EP0128098B1 - Methods and devices for prestressing concrete and similar structures - Google Patents

Abstract

The invention relates to a concrete work prestressed by means of tensioned reinforcements (7) having bell shaped ends (71) and formed from an alternate succession of first sections housed, with interposition of an injected cement, in metal sheaths (9) themselves embedded in the concrete and rectilinear sections outside the concrete. For easy replacement of these reinforcements, the first sections have a rectilinear or curved shape of an arc of a circle and they are housed in plastic material tubes (10) adapted to slide against the metal, the tube ends situated at the level of the bell mouthed reinforcement ends (71) being themselves given the shape of open mouthed sleeves (11) made from plastic material.

Description

The invention relates to methods and devices for prestressing concrete structures using tensile reinforcement and contained, at least in part, in sheaths themselves embedded in these structures.

• - où les armatures en question sont contituées par des faisceaux de fils ou torons logés dans leurs gaines avec remplissage intermédiaire, notamment par un coulis de ciment injecté, l'ancrage des fils ou torons d'un tel faisceau à chacune de ses extrémités se traduisant par un évasement tronconique de cette extrémité,
• - et où les ouvrages considérés sont alvéolés, c'est-à-dire constitués par des blocs de béton prenant appui les uns contre les autres, selon la direction d'application de la précontrainte, par l'intermédiaire d'éléments d'entretoisement faisant généralement corps avec ces blocs et ménageant des alvéoles entre ceux-ci, les armatures traversant alors successivement lesdits blocs et lesdits alvéoles et présentant dans ces alvéoles des tronçons à l'air libre, c'est-à-dire extérieurs au béton.

It specifically targets the case:

• - where the reinforcements in question are formed by bundles of wires or strands housed in their sheaths with intermediate filling, in particular by a grout of injected cement, the anchoring of the wires or strands of such a bundle at each of its ends being reflected by a frustoconical flare of this end,
• - And where the considered works are honeycombed, that is to say constituted by concrete blocks bearing against each other, according to the direction of application of the prestressing, by means of bracing elements generally forming a body with these blocks and providing cells therebetween, the reinforcements then successively passing through said blocks and said cells and having in these cells sections in the open air, that is to say outside the concrete.

To rejuvenate or reinforce at least temporarily such structures, it sometimes happens that one wishes to replace at least some of their prestressing reinforcements with new reinforcements.

This is in particular the case when these reinforcements have undergone local deterioration and / or when it is wished to entrust to the works considered new missions leading to higher stresses, such as during the reinforcement of a bridge intended to support at least temporary overloads or when building is raised.

With the embodiments generally adopted for the sheaths and frames considered, such a replacement is not possible.

The object of the invention is, above all, to make such replacements possible.

To this end, the prestressed concrete structures according to the invention are essentially characterized in that the mean lines of the sections, of their prestressing reinforcements, which are housed in masses of concrete are all straight or in an arc of a circle and in that, at least throughout said sections, each of said reinforcements is housed, with its filling material, in a plastic tube suitable for sliding against the metal, the two ends of this tube preferably being connected to two sleeves flared plastic material respectively surrounding the two corresponding frame ends, sleeves dimensioned and arranged in such a way, relative to the anchoring members of the frame, that they can be released axially through these members.

To form a concrete structure fitted with prestressing reinforcements in accordance with the preceding paragraph, the metal sheath sections intended to receive the reinforcements and to be embedded in the concrete are put into formwork before the concrete is poured. being carried out in such a way that the mean line of each of these sections extends in a straight line or in an arc of a circle and that the consecutive ends of these various mean lines are aligned two by two, then each tube is threaded in plastic material, optionally lined with its reinforcement in advance, successively in the various sheath sections which correspond to it, before or after pouring concrete around these sheath sections.

As regards the ends of the reinforcements, the procedure is advantageously as follows: each end section of sheath is interrupted, on the side of the corresponding reinforcement end, a little below this end and we put in formwork , before pouring the concrete, on the one hand the anchoring member intended to serve as a support for said reinforcing end and on the other hand a frustoconical connection capable of establishing at least temporarily the continuity between the interrupted end of the sheath and said anchoring member, after which the concrete is poured, then the connector is released axially, if it is removable: in this case, in all cases, it is reserved inside the mass of concrete casting, between the interrupted sheath end and the anchoring member, a frustoconical housing suitable for receiving one of the flared sleeves above.

