US3862736A

US3862736A - Device for forming polygonal voids in concrete members

Info

Publication number: US3862736A
Application number: US321007A
Authority: US
Inventors: Richard E Herro
Original assignee: Dearborn Rubber Corp
Current assignee: Dearborn Rubber Corp
Priority date: 1973-01-04
Filing date: 1973-01-04
Publication date: 1975-01-28
Anticipated expiration: 1992-01-28

Abstract

A device for forming polygonal voids in concrete members, such as concrete beams, slabs and the like, includes an elongated, hollow, tubular body formed of a fabric reinforced, elastomeric material. The body maintains a cloverleaf or cross shape having a first predetermined, cross-sectional area when unpressurized and inflates to and maintains, without the necessity for any additional support, a square, rectangular or other polygonal shape having a second cross-sectional area greater than the first cross-sectional area. The device includes a novel end portion configuration that utilizes the tensile strength of the fabric reinforced, elastomeric, tubular body to integrally remove the end portion and the tubular body from a polygonal void formed in a concrete member.

Description

Herro 4 1 Jan. 28, 1975 DEVICE FOR FORMING POLYGONAL VOIDS IN CONCRETE MEMBERS [75] Inventor: Richard E. Herro, Joliet, 111.

[73] Assignee: Dearborn Rubber Corporation,

Broadview, Ill.

[22] Filed: Jan. 4, 1973 [21] Appl. No.: 321,007

Primary E.\amim'rC. W Lanham Assislun! Examiner-D. C. Reiley. lll

Attorney, Agent. or Firm-Mason, Kolehmaincn. Rathburn & Wyss [57] ABSTRACT A device for forming polygonal voids in concrete members, such as concrete beams, slabs and the like, includes an elongated, hollow, tubular body formed of a fabric reinforced, elastomeric material, The body maintains a cloverleaf or cross shape having a first predetermined, cross-sectional area when unpressurized and inflates to and maintains, without the necessity for any additional support, a square, rectangular or other polygonal shape having a second crossscctional area greater than the first cross-sectional area. The device includes a novel end portion configuration that utilizes the tensile strength of the fabric reinforced, elastomeric, tubular body to integrally remove the end portion and the tubular body from a polygonal void formed in a concrete member.

8 Claims, Drawing Figures DEVICE FOR FORMING POLYGONAL VOIDS IN CONCRETE MEMBERS BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to devices, commonly known as cores, for use in the casting of hollow concrete members, such as beams, slabs and the like, and, more particularly, to improved cores for forming generally square, rectangular and other polygonal voids in concrete members.

2. Description of the Prior Art In the manufacture of prestressed concrete, it is a common practice to cast a concrete member, such as a concrete beam, slab and the like, with a longitudinal opening or void extending through its length. In the past, such a void has been formed by using a core that is expanded or pressurized while the concrete is setting and contracted or depressurized and removed from the concrete thereafter.

One widely used core includes an elongated, circular, cylindrical tube having a wall formed of a flexible, elastomeric material, such as rubber. The tube is placed within a mold for a concrete member and the tube is enveloped with concrete when the mold is filled. The tube is pressurized and assumes and maintains a circular, cross-sectional shape while the concrete sets. When the concrete has set sufficiently to retain its shape. the tube is deflated and removed from the concrete. This type of core has the important advantages of simplicity and low cost.

It has been proposed to use a core having a square, rectangular or other polygonal, cross-sectional shape rather than one having a circular, cross-sectional shape. A square configuration, for example, provides a savings in material cost by reducing the amount of concrete used in a concrete member while not reducing the strength of the finished member.

It has not been found possible in the prior art to use a simple square tube formed of an elastomeric material and constructed along the lines of the commonly used round tubes since, when pressurized, such a square tube has consistently been found to assume a rounded or circular shape. Because of this difficulty, square cores developed by the prior art have been subject to the disadvantages of complexity and high cost due to the necessity for external or metallic reinforcing structures to insure that the desired square shape is obtained when the core is pressurized.

