 forms a panel with a given length L and a given width B and a panel thickness P. Panels 1 or engineered wood building elements 1 suitable for timber construction have typically lengths L and widths B of at least 0.5 m up to 16 meter and panel thicknesses P between 50 mm to 500 mm.

[0032] Each acoustic black hole ABH is made as single depression ABH in form of a trough-shaped indentation, in a top surface 100 of the top layer 10 or more than one layer 10, reaching in the panel thickness P. Analogously, the multiplicity of acoustic black holes ABH could also be made in a bottom layer of the lowest layer or in top layer 10 and bottom layer surfaces. Therefore the plurality of single troughs ABH in form of trough-shaped indentations is recessed at least in the top surface 100.

[0033] The shape of each single depression forming the ABH on and in the top surface 100 of the engineered wood building element 1 is formed with circular, elliptical or rectangular diameter D, most preferred with circular diameter D, as shown in the figures here. Diameter D between 0.5m and 3m of the ABHs are useful in engineered wood building elements 1.

[0034] All most preferred identically executed single depression ABH have a maximum depth T at the deepest point of the trough in the panel 1, while the side surfaces are continuous to this maximum depth T. Each ABH shows an identical profile from the level of the top surface 100 to the lowest point of the ABH. The profile of the ABH could be formed according to profile of the ABH : y(x) = axb+ c. where a = T / (0.5*D) / Kb and c = (P-T).

[0035] (P panel thickness, T maximum depth of ABH, D diameter of ABH).

[0036] The formula assumes that ABH is the thinnest point of the plate and does not taper to an infinitesimal (~0) thicknessThe geometrical profile of the indentations ABH should follow the power law with coefficients and can have taper with a constant thickness in the centre of the ABH.

[0037] The maximum depth T can be maximum 95% of the panel thickness P. Experiments showed, that the maximum depth T in the centre of the ABH must be > 50% of the panel thickness P.

[0038] The profile of the trough ABH is formed along the curvature of a spherical surface with a defined radius, if the diameter D is formed as a circle. The radius of the trough curvature is defined by depth T and diameter D of the trough ABH.

[0039] If the diameter D is an ellipse, the curvature of the trough will follow an ellipsoid, while if the cross-section of the trough ABH is rectangular, the trough ABH will have a cuboid shape. These examples are not shown here.

[0040] The distances A, A' between directly adjacent acoustic black holes ABH should be less than or equal to two times the diameter D of one acoustic black hole ABH. Distances A in direction length of the panel are between 0.20m and 1.70m.

[0041] Distances A' in direction of the width B of the panel are between 9cm and 80cm.

[0042] Accordingly, the number of ABH's, the maximum diameter D of each ABH and the distances A, A' of the troughs ABH is to be adjusted to the maximum size (L*B) of the panel 1.

[0043] Most preferred the troughs ABH are identical in design and uniformly filled with the damping bulk material 2.

[0044] The damping bulk material 2 for filling the ABHs is a granular material, like sand, with averaged grain size 0.2 to 2 mm or gravel with averaged grain size between 2 mm and 20 mm, where the sand and gravel particles can be crushed stone with sharp edges or bank gravel with round edges. Also chippings fill is possible for damping bulk material 2.

[0045] The damping bulk material 2 can also be a mixture of different grain sizes and materials, wherein the particles can be loose or elastically bonded to each other.

[0046] We have tried as engineered wood building element 1, single layer solid wood panels and various wood laminate with more than n=2 layers 10 of wood, which are glued or mechanically joined.

[0047] Glued mass timber elements 1 either with multiple layers of lamellas stacked with alternating orientations, such as Cross Laminated Timber (CLT) elements according to EN 16351 :2021 or ANSI / APA PRG 320-2019 or elements, or glued elements consisting of a single layer of boards oriented in the same direction such as glulam beams (glued laminated timber) according to EN 14080:2013 or ANSI A190.1-2022.

[0048] In principle also Dowel Laminated Timber (DLT) or Nail Laminated Timber (NLT) can be used as engineered wood building elements 1. Of course ABHs reduce locally the structural performance of the panel 1 elements. Almost every building layout is unique depending on given boundary conditions (size and location of building lot, urban planning grounds, development zoning, economical aspects, etc.) and the needs of the owners (occupancy, etc.). Floors and walls are structurally designed for the particular building situation and are produced individually with required dimensions and lay-up (number and thickness of layers). Machining of ABH profiles is principally no problem. However, several potential disadvantages arise:

[0049] ABHs have to be taken into account in the structural design process. It is necessary to adjust their location and eventually their size (D, T, profile) to meet the structural requirements.

[0050] For an engineered wood building element 1 as full-size floor prototype consisting of two 5-ply Cross Laminated Timber (CLT) panels 1, (L=5730mm, B=2380mm, P=200mm), test results demonstrate superior sound insulation performance. In each of the CLT floor elements 1 two ABHs were machined, D=2200mm with maximum depth T=160mm and corresponding profile, because of circular diameter D.

