US3909142A

US3909142A - Coupling assembly for stressing tendons of multi-span concrete structures

Info

Publication number: US3909142A
Application number: US416687A
Authority: US
Inventors: Eric Thornton Surr
Original assignee: CCL Systems Ltd
Current assignee: CCL Systems Ltd
Priority date: 1972-12-05
Filing date: 1973-11-16
Publication date: 1975-09-30
Anticipated expiration: 1992-09-30
Also published as: DE2360667A1; BE808271A; ATA1013573A; ES421146A1; BR7309329D0; FR2212843A5; GB1364212A; IT1008070B; CH577087A5; AT331475B; NL7316411A; JPS4996524A

Abstract

A coupling assembly for use in stressing multi-span posttentioned concrete structures, comprising a coupling device in which opposite ends of the stressing wires or strands of two adjacent sections of the stressing tendon are anchored, wherein co-operating cone-shaped elements are operatively associated with said coupling device and with one another to cause said wires or strands of one of said tendon sections to follow an S-shaped path.

Description

United States Patent Surr Sept. 30, 1975 [5 COUPLING ASSEMBLY FOR STRESSING 3450.829 6/1963 Paul 24/122,.6

TENDONS 0F MULTl-SPAN CONCRETE 31775311 12 Surekar 2 STRUCTURES 3.795.949 3/1974 Shorter 254/..9 A [75] Inventor: Eric Thornton Surr, Woodlesford, FOREIGN PATENTS OR APPLICATIONS E l d 1,452,219 8/1966 France 52/230 892,133 3/1944 France 24/1226 1g CCL Systems Limited, surbltont 1,117,114 6/1968 United Kingdom 52/230 England 1.125.176 8/1968 United Kingdom 52/230 [22] Filed: Nov. 16, 1973 Primary Erammer-Bernard A. Gelak 1 PP N95 4161637 Attorney, Agent, or Firm-Baldwin, Wight & Brown [30] Foreign Application Priority Data [57] ABSTRACT 1 1972 United Kingdom 515070/72 A couplin'g assembly for use in stressing multi-span post-tentioned concrete structures, comprising a cou- 1 403/41; 24/1225; 403/364 pling device in which opposite ends of the stressing 1111- (31-2 F16G wires or strands of two adjacent sections of the stress- 1 1 Field Search 24/122-6' 115 R; 403/41; ing tendon are anchored, wherein co-operating cone- 52/2301 254/29 A shaped elements are operatively associated with said coupling device and with one another to cause said 1 References Cited wires or strands of one of said tendon sections to fol- UNITED STATES PATENTS low an S-shaped path.

3.405.490 10/1968 La Marr 52/230 3.449,876 6/1969 Howlett 52/230 9 Claims 3 Drawing Figures g 2 g-x 1 6 r7 r. 22

J 6 fef US. Patent Sept. 30,1975 Sheet 1 of2 3,909,142

Sept. 30,1975 Sheet 2 of 2 3,909,142

US. Patent COUPLING ASSEMBLY FOR STRESSING TENDONS OF MULTl-SPAN CONCRETE STRUCTURES This invention relates to a coupling assembly for the stressing tendons of continuous mum-span posttensioned concrete structures. 1

In continuous multi-span concrete structure's a continuous tendon consisting of a plurality of strands or wires is made up in sections, the strands or wires of each section being coupled or connected together by mechanical means. One such means comprises a coupling bar or a tubular sleeve where all the strands or wires of the tendon are to be tens'ioned simultaneously, or coupling sleeves for each strand or wire where the' strands or wires of the tendonare to be stressed individuallyf Another means is that disclosed in our prior British Pat. No. 1,288,343 and its Patent of Addition No. 1,335,895, wherein a coupling device is formed witha plurality of central apertures to receive and anchor one end of the wires or strands of one sectionof a tendon,

' and with a corresponding number of peripheral slots to receive and anchor one end of the wires or strands of an adjacent section of the tendon.

In using the aforementioned coupling device, after having anchored the ends of the wires or strands of one section in the central apertures,'the endsof the wires or strands of the next adjacent section in the peripheral slots and are enclosed by a tapered grout box the smaller end of which is the same, or substantially the same, size as that of the main duct through which the tendon extends. Thus. when the wires orstrands are tensioned, it will be appreciated that they extend in a straight line between their anchorage pointsand the points at which they change direction on entering the main duct. I

Due to the fact that there is a limit to which any given size wire or strand can be bent to assemble-the anchorage, and a limit to which that wire or strand can be bent, particularly at the point where it leaves its anchorage, .during ultimate tensile load testing thereof without breaking at that point; the grout box must be relatively long. I I

Thus, it will be appreciated that the use of such an assembly results in large voids being created in the concrete structure which has the disadvantage that the structure, in the vicinity of the coupling assembly, has to be of increased size. This disadvantage is particularly noticeable in structures such as bridge beams where the increase in size occurs in the vicinity of the piers.