In U.S. Pat. No. 3,550,897 there are disclosed structures for producing square voids without extraneous reinforcing structures. These structures, however, have been found to suffer from disadvantages such as expense and weight of the materials used.

SUMMARY OF THE INVENTION Accordingly, one object of the present invention is to provide an improved core for use in casting hollow concrete members.

Another object of the present invention is to provide an improved core of a very simple construction, using economical materials not having excessive weight, yet capable of maintaining a square shape when pressurized.

A further object of the present invention is to provide An improved core capable of maintaining a square shape when pressurized without the necessity of external or metallic supporting or reinforcing structures.

In brief, the above and other objects of the present invention are achieved by providing a core for use in casting hollow concrete beams or the like including an elongated, hollow, inflatable core body extending between a pair of sealing end portions. The inflatable body includes inner and outer elastomeric sheets separated by a double layer of fabric. The double layer of fabric is preferably separated by a central sheet of elastomeric material. One or both end portions include means for pressurizing the inflatable body. In its unpressurized condition, the body maintains a cloverleaf or cross shape having a first cross-sectional area. In its pressurized condition, the body inflates to form a square, rectangular or other polygonal shape having a second cross-sectional area greater than the first crosssectional area. In its pressurized condition, the body is capable of maintaining the square, rectangular or other polygonal shape without the necessity for any additional support.

BRIEF DESCRIPTION OF THE DRAWING The above and other objects and advantages and novel features of the present invention may be better understood in light of the following detailed description of a preferred embodiment of the present invention illustrated in the accompanying drawing wherein:

FIG. I is a perspective view of a preferred embodi ment of a core embodying features of the present invention in its unpressurized condition;

FIG. 2 is a perspective view of the core of FIG. I in its pressurized condition;

FIG. 3 is a sectional view of the core of the present invention taken along line 3-3 of FIG. 1;

FIG. 4 is a sectional view of one embodiment of a device for making a core embodying features of the present invention;

FIG. 5 is a fragmentary, partially cross-sectional, side view of an alternate embodiment of an end portion for the core of FIG. 1; and

FIG. 6 is an end view of the end portion illustrated in FIG. 5.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to the drawing and initially to FIGS. 1 and 2, there is illustrated a core constructed in accordance with the principles of the present invention and designated as a whole by the reference numeral 10. The core 10 is used for forming or casting voids or openings in concrete members, such as concrete beams, slabs and the like, and in general includes a central, hollow, inflatable core body 12 extending between a pair of

end portions

14 and 16. In one embodiment, the

end portions

14 and 16 are formed from a solid, elastomeric material, such as rubber. The end portion 14 includes a longitudinally extending aperture or valve 18 for pressurizing and depressurizing the body I2. A similar valve may be provided in the end portion 16. A bail or ring 20 may be provided for pulling the core 10 from a cast concrete member. The ring 20 may, in the alternate embodiment from that illustrated in FIGS. 1 and 2, be suitably attached to the end face of the end portion 14 and designed so that its extremities do not extend beyond the outer periphery of the end portion 14 to enable the core to be removed from either end of a void formed in a concrete member.

In use, the core 10 is supported within a form into which concrete is poured in order to cast a concrete member, such as a concrete beam, slab or the like. The concrete member to be formed may be quite long and extend up to 60 feet or more. Before the concrete is poured, the body 12 is pressurized (FIG. 2), as by admitting a pressurized medium such as air to the interior of the body 12 through the valve 18, until the body 12 assumes a square, rectangular or other polygonal shape. The body 12 is then submerged by the poured concrete and-remains pressurized while the concrete sets. When the concrete has set sufficiently to maintain its shape, the pressure in the body 12 is released by opening the valve 18 and permitting the pressurizing medium to escape. The core 10 is then pulled from the concrete member to reveal a square, rectangular or other polygonal, longitudinal void.

