WO1993000262A1

WO1993000262A1 - Sound absorbing wall panel for use along highways

Info

Publication number: WO1993000262A1
Application number: PCT/US1992/005478
Authority: WO
Inventors: Vernon A. Studdard; Wanda Harris
Original assignee: Harco Steel, Inc.
Priority date: 1991-06-27
Filing date: 1992-06-26
Publication date: 1993-01-07
Also published as: AU2322792A

Abstract

A noise barrier and sound absorption panel system (10) is disclosed. The panel has three layers (11, 12, and 13), the outer two layers (11, 13) comprising a dense, load bearing material such as concrete and the inner layer (12) comprising a foam, sound absorbing material. The noise-facing outside layer (16) defines a series of generally cone-shaped passageways (14) which extend through the layer (11) to expose the sound absorbing material (12) in the center of the panel. The passageways (14) allow a large amount of unwanted noise to be 'funneled' into the sound absorbing material (12) while letting only a minimum amount of sound waves escape from the center layer (12) after reflection.

Description

SOUND ABSORBING WALL PANEL FOR USE

ALONG HIGHWAYS

Technical Field The present invention relates to sound barrier walls of the type used to isolate areas along highways from the noise of traffic, and more specifically relates to such barrier walls constructed of structural load bearing material such as concrete incorporating sound absorbing material.

Background of the Invention

As populations grow more and more dense, city planners and developers find it necessary to widen highways and extend residential areas to within close proximity of right-of-ways. Such adjacent communities need protection from high noise levels of the highway as well as a more aesthetically pleasing view than a major thoroughfare.

There have been many attempts to abate such noise and scenic pollution. Most of these attempts involve the construction of some kind of wall, often made of concrete or metal.

Such walls, standing alone, tend to reflect some of the noise off the inside or traffic-facing wall, and to transmit some of the noise through the wall, rather than absorbing the traffic noise. This may increase the noise level experienced by motorists without adequately reducing transmitted noise. In response to these problems, attempts have been made to construct walls that absorb the sounds instead of just reflecting them back into the source of the noise. For example, one prior structure provided absorptive material adhered to the inner, that is, the traffic-facing surface of such walls, and another provides a sound absorbing foam panel sandwiched between layers of concrete. While such material absorbs some of the sounds, a substantial portion of the noise is reflected back to the noise source off the supporting wall, even if the sound waves must travel through absorptive material on the inner surface of the barrier.

Prior sound barrier walls intended for use along highways are described in U.S. Patents No. 4,838,524; 3,983,956; 3,656,576; 4,402,384; and 3,846,949.

The prior art includes many attempts to reduce the reflection problem in other environments. U.S. Patent No.

3,132,714 discloses one form of prior art sound absorbing panel which includes a perforated sheet on an inside panel of the wall, an intermediate layer of absorptive material, and an outside layer of relatively sound-reflective material. The layers are made of cellular plastic material glued together, with the intermediate layer defining large open cells. In theory, the sound waves enter through the perforated sheet and continually reflect between the perforated sheet and the outside panel until trapped in the large open cells and absorbed in the absorptive material. As noted in U.S. Patent No. 4,838,524, this type of structure allows too much of the noise to exit the panel through the perforations and the inside panel. U.S. Patent No. 3,887,031 discloses another prior art attempt to absorb sound involving the use of a horn-shaped element to absorb the sound. Such horns are "nested" in individual enclosed cavities covered at the "mouth" or noise-receiving end by a sheet of absorptive material. The horns, cavities, and facing material are varied so low and high frequency noises may be absorbed. Such horn assemblies use resonance and absorption techniques to reflect, capture and absorb the majority of incoming frequencies. However, such an assembly is not formed of structural load bearing materials suitable for exterior use, such as along a highway.

Thus, there has been a need in the art for a sound absorbing wall panel that can withstand exterior conditions, absorbs sound transmitted through the wall, and reduces the proportion of sound that is reflected back to the source.

