Patent Application
20050126113
1. Field
Embodiments relate to structural engineering, and in particular, to casting structures.
2. Related Art
Molds are used to cast structures out of many types of materials. Typical structures, especially those related to construction, are cast as solid pieces. An example of such a process is the casting of structural concrete.
In some construction projects, such as bridges or road structures, “pre-stressed” concrete is made by casting concrete around cables that are held at a tension.
Because typical concrete structures are solid concrete (with the exception of the re-bar pieces), structure strength depends on the thickness of the concrete and the re-bar reinforcement. However, a solid structure is not necessarily the most efficient use of material volume and mass to achieve strength. For example, the base of a tall structure may need to support a great deal of weight, including its own. Thus, what is needed, is a method of casting materials in more efficient shapes, thereby saving material cost and mass, while providing a convenient method of forming structures.
In some embodiments, one or more interior mold forms are used to displace material inside a structure being cast. The forms are shaped so as to provide structural integrity in the finished structure cast around them.
In some embodiments, an interior mold form having ridges running in one direction on one side is used to fill the center of a structure during casting. In some embodiments, the structure is cast from concrete and the form is made from polystyrene. In some embodiments, the form is set around a re-bar grid.
In some embodiments, the interior mold form has a second set of ridges on its second side. In some embodiments, the second set of ridges and runs in a cross-direction to the first. In some embodiments the ridges have semi-cylindrical or trapezoidal cross sections.
In some embodiments, the form is created by machining out semi-cylindrical ridges with flat walls, separated by troughs, on one side, then on the other side of a sheet of material. In some embodiments, small holes are bored for plastic inserts to hold the form in position. In some embodiments the form is held away from re-bar to allow concrete to flow around the re-bar.
In some embodiments, the resulting concrete structure, having crossed interior arch-like cells, provides strength equivalent to or greater than that of solid concrete, the displacement of concrete by the form saving weight and cost.
In some embodiments, a process of concrete casting includes laying down a layer of parallel re-bar, forming a 3-D polystyrene mold, and providing the mold with plastic spacers to hold it in correct alignment to the re-bar. The form is placed over the first layer of re-bar, a second layer of re-bar is added over the mold, and the re-bar intersections are attached together. The mold and re-bar are held between sides of a mold, and concrete is poured, and allowed to harden. The external mold sides are removed, and the internal form remains in the concrete structure.
In some embodiments, a mold form comprises an array of semi-spherical bumps.
In some embodiments, a mold is created from an exterior volume and an interior mold form.
In some embodiments, form 200 will resemble a relatively thin sheet, having two major sides (surfaces). For purposes of illustration, an x-axis, which will be “horizontal” in some embodiments, is defined along one side of form 200, parallel to its surface. A y-axis, which will be “vertical” in some embodiments, is defined along the other long side of form 200, parallel to that surface, and perpendicular to the x-axis. A z-axis is defined through form 200, being normal to the surfaces (sides). While the terms “horizontal” and “vertical” are used to illustrate embodiments, because typical vertical walls are commonly cast, such terms are not intended as limiting. In application, embodiments of form 200, related processes, and structures in which it is used, may take on many shapes, orientations, and contours, which may or may not be symmetric, planar, or aligned with gravity.
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In some embodiments, plastic rods 214 are inserted in holes 210 of form 200 to aid in positioning form 200 with respect to re-bar 106 and 108. Plastic rods 214 can stop form 200 from sliding too far onto re-bar 106 or 108. Plastic rods 214 can also supply means of tying form 200 onto re-bar. In some embodiments, rods 214 are not used, and in some embodiments there are fewer rods than pieces of re-bar 106 and 108.
In some embodiments, form 200 is made from 2-lb polystyrene. 2-lb polystyrene has desirable compression (approximately 20 pound per square-inch) and machining properties. Form 200 is stiff enough to resist being crushed by the mass of concrete. Depending on the scale of the casting to be performed other weights of polystyrene may be acceptable, if they provide sufficient compression resistance. In some embodiments, form 200 is made from other lightweight, inexpensive materials, such as fiberglass, composite carbon/graphite, plastic, or other weights of polystyrene. For casting materials other than concrete, form 200 may be formed from materials resistant to adverse conditions during casting (e.g., extreme pressure, chemical damage, high temperatures).
