EP3175057B1 - A pre-tensioned bearing structure - Google Patents

A pre-tensioned bearing structure Download PDF

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Publication number
EP3175057B1
EP3175057B1 EP15759499.5A EP15759499A EP3175057B1 EP 3175057 B1 EP3175057 B1 EP 3175057B1 EP 15759499 A EP15759499 A EP 15759499A EP 3175057 B1 EP3175057 B1 EP 3175057B1
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EP
European Patent Office
Prior art keywords
tensioner
structural element
elongate body
tensioners
concrete
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Application number
EP15759499.5A
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German (de)
French (fr)
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EP3175057A1 (en
EP3175057C0 (en
Inventor
Alain SABBAH
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SABBAH, ALAIN
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Individual
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Publication of EP3175057C0 publication Critical patent/EP3175057C0/en
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    • EFIXED CONSTRUCTIONS
    • E04BUILDING
    • E04CSTRUCTURAL ELEMENTS; BUILDING MATERIALS
    • E04C3/00Structural elongated elements designed for load-supporting
    • E04C3/02Joists; Girders, trusses, or trusslike structures, e.g. prefabricated; Lintels; Transoms; Braces
    • E04C3/20Joists; 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
    • EFIXED CONSTRUCTIONS
    • E04BUILDING
    • E04CSTRUCTURAL ELEMENTS; BUILDING MATERIALS
    • E04C3/00Structural elongated elements designed for load-supporting
    • E04C3/02Joists; Girders, trusses, or trusslike structures, e.g. prefabricated; Lintels; Transoms; Braces
    • E04C3/20Joists; 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
    • E04C3/26Joists; 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
    • EFIXED CONSTRUCTIONS
    • E04BUILDING
    • E04CSTRUCTURAL ELEMENTS; BUILDING MATERIALS
    • E04C3/00Structural elongated elements designed for load-supporting
    • E04C3/02Joists; Girders, trusses, or trusslike structures, e.g. prefabricated; Lintels; Transoms; Braces
    • EFIXED CONSTRUCTIONS
    • E04BUILDING
    • E04CSTRUCTURAL ELEMENTS; BUILDING MATERIALS
    • E04C5/00Reinforcing elements, e.g. for concrete; Auxiliary elements therefor
    • E04C5/01Reinforcing elements of metal, e.g. with non-structural coatings
    • EFIXED CONSTRUCTIONS
    • E04BUILDING
    • E04CSTRUCTURAL ELEMENTS; BUILDING MATERIALS
    • E04C5/00Reinforcing elements, e.g. for concrete; Auxiliary elements therefor
    • E04C5/08Members specially adapted to be used in prestressed constructions
    • E04C5/12Anchoring devices
    • EFIXED CONSTRUCTIONS
    • E04BUILDING
    • E04CSTRUCTURAL ELEMENTS; BUILDING MATERIALS
    • E04C5/00Reinforcing elements, e.g. for concrete; Auxiliary elements therefor
    • E04C5/16Auxiliary parts for reinforcements, e.g. connectors, spacers, stirrups
    • E04C5/162Connectors or means for connecting parts for reinforcements
    • EFIXED CONSTRUCTIONS
    • E04BUILDING
    • E04GSCAFFOLDING; FORMS; SHUTTERING; BUILDING IMPLEMENTS OR AIDS, OR THEIR USE; HANDLING BUILDING MATERIALS ON THE SITE; REPAIRING, BREAKING-UP OR OTHER WORK ON EXISTING BUILDINGS
    • E04G21/00Preparing, conveying, or working-up building materials or building elements in situ; Other devices or measures for constructional work
    • E04G21/12Mounting of reinforcing inserts; Prestressing
    • EFIXED CONSTRUCTIONS
    • E04BUILDING
    • E04BGENERAL BUILDING CONSTRUCTIONS; WALLS, e.g. PARTITIONS; ROOFS; FLOORS; CEILINGS; INSULATION OR OTHER PROTECTION OF BUILDINGS
    • E04B5/00Floors; Floor construction with regard to insulation; Connections specially adapted therefor
    • E04B5/02Load-carrying floor structures formed substantially of prefabricated units
    • E04B5/04Load-carrying floor structures formed substantially of prefabricated units with beams or slabs of concrete or other stone-like material, e.g. asbestos cement
    • E04B5/043Load-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
    • EFIXED CONSTRUCTIONS
    • E04BUILDING
    • E04CSTRUCTURAL ELEMENTS; BUILDING MATERIALS
    • E04C5/00Reinforcing elements, e.g. for concrete; Auxiliary elements therefor
    • E04C5/08Members specially adapted to be used in prestressed constructions
    • E04C5/10Ducts

Definitions

  • the present invention generally relates to the manufacture of structural elements, in particular beams, slabs or concrete moldings.
