US20130340365A1

US20130340365A1 - Tetrahedral Tube Reinforcement of Concrete

Info

Publication number: US20130340365A1
Application number: US13/529,194
Authority: US
Inventors: Howard A. Fromson
Original assignee: Individual
Current assignee: Individual
Priority date: 2012-06-21
Filing date: 2012-06-21
Publication date: 2013-12-26

Abstract

A weight reduced and strength enhanced concrete structure in which at least one tubular reinforcing core is embedded in a solid concrete matrix. Each core is a chain of integrally interconnected hollow tetrahedra. Each tetrahedra has triangular faces connected at common edges and vertices. The planar faces of adjacent tetrahedra are spaced from each other, and concrete fills the spaces. The cores are suspended within the concrete and self-anchored, without anchors at the exterior surface of the structure. With the embedded cores the concrete structure becomes more resistant to compressive, tensile, and bending loads. For even greater strength of the structure, the cores can be tensioned and thereby pre-stress the concrete. Impact or other loads are distributed substantially isotropically, thereby reducing local stresses. These advantages can be achieved with cores that are lighter than the concrete material they displace or rebar they replace.

Description

RELATED APPLICATION

This application claims the benefit under 35 U.S.C. §120 from U.S. application Ser. No. 13/371,774 filed Feb. 13, 2012, for “Cast Bodies With Tetrahedral Tube Reinforcement”.

BACKGROUND

The present invention relates to the reinforcement of concrete and, in particular, to cost-effectively increasing the strength while reducing the overall weight or volume of concrete structures.

SUMMARY

I have conceived a way of achieving this design objective using the invention described in my U.S. Pat. No. 3,237,362 “Structural Unit for Supporting Loads and Resisting Stresses,” the disclosure of which is hereby incorporated by reference. The construction-related technique disclosed therein can be adapted to improve the performance characteristics of concrete and other structures by substituting triangulated tubular cores for conventional reinforcing rods or bars (“rebar”).
The present disclosure is preferably directed to a weight reduced and strength enhanced concrete structure comprising a continuous matrix of concrete reinforced with at least one tubular chain of integrally interconnected hollow tetrahedra, and to a method for reinforcing concrete.
The tetrahedra have triangular planar faces that share common vertices and edges with neighboring tetrahedral in the chain and provide deep, angulated spaces that are filled with concrete. The cores in essence “float” within the concrete in that they are not mechanically fixed to anchors, panels, floors, or the like at the exterior surface of the concrete structure. However, as an option to further stiffen the reinforcement, the cores can be pre-tensioned and/or a plurality of cores can be affixed to each other.
The use of triangulated tubular tetrahedra as reinforcement cores in a concrete matrix, offers a unique combination of advantages. The concrete matrix provides resistance to compression, but with the embedded cores the concrete structure becomes more resistant to tensile, torsional, torque and bending loads. Impact or other loads are distributed substantially isotropically, thereby diffusing the loads and reducing local stresses. Finally, this reinforcement and associated advantages can be achieved with cores that are lighter than the concrete material they displace or the rebar which they replace.
Although not limited thereto, the most straightforward embodiment of the reinforced concrete structure would be as load bearing elements in the building and construction industries. In one embodiment, each core has a longitudinal centerline that is aligned in parallel with the longitudinal center line of the structure. The structure is intended for use where a compressive load is imposed on the structure at the longitudinal ends, in parallel with the centerlines of the cores, e.g., as in a structural column. In this embodiment, the cores reinforce the structure against torsional and bending forces that might arise over time or during transient loading.
In another embodiment, the reinforcing cores area arranged along the length and/or width of a concrete beam or slab, to resist loads that are transverse to the length or width. For a horizontal beam supported at opposite ends, the cores are preferentially situated in the lower region of the beam to resist tensile bending stresses, whereas for a cantilevered beam the cores are preferentially situated in the upper region of the beam.
The cores do not form a self-standing structural frame or skeleton, but rather merely reinforce a concrete structure. In the most common end use, a plurality of cores are independently arranged, i.e., one core is not rigidly connected to another core (although this does not preclude spacers or shims between cores to maintain spacing). For extra strength, the core members can be arranged with the tetrahedra of adjacent core members in closely spaced or connected registry, whereby confronting vertices or edges are in conforming contacting alignment and are rigidly joined directly or indirectly.
Whether or not pre-tensioned, the reinforcing cores of the present invention self-anchor in the concrete and thus can remain entirely within the matrix.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a perspective view of a tubular blank shown partly crimped in the process of converting it into a structural tetrahedral chain core of square transverse outline in accordance with one embodiment of the present invention;