In some embodiments, form 200 is cut from a 3 by 4 by 8-foot block of 2-lb polystyrene. Billets are typically manufactured in 3 by 4 by 24-foot sizes, and 8-foot lengths are convenient to cut from such a billet (also being roughly the size of typical freeway sound barrier segments). Of course, different applications will require different sizes and shapes of concrete castings, so given dimensions are exemplary.
As an example of relative dimensions, in some embodiments form 200 is 3{fraction (9/16)}-inches thick. Ridges 202, 206 (and therefore troughs 204, 208) have a period of 4-inches. Each ridge 202, 206 has a semi-cylindrical diameter of 2{fraction (7/8)}-inches (radius of 1{fraction (7/16)}-inches) and a ⅞-inch base height, for a total height of 2{fraction (1/2)}-inches. Each trough has a width of 1{fraction (1/8)}-inches and a depth of 2{fraction (1/2)}-inches (leaving 1{fraction (1/16)}-inches of material). For a form of these exemplary dimensions, external mold sides 102 are placed so as to create a thickness of {fraction (11/16)}-inch of concrete between each of mold sides 102 and form 200.
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While a vertical mold is exemplary, it is well known to those skilled in the art, that walls for concrete buildings can be cast in a horizontal orientation, on the ground, before being raised into a vertical position. In such a process, all the re-bar (and the x- and y-axis) would be literally horizontal during casting and curing. However, it is convenient to refer to re-bar 106 and 108 as being “vertical” or “horizontal,” and such terms are not intended as limiting.
By means of using form 200, a concrete structure can be created, which is lighter than a solid concrete structure of equal size and strength.
Those skilled in the art will recognize that mold 300 and form 200 need not be rectangular; they can be oval or oddly shaped. Further, those skilled in the art will recognize that mold 300 and form 200 need not be planar, although many applications use planar shapes. Given that modern architecture make use of many curved and irregular surfaces, embodiments of form 200, mold 300, and the molding process will make use of forms and molds of many different shapes, sizes, and contours.
Further, those skilled in the art will recognize that while re-bar 106 and 108 are commonly used in concrete structures, re-bar is not essential to all embodiments of casting processes or resulting structures. Therefore, in some embodiments, there is no re-bar. In some embodiments, structure integrity is reinforced by means other than inserting re-bar 106 and 108 (e.g., inserting graphite fibers).
While concrete casting is exemplary of some embodiments of the present invention, those skilled in the art will recognize that embodiments of the forms and processes herein described are also applicable to other materials on larger or smaller scales. Such materials may include structural plastics, graphite epoxies, metals, and many other materials, where it is desirable to reduce the volume of material required to form a structure.
While chambers 412 and 422 are not filled with concrete, the arched semi-cylindrical shape of chambers 412 and 422 bear stresses within structure 400 more efficiently than solid concrete. Because chambers 412 and 422 are crossed, each of halves 412 and 422 resists stresses along the different axis. Therefore, the double-arched hollows within structure 400 provide superior strength to solid concrete. Further, by creating structures of lighter weight, each structure in, for example a building, needs to support less weight of itself and other structures, thereby making the entire building more efficiently constructed, than if it were made of solid walls.
In some embodiments, form 600 includes base 610, having thickness 612. In some embodiments, thickness 612 is made thick enough to provide convenient strength to mold form 600 for handling and transportation. In some embodiments, thickness 612 is very thin, only thick enough to hold bumps 602 in place during casting. In some embodiments thickness 612 vanishes, and bumps 602 are held in place by wires, rods, or other means, or held in place by friction against the surface under them. In some embodiments, bumps 602 are an array of discrete interior forms.
In some embodiments, material 120 is cast around form 600 and re-bar 106 and 108. In some embodiments, lower layer 620 of material 120 has a thickness of approximately 2-inches, form thickness 612 is approximately 2-inches, making form and upper layer 622 of material 120 has is approximately 12 inches thick. Total thickness 624 is approximately 16-inches.
In some embodiments, a structure, such as a roadway, is formed by preparing the ground, then pouring a thin layer of concrete. Form 600, along with rebar 106, is placed on top of the first layer of concrete, and a thicker main layer is poured.
Thus, embodiments provide strong structures using less material than typical casting.
While various embodiments of the invention have been described, it should be understood that they have been presented by way of example and not limitation. Those skilled in the art will understand that various changes in forms or details may be made without departing from the spirit of the invention. Thus, the above description does not limit the breadth and scope of the invention as set forth in the following claims.
