EP0875636A1 - Prestressing cable and duct element therefor - Google Patents

Abstract

Prestressing cables pass through concrete structures (9) in e.g. high-density polyethylene grout-filled guide sleeves (35), typically following undulating routes. Direction changes are negotiated in curved steel deviation tubes (16). At high points, air, water, etc. are bled off through a short vent channel (41) formed, during duct extrusion, between the upper sleeve wall and a curved longitudinal partition cutting off a relatively small proportion of the cross-section. Optionally, the curved partition is inserted in an excision in the sleeve wall, the excised section being then replaced and sealed. Optionally, a separate tube is used. Perforations (25) extending over the summit zone (L1,L2) admit the unwanted fluids. After bleeding, the discharge point (44) is sealed, e.g. by a screw cap.

Description

The present invention relates to the field of prestressing cables for construction works.

It relates more particularly to cables made up of a set of strands, the setting of which tension exerts prestressing, housed in a sheath tubular filled with protective material. Sheath is usually made of plastic such as high density polyethylene (HDPE). The protective material is typically a cement grout.

The prestressing cables of the works of construction frequently have a curved path with high points and low points, the effort of prestress exerted by the cable being directed downwards in the vicinity of high points and vice versa.

When injecting the sheaths of these cables with the cement grout, the air present in the sheath, water which separates from the cement grout by settling or filtration, and "poor" grout, that is to say the decantation or filtration has extracted the constituents the heaviest, are evacuated at the high points to using devices called vents. These vents are generally consist of a shell made of material plastic tightly attached to the sheath and a tube, forming a body or attached to this shell, which allows channel grout, water and air out of the material constituting the structure (most often concrete).

When the cable sheaths are fully embedded in the structure, this technique is called internal prestressing to concrete. In this case, it is easy to place vents at high points when pouring concrete and equipping them with enough tubes long to ensure the evacuation of air, water and poor grout.

The present invention rather relates to the external prestressing technique, in which the cable sheaths, in the straight sections of their layout, are placed outside the structure. They nevertheless cross the structure in massifs in order to take up the forces exerted by the cable and to forward to the structure. The high and low points of cable are then located in deflecting spacers.

In the particular case of prestressing removable outer, cable sheaths pass through these spacers passing through shuttering tubes of metal, bent and embedded in concrete. The cable can then be dismantled for replacement, by sectioning in and out of accessible areas spacers and anchors.

The space between the shuttering tube and the HDPE tube being small (typically 10 to 20 mm in difference in diameter) and curve, it is impossible to place a conventional vent and thus ensure the correct filling of the sheath. It is therefore common to find voids at high points, due to inability to properly remove air and water from filtration. To overcome the lack of point vent top, grout can be reinjected by orifices placed on either side of the high point. But such a technique is complex and delicate, and does not give not always completely satisfied. The establishment a vent from the top of the structure, through the concrete of the upper slab and the shuttering tube, would appear a complex and delicate operation for install a removable external prestress on a new work under construction, and would moreover impossible to achieve in the case of reinforcement of a pre-existing structure.

An object of the present invention is to facilitate removal of unwanted components from the material filling the sheath at the high points of a external prestressing cable.

To this end, the invention provides an element of sheath as defined in claim 1, as well as a prestressing cable as defined in the claim 9. Preferred embodiments are set out in claims 2 to 8 and 10 to 14.

Poor air, water and / or grout can thus be captured in the first region, where the establishment from a conventional vent can be tricky, and evacuated in the second region, which is accessible from the outside.

The highest point of the cable will normally be included in said first region, although this region could be somewhat offset from this highest point, especially downstream relative to the grout injection direction.

An advantage of the invention is that the first region, in which poor air, water and / or grout are extracted from the sheath during injection, may extend over a certain length of the sheath element, instead of being punctual as in the case of vents conventional. This ensures more efficient evacuation.

The invention is applicable in the field of non-removable external prestressing (concrete of the work being poured around the sheath on part of the length of the element). It then facilitates the implementation place vents, especially when the constitution of the structure is such that it is difficult to predict the passage of a tube towards the top of the structure.

The invention is applicable even more advantageous in the field of external prestressing removable. The vent is integral with the sheath element allows the cable to be dismantled after the hardening of the grout. It can be used as well in the case of new structures than in that of structural reinforcement preexisting.

