Improvements In Tensioning Devices

Abstract

Apparatus for tensioning cables embedded in concrete, including fluid actuated units, cable gripping members, jacking means and a de-tensioning assembly permitting to cut off the excess portion of the cable without danger to personel and equipment.

Description

BACKGROUND OF THE INVENTION AND PRIOR ART

The invention relates to tensioning units for tensioning cables in stressed concrete and in more particular to improvements of tensioning units such as described in my U.S. Pat. Nos. 3,184,219 and 3,194,536. In fact the FIGS. 1 to 8 are exact copies of FIGS. 1,2, 8-11 of U.S. Pat. No. 3,194,536 and FIGS. 1,8 of U.S. Pat. No. 3,184,219. They are placed herein solely for purposes of illustrating the prior art.

The tensioning units disclosed in these patents have the general object of "pre-tensioning" or "post-tensioning" cables embedded in concrete blocks or slabs.

This invention is concerned with improvements to apparatus described in the above noted patents. In such apparatus certain problems have been observed involving the safety of the operator, when the excess cable portion is cut off from the tensioned cable portion which is within the concrete block or slab. For example, in a long precasting bed wherein half of the casting bed is used for preparing a slab, the cable outside the slab can be cut off with a torch. However, there is a danger that the cable upon being cut under tension will snap due to the sudden release and perform a whipping and coiling action which may cause injuries to persons engaged in the preparation of concrete blocks. Also, the cut-off cable may be coiled and twisted to a degree that it is unusable and, therefore, wasted.

SUMMARY OF THE INVENTION

A de-tensioning assembly for de-tensioning cables embedded in concrete blocks. The de-tensioning assembly comprises spacer means and a release member, both mounted on the cable. In de-tensioning the cable the spacer means is removed causing the release member to open the cable gripping means and de-tension the excess portion of the cable which may conveniently be cut off from the stressed cable in the concrete.

It is an object of this invention to provide apparatus and method enabling to cut off the excess cable portion without danger of whipping and coiling .

Other objects and advantages of the invention not at this time enumerated, will become readily apparent as the nature of the invention is better understood from the following description and claims, and are illustrated in the accompanying drawings in which:

FIG. 1 is a fragmentary perspective view of a tensioning device operating with one fluid-actuated unit, as described in my U.S. Pat. No. 3,194,536;

FIG. 2 is a top plan view of the tensioning view shown in FIG. 1;

FIG. 3 is an end elevational view of the chuck embodied in the device shown in FIG. 1;

FIG. 4 is a longitudinal sectional view taken substantially along the line 4--4 in FIG. 3;

FIG. 5 is a longitudinal sectional view similar to FIG. 4 but showing certain parts in different operative positions;

FIG. 6 is a transverse sectional view substantially along the line 6--6 in FIG. 4;

FIG. 7 is a fragmentary top plan view of a tensioning device operating with two fluid-actuated units, as described in my U.S. Pat. No. 3,184,219;

FIG. 8 is an enlarged fragmentary sectional view of the unit as shown in FIG. 7;

FIG. 9 is a schematic illustration of a tension system wherein the excess cable strand is torch-cut under tension;

FIG. 10 illustrates a tensioning system wherein the excess cable strand is cut after de-tensioning thereof, according to the invention;

FIG. 11 is a perspective blown up view of the elements of a de-tensioning assembly according to the invention;

FIG. 12 is a side elevational and partly sectional view of the jacking chair and of the de-tensioning assembly placed between the chuck and the casting bed header;

FIG. 13 is a side elevational and partly sectional view of another embodiment of the de-tensioning assembly;

FIGS. 14, 15 are side and front elevational views of a spacer element;

FIGS. 16, 17 are front elevational and sectional views of a release plunger;

FIGS. 18, 19 are front elevational and side views of a jacking chair.

Referring now to the drawings, FIGS. 1 to 6 show a tensioning device 1 including a supporting frame 2 on which is mounted a fluid-actuated unit 3 operatively connected to an elongated cable-gripping member for gripping cables 57, 62 in the form of a chuck 4 for reciprocating the chuck longitudinally of the supporting frame 2. Two cables 57 and 62 are held in chucks 63, 64 outside walls 55, 58.

The fluid-actuated unit 3 includes an elongated cylinder 9 having cylinder heads 10 and 11 mounted on the respective opposite end portions thereof. FIGS. 3 to 6 illustrate the chuck 4 comprising jaws 41, 42, 43, a cap 50 and a spring 75 disposed between jaws and cap. This tensioning device is described in detail in my U.S. Pat. No. 3,194,536.

