EP0566463B1 - Improvements to prestressed concrete structures by using greased and sheated strands - Google Patents

Abstract

A structure made of concrete which is prestressed by using a plurality of greased and sheathed strands (4) intimately embedded in a set mass over their entire length, except for their exposed ends which project out from this mass at positions which are slightly spaced apart transversely with respect to one another, the said mass consisting exclusively of the set concrete (2) constituting the essential part of the structure. The construction of this structure involves passing a perforated plate (16) over the said ends, this plate ensuring leakproofness only in respect of the cast concrete. <IMAGE>

Description

The invention relates to concrete structures prestressed using the post-tension of a plurality of strands of the so-called "greased sheathed" type or analogues.

It also targets construction processes of these works.

In known embodiments of these last, described here with reference to the general scheme of Figure 1, we place inside the formwork 1 intended to receive the concrete 2 constituting the structure, before pouring of this concrete, at least one plastic tube 3 intended to receive the greased sheathed strands 4.

As visible on the cross section of the Figure 2, each of these strands 4 is constituted by a cable or bundle of metallic wires 5 arranged in a sheath 6, generally made of high density polyethylene, with interposition of a lubricant such as a grease 7 making possible relative slippage of the cable in its sheath.

Each end of the tube 3 is connected, by via a tubular connector 8, to a trumpet 9 -which will be designated in the following by the term "tromplaque" usually used by technicians- which opens to the outside of the formwork through an opening appropriate 10 of it, the perimeter of the trochot being attached to the edge of said hole in a sealed manner to concrete when it is poured, in particular using systems threaded rod nuts 11.

Concrete is then poured into the formwork taking care that no portion of the concrete poured, does not penetrate inside the delimited hollow housing externally by the tube 3 extended by the trochot 9.

After pouring concrete into the formwork, then setting of this concrete, we release said formwork, and we put in place the strands 4 in the hollow housing, in particular of a messy way.

After which, each hole 10 is closed with a cable gland cover 12 drilled so as to receive a classified and sealed manner the sheathed ends of different sections 4 set up.

[To avoid the multiplication of drawings, we have shown in Figure 1 the formwork 1 and the cover cable gland 12. But in reality their implementation in general are successive and not simultaneous, the formwork may not be pierced at the right of the face 9, and the cover 12 can be fixed on this tromplaque by the same systems 11 as the formwork, after release of the latter].

We then inject inside the tube-tracheal assembly, so as to fill the space included in inside this set around sections 4, a grout 13 thin enough and fluid enough to be able to progress all along the tube and coat all of the faces exterior of the different strands 4.

This injection has been shown diagrammatically in FIG. 1 by arrow F.

The bushing of the stuffing box cover 12 by each sheathed end of strand 4 must be made so waterproof to the grout 13.

After setting or hardening, the fine grout 13 forms a solid mass in which are intimately embedded the strands 4 with the exception of their ends, which reinforces protection, metal cables 5, already due to the presence of the sheaths 6 which surround them, while making possible the relative longitudinal sliding subsequent of these cables in their sheaths, sliding involved in the subsequent power up said cables.

After said hardening of the fine grout 13, we releases the cable gland covers 12 and the setting is carried out cables under tension by applying stresses traction on the ends, of the strands 4, which make protrusion out of the solid block formed by the masses hardened concrete 2 and grout 13.

• la suite des étapes qui viennent d'être décrites et qui s'achèvent par le décoffrage du bloc durci dans lequel sont noyés les torons gainés graissés à l'exception de leurs extrémités sortantes,
• et la suite des étapes ultérieures comprenant la mise sous tension des torons et la protection finale des extrémités des torons tendus.

To clarify the description, here we will designate by the expressions "first phase" and "second phase" of the construction process of the structure, respectively:

• the following steps which have just been described and which end with the formwork of the hardened block in which the greased sheathed strands are embedded, with the exception of their outgoing ends,
• and the continuation of the subsequent stages comprising the tensioning of the strands and the final protection of the ends of the stretched strands.

For the prior art method described above, the second phase is for example carried out from the manner which will be described in more detail later in the part of the description of a complete embodiment of the present invention: in fact, as regards this second phase, the present invention does not differ of the prior art considered here.