  • It relates more particularly to a prefabricated structural element comprising an elongated body, and at least a first tensioner which is fixed in the elongated body in such a way that it compresses and bends 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 structure, for example buildings, bridges, dams, etc.
  • a well-known problem with concrete is that, although it resists compressive forces well, it cracks quickly when subjected to tensile forces. It is estimated that concrete resists compressive forces twenty times better than tensile forces.
  • reinforced concrete has certain advantages, its use becomes counter-productive when the stresses exerted on the structure become significant, due to the increased weight of the reinforced concrete section.
  • tensioners are placed in the concrete (generally steel bars or metal cables) on which traction is exerted so that at rest, the concrete is compressed.
  • the first process consists of applying tension to the tensioners before the concrete has completely set. After the concrete has dried, the tensioners are released, thus putting the beam in compression by simple adhesion effect.
  • the tensioners are off-centered relative to the neutral fiber of the beam in such a way that they allow the beam to be bent upwards (we speak of counter-deflection), opposite to the load that the beam will receive (once loaded, the beam will then find itself little deformed).
  • the first disadvantage is that when the beam is unmolded and the tensioners are released, the latter cause excessive forces on the beam which have the effect of bending the latter quickly, with the risk that these tensile or compressive forces generate cracks in the concrete. It is therefore advisable to wait until the concrete has dried well before releasing the tensioners and unmolding the beam.
  • Another disadvantage is that, when the beam is not yet loaded, its bending generates tensile stresses in the concrete (at the level of the convex face of the beam) as well as particularly strong localized compressive stresses (at the level of the concave face of the beam).
  • the prestress generated by the first tensioners must therefore not exceed a threshold beyond which the beam bends too much and it would crack.
  • the second process consists of placing tensioners through straight or curved sheaths incorporated into the concrete of the beams. After the concrete has set, the beam is placed in the structure (building, bridge, etc.) before the tensioners are tensioned. Once the beam is in place, it is gradually loaded (for example by placing slabs on top). It is during this loading stage that the tensioners will be gradually put in tension so as to compress and bend the beams as they are put under load.
  • This technique makes it possible to gradually compensate for the forces exerted on the beam when it is loaded. It then makes it possible to achieve the limits of concrete resistance to compression, so that the beam obtained by this technique can be more loaded than that obtained by pre-tension.
  • the present invention proposes a new structural element which has the advantages of prestressing by pre-tension and which is adapted to support higher loads.
  • a structural element according to claim 1 and a method of constructing a structure according to claim 14.
  • a structural element as defined in the introduction in which there is provided at least a second tensioner which is fixed at two distinct points to said elongated body such that it compresses and flexes the elongated body, and in which there is provided deactivation means for releasing the compression and flexing exerted on the body elongated by said second tensioner.
  • the first and second tensioners will then be put in tension during the molding of the body (beam, slab, etc.) of the structural element in the factory.
  • the process for manufacturing the structural element will therefore be as easy to implement as the prestressing process by pre-tension.
  • 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 deflection of the structural element (the counter-deflection exerted by the first tensioner will be compensated by the deflection exerted by the second tensioner).
  • the second tensioner(s) will make it possible to compress and flex the body temporarily. After the release of the second tensioners, the structural element will behave like a structural element obtained by a pre-tensioning process by pre-tension.
  • the major advantage of the invention will be that, as the body will not flex or only slightly, it will be possible to compress it further.
  • first tensioners it will also be possible to move the first tensioners as far as possible from the neutral fiber of the body so that after extracting the second tensioners from the body, the first tensioners exert a strong bending moment on the body which opposes the bending. generated by the body's own weight and by the loads resting on it.
