Abstract:
A process of manufacturing concrete construction elements is provided. A first sheath is placed in a first mold, the first sheath connected at an end to a first sleeve applied against a wall of the mold, the sleeve engaging a positioning boss placed on the wall. Concrete is poured into the first mold and set to obtain the first element. The first element is extracted from the first mold and includes a contact face shaped by the wall. A second sheath is placed in a second mold, the second mold having one side formed by the contact face. The second sheath includes an end connected to a second sleeve held in position relative to the first sleeve by a positioning joint. Concrete is poured into the second mold and set to obtain a second element. The second element is extracted from the second mold by disengaging the positioning joint.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to the construction of pre-stressed structures from prefabricated matched concrete elements. 
     The invention applies in particular, but not exclusively, to bridges built by cantilevered construction with prefabricated segments having matched coupling surfaces (see for example the article: “Evolution et recents developpements des ponts a voussoirs prefabriques” (“Evolution and recent developments of bridges made of prefabricated segments”) by Jacques Mathivat, Annales de l&#39;lnstitut Technique du Batiment et des Travaux Publics, Supplement to No. 342, September 1976, pages 21—32, or the patent application EP-A-0 462 350). 
     In this technique, the successively assembled elements (segments) of the bridge are manufactured one after the other, the front face of the element n serving to delimit the rear side of the manufacturing mold of the element n+1. This guarantees the matching of the adjacent faces of the elements to be assembled. These faces are glued one on the other during the placing of the element n+1 on the building site. Complementary raised parts are usually provided on these faces to facilitate their mutual positioning and to help to support the element n+1 before its definitive fixing. 
     These structures are frequently subjected to a longitudinal pre-stress by means of pre-stressing cables threaded in sheaths embedded in the concrete of several successive elements. 
     Carrying out this pre-stress is a delicate operation. 
     The positioning of the sheath sections in the elements must be very precise so that the pre-stressing cables can be threaded without difficulty. 
     To guarantee the sealing of the sheath at the interfaces between elements is the most difficult. This sealing is necessary to ensure the durability of the pre-stressing subjected to the risks of infiltrations at the level of the joint between the elements. The joint can be made according to two processes: “dry joint” when the concrete faces are placed side by side without any interface product; or “glued joint” when an interface adhesive is placed at the level of the joint. In this second case, the sealing also fulfils the necessity of avoiding the epoxy or similar adhesive placed between the elements being able to penetrate into the sheaths and hinder the introduction of the cables. On the other hand, the sheaths are generally injected with a filling product (cement grouting, grease, wax, resin, etc) serving in particular to protect the cables against corrosion. This product must not escape to the outside of the sheath during the injection. 
     Certain zones of the structure may have a rather large density of sheaths, and there is not the assurance that the epoxy adhesive will achieve the sealing between these sheaths. The result is the grave risk that grouting injected under pressure into the sheath may infiltrate into one or several neighboring sheaths, where the injection then becomes very difficult, or even impossible. 
     In general, pneumatic tests are carried out to check the sealing of the pre-stress sheaths before installing the cables and injecting the grouting. If leaks are detected between some sheaths, it is necessary to inject the grouting very carefully in a way to attempt to have a single advancing grouting front in these different sheaths. The resulting injection procedures are extremely complicated and very difficult to control. 
     The solutions consisting in interposing O rings around the sheaths between the interconnected faces of the elements are not reliable in terms of sealing, these seals being able to be displaced during the positioning of the element n+1. 
     The patent application FR-A-2 596 439 describes a connection device between pre-stress sheath sections, comprising a cylindrical sleeve engaged between the mouths of two contiguous sections to ensure the continuity of the sheath, and a resilient seal surrounding the cylindrical sleeve to carry out the sealing and to compensate for the positioning irregularities of the units and their dimensional differences. 
     It has also been proposed to introduce a longitudinally pleated sleeve into the sheath after the gluing, this sleeve being brought at the level of the previously assembled contact surfaces then expanded with the aid of a pneumatic device in order to be glued to the internal wall of the sheath by means of an adhesive placed at the bottom of the pleats. This method involves a very complex implementation, moreover impossible when the sheaths are not rectilinear. Moreover, it does not prevent the infiltrations of adhesive into the sheath during the assembly of the elements. 
     An object of the present invention is to propose a simple and efficient solution to the problems encountered when carrying out the pre-stressing of structures constructed from matched prefabricated elements. 
