US3755880A - Tensioning devices - Google Patents

Abstract

A method 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

ted

tats ateiiit 1191 Simms Sept. 4, W73

[ TENSHONING DEVICES 3,207,829 9/1965 Nieber 254/29 2,728,978 l/1956 Birkenmair et al 29 452 [76] Invent m w-pattemn 2,761,649 9 1956 W0O|COCk.............. 29 452 Chwago, 60641 3,255,558 6 1966 Middendorfm 29 452 [22] Filed: Oct 21, 1971 3,298,075 1 1967 Shoe 29 452 [21] App]. NO.I 191,246

Related [1.8. Application Data Primary Examiner-Richard J. Herbst Assistant Examiner.l. W. Davie Attorney-Ernest S. Kettelson [57] ABSTRACT A method for tensioning cables embedded in concrete, including fluid actuated units, cabfle 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.

8 Claims, 19 Drawing Figures Patentgd Sept. 4, 1973 5 Sheets-Sheet l Patented Sept. 4, 1973 3,755,880

5 Sheets-Sheet 2 Patented Sept. 4, 1973 3,755,880

5 Sheets-Sheet I5 Patented Sept. 4, 1973 5 Sheets-Sheet 4 Patented Sept. 4, 1973 5 Sheets-Sheet 5 U 5/ ,223/ K I: I Imp III I 6 'II II I E 1 TENSIONING DEVItIIIS This is a divisional application to my patent application Ser. No. 861,364 filed Sept. 26, 1969, now U.S. Pat. No. 3,703,030 for IMPROVEMENTS IN TEN SIONING DEVICES.

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-II of U.S. PatJNo. 3,194,536 and FIGS. 11,8 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 posttensioning 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 out 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 cabel may be coiled and twisted to a degree that it is unusable and, therefore, wasted.

A method for tensioning cables using a de-tensioning assembly for de-tensioning the cables embedded in concrete blocks. The detensioning 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 a 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. I 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 device shown in FIG. I;

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 sown in FIG. 7;

FIG. 9 is a schematic ilustration 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. II 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 the drawings. FIGS. 1 to 6 show a tensioning device I including a supporting frame 2 on which is mounted a fluid-actuated unit 3 operatively connected to an elongated cable-gripping member for griping 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 II mounted on the respective opposite end portions thereof. FIGS. 3 to 6 illustrate the chuck 4 comprising jaws 41,42,414, a cap 50 and a spring 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 1101 is shown in FIGS. 7 and 8 which includes a supporting frame 1162 on which two fluid-actuated units 1104 and I are mounted with an elongated cable gripping member, in the form of a chuck I96 mounted on the frame I022. The chuck W6 in FIG.7 comprises jaws I39 and I60, the chuck in FIG. 8 includes a spring and jaws I83, 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 detensioning 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, referencemay be had to the two men tioned 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 detensioned.

To obtain a safe and efficient de-tensioning method the invention is described as using a de-tensioning assembly 201, although other de-tensioning assemblies may be used. 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 that 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 tie-tensioning as sembly is positioned between chuck 225 and the casting bed 211 of the casting from for concrete.

In operation, the de-tensioing 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 US. Patents. The de-tensioning is begun by an additional act of tensioning. This may be done by jacking against the jacking chair 221 and tensioning by a very small lnegth 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 the 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 US. 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 srand behind the form at 215 as seen in F1610, 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 F1G.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 detensioned as described heretofore and the chuck,

spacer and release plunger can be reclaimed and used again.

Under this particular method grouted posttensioning, it is sufficient to use a spacer only, as shown in FlG.l3.

The spacer 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.

l have observed that when using a regular strand chuck (F) 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 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.

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 angle of the jacking chair would create dangerous conditions.

Thus while 1 have illustrated and described the preferred embodiment of my invention, it is to be understood that it is capable of variation and modification and 1, therefore, do not wish to be limited to the precise details set forth.

