EP3175057A1 - Structural element with anticipated prestressing - Google Patents

Structural element with anticipated prestressing

Info

Publication number
EP3175057A1
EP3175057A1 EP15759499.5A EP15759499A EP3175057A1 EP 3175057 A1 EP3175057 A1 EP 3175057A1 EP 15759499 A EP15759499 A EP 15759499A EP 3175057 A1 EP3175057 A1 EP 3175057A1
Authority
EP
European Patent Office
Prior art keywords
tensioner
tensioners
structural element
elongate body
concrete
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Granted
Application number
EP15759499.5A
Other languages
German (de)
French (fr)
Other versions
EP3175057B1 (en
EP3175057C0 (en
Inventor
Alain SABBAH
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
SABBAH, ALAIN
Original Assignee
Individual
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Individual filed Critical Individual
Publication of EP3175057A1 publication Critical patent/EP3175057A1/en
Application granted granted Critical
Publication of EP3175057B1 publication Critical patent/EP3175057B1/en
Publication of EP3175057C0 publication Critical patent/EP3175057C0/en
Active legal-status Critical Current
Anticipated expiration legal-status Critical

Links

Classifications

    • E—FIXED CONSTRUCTIONS
    • E04—BUILDING
    • E04C—STRUCTURAL ELEMENTS; BUILDING MATERIALS
    • E04C3/00—Structural elongated elements designed for load-supporting
    • E04C3/02—Joists; Girders, trusses, or trusslike structures, e.g. prefabricated; Lintels; Transoms; Braces
    • E04C3/20—Joists; Girders, trusses, or trusslike structures, e.g. prefabricated; Lintels; Transoms; Braces of concrete or other stone-like material, e.g. with reinforcements or tensioning members
    • E—FIXED CONSTRUCTIONS
    • E04—BUILDING
    • E04C—STRUCTURAL ELEMENTS; BUILDING MATERIALS
    • E04C3/00—Structural elongated elements designed for load-supporting
    • E04C3/02—Joists; Girders, trusses, or trusslike structures, e.g. prefabricated; Lintels; Transoms; Braces
    • E—FIXED CONSTRUCTIONS
    • E04—BUILDING
    • E04C—STRUCTURAL ELEMENTS; BUILDING MATERIALS
    • E04C3/00—Structural elongated elements designed for load-supporting
    • E04C3/02—Joists; Girders, trusses, or trusslike structures, e.g. prefabricated; Lintels; Transoms; Braces
    • E04C3/20—Joists; Girders, trusses, or trusslike structures, e.g. prefabricated; Lintels; Transoms; Braces of concrete or other stone-like material, e.g. with reinforcements or tensioning members
    • E04C3/26—Joists; Girders, trusses, or trusslike structures, e.g. prefabricated; Lintels; Transoms; Braces of concrete or other stone-like material, e.g. with reinforcements or tensioning members prestressed
    • E—FIXED CONSTRUCTIONS
    • E04—BUILDING
    • E04C—STRUCTURAL ELEMENTS; BUILDING MATERIALS
    • E04C5/00—Reinforcing elements, e.g. for concrete; Auxiliary elements therefor
    • E04C5/01—Reinforcing elements of metal, e.g. with non-structural coatings
    • E—FIXED CONSTRUCTIONS
    • E04—BUILDING
    • E04C—STRUCTURAL ELEMENTS; BUILDING MATERIALS
    • E04C5/00—Reinforcing elements, e.g. for concrete; Auxiliary elements therefor
    • E04C5/08—Members specially adapted to be used in prestressed constructions
    • E04C5/12—Anchoring devices
    • E—FIXED CONSTRUCTIONS
    • E04—BUILDING
    • E04C—STRUCTURAL ELEMENTS; BUILDING MATERIALS
    • E04C5/00—Reinforcing elements, e.g. for concrete; Auxiliary elements therefor
    • E04C5/16—Auxiliary parts for reinforcements, e.g. connectors, spacers, stirrups
    • E04C5/162—Connectors or means for connecting parts for reinforcements
    • E—FIXED CONSTRUCTIONS
    • E04—BUILDING
    • E04G—SCAFFOLDING; FORMS; SHUTTERING; BUILDING IMPLEMENTS OR AIDS, OR THEIR USE; HANDLING BUILDING MATERIALS ON THE SITE; REPAIRING, BREAKING-UP OR OTHER WORK ON EXISTING BUILDINGS
    • E04G21/00—Preparing, conveying, or working-up building materials or building elements in situ; Other devices or measures for constructional work
    • E04G21/12—Mounting of reinforcing inserts; Prestressing
    • E—FIXED CONSTRUCTIONS
    • E04—BUILDING
    • E04B—GENERAL BUILDING CONSTRUCTIONS; WALLS, e.g. PARTITIONS; ROOFS; FLOORS; CEILINGS; INSULATION OR OTHER PROTECTION OF BUILDINGS
    • E04B5/00—Floors; Floor construction with regard to insulation; Connections specially adapted therefor
    • E04B5/02—Load-carrying floor structures formed substantially of prefabricated units
    • E04B5/04—Load-carrying floor structures formed substantially of prefabricated units with beams or slabs of concrete or other stone-like material, e.g. asbestos cement
    • E04B5/043—Load-carrying floor structures formed substantially of prefabricated units with beams or slabs of concrete or other stone-like material, e.g. asbestos cement having elongated hollow cores
    • E—FIXED CONSTRUCTIONS
    • E04—BUILDING
    • E04C—STRUCTURAL ELEMENTS; BUILDING MATERIALS
    • E04C5/00—Reinforcing elements, e.g. for concrete; Auxiliary elements therefor
    • E04C5/08—Members specially adapted to be used in prestressed constructions
    • E04C5/10—Ducts

