US2763464A - Apparatus for anchorage of concrete reinforcements - Google Patents

Description

Emma mi, 1956 F. LEONHARDT 2,763,454

APPARATUS FOR ANCHORAGE OF CONCRETE REINFORCEMENTS Filed July 24, 1955 s Sheets-Sheet '1 MIDI- JNVENTOR.

Fritz Leonhard? ATTORNEY t. 1956 F. LEONHARDT ,763,4%

APPARATUS FOR ANCHORAGE 0F CONCRETE REINFORCEMENTS Filed. July 24, 1955 3 Sheets-Sheet 2 60 INVENTOR.

Fritz Leonhard? BY USJLM' X A TTORNE Y F. LEONHARDT APPARATUS FOR ANCHORAGE OF CONCRETE REINFORCEMENTS Filed July 24, 1953 5 Sheets-Sheet 3 i l\ i I INVENTOR.

Fritz Leonhclrdt JITTORNEY APPARATUS FOR ANCHORAGE OF CONCRETE REINFORCEMENTS Fritz Leonhardt, Stuttgart, Germany Application July 24, 1953, Serial No. 369,981 Claims priority, application Germany July 26, 1952 2 Claims. (Cl. 254-29) This invention refers to a method for the anchorage of prestressed concrete reinforcements by means of separate wedges in an anchorage body and to arrangements and a jack for the execution of this method.

A method has been known to anchor prestressed concrete reinforcements, e. g. wires or bars with threads in the structure by means of nailheads, loops or wedges. For the wedge anchorages known to date, two or more wires are spread at the anchorage point and a wedge is pushed between them so that the reinforcing elements are pressed against the cylindrical surface of the opening in the anchorage plate by means of the wedge. By one known method, 12 and more wires are pressed with an inner wedge against the cone shaped inner surface of the anchorage block which is contoured transversely to the direction of prestressing. By doing this, the necessary bending is constantly displaced hence the wires are twice subject to permanent deformation. Prestressing force of the individual wire is transferred only along a contact line at the cone shaped inside surface of the anchorage block. The aiiixed wire must therefore be relatively long. In spite of this, with this construction method the stressing wires are subject to a certain amount of slippage after releasing the jacks before they are permanently seated.

Recently, it has also been learned to retain several reinforcing elements by means of wedges acting from outside towards inside, i. e. against an intermediate bearing body.

It is therefore an object of this invention to provide a jack for anchoring prestressing wires and rods to avoid the aforementioned difficulties. t

It is an object to provide especially an anchorage means for reinforcing rods avoiding the necessity for threading the rods or otherwise specially preparing them for retaining their stress.

It is a further object to provide an anchorage means for reinforcing rods without effecting a deformation of the rods.

These and other objects will become apparent in the remainder of this specification.

This invention consists of the following: Reinforcements in concrete are stressed by means of an apparatus resting on either the structure itself or an anchorage plate arranged thereon and the bearing pressure is then transferred by means of a transfer valve to wedges gripping the prestressed reinforcement on the outside with outer wedges. There is attained the advantage in one embodiment of pulling the outer wedges and the reinforcing elements together without relative motion into a conical opening in the bearing plate and locking them therein. Reinforcing elements may be guided in this way through the opening in the anchorage plate in a straight line so that they are not subject to permanent deformation or bending at this point. If the reinforcement consists of several similar elements, for instance wires or bars, the reinforcing elements are pressed towards one another from the outside towards the inside leaving open a central hole.

For execution of the invention, a jack is used which is States Patent ice 2 equipped in such a manner that during stressing the bearing force acts on the anchorage body and afterwards is transferred to the jaw wedges.

Such a jaw may be arranged in many ways, for instance, so that a hydraulic element supplying reaction force against the prestressing tension is seated on a compound hydraulic ram and is equipped in such a way that when the cylinders are emptied, it acts to seat the wedges. Also it may be arranged so that the part exerting the reaction directly against the stressing force rests on another mechanism, which may be released by bolting it, transferring the prestressing force from the bearing plate to the tops of the wedges, causing them to seat firmly.

For practical reasons, the wedges are in such relation to the reinforcing elements that between them and the reinforcing elements there is circumferential contact. This permits the assembly to use shorter wedges as compared to the case of linear contact. Therefore, the wedges are lying outside of the reinforcement wire or bar group in contradistinction to the inner wedges of the known anchorage methods. Under pressure from the outer wedges, the individual elements support each other.