• la figure 1 est un schéma de principe illustrant un exemple de précontrainte extérieure ;
• la figure 2 est un schéma en coupe longitudinale d'un élément de gaine selon l'invention installé dans une entretoise déviatrice ;
• les figures 3 et 4 sont des vues en coupe transversale de l'élément de gaine de la figure 2 suivant les plans III-III et IV-IV indiqués sur la figure 2 ;
• la figure 5 est un schéma analogue à celui de la figure 2 montrant un autre élément de gaine selon l'invention ;
• la figure 6 est une vue en coupe transversale de cet autre élément suivant le plan VI-VI indiqué sur la figure 5 ;
• la figure 7 est un schéma analogue à celui des figures 2 et 5 montrant une autre réalisation d'une gaine d'un câble de précontrainte selon l'invention ; et
• les figures 8 et 9 sont des vues en coupe transversale de la gaine de la figure 7 suivant les plans VIII-VIII et IX-IX indiqués sur la figure 7.

Other particularities and advantages of the present invention will appear in the description below of nonlimiting exemplary embodiments, with reference to the appended drawings in which:

• Figure 1 is a block diagram illustrating an example of external prestressing;
• FIG. 2 is a diagram in longitudinal section of a sheath element according to the invention installed in a deflecting spacer;
• Figures 3 and 4 are cross-sectional views of the sheath element of Figure 2 along the planes III-III and IV-IV shown in Figure 2;
• Figure 5 is a diagram similar to that of Figure 2 showing another sheath element according to the invention;
• Figure 6 is a cross-sectional view of this other element along the plane VI-VI indicated in Figure 5;
• Figure 7 is a diagram similar to that of Figures 2 and 5 showing another embodiment of a sheath of a prestressing cable according to the invention; and
• FIGS. 8 and 9 are cross-sectional views of the sheath of FIG. 7 along the planes VIII-VIII and IX-IX indicated in FIG. 7.

In the embodiment illustrated by the Figure 1, the prestressed structure 7 is a concrete bridge whose apron is supported on batteries 8, 9. A cable Prestressing device 10, the strands of which are anchored to their ends by means of conventional anchoring devices 11, is used to exert a prestressing force on deck 7. This cable 10 follows, between the devices anchor 11 supported by the end stacks 8, a winding path in broken line whose portions straight lines are accessible from the outside. In the example considered, this winding path has a point top center, where the cable 10 passes through a planned diverter in a central stack 9, and two high points end, where the cable 10 passes through deflectors respectively adjacent to the anchoring devices 11. Between the central stack 9 and each of the end stacks 8, the cable path 10 has a low point where it is guided in a deflecting spacer provided in a pile intermediate 9a.

The sheath of the cable 10 consists of a tube made of plastic material, for example HDPE, which consists successive elements which, in a conventional manner, are welded end to end or connected using heating sleeves.

Figures 2 to 4 show a sheath element 15 according to the invention used in an upper part of the journey winding cable, at the center stack 9. A similar arrangement is provided in the upper parts of the cable located at the end batteries 8. At this level, the use of a sheath element according to the invention provides good protection of the strands at neighborhood of anchors, which can be points sensitive.

In the case of application to prestressing removable exterior, a bent steel formwork tube 16 was drowned in the concrete of pile 9. If the invention was implemented to reinforce a preexisting structure, the formwork tube 16, rather than being directly embedded in the concrete of pile 9, could be in a block concrete added to this pile 9 at the time of carrying out the reinforcement. The shuttering tube 16 has a diameter greater than that of the cable sheath 10. In the example considered, where the cable 10 has nineteen strands 17 of diameter 15.2 mm or 15.7 mm housed in a sheath outer diameter 110 mm, one can for example use a shuttering tube 16 with internal diameter 128 mm.

In the embodiment of Figures 2 to 4, the sheath element 15 has a circular section over its entire length. Inside this circular section are on the one hand a tubular cavity 20 occupying most of the section and intended to receive the strands 17, and on the other hand a vent channel 21. The section of the channel d 'vent 21 is substantially smaller than that of tubular cavity 20 (it is for example from 200 to 500 mm ² ).

When the sheath element 15 is installed in the shuttering tube 16, the vent channel 21 is located above of the tubular cavity 20, that is to say on the side outside of the curvature of the element 15.

The vent channel 21 extends over a part only the length of the sheath element 15. One of its ends, it is provided with an opening 22 (figure 4) which makes it communicate with the outside of the sheath. A threaded end piece 23 is welded around this opening 22 to allow connection of a tube threaded vent 24.

The sheath element 15 is engaged in the tube shuttering 16 by its end opposite to the end piece 23, this tip 23 remaining outside in the position sheath element 15, as shown in the Figure 2. In this position, the vent channel 21 extends beyond the highest point of the cable passage at through the pile 9 relative to the position of the nozzle 23. In a region extending on either side of the point the highest over a length L1, L2, the wall 26 separating the vent channel 21 of the tubular cavity 20 of the element of sheath has orifices 25 which communicate the vent channel 21 with the tubular cavity 20. These orifices 25, the cross section of which is for example of the order of 12 mm, are distributed over the length L1 + L2 of this region. This total length L1 + L2 is preferably at least 50 cm. More preferably, the length L1, L2 of this region on each side of the highest point is at least 50 cm. The orifices 25 are for example arranged in staggered along region L1 + L2, so that some of them (shown schematically by broken lines on the Figure 3) are close to the junction between the wall separator 26 and the cylindrical wall of the cavity tubular 20.