Definitions

  • the present invention generally relates to the manufacture of structural elements, in particular beams, slabs or concrete forms.
  • a prefabricated structural member having an elongate body, and at least a first tensioner which is secured in the elongate body such that it compresses and flexes the elongated body in a first direction.
  • It also relates to a method of installing such a structural element in a structure.
  • the invention applies to any type of work, for example to buildings, bridges, dams ...
  • a well known problem of concrete is that, if it resists compressive forces, it cracks quickly when subjected to tensile forces. It is estimated that concrete withstands compressive forces twenty times better than tensile forces.
  • the solution then considered is to use so-called prestressed concrete.
  • prestressed concrete The idea is to make sure that the concrete always works in compression and never (or little) in traction. For this, we put tensioners in the concrete (usually steel bars or wire ropes) on which we exert traction so that at rest, the concrete is compressed.
  • the first method consists in applying a tension on the tensioners before the complete setting of the concrete. After drying of the concrete, the tensioners are released, thus putting the beam in compression simply by adhering effect.
  • the first disadvantage is that at the moment of release of the beam and the release of the tensioners, the latter cause excessive forces on the beam which have the effect of bending the latter quickly, the risk that these efforts of traction or compression generate cracks in the concrete. It is therefore necessary to wait until the concrete has dried before releasing the tensioners and unmolding the beam.
  • Another disadvantage is that, when the beam is not yet loaded, its flexion generates tensile stresses in the concrete (at the convex face of the beam) as well as localized stress particularly strong (at the level of the beam). the concave face of the beam).
  • the prestressing generated by the first tensioners must not exceed a threshold beyond which the beam bending too much, it would crack.
  • the second method consists of arranging the tensioners through straight ducts or curves incorporated in the concrete beams. After setting the concrete, the beam is placed in the structure (building, bridge, ...) before the tensioners are stretched. Once the beam is put in place, it is progressively loaded (for example by laying slabs on top). It is during this loading step that the tensioners will be gradually tensioned so as to compress and bend the beams as they are loaded.
  • This technique makes it possible to progressively compensate for the forces exerted on the beam when it is loaded. It then makes it possible to reach concrete compressive strength limits, so that the beam obtained by this technique can be more loaded than that obtained by pre-tensioning.
  • the present invention proposes a new structural element which has the advantages of prestressing by pre-tension and which is adapted to withstand higher loads.
  • a structural element as defined in the introduction wherein there is provided at least one second tensioner which is fixed at two distinct points to said elongate body so that it compresses and flexes the elongate body, and wherein there is provided a disabling means for releasing the compression and bending exerted on the elongated body by said second tensioner.
  • the first and second tensioners will then be tensioned during the molding of the body (beam, slab, ...) of the structural element in the factory.
  • the manufacturing method of the structural element will therefore be as easy to implement as the preload preload process.
  • the first and second tensioners will generally be located longitudinally in the body along two opposite faces thereof. In this way, the tension exerted on the first and second tensioners will generate little or no bending of the structural element (the counter-boom exerted by the first tensioner will be compensated by the arrow exerted by the second tensioner).
  • the second or the second tensioners will allow to compress and flex the body temporarily. After releasing the second tensioners, the structural element will behave as a structural element obtained by a preloading preloading method.
  • the major advantage of the invention will be that, as the body will not flex or little, it will be possible to compress it further.
  • the second tensioner being fixed to said elongate body by fixing means, at least one of said fixing means comprises a removable part which forms said deactivation means;
  • the second tensioner being made in two parts which are located in the extension of one another and which are connected to one another by a fixing means, the fixing means comprises a removable portion which forms said deactivation means;
  • said removable part is fusible; - said removable portion is removable;
  • At least a central portion of the second tensioner is accessible from outside the elongate body to be cut or broken;
  • the deactivating means are only adapted to relax the compression and the bending exerted on the elongated body by the central portion of said second tensioner;
  • each second tensioner is adapted to be entirely or partially extracted from said elongated body
  • each second tensioner comprises a wire, a cable or a metal bar
  • At least a central portion of the second tensioner is threaded freely in a sheath attached to the elongated body;
  • At least one central portion of the second tensioner is located outside the elongated body
  • each first tensioner comprises a wire, a cable or a metal bar, embedded in the material of the elongated body
  • the invention also proposes a method of constructing a structure, comprising steps:
  • steps c) and d) are operated concomitantly.
  • said posterior structure comprising at least one structural element according to the invention, steps c) and d) are followed by the steps:
  • FIGS. 1A and 1B are diagrammatic side and sectional views of a beam of rectangular section according to the invention.
  • FIG. 1C is a diagram of the forces and moments acting empty on the body of the beam represented in FIGS. 1A and 1B,
  • FIG. 1D is a diagram of the forces and moments exerted under load on the body of the beam represented in FIGS. 1A and 1B,
  • FIGS. 2A, 2B and 2C are detailed views, in section, of three embodiments of the means for deactivating a second tensioner of the beam represented in FIGS. 1A and 1B,
  • FIGS. 3A and 3B are diagrammatic side and sectional views of an I-section beam according to the invention.
  • FIGS. 4A and 4B are diagrammatic side and sectional views of a slab according to the invention.
  • FIG. 5A and 5B are schematic views of a structure using beams and slabs according to the invention.
  • FIGs 1A, 3A, 4A and 5A there are shown four types of structural elements 10, 20, 30, 40 prefabricated.
  • beams 10, 20 In Figures 1A and 3A, there are beams 10, 20.
  • slabs 30, 40 In Figures 4A and 5A, it is slabs 30, 40. The points common to these various structural elements 10, 20, 30, 40 will be described together in a first part of this presentation. These structural elements 10, 20, 30, 40 will then be described successively in detail in a second part of this disclosure.
  • Each structural element 10, 20, 30, 40 firstly comprises an elongate body 11, 21, 31, 41. This body gives the structural element 10, 20, 30, 40 its general shape. It also incorporates reinforcement to preload.
  • the body 1 1, 21, 31, 41 is made of concrete.
  • another material could be used.
  • this load can be divided into two components: a permanent component and a variable component.
  • the compression obtained will then compensate for the aforementioned tensile stresses, so as to avoid the appearance of cracks.
  • the body 1 1, 21, 31, 41 is thus prestressed by each first tensioner 1.
  • first linear tensioners 1 will be used. These first tensioners 1 may be formed by son, by wire ropes or by steel bars with high capacity. They will preferably be drowned in the concrete, so as to progressively transmit efforts to body of the structural element 10, 20, 30, 40. They are also eccentric with respect to the neutral fiber A1 of the body 1 1, 21, 31, 41 of the structural element 10, 20, 30, 40 considered.
  • these first tensioners 1 are preferably distributed under the neutral fiber A1 of the body 1 1, 21, 31, 41 of the structural element 10, 20, 30, 40 considered.
  • the first tensioners 1 extend in length parallel to the neutral fiber A1 of the body 1 1 of the beam 10, and they are regularly distributed around a lower average fiber A2.
  • the total traction exerted on the first tensioners 1 thus makes it possible to compress the body 1 1 of the beam 10 according to the lower average fiber A2.
  • these first tensioners 1 thus exert a compressive force E1 on the body 1 1 of the beam 10.
  • This compression force E1 generates compression stresses distributed homogeneously over the entire section. of the body 1 1.
  • the lower average fiber A2 is here below the neutral fiber A1, at a distance from it denoted by the difference D1.
  • the first tensioners 1 exert a bending moment M1 on the body 1 1 of the beam 10.
  • This bending moment M1 makes it possible to bend the body 1 1 towards the high, that is to say in a direction opposite to that according to which it tends to bend under the effect of its own weight (it is said of the beam that it presents a "counter-arrow").
  • This bending moment M1 generates, in the upper part of the body 1 1, tensile stresses. It also generates compressive stresses in the lower part of the body 1 1.
  • the bending moment M1 is not compensated and tends to bend the body 1 1, 21, 31, 41 (in particular when the structural element is stored vertically and its own weight no longer bends the body towards the low).
  • the invention then proposes a method for increasing this difference
  • the structural element 10, 20, 30, 40 comprises at least one second tensioner 2 which is fixed at two distinct points to the body 1 1, 21, 31, 41 by two fastening means 3 such that it compresses and flexes the body January 1, 21, 31, 41 downwards, and there is provided a deactivation means 3B for releasing the compression and the sagging exerted on the elongate body 1 1 , 21, 31, 41 by this second tensioner 2.
  • each second tensioner 2 is located on the body January 1, 21, 31, 41 off-center relative to the neutral fiber A1 so that when the structural element is not yet implemented in the structure and is not yet loaded, the compression that it exerts on the structural element makes it possible to avoid the appearance of cracks.
  • each second tensioner 2 is located above the neutral fiber A1 of the body 1 1, 21, 31, 41, so that it exerts on the body a bending moment which is at least partially opposed at the moment of M1 flexion.
  • second tensioners 2 may be formed by wires, by metal cables or by metal bars, preferably made of suitable steel.
  • these second tensioners 2 are preferably distributed above the neutral fiber A1 of the body 1 1, 21, 31, 41 of the structural element 10, 20, 30, 40 considered. As shown for example in Figures 1A and 1B (and it is the same for the other structural elements 20, 30, 40), these second tensioners 2 are here elongate parallel to the neutral fiber A1 of the body 1 1 of the beam 10 and are regularly distributed around a medium upper fiber A3.
  • the total traction exerted on the second tensioners 2 thus makes it possible to compress the body 1 1 of the beam 10 according to the upper middle fiber A3.
  • these second tensioners 2 exert a compressive force E2 on the body 1 1 of the beam 10, which is added to the compression force E1.
  • This compression force E2 generates compression stresses distributed homogeneously over the entire section of the body January 1.
  • this upper middle fiber A3 is situated above the neutral fiber A1, at a distance from it denoted by the difference D2.
  • these second tensioners 2 exert a bending moment M2 on the body 1 1 of the beam 10, in the opposite direction to the bending moment M1.
  • This bending moment M2 makes it possible to bend the body 1 1 downwards, so that it makes it possible to compensate at least in part for the bending of the body 1 1 under the effect of the bending moment M1.
  • this bending moment M2 can simulate a load on the beam 10 when it is not yet loaded.
  • the means for deactivating each second tensioner 2 will then, when the beam 10 begins to be loaded, to release the second tensioner 2 so as to cancel the bending moment M2.
  • the ends of the second tensioners are releasably fixed to the body of the structural member, provision can be made to release only the central portions of these second tensioners. For example, it is possible to cut the second tensioners at their centers, so that their two ends remain fixed to the body of the structural element. In this variant, the ends of the second tensioners will therefore, after cutting, continue to exert compression forces and bending moments at the ends of the body of the structural element. These efforts and moments will then offset the efforts that the first tendons exert on these abouts.
  • the body 1 1 of the beam 10 has a substantially parallelepiped shape.
  • the first tensioners 1 are entirely embedded in the concrete of the body 1 1 of the beam 10, with the possible exception of their ends which can project from the body. They are therefore irremovable relative to the body of the beam 10.
  • the second tensioners 2 are slidably mounted in the body 1 1 of the beam 10. As shown in Figure 2B, the second tensioners 2 are for this purpose threaded into sheaths 4 cast in the concrete, so that their ends open at both ends of the body 1 1. These sheaths 4, here made of plastic, prevent the concrete from catching on the second tensioners 2.
  • the first tensioners 1 are distributed over three rows and five columns.
  • the first tensioner 1 which is located in the center of this matrix therefore extends along the lower average fiber A2.
  • the second tensioners 2 here are twice as numerous as the first tensioners 1 and are distributed relative to one another in substantially the same manner as the first tensioners.
  • the second tensioner 2 which is located in the center of this matrix therefore extends according to the upper middle fiber A3.
  • the neutral fiber A1 which passes to the centers of the cross sections of the body 1 1, therefore extends between the upper middle fibers A3 and lower A2, at equal distances from them.
  • each second tensioner 2 is fixed at two distinct points to the body 1 1 of the beam 10, by two fixing means, and there is provided a deactivation means for releasing each second tensioner 2.
  • each second tensioner 2 is fixed by its two ends 2A to both ends of the body 1 1 of the beam 10. In this way, these 2A ends remain easily accessible from outside the body 1 1.
  • the deactivation means is provided to allow, on site, to release the tension of the second tensioner 2.
  • This deactivation means may be presented in various ways. It can thus be integrated into at least one of the fastening means 3 of the ends 2A of the second tensioners 2 to the body 1 1 of the beam 10.
  • this fastening means 3 comprises a bushing 3A which is pressed against the corresponding end of the body 1 1 of the beam 10 and which internally houses two keys 3B.
  • the sleeve 3A has a cylindrical outer face of revolution, and a frustoconical inner face whose apex is turned towards the body January 1.
  • the keys 2B generally have a cylinder shape cut in half along the length direction. They each have a frustoconical outer face of shape corresponding to that of the inner face of the sleeve 3A, and a notched inner face.
  • the aforementioned deactivation means is then formed by the two keys 3B. These two keys 3B protrude outside the sleeve 3A, so that they are adapted to be pulled mechanically outside the sleeve 3A so as to release the end 2A of the second tensioner 2.
  • the deactivation means is fuse.
  • this deactivation means is formed by a metal layer or a non-metallic paste which covers the end 2A of the second tensioner 2 (or the inner face of the sleeve 3A or keys 3B), whose temperature The melting point is relatively low and has satisfactory mechanical characteristics. It may thus be a layer of zinc or tin, since the melting temperature of these materials is quite low (below 450 ° C., preferably of the order of 200 to 300 ° C.) to allow its fusion on site, and that its rigidity at ambient temperature is sufficient to ensure good grip of the second tensioner 2.
  • the removable fastening means could be under another form.
  • the fastening means used could be in the form of an adhesive or a fusible paste. It could also be in the form of a sleeve easily destructible (for example by cutting), which would be threaded on the second tensioner and which would bear against the body.
  • the end 2A of the second tensioner 2 could be coated with a layer of zinc or tin and be directly sealed in the concrete.
  • the metal layer it will be possible to melt it so that the second tensioner 2 can escape from the concrete and release the compression and bending it exerts on the body 1 1 of the beam 10.
  • the second attachment means designed to lock the other end of the second tensioner 2 may also be in various forms.
  • first removable fastening means can thus be in the same form as the first removable fastening means. It may also be in the form of a sleeve which will be threaded and fixed on the second tensioner and which will simply bear against the body.
  • this second fastening means may fix the second end of the second tensioner 2 immovably to the body 1 1 of the beam 10, in which case the second tensioner 2 can not be extracted from the body 1 1.
  • this second fastening means may fix the second end of the second tensioner 2 immovably to the body 1 1 of the beam 10, in which case the second tensioner 2 can not be extracted from the body 1 1.
  • the deactivating means is not at one end of the second tensioner 2, but at a distance from them.
  • the second tensioner 2 is made in two parts 2C, 2D located in the extension of one another and which are connected together by a fixing means 5.
  • This fixing means 5 comprises a sleeve 5A inside which are housed two pairs of keys 3B.
  • the keys 3B are identical to those shown in Figure 2A.
  • the sleeve 5A has meanwhile an inner face which has two frustoconical parts turned in opposite directions.
  • the contiguous ends of the two parts 2C, 2D of the tensioner are each coated with a coating of zinc or tin or other material which represents suitable characteristics, in which runs a resistance wire.
  • the keys 3B move towards the two ends of the sleeve 5A, which allows them to close in the manner of two jaws on the contiguous ends of the two parts 2C, 2D of the second tensioner 2.
  • the beam can thus have a length of 7 meters, a height
  • the first tensioners 1 can be distributed in such a way that the average lower fiber A2 extends to 6.8 centimeters from the lower face of the body 1 1 of the beam 10.
  • the second tensioners 2 may be distributed in such a way that the upper middle fiber A3 extends 5 centimeters from the upper face of the body 1 1 of the beam 10.
  • This beam 10 can be preloaded thanks to the first tensioners 1 with a compression force E1 equal to 192 tons. It will further be possible to temporarily prestress this beam 10 thanks to the second tensioners 2 with a compressive force E2 equal to 120 tons.
  • FIG. 3A a second embodiment of a beam 20 according to the invention is shown.
  • the body 21 of the beam 20 has a cross section I.
  • the body 21 of the beam 20 thus has two parallel flanges 23 between which a vertical wall 22 extends.
  • the first and second tensioners 1, 2 then extend over the entire length of the beam 20, in parallel with each other.
  • first tensioners 1 embedded in the concrete of the lower sole 23 of the body 21 of the beam 20. These first tensioners 1 are again evenly distributed over the width of the beam 20. Thus, when they compress the body 21 of the beam 10, they do not deform in torsion.
  • These first five tensioners 1 are located near the lower face of the lower sole 23. Thus, when they are tensioned, they allow to bend the body 21 of the beam 20 so that the center of the beam moves to the top.
  • the body 31 of the slab 30 has a generally parallelepiped shape. Its neutral fiber A1 is thus merged with the central longitudinal axis of the body 31.
  • the ends of the slab 30, however, project from the upper face of the body 31, flanges 32. These two edges 32 along the two ends of the body 31. They delimit between them a cavity 33 in which can be cast a screed.
  • the first and second tensioners 1, 2 extend over the entire length of the slab 30, in parallel with each other. It is here provided a plurality of first tensioners 1 embedded in the concrete of the body 31 of the slab 30. These first tensioners 1 are again evenly distributed over the width of the slab 30, under the neutral fiber A1. They are located near the lower face of the body 31 of the slab 30.
  • second tensioners 2 which are regularly distributed over the width of the slab 30, above the neutral fiber A1. These second tensioners 2 pass through the two flanges 32 of the body 31 of the slab 30 so that their ends protrude on either side of the body 31 of the slab 30. A central portion of each of the second tensioners 2, which are extends between these two flanges 32, is instead located in the cavity 33, outside the body 31.
  • the second tensioners 2 are sheathed over their entire length, which ensures their sliding through the flanges 32 and which guarantees their protection vis-à-vis the outside. These sheaths are also useful when a concrete screed is poured into the cavity 33, since they prevent the concrete of the screed from adhering to the second tensioners 2.
  • the second tensioners 2 are sheathed only over a part of their length, that located in the cavity 33.
  • the parts of the second tensioners that pass through the flanges 32 will themselves be coated with zinc or tin and cast in concrete. To allow to relax the forces exerted by these second tensioners, it will then be sufficient to heat the coating zinc or tin.
  • the second tensioners 2 are not sheathed, provided that the height of the concrete screed to be poured into the cavity 33 is small enough so that, once this screed has been poured, the second tensioners are located at above this screed.
  • the flanges 32 make it possible to off-center the second tensioners 2 at a great distance from the neutral fiber A1 of the body 31. In this way, the tensile force exerted on each of the second tensioners 2 may be less than that exerted on the first tensioners 1. It is thus possible to use here second tensioners 2 of a diameter smaller than that of the first tensioners 1 or to reduce the number of second tensioners 2 used.
  • the fastening means provided at the ends of these second tensioners 2 are here again identical to those described with reference to FIGS. 1A, 1B and 2B.
  • the body (31) is devoid of flange (32), in which case the second tensioners would be entirely located through the body of the slab.
  • FIG. 5A shows a second embodiment of slabs 40 according to the invention.
  • the slabs 40 shown in this FIG. 5A differ from the slab 30 shown in FIGS. 4A and 4B only by the honeycombed character of their body 41.
  • honeycombed slabs 40 that is to say slabs 40 whose body is hollowed out of longitudinal conduits called cells. These cells reduce the weight of the slab while preserving its thickness to ensure good rigidity.
  • the solid surface of the section of the slab is here greater because of the absence of cells. Therefore, the slab is able to undergo greater compressive forces.
  • the slab can thus have a length of 9 meters, a height L2 of 20 centimeters, and a width L3 of 1.2 meters.
  • the first tensioners 1 may be distributed in such a way that the lower average fiber A2 extends 4 cm from the lower face of the body 31 of the slab 30, 40.
  • the second tensioners 2 may be distributed in such a way that the upper middle fiber A3 extends 4 cm above the upper face of the body 31 of the slab 30, 40.
  • This slab 40 can be preloaded thanks to the first tensioners 1 with a compression force equal to 140 tons. It will also be possible to preload temporarily this slab 40 through the second tensioners 2 with a compressive force equal to 60 tons. The result will be that this hollow slab 40 will be able to withstand loads twice as heavy as a hollow slab that would not have been equipped with second tensioners 2. It is indeed designed to withstand a prestressing of 140 tons which is much higher than prestressing that could not have been applied in the absence of second tensioners (which would have been about 82 tons).
  • This slab 30 can be preloaded thanks to the first tensioners 1 with a compression force equal to 192 tons. It will further be possible to prestress temporarily this slab 30 thanks to the second tensioners 2 with a compressive force equal to 96 tons.
  • this solid slab 30 can support loads three times heavier than a hollow slab that would not have been equipped with second tensioners 2. It is clear that a solid slab can store more prestressing than hollow slab.
  • the beams 10 and slabs 40 are prefabricated at the factory.
  • Their manufacturing process consists of arranging the first and second tensioners 1, 2 in molds (the second tensioners being here already sheathed and equipped with their frustoconical sleeves 3), to apply a tension on these tensioners, to pour concrete into the molds , and to wait for the complete setting of the concrete. After the concrete has dried, the first and second tensioners 1, 2 are released, thus putting the bodies 1 1, 31 of the beams and slabs in eccentric longitudinal compression.
  • the beams 10 and slabs 40 are then removed from their respective molds. Due to the forces exerted by the first and second tensioners 1, 2, the bodies 1 1, 31 do not tend to bend excessively. Consequently, the exit of the beams 10 and slabs 40 outside their molds does not cause sudden bending of the bodies, which prevents the appearance of cracks in the concrete.
  • the first operation will consist in installing two beams 10 in parallel and at a distance from each other, each cantilever between two supports 50 spaced apart from each other. For this, the ends of each beam 10 will be placed on flanges 51 provided on these supports 50.
  • the second operation will consist of gradually loading the two beams 10 by installing on them slabs 40, the ends of each slab 40 resting respectively on the two beams 10.
  • the slabs used will be honeycombed, it will be possible to place the second tensioners in the cells themselves, so as to facilitate their installation and extraction.
  • a bridge a beam of the type shown in Figures 3A and 3B, with a length of 40 meters, a section of 2.5 meters in height, a lower heel 70 centimeters in width, a heel greater than 1, 2 meters in width, and a core thickness of 24 centimeters.
  • the release of second tensioners makes it possible to obtain an effect similar to a second phase of prestressing by post tension.

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Abstract

The invention relates to a prefabricated structural element comprising an elongate body (11) and at least one first tensioner (1) that is attached in the elongate body such that it compresses the elongate body. According to the invention, the structural element comprises at least one second tensioner (2) that is attached at two separate points to said elongate body by two attachment means so that it compresses the elongate body. At least one of said attachment means is removable so as to make it possible to relax the compression exerted by the second tensioner on the elongate body.