A somehow differently operating tensioning device 101 is shown in FIGS. 7 and 8 which includes a supporting frame 102 on which two fluid-actuated units 104 and 105 are mounted with an elongated cable gripping member, in the form of a chuck 106 mounted on the frame 102. The chuck 106 in FIG. 7 comprises jaws 139 and 140, the chuck in FIG. 8 includes a spring 160 and jaws 183, 184. All further details are given in my U.S. Pat. No. 3,184,219.

The present invention is not concerned with the aspect of the tensioning but rather with that of de-tensioning operation, including apparatus and method therefor.

The details of structure and operation of tensioning devices are set forth and explained in detail in my above noted U.S. patents and do not concern the present invention.

Therefore, reference may be had to the two mentioned U.S. patents for a disclosure of details not specifically disclosed herein.

The principal concept of this invention may be stated in general terms as follows: In order to avoid the dangers described heretofore, there is a departure from the principle of cutting off the excess cable portion under tension. Expressed otherwise, the invention is based on the idea of cutting off the excess cable only after the cable has been de-tensioned.

To obtain a safe and efficient de-tensioning process the invention provides for a novel de-tensioning assembly 201. The assembly 201 comprises a spacer element 202 and a release plunger 203 which may be disposed over the cable strand 205. A jacking chair 221 may be mounted over the de-tensioning assembly abutting the end of the casting bed 222.

The spacer element 202 is a cylindrically shaped body having a central bore 204 of a size sufficient to embrace a part of the release plunger 203. A longitudinal slot 206 having a width which is slightly larger than the diameter of the central bore 204, is cut along the cylindrical body so that the slot extends from the bore 204 to the periphery of the body.

A grip hook 207 may be welded to the cylindrical body, for a purpose to be explained later.

The release plunger 203 comprises a cylindrical sleeve 208 and a cylindrical flange or disk 209 at one end thereof. A central bore 210 extends through the sleeve 208 having a diameter of a size such the cable strand 205 is loosely embraced by the sleeve 208. The outer diameter of the sleeve 208 is dimensioned so that the spacer element 202 may be conveniently mounted over the sleeve. The sleeve 208 may be integral with the disk 209 or they may be separate members and subsequently joined such as by welding or in any other known manner.

As best seen in FIGS. 11 and 12 the de-tensioning assembly is positioned between chuck 225 and the casting bed 211 of the casting form for concrete.

In operation, the de-tensioning process is performed after the tensioning of the cable has been completed up to a desirable degree of tension, in accordance with the operational details set forth in my two previously noted U.S. patents. The de-tensioning is begun by an additional act of tensioning. This is done by jacking against the jacking chair 221 and tensioning by a very small length of about one sixty-fourth of an inch. This additional tensioning has the effect of setting the spacer element 202 free or loose around the cable strand 205. In the event that the slot 206 of the spacer 202 is directed upwardly, the spacer will drop due to gravity and this causes the release plunger 203 to move against and engage the jaws 212 of a chuck 225 having a cap 226 and a spring 227 which jaws 212 grip the cable strand 205. Once the jaws 212 are thus engaged they open the grip on the cable, as explained in detail in my noted U.S. Patents. Once the jaws release the cable, this portion thereof is de-tensioned and can now be cut without any danger of snapping or coiling.

If the slot 206 of spacer 202 is in a direction other than upwardly, a hook 207 welded onto the spacer permits the manual removal of the spacer which is now loosely seated on the cable strand 205.

This arrangement offers also the advantage that the strand may be left on the cable reel and the tensioned and subsequently de-tensioned length of the strand can be saved and used again. Under the previous practice, the strand had to be cut off the cable reel, and the strand portion used for obtaining the necessary stress was wasted, see FIG. 9, wherein the strand is cut off under tension adjacent the casting form 213. The invention permits cutting the strand behind the form at 215 as seen in FIG. 10, after it has been de-tensioned without danger of coiling up.

A modification of the de-tensioning unit as indicated in FIG. 12 may be used in connection with a tensioning method which is based on the principle of grouting. This de-tensioning unit is illustrated in FIG. 13.

The particulars of grouting are old in the art, and there is, therefore, no need to explain them here.

After the tensioning, the strand is grouted. When the grout has reached sufficient strength, the strand is de-tensioned as described heretofore and the chuck, spacer and release plunger can be reclaimed and used again.

Under this particular method of grouted post-tensioning, it is sufficient (FIG. 5) use a spacer only, as shown in FIG. 13.

The spacer 302 is longer than that used in the previous method in order to facilitate the de-tensioning operation. The bearing plate 315 is embedded in the concrete 319. In front of the bearing plate 315 a void 321 is left which is subsequently filled with cement up to outer edge 320 of the concrete 319, after de-tensioning and removal of chuck and spacer.

A metal sheating 317 enabling the grouting is clamped in position with a wire 316.

A small tube 318 is welded to the bearing plate 315 or pressed tight-fit into a drilled hole.