     SUMMARY OF THE INVENTION 
     The invention thus proposes a process of manufacturing concrete construction elements including at least first and second matched elements, the process including the steps of: 
     placing in a mold at least one first pre-stress sheath section having an end connected to a first sleeve applied against a wall of the mold, the first sleeve having an internal shape engaging a positioning boss placed on said wall; 
     pouring concrete into said mold so as to obtain the first element after setting of the concrete; 
     extracting from the mold the first element, one contact face of which has been shaped by said wall; 
     constructing a second mold one side of which consists of said contact face of the first element; 
     placing in the second mold at least one second pre-stress sheath section having an end connected to a second sleeve held in position relative to the first sleeve by means of a positioning joint resiliently held in at least one of the first and second sleeves; 
     pouring concrete into the second mold so as to obtain the second element after setting of the concrete; and 
     extracting the second element from the second mold, by disengaging the positioning joint from at least one of the first and second sleeves. 
     The positioning joint may be the same piece as the joint which will achieve the sealing between the sleeves after the definitive assembly of the elements. In this case, the joint can be left in place in one or other of the two sleeves during the storage of the elements. 
     The sleeves and the joint ensure a precise and correct positioning of each section of sheath in each element, as well as the good alignment of successive sections. The dimensional differences to be compensated are thus minimized. 
     During the assembly of two consecutive elements, the sealing joints, with which the sleeves terminating the sheath sections on the face of one of the elements are provided, engage the sleeves ending the corresponding sheath sections of the other element. This engagement provides the sealing of the sheath in relation to the adhesive, with which one of the complementary faces is generally coated. It ensures moreover the absence of communication with the outside or between neighboring sheaths during injection of the cement grouting or other filling product into the sheaths. 
     The sealing joint may be integral with one of the two sleeves. But it is preferably fixed in a removable manner on one of the two sleeves, for example by screwing or by resilient fitting. 
     In preferred embodiments, the process of manufacturing concrete construction elements according to the invention has one or other of the following features: 
     the positioning boss may be provided with resilient coupling means which engage with an annular groove present in the internal shape of the first sleeve in order to hold it in a removable manner in the mold; 
     the sleeve in which the positioning joint is resiliently held may have an angular opening of at least 30 degrees; 
     the positioning joint may be resiliently held in each one of the first and second sleeves; 
     the positioning joint may be screwed in one of the first and second sleeves; 
     when a feature according to one of the two previous paragraphs is provided, the positioning joint may have an orifice coaxial with the sleeves, extending therethrough, said orifice having a cross-section at least equal to the internal cross-section of the first and second sheath sections, and in this case the positioning joint is left in place in the first or the second sleeve after the extraction of the second element. 
     The invention is also intended for a construction work comprising an assembly of prefabricated elements of a series of elements such as defined above, the contact faces of the matched elements being applied one against the other so that the sheath sections are placed in the extension one of the other to form completed sheaths, with joints engaged in the sleeves in order to connect in a sealed manner the adjacent sheath sections, and wherein pre-stressing cables and a filling product occupy the interior of the sheaths. 
    
    
     Other features and advantages of the present invention will emerge in the description below of non-restrictive embodiment examples, by reference to the appended drawings, in which: 
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective view of a prefabricated segment to which the present invention can be applied; 
     FIG. 1A is a partial lateral view illustrating the assembly of two consecutie segments; 
     FIG. 2 is a section view illustrating the placing of a sheath section in a manufacturing mold of a first element; 
     FIG. 3 is a partial section view of the first fabricated element; 
     FIG. 4 is a section view illustrating the placing of a second sheath section in a fabrication mold of a second element; 
     FIG. 5 is a partial section view of the second fabricated element; 
     FIG. 6 is a section view showing two alternative embodiments of the junction means of two pre-stress sheath sections; and 
     FIG. 7 is a section view showing another alternative embodiment of these means. 
    
    
     DESCRIPTION OF PREFERRED EMBODIMENTS 
     The invention is described below in its application to bridges made of prefabricated segments with matched coupling surfaces. 
     Such a segment  1  is shown in FIG.  1 . The element  1  has the general form of a caisson delimited below by a base  2 , laterally by two symmetrically inclined walls  3 , and above by a deck  4  laterally extended beyond the walls  3  in order to define the width of the bridge. 