In accordance with an important feature of the present invention, the body 12, although extremely simple and inexpensive to construct, is capable of retaining a generally square, rectangular or other polygonal shape when pressurized without the necessity for any additional support. The ability to form a square, rectangular or other polygonally shaped void in a concrete member rather than a circular void enables a savings in material cost since less concrete is required to form the member as compared with the amount required to form a member having a circular void. Furthermore, as compared with a circular void, the square, rectangular or other polygonally shaped void does not detract from the strength of the beam. Although the advantages of a square, rectangular or other polygonally shaped void are widely known and appreciated, the present invention provides the first feasible, simple, inflatable core 10 capable of retaining a square, rectangular or other polygonal shape when pressurized without the necessity of the complex supporting and reinforcing structure heretofore required.

In accordance with an important feature of the present invention, the core body 12 (FIG. 3) includes side walls 12a, corners 12b and a wall portion 22 having an inner sheet 24 of elastomeric material and a similar outer sheet 26 of elastomeric material. The

sheets

24 and 26 are separated by and reinforced by two layers of

fabric

28 and 30. The two

layers

28 and 30 are in turn separated by a central sheet of elastomeric material 32. The elastomeric material utilized for the

sheets

24, 26 and 32 may be butadeiene-styrene rubber, such as GRS rubber, neoprene rubber or any other similar elastomeric material. The hardness of the

sheets

24, 26 and 32 may be comparable to that normally encountered in a typical conveyor belt construction. The fabric utilized as

layers

28 and 30 may be polyester, nylon, or polyester and nylon and is preferably woven into a cloth form to impart strength to the core 10 to enable the core 10 to be easily removed in a single piece from a void formed in a concrete member after the concrete has settled.

The core body 12 (FIG. 3) is illustrated in solid line form in its unpressurized condition and in dotted line form in its pressurized condition. For purposes of setting forth a specific operative embodiment of the present invention, a core body 12 for forming a square void of 6 inches on each side in a concrete member may have the following dimensions. The thickness of the wall portion 22 may be approximately 5/16 of an inch with the inner and

outer sheets

24 and 26 each being approximately 3/32 of an inch thick and with the fabric layers 28 and 30 and the central sheet 32 comprising the remaining Vs of an inch thickness. In its pressurized form the dimension C" is 6 inches. In its unpressurized form the dimension A" between the extremities of the adjacent corners 12b or, in other words. between the most greatly separated portions of opposite side walls 12a, is approximately 5.125 inches. Thus. for this specific embodiment of the present invention the ratio of the distance between the most greatly separated portions of the opposite side walls 12a, with the core body 12 in its unpressurized form, and the distance between the most greatly separated portions of the opposite side walls 12a, with the core body 12 in its pressurized form, (A:C) would be approximately 0.853:I. This ratio (A:C) is not fixed but will vary depending upon the particular construction of the core body 12 including both the materials used to form the core body 12 and the outer dimensions of the core body 12 chosen for a particular embodiment. The dimension B between the most greatly recessed portions of opposite side walls 12a is approximately 2.675 inches. Thus, for this specific embodiment of the present invention in its unpressurized form the ratio of the greatest distance between opposite side walls 12a to the smallest distance between opposite side walls 12a (AzB) would be about 1.92:1. The range of operativeness of a core body 12 in its unpressurized form constructed in accordance with the principles of the present invention is quite wide and includes the ratio range (AzB) of about 1.50:1 to 3.00:1.

In accordance with an important feature of the present invention and as clearly illustrated in FIGS. 1 through 3, the sides of the core body 12 exhibit a toggle-like action when pressurized wherein the corners 12b are driven radially outwardly as are the side walls 12a so as to assume a square shape having a crosssectional area much greater than that occupied by the core body 12 in its unpressurized condition. This feature of the present invention greatly simplifies the removal of the core 10 from a concrete member.

