EP0220113B1 - Prestressing devices for concrete with sinuous stressing cables, and methods for using them - Google Patents

Abstract

The invention relates to the prestressing of a concrete work by means of a relatively long stretched sinuous cable (1) formed by a bundle of several metal strands (2)housed individually in plastic material tubes (3). The different tubes with their strands are positioned without special precautions in a sheath (5) buried in the work then a sufficiently unctuous and fine cement grout (6) is injected into this sheath for filling the spaces in the sheath between the tubes and strands are tensioned individually after solidification of the injected cement grout, by means of relatively light automatically operated actuating cylinders.

Description

The invention relates to devices for prestressing concrete structures using relatively long sinuous tensioned cables constituted by bundles of several metallic strands (wires or strands), bundles which are housed in single-sheaths embedded in the at least part of their length in the concrete structure, especially during its pouring.

It also relates to the methods for implementing these prestressing devices.

It relates more particularly, among these devices and methods, those for which each cable strand is itself contained in a plastic tube with preferably interposition of grease.

It also relates more particularly to the case where the cables considered are intended to withstand high tension forces.

In such a case, it is particularly advantageous to be able to exercise the tensioning of the cables strand by strand.

Such a measure in fact makes it possible to adopt for this tensioning of the cylinders much lighter and less bulky than those necessary to ensure the tensioning in one go, which makes it possible to resort, for the manipulation of these cylinders, to vehicles suitable in particular for automated controls.

To make possible such tension strand by strand, it is necessary that the different tubes remain separated transversely from each other so as to prevent them from rubbing against each other in their positions of mutual contact, which would risk them tear, to put in direct contact the corresponding metal strands and to finally prevent individual tensioning.

As the cable considered is sinuous and not straight, such a transverse separation of the different strands can only be obtained by providing inside the sheath, at least at its elbows, special spacers.

These spacers, generally constituted by ligatures or by molded parts hollowed out by as many housings as strands to be kept apart, are relatively expensive and difficult to set up.

In the French patent n ² 2 511 721 of the applicant, it was proposed to produce a section of curved and highly prestressed cable to connect together two rectilinear portions of a stretched cable, this section itself being constituted by a bundle parallel metal strands arranged as described above.

In other words, the bundle is contained in a sheath itself embedded in a concrete block, each strand is housed in a plastic tube and the different strands are stretched while the tubes are held transversely apart from each other. others according to a provision organized using spacer organs.

In addition, a solidifiable cement mortar is injected into said sheath after the tubes fitted with their cable strands have been placed in it.

In this patent, the sheath is constituted by a tubular metallic section curved according to a relatively short single arc of circle and resistant to axial compression so as to absorb the prestressing tension exerted by the strands between its two ends and it has been proposed, to relieve the metal constituting this tubular section during the application of said prestress, to solidify the cement mortar before the strands are put under tension.

The present invention does not relate to such short and pre-stressed connection sections, but to sinuous and relatively long complete cables for which the transverse arrangement of the various constituent strands does not remain “organized” throughout their extent, but is on the contrary irregular. and messy.

These strands, or more precisely the tubes which contain them, are in fact here introduced into the corresponding long and sinuous sheaths, continuous or discontinuous, in groups or in isolation, without special precautions relating to their mutual spacing, which has the effect of making vary or "disorganize" their mutual transverse arrangement along said sheaths, in particular by bringing all the strands closer to the centers of curvature of the cable in the bent portions of the latter, by crossing some of these strands in a transverse direction, etc.

Under these conditions, the use of preformed spacers is excluded and local contacts of the different tubes with each other are inevitable: or might therefore think that individual tensioning of the strands making up such cables is no longer possible.

However, the Applicant has discovered that such a measure is made possible, despite the length of the cables concerned and the disorder of their component strands, by using altogether as mutual "spacer" of these disordered strands a cement grout injected into the sheath between the tubes, after placing these tubes in this sheath, said grout filling all the gaps between the tubes inside the sheath and being solidified before tensioning the strands.

The grout in question must be sufficiently smooth and fine for this purpose during its injection and it must be solidifiable only at the end of the injection thanks to a sufficiently delayed setting. Such grouts have for example been described in the French patents No. 7,040,367 and No. 8,317,485 of the applicant.

The invention includes, apart from this main arrangement, certain other arrangements which are preferably used at the same time and which will be more explicitly discussed below.

• La figure 1, de ce dessin, montre schématiquement une portion d'un câble de précontrainte sinueux mis en place dans sa gaine, selon l'invention, avant injection du coulis et avant mise sous tension de ses brins.
• La figure 2 montre schématiquement à plus grande échelle une portion du même câble au cours de l'injection du coulis.
• La figure 3 est une couple transversale du câble achevé à une échelle encore plus grande, selon III-III figure 2.