Description

ELÉMENT DE STRUCTURE A PRÉCONTRAINTE ANTICIPÉE  ANTICIPATED PRE-STRUCTURED STRUCTURE ELEMENT
DOMAINE TECHNIQUE AUQUEL SE RAPPORTE L'INVENTION La présente invention concerne de manière générale la fabrication d'éléments de structure, notamment de poutres, de dalles ou d'ourdis en béton. TECHNICAL FIELD TO WHICH THE INVENTION RELATES The present invention generally relates to the manufacture of structural elements, in particular beams, slabs or concrete forms.
Elle concerne plus particulièrement un élément de structure préfabriqué comportant un corps allongé, et au moins un premier tendeur qui est fixé dans le corps allongé de telle manière qu'il comprime et fléchit le corps allongé dans une première direction.  More particularly, it relates to a prefabricated structural member having an elongate body, and at least a first tensioner which is secured in the elongate body such that it compresses and flexes the elongated body in a first direction.
Elle concerne également un procédé d'installation d'un tel élément de structure dans un ouvrage.  It also relates to a method of installing such a structural element in a structure.
L'invention s'applique à tout type d'ouvrage, par exemple aux bâtiments, aux ponts, aux barrages...  The invention applies to any type of work, for example to buildings, bridges, dams ...
ARRIERE-PLAN TECHNOLOGIQUE  BACKGROUND
II est courant, lors de la construction d'un tel ouvrage, d'utiliser des poutres et des dalles en béton.  It is common, during the construction of such a structure, to use concrete beams and slabs.
Un problème bien connu du béton est que, s'il résiste bien aux efforts de compression, il se fissure vite lorsqu'il est soumis à des efforts de traction. On estime ainsi que le béton résiste vingt fois mieux aux efforts de compression qu'aux efforts de traction.  A well known problem of concrete is that, if it resists compressive forces, it cracks quickly when subjected to tensile forces. It is estimated that concrete withstands compressive forces twenty times better than tensile forces.
Il est alors connu de renforcer le béton par des armatures métalliques. On parle de béton armé.  It is then known to strengthen the concrete by metal reinforcements. We are talking about reinforced concrete.
Toutefois, si le béton armé présente certains avantages, son utilisation devient contre-productive lorsque les contraintes exercées sur la structure deviennent importantes, du fait de l'alourdissement de la section de béton armé.  However, if the reinforced concrete presents some advantages, its use becomes counterproductive when the stresses on the structure become important, because of the increase of the section of reinforced concrete.
La solution alors envisagée est d'utiliser du béton dit précontraint. L'idée est alors de s'assurer que le béton travaille toujours en compression et jamais (ou peu) en traction. Pour cela, on place des tendeurs dans le béton (généralement des barres d'acier ou des câbles métalliques) sur lesquels on exerce une traction de telle sorte qu'au repos, le béton soit comprimé.  The solution then considered is to use so-called prestressed concrete. The idea is to make sure that the concrete always works in compression and never (or little) in traction. For this, we put tensioners in the concrete (usually steel bars or wire ropes) on which we exert traction so that at rest, the concrete is compressed.
De cette manière, lorsque le béton subit des efforts de traction, il se décomprime mais ne travaille jamais en traction, ce qui évite l'apparition de fissures.  In this way, when the concrete undergoes traction forces, it decompresses but never works in tension, which prevents the appearance of cracks.
Actuellement, on connaît deux procédés de fabrication de poutres en béton précontraint. At present, two methods of manufacturing beams are known Prestressed concrete.
Le premier procédé, dit de pré-tension, consiste à appliquer une tension sur les tendeurs avant la prise complète du béton. Après séchage du béton, les tendeurs sont libérés, mettant ainsi la poutre en compression par simple effet d'adhérence.  The first method, called pre-tension, consists in applying a tension on the tensioners before the complete setting of the concrete. After drying of the concrete, the tensioners are released, thus putting the beam in compression simply by adhering effect.
Ce procédé est simple à mettre en œuvre. Généralement, lorsque la poutre est prévue pour être placée à l'horizontale et pour être chargée, les tendeurs sont décentrés par rapport à la fibre neutre de la poutre de telle manière qu'ils permettent de fléchir la poutre vers le haut (on parle de contre-flèche), à l'opposé de la charge que la poutre va recevoir (une fois chargée, la poutre se retrouvera alors peu déformée).  This process is simple to implement. Generally, when the beam is intended to be placed horizontally and to be loaded, the tensioners are off-center with respect to the neutral fiber of the beam in such a way that they allow the beam to bend upwards (we speak of counter-arrow), the opposite of the load that the beam will receive (once loaded, the beam will then be slightly deformed).
Ce procédé présente toutefois deux inconvénients.  This method, however, has two disadvantages.
Le premier inconvénient est qu'au moment du démoulage de la poutre et de la libération des tendeurs, ces derniers provoquent des efforts excessifs sur la poutre qui ont pour effet de fléchir cette dernière rapidement, au risque que ces efforts de traction ou de compression génèrent des fissures dans le béton. Il convient donc d'attendre que le béton ait bien séché avant de relâcher les tendeurs et démouler la poutre.  The first disadvantage is that at the moment of release of the beam and the release of the tensioners, the latter cause excessive forces on the beam which have the effect of bending the latter quickly, the risk that these efforts of traction or compression generate cracks in the concrete. It is therefore necessary to wait until the concrete has dried before releasing the tensioners and unmolding the beam.
Un autre inconvénient est que, lorsque la poutre n'est pas encore chargée, sa flexion génère des contraintes de traction dans le béton (au niveau de la face convexe de la poutre) ainsi que des contraintes de compression localisées particulièrement fortes (au niveau de la face concave de la poutre). La précontrainte générée par les premiers tendeurs ne doit donc pas excéder un seuil au-delà duquel la poutre se fléchissant trop, elle se fissurerait.  Another disadvantage is that, when the beam is not yet loaded, its flexion generates tensile stresses in the concrete (at the convex face of the beam) as well as localized stress particularly strong (at the level of the beam). the concave face of the beam). The prestressing generated by the first tensioners must not exceed a threshold beyond which the beam bending too much, it would crack.
Le second procédé, dit de post-tension, consiste à disposer des tendeurs au travers de gaines rectilignes ou courbes incorporées au béton des poutres. Après la prise du béton, la poutre est mise en place dans l'ouvrage (bâtiment, pont, ...) avant que les tendeurs ne soient tendus. Une fois la poutre mise en place, elle est progressivement chargée (par exemple en posant des dalles par dessus). C'est au cours de cette étape de chargement que les tendeurs vont être progressivement mis en tension de manière à comprimer et fléchir les poutres au fur et à mesure que celles-ci seront mises en charge.  The second method, called post-tension, consists of arranging the tensioners through straight ducts or curves incorporated in the concrete beams. After setting the concrete, the beam is placed in the structure (building, bridge, ...) before the tensioners are stretched. Once the beam is put in place, it is progressively loaded (for example by laying slabs on top). It is during this loading step that the tensioners will be gradually tensioned so as to compress and bend the beams as they are loaded.
Cette technique permet de compenser progressivement les efforts qui s'exercent sur la poutre lorsqu'on la charge. Elle permet alors d'atteindre les limites de résistance du béton à la compression, si bien que la poutre obtenue par cette technique peut être davantage chargée que celle obtenue par pré-tension. This technique makes it possible to progressively compensate for the forces exerted on the beam when it is loaded. It then makes it possible to reach concrete compressive strength limits, so that the beam obtained by this technique can be more loaded than that obtained by pre-tensioning.
Cette technique, relativement complexe, est en revanche généralement réservée aux grands ouvrages puisqu'elle nécessite la mise en œuvre de machines de mise en tension encombrantes. Elle s'avère en outre onéreuse non seulement à cause de l'utilisation de ces machines, mais également car les tendeurs sont enfilés au travers de gaines spéciales et onéreuses dans lesquelles est injecté un enduit spécial qui permet de transmettre les efforts à la poutre.  This relatively complex technique is however generally reserved for large structures since it requires the implementation of cumbersome tensioning machines. It is also expensive not only because of the use of these machines, but also because the tensioners are threaded through special sheaths and expensive in which is injected a special coating that can transmit the forces to the beam.
OBJET DE L'INVENTION  OBJECT OF THE INVENTION
Afin de remédier aux inconvénients précités de l'état de la technique, la présente invention propose un nouvel élément de structure qui présente les avantages de la précontrainte par pré-tension et qui est adapté à supporter de plus fortes charges.  In order to overcome the aforementioned drawbacks of the state of the art, the present invention proposes a new structural element which has the advantages of prestressing by pre-tension and which is adapted to withstand higher loads.
Plus particulièrement, on propose selon l'invention un élément de structure tel que défini dans l'introduction, dans lequel il est prévu au moins un second tendeur qui est fixé en deux points distincts audit corps allongé de telle sorte qu'il comprime et fléchit le corps allongé, et dans lequel il est prévu un moyen de désactivation pour relâcher la compression et le fléchissement exercés sur le corps allongé par ledit second tendeur.  More particularly, there is provided according to the invention a structural element as defined in the introduction, wherein there is provided at least one second tensioner which is fixed at two distinct points to said elongate body so that it compresses and flexes the elongate body, and wherein there is provided a disabling means for releasing the compression and bending exerted on the elongated body by said second tensioner.
Les premier et second tendeurs seront alors mis en tension lors du moulage du corps (poutre, dalle, ...) de l'élément de structure en usine. Le procédé de fabrication de l'élément de structure sera donc aussi facile à mettre en œuvre que le procédé de précontrainte par pré-tension.  The first and second tensioners will then be tensioned during the molding of the body (beam, slab, ...) of the structural element in the factory. The manufacturing method of the structural element will therefore be as easy to implement as the preload preload process.
Les premier et second tendeurs seront généralement situés longitudinalement dans le corps, le long de deux faces opposées de celui-ci. De cette manière, la tension exercée sur les premier et second tendeurs ne générera pas ou peu de fléchissement de l'élément de structure (la contre-flèche exercée par le premier tendeur sera compensée par la flèche exercée par le second tendeur).  The first and second tensioners will generally be located longitudinally in the body along two opposite faces thereof. In this way, the tension exerted on the first and second tensioners will generate little or no bending of the structural element (the counter-boom exerted by the first tensioner will be compensated by the arrow exerted by the second tensioner).
On comprend ainsi que cet élément de structure pourra être démoulé plus tôt puisqu'il n'y aura pas de risque de fissuration au moment du relâchement des tendeurs et du démoulage. Sa fabrication sera donc plus rapide, au bénéfice de son coût de production.  It is thus understood that this structural element can be demolded sooner since there will be no risk of cracking at the moment of release of the tensioners and demolding. Its manufacture will therefore be faster, to the benefit of its cost of production.
Grâce à l'invention, le ou les seconds tendeurs vont permettre de comprimer et de fléchir le corps de manière provisoire. Après le relâchement des seconds tendeurs, l'élément de structure se comportera comme un élément de structure obtenu par un procédé de précontrainte par pré-tension. Thanks to the invention, the second or the second tensioners will allow to compress and flex the body temporarily. After releasing the second tensioners, the structural element will behave as a structural element obtained by a preloading preloading method.
L'avantage majeur de l'invention sera que, comme le corps ne fléchira pas ou peu, il sera possible de le comprimer davantage.  The major advantage of the invention will be that, as the body will not flex or little, it will be possible to compress it further.
En effet, tant que les seconds tendeurs seront tendus, l'élément de structure sera pas ou peu fléchi. On pourra alors prévoir de relâcher ces seconds tendeurs au fur et à mesure que l'élément de structure sera chargé, de manière que ces relâchements successifs des seconds tendeurs permettent de compenser la déformation de l'élément de structure provoqué par la charge.  Indeed, as long as the second tensioners will be stretched, the structural element will be not or little flexed. It will then be possible to release these second tensioners as the structural element is loaded, so that these successive releases of the second tensioners make it possible to compensate for the deformation of the structural element caused by the load.
Par conséquent, comme la flexion sera moins importante, les risques d'apparition de fissures seront moindres, si bien qu'il sera possible de tendre davantage les premiers tendeurs (et les seconds tendeurs) jusqu'à approcher les limites de tenue du béton à la compression.  Therefore, as the bending will be less important, the risk of crack occurrence will be less, so that it will be possible to stretch more the first tensioners (and the second tensioners) to approach the limits of holding the concrete to the compression.
II sera également possible d'écarter les premiers tendeurs au maximum de la fibre neutre du corps de manière qu'après avoir extrait les seconds tendeurs du corps, les premiers tendeurs exercent sur le corps un fort moment de flexion qui s'oppose à la flexion générée par le poids propre du corps et par les charges qui reposent sur celui-ci.  It will also be possible to remove the first tensioners at the maximum of the neutral fiber of the body so that after extracting the second tensioners of the body, the first tensioners exert on the body a strong bending moment which opposes the bending generated by the weight of the body and the loads that rest on it.
Du fait de la précontrainte plus importante, l'élément de structure sera donc à même de supporter des charges plus lourdes.  Due to the greater prestressing, the structural element will therefore be able to withstand heavier loads.
Pour supporter une charge de même poids, il sera sinon possible de réduire la section de la poutre, ce qui générera des gains de poids, d'encombrement et de coûts.  To support a load of the same weight, it will otherwise be possible to reduce the section of the beam, which will generate gains in weight, bulk and costs.
D'autres caractéristiques avantageuses et non limitatives de l'élément de structure conforme à l'invention sont les suivantes :  Other advantageous and non-limiting features of the structural element according to the invention are the following:
- le second tendeur étant fixé audit corps allongé par des moyens de fixation, l'un au moins desdits moyens de fixation comporte une partie amovible qui forme ledit moyen de désactivation ;  the second tensioner being fixed to said elongate body by fixing means, at least one of said fixing means comprises a removable part which forms said deactivation means;
- le second tendeur étant réalisé en deux parties qui sont situées dans le prolongement l'une de l'autre et qui sont raccordées l'une à l'autre par un moyen de fixation, ce moyen de fixation comporte une partie amovible qui forme ledit moyen de désactivation ;  - the second tensioner being made in two parts which are located in the extension of one another and which are connected to one another by a fixing means, the fixing means comprises a removable portion which forms said deactivation means;
- ladite partie amovible est fusible ; - ladite partie amovible est démontable ; said removable part is fusible; - said removable portion is removable;
- au moins une partie centrale du second tendeur est accessible depuis l'extérieur du corps allongé pour être découpée ou cassée ;  - At least a central portion of the second tensioner is accessible from outside the elongate body to be cut or broken;