Summary pf the Invention

Generally described, the present invention provides a sound barrier which comprises a three-layered sound absorbing panel. The inside of the panel, or the side facing the sound source, is made of a dense, load-bearing surface, such as concrete. On the inner surface of this inner layer is a plurality of passageways that narrow in cross-sectional area from the inner part of the inside layer to the outer side of the inner layer. The central layer of the panel is comprised of sound absorbing material. This central layer is exposed through the passageways of the inner layer. Finally, the outer layer is composed of a dense, load-bearing material.

This sound absorbing wall of the present invention solves the aforementioned problems by the novel use of the passageways in the inner wall. The wider part of each passageway receives unwanted noise and "funnels" it into the sound absorbing material. Thus, sounds will be partially absorbed by the central layer. Sounds not absorbed will reflect off the outer layer back into the central sound absorbing material. Once again, the central layer will absorb more of the sound. Sound not absorbed in the return passage will return to the inner layer and become trapped between the inner and outer layers. Since the passageway's cross-sectional area is small at the junction of the central layer and the inner layer, the sound waves are most likely to contact the inner wall and reflect back into the absorptive material rather than exiting out through a passageway. This process of reflection and absorption continues until the sound waves attenuate. Thus, the conical passageways of the present invention act as a gathering and focusing aperture, allowing the maximum amount of unwanted sound to enter the wall panel and letting only a minimum amount of reflective waves escape.

In a preferred embodiment of the invention, the dense, load bearing material is concrete and the sound absorbing layer is polystyrene. The sound absorbing layer is preferably protected from direct sunlight and other weather conditions by use of a protective layer such as special paint or a silk screen. Further, the passageways through the inner layer are preferably circumscribed by a plurality of flat planes such that a cross section of the passageway forms a polygon. The outer surface of the sound absorbing wall panel could be cast into any pattern, improving over aesthetics of typical highway sound barriers.

The present invention also provides a method of fabricating a sound barrier wall, comprising the steps of inserting into a mold, comprising a back mold wall and a front mold wall, a sound absorbing central panel and means for spacing the central panel from the back mold wall, holding the central layer with the front mold wall, the front mold wall defining a plurality of tapering elements extending from the face of the front mold wall, each tapering element narrowing in cross section from the front mold wall to a contact point of the tapering element with the central layer, casting an outer layer of the sound absorbing wall panel by placing a load bearing casting material between the central layer and the back mold wall, the outer layer including the spacing means for the central panel, casting an inner layer of the sound absorbing wall panel by placing a load bearing casting material between the central layer and front mold wall, during the casting steps anchoring the inner and outer layers together, and removing the wall panel from the mold, leaving in the inner layer a plurality of passageways formed by the tapering elements with the central layer being exposed through the passageways.

Accordingly, it is an object of the present invention to provide an improved sound barrier that absorbs unwanted noise as opposed to simply reflecting it back at the source. It is a further object of the present invention to provide a sound absorbing wall which directs sound to a focused point of absorption and traps the sound waves in an interior portion of the wall.

It is a further object of the present invention to provide an aesthetically pleasing outer surface to noise barriers.

It is a further object of the present invention to provide a simple method of fabricating the sound-absorbing walls.

Other objects, features and advantages will become apparent upon consideration of the following detailed description of the invention when taken in conjunction with the drawing and the appended claims.

Brief Description of the Drawings

Fig 1. is a pictorial view of a fully assembled sound absorbing wall panel of the present invention.

Fig. 2 is an exploded pictorial end view of the wall panel of Fig. 1

Fig. 3 is a vertical cross sectional view taken along line 3—3 of Fig. 5. Fig. 4 is a horizontal cross sectional view taken along line 4-

-4 of Fig. 1.

Fig. 5 is a front plan view of the inner layer of the wall panel of Fig. 1.

Fig. 6 is a rear plan view of the outer side of the outer layer of the wall panel.

Fig. 7 is a pictorial view of a spacer utilized in casting a wall panel according to the present invention.

