US3034537A

US3034537A - Prestressed concrete pipes

Info

Publication number: US3034537A
Application number: US736489A
Authority: US
Inventors: Francis Eugene Seaman; Edmund Charles Garrabrant
Original assignee: Lock Joint Pipe Co
Current assignee: Lock Joint Pipe Co
Priority date: 1958-05-20
Filing date: 1958-05-20
Publication date: 1962-05-15
Anticipated expiration: 1979-05-15
Also published as: NL238632A; DE1186700B; GB852105A; NL121389C

Description

May 15, 1962 F. E. SEAMAN ET AL PRESTRESSED CONCRETE PIPES 2 Sheets-Sheet 1 Filed May 20, 1958 avvavraes FeAAlc/s E. JZ/I/V/M/ p/vun/a 6, GAEEABPA/VT BY W A 7'70/P/VE Y y 1962 F. E. SEAMAN ETAL 3,034,537

PRESTRESSED CONCRETE PIPES Filed May 20, 1958 2 Sheets-Sheet 2 EPA/v05 6 jfAMA/V EDMUND (Z A/P/PABKAA/T United States Patent Uffice 3,034,537 Patented May 15, 1962 Jersey Filed May 20, 1958, Ser. No. 736,489 Claims. (Cl. 138-476) This invention relates to the manufacture of prestressed concrete and more particularly to pipes and other tubular bodies of originally plastic and subsequently hardened materials which are subjected to strain in their manufacture. Prestressed longitudinal reinforcements and Wrappings of tensioned Wire are employed for reinforcing the concrete walls of pipes in order to make the concrete effective to withstand severe conditions of use and to confine fluids under relatively high pressures. Longitudinal reinforcements impart compressive strain in the lengthwise direction of a pipe and the tensioned wire wrappings subjects the concrete to circumferential compression. A high order of barrel strength is obtainable in this type of a pipe but in some designs of high pressure pipe the concrete adjacent the ends of a pipe tends to flare and crack owing to differential prestressing. Cracking of the concrete results in economic Waste because of the expensive quality of the steel contained in the pipe and the practice of down-grading a pipe for use for containing hydraulic pressures below that which the construction was intended to contain without cracking.

A primary purpose of the present invention is to provide suitable reinforcings of moulded tubular structures to effect circumferential compression to restrain the development of cracks adjacent their ends. This object is of particular importance in the construction of prestressed concrete pipes or pipe cores having ends moulded or otherwise formed to provide jointing and gasket-receiving surfaces for making joints with other pipes and over and beyond which the tensioned wire wrapping does not extend. The results desired are achieved by the use of a tubular arrmgement of embedded prestressing means exerting circumferential compressive strain in end zones of a pipe as well as compressive strain in the longitudinal direction of the pipe.

The embedded prestressing means comprise a plurality of prestressed wires in the form of elongated wire links or loops having side elements and end elements respectively extending longitudinally and laterally of the pipe with the side elements spacially arranged circumferentially of the pipe and the end elements defining chords lying between the interior and exterior of the pipe, and prestressed anchoring wires or loops circumferentially distributed in spaced relationship adjacent the ends of the pipe and interlaced with different pairs of the prestressed links. Anchoring wires in the form of openended loops and the end elements of the several links constitute together an embedded prestressed ring which exerts compression circumferentially in the concrete contiguous to the ring and the end of the pipe.

The links and the anchoring wires are assembled in a mould and they are stretched and held in tension before the concrete is placed. The anchoring wires and the links are preferably constituted of high tensile steel wires which may be subjected to a tensile stress of 130,000 pounds per square inch and upwards in accordance with the specifications of the particular pipe intended to be constructed. Tension is initially applied to the assembled links and anchoring wires by a traction device pulling on the legs of the anchoring Wires and the tension thereby applied is maintained in the wires of the tensioned system of links and anchoring wires by clamping devices or wedges mounted on the mould. The established tension is maintained by external anchoring devices until after the concrete has fully hardened.

Upon removal of the clamping devices and the mould, the external forces theretofore exerted on the wires are transferred to the hardened concrete. As a consequence the concrete is longitudinally compressed by the longitudinals or side elements of the links and the concrete in the end zones is circumferentially compressed by the tensioned end elements of the links and the tensioned anchoring wires which together constitute a force ring locked in place by the concrete.

