FR2690189A1 - Improvements to prestressed concrete structures using greased sheathed strands and their construction processes. - 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.

Description

i Improvements to prestressed concrete structures using strands

  sheathed greased and their construction processes. The invention relates to prestressed concrete structures implementing the post-tensioning of a plurality of strands of the so-called "greased sheathed" type or the like. It also targets construction processes

of these works.

  In known embodiments of the latter, described here with reference to the general diagram 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 tube 3 of plastic material

  that intended to receive the greased sheathed strands 4.

  As visible in the cross section of FIG. 2, each of these strands 4 is constituted by a cable or bundle of metallic wires 5 disposed in a sheath 6, generally made of high density polyethylene, with the interposition of a lubricant such as a grease 7 rendering

  possible relative slippage of the cable in its sheath.

  Each end of the tube 3 is connected, via a tubular connector 8, to a trumpet

  9 -which will be designated in the following by the term "trompla-

  that "usually used by technicians, which opens to the outside of the formwork through an appropriate opening 10 thereof, the periphery of the trochot being fixed on the edge of said hole in a manner sealed to concrete during its casting, especially using systems

threaded rod nuts 11.

  Concrete is then poured into the formwork, taking care that no portion of the poured concrete enters the interior of the hollow housing delimited externally by the tube 3 extended by the trochus 9. After pouring the concrete into the formwork, then taking this concrete, said formwork is released, and the strands 4 are placed in the hollow housing, in particular of a

messy way.

  After which, each hole 10 is closed off with a stuffing box cover 12 drilled so as to receive in a classified and sealed manner the sheathed ends of the

  different sections 4 set up.

  lTo avoid the multiplication of drawings, we have shown in Figure 1 the formwork 1 and the gland cover 12 But in reality their implementation

  are generally successive and not simul-

  tanned, the formwork may not be pierced in line with the trochot 9, and the cover 12 may be fixed on

  this tromplaque by the same systems It as the cof-

  frage, after release of the latterl.

  Then injected inside the tube assembly-

  tromplaque, so as to fill the space included inside this set around sections 4, a

  grout 13 thin enough and fluid enough to be able to progress-

  be all along the tube and coat all the faces

  of the various strands 4.

  This injection has been shown diagrammatically in FIG. 1 by the arrow F. The crossing of the stuffing box cover 12 by each sheathed end of strand 4 must be carried out so

waterproof to said grout 13.

  After setting or hardening, the fine grout 13 forms a solid mass in which the strands 4 are intimately embedded except for their ends, which reinforces the protection, of the metal cables 5, already due to the presence of the sheaths 6 which surround them, while making possible the subsequent relative longitudinal sliding of these cables in their sheaths, sliding which occur during the subsequent tensioning

said cables.

  After said hardening of the fine grout 13, the gland covers 12 are released and the cables are tensioned by applying tensile forces to the ends, of the strands 4, which protrude out of the one-piece block formed by the masses

  hardened concrete 2 and grout 13.

  To clarify the description, we will designate here

  by the expressions "first phase" and "second phase" of the construction process of the structure, respectively: the continuation of the steps which have just been described and which end with the formwork removal of the hardened block in which the strands are embedded sheathed greased with the exception of their outgoing ends, and the following subsequent steps including the tensioning of the strands and the final protection

of the ends of the stretched strands.

  For the prior art method described above

  above, the second phase is for example carried out in 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

  above the method according to the prior art, it should be noted that it involves, inter alia, a relatively large tube 3, a relatively expensive stuffing box cover 12 which must be the subject of a sealed passage, vis-à-vis grout screw, by the ends of the strands 4, and a fine grout 13 which must be the subject of a special injection. The invention proposes a solution which makes it possible to remove these various elements and even further, in

  in some cases, trochot 9 itself.

  To this end, the prestressed concrete structures according to the invention also comprise a plurality of greased sheathed strands intimately embedded in a hardened mass over their entire length, with the exception of their bare ends, which protrude out of this mass in positions slightly spaced transversely from each other, and they are essentially characterized in that said mass is exclusively constituted by

  the hardened concrete constituting the bulk of the structure.

  As for the first phase of the construction process for prestressed concrete structures of the type in question, the following steps are used: the strands are placed directly in the formwork intended to receive the concrete constituting the structure. sheathed greased intended to prestress this structure, in parallel or substantially such positions and slightly spaced from one another, an opening made in the formwork is made to pass through one of the ends of said strands, a support ring applied against the edge from this opening, on the inside of the formwork, and a perforated plate

  spacing and classification, crossing the perforations

  tions of the plate by the strands being only leaktight with respect to the poured concrete, the concrete is poured into the formwork so that this concrete cohesively coats all of the outer faces of the strands disposed inside the formwork, and we release the formwork and possibly the

  perforated plate after hardening of said concrete.

  In advantageous embodiments, recourse is also had to one or the other of the following arrangements: the positioning of the strands in the formwork, in positions slightly spaced from one another, is ensured by the using crossbars for support and spacing, the support ring constitutes the enlarged base

  a trochot surrounding all the strands and it-

  even filled with concrete when it is poured into the formwork, when the concrete is poured into the formwork, the penetration of this concrete between the different strands is

favored by vibrations.

  The invention comprises, apart from these arrangements

  main provisions, certain other provisions which are preferably used at the same time and which will be

  more explicitly question below.

  In the following, we will describe preferred embodiments of the invention with reference to Figures 3 to 8 of the accompanying drawings in a manner well

heard without limitation.

  It will be recalled that FIGS. 1 and 2 of these drawings have already been mentioned previously with reference

to the prior art.

  FIG. 3, of said drawings, illustrates diagrammatically

  only the first phase of a construction process

  of prestressed structure according to the invention.