• - le raccord tronconique est amovible et constitué par un bouchon au moins délimité latéralement par une paroi annulaire en caoutchouc ou matériau analogue propre à être gonflée radialement par sa compression axiale et à assurer ainsi une liaison étanche entre les deux sièges annulaires à réunir,
• - la paroi annulaire selon l'alinéa précédent est montée jointivement autour d'un mandrin tubulaire rigide axialement plus court que lui et sa compression axiale est assurée par vissage d'un écrou extérieur sur un tirant fileté traversant axialement deux plaques d'extrémité transversales qui prennent appui respectivement sur les deux extrémités de ladite paroi,
• - l'une des plaques transversales selon l'alinéa précédent prend appui axialement en outre sur la face extérieure de l'organe d'ancrage.

In special embodiments, use is also made of one and / or the other of the following provisions:

• the frustoconical connection is removable and constituted by a plug at least delimited laterally by an annular wall of rubber or similar material capable of being inflated radially by its axial compression and thus ensuring a tight connection between the two annular seats to be joined,
• - The annular wall according to the preceding paragraph is joined together around a rigid tubular mandrel axially shorter than it and its axial compression is ensured by screwing an external nut on a threaded tie rod passing axially through two transverse end plates which bear respectively on the two ends of said wall,
• - One of the transverse plates according to the preceding paragraph is also supported axially on the outer face of the anchoring member.

To remove an improved reinforcement as indicated above for replacement, this reinforcement is cut in at least one of its exposed areas outside the concrete so as to be able to extract axially all of the reinforcement sections thus cut which remain housed in the concrete, then these different axial extractions are carried out, the end sections being extracted with their flared ends at the head.

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

• La figure 1, de ce dessin, montre en coupe verticale longitudinale une travée de pont alvéolée en béton équipée d'une armature de précontrainte conforme à l'invention.
• La figure 2 montre semblablement la même travée au cours du démontage de ladite armature.
• La figure 3 montre en coupe axiale une extrémité d'une telle armature mise en place et sous tension à une extrémité de la travée en béton.
• La figure 4 montre selon une coupe axiale semblable à celle de la figure 3 l'une des phases de la fabrication de ladite extrémité d'armature.

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.

• FIG. 1, of this drawing, shows in longitudinal vertical section a honeycombed concrete bridge span equipped with a prestressing reinforcement according to the invention.
• Figure 2 similarly shows the same span during the disassembly of said frame.
• Figure 3 shows in axial section one end of such a reinforcement in place and under tension at one end of the concrete span.
• Figure 4 shows in an axial section similar to that of Figure 3 one of the phases of the manufacture of said armature end.

The concrete structure which it is desired to subject, in accordance with the invention, to an "interchangeable prestress" is honeycombed, that is to say composed of masses or blocks 1, 2, 3 of concrete resting on one against the others by means of webs or bracing slabs 4, 5, which reserves between the blocks of the cells 6.

In the embodiment illustrated in FIGS. 1 and 2, the structure in question is a bridge span constructed in any desirable manner, for example poured on site or in progress, or even prefabricated by elements.

To subject this span to prestressing, in a manner known per se, reinforcements 7 are made up of multiple wires or strands 8 (FIG. 3) and stretched between their ends A and B at the level of anchoring members each bearing on one of blocks 1, 2, 3.

Each frame comprises an alternating succession of first sections crossing the blocks 1, 2, 3 in metal sheaths themselves embedded in these blocks, and second rectilinear sections outside the concrete, extending between said blocks.

But whereas, in known embodiments, at least some of the average lines of the first reinforcement sections had variable curvatures along these sections, - which made it impossible to move axially these sections after mounting - said average lines, according to a first characteristic of the invention, all extend according to an arc of a circle or along a straight line segment and the same is true for metal sheaths, the formwork for which, before pouring concrete, must be specially planned accordingly.

These metal sheaths 9 must be smooth, as illustrated in FIGS. 3 and 4.

Each end 7 of frame 7 takes, when it is under tension, a flared shape in a truncated cone.

After this tensioning, in the known embodiments, the volumes inside the metal sheaths which are not occupied by the reinforcements were filled with a grout of injected cement.

When set, this grout adhered to the inner face of the metal sheaths 9: this is a second reason why, after said setting, it is no longer possible to extract axially the reinforcements from their sheaths.

To make such extraction possible, according to a second characteristic of the present invention, each armature is housed end to end in a tube 10 made of a plastic material capable of sliding along the metal sheaths 9, the ends of this tube ending by open sleeves 11 (fig. 3) at the flared ends of the frame.

