US3111965A

US3111965A - Prestressed concrete structure and method of making the same

Info

Publication number: US3111965A
Application number: US716687A
Authority: US
Inventors: Robert W Hodge
Original assignee: Individual
Current assignee: Individual
Priority date: 1958-02-21
Filing date: 1958-02-21
Publication date: 1963-11-26
Anticipated expiration: 1980-11-26

Description

Nov. 26, 1963 R. w. HODGE 3,111,965

PRESTRESSED CONCRETE STRUCTURE AND METHOD OF MAKING THE SAME Filed Feb. 21. 1958 E I I! 'HWW INVEVTOR.

2 0162; Haifa.

zw wm United States Patent 3,111,965 PRESTRESEED CONCRETE STRUCTURE AND METHUD OF MAKING THE SAME Robert W. Hodge, Lake Angelus, Mich. (1307 Pontiac State Bank Bldg, Pontiac 15, Mich.) Filed Feb. 21, 1958, Ser. No. 716,637 3 (Claims. (til. 138-l76) This invention relates to prestressed concrete articles and to a method of making them. More particularly, the invention relates to the prestressing of generally cylindrical or annular concrete structures such as storage tanks, pressure containers, sections of pipe and the like.

The prestressing of concrete structures may be accomplished by applying a longitudinal stress or tension to one or more wires or cables, and then casting concrete around the stressed wires and allowing the concrete to set to obtain a bond between the concrete and the prestressing elements. After a firm bond has been obtained, the prestressing elements exert a compressive force on the concrete in the direction or" the length of the elements to give very great beam strength and shear resistance to the concrete structure. When the prestressed structure is of generally cylindrical or annular form, it is frequently desirable or necessary that the article he prestressed circumferentially as well as longitudinally. In the past the longitudinal and circumferential prestress has been accomplished in two separate steps or operations and generally consists in casting the concrete around longitudinal prestressing elements and, after hardening of the partially formed structure, winding circumferential prestressing elements around the structure and casting an additional shell or covering over the circumferential prestressing elements.

The present invention contemplates a longitudinally and circumferentially prestressed concrete structure of generally cylindrical form in which each prestressing element provides both longitudinal and circumferential prestressing of the article, thereby making it possible to fabricate such structures in a single casting or other forming operation. This objective is accomplished by employing prestressing elements each of which corresponds to one of the straight-line elements of a hyperboloid of revolution, with the angularity of the successive elements in the series being oppositely directed to eliminate torsional stress and provide a stable structure.

A principal object of the invention is to provide a new and improved prestressed concrete structure.

A further object of the invention is to provide a new and improved method of making prestressed concrete articles.

Another object of the invention is to provide a means for obtaining both longitudinal and circumferential prestress in a generally cylindrical concrete article by the use of a single series of prestress elements.

Other and further objects of the invention will be a parent from the following description and claims and may be understood by reference to the accompanying drawing, which by way of illustration shows a preferred embodiment of the invention and what I now consider to be the best mode in which I have contemplated applying the principles of my invention. Other embodiments of the invention may be used without departing from the scope of the present invention as set forth in the appended claims.

In the drawing:

FIG. 1 is a perspective view with parts broken away illustrating the arrangement of the prestressing elements in a form or mold in which a cylindrical structure is to be cast;

FIG. 2 is a fragmentary perspective view of a section a 3,1 l L965 Patented Nov. 26, 1963 ice 2 of cylindrical pipe made according to the present invention;

FIG. 3 is a diagrammatic view illustrating certain principles of the invention; and

FIG. 4 is an elevational view of a series of prestressing elements arranged in accordance with the present invention and illustrating a further modification of the invention.

As stated above, the present invention is applicable to the production of hollow concrete structures of various types having generally cylindrical or ellipsoidal cross sections and is particularly suited for the production of concrete pipe, pressure containers or storage tanks and similar concrete structures. The invention is illustrated in the drawing as applied to the production of a section of cylindrical concrete pipe indicated at it) in FIG. 2. The apparatus employed for carrying out the invention may be varied as required according to the type of structure being reduced, and the apparatus disclosed in FIG. 1 is merely illustrative of one form of apparatus that may be used.

in FlG. 1 there is disclosed a concrete form or mold comprising an inner core 12 and an outer shell 14 spaced apart a distance corresponding to the wall thickness required in the finished product. A pair of

end plates

16 and 18 are suitably supported on either the inner or outer form 12 or 14 and, together with the forms 12 and 14, define a space conforming to the shape of the article to be produced.

The

end plates

16 and 18 are provided with suitable means to receive and clamp the ends of a series of prestressing elements in the form of wires or cables 2d. Each of the prestressing elements 2% corresponds to one of the straight-line elements of a hyperboloid of revolution having its axis coincident with the axis of the concrete article to be produced. As shown in FIGS. 1 and 4, certain of the elements 29 extend from the upper end plate 18 to a point on the lower end plate 16 which is advanced approximately 30 in a counterclockwise direction from the point on the lower end plate is which corresponds to the point at which such elements are fixed to the upper end plate 18. The remaining prestressing elements 2i) have an opposite angularity to provide a cage-like structure of annular form.