Fig. 8 is a front plan view of the cone shape of the passageways of the preferred invention. Fig. 9 is a pictorial view of a conventional hinge mold for fabricating the sound absorbing wall panel of Fig. 1, shown in an open configuration. Detailed Description of the Preferred Embodiment

Referring now in more detail to the drawing, in which like numerals refer to like parts throughout the several views, Fig. 1 shows a sound absorbing wall panel 10 embodying the present invention. The wall panel 10 includes three layers, an inner layer 11, a central layer 12, and an outer layer 13. As used herein, the terms "inside" or "inner" refer to the noise-facing or traffic-facing side of the panel 10. The terms "outer" and "outside" refer to the side away from the noise source, or the side facing the area to be protected from the noise.

Fig 5 shows a front view of the inner layer 11. An expanded end view of the inner layer 11 is supplied by Fig. 2. A vertical cross section of the inner layer 11 is included in Fig. 3, and horizontal cross section is included in Fig. 4. The inner layer 11 is comprised of a dense, load bearing material, preferably concrete. The concrete is reinforced with a rigid supporting structure 29, such as re-bar, which is well known in the art. The re-bar grid runs horizontally and vertically throughout inner layer 11. The inner layer 11 includes a plurality of passageways 14 that allow passage from an inner surface 16 of inner layer 11 to an outer surface 17 of the inner layer 11. Each passageway 14 begins at an inner opening 18 at the inner surface 16 and narrows in cross section from the inner surface 16 to an outer opening 19 at the outer surface 17. Preferably, the inner opening 18 and outer opening 19 are octagonal in shape as shown in Fig. 8. The walls of the passageway 14 then consist of planes 15, the ends of each being corresponding sides 18a and 19a of octagonal openings 18 and 19 of the passageway 14. Preferably the diameter D of the inner opening 18 of the passageway 14 is 3-3/4 inches and the diameter E of the outer opening 19 is 1-

3/8 inches. Each of the passageways 14 is spaced 9-1/2 inches apart from center to center and the passageways are arranged in horizontal and vertical rows. The passageways 14 begin 5 inches from the top and 7-3/4 inches from the sides of the wall panel 10. Although the cross section of the passageway of the preferred embodiment is an octagon, the perimeter openings 18 and 19 may be any of various configurations, and the walls of the passageway 15 may be smoothly shaped or segmented to maximize the focusing effect of the passageways. An exploded end view of the central layer 12 is supplied by

Fig. 2. A vertical cross section of the central layer 12 is included in Fig. 3, and a horizontal cross section is included in Fig. 4. The central layer 12 includes a sound absorbing material, preferably polystyrene. The polystyrene of the present invention is preferably an extruded polystyrene insulation, 2 inches thick with an "R" value of 10 at 75 degrees Fahrenheit and a U.L. class certification of D- 369. The inner surface 27 of the central layer 12 of the preferred embodiment is optionally covered by a protective coating 26. The protective coating 26 shields the polystyrene or foam layer 25 from damaging solar rays and weather. The preferred protective coating

26 is a special ultraviolet shielding foundation coating known as "Retro Flex", manufactured by Retro Technologies, Incorporated of Waunakee, Wisconsin. Alternately, the protective layer 26 may be made of silk screen material. A series of conventional anchoring pins 20 are used to connect the central layer 12 to the inner layer 11 and the outer layer 13. Holes are drilled through the central layer 12 and the pins 20 are inserted therethrough. The pins 20 are spaced at one foot intervals in horizontal and vertical rows. A flange on the pin 20 helps to keep the pin 20 from being inserted too far and a lock washer (not shown) is placed on the inserted end to keep the pin 20 in place. The pins 20 increase in thickness from the inner 27 and outer 28 surfaces of the central layer creating a barbed effect that will make the pins stay in position once concrete is placed adjacent to the central layer.

The outer layer 13 is shown in Fig. 2. The vertical cross section of the outer layer 13 is included in Fig. 3, and a horizontal cross section is included in Fig. 4. The outer layer 13 is preferably made of concrete and contains the same rigid supporting structure 29 as the inner layer 11. The outer layer 13 further comprises chair spacers 30 that are helpful in the casting process. The function and description of the chair spacers 30 will be explained below. The outer surface 36 of the outer layer 13 is cast with an aesthetically pleasing pattern. Fig. 6 shows the outer surface having a pattern resembling a stone wall.