- le second tendeur étant fixé audit corps allongé par ses extrémités, les moyen de désactivation sont uniquement adaptés à relâcher la compression et le fléchissement exercés sur le corps allongé par la partie centrale dudit second tendeur ;  - the second tensioner being fixed to said elongate body by its ends, the deactivating means are only adapted to relax the compression and the bending exerted on the elongated body by the central portion of said second tensioner;
- chaque second tendeur est adapté à être entièrement ou partiellement extrait dudit corps allongé ;  each second tensioner is adapted to be entirely or partially extracted from said elongated body;
- chaque second tendeur comporte un fil, un câble ou une barre métallique;  each second tensioner comprises a wire, a cable or a metal bar;
- au moins une partie centrale du second tendeur est enfilée librement dans une gaine fixée au corps allongé ;  - At least a central portion of the second tensioner is threaded freely in a sheath attached to the elongated body;
- au moins une partie centrale du second tendeur est située à l'extérieur du corps allongé ;  at least one central portion of the second tensioner is located outside the elongated body;
- chaque premier tendeur comporte un fil, un câble ou une barre métallique, noyé dans le matériau du corps allongé ; et  each first tensioner comprises a wire, a cable or a metal bar, embedded in the material of the elongated body; and
- le corps est formé par une poutre en béton ou par une dalle en béton. L'invention propose également un procédé de construction d'un ouvrage, comportant des étapes :  the body is formed by a concrete beam or a concrete slab. The invention also proposes a method of constructing a structure, comprising steps:
a) d'installation d'une structure initiale,  a) installation of an initial structure,
b) de fixation d'un élément de structure tel que précité à ladite structure initiale,  b) fixing a structural element as mentioned above to said initial structure,
c) d'installation d'une structure postérieure sur ledit élément de structure, de telle sorte que ledit élément de structure est mis en charge,  c) installing a posterior structure on said structural element, such that said structural element is loaded,
d) de désactivation de chaque second tendeur dudit élément de structure pour relâcher la compression et la flexion exercées par le second tendeur sur le corps allongé dudit élément de structure.  d) deactivating each second tensioner of said structural member to release compression and flexion exerted by the second tensioner on the elongated body of said structural member.
Préférentiellement, les étapes c) et d) sont opérées de manière concomitante.  Preferably, steps c) and d) are operated concomitantly.
Avantageusement, ladite structure postérieure comportant au moins un élément de structure conforme à l'invention, les étapes c) et d) sont suivies des étapes :  Advantageously, said posterior structure comprising at least one structural element according to the invention, steps c) and d) are followed by the steps:
e) d'ajout d'une chape ou d'une table de compression ou d'une charge de poids permanente sur ladite structure postérieure, et e) adding a clevis or compression table or a load of permanent weight on said posterior structure, and
f) de désactivation de chaque second tendeur de l'élément de structure de ladite structure postérieure pour relâcher la compression et la flexion exercées par le second tendeur sur le corps allongé dudit élément de structure.  f) deactivating each second tensioner of the structural member of said posterior structure to release the compression and bending exerted by the second tensioner on the elongate body of said structural member.
DESCRIPTION DÉTAILLÉE D'UN EXEMPLE DE RÉALISATION DETAILED DESCRIPTION OF AN EXEMPLARY EMBODIMENT
La description qui va suivre en regard des dessins annexés, donnés à titre d'exemples non limitatifs, fera bien comprendre en quoi consiste l'invention et comment elle peut être réalisée. The following description with reference to the accompanying drawings, given by way of non-limiting examples, will make it clear what the invention consists of and how it can be achieved.
Sur les dessins annexés :  In the accompanying drawings:
- les figures 1A et 1 B sont des vues schématiques de côté et en coupe d'une poutre de section rectangulaire conforme à l'invention,  FIGS. 1A and 1B are diagrammatic side and sectional views of a beam of rectangular section according to the invention,
- la figure 1 C est un diagramme des efforts et moments s'exerçant à vide sur le corps de la poutre représentée sur les figures 1 A et 1 B,  FIG. 1C is a diagram of the forces and moments acting empty on the body of the beam represented in FIGS. 1A and 1B,
- la figure 1 D est un diagramme des efforts et moments s'exerçant sous charge sur le corps de la poutre représentée sur les figures 1 A et 1 B,  FIG. 1D is a diagram of the forces and moments exerted under load on the body of the beam represented in FIGS. 1A and 1B,
- les figures 2A, 2B et 2C sont des vues de détail, en coupe, de trois modes de réalisation des moyens de désactivation d'un second tendeur de la poutre représentée sur les figures 1 A et 1 B,  FIGS. 2A, 2B and 2C are detailed views, in section, of three embodiments of the means for deactivating a second tensioner of the beam represented in FIGS. 1A and 1B,
- les figures 3A et 3B sont des vues schématiques de côté et en coupe d'une poutre de section en I conforme à l'invention,  FIGS. 3A and 3B are diagrammatic side and sectional views of an I-section beam according to the invention,
- les figures 4A et 4B sont des vues schématiques de côté et en coupe d'une dalle conforme à l'invention, et  FIGS. 4A and 4B are diagrammatic side and sectional views of a slab according to the invention, and
- les figures 5A et 5B sont des vues schématiques d'un ouvrage utilisant des poutres et des dalles conformes à l'invention.  - Figures 5A and 5B are schematic views of a structure using beams and slabs according to the invention.
Les ouvrages de grandes tailles (immeubles, ponts) sont généralement réalisés à l'aide d'éléments de structure préfabriqués, qui sont assemblés les uns avec les autres sur le chantier.  Large structures (buildings, bridges) are usually made using prefabricated structural elements, which are assembled together on site.
Dans la description, les termes «inférieur » et «supérieur » seront utilisés par rapport à cet ouvrage une fois assemblé, la partie inférieure d'un élément désignant la partie de cet élément qui est située du côté du sol et la partie supérieure désignant la partie de cet élément qui est située du côté opposé.  In the description, the terms "lower" and "upper" will be used with respect to this work when assembled, the lower part of an element designating the part of this element which is located on the ground side and the upper part designating the part of this element which is located on the opposite side.
Sur les figures 1A, 3A, 4A et 5A, on a représenté quatre types d'éléments de structure 10, 20, 30, 40 préfabriqués. Sur les figures 1A et 3A, il s'agit de poutres 10, 20. Sur les figures 4A et 5A, il s'agit de dalles 30, 40. Les points communs à ces différents éléments de structure 10, 20, 30, 40 seront décrits ensemble dans une première partie de cet exposé. Ces éléments de structure 10, 20, 30, 40 seront ensuite décrits successivement en détail dans une seconde partie de cet exposé. In Figures 1A, 3A, 4A and 5A, there are shown four types of structural elements 10, 20, 30, 40 prefabricated. In Figures 1A and 3A, there are beams 10, 20. In Figures 4A and 5A, it is slabs 30, 40. The points common to these various structural elements 10, 20, 30, 40 will be described together in a first part of this presentation. These structural elements 10, 20, 30, 40 will then be described successively in detail in a second part of this disclosure.
Chaque élément de structure 10, 20, 30, 40 comporte tout d'abord un corps 1 1 , 21 , 31 , 41 allongé. Ce corps confère à l'élément de structure 10, 20, 30, 40 sa forme générale. Il intègre en outre des ferraillages permettant de le précontraindre.  Each structural element 10, 20, 30, 40 firstly comprises an elongate body 11, 21, 31, 41. This body gives the structural element 10, 20, 30, 40 its general shape. It also incorporates reinforcement to preload.
On considérera ici le cas où le corps 1 1 , 21 , 31 , 41 est réalisé en béton. En variante, un autre matériau pourrait être utilisé.  We will consider here the case where the body 1 1, 21, 31, 41 is made of concrete. Alternatively, another material could be used.
On considérera en outre le cas où le corps 1 1 , 21 , 31 , 41 est conçu pour être placé horizontalement dans l'ouvrage, pour y être fixé par ses deux extrémités, et pour être chargé (c'est-à-dire pour supporter des éléments pesants).  Consider also the case where the body 1 1, 21, 31, 41 is designed to be placed horizontally in the work, to be fixed by its two ends, and to be loaded (that is to say for bear heavy elements).
On comprend que l'élément de structure 10, 20, 30, 40 considéré sera alors soumis à deux efforts : son poids propre et le poids de la charge. De manière usuelle, on pourra subdiviser cette charge en deux composantes : une composante permanente et une composante variable.  It is understood that the structural element 10, 20, 30, 40 considered will then be subjected to two forces: its own weight and the weight of the load. In the usual way, this load can be divided into two components: a permanent component and a variable component.
Sous l'effet de ces deux efforts, le corps 1 1 , 21 , 31 , 41 aura naturellement tendance à se déformer, en fléchissant vers le bas (on dit alors du corps qu'il présente une « flèche »). Cette flexion engendrera des contraintes de compression dans la partie supérieure du corps, et des contraintes de traction dans la partie inférieure du corps. Le risque serait alors que, du fait de ces contraintes de traction ou de compression, le béton se fissure sur la face inférieure ou sur la face supérieure du corps.  Under the effect of these two forces, the body January 1, 21, 31, 41 will naturally tend to deform, bending down (we say the body that it has an "arrow"). This bending will cause compression stresses in the upper body, and tensile stresses in the lower body. The risk would be that, due to these tensile or compressive stresses, the concrete cracks on the underside or on the upper face of the body.
Pour éviter l'apparition de telles fissures, les éléments de structure 10, To avoid the appearance of such cracks, the structural elements 10,
20, 30, 40 sont équipés chacun d'au moins un premier tendeur 1 qui est fixé dans le corps 1 1 , 21 , 31 , 41 de telle manière que ce dernier s'en trouve comprimé. 20, 30, 40 are each equipped with at least one first tensioner 1 which is fixed in the body January 1, 21, 31, 41 so that the latter is compressed.
La compression obtenue permettra alors de compenser les contraintes de traction précitées, de manière à éviter l'apparition de fissures. Le corps 1 1 , 21 , 31 , 41 est donc ainsi précontraint par chaque premier tendeur 1 .  The compression obtained will then compensate for the aforementioned tensile stresses, so as to avoid the appearance of cracks. The body 1 1, 21, 31, 41 is thus prestressed by each first tensioner 1.
Généralement, on utilisera plusieurs premiers tendeurs 1 rectilignes. Ces premiers tendeurs 1 pourront être formés par des fils, par des câbles métalliques ou encore par des barres en acier à haute capacité. Ils seront préférentiellement noyés dans le béton, de manière à transmettre progressivement les efforts au corps de l'élément de structure 10, 20, 30, 40. Ils sont par ailleurs excentrés par rapport à la fibre neutre A1 du corps 1 1 , 21 , 31 , 41 de l'élément de structure 10, 20, 30, 40 considéré. Generally, several first linear tensioners 1 will be used. These first tensioners 1 may be formed by son, by wire ropes or by steel bars with high capacity. They will preferably be drowned in the concrete, so as to progressively transmit efforts to body of the structural element 10, 20, 30, 40. They are also eccentric with respect to the neutral fiber A1 of the body 1 1, 21, 31, 41 of the structural element 10, 20, 30, 40 considered.
Comme le montrent bien les figures 1 B, 3B, 4B et 5, ces premiers tendeurs 1 sont préférentiellement répartis sous la fibre neutre A1 du corps 1 1 , 21 , 31 , 41 de l'élément de structure 10, 20, 30, 40 considéré.  As shown in FIGS. 1B, 3B, 4B and 5, these first tensioners 1 are preferably distributed under the neutral fiber A1 of the body 1 1, 21, 31, 41 of the structural element 10, 20, 30, 40 considered.
Comme le montrent bien les figures 1A et 1 B (et il en est de même pour les autres éléments de structure 20, 30, 40), les premiers tendeurs 1 s'étendent en longueur parallèlement à la fibre neutre A1 du corps 1 1 de la poutre 10, et ils sont régulièrement répartis autour d'une fibre moyenne inférieure A2.  As clearly shown in FIGS. 1A and 1B (and the same is true for the other structural elements 20, 30, 40), the first tensioners 1 extend in length parallel to the neutral fiber A1 of the body 1 1 of the beam 10, and they are regularly distributed around a lower average fiber A2.
La traction totale exercée sur les premiers tendeurs 1 permet donc de comprimer le corps 1 1 de la poutre 10 selon la fibre moyenne inférieure A2.  The total traction exerted on the first tensioners 1 thus makes it possible to compress the body 1 1 of the beam 10 according to the lower average fiber A2.
Comme le montre la figure 1 C, ces premiers tendeurs 1 exercent donc un effort de compression E1 sur le corps 1 1 de la poutre 10. Cet effort de compression E1 génère des contraintes de compression réparties de manière homogène sur l'ensemble de la section du corps 1 1 .  As shown in FIG. 1C, these first tensioners 1 thus exert a compressive force E1 on the body 1 1 of the beam 10. This compression force E1 generates compression stresses distributed homogeneously over the entire section. of the body 1 1.
Comme le montre la figure 1A, la fibre moyenne inférieure A2 est ici située sous la fibre neutre A1 , à une distance de celle-ci notée écart D1 .  As shown in FIG. 1A, the lower average fiber A2 is here below the neutral fiber A1, at a distance from it denoted by the difference D1.
Comme le montre la figure 1 C, du fait de cet écart D1 , les premiers tendeurs 1 exercent un moment de flexion M1 sur le corps 1 1 de la poutre 10. Ce moment de flexion M1 permet de faire fléchir le corps 1 1 vers le haut, c'est-à-dire dans une direction opposée à celle selon laquelle elle a tendance à fléchir sous l'effet de son poids propre (on dit alors de la poutre qu'elle présente une « contre- flèche). Ce moment de flexion M1 génère, dans la partie supérieure du corps 1 1 , des contraintes de traction. Il génère en outre des contraintes de compression dans la partie inférieure du corps 1 1 .  As shown in FIG. 1C, because of this difference D1, the first tensioners 1 exert a bending moment M1 on the body 1 1 of the beam 10. This bending moment M1 makes it possible to bend the body 1 1 towards the high, that is to say in a direction opposite to that according to which it tends to bend under the effect of its own weight (it is said of the beam that it presents a "counter-arrow"). This bending moment M1 generates, in the upper part of the body 1 1, tensile stresses. It also generates compressive stresses in the lower part of the body 1 1.
Lorsque le corps 1 1 , 21 , 31 , 41 de l'élément de structure 10, 20, 30, 40 est en place dans l'ouvrage et est chargé, ce moment de flexion M1 permet de compenser la flexion du corps sous l'effet de son propre poids et sous l'effet de la charge qu'il porte.  When the body 1 1, 21, 31, 41 of the structural element 10, 20, 30, 40 is in place in the structure and is loaded, this bending moment M1 makes it possible to compensate for the bending of the body under the effect of its own weight and under the effect of the load it carries.
En revanche, avant la mise en place de l'élément de structure 10, 20, 30, 40 dans l'ouvrage, le moment de flexion M1 n'est pas compensé et a tendance à fléchir le corps 1 1 , 21 , 31 , 41 (notamment lorsque l'élément de structure est stocké à la verticale et que son poids propre ne fait plus fléchir le corps vers le bas). On the other hand, before the establishment of the structural element 10, 20, 30, 40 in the structure, the bending moment M1 is not compensated and tends to bend the body 1 1, 21, 31, 41 (in particular when the structural element is stored vertically and its own weight no longer bends the body towards the low).
En pratique, tant que l'écart D1 et/ou que l'effort de traction exercé sur les premiers tendeurs 1 reste inférieur à un seuil, les contraintes de traction générées par le moment de flexion M1 sont compensées par les contraintes de compression générées par l'effort de compression E1 : les contraintes restent dans des limites admissibles. Il n'y a donc pas de risque de fissure.  In practice, as long as the difference D1 and / or the tensile force exerted on the first tensioners 1 remains below a threshold, the tensile stresses generated by the bending moment M1 are compensated by the compression stresses generated by the compression force E1: the stresses remain within admissible limits. There is no risk of cracking.
