US2414011A - Reinforced concrete body - Google Patents

Description

J n- 7, 1947. K. P. BILLNER 2,414,011

REINFORCED CONCRETE BODY Original Filed June 7, 1942 Patented Jan. 7, 1947 REINFORCED CONCRETE BODY Karl P. Billner, Tampa, Fla.

Original application June 7, 1942, Serial No.

Divided and this application March 447,047. 16, 1943, Serial No. 479,381

9 Claims. 1 This invention relates to reinforced plastic bodies.

The formation of cracks in concrete structures has always been a particularly troublesome problem. By its very nature, concrete is intended to assume compressive stresses only, while its reinforcing elements arerelied upon to receive the tensile stresses. Yet an inevitable tendency accompanying the setting and hardening of concrete is the formation of internal stresses which are in turn responsible for the objectionable cracking. Among the various proposals for overcoming these effects is what is known as prestressing.

In concrete ships, for example, it has been considered advisable in the past to permit only very low working stresses in the steel reinforcement, since with higher stresses, small cracks have been observed in the concrete in portions of the ship which are subjected to tension. By way of contrast, much higher stresses have been permitted in ordinary concrete structures, such as buildings, whereby the properties of the steel reinforcement are utilized to much greater advantage. But, by prestressing the reinforcement, cracks and fissures can be avoided, air and water tightness achieved, and economy in reinforcement realized. Hence the use of prestressing adapts itself admirably to ship, tank and similar construction.

The advantages of prestressing reinforced plastic bodies, particularly concrete, have been known to the engineering profession for many years. Yet in spite of the appreciable thought and effort which have been expended in attempting to reduce this knowledge to a practicable basis, there has been no widespread adoption of any method thus far proposed. Most of the previously known methods have been directed along the lines of physically stretching the reinforcing elements, pouring the plastic material about them, allowing the material to harden and then releasing the reinforcing elements and permitting their contracting force to set up compressive stresses in the concrete. These methods have been fraught with difliculties in applying the tensile stresses and in regulating the magnitude of the forces which are ultimately imposed upon the hardened body.

It has been proposed also to prevent a bond between concrete and its reinforcing elements by coating the reinforcing bars with petroleum or asphaltic materials as described in the patents to Dill, No. 1,684,663, dated September 18, 1928, and Hewett. No. 1,818,254, dated August 11, 1931;

and by surrounding the reinforcing bars with metal tubes as disclosed in the patent to Kennedy, No. 2,185,749, dated January 2, 1940. And in the'patent to Steiner, No. 903,909, dated November 17, 1908, the progressive tensioning of reinforcing elements while'the concrete is hardening has been described. Prestressing of reinforcing elements prior to pouring concrete about them has also been proposed by Freyssinet in British Patent No. 338,864, dated June 18, 1929, wherein the elements are expanded by the heating effect of an electric current passed therethrough.

In accordance with the present invention, the eilects of prestressing are obtained by thermally expanding the reinforcing elements after the plastic body has hardened. This is accomplished by forming the plastic body about the reinforcing element and releasing the bond between the body and the element so that the element may be expanded with respect to the body, whereupon. the element is permitted to partially contract so as to bear upon the body and produce compressive stresses therein.

The reinforcing element is expanded prefer-" Y material is utilized so the heating effect will soften it to permit the reinforcing element to expand. Under some circumstances, thermosetting materials will be used. Where there is danger of short circuiting or leakage, the cover-- ing material may be electrically insulating, but in other cases, low melting metals or alloys may serve satisfactorily. The covering or coating materials should have melting or at least softening points which are sufliciently low as to permit the desired results without requiring the temperature of the reinforcing elements to be raised to a degree that would adversely affect their reinforcing characteristics. And the melting or softening point is also preferably above atmospheric temperatures to which the structure will ordinarily be exposed.

