US3137971A

US3137971A - Stressed concrete structures

Info

Publication number: US3137971A
Application number: US42136A
Authority: US
Inventors: Rhodes Brian
Original assignee: Cable Covers Ltd
Current assignee: Cable Covers Ltd
Priority date: 1959-07-15
Filing date: 1960-07-11
Publication date: 1964-06-23
Anticipated expiration: 1981-06-23

Description

June 23, 1964 RHODES 3,137,971

STRESSED CONCRETE STRUCTURES Filed July 11, 1960 United States Patent 3,137,971 STRESSEID CONCRETE STRUCTURES lirian Rhodes, Epsom, England, assignor to Cable Covers Limited, London, England, a company of the United Kingdom Filed July 11, 1960, Ser. No. 42,136 Claims priority, application Great Britain July 15, 1959 1 Claim. (Cl. 50-128) This invention relates to the post-tensioning of concrete structures by means of wire or strand, either individually or in the form of a cable and hereinafter referred to as the tensioning cable or cables. In particular this invention concerns an anchorage device for use in anchoring the cable or cables in the structure.

It is usual in the construction of post-tensioned con crete to anchor the cable by means of grips abutting against a bearing plate, which in turn bears against a thrust ring previously cast into the concrete. Furthermore helical reinforcement is usually provided behind the bearing plate to resist anchorage bursting forces. This invention is concerned with an improved form of anchorage, mainly to improve the distribution of forces into the concrete.

According to the invention an anchorage device for use in post-tensioned concrete structures comprises a socket member having an axial bore through which the tensioning cable or cables can be passed, the socket having at one end thereof a locating flange and being formed over the whole or part of its outer surface with a rib or ribs which serve to increase its effective bearing area and which, in use, ensure an even distribution of the load over the length of the socket.

In a preferred construction in accordance with the invention the socket consists of a tapered tube having a spiral rib.

The invention is diagrammatically illustrated by Way of example in the accompanying drawings in which,

FIGURE 1 is a side elevation of one form of the anchorage device according to the invention,

FIGURE 2 is a corresponding end elevation in the direction of the arrow 2 of FIGURE 1,

FIGURE 3 is a corresponding end elevation in the direction of the arrow 3 of FIGURE 1,

FIGURE 4 is a longitudinal section corresponding to FIGURE 1, and

FIGURE 5 is a longitudinal section through an alternative form of the device.

Referring to FIGURES 1 to 4 of the drawings the device, as applied for use with a plurality of single tensioning wires 1, comprises a frusto-conical metal socket member 2 having a tapered sleeve portion 3 and a locating flange 4 formed at one end of the sleeve portion 3. The outer surface of the sleeve portion is formed with a deep spiral rib 5 which extends over the whole or part thereof. The rib 5 is disposed at an angle to the central longitudinal axis of the socket and increases in depth from the end of the sleeve portion having the largest diameter to the end of the sleeve portion having the smallest diameter so that the effective outside diameter of each convolution of the rib is constant throughout the length thereof.

In use the socket member 2 is cast in the concrete indicated at 6 so that the locating flange 4 is in alignment 3,137,971 Patented June 23, 1964 with the face thereof as shown in FIGURE 1. The wires 1 are passed through the bore 7 of the socket 2 and thence individually through holes 8 drilled in a bearing plate 9 which bears on the locating flange 4. Each wire is then locked off by means of anchor grips 10 which abut the bearing plate 9. Each anchor grip 10 consists of a cylindrical barrel member 11 having a central tapered bore through which the wire is passed the wire being held therein by two or more wedges 12.

The extreme end opposite the flange 4 of the bore 7 is of untapered cross-section to receive a tubular sheath 13 for containing the wires 1 within the concrete structure.

In its alternative form as shown in FIGURE 5 the device is adapted for use with a single stranded cable 14. In this form the bearing plate 9 and the anchor grips 10 are dispensed with and the cable 14 is locked in the bore 7 by means of two or more steel wedges 15. To increase the gripping power on the cable 14 the taper of the bore 7 in this form is made more acute. This taper extends over a part only of the bore, the remainder of the bore being provided as an oppositely disposed taper 16 which opens out to receive the tubular sheath 13.

In a further modification not illustrated the wires 1 may be locked off by providing the bearing plate 9 of increased thickness and forming the holes 8 as tapered holes to receive wedges to engage the wires.

Thus it will be understood that the forces transmitted from the cable or cables are distributed through the anchorage into the concrete. These forces, according to the invention, are resisted by a combination of the bearing area of the location flange 4 and the spiral rib 5 which forms a continuous abutment and distributes the load in the concrete over the entire length of the socket. This gradual distribution of forces greatly reduces the intensity of stress in the concrete behind the anchorage, and provides a more eflicient end block condition. In addition, by forming the edge of the rib 5 parallel to the longitudinal axis of the socket member the Wedge action of the socket which would otherwise occur due to the external taper of the sleeve portion 3, is neutralized.

What I claim is:

A post-tensioned concrete structure including a stressing cable; and means for anchoring said stressing cable in a predetermined position in said structure, in which said anchoring means comprises a socket member having an external frusto-conical shape and having at its end of larger diameter a transversely disposed flange locating said socket member in said concrete structure and having a tapered axial bore extending through said socket member through which said stressing cable extends, an apertured bearing plate abutting said locating flange through which said cable extends, and at least one anchor grip gripping said cable and bearing against said bearing plate and securing said cable in position, said socket member being further provided with a continuous spiral rib which extends over at least part of the outer surface of said socket member, said rib increasing in depth from the end of said socket member of larger diameter to the end of said socket member of smaller diameter so that the effective outer diameter of each convolution of said rib is constant, the edge of the rib being parallel to the longitudinal axis of the socket member, and the inner diameters of successive convolutions progressively decrease from said large diameter end of said socket member to said smaller diameter end thereof, said rib serving to increase the effective bearing area of said socket member and ensuring an even distribution of the load over said socket member.

References Cited in the file of this patent UNITED STATES PATENTS 2,525,198 Beijl Oct. 10, 1950 A} Dyche July 15, 1952 Freyssinet Aug. 24, 1954 Finsterwalder July 24, 1956 Leonhardt Sept. 18, 1956 Dobell Feb. 19, 1957 FOREIGN PATENTS France Dec. 22, 1911 Great Britain May 29, 1957