[0051] The ABHs were filled with gravel fill 2, loose crushed stone, grain-size 4 mm to 8 mm as damping bulk material 2. The localised gravel ballast / particle 2 damping inside the ABHs attenuates structure-borne sound more efficiently than without the ABHs and hence improves the sound insulation.

[0052] Laboratory experiments demonstrated an excellent improvement of airborne and impact sound insulation in the whole frequency range, as shown in Figure 2a and 2b, while the total mass of the bare CLT floor was increased by less than 60%. Four manufactured and filled ABHs in a 200mm thick plate 1 led to the results shown in Figures 2a and 2b. The single wood elements 1 were in one embodiment glued to build the plate 1 and in another embodiment connected by screws, better said held by a screw connection.

[0053] In another embodiment the whole floor consisted of two engineered wood building elements 1, 1', each comprising layer 10 which are glued together, each contained two ABHs. The connection between the two elements 1, 1' was tried as lap joint screwed and as butt joint with glued interfaces. The glued joint showed better results.

[0054] The results in lowered sound levels and improved sound reduction index in this examples speak for themselves.

[0055] The design range for the geometrical ABH parameters was also explored in a numerical analysis. In Figures 3a and 3b, a comparison of the vibrations (eigenmodes) of a 200 mm thick 5-ply CLT-panel 1 with two ABHs with diameter D= 2.2 m is compared with the vibrations of a 200 mm thick 5-ply CLT-panel 1 with ten ABH with a smaller diameter D = 1 m, but with a steeper and deeper ABH profile, as indicated with rings in the first image of figure 3a.

[0056] The first mode shape with high amplitudes at the ABHs, i.e. the cut-on of the ABH effect, occur at similar frequencies for both panels 1, 1', approx. 49 Hz.

[0057] For glued engineered wood floor 1 with two dimensional ABH and sand- / gravel-fillings, tests according to applicable standards on a full-size prototype floor demonstrated the superior airborne and impact sound insulation performance. The geometrical ABH design parameters were determined by using computational very efficient numerical methods and are suitable to be implemented in optimisation algorithms. So far, a focused numerical parametric study explored the appropriate range of ABH geometrical design parameters to improve the impact sound insulation in the low frequency range (50 Hz to 500 Hz). When two wood building elements 1 with multiplicities of ABH in their top surface 100 of layer 10 are connected at their layer 10, cavities can be build. Such cavities can also be filled with damping bulk material 2, before filling or by introducing a filling channel. To prevent damping bulk material 2 from falling out of the ABHs, a protective layer can be placed on the filled ABH layer before both wood building elements 1 are joined. The protective layer can be a wooden layer, like another layer 10 as finish or a flat synthetic material sheet or layer or a suitable compound.

[0058] Trough, indentations ABH or cavities ABH will be filled with damping bulk material 2.

[0059] The damping bulk material 2 should most preferred completely fill the trough ABH and be flush with the top surface 100. All calculations and measurements were made with damping bulk materials 2 filling the depth of the ABH, whereby even incomplete filling of at least 50% of the trough ABH has a sound-reducing effect. Best results were achieved with filling between 75% and 100% of the ABH.

[0060] The ABHs in all panels 1 have a broadband effect, so that they improve sound insulation even though their design parameters are not optimized for a particular engineered wood element 1.

[0061] The present disclosure describes particular embodiments and their detailed construction and operation. The embodiments described herein are set forth by way of illustration only and not limitation. Those skilled in the art will recognize, in light of the teachings herein, that there may be a range of equivalents to the exemplary embodiments described herein. Most notably, other embodiments are possible, variations can be made to the embodiments described herein, and there may be equivalents to the components, parts, or steps that make up the described embodiments. As tests have shown, the ABH effect can be seen particularly well when five-layer wood panels 1 with n=5 wood layers 10 arranged in parallel, glued together in parallel to form a multi-ply cross laminated timber, are used. Various arrangements of the Acoustic Black Holes (ABHs) in such five-layer wood panels 1 are presented in Figure 4. In each of the various large five-layer wood panels 1, two or eight ABHs with a circular base and spherical profile with diameters of lm or 2.20m and depths of 0.08m to 0.18m were inserted. After filling with damping bulk material 2 up to 100% completely filling the trough ABH be flush with the top surface 100, frequency measurements were carried out. The results are presented in Figure 4. P is the total thickness of the panel, while n is the number of layers of the panel. The maximum profile depth varies between 50% and 95% of the panel thickness P, most preferred between 80% and 90% of the panel thickness. fO is the cut-on nascent frequency of the ABH effect. This frequency fO is formed in thin panels 1 in which the ABHs are inserted at different depths and profiles as shown in Figure 4. The flexural modes of the plate as entity occur already at lower frequencies. At the ABH cut-on frequency the first mode occurs withhigh displacement amplitudes in the ABH area followed by a series of subsequent modes. Since this high displacement occurs in the ABH, the plate interacts with the damping material and Lamb waves are attenuated.