FIG. 2 is a transverse section of the crimped tubular blank taken along the lines 2-2 of FIG. 1;

FIG. 3 is a transverse section of the crimped tubular blank taken along the lines 3-3 of FIG. 1;

FIG. 4 is a side elevation of a structure comprised of a tetrahedral chain core reinforced with tie rods along the rows of tetrahedral vertices in accordance with an optional feature;

FIG. 5 is a transverse section of the reinforced core taken along the lines 5-5 of FIG. 4;

FIGS. 6 and 7 show longitudinal and cross sections, respectively, of a reinforced cylindrical concrete structure in accordance with one embodiment;

FIG. 8 shows another embodiment, of a rectilinear concrete structure in which a first set of cores are aligned with the width direction and a second set of cores are interleaved with and aligned transversely to the first set;

FIGS. 9 and 10 show a curved concrete structure and detail of how adjacent cores can optionally be connected together along confronting edges;

FIG. 11 shows a concrete beam with a plurality of reinforcing cores offset below the centerline;

FIG. 12 shows the beam of FIG. 11 supported at both ends against a transverse load;

FIG. 13 shows a beam supported at only one end against a transverse load at the other end, with a plurality of reinforcing cores offset above the centerline;

FIGS. 14 and 15 show concrete slab having a plurality of reinforcing cores arranged perpendicularly below the center plane of the slab; and

FIGS. 16A, B, and C are schematic representations of how a pre-stressed concrete beam can be fabricated with pre-tensioned cores.