The wall panel 10 may be manufactured utilizing a standard hinge style mold 37, shown in Fig. 9. The mold 37 is oriented vertically during casting. Before casting can take place, the central panel 12 is prepared by coating its inner surface with protective paint 26, or by attaching the silk screen to the inner surface, and by inserting the connecting pins 20 through the layer 12. Once prepared, the central panel is placed between a front mold wall 38 and a back mold wall 39 of the mold 37. The front mold wall corresponds to the inner side 16 of the wall panel 10, and defines a plurality of tapering elements 40. The central layer 12 is held in place against the front mold wall tapering elements 40. The tapering elements 40 correspond to the as-cast passageways on the finished sound panel 10. A re-bar grid 29 fits around the elements 40. The contact point 41 of the tapering elements 40 with the silk screen 26 is the most narrow cross section of the tapering elements. The central layer 12 rests against all of these contact points 41. The back mold wall 39 corresponds to the outer side of the sound absorbing wall panel 10 and includes a three-dimensional pattern.

The central layer 12 is spaced from the back mold wall 39 by means of the chair spacers 30. A chair spacer 30 is shown in Fig.

7. The structure of the spacers 30 is such that several "chairs" 31 arc welded perpendicular to a rod 32. The rod extends the height of the sound panel 10. The "chairs" define a shape that begins as an arc which is attached at the center of the arc to the vertical rod 32. However, the ends of the arc are bent away from each other so that they form a plurality of feet 33 all lying in approximately the same plane. The function of the chair spacer 30 can be seen in Fig. 4. The rods 32 of the chair spacers 30 are tied to both sides of the re- bars 29 so that the feet 33 point outwardly and the planes of the feet of the chairs lie adjacent to the central layer 12 on one side of the re- bar and adjacent to the back mold wall 39 on the other side of the

re-bar. The chair spacers 30 run vertically and are spaced at approximately two foot intervals.

Thus, the front mold wall holds the central layer 12 in position while the chair spacers 30 determine the thickness of the outer layer until concrete is poured. The concrete for the outer layer is poured between the central layer 12 and back mold wall 39. The chair spacers 30 should be loosely fitted so that the concrete may work between the back mold wall 39 and the spacers 30 so that the spacers 30 will not be visible on the outer surface 36 of the outer layer 13. Concrete for the inner layer 11 is poured between the front mold wall 38 and the central layer 12, around the tapering elements 40. The concrete should not be poured continually into one side until completed, but instead should be alternated between the inner layer 11 and the outer layer 13 so as to equalize pressure on the central layer 12. It is important that none of the concrete work its way between the contact points of the tapering elements 41 and the central layer 12. If this should inadvertently occur, the layer of concrete thus formed at the inner openings 19 should be broken away to expose the central layer. The central layer 12 need not extend the entire length of the mold 37. In fact, the concrete should extend around all four edges of the central layer 12, as shown at region 44 in Fig. 3, so as to integrally join the inner and outer layers and add structural strength. Once the casting has been completed, the sound absorbing wall panel may be removed from the mold 37. The passageways will have formed from the tapering elements 40 and the outer surface 36 of outer layer 13 will have an aesthetically pleasing pattern.

The finished sound wall panel 10 is now ready to be placed along the highway. Sound wall panels 10 are held in place by lowering or inserting their side edges between spaced apart I-beams

42, in the manner shown in Fig. 4, with the inner layer and its passageways 14 facing the noise source. The panels 10 may be stacked as high as needed between the I-beams; higher walls simply require longer I-beam 42 and stronger foundations. The pattern on the outer surface 36 can be varied to match any community plan. A significant amount of unwanted traffic noise approaching the wall 10 is "funnelled" into the sound absorbing material of the central wall 12 by means of the novel passageways. Residents on the outside of the wall are not subjected to the street sounds because the sounds are either absorbed by the central layer 12 or are reflected back from the inner layer 11 or the outer layer 13. Commuters are not subject to as much reflected noise because the sounds are absorbed into the central layer 12 on return or are effectively trapped in reflection between the inner layer 11 and the outer layer 13. Since the cross sectional area of the passageways 14 is small at the central layer 12, very little sound reflects back out of the passageways. Thus, most of the sound stays in the wall until it has attenuated.