Regarding the first phase described above of the process according to the prior art, it should be noted that it involves, among other things, a relatively large tube 3, a relatively stuffing box cover 12 expensive which must be the subject of a watertight crossing, opposite the grout, by the ends of the strands 4, and a fine grout 13 which must be injected special.

The invention proposes a solution which makes it possible to delete these different elements and even further in in some cases, trochot 9 itself.

A description of an example of anchoring of the type considered above with reference to Figure 1 can be found in: "FREYSSINET Processes - Anchors for interior and exterior prestressing - System C ", February 1991. Technical notice published by the Commission Interministerial of Prestressing (CIP), pages 25, 26 and 48.

Other systems have also been proposed. anchor, by which one or more sheathed strands greased can be individually drowned, on the most of their length in hardened concrete constituting the essential of the work. Such systems anchors are described in documents FR-A-2 638 771 and EP-A-0 129 976. In the system described in the latter document, the hardened concrete in which the strand is embedded belongs to a stripped block after casting and the hardening of the concrete, and the end of the strand is stripped beyond an outer face of this block, where it projection and where it is anchored by means of a key sectional. A support plate belonging to the block stripped is between said outer face of the block and the end of the sheath of the strand, which poses a serious sealing problem when pouring concrete, which can result in premature corrosion of the strand.

The present invention aims to simplify the prestressed concrete structures relative to a structure conventional such as that illustrated in FIG. 1, and therefore to make them more economical, without encounter too serious problems with sealing and corrosion.

The invention thus provides a work such as defined in claim 1.

Regarding the first phase of the processes for the construction of prestressed concrete structures from genre in question, we resort to following the steps listed in claim 2:

• l'anneau d'appui constitue la base élargie d'une tromplaque entourant l'ensemble des torons et elle-même remplie de béton lors de la coulée de celui-ci dans le coffrage.

In advantageous embodiments, use is also made of the following arrangement:

• the support ring constitutes the enlarged base of a trochus surrounding all of the strands and itself filled with concrete when it is poured into the formwork.

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

In what follows, we will describe modes of preferred embodiments of the invention with reference to Figures 3 to 8 of the accompanying drawings in a good manner heard without limitation.

Recall that Figures 1 and 2, of these drawings, have already been mentioned previously with reference to the prior art.

Figure 3 of said drawings schematically illustrates the first phase of a construction process of prestressed structure according to the invention.

Figures 4, 5, 6 and 7 show schematically the four stages making up the second phase of this process.

Finally, Figure 8 shows a variant of the figure 3.

As in the process according to the prior art described above, this involves building a concrete structure prestressed using a plurality of strands 4 of the type sheathed greased shown in Figure 2.

Here we put the strands 4 directly in place question inside the formwork 1, in particular by orienting according to parallel sheets with interposition of metal bars 14 of spacing and support themselves supported by the formwork.

• une ouverture 10 évidée dans le coffrage 1,
• un anneau d'appui 15 appliqué contre la face, du bord de l'ouverture 10, orientée vers l'intérieur du coffrage 1, ledit anneau étant fixé de façon amovible sur le coffrage 1, notamment à l'aide de systèmes écrous-tiges filetées 11, et une plaque 16 placée dans l'ouverture 10 et perforée elle-même par des lumières 17.

One makes cross by one end of each strand 4:

• an opening 10 hollowed out in the formwork 1,
• a support ring 15 applied against the face, of the edge of the opening 10, oriented towards the inside of the formwork 1, said ring being detachably fixed on the formwork 1, in particular by means of nut-rod systems threaded 11, and a plate 16 placed in the opening 10 and perforated itself by holes 17.

This plate 16 can be fixed anyway desirable on the ring 15 and / or on the formwork 1, by example using systems 11 themselves or using legs, angled or not, fixed to the formwork using of said systems.

The lights 17 are suitable for receiving the ends of the strands 4 with a small visible play in j which is compatible with sealing of the bushings considered vis-à-vis the poured concrete.