L'inconvénient est alors que le moment de flexion M1 reste alors limité du fait de cet écart D1 , si bien que les charges que l'élément de structure 10, 20, 30, 40 peut supporter sont également limitées.  The disadvantage is that the bending moment M1 then remains limited because of this difference D1, so that the loads that the structural element 10, 20, 30, 40 can withstand are also limited.
L'invention propose alors une méthode permettant d'accroître cet écart The invention then proposes a method for increasing this difference
D1 et/ou d'accroître les efforts exercés sur les premiers tendeurs afin de pouvoir charger davantage l'élément de structure 10, 20, 30, 40, sans pour autant risquer de voir apparaître des fissures dans le béton. D1 and / or increase the forces exerted on the first tensioners to be able to further load the structural element 10, 20, 30, 40, without risking to appear cracks in the concrete.
Ainsi, selon une caractéristique particulièrement avantageuse de l'invention, l'élément de structure 10, 20, 30, 40 comporte au moins un second tendeur 2 qui est fixé en deux points distincts au corps 1 1 , 21 , 31 , 41 par deux moyens de fixation 3 de telle sorte qu'il comprime et fléchit le corps 1 1 , 21 , 31 , 41 vers le bas, et il est prévu un moyen de désactivation 3B pour relâcher la compression et le fléchissement exercés sur le corps allongé 1 1 , 21 , 31 , 41 par ce second tendeur 2.  Thus, according to a particularly advantageous characteristic of the invention, the structural element 10, 20, 30, 40 comprises at least one second tensioner 2 which is fixed at two distinct points to the body 1 1, 21, 31, 41 by two fastening means 3 such that it compresses and flexes the body January 1, 21, 31, 41 downwards, and there is provided a deactivation means 3B for releasing the compression and the sagging exerted on the elongate body 1 1 , 21, 31, 41 by this second tensioner 2.
En pratique, chaque second tendeur 2 est situé sur le corps 1 1 , 21 , 31 , 41 de manière décentrée par rapport à la fibre neutre A1 de telle sorte que, lorsque l'élément de structure n'est pas encore mis en place dans l'ouvrage et n'est pas encore chargé, la compression qu'il exerce sur l'élément de structure permet d'éviter l'apparition de fissures.  In practice, each second tensioner 2 is located on the body January 1, 21, 31, 41 off-center relative to the neutral fiber A1 so that when the structural element is not yet implemented in the structure and is not yet loaded, the compression that it exerts on the structural element makes it possible to avoid the appearance of cracks.
Préférentiellement, chaque second tendeur 2 est situé au-dessus de la fibre neutre A1 du corps 1 1 , 21 , 31 , 41 , de manière qu'il exerce sur le corps un moment de flexion qui s'oppose au moins partiellement au moment de flexion M1 .  Preferably, each second tensioner 2 is located above the neutral fiber A1 of the body 1 1, 21, 31, 41, so that it exerts on the body a bending moment which is at least partially opposed at the moment of M1 flexion.
On utilisera généralement plusieurs seconds tendeurs 2 rectilignes. Ces seconds tendeurs 2 pourront être formés par des fils, par des câbles métalliques ou encore par des barres métalliques, préférentiellement en acier adapté.  There will generally be used a plurality of second rectilinear tensioners 2. These second tensioners 2 may be formed by wires, by metal cables or by metal bars, preferably made of suitable steel.
Comme le montrent bien les figures 1 B, 3B, 4B et 5, ces seconds tendeurs 2 sont préférentiellement répartis au-dessus de la fibre neutre A1 du corps 1 1 , 21 , 31 , 41 de l'élément de structure 10, 20, 30, 40 considéré. Comme le montrent par exemple les figures 1A et 1 B (et il en est de même pour les autres éléments de structure 20, 30, 40), ces seconds tendeurs 2 sont ici allongés parallèlement à la fibre neutre A1 du corps 1 1 de la poutre 10 et sont régulièrement répartis autour d'une fibre moyenne supérieure A3. As FIGS. 1B, 3B, 4B and 5 clearly show, these second tensioners 2 are preferably distributed above the neutral fiber A1 of the body 1 1, 21, 31, 41 of the structural element 10, 20, 30, 40 considered. As shown for example in Figures 1A and 1B (and it is the same for the other structural elements 20, 30, 40), these second tensioners 2 are here elongate parallel to the neutral fiber A1 of the body 1 1 of the beam 10 and are regularly distributed around a medium upper fiber A3.
La traction totale exercée sur les seconds tendeurs 2 permet donc de comprimer le corps 1 1 de la poutre 10 selon la fibre moyenne supérieure A3.  The total traction exerted on the second tensioners 2 thus makes it possible to compress the body 1 1 of the beam 10 according to the upper middle fiber A3.
Comme le montre la figure 1 C, ces seconds tendeurs 2 exercent un effort de compression E2 sur le corps 1 1 de la poutre 10, qui s'ajoute à l'effort de compression E1 . Cet effort de compression E2 génère des contraintes de compression réparties de manière homogène sur l'ensemble de la section du corps 1 1 .  As shown in Figure 1 C, these second tensioners 2 exert a compressive force E2 on the body 1 1 of the beam 10, which is added to the compression force E1. This compression force E2 generates compression stresses distributed homogeneously over the entire section of the body January 1.
Comme le montrent par exemple les figures 1A et 1 B, cette fibre moyenne supérieure A3 est située au-dessus de la fibre neutre A1 , à une distance de celle-ci notée écart D2.  As shown for example in FIGS. 1A and 1B, this upper middle fiber A3 is situated above the neutral fiber A1, at a distance from it denoted by the difference D2.
Comme le montre la figure 1 C, du fait de cet écart D2, ces seconds tendeurs 2 exercent un moment de flexion M2 sur le corps 1 1 de la poutre 10, de sens opposé au moment de flexion M1 . Ce moment de flexion M2 permet de faire fléchir le corps 1 1 vers le bas, si bien qu'il permet de compenser au moins en partie la flexion du corps 1 1 sous l'effet du moment de flexion M1 .  As shown in FIG. 1C, because of this difference D2, these second tensioners 2 exert a bending moment M2 on the body 1 1 of the beam 10, in the opposite direction to the bending moment M1. This bending moment M2 makes it possible to bend the body 1 1 downwards, so that it makes it possible to compensate at least in part for the bending of the body 1 1 under the effect of the bending moment M1.
Autrement formulé, ce moment de flexion M2 permet de simuler une charge sur la poutre 10 lorsque celle-ci n'est pas encore chargée. Le moyen de désactivation de chaque second tendeur 2 permettra ensuite, lorsque la poutre 10 commencera à être chargée, de relâcher le second tendeur 2 de manière à annuler le moment de flexion M2.  Otherwise formulated, this bending moment M2 can simulate a load on the beam 10 when it is not yet loaded. The means for deactivating each second tensioner 2 will then, when the beam 10 begins to be loaded, to release the second tensioner 2 so as to cancel the bending moment M2.
Grâce à l'invention, il est alors possible de maximiser les écarts D1 et D2 et les forces de traction exercées sur les premiers et seconds tendeurs 1 , 2 tout en évitant une flexion trop importante du corps lorsque celui-ci n'est pas encore chargé, ce qui évite l'apparition de fissures dans le béton et ce qui évite d'excéder les limites de compression admissibles du béton.  Thanks to the invention, it is then possible to maximize the differences D1 and D2 and the tensile forces exerted on the first and second tensioners 1, 2 while avoiding excessive bending of the body when it is not yet loaded, which avoids the appearance of cracks in the concrete and which avoids exceeding the permissible compression limits of the concrete.
Cette maximisation des écarts D1 et D2 et des forces de traction permet donc d'augmenter les valeurs des moments de flexion M1 , M2. De cette manière, lorsque les seconds tendeurs 2 auront été extraits du corps 1 1 , 21 , 31 , 41 de l'élément de structure (ce dernier ayant été progressivement chargé), le moment de flexion M1 permettra à l'élément de structure 10, 20, 30, 40 de supporter des charges plus lourdes que celles qu'il aurait pu supporter si l'écart D1 ou si l'effort exercé sur les premiers tendeurs 1 avait été moindre. This maximization of the differences D1 and D2 and of the tensile forces thus makes it possible to increase the values of the bending moments M1, M2. In this way, when the second tensioners 2 have been extracted from the body 1 1, 21, 31, 41 of the structural element (the latter having been progressively loaded), the bending moment M1 will allow the structural element 10 , 20, 30, 40 to support heavier loads than those he could have supported if the difference D1 or if the force exerted on the first tensioners 1 had been less.
Le seul frein à ce procédé reste la limite de la tenue à la compression du béton, qu'il ne faut pas dépasser. C'est la raison pour laquelle on jouera davantage sur la maximisation des écarts D1 et D2 que sur l'accroissement des efforts de traction exercés sur les premiers et seconds tendeurs 1 , 2.  The only obstacle to this process is the limit of the compressive strength of the concrete, which must not be exceeded. This is the reason why we will play more on the maximization of the differences D1 and D2 than on the increase of the tensile forces exerted on the first and second tensioners 1, 2.
Sur la figure 1 C, la somme des efforts et moments exercés par les premiers et seconds tendeurs 1 , 2 est noté C1 .  In FIG. 1C, the sum of the forces and moments exerted by the first and second tensioners 1, 2 is denoted C1.
Comme le montre la figure 1 D, lorsque l'élément de structure 10, 20, 30, 40 est mis en charge, cette charge et le poids propre de l'élément de structure exercent un moment de flexion M3 qui s'ajoute à la somme C1 précitée.  As shown in FIG. 1D, when the structural element 10, 20, 30, 40 is loaded, this load and the self weight of the structural element exert a bending moment M3 which is added to the sum C1 mentioned above.
En relâchant les seconds tendeurs 2, il est alors possible de supprimer l'effort de compression E2 et le moment de flexion M2 qui s'exerçaient sur l'élément de structure, de manière à compenser au moins partiellement le moment de flexion M3.  By releasing the second tensioners 2, it is then possible to eliminate the compressive force E2 and the bending moment M2 which were exerted on the structural element, so as to at least partially compensate for the bending moment M3.
Alors, la somme des efforts et moments qui s'exercent sur l'élément de structure, notée C2 permet de faire en sorte que :  Then, the sum of the efforts and moments exerted on the element of structure, denoted C2 makes it possible to make sure that:
- aucune contrainte de traction n'apparaît dans l'élément de structure, et - no tensile stress appears in the structural element, and
- les contraintes de compression que subit l'élément de structure demeurent inférieures à la limite de compression du béton. the compressive stresses experienced by the structural element remain below the compression limit of the concrete.
Dans une variante de l'invention où les extrémités des seconds tendeurs sont fixés de manière indémontable au corps de l'élément de structure, on peut prévoir de relâcher seulement les parties centrales de ces seconds tendeurs. On peut ainsi par exemple prévoir de découper les seconds tendeurs en leurs centres, de manière que leurs deux extrémités restent fixées au corps de l'élément de structure. Dans cette variante, les extrémités des seconds tendeurs permettront donc, après leur découpe, de continuer à exercer des efforts de compression et des moments de flexion au niveau des abouts du corps de l'élément de structure. Ces efforts et moments permettront alors de compenser les efforts que les premiers tendeurs exercent sur ces abouts.  In a variant of the invention where the ends of the second tensioners are releasably fixed to the body of the structural member, provision can be made to release only the central portions of these second tensioners. For example, it is possible to cut the second tensioners at their centers, so that their two ends remain fixed to the body of the structural element. In this variant, the ends of the second tensioners will therefore, after cutting, continue to exert compression forces and bending moments at the ends of the body of the structural element. These efforts and moments will then offset the efforts that the first tendons exert on these abouts.
On peut maintenant s'intéresser plus en détail au cas particulier de la poutre de section rectangulaire représentée sur les figures 1A et 1 B.  We can now look in more detail at the particular case of the rectangular section beam shown in Figures 1A and 1B.
Dans ce mode, le corps 1 1 de la poutre 10 présente une forme sensiblement parallélépipédique. Les premiers tendeurs 1 sont entièrement noyés dans le béton du corps 1 1 de la poutre 10, à l'exception éventuelle de leurs extrémités qui peuvent faire saillie du corps. Ils sont donc inamovibles par rapport au corps de la poutre 10. In this mode, the body 1 1 of the beam 10 has a substantially parallelepiped shape. The first tensioners 1 are entirely embedded in the concrete of the body 1 1 of the beam 10, with the possible exception of their ends which can project from the body. They are therefore irremovable relative to the body of the beam 10.
Les seconds tendeurs 2 sont quant à eux montés coulissants dans le corps 1 1 de la poutre 10. Comme le montre la figure 2B, les seconds tendeurs 2 sont à cet effet enfilés dans des gaines 4 coulées dans le béton, de telle manière que leurs extrémités débouchent aux deux extrémités du corps 1 1 . Ces gaines 4, ici en matière plastique, évitent que le béton ne vienne s'accrocher aux seconds tendeurs 2.  The second tensioners 2 are slidably mounted in the body 1 1 of the beam 10. As shown in Figure 2B, the second tensioners 2 are for this purpose threaded into sheaths 4 cast in the concrete, so that their ends open at both ends of the body 1 1. These sheaths 4, here made of plastic, prevent the concrete from catching on the second tensioners 2.
Comme cela a été exposé supra, on pourra toutefois prévoir de noyer les extrémités des seconds tendeurs dans les abouts du corps de l'élément de structure.  As has been explained above, however, it will be possible to drown the ends of the second tensioners in the ends of the body of the structural element.
En variante, comme le montre la figure 2A, on pourrait ne pas utiliser de gaine, auquel cas il faudrait prévoir de faire bouger les seconds tendeurs 2 (par exemple en les faisant pivoter sur eux-mêmes) pendant le séchage du béton, de manière que le béton n'adhère pas aux seconds tendeurs 2. Encore en variante, on pourrait appliquer sur les seconds tendeurs un produit empêchant l'adhésion du béton. On pourrait encore prévoir de placer les seconds tendeurs en dehors du béton, comme cela sera par exemple exposé en référence à la figure 4A.  Alternatively, as shown in Figure 2A, one could not use a sheath, in which case it would be necessary to move the second tensioners 2 (for example by rotating them on themselves) during the drying of the concrete, so that concrete does not adhere to the second tensioners 2. Alternatively, could be applied to the second tensioners a product preventing the adhesion of concrete. One could also provide to place the second tensioners outside the concrete, as will be for example explained with reference to Figure 4A.
Ici, comme le montre la figure 1 B, les premiers tendeurs 1 sont répartis sur trois lignes et cinq colonnes. Le premier tendeur 1 qui est situé au centre de cette matrice s'étend donc selon la fibre moyenne inférieure A2.  Here, as shown in Figure 1 B, the first tensioners 1 are distributed over three rows and five columns. The first tensioner 1 which is located in the center of this matrix therefore extends along the lower average fiber A2.
Les seconds tendeurs 2 sont ici deux fois moins nombreux que les premiers tendeurs 1 et sont répartis les un par rapport aux autres sensiblement de la même manière que les premiers tendeurs. Le second tendeur 2 qui est situé au centre de cette matrice s'étend donc selon la fibre moyenne supérieure A3.  The second tensioners 2 here are twice as numerous as the first tensioners 1 and are distributed relative to one another in substantially the same manner as the first tensioners. The second tensioner 2 which is located in the center of this matrix therefore extends according to the upper middle fiber A3.
La fibre neutre A1 , qui passe aux centres des sections transversales du corps 1 1 , s'étend donc entre les fibres moyennes supérieure A3 et inférieure A2, à égales distances de celles-ci.  The neutral fiber A1, which passes to the centers of the cross sections of the body 1 1, therefore extends between the upper middle fibers A3 and lower A2, at equal distances from them.
Comme cela a été exposé supra, chaque second tendeur 2 est fixé en deux points distincts au corps 1 1 de la poutre 10, par deux moyens de fixation, et il est prévu un moyen de désactivation pour relâcher chaque second tendeur 2.  As has been explained above, each second tensioner 2 is fixed at two distinct points to the body 1 1 of the beam 10, by two fixing means, and there is provided a deactivation means for releasing each second tensioner 2.