  • steps c) and d) are carried out concomitantly.
  • Each structural element 10, 20, 30, 40 firstly comprises an elongated body 11, 21, 31, 41. This body gives the structural element 10, 20, 30, 40 its general shape. It also incorporates reinforcements allowing it to be pre-stressed.
  • the body 11, 21, 31, 41 is made of concrete.
  • another material could be used.
  • the body 11, 21, 31, 41 will naturally tend to deform, bending downwards (the body is then said to have an “arrow”). This flexion will generate compressive stresses in the upper part of the body, and tensile stresses in the lower part of the body. The risk would then be that, due to these tensile or compressive stresses, the concrete would crack on the lower face or on the upper face of the body.
  • the structural elements 10, 20, 30, 40 are each equipped with at least a first tensioner 1 which is fixed in the body 11, 21, 31, 41 in such a way that the latter is compressed.
  • the compression obtained will then make it possible to compensate for the aforementioned tensile stresses, so as to avoid the appearance of cracks.
  • the body 11, 21, 31, 41 is therefore prestressed by each first tensioner 1.
  • first rectilinear tensioners 1 will be used. These first tensioners 1 could be formed by wires, by metal cables or by high-capacity steel bars. They will preferably be embedded in concrete, so as to gradually transmit the forces to the body of the structural element 10, 20, 30, 40. They are also eccentric with respect to the neutral fiber A1 of the body 11, 21, 31, 41 of the structural element 10, 20, 30, 40 considered .
  • these first tensioners 1 are preferentially distributed under the neutral fiber A1 of the body 11, 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 11 of the beam 10, and they are regularly distributed around 'a lower middle fiber A2.
  • the total traction exerted on the first tensioners 1 therefore makes it possible to compress the body 11 of the beam 10 along the lower middle fiber A2.
  • these first tensioners 1 therefore exert a compressive force E1 on the body 11 of the beam 10.
  • This compressive force E1 generates compressive stresses distributed homogeneously over the entire section of the body 11.
  • the lower average fiber A2 is here located under the neutral fiber A1, at a distance from it denoted difference D1.
  • the first tensioners 1 exert a bending moment M1 on the body 11 of the beam 10.
  • This bending moment M1 makes it possible to bend the body 11 upwards, that is to say in a direction opposite to that in which it tends to deflect under the effect of its own weight (the beam is then said to have a “counter-deflection).
  • This bending moment M1 generates, in the upper part of the body 11, tensile stresses. It also generates compressive stresses in the lower part of the body 11.
  • the bending moment M1 is not compensated and tends to bend the body 11, 21, 31, 41 (especially when the structural element is stored vertically and its own weight no longer causes the body to bend towards the down).
  • the invention then proposes a method making it possible to increase this gap D1 and/or to increase the forces exerted on the first tensioners in order to be able to further load the structural element 10, 20, 30, 40, without risking damage. see cracks appear in the concrete.
  • the structural element 10, 20, 30, 40 comprises at least one second tensioner 2 which is fixed at two distinct points to the body 11, 21, 31, 41 by two means fixing means 3 such that it compresses and bends the body 11, 21, 31, 41 downwards, and there is provided a deactivation means 3B to release the compression and bending exerted on the elongated body 11, 21, 31, 41 by this second tensioner 2.
  • each second tensioner 2 is located on the body 11, 21, 31, 41 off-centered relative to the neutral fiber A1 so that, when the structural element is not yet placed in the work and is not yet loaded, the compression it exerts on the structural element helps prevent the appearance of cracks.
  • each second tensioner 2 is located above the neutral fiber A1 of the body 11, 21, 31, 41, so that it exerts on the body a bending moment which at least partially opposes the bending moment M1.
  • second straight tensioners 2 may be formed by wires, by metal cables or even by metal bars, preferably made of suitable steel.
  • these second tensioners 2 are preferably distributed above the neutral fiber A1 of the body 11, 21, 31, 41 of the structural element 10, 20, 30, 40 considered.
  • these second tensioners 2 are here elongated parallel to the neutral fiber A1 of the body 11 of the beam 10 and are regularly distributed around an average fiber superior A3.