DETAILED DESCRIPTION

FIGS. 1-3 show a representative triangulated tubular tetrahedral core to be completely embedded in a solid matrix. An imperforate tubular blank 10 has a circular cross-section and specifically of cylindrical form made of bendable or deformable material such as metal, as for example, steel, copper and aluminum. The tubular blank can also be made of plastic material, and especially of thermoplastic material, so that it will be deformable upon heating. Other suitable materials may be paper and fibrous material embedded or bonded with plastic.
The tubular blank 10 may be welded, glued, seamless or lock-seamed and is crimped at spaced transverse linear sections 11 and 12 in planes at right angles to the axis of the tubular blank to collapse this blank along these sections and to form a structural core or web 13. This crimping operation may be performed while the tubular blank 10 is cold or hot according to the nature of the material from which the blank is formed and may be carried out in such a way that successive sections 11 and 12 are crimped in parallel planes but in different directions and alternate sections 11 or 12 are crimped in parallel planes and in parallel directions. Each of the crimped sections 11 and 12 is produced by collapsing the wall of the tubular blank 10 from diametrically opposite sides of the blank to an equal extent by a pinching action to form each crimped section substantially diametrically across the blank. In the specific form of the tube shown in FIG. 1, the two sets of crimped sections 11 and 12 extend in planes at right angles to each other, so that the transverse general outline of the core is square, However, the two sets of crimped sections 11 and 12 may extend in planes at an angle other than 90° to each other to define a transverse core outline which is of rectangular oblong shape. The crimped sections are shown as equally spaced and the distances between these sections are such in relation to the diameter of the tubular blank as to form regular tetrahedra, but this is not necessary.
For producing the structural core or web 13, the tubular blank 10 is first crimped in a plane at right angles to the axis of the blank in diametrically opposed directions near one end of the blank to form a first crimped section 11 at the region A and to close the blank; the blank is then crimped at a linear interval from the first crimped section at right angles to the axis of the blank in diametrically opposed directions transverse to the first mentioned directions and more specifically at right angles to the first mentioned directions to form a second crimped section 12 at the region B and to form thereby a hollow tetrahedron 14. The blank is further crimped at the same linear interval at right angles to the axis of the blank in diametrically opposed directions parallel to the first mentioned directions to form a third crimped section 11 at the region C and thereby a second tetrahedron 15. This crimping action is continued for successive sections in alternate directions until the tubular blank 10 has been shaped into a structural core 13 having the desired configuration. This core 13 will consist of a chain of tetrahedra 14 and 15 interconnected along the crimp sections 11 and 12 and arranged so that successive tetrahedra are mirror images of each other in the form of optical antipodes.
Another alternative procedure for forming the tetrahedral chain core or web 13 is to crimp one end and at a linear interval corresponding to two successive tetrahedra, the blank is crimped in diametrically opposed directions parallel to the diametrically opposed first crimping directions to form a hollow pillow-shaped body between end crimp sections. A third crimp is then formed in the middle of the pillow-shaped body between these crimped sections but in diametrically opposed directions transverse to and specifically at right angles to the first crimping directions. This third crimp deforms the pillow-shaped body into two hollow tetrahedra 14 and 15.
Each of the tetrahedra 14 and 15 is bounded by four substantially plane triangular faces 16 and will contain six edges 17, two of which are at opposite ends of the tetrahedron along successive crimped sections 11 and 12 and four vertices 18 located at the ends of these crimp sections. These vertices 18 are arranged in four parallel linear rows extending along the core 13 and encompassing a rectangular area transverse to the core and more specifically a square area. A tie rod or cord can be welded to successive vertices in each row of vertices. Such ties in conjunction with successive triangular plane sections 16 of the tetrahedra form chains of interconnected triangular trusses.
In FIGS. 4 and 5, the ties between the vertices of the core 13 are shown constituting steel rods or wires 20, brazed, welded or otherwise affixed to the core 13 at all vertices 18 in accordance with the nature of the core material, so that these rods or wires constitute parallel chords forming part of the structure unit. These chordal rods 20 serve to further rigidize the core 13 and to form a composite unit.
Although the core unit 13, 20 has been deformed or prebuckled into a series of continuous tetrahedra, it is still a tubular structure and still retains the high torsional or twist resistance of a tube. Moreover, the structure 13, 20 is isotropic in character. Its plane face sections 16 are equally strong and are oriented in different directions, so that the structure can stand stresses in all directions and will distribute stress applied in any region in all directions. The core structure 13 can be manufactured with ease from tubular stock of from ⅛″ diameter to as much as 6″ or more in diameter.
The composite unit 13, 20 has an unusually high strength to weight ratio because of the mutually braced triangular planes and because tetrahedra have the highest ratio of surface area per unit volume of any regular polyhedrons, and consequently are the most stable of all polyhedrons. By combining this property of the tetrahedra with the high twist resistance of the original tube, a very stable structure created.
FIGS. 6 and 7 show a first embodiment 100 of a reinforced concrete structure, in the form of a cylinder having a length L. FIG. 6 is a longitudinal section and FIG. 7 is a cross section. The reinforcing core 102 is embedded within a solid matrix 104. The circular outer surface 106 of the concrete structure is continuously contoured about the axis, and the centerline 108 of the core is at the center of the surface, i.e., congruent with the axis. These figures show only one core embedded longitudinally within an elongated matrix, but in some embodiments a plurality of cores could be provided in a circular pattern around the central core (not shown). It should be understood that the matrix and thus the concrete structure can have any uniform or non-uniform cross sectional shape and can taper longitudinally. Generally, the resulting concrete structure would be used as a construction element, such as a column, whereby the longitudinal ends would be under compression (as indicated by the axially directed arrows).
Especially when the concrete structure will be subjected to a potentially corrosive natural or man-made (e.g., industrial) climate, a metal tube blank can be externally galvanized or treated with an organic material before crimping.
FIG. 8 shows another embodiment 200 of a rectilinear concrete structure having length L, width W and thickness T. A first plurality of cores 202 a and 202 b are aligned with the width direction and a second plurality of cores 202 c and 202 d are interleaved with and aligned transversely to the first plurality. This configuration reinforces the matrix 204 against stresses applied anywhere and in any direction on the surface 206 of the concrete structure 200. FIG. 8 also shows that when viewed along the centerline 208 of each core, each tetrahedron envelopes a relatively large internal volume 210 of air.