It is among the objects of the present invention to provide a coupling assembly which avoids, or substantially reduces, the aforementioned disadvantage.

According to the present inventiomthere is provided a coupling assembly for the stressing tendons of multispan post-tensioned concrete structures, comprising a coupling device having centrally'disposed axiallyextending means for anchoring one end of the wires or strands of one section of the stressing tendon, and other means formed on the periphery thereof for anchoring one end of the wires or strands of an adjacent section of the stressing tendon, a'wireor strand deflector attached to the coupling device to extend in the same general direction as the wires or strands'of said adja cent section of the stressingten don, and a reducing ele device to extend in the same general direction as the wire or strand deflector, the arrangement being such that, in use, the wires or strands of said adjacent section ment attached to the outer periphery of the coupling are disposed between the deflector and the reducing element.

The deflector and the reducing element are both preferably of frusto-conical formation and the shapes thereof are such that the external surface of the deflector and the internal surface of the reducing element determine the bending angle of the wires or strands.

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

FIG. 1 is a longitudinal section through a coupling assembly according to the invention,

FIG. 2 is a section on the line 22 of FIG. I, and

FIG. 3 is a section corresponding to part of FIG. 1 showing a modification.

Referring to FIGS. 1 and 2 of the drawings, there is shown a coupling assembly comprising a coupling de vice 1 consisting of an annular bearing plate 2 formed with an integral flange 3, and a disc-like bearing plate 4 positioned over the bore 5 of the annular bearing plate 2 to engage one face of the latter.

A plurality of transverse bores 6 of conical formation, the number of which varies according to the size of the tendon to bejoined, are provided to extend through the plate 4 and are each adapted, in use, to receive a wire or strand, indicated at S, of one section of the tendon.

The bores 6 are each formed to receive, in addition to the wire or strand S, a wedge device 7 by which the wire or strand is anchored in the bearing plate. The wedge devices 7 are of known construction and each comprise two or more arcuate wedge elements which are positioned between the bore 6 and the wire or strands.

The peripheral edge of the flange 3 of the bearing plate 2 is formed with a plurality of transverse recesses or grooves 8 which are of a width to receive a single wire or strand, indicated at S, of the next adjacent section of the tendon. The number of grooves or recesses 8 correspond to the number of bores 6 and will of course vary with the number of wires or strands in the tendon.

The ends of the strands S extend through the bores 6 and are anchored in the bores, as hereinbefore described, by the wedge devices 7. The strands S' however are held in position in the grooves or recesses 8 by means of anchoring fittings 9 which are secured to the ends of the strands.

The anchoring fittings 9 may each comprise a compression fitting of known construction consisting of a cylindrical sleeve one end of which is formed with an inwardly directed annular flange, and an insert received in the sleeve, the insert being provided with at least two longitudinally disposed slots and being knurled or otherwise roughened, both internally and externally, to increase friction between the insert and the wire or strand. After positioning the sleeve is compressed onto the wire or strand to provide a permanent fitting.

An alternative form of anchoring fitting 9 may comprise a so-called barrel and wedge type fitting consisting of a cylindrical barrel having a frusto-conical bore to receive a wire or strand and a plurality of wedge elements which grip and anchor the wire or strand in the barrel thereby providing an end fitting which can, if necessary, be removed from the wire or strand.

To ensure against any tendency for the anchoring fittings 9, which are preferably of a metal having a relatively low shear value compared with that of the coupling device 1, from shearing through the open grooves or recesses 8 when the strands S are under tension, a hard metal washer is positioned between each fitting 9 and the face of the bearing plate flange 3. The washers 10 are passed over the ends of the strands before the fittings 9 are fixed thereon.

The coupling assembly further comprises a wire or strand deflector 11 of generally frusto-conical formation. The deflector 11 is preferably of cast iron and is supported at one end by being fitted over the plate 4. The sizes of the plate 4 and the deflector 11 are such that the portions of the strands S in the vicinity of the coupling device I extend parallel to the axis of the assembly and are not therefore subjected to bending at the points where they leave their co-acting anchoring fittings 9 which are also disposed parallel to the axis of the assembly.

That portion of the deflector 11 away from the coupling device 1 is arcuately tapered to present a support surface which corresponds to the permissable bending angle of the strands S, the angle depending on the diameter of the strands.

Surrounding the strands S is a reducing element 12 of generally frusto-conical formation. The wide end of the element 12 is positioned over the coupling device 1 and the narrow end thereof is arcuately tapered, in the opposite sense to that of the deflector 1 l, to present a surface which corresponds to the permissable bending angle of the strands S. The extreme narrow end of the element 12 corresponds to the size of the main duct of the structure through which the tendon passes. Thus, it will be seen that the assembly is such that the strands S are not subjected to bending at the point where they leave their anchoring fittings 9, or at the points where they enter the main duct. Furthermore, at a position between the aforementioned points, they are bent in two opposite directions to present an S formation to an extent which does not exceed the permissable amount.