It should be noted that this seal against the poured concrete is much less rigorous than waterproofing vis-à-vis the fine grout according to the prior art, because concrete components are much coarser than those of the grout: it is therefore unnecessary to provide here cable gland or similar sealing members.

Then we pour the concrete 2 into the formwork 1, operation which is represented by the arrow G.

During this pouring, we make sure that the concrete penetrates well between the different strands 4 so as to externally coat all of the exterior faces portions, of these strands 4, arranged inside the formwork 1.

To obtain this result, we advantageously submit concrete being poured in vibrations, in particular by subjecting the formwork itself 1 to vibrations or, if this is not possible, transferring the concrete to vibrations applied to needles introduced into this one.

After setting or hardening of concrete 2, we release the formwork 1 and the perforated plate 16.

We then have a hardened block on one side from which protrude the sheathed ends of strands 4, as seen in Figure 4.

The block thus equipped with strands is completely comparable to that described above, as obtained from the end of the "first phase" of the construction process according to the prior art.

• d'une part, le second bloc ne comprend plus le tube 3 et le raccord 8 qui étaient incorporés dans le premier, ni la tromplaque 9 qui est ici remplacée par l'anneau 15,
• d'autre part, le bloc durci, qui était composé d'une masse 2 de béton et d'une masse 13 de coulis fin dans le premier cas est, dans le second cas, exclusivement constitué par du béton 2.

But there are important differences between the two blocks since:

• on the one hand, the second block no longer comprises the tube 3 and the fitting 8 which were incorporated in the first, nor the trochot 9 which is here replaced by the ring 15,
• on the other hand, the hardened block, which was composed of a mass 2 of concrete and a mass 13 of fine grout in the first case is, in the second case, exclusively constituted by concrete 2.

It is therefore, in the second case, concrete 2 and not plus the coulis 13 which has the task of coating for the purposes protection of the sheaths of the strands 4.

Experience has shown that, contrary to what those skilled in the art could wait, although the particle size concrete is much thinner than that of grout, said mission is perfectly fulfilled by said concrete.

It follows from these two observations, that the process which has just been described, resulting in the same result that the method according to the prior art is much more economical than this one.

The observation made previously on the use of a perforated plate 16 crossed with clearance by the ends of the strands instead of using a stuffing box cover 12 crossed by said ends grout tightness further enhances the advantage economic of the new process described compared to previous.

• on dégarnit de sa gaine 6 chaque extrémité de toron 4 faisant saillie hors du bloc de béton durci 2, au niveau même de la surface S de ce bloc (figure 5), de sorte qu'il subsiste uniquement hors dudit bloc des tronçons dénudés de câble 5,
• on place sur l'anneau 15, avec interposition d'un joint 18 (figure 6) en un mélange amiante-élastomère ou autre matériau souple imputrescible, un bloc d'ancrage 19 percé de part en part de façon à être traversé par les tronçons 5 et équipé de mors d'ancrage tronconiques fendus 20 entourant ces tronçons,
• à l'aide de vérins appropriés (non représentés), on exerce les tractions désirées sur les extrémités, des tronçons 5, faisant saillie en dehors des mors 20, tractions qui sont ensuite conservées dans les câbles, grâce au serrage desdits mors, et transmises au bloc durci 2 par l'intermédiaire du bloc d'ancrage 19 et de l'anneau d'appui 15,
• et l'on recouvre l'ensemble du bloc d'ancrage 19 et des éléments qu'il porte par un capot 21 (figure 7) rempli d'un produit de protection 22 tel qu'une graisse.

As regards the "second phase" of the construction process considered here of a prestressed concrete structure, it is advantageously made to understand, in a manner known per se, the following stages:

• each end of the strand 4 protruding from its sheath 6 protruding from the hardened concrete block 2, at the same level as the surface S of this block (FIG. 5), so that only stripped sections of cable 5,
• is placed on the ring 15, with the interposition of a seal 18 (Figure 6) in an asbestos-elastomer mixture or other flexible rot-proof material, an anchor block 19 drilled right through so as to be crossed by the sections 5 and equipped with split frustoconical anchoring jaws 20 surrounding these sections,
• using appropriate jacks (not shown), the desired pulls are exerted on the ends, sections 5, protruding outside the jaws 20, pulls which are then kept in the cables, thanks to the tightening of said jaws, and transmitted to the hardened block 2 by means of the anchoring block 19 and the support ring 15,
• and the whole of the anchoring block 19 and of the elements which it carries is covered by a cover 21 (FIG. 7) filled with a protective product 22 such as a grease.