  • the total traction exerted on the second tensioners 2 therefore makes it possible to compress the body 11 of the beam 10 along the upper middle fiber A3.
  • these second tensioners 2 exert a compressive force E2 on the body 11 of the beam 10, which is added to the compressive force E1.
  • This compressive force E2 generates compressive stresses distributed homogeneously over the entire section of the body 11.
  • this upper average fiber A3 is located above the neutral fiber A1, at a distance from it denoted difference D2.
  • these second tensioners 2 exert a bending moment M2 on the body 11 of the beam 10, in the opposite direction to the bending moment M1.
  • This bending moment M2 makes it possible to bend the body 11 downwards, so that it makes it possible to compensate at least in part for the bending of the body 11 under the effect of the bending moment M1.
  • this bending moment M2 makes it possible to simulate a load on the beam 10 when it is not yet loaded.
  • the means for deactivating each second tensioner 2 will then allow, 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 fixed in a non-removable manner to the body of the structural element, provision can be made to release only the central parts of these second tensioners. It is thus possible, for example, to cut the second tensioners at their centers, so that their two ends remain fixed to the body of the structural element.
  • the ends of the second tensioners will therefore allow, after their cutting, to continue to exert compressive forces and bending moments at the ends of the body of the structural element. These efforts and moments will then make it possible to compensate for the forces that the first tensioners exert on these ends.
  • the body 11 of the beam 10 has a substantially parallelepiped shape.
  • the first tensioners 1 are entirely embedded in the concrete of the body 11 of the beam 10, with the possible exception of their ends which can project from the body. They are therefore immovable relative to the body of beam 10.
  • the second tensioners 2 are mounted slidingly in the body 11 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, such that their ends open out at both ends of the body 11. These sheaths 4, here made of plastic, prevent the concrete from coming hang 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 middle fiber A2.
  • the second tensioners 2 are here half as numerous as the first tensioners 1 and are distributed relative to each other in substantially the same way as the first tensioners.
  • the second tensioner 2 which is located in the center of this matrix therefore extends along the upper middle fiber A3.
  • the neutral fiber A1 which passes through the centers of the cross sections of the body 11, 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 11 of the beam 10, by two fixing means, and a deactivation means is provided to release each second tensioner 2.
  • each second tensioner 2 is fixed by its two ends 2A to the two ends of the body 11 of the beam 10. In this way, these ends 2A remain easily accessible from outside the body 11.
  • the deactivation means is provided to allow, on site, to release the tension of the second tensioner 2.
  • this fixing means 3 comprises a socket 3A which is pressed against the corresponding end of the body 11 of the beam 10 and which internally houses two keys 3B.
  • the socket 3A has a cylindrical outer face of revolution, and a frustoconical inner face whose top is turned towards the body 11.
  • the keys 2B overall have the shape of a cylinder cut in two lengthwise. They each have a frustoconical outer face with a shape corresponding to that of the inner face of the socket 3A, and a notched inner face.
  • the aforementioned deactivation means is then formed by the two keys 3B. These two keys 3B in fact project outside the socket 3A, so that they are adapted to be mechanically pulled outside the socket 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 layer of metal or by a non-metallic paste which covers the end 2A of the second tensioner 2 (or the internal face of the socket 3A or the keys 3B), the temperature of which melting temperature is relatively low, and which has satisfactory mechanical characteristics. It could thus be a layer of zinc or tin, since the melting temperature of these materials is low enough (less than 450°C, preferably around 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 fixing means could be in the form of another form.
  • the fixing means used could be in the form of a glue or a meltable paste. It could also be in the form of an easily destructible sleeve (for example by cutting), which would be slipped onto the second tensioner and which would rest 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 that it exerts on the body 11 of the beam 10.
  • the second fixing means intended to block the other end of the second tensioner 2
  • the second fixing means can also be presented in various forms.
  • the second tensioner 2 can be extracted from the body 11 of the beam 10 and can be reused on other beams, which will reduce costs.
  • this second fixing means can fix the second end of the second tensioner 2 in an immovable manner to the body 11 of the beam 10, in which case the second tensioner 2 cannot be extracted from the body 11.