After removing the chuck 310 the strand 305 is welded to the bearing plate 315 as at 322. Subsequently the void 321 is filled with cement as noted heretofore. The welding constitutes an additional safeguard to that of the grouting.

I have observed that when using a regular strand chuck FIG. 5 with cap 50 and spring 75, it usually takes one fourth of an inch of elongation to seat the jaws 41-43. The spacer 202 will fall out upon the creation of a clearance of one sixty-fourth of an inch between the release plunger 203 and the chuck 225. Therefore, all that has to be done is tensioning the strand to the original load and the spacer will fall out.

It has also been found out that in order to facilitate the release of the jaws, it is advisable to loosen the chuck cap 226 prior to positioning the jacking chair 221 for de-tensioning (FIG. 12).

The release of the jaws may further be made easier by using micro mesh graphite as a chuck releasing agent.

Finally, it is to be noted that when jacking against the jacking chair 221 care has to be taken that the chair legs 231 are positioned in a direction perpendicular to the header 211 of the casting form. Any other position of the jacking chair would create dangerous conditions.

Thus while I have illustrated and described the preferred embodiment of my invention, it is to be understood that it is capable of variation and 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 within the preview of the following claims.

Claims

I claim:

1. An apparatus for tensioning cables, comprising, in combination,

1. a fluid actuated driving unit including,

a. a rear frame assembly

b. a cylinder supported in said frame assembly

c. a piston reciprocable in said cylinder

d. front and rear end cylinder heads on said cylinder, including a front opening in said front end cylinder head,

e. a forwardly extending piston rod attached to said piston and extending through said opening, and

f. means for supplying driving fluid to either end of said cylinder for reciprocably driving said piston and said rod,

2. a front frame and chuck holder assembly including,

a. rigid members forming the sides of said front frame, and disposed across said members and forming the front end portion of said frame,

b. a rigid front plate including a front surface portion for abutting the rear of a chuck disposed on a cable to be tensioned, and for preventing rearward movement of said chuck during tensioning of the cable, while applying a tensioning force to said cable, and

c. a chuck holder attached to said piston rod and reciprocable between said front end plate and said front cylinder head, said chuck holder including a cable receiving slot in the front face thereof, and

3. means for de-tensioning the cable including

a. a spacer element disposed over the cable so as to being capable of surrounding the same

b. a release plunger mounted over the cable, whereby upon removal of the spacer element an excess portion of the cable may be cut off without danger.

2. The apparatus as set forth in claim 1, wherein the spacer element includes a cylindrical body having a central bore and a slot extending from the bore to the periphery of the body and parallel to the axis of the bore.

3. The apparatus as set forth in claim 2 including means integrally connected to the cylindrical body for removing the spacer element from the cable strand.

4. The apparatus as set forth in claim 3, wherein the means for removing the spacer element comprises a hook member.

5. The apparatus as set forth in claim 1 wherein the release plunger includes a cylindrical sleeve and a cylindrical flange integrally connected with the sleeve at one end thereof.

6. The apparatus as set forth in claim 5 wherein a central bore extends through the sleeve, said bore having a diameter such that the sleeve is capable of loosely embracing the cable strand.

7. The apparatus as set forth in claim 8 wherein the outer diameter of the sleeve is of such magnitude that the spacer element may be conveniently mounted over the sleeve.

8. The apparatus as set forth in claim 1, wherein the detensioning means is positioned intermediate the chuck means and the end of the casting bed.

9. A de-tensioning unit for use with apparatus for tensioning a cable strand extending through a casting bed, said apparatus including chuck means for gripping the cable strand, said de-tensioning unit comprising a spacer element disposed over the cable strand so as to being capable of surrounding the strand, and a release plunger mounted over the cable strand, whereby upon removal of the spacer element an excess portion of the cable strand may be cut off without danger.

10. The de-tensioning unit as set forth in claim 9, wherein the spacer element includes a cylindrical body having a central bore and a slot extending from the bore to the periphery of the body and parallel to the axis of the bore.

11. The de-tensioning unit as set forth in claim 10, including means integrally connected to the cylindrical body for removing the spacer element from the cable strand.

12. The de-tensioning unit as set forth in claim 11, wherein the means for removing the spacer element comprises a hook member.

13. The de-tensioning unit as set forth in claim 9, wherein the release plunger includes a cylindrical sleeve and a cylindrical flange integrally connected with the sleeve at one end thereof.

14. The de-tensioning unit as set forth in claim 13, wherein a central bore extends through the sleeve, said bore having a diameter such that the sleeve is capable of loosely embracing the cable strand.

15. The de-tensioning unit as set forth in claim 14, wherein the outer diameter of the sleeve is of such magnitude that the spacer element may be conveniently mounted over the sleeve.

16. The de-tensioning unit as set forth in claim 9, wherein the unit is positioned intermediate the chuck means and the end of the casting bed.