After the prestress elements 2.6 have been arranged in the manner described, one of the end plates 15 or 18 may be moved axially away from the other to impart a longitudinal stress or tension to the elements 29. Any suitable means may be employed for stressing the elements 25 such as hydraulic jacks, screw jacks or the like, the particular apparatus used not being illustrated herein. It is contemplated that the wires 29 may be stressed individually or that a series or all of the elements may be stressed at the same time. After the elements 2%} have been uniformly stressed the required amount, concrete or other cementitious material is poured or otherwise forced into the mold in any suitable manner and allowed to harden while the tension is maintained on the prestressing elements Zil. The length of time required for bonding the concrete to the prestressing elements will depend upon the type of material used, but in any event should be long enough to obtain a firm bond between the concrete material and the prestressing elements. The tension on the elements may then be released and the article removed from the mold. Adjacent wires Zn in the series have opposite angularity, so that one-half of the wires correspond to the first generation elements of the hyperboloid of revolution While the remainder correspond to the elements of the second generation. An article produced in accordance with the above described method will have both a longitudinal and a circumferential pre- 3 stress, as will be describedin connection with the force diagram of FIG. 3.

In FIG. 3 the two circles represent the upper and lower circles of the hyperboloid of revolution which is approximated by the entire series of elements 20. The line H is perpendicular to both circles and represents the height or length of the article to be produced, R indicates the radius of either circle, and angle A is the angle through which the lower end of an element 20 is advanced in a counterclockwise direction from the position of the upper end of the element 20 on the upper circle, from which the length of chord C can readily be determined. From the foregoing it can be calculated that the angle B that the element 20 makes with the line H can be determined by the equation:

2R sing Having determined the angle 13, and with a tension of F pounds on the element 29, it will be seen that the tension on the element will be resolved into longitudinal prestress of F cos B, and a circumferential prestress of F sin B.

By varying the angle A, the distribution of the prestress in the longitudinal and circumferential directions may be varied as desired. It is apparent that, as the angle A is increased, the wall thickness of the article must be increased. While in the illustrated embodiment of the invention a cylindrical article has been shown, it will be apparent that articles having a larger diameter at one end than at the other may be produced according to the present invention. The invention is also useful in the production of articles ranging from relatively small diameter pipe up to very large structures such as tanks or the like, and similarly the prestressing elements may range in size from small diameter wires up to large diameter steel cables.

In FIG. 4 there is disclosed an arrangement of prestressing elements 20 arranged as described above and having a longitudinal stress applied thereto. In order to provide additional reinforcement circumferentially of the structure, a series of additional wires or cables 22 may be wrapped around and suitably fastened to the prestressing elements 22 The additional reinforcing elements 22 need not be prestressed or tensioned but would perform the function of taking up or resisting the load on the prestressed concrete structure when the bursting strength of the pretensioned wall is reached. Such additional circumferential reinforcing elements would materially increase the pressure capacity of the article.

Tan B= From the foregoing it will be seen that the present invention provides a relatively simple and inexpensive means of making articles of. the type described having both longitudinal and circumferential prestress by a series of similarly arran ed prestressing elements.

While I have illustrated and described a preferred embodiment of my invention, it is understood that this is capable of modification, and I therefore do not wish to be limited to the precise details set forth but desire to avail myself of such changes and alterations as fall withi in the purview of the following claims.

I claim: l

1. The method of making longitudinally and circumferentially prestressed concrete structures of generally annular cross-section in a single casting operation, which comprises arranging a series of wires to form a cage-like structure with each wire conforming substantially to a straight line element of a hyperboloid of revolution and with successive wires in the series having equal and opposite angularity, tensioning said wires longitudinally thereof while maintaining said wires in said straight line condition, casting cementitious material around and over said tensioned wires in the form of the structure to be produced, and allowing said material to harden while maintaining said tension to form a bond between said material and said tensioned wires whereby each of said wires imparts both longitudinal and circumferential prcstress to the hardened material.

2. A prestressed concrete structure of generally annular cross-section having embedded therein and bonded thereto a series of longitudinally tensioned prestressing wires each of which corresponds to a straight line element of a hyperboloid of revolution having its axis coincident with the axis of said structure, successive wires in said series having equal and opposite angularity whereby the series of wires imparts both longitudinal and circumferential prestress to said structure.

3. A structure according to claim 2 including a series of circumferentially extending, longitudinally spaced reinforcing wires surrounding said prestressing wires and also embedded in and bonded to said concrete.

References Cited in the file of this patent UNITED STATES PATENTS 950,264 Hugo Feb. 22, 1910 958,043 Stockley May 17, 1910 2,522,165 Crorn Sept. 12, 1950 FOREIGN PATENTS 457,227 Italy May 12, 1950