En pratique, chaque second tendeur 2 est fixé par ses deux extrémités 2A aux deux extrémités du corps 1 1 de la poutre 10. De cette manière, ces extrémités 2A restent facilement accessibles depuis l'extérieur du corps 1 1 . In practice, each second tensioner 2 is fixed by its two ends 2A to both ends of the body 1 1 of the beam 10. In this way, these 2A ends remain easily accessible from outside the body 1 1.
Le moyen de désactivation est prévu pour permettre, sur chantier, de relâcher la tension du second tendeur 2.  The deactivation means is provided to allow, on site, to release the tension of the second tensioner 2.
Ce moyen de désactivation pourra se présenter de diverses manières. II pourra ainsi être intégré à l'un au moins des moyens de fixation 3 des extrémités 2A des seconds tendeurs 2 au corps 1 1 de la poutre 10.  This deactivation means may be presented in various ways. It can thus be integrated into at least one of the fastening means 3 of the ends 2A of the second tensioners 2 to the body 1 1 of the beam 10.
Tel qu'il apparaît sur la figure 2A, ce moyen de fixation 3 comporte une douille 3A qui est plaquée contre l'extrémité correspondante du corps 1 1 de la poutre 10 et qui loge intérieurement deux clavettes 3B.  As it appears in FIG. 2A, this fastening means 3 comprises a bushing 3A which is pressed against the corresponding end of the body 1 1 of the beam 10 and which internally houses two keys 3B.
La douille 3A présente une face extérieure cylindrique de révolution, et une face intérieure tronconique dont le sommet est tourné vers le corps 1 1 .  The sleeve 3A has a cylindrical outer face of revolution, and a frustoconical inner face whose apex is turned towards the body January 1.
Les clavettes 2B présentent globalement ensemble une forme de cylindre coupé en deux dans le sens de la longueur. Elles présentent chacune une face extérieure tronconique de forme correspondant à celle de la face intérieure de la douille 3A, et une face intérieure crantée.  The keys 2B generally have a cylinder shape cut in half along the length direction. They each have a frustoconical outer face of shape corresponding to that of the inner face of the sleeve 3A, and a notched inner face.
Ces deux clavettes 2B forment ainsi une sorte de mâchoire qui, lorsqu'elles s'enfoncent dans la douille 3A vers le corps 1 1 , permettent de bloquer rigidement l'extrémité 2A du second tendeur 2.  These two keys 2B thus form a kind of jaw which, when they sink into the bushing 3A towards the body January 1, rigidly lock the end 2A of the second tensioner 2.
Dans ce mode de réalisation représenté sur la figure 2A, le moyen de désactivation précité est alors formé par les deux clavettes 3B. Ces deux clavettes 3B font en effet saillie à l'extérieur de la douille 3A, si bien qu'elles sont adaptées à être tirées mécaniquement à l'extérieur de la douille 3A de manière à relâcher l'extrémité 2A du second tendeur 2.  In this embodiment shown in FIG. 2A, the aforementioned deactivation means is then formed by the two keys 3B. These two keys 3B protrude outside the sleeve 3A, so that they are adapted to be pulled mechanically outside the sleeve 3A so as to release the end 2A of the second tensioner 2.
Dans le mode de réalisation représenté sur la figure 2B, le moyen de désactivation est fusible. En l'espèce, ce moyen de désactivation est formé par une couche de métal ou par une pâte non métallique qui recouvre l'extrémité 2A du second tendeur 2 (ou la face interne de la douille 3A ou des clavettes 3B), dont la température de fusion est relativement basse, et qui présente des caractéristiques mécaniques satisfaisantes. Il pourra ainsi s'agir d'une couche de zinc ou d'étain, puisque la température de fusion de ces matériaux est assez basse (inférieure à 450 °C, préférentiellement de l'ordre de 200 à 300°C) pour permettre sa fusion sur chantier, et que sa rigidité à température ambiante est suffisante pour assurer une bonne accroche du second tendeur 2.  In the embodiment shown in Figure 2B, the deactivation means is fuse. In this case, this deactivation means is formed by a metal layer or a non-metallic paste which covers the end 2A of the second tensioner 2 (or the inner face of the sleeve 3A or keys 3B), whose temperature The melting point is relatively low and has satisfactory mechanical characteristics. It may thus be a layer of zinc or tin, since the melting temperature of these materials is quite low (below 450 ° C., preferably of the order of 200 to 300 ° C.) to allow its fusion on site, and that its rigidity at ambient temperature is sufficient to ensure good grip of the second tensioner 2.
En variante, le moyen de fixation amovible pourrait se présenter sous une autre forme. As a variant, the removable fastening means could be under another form.
Il pourrait ainsi se présenter sous la forme d'un manchon fileté fixé sur le second tendeur, qui viendrait se visser dans un écrou engagé dans l'extrémité de la gaine 4. Pour relâcher la compression exercée par le second tendeur sur le corps de la poutre, il suffirait alors de dévisser le manchon fileté de manière qu'il s'échappe de l'écrou.  It could thus be in the form of a threaded sleeve fixed on the second tensioner, which would be screwed into a nut engaged in the end of the sheath 4. To release the compression exerted by the second tensioner on the body of the Beam, it would then be enough to unscrew the threaded sleeve so that it escapes from the nut.
Selon une autre variante, le moyen de fixation utilisé pourrait se présenter sous la forme d'une colle ou d'une pâte fusible. Il pourrait aussi se présenter sous la forme d'un manchon facilement destructible (par exemple par découpe), qui serait enfilé sur le second tendeur et qui serait en appui contre le corps.  According to another variant, the fastening means used could be in the form of an adhesive or a fusible paste. It could also be in the form of a sleeve easily destructible (for example by cutting), which would be threaded on the second tensioner and which would bear against the body.
Encore en variante, l'extrémité 2A du second tendeur 2 pourrait être enduite d'une couche de zinc ou d'étain et être directement scellée dans le béton. Ainsi, en chauffant la couche métallique, il sera possible de la faire fondre de telle sorte que le second tendeur 2 puisse s'échapper du béton et relâcher la compression et la flexion qu'il exerce sur le corps 1 1 de la poutre 10.  Alternatively, the end 2A of the second tensioner 2 could be coated with a layer of zinc or tin and be directly sealed in the concrete. Thus, by heating the metal layer, it will be possible to melt it so that the second tensioner 2 can escape from the concrete and release the compression and bending it exerts on the body 1 1 of the beam 10.
Quoi qu'il en soit, le second moyen de fixation, prévu pour bloquer l'autre extrémité du second tendeur 2, pourra également se présenter sous diverses formes.  In any event, the second attachment means, designed to lock the other end of the second tensioner 2, may also be in various forms.
II sera préférentiellement amovible. De cette manière, le second tendeur It will be preferentially removable. In this way, the second tensioner
2 pourra être extrait du corps 1 1 de la poutre 10 et pourra être réutilisé sur d'autres poutres, ce qui réduira les coûts. 2 can be extracted from the body 1 1 of the beam 10 and can be reused on other beams, which will reduce costs.
Il pourra ainsi se présenter sous la même forme que le premier moyen de fixation amovible. Il pourra aussi se présenter sous la forme d'un manchon qui sera enfilé et fixé sur le second tendeur et qui viendra simplement en appui contre le corps.  It can thus be in the same form as the first removable fastening means. It may also be in the form of a sleeve which will be threaded and fixed on the second tensioner and which will simply bear against the body.
En variante, ce second moyen de fixation pourra fixer la seconde extrémité du second tendeur 2 de manière inamovible au corps 1 1 de la poutre 10, auquel cas le second tendeur 2 ne pourra pas être extrait du corps 1 1 . Ainsi, on pourrait prévoir de noyer cette seconde extrémité du second tendeur 2 dans le béton du corps 1 1 .  As a variant, this second fastening means may fix the second end of the second tensioner 2 immovably to the body 1 1 of the beam 10, in which case the second tensioner 2 can not be extracted from the body 1 1. Thus, one could provide to drown the second end of the second tensioner 2 in the concrete of the body January 1.
Comme le montre la figure 2C, on pourrait en variante prévoir que le moyen de désactivation se trouve non pas à l'une des extrémités du second tendeur 2, mais à distance de celles-ci. Dans cette variante, on pourra bloquer les extrémités 2A du second tendeur 2 au corps 1 1 de la poutre 10 de manière inamovible (ou non). As shown in Figure 2C, it could alternatively be provided that the deactivating means is not at one end of the second tensioner 2, but at a distance from them. In this variant, we can block ends 2A of the second tensioner 2 to the body 1 1 of the beam 10 irremovably (or not).
Dans cette variante, le second tendeur 2 est réalisé en deux parties 2C, 2D situées dans le prolongement l'une de l'autre et qui sont raccordées ensemble par un moyen de fixation 5.  In this variant, the second tensioner 2 is made in two parts 2C, 2D located in the extension of one another and which are connected together by a fixing means 5.
Ce moyen de fixation 5 comporte un manchon 5A à l'intérieur duquel sont logées deux paires de clavettes 3B. Les clavettes 3B sont identiques à celles représentées sur la figure 2A. Le manchon 5A présente quant à lui une face intérieure qui présente deux parties tronconiques tournées dans des directions opposées.  This fixing means 5 comprises a sleeve 5A inside which are housed two pairs of keys 3B. The keys 3B are identical to those shown in Figure 2A. The sleeve 5A has meanwhile an inner face which has two frustoconical parts turned in opposite directions.
Ici, les extrémités jointives des deux parties 2C, 2D du tendeur sont chacune revêtues d'un enduit en zinc ou en étain ou d'une autre matière qui représente des caractéristiques adéquates, dans lequel courre un fil de résistance.  Here, the contiguous ends of the two parts 2C, 2D of the tensioner are each coated with a coating of zinc or tin or other material which represents suitable characteristics, in which runs a resistance wire.
Lorsque le second tendeur 2 est mis en traction (lors du moulage du corps 1 1 de la poutre 10), les clavettes 3B se déplacent vers les deux extrémités du manchon 5A, ce qui leurs permet de se refermer à la manière de deux mâchoires sur les extrémités jointives des deux parties 2C, 2D du second tendeur 2.  When the second tensioner 2 is put in traction (during the molding of the body 1 1 of the beam 10), the keys 3B move towards the two ends of the sleeve 5A, which allows them to close in the manner of two jaws on the contiguous ends of the two parts 2C, 2D of the second tensioner 2.
Pour désactiver ce second tendeur 2, il faudra alors alimenter en courant électrique le fil de résistance (depuis l'extérieur du corps 1 1 de la poutre 10), de manière que l'enduit fonde et que les extrémités jointives des deux parties 2C, 2D du second tendeur s'échappent hors du manchon 5A.  To deactivate this second tensioner 2, it will then be necessary to supply electrical current to the resistance wire (from outside the body 1 1 of the beam 10), so that the coating melts and the contiguous ends of the two parts 2C, 2D of the second tensioner escape out of the sleeve 5A.
On peut maintenant donner un exemple précis de poutre 10 utilisable sur chantier.  We can now give a specific example of beam 10 usable on site.
La poutre pourra ainsi présenter une longueur de 7 mètres, une hauteur The beam can thus have a length of 7 meters, a height
L2 de 60 centimètres, et une largeur L3 de 40 centimètres. L2 of 60 centimeters, and a width L3 of 40 centimeters.
Les premiers tendeurs 1 pourront être répartis de telle manière que la fibre moyenne inférieure A2 s'étende à 6,8 centimètres de la face inférieure du corps 1 1 de la poutre 10.  The first tensioners 1 can be distributed in such a way that the average lower fiber A2 extends to 6.8 centimeters from the lower face of the body 1 1 of the beam 10.
Les seconds tendeurs 2 pourront être répartis de telle manière que la fibre moyenne supérieure A3 s'étende à 5 centimètres de la face supérieure du corps 1 1 de la poutre 10.  The second tensioners 2 may be distributed in such a way that the upper middle fiber A3 extends 5 centimeters from the upper face of the body 1 1 of the beam 10.
On pourra précontraindre cette poutre 10 grâce aux premiers tendeurs 1 avec un effort de compression E1 égal à 192 tonnes. On pourra en outre précontraindre de manière provisoire cette poutre 10 grâce aux seconds tendeurs 2 avec un effort de compression E2 égal à 120 tonnes. This beam 10 can be preloaded thanks to the first tensioners 1 with a compression force E1 equal to 192 tons. It will further be possible to temporarily prestress this beam 10 thanks to the second tensioners 2 with a compressive force E2 equal to 120 tons.
Sur la figure 3A, on a représenté un second mode de réalisation d'une poutre 20 selon l'invention.  In FIG. 3A, a second embodiment of a beam 20 according to the invention is shown.
Dans ce mode, le corps 21 de la poutre 20 présente une section transversale en I.  In this mode, the body 21 of the beam 20 has a cross section I.
Comme le montre la figure 3B, le corps 21 de la poutre 20 présente donc deux semelles 23 parallèles entre lesquelles s'étend une paroi verticale 22.  As shown in FIG. 3B, the body 21 of the beam 20 thus has two parallel flanges 23 between which a vertical wall 22 extends.
Les premiers et seconds tendeurs 1 , 2 s'étendent alors sur toute la longueur de la poutre 20, en parallèle les uns des autres.  The first and second tensioners 1, 2 then extend over the entire length of the beam 20, in parallel with each other.
Il est ici prévu cinq premiers tendeurs 1 noyés dans le béton de la semelle inférieure 23 du corps 21 de la poutre 20. Ces premiers tendeurs 1 sont ici encore régulièrement répartis sur la largeur de la poutre 20. Ainsi, lorsqu'ils compriment le corps 21 de la poutre 10, ils ne la déforment pas en torsion.  It is here provided five first tensioners 1 embedded in the concrete of the lower sole 23 of the body 21 of the beam 20. These first tensioners 1 are again evenly distributed over the width of the beam 20. Thus, when they compress the body 21 of the beam 10, they do not deform in torsion.
Ces cinq premiers tendeurs 1 sont situés à proximité de la face inférieure de la semelle inférieure 23. Ainsi, lorsqu'ils sont tendus, ils permettent de faire fléchir le corps 21 de la poutre 20 de telle sorte que le centre de la poutre se déplace vers le haut.  These first five tensioners 1 are located near the lower face of the lower sole 23. Thus, when they are tensioned, they allow to bend the body 21 of the beam 20 so that the center of the beam moves to the top.
II est en outre prévu trois seconds tendeurs 2, qui sont régulièrement répartis sur la largeur de la poutre 20. Les moyens de fixation des extrémités de ces seconds tendeurs 2 au corps 21 de la poutre 20 sont identiques à ceux décrits en référence aux figures 2B.  There are further provided three second tensioners 2, which are regularly distributed over the width of the beam 20. The fastening means of the ends of these second tensioners 2 to the body 21 of the beam 20 are identical to those described with reference to FIGS. 2B .
Sur les figures 4A et 4B, on a représenté un premier mode de réalisation d'une dalle 30 conforme à l'invention.  In Figures 4A and 4B, there is shown a first embodiment of a slab 30 according to the invention.
Dans ce mode, le corps 31 de la dalle 30 présente une forme globalement parallélépipédique. Sa fibre neutre A1 est donc confondue avec l'axe longitudinal central du corps 31 .  In this mode, the body 31 of the slab 30 has a generally parallelepiped shape. Its neutral fiber A1 is thus merged with the central longitudinal axis of the body 31.
Ici, les extrémités de la dalle 30 présentent toutefois, en saillie de la face supérieure du corps 31 , des rebords 32. Ces deux rebords 32 longent les deux extrémités du corps 31 . Ils délimitent entre eux une cavité 33 dans laquelle pourra être coulée une chape.  Here, the ends of the slab 30, however, project from the upper face of the body 31, flanges 32. These two edges 32 along the two ends of the body 31. They delimit between them a cavity 33 in which can be cast a screed.
Les premiers et second tendeurs 1 , 2 s'étendent sur toute la longueur de la dalle 30, en parallèle les uns des autres. Il est ici prévu une pluralité de premiers tendeurs 1 noyés dans le béton du corps 31 de la dalle 30. Ces premiers tendeurs 1 sont ici encore régulièrement répartis sur la largeur de la dalle 30, sous la fibre neutre A1 . Ils sont situés à proximité de la face inférieure du corps 31 de la dalle 30. The first and second tensioners 1, 2 extend over the entire length of the slab 30, in parallel with each other. It is here provided a plurality of first tensioners 1 embedded in the concrete of the body 31 of the slab 30. These first tensioners 1 are again evenly distributed over the width of the slab 30, under the neutral fiber A1. They are located near the lower face of the body 31 of the slab 30.