The connecting and interlocking chords of the anchoring wires and links at one end of a pipe provide a single force ring around the pipe which is counteracted by the concrete, and the principle employed may be utilized to provide two or more single force rings to thereby multiply the circumferential compressing force of a single ring.

An advantage of the invention lies in the fact that the stress-distributing anchoring wires and ends of the links provide an extensive bearing for anchoring the ends of the longitudinals which are constituted of the side elements of the links. The use of exposed bearing or force distributing devices or anchorages for pretensioned longitudinals is avoided. 7

Other objects and advantages of the invention will appear more fully from a detailed explanation of the application of the invention to representative forms of prestressed concrete pipes.

In the drawing, FIG. 1 is illustrative of a pipe employing the present invention, part of the pipe being broken away to show a longitudinal section;

FIG. 2 illustrates diagrammatically the relationship of the embedded reinforcing as viewed from one end of a r e; p FIG. 3 is a diagrammatic illustration in perspective of part of the tubular arrangement of the reinforcing members shown on FIG. 2;

FIG. 4 is an enlarged sectional view of part of one end of the pipe illustrated in P16. 1;

FIG. 5 is a perspective view of one of the loops or anchoring wires;

FIG. 6 is a perspective view of one of the wire links or loops which extends longitudinally of the pipe;

FIG. 7 is a diagrammatic representation of a portion of a mould with several prestressed reinforcing members in place;

FIG. 8 is a diagrammatic showing of one end of a pipe with the links and anchoring wires arranged to provide two single force rings;

FIG. 9 is a diagrammatic illustration in perspective of part of the tubular arrangement of the reinforcing members shown in FIG. 8; and

FIG. 10 is a sectional view of a connector and joined ends of a wire of a single link. a

It is intended that the pipe illustrated in the drawing and specifically referred to in the following description be illustrative of the application of the invention to other forms of moulded tubular bodies. The moulded pipe contains pairs of prestressed

longitudinal members

11 and 12, as best seen in FIG. 3. The longitudinal members are provided by the side elements of a plurality of elongated links or loops 13, such as shown in FIG. 6. The number of links employed depends in general upon the size of the Wire, the size of the pipe and the hydraulic pressure the pipe is designed to withstand. The links 13 are arranged spacially around the circumference of the pipe wall and in a manner to provide longitudinals in spaced relationship to one another.

As shown in FIGS. 2 and 3, the end elements or end loops 14 of an adjacent pair of links 13 are engaged by the bight 15 of a single anchoring wire 16 having ends or

legs

17 and 18 extending toward the outer end of the pipe. Each of the several anchoring wires 16 is between and ties together two of the links 13. A similar arrangement of anchoring wires are interlaced with end elements 19 of the links at the other end of the pipe (FIG. 1).

The pipe illustrated in FIG. 1 is a bell and spigot type of pipe moulded in one piece and having a spigot at one end with jointing surfaces, including gasket-receiving surfaces 21, spaced inwardly from the extreme end of the spigot, and a bell with an internal jointing surface 22 for forming a coupling with a similar pipe. A steel hoop 23 is provided for changing the pitch of the longitudinals as they enter the enlarged end of the pipe barrel, although in a straight-walled, double spigot type of pipe the longitudinals would be straight from end to end.

The pipe is circumferentially compressed by a wrapping of tensioned wire 24 helically wound in contact with the exterior of the concrete. The ends of the wire may be anchored by any suitable means, as, for example, a sleeve 25 compressed upon the Wire and Welded to a cinch plate 26;

In assembling the embedded reinforcement, each of the links 13 is formed by bending a wire of sufiicient length to provide a quadrilateral which, when stressed and extended under traction in a mould will have side elements extending for nearly the full length of the mould or of the pipe core. The ends of the wire are inseparably fastened together by a connector in the form of a compressed sleeve 27 or by any other fastening means, such as a fine high strength wire Wound tightly around overlapping ends of the reinforcement wire. A form of a sleeve connector is shown in FIG. 10. This connector comprises a soft or mild steel sleeve 28 having a lining 29 which includes sharp particles of a hard material which bite into the wire and the sleeve when the sleeve is compressed onto the wire.