FIG. 9 shows a section view of a portion of a curved concrete structure 300, in which the centerlines 308 of adjacent reinforcing cores 302 extend in the length direction L of the structure while embedded in a concrete matrix 304 that defines the overall shape 306. The depiction in FIG. 9 can be considered an arc section of a large concrete conduit or the like that extends along an axial length L (only a portion of which is shown). The tetrahedra in the core envelope volumes 310. Adjacent cores such as 302 a and 302 b can be rigidly connected to each other directly along confronting edges 312 a and 312 b (as shown in FIG. 10) or the vertices 314 a, 314 b can be connected indirectly by mutual connection to a common rigid support such as longitudinally extending tie rods or angled strips.
For the preferred embodiment such as shown in FIG. 1, the succession of triangle planes or faces are equal and opposite, forming regular tetrahedra. Triangulated, tetrahedral reinforcing cores not only greatly increase the volume to weight ratio, but also the strength to weight ratio relative to a cylinder made entirely from concrete. The cores resist stresses by distributing tension, torsion, and bending forces imposed on the structure, while the concrete resists compressive forces.
FIG. 11 shows a rectilinear concrete beam 22 having a length L, width W, and thickness T. The beam has an upper surface 24 and a lower surface 26, with a centerline or center plane 28 extending longitudinally midway between the upper and lower surfaces, from the left or front end 30 to the back or right end 32. In this embodiment, a plurality of reinforcing cores 13A, 13B and 13C extend in spaced apart, parallel relationship offset from and below the centerline 28. Thus, the reinforcing cores 13 are situated in the portion of the matrix 34 that is below the centerline 28.
FIG. 12 shows the beam 22 anchored 36 at the left end 20 and anchored 38 at the right end 32, as commonly found in building and other constructions. The beam is designed to support a local or distributed load indicated by force F, which would tend to bend the beam 22 downwardly, thereby compressing the matrix closer to the upper surface 24 while inducing a tensile stress in the matrix portion 34 closer to bottom surface 26. According to the present embodiment, the cores 13 located below the centerline 28 resist the tensile force in the lower region 34 and thereby enable the beam 22 to bear a higher load F than would be possible without such reinforcement.
It should further be appreciated that the reinforcing cores 13 need not be anchored at the ends 30, 32 of the beam 22. Due to the large surface areas presented by the planes of the plurality of tetrahedra in intimate contact with the surrounding matrix, the cores are in effect self-locking in place within the matrix portion 34. Thus, the reinforcing core remains in fixed relation to the matrix material.
FIG. 13 represents another configuration that can be found in building construction or the like, where the beam 22′ is anchored 36 only at one end 30, with the other end 32 unsupported, i.e., cantilevered. If the load F is imparted toward the free end 32, the upper surface 24 experiences a tensile stress whereas the material closer to the lower surface 26 experiences a compressive stress. In this configuration, the reinforcing cores 13 are situated longitudinally above the centerline 28. Thus, the upper region 40 of the matrix closer to the upper surface 24 is reinforced against the tensile loads on the concrete.
FIGS. 14 and 15 show a different configuration 42, of a concrete slab 44, such as would be used for flooring in a building, supported in four corners by columns or posts 46A, 46B, 46C and 46D. Alternatively, at least two of the sides are supported along their full length (as would also be represented by FIG. 12). The length L and width W are shown as different, but could be of equal dimensions. Because in a slab 44 the length and width are generally somewhat similar, reinforcement is needed in both directions. A first plurality of reinforcing cores 13D extend in laterally spaced apart relation in the length direction and another plurality of reinforcing cores 13E and 13F extend in the width dimension, in alternation above and below the cores 13D. Because in general a slab as shown would only need to bear loads imposed on the top surface, only the region of the slab below the center plane need be reinforced.
FIGS. 16A, B and C illustrate schematically a variation by which a concrete beam or slab can be pre-stressed with the reinforcing cores. One core 48 has a succession of tetrahedra 50 connected together via successive crimps or webs 52, 54, which alternate in perpendicular relationship, (i.e., 52 is vertical and 54 is horizontal). Each tetrahedron has four triangular planes 56, as previously described in connection with FIG. 1. An arbitrary number of tetrahedra can be provided on any given core, with the first tetrahedron indicated at 50A and the last indicated at 50B. The core is tensioned (i.e., pulled in opposite directions along the axis) as indicated by the arrows at P, thereby elastically straining the core to some extent.
While the core is in tension, concrete is poured around the core 48, preferably with the lead and trailing tetrahedra 50A, 50B outside the matrix 58, as one way of providing convenient surfaces for devices represented by P to maintain the tension in the core while the matrix cures. Upon curing of the matrix 58, the tension on the device is released, and the end tetrahedra 50A, 50B removed as by cutting, thereby creating a reinforced beam, pole, or the like, in which the core retains restorative forces indicated at 62. These forces 62 tend to compress the concrete at the concrete interface. The triangular planes do not move, and thereby provide great strength for resisting bending loads on the beam 60. The deep notches formed by successive tetrahedra are filled with concrete and provide a much higher surface area in contact with concrete, which resists longitudinal displacement of the core relative to the concrete, to a much greater degree than ribs or the like on rebar. Moreover, this self-locking maintains the core in a pre-stressed condition, especially deep within the matrix, without external anchoring of the core. In essence, the core is internally anchored at every tetrahedron.
The cores are very strong in resisting tension, in part because the webs formed by the crimps are aligned with the core axis so cannot readily be strained longitudinally and tensile forces would not act across the web to separate the closely compacted walls formed the crimp. Furthermore, the any tensile forces that act on the core would tend to urge the planes against and thereby compress the concrete in the notches.
For an especially rigid reinforcement, each core can have tie rods 20 or the like as shown in FIGS. 4 and 5, connecting successive vertices, and thereby assure longitudinal alignment of the vertices at the four corners as indicated in FIG. 5. If each core 13 is horizontally oriented as shown in FIG. 5, the crimped webs 11, 12 will be oriented obliquely to the centerlines or center planes of the beams. Since the beams will bear vertical loads, none of the crimped webs will be subjected to a perpendicular load, and thus the cores will be doubly strong, i.e., due to the connection of the tie means at the four corners, as well as the minimization of the load acting perpendicular to the crimped webs.
It should thus be appreciated that with the present invention, concrete structures or bodies of a given size can be strengthened while reducing the average density (and thus overall weight), relative to a structure or body of that given size made of homogenous concrete or rebar-reinforced concrete. Alternatively, a desired degree of strength can be achieved with a smaller and/or lighter structure than if made of homogenous concrete or rebar-reinforced concrete. If very high strength is desired, each core can be stiffened by connecting successive vertices with a tie rod or the like, while the weight of the tie rods. Is offset to some degree by hollow nature of the tetrahedra. Concrete structures or bodies can be reinforced with a substantially uniform pattern or array of individual, unconnected tetrahedral cores, or the cores can be arrayed non-uniformly.