     In the longitudinal direction, the element  1  is delimited by a rear face  6  and a substantially parallel front face  7 . The rear face  6  is intended to come into contact against the front face, of complementary shape, of the previous element installed on the structure during construction (in the case of the first element installed on a bridge pier, the complementary face belongs to this pier). Likewise, the front face  7  of the element  1  is intended to receive the rear face of the next element which is to be placed. 
     The contact faces of complementary shapes of the adjacent elements are provided with raised parts  8   a ,  8   b  ensuring a good relative positioning of the elements when they are brought together. In the particular example shown in FIGS. 1 and 1A, these raised parts are located on the end faces of the lateral walls  3  of the elements, and have the shape of trapezoidal profile projections  8   a  made during the molding on the front face  7   a  of the element  1   a , and on the other hand by complementary trapezoidal profile recesses  8 ,  8   b  made during the molding on the rear face  6 ,  6   b  of the element  1 , 1   b.    
     When an assembly adhesive is used, this is for example an epoxy resin with which one or other of the two complementary faces is coated before assembly. After its placing, the element  1 ,  1   b  is clamped against the previous element  1   a , so that the trapezoidal profile recesses  8 ,  8   b  formed on its rear face  6 ,  6   b  engage the complementary projections  8   a  of the front face  7   a  of the previous element  1   a  in order to support it before setting of the adhesive. After the setting of the adhesive the projecting parts take up at least partly the shearing force exerted at the level of the joint by the structure load. 
     The element  1  comprises a number of longitudinal sheath sections  10 , intended to receive pre-stressing cables. These cables are anchored on the structure at their ends by means of appropriate anchoring devices. Some of these anchoring devices  11  can possibly be placed on bosses  12  provided inside the caisson shape of the element. The sheath sections  10  emerge on the rear face  6  and/or on the front face  7  of the element. It is important to ensure the continuity and the sealing of each pre-stress sheath at the level of the contact faces of the adjacent elements. To do that, according to the invention, connection pieces are used (sleeves and joints) which are described below. 
     After placing the element, it is clamped against the previous element, at least until the setting of the assembly adhesive. This clamping can be carried out by placing certain pre-stressing cables if anchoring devices  11  orientated to the rear are provided on the element. Otherwise, or as a complement, external actuators are used to clamp the elements against each other. 
     Once the successive sections of a complete sheath have been assembled, the sealing of this sheath is verified by means of a pneumatic device. It is then possible to thread the strands of the pre-stressing cable into the sheath, to tension them, to anchor them at their ends, then to inject a filling product such as a cement grout into the sheath in order to fill in the voids and protect the cables against corrosion. 
     The successive elements  1  are prefabricated in molded concrete. FIGS. 2 to  5  illustrate the prefabrication of two consecutive elements  1   a ,  1   b.    
     To fabricate the first element  1   a , a mold having the required shape is used. On the front side of the element, the mold is delimited by a metal wall  15  (FIG. 2) of general plane shape, having recesses complementary to the projections  8   a  in the specified places. 
     Positioning bosses  16  are fixed on the internal side of the wall  15 , for example by welding. These bosses  16 , of general cylindrical shape, serve to install the sheath sections  10   a  of the first element  1   a  in the mold. 
     The front end of each sheath section  10   a  is engaged in a sleeve  18   a  up to an internal stop  19   a  provided in this sleeve. The sealing between the sheath section  10   a  and the sleeve  18   a  is conventionally carried out by means of a thermo-retractable sheath or by an adhesive tape  20 . 
     The sleeve  18   a  is in a material sufficiently rigid so as not to deform when the concrete is poured into the mold, for example a plastic material such as a high density polyethylene. 
     Beyond the stop  19   a , the sleeve  18   a  has a widened portion  21   a  with a shape adapted to engage on the positioning boss  16 . The sleeve  18   a  connected to the sheath section  10   a  is engaged on the boss  16  by an operator. The sleeve  18   a  is thus positioned with precision against the wall  15  of the mold, and held in this place by resilient anchoring means provided on the positioning boss  16 . These means can include a resilient part  22  housed in an annular groove  23  provided in the outside of the cylindrical shape of the positioning boss  16 , and engaging with another annular groove  24   a  provided in the internal shape of the widened portion  21   a  of the sleeve  18   a . The part  22  consists for example of a flat coiled spring being able to be flattened when it is compressed radially. 