It is advantageous to increase the gripping power to contour the inner surfaces of the wedge. The contours do not have to have sharp edges, but they may be for instance corrugated. Since there is no relative motion between the reinforcing elements and the wedges, the deformations, teeth, ribs or other contours grip into the material of the reinforcing elements without weakening them.

Further characteristics appear from the following description of the drawings, it being understood that these are illustrative embodiments which should not be deemed limiting, the limits being determined by the appended claims.

Fig. 1 is a schematic representation of a jack double acting to carry out this invention.

Fig. 2 is a cross section through section 2-2 of Fig. 1 showing an outer wedge in circular form.

Fig. 3 is a cross section through section 3-3 of Fig. 1 showing the outer wedge in rectangular form.

Fig. 4 is a cross section through section 44 of Fig. 1 showing a round lower wedge.

Fig. 5 is a cross section through section 5-5 of Fig. 1 showing a rectangular wedge.

Fig. 6 is a cross section showing the lower wedge locked position.

Fig. 7 is a cross section of another embodiment of anchoring plate.

Fig. 8 is a cross section of a mechanical embodiment of a jack.

In the example in Fig. 1, steel anchor plate 62 is inserted into the concrete structure which shows an opening for the wire or rod bundle 34. The concrete structure can be any of the structures known to the art that can be reinforced by prestressed wires or rods. Stressing rods 34 pass straight through opening 61 without bending. Above the opening 61 the stressing rod (or rods) is surrounded by outer wedges 52. A hydraulic jack 10 is set on the anchorage plate 62. A ring-like piston element part 36 is placed on the circular basic element 42 of the jack resting on anchorage plate 62. Between parts 36 and 42 circular chamber 48 is formed presenting a hydraulic cushion. The chamber is sealed to the outside by gasket 44. Inside the chamber, springs 46 are arranged, which hold apart parts 36 and 42. Circular chamber 48 is connected by pipe 54, pressure gauge 56 and valve 53 to an external chamber (not shown) for holding a small supply of hydraulic fluid with means for forcing the hydraulic fluid into chamber 48 under pressure. On ring piston 36 there is a ring cylinder 12, which forms in relation to ring piston 36 a pressure chamber 20, inasmuch as hydraulic fluid may be forced in by way of channel 24, controlled by valve 28 and pressure gauge 26 and means for forcing the hydraulic fluid into chamber 20 under pressure. Ring piston 36 and ring cylinder 12 are sealed towards each other by gaskets 22. The intermediate piece 18 of the ring cylinder 12 is provided with a borehole which has a conically widening part 30 and through which the stressing rods 34 pass in line with the anchorage opening 61. Within the conical parts 30 of the opening the stressing rods are surrounded by pinch wedges 32.

If a hydraulic fluid is admitted under pressure through pipe 24, this tries to press the ring cylinder 12 in Fig. 1 upwards. Thus the wedges 32 are pushed towards the stressing rods 34 and the latter are pushed towards one another so that the stressing rods are stressed when more liquid is forced in which make them elongate elastically. The elongation is increased over and beyond the amount necessary for the working stress to the extent that a small movement backwards of the ring piston 36 for attaining the gripping of the stressing wires in or on the anchorage plate 62 is possible without the stress decreasing beneath the required measure. During the stressing the ring piston 36 rests on the liquid containing cushion formed in chamber 48. The valve 58 is closed. Prior to stressing the valve 58 was opened long enough for the ring piston to sit on the wedges 52. If the valve 58 is now opened so that the hydraulic fluid may flow into the storage chamher (not shown) the pressure force in chamber 20 acts through ring piston 36 onto outer wedge 50 so that it is forced down over inner wedge 52 causing the latter to be anchored firmly to the rods 34. Figure 6 shows the wedges in locked position. Thereafter the pressure liquid supply is released at valve 28 so that the stressing wedges 32 may be removed. Then the jack may be lifted from the anchorage plate 62. The springs 46 force the parts 42 and 36 apart again when the jack is removed as soon as the valve is opened again, this movement being limited to such degree that ring piston 42 cannot be completely pushed out from ring piston 36.

The outer wedges surrounding the stressing elements, i. e. both wedges 52 as well as wedges 32 may have the greater cross section represented by ribs or corrugations which under pressure are impressed into the reinforcing elements they grip.

It is possible to guide the stressing elements individually through separate openings in the anchorage plate. In this case every prestressing element is surrounded by its own outer wedge which could be a conical casing slit on one side. However, several wedges may also be placed around the individual elements.

Figure 3 shows an alternative embodiment for upper Wedges 32 in which rectangular wedges 32c and 32d are used.

The lower wedges 52 may also be rectangular as shown by wedges 52c and 52d in Figure 5.