Other lengths of wire are cut and bent to form U-shaped anchoring wires 16 (FIG. having legs adapted to be threaded through openings in the end rings of a mould after they have been interlaced with adjacent links.

A portion of a mould showing several of the links 13 and anchoring wires 16 is illustrated in FIG. 7. The ends of one setof anchoring wires 16 extend through openings in an end ring or plate 31 at one end of the mould and a second set' of anchoring wires are similarly disposed with reference to the end ring or plate 32 at the other end of the mould;

The bights 15 of the first set of anchoring wires and the end elements 19 of the links 13 are located in positions quite near to the mould end 31 by anchors 33 having jaws tightly engaged with the

legs

17, 18 of the wires. Each of the anchoring wires at the other end of the mould is held by a clamping device, including a fixed outer member 34 hearing on the mould end 3 2 and a movable wedge plate 35. The end plates of the mould are spaced apart by a tubular shell 36 which counteracts the combined pull exerted on the mould ends by the tensioned longitudinals. i

As shown in FIG. 7, the wires are tensioned and'the mould is prepared for receiving concrete. Tension is initially applied to the wires by a traction device which has a base to engage a mould end. Any suitable traction or pulling device may be employed as, for example, the traction device disclosed in the United States Patent No.

2,637,895, granted May 12, 1953. Extensions of each of V the anchoring wires at one end of the mould may be attached to a pulling wedgerof the traction device and each wire maybe pulled individually and successively until all of the wires have been subjected to the same pulling force,

or all of the wires may be pulledat one time. When they desired tension has been applied to all of the internal reinforcement, the wedges 35 are firmly'secured in place against the legs of the anchoring wires and the traction device is removed. The extensions of the anchoring wires are then severed close to the clamping devices 34-35 and the mould is ready for filling with concrete.

The mould may be of a conventional form, but it is advantageous to mould high pressureconcrete pipe centrifugally in a mould by which the jointing and gasketreceiving surfaces at the ends of a pipe or tubular core are formed from the moulded concrete. The rotation of the mould and the hardening of the concrete develops a wellcompacted concrete in bonded relationship to the embedded system of tensioned wires. The concrete hardens in an unstressed state and free from strain. After the concrete has thoroughly hardened, the clamping devices and the mould are removed and the reaction of the tension wires is transferred to the concrete. Owing to the bond of the concrete to the wires and the hooked relationship of the wires to the concrete and to each other, the incased system of tensioned wires remains in tension and the concrete reacts in compression in the divers lines of directions of each of the several wires.

The longitudinals or

side elements

11, 12 subject the concrete to compressive strain in the longitudinal direction of the pipe. As the anchoring wires and the links are interlaced, the bights 15 of the anchoring wires and the

end elements

14, 19, constitute force rings which subject the concrete adjacent the ends of the pipe to compressive strain in the direction of the rings.

In FIGS. 8 and 9 there is shown a modified arrangement of links 37 and anchoring wires 38 at one end of a tubular core. In this arrangement the end elements 39 of the various links are lengthened to extend between every other of the anchoring wires 33 in a manner to provide two force rings instead of one. The desired tension is applied to the assembled anchoring wires and links in the manner previously explained. This arrangement enables subjecting an end zone of a concrete pipe to twice the tension in any of the wires included in the embedded system of reinforcements.

Circumferential prestressing may be applied to only a single end of a tubular body by substituting an openended loop of Wire for each of the links. The straight ends of the longitudinals or side elements would be anchored to the mould by external anchoring devices similar to those described, and the looped ends at the other end of the mould would be interlaced with U-shaped anchoring Wires in the manner described to form a force ring.

After a concrete core or pipe has cured sufficiently, the protruding ends of the anchoring wires are severed or broken off preferably within the concrete. The holes remaining in the concrete are filled with a Portland cement mortar 4%}; 'As thus completed, none of the embedded reinforcement isexposed and electrical conduction through the embedded reinforcement and joints of connected pipes is impossible. A covering of mortar 41 is usually employed to protect the wire wrapping 24, FIG. 1.