When the reinforcing element has expanded an amount sufiicient to impose the desired stresses upon subsequent contraction, it is suitably secured against excessive contraction so that the desired amount of its contracting force will be applied to produce compressive stresses within the body. The mode of securing the element may vary according to the type of structure involved, but such expedients as welding, clamping, threading and pinning suggest themselves. Where the securing arrangement employed requires a recess in the concrete body, for ex:

ample, a dry packed concrete filling may be used to protect the Joint and to impart to the structure a finished appearance.

A thermoplastic material such as sulfur, melting at approximately 120 C. is a good electrical insulator and at the same time furnishes a reasonably good bond between steel and concrete. In some cases, the thermoplastic or thermosettlng covering or sheathing material may assume a preformed tubular shape.

For purposes of illustration, reference is made to the accompanying drawing wherein:

Fig. 1 is a sectional elevation of a reinforced member embodying the present invention;

Fig. 2 is a sectional elevation of an arcuate member;

Fig. 3 is a sectional elevation of a helically reinforced cylindrical body;

Fig. 4 is a sectional elevation of a cylindrical body containing an annular reinforcing element; and

Fig. 5 is a perspective of a clip for securing the ends of the reinforcing elements of Figs. 3 and 4.

The plastic body In, depicted as concrete in the drawing, is provided with one or more reinforcing elements I2, and each element is covered by a material H which prevents a direct bond between the plastic body and its reinforcement. Where the plastic body is thermoplastic itself or where it possesses no tendency to adhere to the reinforcing element, the interposed material Il may be omitted. But since concrete and steel have been indicated in the various figures of the drawing, the interposed material also has been indicated. Among the materials considered to be suited for interposition between the body and its reinforcement under proper conditions are sulfur. low melting resins, low melting alloys, various other thermoplastic and thermosetting substances, or other suitable materials which may be wrapped, coated, molded or otherwise formed about the reinforcing elements.

In Fig. 1, the body may represent a slab, beam, floor, deck, road, wall, or other member in which the effect of prestressing is desired. After the concrete has hardened sumciently to resist substantial deformation upon application of the desired stresses, heat is applied to the renforcing element I! as by attaching electrical conductors to its ends and allowing a predetermined type and amount of current to flow so as to melt or soften the interposed material I and to elongate or axially expand the element [2 a desired amount. At this point the nuts I are advanced a predetermined amount upon the threaded ends ll of the relatively smooth rod l2, so that when the thermal effect is reduced, as by decreasing the current flow, the rod will contract until the washers or hearing plates 20 engage the concrete body and the further contracting force of the reinforcing element will apply compressive stresses to the concrete body. Whereas but one reinforcing element has beenshown in Fig. 1, it will be understood that any number may be employed depending upon the dimensions of the plastic body. the yield point of the reinforcing elements and the stresses to be imposed. Such additional reinforcing elements may be arranged parallel to or at any desired angle to the one shown.

Fig. 2 illustrates the invention as applied to an arcuate or curved member which may be an arch, floor, roof, wall, hull, or any reinforced body to which such a shape adapts itself. In this case, two reinforcing elements having threaded ends l8 and covered with sheathing material ll have been shown, provided with nuts I6 and bearin plates or washers 22. In this instance, the reinforcing elements may be heated and clamped sequentially or simultaneously, the mode of operation being substantially the same as that described with reference to Fig. 1. I

Fig. 3 illustrates a cylindrical concrete body reinforced with oppositely directed helices 24, the opposed upper ends of which are joined by welds 26 or other suitable means. In such an arrangement, the helices are preferably heated simultaneously so that they will both attain their desired degree of expansion at the same time, whereupon their free ends provided with enlarged heads 28 are engaged by the bifurcated ends of a clip 32 of predetermined length or otherwise suitably connected to restrict contraction. After the joints have been made, tendency of the helices to contract will cause the convolutions to embrace the adjacent concrete surfaces whereby the concrete body as a whole will be subjected to compressive stresses. As indicated by broken lines, the joint at the lower ends of the helices may be formed within a. recess provided in the concrete body. Examples of structures to which this form of the invention may be applied include tanks, silos. linings, pipes, rings and other bodies.