These sleeves 11 are dimensioned and mounted so as to be able to be released axially through the corresponding anchoring members 12.

They are tightly connected vis-à-vis the injection grout both to said anchoring members, by crushing an O-ring 26, and to the tube 10 which they extend, in particular by mutual joint fitting.

The plastic material constituting the tubes 10 and sleeves 11 is advantageously polyethylene but could be any other sufficiently economical plastic material, not adhering to metal and concrete and capable of forming continuous and tight envelopes.

To mount such a frame, proceed as follows.

Before pouring the concrete, the various sections of metal sheath 9 are placed in the formwork intended to receive the concrete, sections the mean lines of which extend in straight lines or in arcs of a circle.

The ends C (fi ^g. 1) of these sheath sections 9 are provided, which do not correspond to the ends of the reinforcements, so that they protrude slightly beyond the corresponding concrete blocks after casting those -this.

On the contrary, the ends D (fig. 3 and 4) of said sheath sections 9 are interrupted, corresponding to the reinforcing ends, a little below the corresponding orifices of the concrete blocks to be manufactured.

Then the corresponding anchoring members 12 are put in place, which are constituted in particular by cast iron or steel plates hollowed out from a central orifice 13.

The diameter of this orifice 13, greater than that of the sheath 9, is determined as a function of the flared end of the armature 7 ₁ to be received, the end comprising in particular a plurality of frustoconical split jaws 14 (fig. 3) each enclosing a end of wire or strand 8 and each received in a complementary housing of an anchoring head 15, the periphery of which bears on the member 12.

To reserve, during the pouring of the concrete, a frustoconical housing between the orifice 13 and the interrupted end D of the sheath 9 located near this orifice, these two annular seats 13 and D can be brought together using 'a frustoconical connection in sheet metal shown in Figure 3 by the broken lines 27, the various linear assemblies being executed in a sealed manner to the poured concrete, in particular by continuous welding or by spot welding and covering with a flexible flexible strip adhesive or retractable.

According to the variant illustrated in FIG. 4, to reserve the frustoconical housing above, a plug 16 with frustoconical outer surface is temporarily installed between the two annular seats 13 and D.

To ensure a suitable seal vis-à-vis the concrete poured between this plug 16 and these two seats, at least the peripheral zone of this plug is advantageously made of a radially inflatable material.

In the embodiment illustrated in FIG. 4, this radial inflation is ensured by axial compression and the plug 16 comprises for this purpose a rigid central tubular mandrel 17 surrounded contiguously by a sheath 18 of rubber or other elastomeric material with frustoconical external surface, this sleeve 18 extending axially on either side of the mandrel 17. In addition a central tie 19 extending along the axis of the mandrel 17 passes through two transverse plates 20 and 21 bearing axially on the two ends of the sleeve 18 so such that the simple screwing and unscrewing of a nut 22 on the outer end of this tie rod 19 makes it possible to inflate and deflate said sleeve 18 radially.

To ensure good axial positioning of the plug 16, the outer plate 21 advantageously bears against the anchoring member 12.

After fitting the plug 16 - and its possible radial swelling by screwing, if this solution is chosen - the concrete 23 is poured.

The plug 16 is then released after having deflated radially by unscrewing in the above hypothesis.

There is thus a flared opening conduit adapted to receive one end of the tube 10 and the corresponding end sleeve 11.

Said tube 10 is then put in place, which is composed of two successive strands each extending over substantially half of the total length and each terminated by a sleeve 11, fitted and glued or welded on its end E.

To this end, each of said strands is introduced into a discontinuous series of conduits formed by the sheath sections 9 embedded in the concrete, with the sleeve 11 corresponding to the rear, the two suites considered being arranged in the extension one on the other and covering all the sections in question.

At the end of this introduction, the front ends of the two strands are connected to each other by means of a housing 24 (FIG. 1) and the two frustoconical sleeves are housed in the flared mouths of the terminal conduits. , without any mutual adhesion between these sleeves "and the facing faces of these mouths.

The wires or strands 8 making up the frame are then threaded into the tube 10.

Then these wires or strands are stretched between their ends, after which the ends thus stretched are retained with the jaws 14.

The anchor heads 15 are then capped using suitable covers 25 fixed to the anchor members 12 in any desirable manner, in particular by bolting, and a cement grout is injected into the volumes inside the tubes 10 , to the end fittings 11 and to the covers 25, in particular from the housing 24, suitable vents then being provided in the covers 25.

The reinforcement is thus tensioned, protected, and exerts the desired prestress on the concrete structure.