After the concrete has set sufficiently to retain its shape, the core body 12 is deflated and returned to its unpressurized condition by opening the valve 18. The core body 12 then returns to its unpressurized cloverleaf or cross shape due to the tension created in the elastomeric side walls 12a. The separation or stripping of the core body 12 from the concrete initially takes place along radially spaced, longitudinally extending zones where the tension of the elastomeric side walls 12a is the greatest, that is, at those portions of the side walls 12a that will return to be the most inwardly bowed or recessed portions of the side walls 120. As the core body 12 continues to be deflated, the separation from the concrete continues from these initial zones in outward perimetric directions. When completely deflated, the core body 12 will have completely stripped itself from contact with the inner surfaces of the concrete void thus formed and the core 10 may then be easily removed from the void in the concrete member.

In accordance with a further important feature of the present invention, a method of making the core 10 of the present invention is illustrated in cross section in FIG. 4. A first step in making the core 10 is to place the core body 12 over a frame or mandrel 34 formed of four similar, longitudinally extending rods 36 held together at their ends by cloverleaf or cross shaped end portions (not shown). The rods 36 may extend longitudinally for 60 feet or more in order to accommodate core bodies 12 of the same length. The core body 12 initially is extended over the sides and end of the end portion 16 held in place on the frame 34. Subsequently, four similar, longitudinally extending rods 38 are secured in place on the frame 34 to thereby force the core body 12 into a cloverleaf or cross shape. The core body 12 is then cured by steam, heat, pressure or by a combination of these processes for several hours on the frame 34. This fuses the

elastomeric sheets

24, 26 and 32 (FIG. 3) of the core body 12 together and to the end portion 16 and causes the core body 12 to permanently retain its cloverleaf or cross shape (FIGS. 1 and 3) when in its unpressurized condition. After the core body 12 is cured, the rods 38 are removed; and the core body 12 is removed from the frame 34. The other end portion 14 is then secured in an airtight engagement to the core body 12 by conventional fastening means.

Alternately, the core may be placed over a frame or mandrel 34 formed by an integral elongated, hollow member having the desired cross or cloverleaf crosssectional shape. Before curing, the core body 12 may be forced to conform to the cloverleaf or cross shape of such a frame 34 by providing slots in the elongated, hollow member of the frame 34 and by applying a vacuum to the hollow interior of the frame 34. Alternately, the exterior of the core body 12 overlying the frame 34 may be pressurized to force the core body 12 into the cloverleaf or cross shape of the frame 34. The core body 12 is then cured by steam, heat, pressure or by a combination of these processes usually for several hours on the frame 34. After the core body 12 is fully cured, it is removed from the frame 34 and the end portion 14 is secured to the core body 12 as described above.

An alternate embodiment of the end portion 16 is illustrated in FIGS. 5 and 6 and is generally designated as 40. The end portion 40 is illustrated as fixed in position on a mandrel or frame 34 during the curing process. During the curing process, the end portion 40 is fused to the core body 12.

The end portion 40 includes a plurality of relatively thin, uncured elastomeric fillers 42 each having the characteristic cloverleaf or cross shape of the core body 12. In a preferred embodiment, the elastomeric fillers 42 may be 3/16 of an inch thick and number 16 individual fillers each formed of natural rubber. The fillers 42 are sandwiched between an inner plate 44, having generally the same shape as the fillers 42 and securely fixed to a hollow, threaded pipe 46, and an oversized backup plate 48. The hollow pipe 46 may, subsequently, be provided with a valve for admitting or releasing a pressurizing medium after the curing process. Furthermore, a bail or ring 20, as described above, may be subsequently attached to the outermost end of the hollow pipe 46 to serve as a means for removing the end portion 40 and the core body 12 from a void formed in a concrete member. In order to compressively load the fillers 42 during the curing process, a nut 50 is placed on the threaded end of the pipe 46 to compress the sandwich of the inner plate 44, the fillers 42 and the back-up plate 48. A removable configuration retainer 52 is used during the curing process to hold the fillers 42 and the inner plate 44 in a precisely aligned relationship.