Fig. 4 is directed to a cylindrical body of reinforced concrete wherein the enlarged ends 28 of the reinforcing element l2 are received in a recess 30 which is formed to permit the joint to be made internally of the structure. When current is applied to the ends 28, the thermoplastic or other suitable material l4 will soften and the discontinuous annulus or hoop will expand axially. After expansion has progressed suflicienily, the current is discontinued and a clip 32 having bifurcated ends 34 is slipped over the enlarged heads 28. Then the element l2 will partially contract and impose the desired compressive stresses upon the body of the plastic structure l2. If desired, the recess 30 may be filled with dry packed concrete 33 or the like to provide the body with an unbroken periphery and also protect the joint against the elements.

Where thermoplastic or thermosetting covering materials are used, upon reduction of the thermal effects below their melting or softening points, they will harden and effect a bond between the plastic body and its reinforcement. In connection with such covering materials, where it is desired to prevent undue abrasion during handling, a protective sheath such as mesh or other suitable fabric may be employed, or a suitable substance such as asbestos fibers may be incorporated in the covering material itself.

The heating current may be D. C. or A. C. of

desired frequency, and of various voltages as will be determined by the resistance of the reinforcing elements, desired degree of expansion and the temperature limit to be observed to avoid injury to the properties of the steel or other materials.

Among the many uses to which the principles of the present invention may be applied, there will be mentioned but a few, namely: bridges, roads, piles, floors, roofs, arches, walls. ship pipes,

tanks, silos, tunnel linings, dome foundation rings, columns, beams and slabs.

This application is considered to be a division of application Serial No. 447,407, filed on June 1'7, 1942 (Patent No. 2,319,105)

The foregoing description is illustrative of the invention whose scope is set forth in the following claims. 1

I claim:

1. A reinforced structure comprising a hardened plastic body having a stressed reinforcing element therein normally subjecting said body to compressive stresses, and a solidifying thermoplastic material interposed and effecting a rigid bond between said element and said body.

2. A reinforced concrete structure'comprising a hardened concrete body having a stressed reinforcing element therein-normally imposing compressive stresses upon the concrete, and an electrical insulating thermoplastic material effecting I a rigid bond between said element and said body.

3. A reinforced concrete structure comprising a hardened concrete body, a pretensioned reinforcing element having a bearing upon said body to maintain a substantial portion thereof in compression, and a hardened thermoplastic material rigidly bonding said element to said body.

4. A reinforced concrete structure comprising a hardened concrete body, a pretensioned reinforcing element having a bearing upon said body to maintain a substantial portion thereof in compression, and a, hardened thermosetting material rigidly bonding said element to said body.

5. A reinforced concrete structure comprising a hardened concrete body, a'pretensioned reinforcing element having a bearing upon said body to maintain a substantial portion thereof in compression,'and a body of hardened sulfur bonding said element to said concrete body.

6. A reinforced concrete structure comprising a hardened concrete body, a pretensioned reinforcing element having a bearing upon said body to maintain a substantial portion thereof in compression, and a hardenedthermopla-stic material rigidly bonding said element to said body, said thermoplastic material having a melting point in excess of atmospheric temperatures to which said structure is ordinarily exposed.

7. A reinforced concrete structure comprising a hardened concrete body, a pretensioned reinforcing element having a bearing upon said body to maintain a, substantial portion thereof in compression, and a hardened thermoplastic material rigidly bonding said element to said body, said thermoplastic material having a melting point in excess of atmospheric temperatures to which said structure is ordinarily exposed and below" that which would adversely affect the properties of the reinforcing element.

8. A reinforced concrete structure comprising a hardened concrete body, a pretensioned reinforcing element embedded within and having a bearing upon said body to maintain a substantial portion thereof in compression, and a hardened thermoplastic material surrounding said element and rigidly bonding it to said body.

9. A reinforced concrete structure comprising va hardened concrete body, a pretensioned reinforcing element having a bearing upon said body to maintain a substantial portion thereof in compression, and a hardened thermoplastic material interposed between said element and said body and serving as a rigid bond between them.

KARL P. BILLNER.

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