To release this reinforcement, it suffices to shear its exposed sections out of the concrete, then to release axially in the direction of the arrows F (fig. 2) its sections housed in the sheaths 9.

These extractions are possible due on the one hand to the general shape (straight or in an arc) adopted for the sections concerned and on the other hand to the absence of adhesion between the tube 10, including its end pieces 11, and the internal faces of the housings which contain it. It can even be observed that these extractions require only relatively low forces.

It is then possible to proceed with the installation of a new armature in the manner explained above.

As a result of which, and whatever the embodiment adopted, there are means for equipping cellular concrete structures with interchangeable prestressing reinforcements, means the constitution and implementation of which result sufficiently from the above.

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 the variants within the framework of the claims, in particular those where the volume, inside the tube 10, which is not occupied by the reinforcements, would not be filled with a grout, but with another material such as a rubber or elastomer plug hollowed out from multiple channels for the reception of the various wires or strands, this formula being especially advantageous in the case where the tube 10 in question is provided only along the sections of the reinforcement , housed inside the concrete masses.

Claims (10)

1. A concrete work prestressed by means of tensioned reinforcements (7) having bell mouthed ends (7₁) and formed from an alternating succession of first sections housed, with interpositioning of a filling material, in metal sheaths (9) themselves embedded in the concrete and second rectilinear sections external to the concrete, characterized in that the mean line of each of the first sections extends along a straight line segment or along an arc of a circle and in that each reinforcement is housed, with its filling material, at least all along said first sections, in a plastic material tube (10) adapted to slide along the metal.

2. The concrete work according to claim 1, characterized in that the ends of the tube (10) are connected to two bell mouthed sleeves (11) made from a plastic material and surrounding respectively the two corresponding ends of reinforcements (7₁), these bell mouthed sleeves being dimensioned and disposed so that, with respect to the members (12) for anchoring the reinforcement, they may be disengaged axially through these members.

3. The concrete work according to anyone of claims 1 and 2, characterized in that each bell mouthed sleeve (11) is assembled sealingly with respect to the injected filling material on the tube (10) and the anchoring member (12) which it connects together.

4. The concrete work according to anyone of claims 1 to 3, characterized in that the plastic material forming the tubes (10) and the sleeves (11) is polyethylene.

5. A process for prestressing a concrete work according to anyone of the preceding claims, characterized in that the metal sheath sections (9) intended to receive the reinforcements and to be embedded in the concrete are positioned in shuttering before casting of the concrete, this positioning being carried out so that the mean line of each of these sections extends along a straight line segment or along an arc of a circle and so that the consecutive ends of these different mean lines are aligned in pairs, then in that each plastic material tube (10), previously provided if necessary with its reinforcement, is fitted successively into the different sheath sections (9) which correspond thereto, before or after the concrete is cast about these sheath sections.

6. The process according to claim 5 for prestressing a work according to any one of claims 2 to 4, characterized in that for each of the endmost sheath sections (9), said section is interrupted, on the same side as the corresponding ends (7₁) of armature (7), a little short of this end (D) and, before casting of the concrete, on the one hand the anchorage member (12) intended to serve as a support for said reinforcement end and on the other hand a truncated cone shaped connection (16, 27) adapted to establish at least temporarily the continuity between the interrupted end (D) of the sheath and said anchorage member (12) are positioned in shuttering, after which the concrete (23) is cast then the connection is disengaged axially, if it is removable.

7. The process according to claim 6, characterized in that the truncated cone shaped connection is formed by a plug (16) defined at least laterally by an annular wall (18) made from rubber or a similar material adapted to be distended or expanded radially by axial compression thereof and thus to provide a sealing connection between the two annular seats (D and 13) to be joined together.

8. The process according to claim 7, characterized in that the annular wall (18) is jointingly mounted about a rigid tubular mandrel (17) axially shorter than it and in that axial compression thereof is provided by screwing an outer nut (22) onto a threaded tiebolt (19) passing axially through two transverse end plates (20, 21) which bear respectively on the two ends of said annular wall (18).

9. The process according to claim 8, characterized in that one of the transverse plates (21) further bears axially on the outer face of the anchorage member (12).

10. A process for removing a prestress reinforcement from a work according to anyone of claims 1 to 4, characterized in that this reinforcement (7) is cut in one at least of its zones exposed outside the concrete so as to be able to remove axially the whole of the reinforcement sections thus cut which remain housed in the concrete, then in that these axial removals are performed, the endmost sections being removed with their bell mouthed ends (7₁) first.

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