In accordance with an important feature of the present invention, the tensile strength of the core body 12 is utilized to integrally remove the end portion 40 with the core body 12 from a void formed in a concrete member after the concrete has sufficiently set so as to retain its shape. The novel use of the tensile strength of the core body 12 to integrally remove the end portion 40 with the core body 12 is achieved by extending an end portion of the core body 12 beyond and in an overlapping relationship to the outermost filler 42 in a direction substantially transverse to the direction of the longitudinal axis of the core body 12. An additional elastomeric filler 54 of the same configuration and. preferably, of the same material as the fillers 42 is placed between the end portion 120 and the back-up plate 48. The nut 50 is then tightened to apply a compressive force to the elements between the inner plate 44 and the back-up plate 48 during the curing process.

After the curing process, the nut 50, the back-up plate 48 and the configuration retainer 52 are removed from the end portion 40; and the core 10, including the core body 12 integrally connected with the end portion 40, may be removed from the frame 34. An end portion for the other end of the core body 12, either similar to the end portion 14 or to the end portion 40, is then securely fastened by any conventional means to the other end of the core body 12. Alternatively, a serrated alu' minum plug, preferably wire bound to the core body 12 and having a valve for admitting or releasing a pressurizing medium, may be used as an end portion for the other end of the core body 12.'The core 10 is then ready for use in forming polygonal voids in concrete members in accordance with the principles of the present invention.

Many modifications and variations of the present invention are possible in light of the above teachings. Thus, it is to be understood that, within the scope of the appended claims, the invention may be practiced otherwise than as specifically described.

What is claimed and desired to be secured by Letters Patent of the United States is:

1. A core for use in casting hollow concrete members comprising a first, elongated, inflatable body formed of at least two elastomeric layers separated by a double layer of reinforcing fabric,

means for sealing the ends of said first body, and

means for admitting a pressurized medium to the interior of said first body,

said first body in its unpressurized condition having a substantially cloverleaf shape of a first crosssectional area and in its pressurized condition being capable of maintaining a substantially polygonal shape of a second cross-sectional area substantially greater than said first cross-sectional area without the necessity of any additional support.

2. A core as defined in claim 1 wherein at least one of said sealing means comprises a second body formed of elastomeric material and having said cloverleaf shape, said second body being integrally connected by curing to at least an end portion of said first body, said end portion extending in a direction substantially transverse to the direction of the longitudinal axis of said first body.

3. A core as defined in claim 1 wherein said polygonal shape comprises a square shape.

4. A core as defined in claim 1 wherein said cloverleaf shape is formed by said first body having a plurality of corners separated by greatly recessed side portions.

5. A core as defined in claim 4 wherein the ratio of the distance between the most greatly separated sections of two, opposite ones of said recessed side portions to the distance between the most recessed sections of said two, opposite ones of said recessed side portions is in the range of from 1.50:1 to 3.00:1.

6. A core as defined in claim 5 wherein said ratio is approximately 1.92:1.

7. A core as defined in claim 4 wherein the ratio of the distance between the most greatly separated secseparated and reinforced by two fabric means.

Claims

1. A core for use in casting hollow concrete members comprising a first, elongated, inflatable body formed of at least two elastomeric layers separated by a double layer of reinforcing fabric, means for sealing the ends of said first body, and means for admitting a pressurized medium to the interior of said first body, said first body in its unpressurized condition having a substantially cloverleaf shape of a first cross-sectional area and in its pressurized condition being capable of maintaining a substantially polygonal shape of a second cross-sectional area substantially greater than said first cross-sectional area without the necessity of any additional support.

6. A core as defined in claim 5 wherein said ratio is approximately 1.92:1.

7. A core as defined in claim 4 wherein the ratio of the distance between the most greatly separated sections of two opposite ones of said recessed side portions of said first body in its unpressurized condition to the distance between the most greatly separated sections of said two, opposite ones of said recessed side portions of said first body in its pressurized condition is approximately 0.853:1.

8. A core as defined in claim 1 wherein said first body comprises an integrally cured sandwich structure including three sheets or layers of elastomeric material separated and reinforced by two fabric means.