  Figures 4, 5, 6 and 7 schematically show the four steps 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, it is a question here of building a prestressed concrete structure using a plurality of strands 4 of the type

  sheathed greased shown in Figure 2.

  Here we put the strands 4 in question directly inside the formwork 1, in particular by orienting them along parallel sheets with interposition

  of metal bars 14 of spacing and of support themselves

same supported by the formwork.

  An end 10 of each strand 4 is made to pass through an opening 10 hollowed out in the formwork 1, a support ring 15 applied against the face, from the edge of the opening 10, oriented towards the inside of the formwork 1, said ring being removably attached to the formwork 1, in particular using threaded rod nut systems 11, and a plate 16 placed in the opening 10

  and perforated itself by lights 17.

  This plate 16 can be fixed in any desirable manner to the ring 15 and / or to the formwork 1, for example using the systems 11 themselves or using legs, bent or not, fixed on 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 tightness of the bushings

  flabbergasted vis-à-vis the poured concrete.

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

  cable gland or the like.

  Then the concrete 2 is poured into the formwork 1, an operation which is shown diagrammatically by the arrow G. During this pouring, it is ensured that the concrete penetrates well between the different strands 4 so as to externally coat all of the external faces of the portions of these strands 4, arranged inside the

formwork 1.

  To achieve this result, the concrete during casting is advantageously subjected to vibrations, in particular by subjecting the formwork itself 1 to vibrations or, if this is not possible, by transferring to the concrete the vibrations applied to needles. introduced into it. After setting or hardening of concrete 2, we release

  the formwork 1 and the perforated plate 16.

  There is then a hardened block on one face of which protrude ends sheathed with strands 4, as can be seen in FIG. 4. The block thus equipped with strands is quite comparable to that described above, such as 'obtained at the end of the "first phase" of the construction process

according to the prior art.

  But there are important differences between the two blocks since: on the one hand, the second block no longer includes 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

consisting of concrete 2.

  It is therefore, in the second case, the concrete 2 and no longer the grout 13 which has the task of coating for the purposes

  for protecting the sheaths of the strands 4.

  Experience has shown that, contrary to what

  those skilled in the art could wait, although the particle size

  sorting of concrete is much less fine 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, leading to the same result as the process according to the prior art, is

  much more economical than this one.

  The observation made previously on the use of

  tion of a perforated plate 16 crossed with clearance by the ends of the strands in place of the use of a cable gland cover 12 crossed by said ends in a grout tight manner further enhances the economic advantage of the new process described in relation to the previous one. 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 is stripped of its sheath 6 of strand 4 protruding from the hardened concrete block 2, at the same level as the surface S of this block (FIG. 5), so that there remain only outside of said block sections of stripped cable 5, place on the ring 15, with the interposition of a seal 18 (FIG. 6) in an asbestos-elastomer mixture or other flexible rot-proof material, an anchoring block 19 drilled right through so as to be crossed by the sections 5 and fitted with jaws tapered split anchors surrounding these sections,

  using suitable cylinders (not shown

  tees), 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 via the anchor block 19 and the support ring 15, and the whole of the anchor block 19 and 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 only one end of the strand

  considered, its other end being simply anchored.

  Following this, and whatever the embodiment adopted, a prestressed concrete structure is obtained using a plurality of strands of the type

  sheathed greased, work whose constitution and con-

  struction result sufficiently from the above, and which-

  presents among others on those of the same kind previous-

  the advantage of a much lower cost price

  for completely identical performance.

  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; she embraces it,

on the contrary, all variants.

  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 external collar or bulge

  medial 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 trunk plate with a hole 26

  hollowed out in the formwork 1 so as to facilitate filling

  wise of this trachaque by concrete 2 during the pouring

of the last.

  In this regard, it should be noted that it is entirely

  unusual to find concrete inside a trompla-

  that: before the present invention, only a fine grout was authorized to penetrate inside this part and one took on the contrary precautions to prohibit

  any introduction of concrete inside it.

  One 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 can then be directly hollowed out in said formwork, constituted by

wooden example.

Claims (4)

  1 Prestressed concrete structure using a plurality of greased sheathed strands (4) intimately embedded in a hardened mass over their entire length, with the exception of their bare ends, which protrude out of this mass in positions slightly spaced transversely from each other, characterized in that said mass consists exclusively of concrete   hardened (2) constituting the main part of the work.   2 A method of building a prestressed concrete structure according to claim 1, characterized in that one uses the following steps: it is placed directly in the formwork (1) intended to receive the concrete (2) constituting of the structure, the greased sheathed strands (4) intended to prestress this structure, in parallel or substantially such positions and slightly spaced from one another, an opening (10) is hollowed out through one of the ends of said strands. the formwork, a support ring (15) applied against the edge of this opening, on the side of the interior of the formwork, and a perforated plate (16) for spacing and filing, the crossing of the perforations (17) of the plate by the strands being only leaktight vis-a-vis the poured concrete, the concrete is poured into the formwork so that this concrete cohesively coats all of the external faces of the strands disposed inside. r from the formwork, and the formwork and possibly the perforated plate are released after hardening of said concrete, after which the various strands are tensioned and   the protruding ends are protected.   3 Construction method according to claim 2, characterized in that the establishment of the strands (4) in the formwork (1), in positions slightly spaced there from each other, is ensured using bars   transverse (14) support and spacing.   4 Construction method according to any one   claims 2 and 3, characterized in that the ring   of support constitutes the enlarged base of a trochot (9) surrounding the set of strands (4) and itself filled with concrete (2) when it is poured into the formwork. Construction method according to any one   of the preceding claims, characterized in that when   pouring the concrete (2) into the formwork (1), the penetration of this concrete between the different strands (4) is favored by vibrations.