Claims

1. A weight reduced and strength enhanced concrete structure comprising a continuous matrix of concrete reinforced with at least one tubular chain of integrally connected hollow tetrahedra.

2. The concrete structure of claim 1, wherein a plurality of said chains are independently embedded and self-anchored in the matrix.

3. The concrete structure of claim 2, wherein each chain is in tension, thereby pre-stressing the concrete structure.

4. A reinforced structural member comprising:

a body of rigid matrix material, having a length and width;

at least one reinforcing core embedded in the matrix, having a chain of integrally connected hollow tetrahedra, each tetrahedron defining four triangular planes with each plane in intimate contact with matrix material, thereby locking the reinforcing core in fixed relation to the matrix material.

5. The structural member of claim 4, wherein the member is a beam having a longitudinal centerline and the at least one reinforcing core extends along the length of the beam parallel to and offset from the centerline.

6. The structural member of claim 5, wherein

the beam centerline extends horizontally;

the beam has longitudinal ends that are both anchored; and

the at least one reinforcing core is vertically below the centerline.

7. The structural member of claim 5, wherein

the beam centerline extends horizontally;

the beam has longitudinal ends, and is anchored only at one end with a cantilevered other end; and

the at least one reinforcing core is vertically above the centerline.

8. The structural member of claim 4, comprising

a rectangular slab anchored on at least two sides, and having a center plane between upper and lower surfaces; and

a plurality of reinforcing cores extending through the matrix below the center plane.

9. The structural member of claim 8, wherein

a first plurality of laterally spaced apart reinforcing cores extend parallel to the length of the slab below the center plane; and

a second plurality of laterally spaced apart reinforcing cores extend parallel to the width below the center plane.

10. The structural member of claim 4, wherein each reinforcing core is in tension and thereby longitudinally pre-compresses adjacent matrix material, whereby when the structural member bears no external load, the faces on the tetrahedra apply a compression force on the matrix material that is in intimate contact therewith.

11. The structural member of claim 4, wherein the matrix is concrete.

12. The structural member of claim 4, wherein the matrix is plastic foam.

13. The structural member of claim 5, wherein the matrix is concrete.

14. The structural member of claim 11, wherein a plurality of parallel, spaced apart and unconnected cores extend longitudinally and entirely within the structural member.

15. The structural member of claim 11, wherein each core includes means for rigidly tying the apices of successive tetrahedra in said chains.

16. The structural member of claim 15, wherein

the cores are embedded in a beam that extends in a longitudinal direction;

the edges of successive tetrahedra are connected by a rigid web; and

all the webs of the cores are oriented obliquely when viewed in cross section to said longitudinal direction.

17. The structural member of claim 11, wherein the member is a horizontally extending concrete beam having a horizontally extending centerline, and all of said reinforcing cores are embedded in the concrete parallel to and vertically offset from the centerline.

18. A reinforced concrete beam or slab having a length and width, comprising: a plurality of elongated metal reinforcing cores embedded in a concrete matrix, each core having a chain of integrally connected hollow tetrahedra, each tetrahedron defining four triangular planes with each plane in intimate contact with matrix material, thereby locking each reinforcing core in fixed relation to the matrix material.

19. The reinforced concrete beam or slab of claim 18, wherein at least some of said plurality of cores are rigidly secured together in a side-by-side parallel array,

20. The reinforced concrete beam or slab of claim 18, constituting a building element subject to a bending load transverse to the length or width.