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.
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.
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
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
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.
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.
For the preferred embodiment such as shown in
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.
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
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.
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”.