The deflector 11 has the particular advantage that it serves to distribute the load transmitted from the strands S back into the previous span of the structure, and the S formation imparted to the strands S has the advantage that it reduces the length of the whole assembly compared with the prior art assemblies, and thus reduces the size of the voids in the structure.

The reducing element 12 is provided with a grout pipe 13 and is preferably formed of a synthetic plastics glass fibre reinforced material. However, and other suitable materials such as metal may be used provided only that the element is sufficiently rigid to withstand the pressure of the concrete which is poured over it to form the structure prior to the tensioning of the strands S.

In building a concrete structure, the first span of the structure, which is partly indicated at 14, terminates at the coupling point in a conventional tube unit 15 which is cast into the concrete, and which is connected by conventional ducting to a further tube unit cast into the concrete at the other end of the structure.

Strands S are then threaded through the ducting, the

bore 5 of the plate 2, and the bores 6 of the bearing plate 4, the opposite ends of the strands being anchored at the other end of the structure. The bearing plate 4 is then temporarily attached to thetube unit 15 by means of bolts (not shown) which are positioned in lugs 16 provided on the plate 2.

The strands S are then tensioned either individually or collectively and anchored in position by the wedge devices 7.

The bolts holding the coupling device are then released and, using the same bolts, a grouting cover is positioned over the projecting ends of the anchored strands to form a sealed cavity around the wedge devices. Grout is then injected into the grout cover and flows, via grout holes (not shown) into the ducting whereby the tendon is grouted in the normal manner. The grout cover is then removed leaving a covering of grout indicated at 17, the coupling device being held in position against the tube unit 15 of the structure with the bearing plate 4 spaced from the structure bythe bearing plate 2.

The construction of the next section of span of the structure, and thus of the tendon, is now commenced. Firstly, the deflector 11 is placed in position. The reducing element is threaded over the. ends of the strands and the anchoring fittings 9 and washers 10 are then applied to one end of each of the strands S. and the other ends of the strands are threaded through the main ducting of said next section or span. The strands complete with the fittings 9 are then placed around the deflector 11 and the fittings 9 are placed in their respective slots to take up the positions shown in the drawings. The strands are held in position by tape or other. binding and the reducing element 12 is then pushed axially towards the anchorage thereby forcing the strands to adopt the S-shaped formation which occurs when the element 12 is in its final position as shown in the drawings.

In the latter respect, the angle of deviation of the strand, or the radii through which the strand bends should be approximately 15 to the horizontal. The

maximum radius that can be utilised, is dependent on the force required to position the reducing element be fore stressing. It will be appreciated that this will be forced axially towards the anchorage and it should be possible for two men to finally position the reducing element with the use of excessive force. On examination it will be noted that different sizes of strand diameter and construction are used in pre-stressed concrete anchorages, because of this, the number of strands in any anchorage will vary and therefore the geometric determination of the angle forming the S configuration must be a compromise between the maximum S configuration, giving maximum reduction in length, and minimum S configuration giving greatest ease of assembly.

With the parts in the aforementioned position, the concrete is poured into the second section of the structure thus covering the element 12 enclosing the coupling device. At a suitable time, the second section of the tendon is tensioned and subsequently grouted in the same manner as that hereinbefore described, the load in this case being taken by the fittings 9 and transmitted by the first section coupling device to the first section of the tendon.

Thus, it will be appreciated that any number of concrete sections or spans can be added on the same principle as that hereinbefore described.

In the modified arrangement shown in FIG. 3, the coupling device 1 is provided as a single block element which is cut away at 18 to receive the deflector 1 l. The block may be solid or it may be formed with a recess as indicated by dot dash lines 19. In other respects, the assembly of this embodiment is constructionally and operationally the same as that described with reference to FIGS. 1 and 2.

Although the deflector 11 has been described as being of cast iron, it will be understood that the invention is not limited in this respect. Thus, the deflector may be of pre-cast concrete or any other material having sufficient strength to withstand the inward radial pressure applied thereto.

1 claim:

1. A coupling assembly for the stressing of multi-span post-tensioned concrete structures, comprising a coupling device having centrally disposed axially extending means for anchoring one end of strands of one section of a stressing tendon in a first direction, and other means formed on and about the periphery of said coupling device for anchoring one end of strands of an adjacent section of said stressing tendon in an opposite direction, a strand deflector operatively associated with said coupling device and extending beyond said coupling device in the same general direction as said strands of said adjacent section of said stressing tendon, said strand deflector extending generally from said other anchoring means and sloping radially inwardly therefrom, and a reducing element fitted over said coupling device adjacent said other anchoring means and extending beyond said coupling device in the same direction as that of said deflector, said deflector having a portion adjacent said coupling device generally corresponding in outline to adjacent portions of said reducing element whereby strands of said adjacent section adapted to lie between and axially of said deflector and said reducing element will be shaped by said deflector and said reducing element.