[0062] Sound in a frequency range starting at 47Hz up to 162Hz, i.e. roughly above 40Hz, can be damped and thus attenuated by such ABHs designs in five-layer wood panels 1. This is sufficient for low-frequency impact sound between 50 Hz and 250 Hz.

[0063] The ABHs shown here are shown uncovered in the figures, whereby a protective layer, for example could be a floating floor topping, should be designed to cover the top surface 100. The damping bulk material 2 filled in cannot then be lost.

[0064] For example, the term b describes the profile of each trough ABH : y(x) = axb+ c. where a = (T) / (0.5*D) / Kb and c = (P-T). (P panel thickness, T maximum depth, D diameter of ABH)

[0065] Some design criteria for a low cut-on frequency are: - For a smaller diameter D a steeper profile with a bigger design parameter b and bigger maximum depth T is required

[0066] When ABH diameter D is smaller, the number m of the ABH has to be increased

[0067] The smaller diameter D and steeper the slope, the smaller is the effective bandwidth of the ABH

[0068] The smaller bandwidth can be compensated by additional ABHs with alternative profiles tuned to higher frequency.

[0069] LIST OF REFERENCE NUMERALS

[0070] 1 engineered wood building element / panel

[0071] 10 layer / ply

[0072] L length of panel (0.5m to 16m)

[0073] B width of panel (0.5m to 16m)

[0074] P panel thickness (50 mm to 500mm) n >1

[0075] 100 top surface

[0076] ABH acoustic black hole / trough / depression

[0077] D diameter (0.5m bis 3m)

[0078] T maximum depth (> 50% , up to 95% of panel thickness)

[0079] A distance (between directly adjacent ABH) profile (steeper and deeper) of ABH m number of ABH b profile parameter

[0080] 2 damping bulk material / gravel fill or chippings fill height of filling > 50%

Claims

PATENT CLAIMS1. Low noise engineered wood building element (1) with a length (L) a width (B) and a panel thickness (P), consisting of at least one solid wooden layer (10) or a wood laminate with a given number n > 2 of wood layer (10), wherein a functional top surface (100) is engineered, characterized in that a plurality of single troughs (ABH) in form of trough-shaped indentations are recessed at least in the top surface (100), distributed over the top surface (100) of the panel (1), each with a defined spherical, ellipsoid or cuboid shaped profile and maximum depth (T) between 75% and 95% of the panel thickness (P), each trough (ABH) has a circular, elliptical or rectangular diameter (D) between 0.5m and 3m, wherein the troughs (ABH) are filled between at least 50% to 100% of their profile with damping bulk material (2) in form of granular material, like sand, with averaged grain size 0.2 to 2 mm or gravel with averaged grain size between 2 mm and 20 mm or chippings fill.

2. Low noise engineered wood building element (1) according to claim 1, wherein a protective layer is placed on the top surface (100) of the panel (1) and the plurality of filled troughs (ABH).

3. Low noise engineered wood building element (1) according to one of the preceding claims, wherein the troughs (ABH) are filled with damping bulk material (2) flush with the top surface (100) of the troughs (ABH).

4. Low noise engineered wood building element (1) according to one of the preceding claims, whereinthe panels (1) are formed of wood layer (10), which are mechanically joined by a screw connection.

5. Low noise engineered wood building element (1) according to one of the preceding claims, wherein the number of filled troughs (ABH) in each panel (1) is higher than two and a plurality of such wood building elements (1) are mechanically connected or glued and forming a floor.

6. Low noise engineered wood building element (1) according to one of the preceding claims, wherein the panels (1) in form of wood laminate are formed of five Cross Laminated Timber wood layer (10) glued or mechanically joined, building the panel (1) with its length (L), width (B) and panel thickness (P).

7. Low noise engineered wood building element (1) according to one of the preceding claims, wherein the engineered wood building element (1) is made of connected single plies, forming Dowel Laminated Timber (DLT) or Nail Laminated Timber (NLT) or mechanically connected stacks with the multiplicity of troughs (ABH) in the top surface (100).

8. Low noise engineered wood building element (1) according to one of the preceding claims, wherein the troughs (ABH) are identical in design and uniformly filled with the damping bulk material (2).

9. Low noise engineered wood building element (1) according to one of the preceding claims, wherein the distances (A) between directly adjacent troughs (ABH) in the top surface (100) in direction of the length (L) are between 0.20m and 1.70m.

10. Low noise engineered wood building element (1) according to one of the preceding claims, wherein the distances (A') between directly adjacent troughs (ABH) in the top surface (100) in direction of the width (B) are between 9cm and 80cm.

11. Low noise engineered wood building element (1) according to one of the preceding claims, wherein the damping bulk material (2) is a gravel fill of loose crushed stones with average diameter grain-sizes between 4 mm and 8 mm.

12. Low noise engineered wood building element (1) according to one of the preceding claims 1 to 10, wherein the particles of the damping bulk material (2) are crushed stone with sharp edges or bank gravel with round edges.

13. Low noise engineered wood building element (1) according to one of the preceding claims 1 to 10, wherein the damping bulk material (2) comprises elastically bonded particles.

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