With the example in Fig. 1 it is assumed that anchor plate 62 ended with the outside surface of the structure 60. However, it is also known that the anchor plates may be sunk in the structure 60 and to cover it with concrete as shown in Fig. 7. The anchorage method which is the subject of the invention may also be used advantageously with a covered anchor plate.

The jack in Fig. 8 is formed in the same manner as Fig. l inasmuch as it can rest, if so chosen, on either the anchorage body or on the clamp wedges. Also here the load is so transferred that the clamping wedges are seated by the stressing force when the counterforce supporting the jack is transferred from the anchorage body to the wedges after stressing. While, however, with jack in Fig. 1 the jack element supplying the supporting force against the stressing for pressure was resting on a hydraulic element, in construction method according to Fig. 8 the corresponding jack part rests on de-boltable apparatus, for instance on a secured and releasable steep spiral and is formed in such a manner that it seats the clamping wedges if this support is released.

The inside part 121 of the section 117 has at the lower end spiral 147 on which a stressing head 146 is screwed on. The conical inner bore hole of this stressing piece contains the stressing wedges 124 which are retained at the cone enclosure surface by a pressure spring 148 which is inserted between the inner parts 121 and the wedges.

The ring piston 19 rests on an inner ring 149 which is retained on an anchorage ring 150. The inner ring 149 is screwed onto anchorage ring 150 by means of a steep multi-thread spiral, preferably trapezoidal spiral. The pitch is so great that there is no excessive friction. Ring piston 19 has at its lower part spiral 152 which is selflocking and to which a safety ring 153 is screwed, and resting on anchorage 150 which prevents the ring piston 19 with inner ring 149 from slipping downward on spiral 151 inside the anchorage ring 150 when fluid pressure is pumped into the pressure chamber 118 between ring pisten 19 and ring piston 117. There are one or more wedges set into the opening provided in anchorage plate 262 the thickness of which wedges increase in the example in the drawing and forms a flange 145. If the retaining ring 153 is screwed up ring piston 19, the pressure in chamber 118 due to the tension in the reinforcing elements will cause the member 149 to travel downwards in the spiral guides 151 until piece 149 rests on the flange 145 of the wedges 160.

This force causes the wedges 160 to seat and grip the reinforcing elements 34. Thereafter the stressing wedges 124 may be released in the same manner as has been described for the wedges of the jack in Figure 1. The bearing area of the ring piston 19 with the inner ring 149 is formed in such a manner that a turning movement between these two parts remains possible without the ring piston 117 turning also. If necessary, a roller bearing may be placed between these two parts. Otherwise, the dimensions have to be so chosen that the lowering movement to clamp the wedges 160 does not release more than a minor part of the stress in the reinforcing elements 34.

The back surfaces at the outer wedges do not necessarily have to be carefully finished to reduce friction.

In addition to the type wedges shown, any other suitable wedges may be used. The bearing plate may have, for instance, a conical opening similar to opening 30 in Figure 1, and a wedge similar to that shown as 32 in Figure 1 may be used. The wedge 32 shown in Figure 1 may be substituted by a wedge combination 5052, with wedge 52 being seated by a hammer, etc.

I claim:

1. A jack of the class described comprising a cylinder and a piston coacting therewith, a hydraulic chamber between them for forcing them apart, said chamber connected to a source of hydraulic fluid and means for forcing the hydraulic fluid into the chamber under pressure, a bore hole in the cylinder for passing therethrough material to be jacked, means for securing such material to the cylinder, a retractable ring mounted in the piston and of length suflicient to project therefrom and act as a bearing surface for the piston, means for holding the ring in an extended position, means for permitting retraction of the ring into the piston and a receptacle in the piston adjacent the retractable ring and surrounding the bore hole for holding and seating a wedge around the material to be jacked.

2. A jack of the class described comprising a cylinder and a piston coacting therewith, a hydraulic chamber be tween them for forcing them apart, said chamber connected to a source of hydraulic fluid and means for forcing the hydraulic fluid into the chamber under pressure, a borehole in the cylinder for passing therethrough material to be jacked, means for securing such material to the cylinder, a retractable ring mounted in the piston and of length sufl icient to project therefrom and act as a bearing surface for the piston, a hydraulic chamber between the piston and the ring, a container for hydraulic fluid connected to the chamber, a spring for holding the ring in an extended position and a receptacle in the piston adjacent the retractable ring and surrounding the bore hole for holding and seating a Wedge around the material to be jacked.

References Cited in the file of this patent UNITED STATES PATENTS 1,312,009 Thrift Aug. 5, 1919

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