Background

[0001] 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

[0002] I have conceived a way of achieving this design objective using the invention described in my U.S. Patent 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").

[0003] 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.

[0004] 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. Another option is to strengthen the integral connection between tetrahedra, as by bonding together the opposed walls at the crimps where a cylindrical tube was successively deformed to produce the chain of hollow tetrahedra.

[0005] 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.

[0006] 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.

[0007] 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.

[0008] 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.

[0009] 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. [0010] In one embodiment, the tube blank is metal and the crimped walls of the web are welded by melting due to application of external heat on both sides of the crimp.

[0011] In another embodiment, the inside surface of the tube blank is coated with a bonding agent such that after the tetrahedral chain has been formed, heat and/or pressure applied at the web, joins the opposed wall surfaces.

[0012] Unbonded webs between tetrahedra are strong in resisting tensile and rotational forces, but are relatively weaker than the tetrahedra in resisting certain bending forces. When the webs are strengthened the highly desirable attributes of the tetrahedra are thus preserved even in very highly stressed conditions.

Brief Description of the Drawing

[0013] Figure 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;

[0014] Figure 2 is a transverse section of the crimped tubular blank taken along the lines 2-2 of Figure 1 ;

[0015] Figure 3 is a transverse section of the crimped tubular blank taken along the lines 3-3 of Figure 1 ;

[0016] Figure 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;

[0017] Figure 5 is a transverse section of the reinforced core taken along the lines 5-5 of Figure 4;

[0018] Figures 6 and 7 show longitudinal and cross sections, respectively, of a reinforced cylindrical concrete structure in accordance with one embodiment;

[0019] Figure 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; [0020] Figure 9 shows a concrete beam with a plurality of reinforcing cores offset below the centerline;

[0021] Figure 10 shows the beam of Figure 9 supported at both ends against a transverse load;

[0022] Figure 1 1 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;

[0023] Figures 12 and 13 show a concrete slab having a plurality of reinforcing cores arranged perpendicularly below the center plane of the slab;

[0024] Figures 14 A, B, and C are schematic representations of how a pre- stressed concrete beam can be fabricated with pre-tensioned cores;

[0025] Figures 15 A, B, and C are schematic representations of a portion of process line in which opposed walls of a sequence of crimps are joined by the application of heat;

[0026] Figure 16 is a plan view of a thin metal plate, with the visible surface coated with a material that is weldable or fusible to the metal surface by heat and/or pressure;

[0027] Figure 17 shows the plate of Figure 16, rolled into a cylinder and joined at the longitudinal seam to form a cylindrical tube blank with the coated surface at the internal diameter of the tube, to be crimped as shown in Figure 1 ; and

[0028] Figure 18 is a cross section of the cylindrical tube of Figure 17.

Detailed Description

[0029] Figures 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.

[0030] The tubular blank 10 may be welded, glued, seamless or lock-seamed and is crimped at spaced transverse linear sections 1 1 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 1 1 and 12 are crimped in parallel planes but in different directions and alternate sections 1 1 or 12 are crimped in parallel planes and in parallel directions. Each of the crimped sections 1 1 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 Figure 1 , the two sets of crimped sections 1 1 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 1 1 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.

[0031] 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 1 1 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 1 1 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 1 1 and 12 and arranged so that successive tetrahedra are mirror images of each other in the form of optical antipodes. [0032] 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.

[0033] 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 1 1 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.

[0034] In Figures 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.

[0035] 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 ½" diameter to as much as 6" or more in diameter.

[0036] 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.

[0037] Figures 6 and 7 show a first embodiment 100 of a reinforced concrete structure, in the form of a cylinder having a length L. Figure 6 is a longitudinal section and Figure 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 nonuniform 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.

[0038] 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.

[0039] Figure 8 shows another embodiment 200 of a rectilinear concrete structure having length L, width W and thickness T. A first plurality of cores 202a and 202b are aligned with the width direction and a second plurality of cores 202c and 202d 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. Figure 8 also shows that when viewed along the centerline 208 of each core, each tetrahedron envelopes a relatively large internal volume 210 of air.

[0040] For the preferred embodiment such as shown in Figure 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. .

[0041] Figure 9 shows a rectilinear concrete beam 300 having a length L, width W, and thickness T. The beam has an upper surface 302 and a lower surface 304, with a centerline or center plane 306 extending longitudinally midway between the upper and lower surfaces, from the left or front end 308 to the back or right end 310. In this embodiment, a plurality of reinforcing cores 312A, 312B and 312C extend in spaced apart, parallel relationship offset from and below the centerline 306. Thus, the reinforcing cores 312 are situated in the portion of the matrix 314 that is below the centerline 306.