2. An assembly as claimed in claim 1, in which said deflector is generally in the form of a truncated cone, said deflector having a portion adjacent said coupling device lying substantially parallel with the axis of the assembly and the remainder of said deflector being of convex tapered formation.

3. An assembly as claimed in claim 2, in which said reducing element is generally in the form of a truncated cone, a portion of said reducing element being of concave tapered formation being cooperable with said convex portion of said deflector to react on said strands of said adjacent section to constrain the same to follow an S-shaped path.

4. A coupling assembly for the stressing of multi-span post-tensioned concrete structures, said coupling assembly comprising an annular coupling device having a bore, said device having centrally disposed axially extending anchorage means for anchoring one end of strands of one section of a stressing tendon, and other anchoring means formed on andabout the periphery of said annular coupling device for anchoring one end of strands of an adjacent section of said stressing tendon, a strand deflector of truncated cone shape attached at one end to said coupling device and extending beyond said coupling device in the same general direction as said strands of said adjacent section of said stressing tendon, said deflector having a portion adjacent said coupling device lying substantially parallel with the axis of the assembly and the remainder of said deflector being of convex tapered formation, a reducing element of truncated cone shape fitted at one end over said coupling device and extending beyond said coupling device in the same direction as that of said deflector, said reducing element having a portion of concave tapered formation, strands of said adjacent section being adapted to extend between and axially of said deflector and said reducing element with said convex portion of said deflection and said concave tapered portion of said reducing element being cooperable to reset strands of said adjacent section to constrain the same to follow a generally S-shaped path adjacent said coupling device.

5. An assembly as claimed in claim 4, in which said coupling device comprises a single metal block.

6. An assembly as claimed in claim 4, in which said coupling device comprises an annular bearing plate and a co-acting disc-like bearing plate positioned over the bore of said annular bearing plate.

7. An assembly as claimed in claim 4, in which said centrally disposed anchorage means comprise a plurality of tapered holes formed in said coupling device, said tapered holes being formed to receive said strands and retaining wedges which anchor said strands in said holes.

8. An assembly as claimed in claim 7, in which the said other anchoring means comprise a plurality of circumferentially spaced axially disposed recesses formed in the periphery of said coupling device.

9. An assembly as claimed in claim 8, in which said strands are anchored in said recesses by means of anchoring fittings attached to said strands, said anchoring fittings, in use, lying parallel to the axis of the assembly.

Claims

1. A coupling assembly for the stressing of multi-span posttensioned concrete structures, comprising a coupling device having centrally disposed axially extending means for anchoring one end of strands of one section of a stressing tendon in a first direction, and other means formed on and about the periphery of said coupling device for anchoring one end of strands of an adjacent section of said stressing tendon in an opposite direction, a strand deflector operatively associated with said coupling device and extending beyond said coupling device in the same general direction as said strands of said adjacent section of said stressing tendon, said strand deflector extendIng generally from said other anchoring means and sloping radially inwardly therefrom, and a reducing element fitted over said coupling device adjacent said other anchoring means and extending beyond said coupling device in the same direction as that of said deflector, said deflector having a portion adjacent said coupling device generally corresponding in outline to adjacent portions of said reducing element whereby strands of said adjacent section adapted to lie between and axially of said deflector and said reducing element will be shaped by said deflector and said reducing element.

4. A coupling assembly for the stressing of multi-span post-tensioned concrete structures, said coupling assembly comprising an annular coupling device having a bore, said device having centrally disposed axially extending anchorage means for anchoring one end of strands of one section of a stressing tendon, and other anchoring means formed on and about the periphery of said annular coupling device for anchoring one end of strands of an adjacent section of said stressing tendon, a strand deflector of truncated cone shape attached at one end to said coupling device and extending beyond said coupling device in the same general direction as said strands of said adjacent section of said stressing tendon, said deflector having a portion adjacent said coupling device lying substantially parallel with the axis of the assembly and the remainder of said deflector being of convex tapered formation, a reducing element of truncated cone shape fitted at one end over said coupling device and extending beyond said coupling device in the same direction as that of said deflector, said reducing element having a portion of concave tapered formation, strands of said adjacent section being adapted to extend between and axially of said deflector and said reducing element with said convex portion of said deflection and said concave tapered portion of said reducing element being cooperable to reset strands of said adjacent section to constrain the same to follow a generally S-shaped path adjacent said coupling device.