EP0220113A1 - Prestressing devices for concrete with sinuous stressing cables, and methods for using them - Google Patents

Abstract

This involves prestressing a concrete structure using at least one relatively long sinuous stretched cable (1) consisting of a bundle of several metal strands (2) housed individually in these plastic tubes (3 ). The various tubes filled with their strands are put in place without special precautions in a sheath (5) embedded in the structure, then a cement grout (6) sufficiently smooth and fine is injected into this sheath to fill the voids included. in the sheath between the tubes and the strands are individually tensioned after solidification of the grout injected, using relatively light cylinders handled automatically.

Description

• dans l'ouvrage en béton, notamment au cours de son coulage. Elle vise également les procédés pour mettre
• en oeuvre ces dispositifs de précontrainte. Elle concerne plus particulièrement, parmi

ces dispositifs et procédés, ceux pour lesquels chaque brin de câble est lui-même contenu dans un tube en matière plastique avec de préférence interposition de graisse.The invention relates to prestressing devices for concrete structures using relatively long sinuous tensioned cables constituted by bundles of several metal strands (wires or strands), bundles which are housed in sheaths themselves embedded in at least one part of their length

• in the concrete structure, especially during its pouring. It also covers the processes for putting
• using 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 common machines suitable in particular for automated controls.

rour make possible such a 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 tearing them apart, bringing the corresponding metal strands into direct contact and ultimately preventing them individual tensioning.

As the cable considered is sinuous and not straight, such a transverse spacing 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 ° 2,511,721 of the applicant, it has been proposed to produce a section of curved and highly prestressed cable to connect together two straight portions of a stretched cable, this section itself being constituted by a bundle of 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 in a relatively short single arc of arc 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 putting the strands under tension.

The present invention does not relate to such short and prestressed 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: one 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. 70 40367 and No. 83 17485 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 coupe transversale du câble achevé à une échelle encore plus grande, selon III-III figure 2.
• Le câble de précontrainte 1 ici considéré est composé d'une pluralité de brins métalliques 2 (fils ou torons torsadés) s'étendant sensiblement parallèlement de façon à former un faisceau.

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.
• Figure 3 is a cross section of the completed cable on an even larger scale, according to III-III Figure 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 that it comprises a succession of several curved sections and / or rectilinear, and in particular a series of several sections curved 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 concerned 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 sliding 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 achieve 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 controls: 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 its variants.

Claims (3)

1. Device for prestressing a concrete structure (4) using at least one relatively long sinuous tensioned cable (1) constituted by a bundle of several metallic strands (2), a bundle which is housed in a sheath (5) continuous or discontinuous itself embedded in at least part of its length in the concrete structure, each. cable strand itself being contained in a plastic 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 positions disordered to the using only a solidified cement grout (6) filling the voids between these tubes inside the sheath (5). 2. Method for implementing the prestressing device according to claim 1, characterized in that, after having put in place without special precautions in the sheath (5) the various tubes (3) furnished with strands (2) making up the cable (1), a grout of cement (6) sufficiently smooth and thin to ensure complete filling is injected into the sheath between the tubes (6), said grout being solidifiable only at the end of the injection, then the strands are placed individually under tension after solidification of the injected grout. 3. Prestressing method according to claim 2, characterized in that, in order to tension the strands (2) in turn, use is made of relatively light jacks which are handled automatically.

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