After assembling the sheath elements successive, having threaded the strands 17 there and having tension and anchored these strands 17, we proceed to the injection cement grout in the sheath to fill the space left free by the strands.

In a first phase, the grout is injected by one end of the sheath, or by one of the points down its winding path. In this phase, the vent tube 24 is open to let the air from inside the sheath. It could also be blocked, especially if a thixotropic grout is used. Decanting the grout and filtering it through internal interstices of strands 17 cause formation pockets of water and poor grout at the points top of the sheath. Once a period of time has elapsed the order of half an hour to two hours after this first injection phase, two re-injections are carried out successive grout by two orifices not shown, provided in the sheath on either side of the stack 9. When of these two reinjections, the vent tube 24 is open. The first is carried out from the downstream orifice of stack 9 relative to the direction of injection performed in the first phase. During this first reinjection, the vent tube 24 rejects water, grout poor and possibly air that may have subsisted in the sheath element due to turbulence which may occur during the first injection downstream of the point on upper. During the second reinjection, performed from the opposite side, water and poor grout can remain in the sheath are in turn evacuated by the channel 21 and the vent tube 24.

The sheath element 15 has the advantage that the collection of the components to be evacuated is not punctual, but distributed over the length L1 + L2.

As shown in Figure 2, the wall 26 separating the vent channel 21 of the tubular cavity 20 is connected gently, grazing, to the wall cylindrical of the tubular cavity 20 at both ends of the vent channel 21. This prevents the ends of the channel 21 form obstacles for threading the strands 17 inside the tubular cavity 20.

In the embodiment illustrated by Figures 2 to 4, the tubular cavity 20 of the element sheath has a circular section which includes the section of the vent channel 21. To make such a sheath element, one possibility is to weld together two pieces of general tubular shapes obtained from two plastic tubes. One of these pieces 32 constitutes the major part of the sheath element 15. It corresponds to a tube with a longitudinal notch produced by cutting a first strip 27 which will constitute the upper wall of the vent channel 21. The opening 22 is pierced at one end of this strip 27, and the end piece 23 is welded, at 28, around this opening 22 on the outer face of the strip 27. The other plastic tube is cut to clear a second strip which will constitute the wall bottom 26 of the vent channel 21, separating it from the tubular cavity 20. The holes 25 are drilled in this second strip 26, the longitudinal edges of which are then welded in 30, on the inside of the first strip 27. The first strip 27 thus completed by the formation of the vent channel 21 is ultimately rewelded, at 31, onto the tube from which it comes.

As is usual in plastic boilermaking, the welds 28, 30, 31 can be carried out by depositing a rod of HDPE melted using an air gun hot.

The sheath element 35 shown in Figures 5 and 6 differs from that previously described by the constitution of its vent channel 41. This vent channel 41 is made from a tubular piece of HDPE 47, the section is generally circular. This piece 47, which has the orifices 25 distributed on the side inside of its curvature, is welded to another part 52 obtained as previously by making a notch longitudinal on a plastic tube. The room 47 forming the vent channel 21 is fixed, using two diametrically opposed weld seams 51 on the edges of the notch in room 52. So, as shown in the Figure 6, the section of the vent channel 41 exceeds some little of the circular section of the tubular cavity 20. As the cross section of the vent channel 41 is reduced, it is possible to make sure that this overshoot does not interfere the introduction of the sheath element 35 into the tube formwork 16.

On the side of its free end 44, provided with sealing means not shown, the vent channel 41 separates tangentially from the wall of the cavity tubular 20, as shown in the right part of the figure 5.

In the embodiment of FIGS. 7 to 9, the sheath element 55 having the vent channel 61 is produced by extrusion, which minimizes the cost of come back. The vent channel 61 is formed over the entire length of element 55 inside the cavity cylindrical tubular 20 receiving the strands 17. A the inside of the shuttering tube 16, this sheath element 55 is connected to another sheath element 54, devoid of vent channel. This other element 54, also extruded, simply presents the cylindrical tubular cavity of same diameter as element 55.

The junction 56 between the sheath elements 54 and 55 is located approximately at the level of the most top of the cable path in section 9 of the structure comprising the shuttering tube 16 (Figure 7), so that ensure the capture of the separate components of the grout at this highest point. Before welding the two together elements, the internal wall of the vent channel 61 is beveled at the end of element 55 to prevent its end 57 obstructs the introduction of strands 17. The other end of the vent channel 61 is closed, and bevelled also before making its junction with the adjacent sheath element.