Of course, and in a manner known per se, the tensioning of each strand can be carried out similarly at its two ends or, more simply, it is carried out at one end only of the strand considered, its other end being simply anchored.

As a result of what, and whatever the mode of adopted implementation, we get a concrete structure prestressed using a plurality of strands of the type sheathed greased, work whose constitution and construction sufficiently result from the above, and which present among others on those of the same kind previously known the advantage of a much lower cost price for completely identical performance.

As it goes without saying, and as it results from elsewhere already from the above, the invention is in no way limited to those of its modes of application and embodiment which have been more specifically considered; she embraces it, on the contrary, all the variants covered in the claims.

• une collerette ou renflement extérieur intermédiaire 24 permettant d'améliorer la répartition de la pression axiale de précontrainte dans le béton durci 2,
• et un évent supérieur 25 propre à faire communiquer l'intérieur de la tromplaque avec un trou 26 évidé dans le coffrage 1 de façon à faciliter le remplissage de cette tromplaque par le béton 2 lors de la coulée de ce dernier.

This is how the support ring 15 could be replaced by a trachelate 9 (FIG. 8) quite comparable to those used according to the prior art, trachelate comprising in particular:

• an intermediate external flange or bulge 24 making it possible to improve the distribution of the axial prestressing pressure in the hardened concrete 2,
• and an upper vent 25 suitable for communicating the interior of the tromplaque with a hole 26 hollowed in the formwork 1 so as to facilitate the filling of this tromplaque with concrete 2 during the pouring of the latter.

In this regard, it should be noted that it is entirely unusual to find concrete inside a trochot : before the present invention, only a fine grout was allowed to enter this room and on the contrary, precautions were taken to prohibit any introduction of concrete inside it.

We could also replace the perforated plate 16 by a portion of the formwork 1, the holes 17 intended to receive the ends of the strands 4 which can then be directly hollowed out in said formwork, constituted by wooden example.

Claims (3)

1. A concrete structure prestressed by means of a plurality of sheathed and greased strands (4) individually embedded over the major part of their length in the set concrete (2) forming the main body of the structure, the set concrete in which the strands are embedded belonging to a block from which the formwork is removed after the pouring and setting of the said concrete (2), the ends of the strands being stripped beyond one outer surface (S) of the said block, where they project in positions which are slightly spaced from one another transversely and where they are anchored in the wedges of a plate (19), characterised in that the sheath (6) of each strand (4) extends, and is surrounded by the said set concrete (2), as far as the said outer surface (S) of the block in such manner that the concrete contiguously covers all the outer surfaces of the strands which were disposed inside the formwork used to form the said block.
2. A method of constructing a prestressed concrete structure according to Claim 1, wherein the sheathed and greased strands (4) intended to prestress the structure are disposed directly in a formwork (1) intended to receive the concrete (2) forming the structure, in positions which are parallel or substantially parallel and slightly spaced from one another, one of the ends of each of the said strands is passed through an opening (10) formed in the formwork and a support ring (15) applied against the edge of said opening, on the inside of the formwork, the said end is also passed through a perforate plate (16) for spacing and positioning the ends of the strands, the passage of the strands through the perforations (17) in the plate (16) being sealing-tight only with respect to the poured concrete, the concrete is then poured into the formwork so that the said concrete contiguously covers all the outer surfaces of the strands disposed inside the formwork, and the formwork is removed and, if required, the perforate plate (16) after the setting of the said concrete, whereafter the various strands are tensioned and their projecting ends are protected.
3. A construction method according to Claim 2, characterised in that the support ring forms the widened base of a flared tube (9) surrounding all the strands (4) and itself filled with concrete (2) when the latter is poured into the formwork.

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