[0042] Figure 10 shows the beam 300 anchored 316 at the left end 308 and anchored 318 at the right end 310, 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 300 downwardly, thereby compressing the matrix closer to the upper surface 302 while inducing a tensile stress in the matrix portion 314 closer to bottom surface 304. According to the present embodiment, the cores 312 located below the centerline 306 resist the tensile force in the lower region 314 and thereby enable the beam 300 to bear a higher load F than would be possible without such reinforcement.

[0043] It should further be appreciated that the reinforcing cores 312 need not be anchored at the ends 308, 310 of the beam 300. 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 lower matrix 314. Thus, the reinforcing cores remain in fixed relation to the matrix material.

[0044] Figure 1 1 represents another configuration that can be found in building construction or the like, where the beam 300' is anchored 316 only at one end 308, with the other end 310 unsupported, i.e., cantilevered. If the load F is imparted toward the free end 310, the upper surface 302 experiences a tensile stress whereas the material closer to the lower surface 304 experiences a compressive stress. In this configuration, the reinforcing cores 312 are situated longitudinally above the centerline 306. Thus, the upper region of the matrix closer to the upper surface 302 is reinforced against the tensile loads on the concrete.

[0045] Figures 12 and 13 show a different configuration 400, of a concrete slab 402, such as would be used for flooring in a building, supported in four corners by columns or posts 404A, 404B, 404C and 404D. Alternatively, at least two of the sides are supported along their full length (as would also be represented by Figure 10). The length L and width W are shown as different, but could be of equal dimensions. Because in a slab 402 the length and width are generally somewhat similar, reinforcement is needed in both directions. A first plurality of reinforcing cores 406a extend in laterally spaced apart relation in the length direction and another plurality of reinforcing cores 406b and 406c extend in the width dimension, in alternation above and below the cores 406a. 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.

[0046] Figures 14 A, B and C illustrate schematically a variation 500 by which a concrete beam or slab can be pre-stressed with the reinforcing cores. One core 502 has a succession of tetrahedra 504 connected together via successive crimps or webs 506, 508, which alternate in perpendicular relationship, (i.e., 506 is vertical and 508 is horizontal). Each tetrahedron has four triangular planes 510, as previously described in connection with Figure 1 . An arbitrary number of tetrahedra can be provided on any given core, with the first tetrahedron indicated at 504a and the last indicated at 504b. 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.

[0047] While the core is in tension, concrete is poured around the core 502, preferably with the lead and trailing tetrahedra 504a, 504b outside the matrix 512, 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 512, the tension on the device is released, and the end tetrahedra 504a, 504b removed as by cutting, thereby creating a reinforced beam, pole, or the like, in which the core retains restorative forces indicated at 514. These forces 514 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 500. 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.

[0048] 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.

[0049] For an especially rigid reinforcement, each core can have tie rods 20 or the like as shown in Figures 4 and 5, connecting successive vertices, and thereby assure longitudinal alignment of the vertices at the four corners as indicated in Figure 5. If each core 13 is horizontally oriented as shown in Figure 5, the crimped webs 1 1 , 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 on the flat walls, 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.

[0050] 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. [0051] Figures 15A-C show a preferred processing technique whereby a core 600 of successive tetrahedra has web regions 602a-602c. These web regions are defined by wall portions 604a, 604b of the original cylindrical tube, which were compressed toward each other and flattened to form a web or the like of abutting or closely spaced (i.e., confronting) metal. After or in conjunction with the production of the core 600, a heating and/or pressing device 606 joins the confronting walls as shown at 608 and thereby increases the rigidity of the crimps and nodes. The joint formed at 608 can be welded or brazed.

[0052] In a further preference, the joining of the confronting walls is facilitated by providing a bonding agent on the inside surfaces of the walls. Figures 16-18 illustrate an example for the production of metal units. A plate or sheet 700 of metal has a flat side 702 defining a rectangular surface that is coated with a bonding agent 704. This agent can facilitate welding or brazing in the context of Figure 15. The sheet 700 is bent into a cylinder 706 and welded along seam 708 to form a tubular blank. The tube 706 is hollow, with the inside diameter carrying the bonding agent 704.