1 claim:

1. A method of tensioning a cable strand extending through a casting bed of any length, using a driving unit, chuck means including a cap and jaws for gripping the cable strand, a jacking chair, and de-tensioning means including a spacer element and a release plunger, wherein the same spacer element and release plunger may be used for any length of casting bed, said method comprising the steps of mounting the spacer element upon the release plunger and placing both intermediate the chuck means and the end wall of the casting bed, and jacking the fluid actuated driving unit against the jacking chair for tensioning the cable to a desired degree.

2. The method as set forth in claim ll, including the steps of a further slight tensioning of the cable whereby the spacer is rendered loose and may be removed.

3. The method as set forth in claim 2, including the step of removing the spacer, whereby the release plunger is removed towards the chuck means cuasing it to release the strand, such that the strand may be cut without danger of snapping or coiling.

4. The method as set forth in claim 3, wherein the further slight tensioning of the cable is done to the original degree of tension.

5. The method as set forth in claim 4, including the step of loosening the chuck cap prior to positioning the jacking chair.

6. The method as set forth in claim 5, including the step of applying micro mesh graphite as a chuck releasing agent.

7. A method of tensioning a cable strand extending through a casting bed using a driving unit, chuck means including a cap and jaws for gripping the cable strand, a jacking chair, and de-tensioning means including a spacer element and a release plunger, said method comprising the steps of providing a metal sheath tubing around the cable strand within the casting bed, inserting a small tube into the metal tubing with the end of the small tube slightly protruding from the metal tubing, clamping the metal tubing over the small tube as by a wire ring, positioning a bearing plate in a void at the end of the bed perpendicular to the small tube and joining the plate to the tube as by welding, placing the spacer element over the cable strand in front of the bearing plate, mounting the chuck means over the cable strand in front of the spacer element, tensioning the cable strand, grouting within the metal sheath tubing, tensioning the cable strand additionally, removing the chuck means and the spacer element, and filling the void with cement.

8. The method as set forth in claim 7, including the step of welding the cable strand to the bearing plate subsequent to removal of the chuck means and the spacer element and prior to filling the void with ce-

Claims (8)

1. A method of tensioning a cable strand extending through a casting bed of any length, using a driving unit, chuck means including a cap and jaws for gripping the cable strand, a jacking chair, and de-tensioning means including a spacer element and a release plunger, wherein the same spacer element and release plunger may be used for any length of casting bed, said method comprising the steps of mounting the spacer element upon the release plunger and placing both intermediate the chuck means and the end wall of the casting bed, and jacking the fluid actuated driving unit against the jacking chair for tensioning the cable to a desired degree.

2. The method as set forth in claim 1, including the steps of a further slight tensioning of the cable whereby the spacer is rendered loose and may be removed.

3. The method as set forth in claim 2, including the step of removing the spacer, whereby the release plunger is removed towards the chuck means cuasing it to release the strand, such that the strand may be cut without danger of snapping or coiling.

4. The method as set forth in claim 3, wherein the further slight tensioning of the cable is done to the original degree of tension.

5. The method as set forth in claim 4, including the step of loosening the chuck cap prior to positioning the jacking chair.

6. The method as set forth in claim 5, including the step of applying micro mesh graphite as a chuck releasing agent.

7. A method of tensioning a cable strand extending through a casting bed using a driving unit, chuck means including a cap and jaws for gripping the cable strand, a jacking chair, and de-tensioning means including a spacer element and a release plunger, said method comprising the steps of providing a metal sheath tubing around the cable strand within the casting bed, inserting a small tube into the metal tubing with the end of the small tube slightly protruding from the metal tubing, clamping the metal tubing over the small tube as by a wire ring, positioning a bearing plate in a void at the end of the bed perpendicular to the small tube and joining the plate to the tube as by welding, placing the spacer element over the cable strand in front of the bearing plate, mounting the chuck means over the cable strand in front of the spacer element, tensioning the cable strand, grouting within the metal sheath tubing, tensioning the cable strand additionally, removing the chuck means and the spacer element, and filling the void with cement.

8. The method as set forth in claim 7, including the step of welding the cable strand to the bearing plate subsequent to removal of the chuck means and the spacer element and prior to filLing the void with cement.

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