II est en outre prévu des seconds tendeurs 2, qui sont régulièrement répartis sur la largeur de la dalle 30, au-dessus de la fibre neutre A1 . Ces seconds tendeurs 2 traversent les deux rebords 32 du corps 31 de la dalle 30 de telle sorte que leurs extrémités font saillie de part et d'autre du corps 31 de la dalle 30. Une partie centrale de chacun des seconds tendeurs 2, qui s'étend entre ces deux rebords 32, est en revanche située dans la cavité 33, à l'extérieur du corps 31 .  There are further provided second tensioners 2, which are regularly distributed over the width of the slab 30, above the neutral fiber A1. These second tensioners 2 pass through the two flanges 32 of the body 31 of the slab 30 so that their ends protrude on either side of the body 31 of the slab 30. A central portion of each of the second tensioners 2, which are extends between these two flanges 32, is instead located in the cavity 33, outside the body 31.
Ici, les seconds tendeurs 2 sont gainés sur l'ensemble de leur longueur, ce qui assure leur coulissement au travers des rebords 32 et ce qui garantie leur protection vis-à-vis de l'extérieur. Ces gaines sont en outre utiles lorsqu'une chape en béton est coulée dans la cavité 33, puisqu'elles évitent que le béton de la chape n'adhère aux seconds tendeurs 2.  Here, the second tensioners 2 are sheathed over their entire length, which ensures their sliding through the flanges 32 and which guarantees their protection vis-à-vis the outside. These sheaths are also useful when a concrete screed is poured into the cavity 33, since they prevent the concrete of the screed from adhering to the second tensioners 2.
En variante, on pourrait envisager que les seconds tendeurs 2 ne soient gainés que sur une partie de leur longueur, celle située dans la cavité 33. Les parties des seconds tendeurs qui traversent les rebords 32 seront quant à elles enduites de zinc ou d'étain et coulées dans le béton. Pour permettre de relâcher les efforts exercés par ces seconds tendeurs, il suffira alors de chauffer l'enduit en zinc ou en étain.  Alternatively, it could be envisaged that the second tensioners 2 are sheathed only over a part of their length, that located in the cavity 33. The parts of the second tensioners that pass through the flanges 32 will themselves be coated with zinc or tin and cast in concrete. To allow to relax the forces exerted by these second tensioners, it will then be sufficient to heat the coating zinc or tin.
On pourrait encore en variante envisager que les seconds tendeurs 2 ne soient pas gainés, pour autant que la hauteur de la chape en béton à couler dans la cavité 33 soit suffisamment faible pour que, une fois cette chape coulée, les seconds tendeurs soient situés au-dessus de cette chape.  It could alternatively be envisaged that the second tensioners 2 are not sheathed, provided that the height of the concrete screed to be poured into the cavity 33 is small enough so that, once this screed has been poured, the second tensioners are located at above this screed.
Les rebords 32 permettent d'excentrer les seconds tendeurs 2 à une grande distance de la fibre neutre A1 du corps 31 . De cette manière, l'effort de traction exercé sur chacun des seconds tendeurs 2 peut être inférieur à celui exercé sur les premiers tendeurs 1 . On peut ainsi utiliser ici des seconds tendeurs 2 d'un diamètre inférieur à celui des premiers tendeurs 1 ou diminuer le nombre de seconds tendeurs 2 utilisés.  The flanges 32 make it possible to off-center the second tensioners 2 at a great distance from the neutral fiber A1 of the body 31. In this way, the tensile force exerted on each of the second tensioners 2 may be less than that exerted on the first tensioners 1. It is thus possible to use here second tensioners 2 of a diameter smaller than that of the first tensioners 1 or to reduce the number of second tensioners 2 used.
Les moyens de fixation prévus aux extrémités de ces seconds tendeurs 2 sont ici encore identiques à ceux décrits en référence aux figures 1 A, 1 B et 2B.  The fastening means provided at the ends of these second tensioners 2 are here again identical to those described with reference to FIGS. 1A, 1B and 2B.
Selon une variante de réalisation de la dalle, on aurait pu prévoir que le corps (31 ) soit dépourvu de rebord (32), auquel cas les seconds tendeurs seraient entièrement situés au travers du corps de la dalle. According to an alternative embodiment of the slab, it could have been expected that the body (31) is devoid of flange (32), in which case the second tensioners would be entirely located through the body of the slab.
Sur la figure 5A, on a représenté un second mode de réalisation de dalles 40 selon l'invention. Les dalles 40 représentées sur cette figure 5A ne diffèrent de la dalle 30 représentée sur les figures 4A et 4B que par le caractère alvéolé de leur corps 41 .  FIG. 5A shows a second embodiment of slabs 40 according to the invention. The slabs 40 shown in this FIG. 5A differ from the slab 30 shown in FIGS. 4A and 4B only by the honeycombed character of their body 41.
Il est en effet connu d'utiliser des dalles 40 alvéolées, c'est-à-dire des dalles 40 dont le corps est creusé de conduits longitudinaux appelés alvéoles. Ces alvéoles permettent de réduire le poids de la dalle tout en préservant son épaisseur pour lui assurer une bonne rigidité.  It is in fact known to use honeycombed slabs 40, that is to say slabs 40 whose body is hollowed out of longitudinal conduits called cells. These cells reduce the weight of the slab while preserving its thickness to ensure good rigidity.
Toutefois ici, comme le montrent les figures 4A et 4B, on préférera utiliser une dalle 30 dont le corps 31 est plein (par opposition à alvéolé).  However, here, as shown in Figures 4A and 4B, it is preferred to use a slab 30 whose body 31 is full (as opposed to honeycomb).
En effet, pour une même section de dalle, la surface pleine de la section de la dalle est ici plus grande du fait de l'absence d'alvéoles. Par conséquent, la dalle est à même de subir des efforts de compression plus importants.  Indeed, for the same section of slab, the solid surface of the section of the slab is here greater because of the absence of cells. Therefore, the slab is able to undergo greater compressive forces.
Il est ainsi possible d'exercer davantage d'efforts sur les premiers et seconds tendeurs 1 , 2, de manière que la dalle 30 soit à même de supporter des moments de flexion plus importants.  It is thus possible to exert more effort on the first and second tensioners 1, 2, so that the slab 30 is able to withstand greater bending moments.
On peut maintenant donner un exemple précis de dalle 30, 40 utilisable sur chantier.  We can now give a specific example of slab 30, 40 usable on site.
La dalle pourra ainsi présenter une longueur de 9 mètres, une hauteur L2 de 20 centimètres, et une largeur L3 de 1 ,2 mètre.  The slab can thus have a length of 9 meters, a height L2 of 20 centimeters, and a width L3 of 1.2 meters.
Les premiers tendeurs 1 pourront être répartis de telle manière que la fibre moyenne inférieure A2 s'étende à 4 centimètres de la face inférieure du corps 31 de la dalle 30, 40.  The first tensioners 1 may be distributed in such a way that the lower average fiber A2 extends 4 cm from the lower face of the body 31 of the slab 30, 40.
Les seconds tendeurs 2 pourront être répartis de telle manière que la fibre moyenne supérieure A3 s'étende à 4 centimètres au-dessus de la face supérieure du corps 31 de la dalle 30, 40.  The second tensioners 2 may be distributed in such a way that the upper middle fiber A3 extends 4 cm above the upper face of the body 31 of the slab 30, 40.
Considérons tout d'abord le cas où le corps 41 de la dalle 40 est alvéolé (figure 5).  Consider firstly the case where the body 41 of the slab 40 is honeycombed (Figure 5).
On pourra précontraindre cette dalle 40 grâce aux premiers tendeurs 1 avec un effort de compression égal à 140 tonnes. On pourra en outre précontraindre de manière provisoire cette dalle 40 grâce aux seconds tendeurs 2 avec un effort de compression égal à 60 tonnes. Le résultat sera que cette dalle 40 alvéolée pourra supporter des charges deux fois plus lourdes qu'une dalle alvéolée qui n'aurait pas été équipée de seconds tendeurs 2. Elle est en effet prévue pour supporter une précontrainte de 140 tonnes qui est bien supérieure à la précontrainte qu'on n'aurait pu appliquer en l'absence de seconds tendeurs (qui aurait été d'environ 82 tonnes). This slab 40 can be preloaded thanks to the first tensioners 1 with a compression force equal to 140 tons. It will also be possible to preload temporarily this slab 40 through the second tensioners 2 with a compressive force equal to 60 tons. The result will be that this hollow slab 40 will be able to withstand loads twice as heavy as a hollow slab that would not have been equipped with second tensioners 2. It is indeed designed to withstand a prestressing of 140 tons which is much higher than prestressing that could not have been applied in the absence of second tensioners (which would have been about 82 tons).
Considérons maintenant le cas où le corps 31 de la dalle 30 est plein (figures 4A et 4B).  Now consider the case where the body 31 of the slab 30 is full (Figures 4A and 4B).
On pourra précontraindre cette dalle 30 grâce aux premiers tendeurs 1 avec un effort de compression égal à 192 tonnes. On pourra en outre précontraindre de manière provisoire cette dalle 30 grâce aux seconds tendeurs 2 avec un effort de compression égal à 96 tonnes.  This slab 30 can be preloaded thanks to the first tensioners 1 with a compression force equal to 192 tons. It will further be possible to prestress temporarily this slab 30 thanks to the second tensioners 2 with a compressive force equal to 96 tons.
Le résultat sera que cette dalle 30 pleine pourra supporter des charges trois fois plus lourdes qu'une dalle alvéolée qui n'aurait pas été équipée de seconds tendeurs 2. On comprend en effet qu'une dalle pleine peut emmagasiner davantage de précontrainte qu'une dalle alvéolée.  The result will be that this solid slab 30 can support loads three times heavier than a hollow slab that would not have been equipped with second tensioners 2. It is clear that a solid slab can store more prestressing than hollow slab.
On peut maintenant décrire comment sont utilisées les poutres 10 et dalles 40 précitées, en référence aux figures 5A et 5B.  We can now describe how are used the beams 10 and slabs 40 above, with reference to Figures 5A and 5B.
Les poutres 10 et dalles 40 sont préfabriquées en usine.  The beams 10 and slabs 40 are prefabricated at the factory.
Leur processus de fabrication consiste à disposer les premiers et seconds tendeurs 1 , 2 dans des moules (les seconds tendeurs étant ici déjà gainés et équipés de leurs manchons tronconiques 3), à appliquer une tension sur ces tendeurs, à couler du béton dans les moules, et à attendre la prise complète du béton. Après séchage du béton, les premiers et seconds tendeurs 1 , 2 sont libérés, mettant ainsi les corps 1 1 , 31 des poutres et dalles en compression longitudinale excentrée.  Their manufacturing process consists of arranging the first and second tensioners 1, 2 in molds (the second tensioners being here already sheathed and equipped with their frustoconical sleeves 3), to apply a tension on these tensioners, to pour concrete into the molds , and to wait for the complete setting of the concrete. After the concrete has dried, the first and second tensioners 1, 2 are released, thus putting the bodies 1 1, 31 of the beams and slabs in eccentric longitudinal compression.
Les poutres 10 et dalles 40 sont ensuite sorties de leurs moules respectifs. Du fait des efforts exercés par les premiers et seconds tendeurs 1 , 2, les corps 1 1 , 31 n'ont pas tendance à se courber exagérément. Par conséquent, la sortie des poutres 10 et dalles 40 en dehors de leurs moules ne provoque pas de cintrage brusque des corps, ce qui évite l'apparition de fissures dans le béton.  The beams 10 and slabs 40 are then removed from their respective molds. Due to the forces exerted by the first and second tensioners 1, 2, the bodies 1 1, 31 do not tend to bend excessively. Consequently, the exit of the beams 10 and slabs 40 outside their molds does not cause sudden bending of the bodies, which prevents the appearance of cracks in the concrete.
Sur le chantier, on considérera ici qu'une structure initiale de l'ouvrage a déjà été assemblée. En l'espèce, des appuis 50 verticaux auront déjà été installés à distance les uns des autres.  On site, we will consider here that an initial structure of the work has already been assembled. In this case, vertical supports 50 will have already been installed at a distance from each other.
La première opération consistera alors à installer deux poutres 10 en parallèles et à distance l'une de l'autre, chacune en porte-à-faux entre deux appuis 50 écartés l'un de l'autre. Pour cela, les extrémités de chaque poutre 10 seront posées sur des rebords 51 prévus sur ces appuis 50. The first operation will consist in installing two beams 10 in parallel and at a distance from each other, each cantilever between two supports 50 spaced apart from each other. For this, the ends of each beam 10 will be placed on flanges 51 provided on these supports 50.
La seconde opération consistera à charger progressivement les deux poutres 10 en installant sur elles des dalles 40, les extrémités de chaque dalle 40 reposant respectivement sur les deux poutres 10.  The second operation will consist of gradually loading the two beams 10 by installing on them slabs 40, the ends of each slab 40 resting respectively on the two beams 10.
La mise en place progressive des dalles sur les poutres 10 aura pour effet de faire ployer graduellement les poutres 10 vers le bas. Pour endiguer ce phénomène de flexion, les ouvriers pourront libérer progressivement les seconds tendeurs 2 des poutres 10 de manière que ces tendeurs cessent d'exercer un moment de flexion vers le bas sur les corps 1 1 des poutres 10. On pourra ainsi prévoir de libérer les seconds tendeurs 2 au fur et à mesure qu'on charge les poutres 10, de manière que les poutres 10 conservent toujours des meilleures formes (sensiblement rectilignes).  The gradual placement of the slabs on the beams 10 will have the effect of gradually bending the beams 10 down. To stem this bending phenomenon, the workers will be able to gradually release the second tensioners 2 of the beams 10 so that these tensioners stop exerting a downward bending moment on the bodies 1 1 of the beams 10. It can thus be expected to release the second tensioners 2 as and when the beams 10, so that the beams 10 always retain better shapes (substantially rectilinear).
Une fois l'ensemble des dalles 40 mises en place, on pourra prévoir de recouvrir ces dernières par une chape de béton (également appelée « table de compression »).  Once the set of slabs 40 put in place, it can be expected to cover them with a concrete screed (also called "compression table").
Préalablement à cette opération, on pourra retirer tout ou partie des seconds tendeurs 2 présents dans les dalles 40. Si on souhaite extraire une partie de ces seconds tendeurs 2 au moment du coulage de la chape ou après la prise du béton, on pourra alors avantageusement utiliser des boîtes au niveau des extrémités des seconds tendeurs 2, afin de conserver un accès à ces extrémités.  Prior to this operation, it will be possible to remove all or part of the second tensioners 2 present in the slabs 40. If it is desired to extract a portion of these second tensioners 2 at the time of pouring the screed or after the setting of the concrete, then it will be advantageous to use boxes at the ends of the second tensioners 2, to maintain access to these ends.
La présente invention n'est nullement limitée aux modes de réalisation décrits et représentés, mais l'homme du métier saura y apporter toute variante conforme à son esprit.  The present invention is not limited to the embodiments described and shown, but the skilled person will be able to make any variant within his mind.
En particulier, lorsque les dalles utilisées seront alvéolées, on pourra prévoir de placer les seconds tendeurs dans les alvéoles elles-mêmes, de manière à faciliter leur installation et leur extraction.  In particular, when the slabs used will be honeycombed, it will be possible to place the second tensioners in the cells themselves, so as to facilitate their installation and extraction.
Selon une autre variante non représentée de l'invention, on pourrait utiliser, pour la construction d'un pont, une poutre du type de celle représentée sur les figures 3A et 3B, avec une longueur de 40 mètres, une section de 2,5 mètres de hauteur, un talon inférieur de 70 centimètres de largeur, un talon supérieur de 1 ,2 mètre de largeur, et une épaisseur d'âme de 24 centimètres. Le relâchement de seconds tendeurs permet d'obtenir un effet similaire à une seconde phase de précontrainte par post tension. According to another variant not shown of the invention, could be used, for the construction of a bridge, a beam of the type shown in Figures 3A and 3B, with a length of 40 meters, a section of 2.5 meters in height, a lower heel 70 centimeters in width, a heel greater than 1, 2 meters in width, and a core thickness of 24 centimeters. The release of second tensioners makes it possible to obtain an effect similar to a second phase of prestressing by post tension.