     Once the different sheath sections  10   a  of the element  1   a  have been installed in that way, the concrete is poured into the mold. After its setting, the element  1   a  can be extracted from the mold, the wall  15  being withdrawn by pulling out the positioning bosses  16  from the sleeves  18   a . This wall  15  releases the front face  7   a  of the element. The front end  25   a  of the sleeve  18   a , which was applied against the wall  15 , is in the plane of the front face  7   a . The constitution of the element  1   a  near the front end of a sheath section  10   a  is shown in FIG.  3 . 
     The front face  7   a  of the element  1   a  serves to delimit the rear side of the fabrication mold of the following element  1   b  (FIG.  4 ). 
     To mount the sheath sections  10   b  of the element  1   b , a positioning joint is engaged in the widened portion  21   a  of each sleeve  18   a  appearing on the front face  7   a  of the first element  1   a.    
     This joint  30  can be made in a material more flexible than the sleeve  18   a , for example in a low density polyethylene having a modulus of elasticity of the order of 500 N/mm 2 . 
     A rear part of the joint  30  has an external shape corresponding to the internal shape of the widened portion  21   a  of the sleeve  18   a , with in particular an annular ridge  31  complementary to the annular groove  24   a  of the sleeve  18   a . This rear part of the joint  30  is pushed into the widened portion  21   a  of the sleeve  18   a , where it is held in place by the engagement of the ridge  31  with the annular groove  24   a.    
     The other (front) part of the joint  30  projects beyond the front face  7   a  of the element  1   a . This front part can have an external contour of general frusto-conical shape provided with another annular ridge  32 . Preferably, this frusto-conical shape, which converges away from the element, has a half angle β less than the angle θ formed by the sides of the trapezoidal profile of the raised parts  8   a ,  8   b  with the perpendicular direction of the end surfaces  7   a ,  6   b , which ensures that the part  30  is not damaged during handling of the element  1   b.    
     Each sheath section  10   b  of the second element  1   b  is engaged in another sleeve  18   b  up to an internal stop  19   b , with a thermo-retractable sheath or an adhesive tape  20  to ensure the sealing between the sheath and the sleeve. Away from the sheath section  10   b , the sleeve  18   b  has a widened portion  21   b  the internal shape of which is complementary to the external shape of the front projecting part of the positioning joint  30 . In particular, this widened portion  21   b  has an internal annular groove  24   b  which engages with the annular ridge  32  of the positioning joint to hold the sleeve  18   b  in place against the sleeve  18   a  in the fabrication mold of the second element (FIG.  4 ). 
     Once all the sheath sections  10   b  of the second element have been placed in the mold by means of the joints  30  and the sleeves  18   b , the concrete is poured into this mold to make the second element. After setting of the concrete and extraction from the mold, by pulling out the joints  30  away from the widened portions  21   b  of the sleeves  18   b , the second element  1   b  has the configuration shown in FIG. 5 near the rear end of the sheath section  10   b , the sleeve  18   b  having its rear end  25   b  in the plane of the rear face  6   b  of the element. 
     The fact that the positioning joint  30  stays in place on the first element  1   a  rather than on the second element  1   b  results from the angular opening of the widened portion  21   b  of the sleeve  18   b , which is larger than the angular opening of the widened portion  21   a  of the other sleeve  18   a.    
     The positioning joint  30  staying on the first element  1   a  will serve as a sealing joint between the corresponding sheath sections  10   a ,  10   b  during the assembly of the elements on the building site. This joint  30  is thus provided with an orifice coaxial with the sheath sections  10   a ,  10   b , the cross-section of which is preferably at least equal to the internal cross-section of these sheath sections. Because of its external shape complementary to the housing defined between the widened portions  21   a ,  21   b  of the sleeves, of the relative elasticity of its material and of its constant and relatively small thickness, the joint  30  is subjected to a certain radial compression which ensures the sealing of the sheath at the level of the interface between the elements  1   a ,  1   b.    
     The angular opening of the widened portion  21   b  of the sleeve  18   b , which corresponds substantially to the angle  2 β of the front frusto-conical part of the joint  30  is preferably greater than 30 degrees. Because of this arrangement, the joint  30  can easily penetrate into its housing when the second element  1   b  is brought to the first element  1   a.    
     If the front projecting part of the joint  30  is damaged during the storage of the elements, this joint  30  can be pulled from the sleeve  18   a  in which it is resiliently held, and replaced by another joint. 
     Alternatively, the positioning joint  30  used during the prefabrication of the elements  1   a ,  1   b  could be separate from the sealing joint installed for the definitive assembly of the elements, provided that the joint  30  correctly positions the sleeve  18   b  in the fabrication mold of the second element. 