While this invention has been described in detail with particular reference to preferred embodiments thereof, it will be understood that variations and modifications can be affected with the spirit and scope of the invention as described herein and before and as described in the appended claims.

Claims

ClaimsWhat is claimed is:

1. A sound absorbing wall panel comprising: an inner layer comprising a dense, load bearing material defining an array of spaced apart passageways therethrough, each of said passageways narrowing in cross section from a first opening at an inner surface of said inner layer to a second opening at an outer surface of said inner layer; a central sound absorbing layer adjacent to said inner layer, said central layer being exposed through said passageways; and an outer layer comprising a dense, load bearing material.

2. The sound absorbing wall panel of Claim 1, wherein said passageways are circumscribed by a plurality of flat planes, said flat planes extending from said first opening at said inner surface of said inner layer to said second opening at said outer surface of said inner layer, such that a cross section of said passageway forms a polygon.

3. The sound absorbing wall panel of Claim 1, wherein said dense load bearing material comprises concrete.

4. The sound absorbing wall of Claim 3, wherein said central panel comprises polystyrene foam.

5. The sound absorbing wall panel of Claim 4, further comprising a rigid supporting structure contained within said concrete.

6. The sound absorbing wall panel of Claim 1, wherein said central layer comprises a foam panel.

7. The sound absorbing wall panel of Claim 6, wherein said central layer further comprises a protective covering positioned between said foam panel and said outer surface of said inner layer, whereby said protective covering is exposed through said passageways in said inner layer.

8. The sound absorbing wall panel of Claim 6, wherein said protective covering comprises an ultraviolet shield.

9. The sound absorbing wall panel of Claim 6, wherein said foam layer comprises polystyrene.

10. The sound absorbing wall panel of Claim 1, further comprising connecting means passing through said central layer for connecting said central layer to said inner layer and said outer layer.

11. The sound absorbing wall panel of Claim 1, wherein said outer layer includes an outer surface defining an aesthetically pleasing pattern.

12. A method of fabricating a sound absorbing wall panel, comprising the steps of: inserting into a mold, comprising a back mold wall and a front mold wall, a sound absorbing central panel and means for spacing said central panel from said back mold wall; holding said central layer with said front mold wall, said front mold wall defining a plurality of tapering elements extending from the face of said front mold wall, each such tapering element narrowing in cross section from said front mold wall to a contact point of said tapering element with said central layer; casting an outer layer of said sound absorbing wall panel by placing a load bearing casting material between said central layer and said back mold wall, said outer layer including said spacing means; casting an inner layer of said sound absorbing wall panel by placing a load bearing casting material between said central layer and said front mold wall; during said casting steps, anchoring said inner and outer layers together; and removing said sound absorbing wall panel from said mold, leaving in said inner layer a plurality of passageways formed by said tapering elements, said central layer being exposed through said passageways.

13. The method of Claim 12, wherein during said step of casting said inner layer, no casting material of said inner layer is cast between said central layer and said contact point of said tapering elements.

14. The method of Claim 12, wherein said casting material comprises concrete.

15. The method of Claim 14, wherein said concrete incorporates a rigid supporting structure.

16. The method of Claim 12, wherein said central layer comprises polystyrene.

17. The method of Claim 12, wherein said central layer comprises a foam layer and a protective covering adjacent to a side of said foam layer facing said tapering elements, said protective covering contacting said tapering elements at said contact point during casting.

18. The method of Claim 17, wherein said foam layer comprises polystyrene.

19. The method of Claim 18 wherein said protective covering comprises an ultraviolet shield.

20. The method of Claim 12, wherein said step of anchoring said layers comprises inserting a plurality of anchors through said central layer and extending into said inner and outer layers, such that said anchors are embedded in said inner and outer layers upon casting.

21. The method of Claim 12, wherein said step of casting said outer layer comprises forming an aesthetically pleasing pattern on an exterior surface of said outer layer.