Claims

REVENDICATIONS
1 . Elément de structure (10, 20, 30, 40) préfabriqué comportant :1. Prefabricated structural element (10, 20, 30, 40) comprising:
- un corps allongé (1 1 , 21 , 31 , 41 ), et an elongated body (1 1, 21, 31, 41), and
- au moins un premier tendeur (1 ) qui est fixé dans le corps allongé (1 1 , at least one first tensioner (1) which is fixed in the elongated body (1 1,
21 , 31 , 41 ) de telle manière qu'il comprime et fléchit le corps allongé (1 1 , 21 , 31 , 41 ) dans une première direction, 21, 31, 41) in such a way that it compresses and flexes the elongated body (1 1, 21, 31, 41) in a first direction,
caractérisé en ce qu'il comporte au moins un second tendeur (2) qui est fixé en deux points distincts audit corps allongé (1 1 , 21 , 31 , 41 ) de telle sorte qu'il comprime et fléchit le corps allongé (1 1 , 21 , 31 , 41 ) dans une direction opposée à ladite première direction, et  characterized in that it comprises at least one second tensioner (2) which is fixed at two distinct points to said elongated body (1 1, 21, 31, 41) so that it compresses and flexes the elongate body (1 1 , 21, 31, 41) in a direction opposite to said first direction, and
en ce qu'il est prévu un moyen de désactivation (3B) pour relâcher la compression et le fléchissement exercés sur le corps allongé (1 1 , 21 , 31 , 41 ) par ledit second tendeur (2).  in that a deactivation means (3B) is provided for releasing the compression and bending exerted on the elongate body (1 1, 21, 31, 41) by said second tensioner (2).
2. Elément de structure (10, 20, 30, 40) selon la revendication 1 , dans lequel, le second tendeur (2) étant fixé audit corps allongé (1 1 , 21 , 31 , 41 ) par des moyens de fixation (3), l'un au moins desdits moyens de fixation (3) comporte une partie amovible (3B ; 3C) qui forme ledit moyen de désactivation.  2. Structure element (10, 20, 30, 40) according to claim 1, wherein, the second tensioner (2) being fixed to said elongated body (1 1, 21, 31, 41) by fixing means (3). ), at least one of said fixing means (3) comprises a removable portion (3B; 3C) which forms said deactivating means.
3. Elément de structure (10, 20, 30, 40) selon la revendication 1 , dans lequel, le second tendeur (2) étant réalisé en deux parties (2C, 2D) qui sont situées dans le prolongement l'une de l'autre et qui sont raccordées l'une à l'autre par un moyen de fixation (5), ce moyen de fixation (5) comporte une partie amovible (3B ; 3C) qui forme ledit moyen de désactivation.  3. structural element (10, 20, 30, 40) according to claim 1, wherein, the second tensioner (2) being made in two parts (2C, 2D) which are located in the extension of one of the other and which are connected to each other by a fixing means (5), this fixing means (5) comprises a removable portion (3B; 3C) which forms said deactivating means.
4. Elément de structure (10, 20, 30, 40) selon l'une des revendications 2 et 3, dans lequel ladite partie amovible (3C) est fusible.  4. Structure element (10, 20, 30, 40) according to one of claims 2 and 3, wherein said removable portion (3C) is fusible.
5. Elément de structure (10, 20, 30, 40) selon l'une des revendications 2 et 3, dans lequel ladite partie amovible (3B) est démontable.  5. Element structure (10, 20, 30, 40) according to one of claims 2 and 3, wherein said removable portion (3B) is removable.
6. Elément de structure selon l'une des revendications précédentes, dans lequel au moins une partie centrale du second tendeur est accessible depuis l'extérieur du corps allongé pour être découpée ou cassée.  6. Structure element according to one of the preceding claims, wherein at least a central portion of the second tensioner is accessible from outside the elongate body to be cut or broken.
7. Elément de structure selon la revendication précédente, dans lequel le second tendeur étant fixé audit corps allongé par ses extrémités, les moyens de désactivation sont uniquement adaptés à relâcher la compression et le fléchissement exercés sur le corps allongé par la partie centrale dudit second tendeur. 7. structural element according to the preceding claim, wherein the second tensioner being fixed to said elongate body by its ends, the deactivating means are only adapted to relax the compression and the bending exerted on the elongate body by the central portion of said second tensioner.
8. Elément de structure (10, 20, 30, 40) selon l'une des revendications précédentes, dans lequel chaque second tendeur (2) est adapté à être entièrement ou partiellement extrait dudit corps allongé (1 1 , 21 , 31 , 41 ).  8. Element of structure (10, 20, 30, 40) according to one of the preceding claims, wherein each second tensioner (2) is adapted to be wholly or partially extracted from said elongate body (1 1, 21, 31, 41 ).
9. Elément de structure (10, 20, 30, 40) selon l'une des revendications précédentes, dans lequel chaque second tendeur (2) comporte un fil, un câble ou une barre métallique.  9. Structure element (10, 20, 30, 40) according to one of the preceding claims, wherein each second tensioner (2) comprises a wire, a cable or a metal bar.
10. Elément de structure (10, 20, 30, 40) selon l'une des revendications précédentes, dans lequel au moins une partie centrale du second tendeur (2) est enfilée librement dans une gaine (4) fixée au corps allongé (1 1 , 21 , 31 , 41 ).  10. Element of structure (10, 20, 30, 40) according to one of the preceding claims, wherein at least a central portion of the second tensioner (2) is threaded freely in a sheath (4) fixed to the elongate body (1). 1, 21, 31, 41).
1 1 . Elément de structure (10, 20, 30, 40) selon l'une des revendications précédentes, dans lequel au moins une partie centrale du second tendeur (2) est située à l'extérieur du corps allongé (1 1 , 21 , 31 , 41 ).  1 1. Structure element (10, 20, 30, 40) according to one of the preceding claims, wherein at least one central portion of the second tensioner (2) is located outside the elongate body (1 1, 21, 31, 41).
12. Elément de structure (10, 20, 30, 40) selon l'une des revendications précédentes, dans lequel chaque premier tendeur (1 ) comporte un fil, un câble ou une barre métallique, noyé dans le matériau du corps allongé (1 1 , 21 , 31 , 41 ).  12. Structure element (10, 20, 30, 40) according to one of the preceding claims, wherein each first tensioner (1) comprises a wire, a cable or a metal bar, embedded in the material of the elongated body (1). 1, 21, 31, 41).
13. Elément de structure (10, 20, 30, 40) selon l'une des revendications précédentes, dans lequel le corps est formé par une poutre (1 1 , 21 ) en béton ou par une dalle (31 , 41 ) en béton.  13. Structure element (10, 20, 30, 40) according to one of the preceding claims, wherein the body is formed by a beam (1 1, 21) of concrete or a slab (31, 41) of concrete .
14. Procédé de construction d'un ouvrage, comportant des étapes :  14. A method of constructing a structure, comprising steps:
a) d'installation d'une structure initiale (50),  a) installing an initial structure (50),
b) de fixation d'un élément de structure (20) conforme à l'une des revendications précédentes à ladite structure initiale (50), chaque premier tendeur (1 ) étant à cette étape fixé dans le corps allongé (1 1 , 21 , 31 , 41 ) de telle manière qu'il comprime et fléchit le corps allongé (1 1 , 21 , 31 , 41 ) dans une première direction, et chaque second tendeur (2) de cet élément de structure (20) étant fixé en deux points distincts audit corps allongé (1 1 , 21 , 31 , 41 ) de telle sorte qu'il comprime et fléchit le corps allongé (1 1 , 21 , 31 , 41 ) dans une direction opposée à ladite première direction,  b) fixing a structural element (20) according to one of the preceding claims to said initial structure (50), each first tensioner (1) being at this stage fixed in the elongate body (1 1, 21, 31, 41) in such a way that it compresses and flexes the elongated body (1 1, 21, 31, 41) in a first direction, and each second tensioner (2) of this structural element (20) being fixed in two distinct points to said elongate body (1 1, 21, 31, 41) such that it compresses and flexes the elongate body (1 1, 21, 31, 41) in a direction opposite to said first direction,
c) d'installation d'une structure postérieure (40) sur ledit élément de structure (20), de telle sorte que ledit élément de structure (20) est mis en charge, d) de désactivation de chaque second tendeur (2) dudit élément de structure (20) pour relâcher la compression et la flexion exercées par le second tendeur (2) sur le corps allongé (21 ) dudit élément de structure (20). c) installing a posterior structure (40) on said structural element (20), such that said structural element (20) is loaded, d) deactivating each second tensioner (2) of said structural member (20) for releasing compression and flexion exerted by the second tensioner (2) on the elongate body (21) of said structural member (20).
15. Procédé selon la revendication précédente, dans lequel les étapes c) et d) sont opérées de manière concomitante. 15. Method according to the preceding claim, wherein steps c) and d) are operated concomitantly.
16. Procédé selon l'une des deux revendications précédentes, dans lequel, ladite structure postérieure comportant au moins un élément de structure (40) selon l'une des revendications 1 à 13, les étapes c) et d) sont suivies des étapes :  16. Method according to one of the two preceding claims, wherein, said posterior structure comprising at least one structural element (40) according to one of claims 1 to 13, steps c) and d) are followed by the steps:
e) d'ajout d'une chape ou d'une table de compression ou d'une charge de poids permanente sur ladite structure postérieure, et  e) adding a clevis or compression table or a permanent weight load on said posterior structure, and
f) de désactivation de chaque second tendeur (2) de l'élément de structure (40) de ladite structure postérieure (40) pour relâcher la compression et la flexion exercées par le second tendeur (2) sur le corps allongé (41 ) dudit élément de structure (40).  f) deactivating each second tensioner (2) of the structural element (40) of said rear structure (40) to release the compression and bending exerted by the second tensioner (2) on the elongated body (41) of said structural member (40).
EP15759499.5A 2014-07-31 2015-07-08 A pre-tensioned bearing structure Active EP3175057B1 (en)

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FR1457470A FR3024480B1 (en) 2014-07-31 2014-07-31 STRUCTURAL ELEMENT WITH ANTICIPATED PRECONTRAIN
PCT/FR2015/051894 WO2016016536A1 (en) 2014-07-31 2015-07-08 Structural element with anticipated prestressing

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FR3067375B1 (en) 2017-06-13 2020-10-30 Alain Sabbah TEMPORARY PRE-STRESSING ELEMENT
FR3069870B1 (en) * 2017-08-03 2020-10-09 Alain Sabbah MANUFACTURING PROCESS OF A STRUCTURAL ELEMENT

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US20110041433A1 (en) * 2009-08-18 2011-02-24 Yidong He Method to Compress Prefabricated Deck Units with External Tensioned Structural Elements
US20110099941A1 (en) * 2009-10-29 2011-05-05 Yegge Lawrence R Process for producing high-capacity concrete beams or girders

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US6668412B1 (en) * 1997-05-29 2003-12-30 Board Of Regents Of University Of Nebraska Continuous prestressed concrete bridge deck subpanel system

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Publication number Priority date Publication date Assignee Title
US20110041433A1 (en) * 2009-08-18 2011-02-24 Yidong He Method to Compress Prefabricated Deck Units with External Tensioned Structural Elements
US20110099941A1 (en) * 2009-10-29 2011-05-05 Yegge Lawrence R Process for producing high-capacity concrete beams or girders

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Title
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EP3175057C0 (en) 2023-12-13
FR3024480B1 (en) 2018-03-09

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