While we have disclosed preferred forms of the invention, numerous modifications, alterations and substitutions will be obvious to thoseskilled in the art after a study of the foregoing description. Consequently the description is to be considered in an illustrative rather than a limiting sense; and it is our desireand intention to reserve all modifications and substitutions falling within the scope of the claims which follow.

. What is claimed is:

1. In combiiiation, a moulded tubular body of originally plastic and subsequently hardened material, a tensioned wire Wrapping secured about the exterior of said tubular body, a tubular arrangement of prestressing means embedded in said tubular body and subjecting the material thereof to compressive strain, said prestressing means comprising a plurality of pretensioned looped wires, the

tubular body and each looped wire having lengths extending longitudinally of said tubular body from the loop in the wire, said lengths of said looped wires spaced from one another circumferentially around said tubular body with the loop of each wire extending laterally to the said lengths of the wire, and a plurality of pretensioned members, each member interengaged with a pair of said looped wires and together with said loops of the looped wires forming a pretensioned ring of alternating loops and members embedded adjacent said end of said tubular body.

2. A tubular body according to claim 1, wherein each of said looped wires is provided with a second loop embedded in said tubular body, and additional pretensioned members are embedded in said tubular body at intervals around said tubular body, said last mentioned pretensioned members each interengaged with a pair of said second loops and thereby forming therewith another pretensioned ring.

3. A tubular body according to claim 1, wherein a second pretensioned ring is provided adjacent to said first named pretensioned ring, said second pretensioned ring comprising additional pretensioned members alternately arranged around said tubular body with respect to the pretensioned members of said first pretensioned ring, each of said additional pretensioned members interengaged with a difierent pair of said looped Wires.

4. In a prestressed pipe, the combination comprising a moulded tubular body of originally plastic and subsequently hardened material with exterior gasket-receiving surfaces adjacent one end thereof for forming a connection with another tubular body, a tensioned wire Wrapping secured about the exterior of said tubular body, said tensioned wire wrapping ending short of said gasketreceiving surfaces, a tubular arrangement of prestressing means embedded in said tubular body and subjecting the material thereof to compressive strain, said prestressing means including a plurality of prestressed wires having loops disposed transversely to the axis of said tubular body and distributed around said tubular body in a plane adjacent to said end of said tubular body, each loop having straight ends extending from the loop in the axial direction of said tubular body, and means tying together adjacent loops, said last-named means comprising pretensioned anchoring wires formed with bights interconnecting between pairs of said loops, said anchoring wires having open ends extending from said bights toward said end of said tubular body in the direction opposite from the direction of extension of said straight ends of the engaged loops.

5. In 1 a prestressed concrete pipe, the combination comprising a tubular core of concrete and a tubular arrangement of prestressing means comprising a first group and a second group of pretensioned wires embedded in the concrete of said core and having a bond to the concrete characteristic of the bond formed by a Wire embedded in concrete, said first group of pretensioned Wires including lengths of wires extending substantially the full length of said core at intervals around the core and subjecting the core to compression in the longitudinal direction of the core, said lengths of wires having loops connecting said lengths in pairs within the concrete of said core in a plane transverse to the axis of said core adjacent an end of said core, said second group of pretensioned wires also disposed at intervals around said core and having loops engaged with said first-named loops of said first group of wires, one of each of said wires of said second group engaged with a first-named loop connecting between a pair of said lengths of wires of said first group and engaged with another first-named loop connecting between another pair of said lengths of wires of said first group, said loops of said second group of Wires ending in legs extending away from the plane of said engaged loops in the direction opposite to the direction of extension of said lengths of Wires away from said plane, the engaged loops of said first and second groups of Wires forming a pretensioned ring in said transverse plane and reacting on the adjacent concrete of said core and subjecting the concrete to compression in the circular direction around said core.

References Cited in the file of this patent UNITED STATES PATENTS 937,793 Haas Oct, 26, 1909 1,900,145 Whiting Mar. 7, 1933 2,706,498 Upson Apr. 19, 1955 2,805,683 Kennison Sept. 10, 1957 2,913,798 Breguet Nov. 24, 1959 FOREIGN PATENTS 22,718 Australia Sept. 5, 1930 64,733 Netherlands Nov. 15, 1949 1,045,807 France July 1, 1953 1,076,592 France Apr. 21, 1954 1,087,848 France Sept. 1, 1954