To carry out the communication of the vent channel 61 with the outside of the sheath outside the shuttering tube 16, an orifice 62 is drilled in the wall of the element 55 as shown in FIGS. 7 and 9. This orifice 62 is for example tapped to allow mounting of a tube threaded vent not shown. We have a certain freedom as to where to drill hole 62 along element 55. It is desirable to pierce it as close as possible from the outlet of tube 16, but we can also choose a more convenient place for the operator.

Claims (14)

Sheath element for a prestressing cable (10) to be installed along a winding path on a structure of construction (7), the cable comprising, inside the sheath, strands (17) stretched to prestress the work and a material for filling the sheath and protection of the strands, said sheath element (15; 35; 55) being provided to cross at least partially a portion (8,9) of the structure in an upper part of said path sinuous, characterized in that it comprises a vent channel (21; 41; 61) parallel to the tubular cavity (20) receiving the strands and of section substantially smaller than said tubular cavity, and in that the vent channel is arranged so that after placing the element sheath in said portion of the structure, the vent channel either positioned above the tubular cavity and communicates with the tubular cavity in a first sheath element region located within said portion of the work and with the outside of the sheath in a second region of the sheath element located outside of said portion of the structure. Sheath element according to claim 1, in which said first region of the sheath element, where the vent channel (21; 41) communicates with said cavity tubular (20), extends over a length (L1 + L2) of at least minus 50 cm. Sheath element according to claim 2, in which the length (L1, L2) of said first region is at least 50 cm on either side of the highest point of said upper part of the sinuous path of the cable. Sheath element according to any one of claims 1 to 3, wherein the vent channel (21; 41) is separated from said tubular cavity by a wall (26) provided with orifices (25) distributed along said first region of the sheath element (15; 35). Sheath element according to any one of claims 1 to 4, produced by first and second welding second plastic parts of general shape tubular, the first part (26,27; 47) corresponding to the wall of the vent channel (21; 41) and the second part (32; 52) corresponding to the wall of said cavity tubular (20) with a longitudinal notch at the edges from which the first part is welded. Sheath element according to claim 5, in which said first part (47) has a section substantially circular. Sheath element according to any one of claims 1 to 4, wherein the tubular cavity (20) has a circular section which includes the channel section vent (21). Sheath element according to any one of claims 1 to 7, wherein the vent channel (21; 41; 61) is separated from said tubular cavity (20) by a wall (26) which, at its two ends, is connected gently to the wall of the tubular cavity so that do not obstruct the threading of the strands (17). Prestressing cable (10) installed in accordance with winding path on a construction work (7) and having a sheath formed from assembled sheath elements end to end and, inside the sheath, strands (17) tensioned to prestress the structure and a material filling of the sheath and protection of the strands, the sheath passing through at least a portion (8.9) of the structure in an upper part of said winding path, characterized by that an element (15; 35; 55) of the sheath, crossing at less partially said portion (8,9) of the structure, has a vent channel (21; 41; 61) parallel to the tubular cavity (20) receiving the strands and section substantially smaller than said tubular cavity, and in that the vent channel is positioned above the tubular cavity and communicates with the tubular cavity in a first region of said sheath element located at the interior of said portion of the structure and with the outside of the sheath in a second region of said sheath element located outside said portion of the book. Prestressing cable according to claim 9, in which the vent channel (21; 41; 61) is separated from said tubular cavity (20) by a wall (26) which, at its two ends, gently connects to the wall of the tubular cavity so as not to obstruct threading the strands (17). Prestressing cable according to claim 9 or 10, wherein said sheath element (15; 35) is made by welding first and second parts in plastic material of general tubular shapes, the first part (26,27; 47) corresponding to the wall of the vent channel (21; 41) and the second part (32; 52) corresponding to the wall of said tubular cavity (20) with a longitudinal notch at the edges of which is welded the first part. Prestressing cable according to claim 9 or 10, in which the tubular cavity (20) has a section circular which includes the section of the vent channel (21). Prestressing cable according to claim 9 or 10, wherein said sheath element (55) is made by extrusion, the vent channel (61) being formed at the interior of the generally shaped tubular cavity (20) cylindrical over substantially the entire length of said element, wherein said sheath element provided with vent channel is connected to another sheath element (54) having a generally shaped tubular cavity cylindrical of the same diameter but without channel vent, the junction (56) between these two sheath elements being located in said portion (8,9) of the work at vicinity of the highest point of the winding path of the cable in said portion. Prestressing cable according to claim 13, wherein the communication of the vent channel (61) with the outside of the sheath in the second region of said sheath element (55) takes place through an orifice (62) tapped in a wall of said sheath element.

Images