In what follows, a preferred embodiment of the invention will be described with reference to the attached drawing, of course in a non-limiting manner.

• Figure 1, of this drawing, schematically shows a portion of a sinuous prestressing cable placed in its sheath, according to the invention, before injection of the grout and before tensioning of its strands.
• Figure 2 shows schematically on a larger scale a portion of the same cable during the injection of the grout.
• FIG. 3 is a transverse torque of the cable completed on an even larger scale, according to III-III in FIG. 2.

The prestressing cable 1 considered here is composed of a plurality of metal strands 2 (twisted wires or strands) extending substantially parallel so as to form a bundle.

Each strand is housed in a plastic tube 3 with the interposition of grease or any other lubricating product, the lubricating properties of this product may be permanent or limited in time.

The cable in question is intended to subject the prestressing to a concrete structure 4 in which a sheath 5, for example made of polyethylene, is embedded, this sheath having been put in place, with its final shape, in the formwork of the structure before the pouring concrete.

Said shape is sinuous in the sense that it comprises a succession of several curved and / or straight sections, and in particular a series of several sections in opposite directions.

The sheath considered can be continuous or discontinuous and then limited to concrete crossings, the sections of unsheathed cable being straight and outside the concrete.

To ensure the prestressing of structure 4, the procedure is as follows.

Is introduced into the sheath 5, from one of its open ends, the various tubes 3 lined with strands 2 making up the cable 1, and this without any special precautions, which generates in their transverse distribution a certain disorder as well as visible in Figures 1 and 2.

Then a cement grout 6 is sufficiently smooth and fine to be injected into the sheath 5 to fill all of the voids between the tubes 3 inside the sheath 5, said grout being chosen so that its setting is sufficiently delayed for intervene only at the end of full filling.

The injection in question is provided according to arrow C (FIG. 2) through a lumen 7 passing through a suitable cover 8 tightly connected to the relevant end of the sheath 5.

The final setting of the grout has the effect of hardening it by freezing the disorder of the strands 2 - or more precisely the irregular evolution of their transverse distribution along their extent -, in the same state as they were at the end of their installation inside the sheath 5.

After this connection, it is possible to tension each strand 2 in isolation.

In fact, the tubes 3 are then lined all along their extent by the rigid mass of the solidified grout 6 and they are totally blocked by this mass by forming excellent reinforced guides for the sliding of the metal strands against their internal surfaces.

We can even consider that some of the tubes are in mutual contact in pairs at a point or over a certain length: even in this case, the grout is interposed between the two tubes considered on either side of their mutual contact zone by prohibiting their relative movements when the individual strands are energized.

This tensioning of the cable strand by strand is made possible without the use of any preformed spacer, despite the great length and the sinuous layout of the cable.

It is this which makes it possible to carry out prestresses of very high value, thanks to the use of relatively light tension cylinders, compact and therefore easy to handle, in particular using means suitable for automatic commands: in the latter case, the crossing of the cover 8 by the corresponding ends of the cable strands 2 can be organized according to a predetermined regular distribution without however being eliminated the "disorganization" indicated above, which concerns the greatest length of said cable.

As is obvious, and as already follows from the foregoing, the invention is in no way limited to those of its modes of application and embodiments which have been more especially envisaged; on the contrary, it embraces all variants thereof within the limit defined by the claims.

Claims (3)

1. Device for prestressing a concrete work (4) using at least one relatively long stretched sinuous cable (1) formed by a bundle of several metal strands (2), which bundle is housed in a continuous or discontinuous sheath (5) itself buried over at least a part of its length in the concrete work, each cable strand being itself contained in a plastic material tube (3) and the transverse distribution of these tubes being irregular along the cable, characterized in that the different tubes (3) are locked in their relative disordered positions exclusively by means of a solidified cement grout (6) filling the spaces between these tubes on the inside of the sheath (5).

2. Method for using the prestressed device according to claim 1, characterized in that, after having positioned the different tubes (3) comprising strands (2) forming the cable (1) without special precautions in the sheath (5), a cement grout (6) is injected into the sheath, between the tubes, which cement grout is sufficiently unctuous and fine so as to ensure complete filling, said cement grout being solidifiable only at the of injection, then the strands are tensioned individually after solidification of the injected cement grout.

3. Prestressing method according to claim 2, characterized in that, for tensioning the strands (2) in turn, relatively light automatically operated actuating cylinders are used.

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