     In another alternative embodiment, the positioning and sealing joint could be integral with one of the two sleeves. For example, the first element could be fabricated in the way illustrated by reference to FIGS. 2 and 3 (but preferably with sleeves  18   a  the widened portion  21   a  of which would have a greater angular opening), and the second sleeves joined to the rear ends of the sheath sections  10   b  could be extended by a more flexible rear part the external contour of which would be complementary to the internal shape of the widened portion  21 . In order for this rear part to be made more flexible, its thickness can be reduced relative to the rest of the sleeve, and/or this sleeve can be made from two materials having different moduli of elasticity. With such an embodiment, the number of required pieces to achieve the sealing is minimized. 
     In other embodiments (FIG.  6 ), the positioning and/or sealing joint is screwed into one or other of the two sleeves. 
     In the embodiment illustrated in FIG. 6, the positioning and sealing joint  50  has a cylindrical rear part engaged in the sleeve  38   a  to which is connected the sheath section  10   a  of the first element, and a frusto-conical front part provided with an external annular ridge  52 . Between these two parts, the joint  50  has a transverse shoulder  54  which abuts against the front end  45   a  of the sleeve  38   a  and against the front face of the first element. The cylindrical part of the joint  50  is provided with a female thread  53  complementary to a male thread  46   a  provided inside the sleeve  18   a . In this way, the joint  50  can be screwed into the first sleeve  38   a , the threads contributing to the sealing. 
     In the frusto-conical part of the joint  50 , the sealing results from the engagement of the ridge  52  in the groove  44   b  provided inside the widened portion  41   b  of the second sleeve  38   b.    
     In the example shown in the lower part of FIG. 6, the sealing is enhanced by the fact that the two ends of the joint  50  have thinned lips  55   a ,  55   b  which bend resiliently inwards when the joint  50  is installed in the sleeves  38   a ,  38   b . This bending can be caused by curved internal surfaces provided in the sleeves  38   a ,  38   b , at the back of the stops  39   a ,  39   b  receiving respectively the ends of the sheath sections. 
     In the alternative embodiment shown in the upper part of FIG. 6, an annular housing  47   a ,  47   b , open to the front side, is provided in the internal shape of the sleeve  38   a ,  38   b , at the back of the stop  39   a ,  39   b . The two ends of the positioning and sealing joint then compress flat sealing joints  48   a ,  48   b , placed in the housing  47   a ,  47   b.    
     In the embodiment illustrated by FIG. 7, the two sleeves  58   a ,  58   b  are parts having the same shape: 
     a cylindrical part  59  to receive the end of the sheath sections  10   a ,  10   b ; 
     an internal shoulder  60  at the end of the cylindrical portion  59 , against which abuts the end of the sheath section; 
     a constriction  61  to fasten the sleeve to the positioning boss  16  on the wall  15  delimiting the front side of the mold, the coil spring  22  of the boss  16  engaging in the annular groove formed behind the constriction  61 ; 
     a frusto-conical part  62  widening outwards and extending from the constriction  61  to the front end of the sleeve  58   a ,  58   b;    
     in the frusto-conical part  62 , a cylindrical recess  63  provided with an internal threading  64  towards the front end of the sleeve, and with an annular groove  65 , and the bottom of which comprises an annular rim  66  directed towards the front end. 
     The positioning and sealing joint  70  has a general shape complementary to that of the frusto-conical parts  62  and the cylindrical recesses  63  of the two opposite sleeves, with a central cylindrical bore having approximately the internal section of the sheath sections. To optimize the sealing, the joint  70  is provided with a series of radial notches  71  in the frusto-conical part of its external surface which makes it more flexible, with two annular ridges  72  which engage in the corresponding grooves  65  of the two sleeves and, on its two end faces, with two respective annular grooves  73  which enable a bending of the portions having the ridges  72  so that these engage resiliently in the grooves  65  of the sleeves, and which define, towards the inside of the joint, annular lips  74  being applied in a sealed manner against the annular rims  66  of the sleeves. 
     On only one of its sides, the joint  70  has a threading  75  intended to be screwed in the threading  64  of one of the sleeves. This screwing is carried out on the sleeve of the element made first, after its taking from the mold. On the opposite side of the joint  70 , there is no threading  75 , in order to enable the easy assembly of the elements. 
     The advantage of the embodiment of FIG. 7 is its lower cost considering the identity of the two sleeves  58   a ,  58   b  used.