  • this second fixing means can fix the second end of the second tensioner 2 in an immovable manner to the body 11 of the beam 10, in which case the second tensioner 2 cannot be extracted from the body 11.
  • the deactivation means is not at one of the ends 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 two pairs of keys 3B are housed.
  • the 3B keys are identical to those shown on the Figure 2A .
  • the sleeve 5A has an interior face which has two frustoconical parts facing 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 another material which represents suitable characteristics, in which a resistance wire runs.
  • 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 could thus have a length of 7 meters, a height L2 of 60 centimeters, and a width L3 of 40 centimeters.
  • the first tensioners 1 can be distributed in such a way that the lower middle fiber A2 extends 6.8 centimeters from the lower face of the body 11 of the beam 10.
  • the second tensioners 2 can be distributed in such a way that the upper average fiber A3 extends 5 centimeters from the upper face of the body 11 of the beam 10.
  • This beam 10 can be prestressed using the first tensioners 1 with a compression force E1 equal to 192 tonnes.
  • the body 21 of the beam 20 has an I-shaped cross section.
  • the body 21 of the beam 20 therefore 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, parallel to 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 here again regularly distributed over the width of the beam 20. Thus, when they compress the body 21 of beam 10, they do not deform it in torsion.
  • These first five tensioners 1 are located near the underside of the lower sole 23. Thus, when they are tensioned, they make it possible to bend the body 21 of the beam 20 such that the center of the beam moves to the top.
  • Three second tensioners 2 are also provided, which are regularly distributed over the width of the beam 20.
  • the means for fixing the ends of these second tensioners 2 to the body 21 of the beam 20 are identical to those described with reference to the figures 2B .
  • the body 31 of the slab 30 has a generally parallelepiped shape. Its neutral fiber A1 therefore coincides with the central longitudinal axis of body 31.
  • the ends of the slab 30 however have, projecting from the upper face of the body 31, flanges 32. These two flanges 32 run along the two ends of the body 31. They delimit between them a cavity 33 into which a screed.
  • the first and second tensioners 1, 2 extend over the entire length of the slab 30, parallel to each other.
  • first tensioners 1 embedded in the concrete of the body 31 of the slab 30. These first tensioners 1 are here again regularly distributed over the width of the slab 30, under the neutral fiber A1. They are located near the lower face of body 31 of slab 30.
  • Second tensioners 2 are also provided, which are regularly distributed over the width of the slab 30, above the neutral fiber A1. These second tensioners 2 pass through the two edges 32 of the body 31 of the slab 30 such that their ends project from either side of the body 31 of the slab 30. A central part of each of the second tensioners 2, which extends between these two edges 32, is on the other hand located in the cavity 33, outside the body 31.
  • the second tensioners 2 are sheathed over their entire length, which ensures their sliding across the edges 32 and which guarantees their protection from 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 only sheathed over part of their length, that located in the cavity 33.
  • the parts of the second tensioners which pass through the edges 32 will be coated with zinc or tin. and cast in concrete. To allow the forces exerted by these second tensioners to be released, it will then be sufficient to heat the zinc or tin coating.
  • the second tensioners 2 are not sheathed, provided that the height of the concrete screed to be poured into the cavity 33 is sufficiently low so that, once this screed has been cast, the second tensioners are located at above this screed.
  • the edges 32 make it possible to offset the second tensioners 2 to a large distance from the neutral fiber A1 of the body 31. In this way, the tensile force exerted on each of the second tensioners 2 can be less than that exerted on the first tensioners 1.
  • the body (31) is devoid of rim (32), in which case the second tensioners would be located entirely through the body of the slab.
  • FIG. 5A a second embodiment of slabs 40 according to the invention is shown.
  • the 40 slabs represented on this figure 5A do not differ from the slab 30 shown on the Figures 4A and 4B than by the honeycombed nature of their body 41.
  • the full surface area of the slab section is larger here due to the absence of cells. Consequently, the slab is able to undergo greater compressive forces.
  • the slab could 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 can be distributed in such a way that the lower average fiber A2 extends 4 centimeters from the lower face of the body 31 of the slab 30, 40.
  • the second tensioners 2 can be distributed in such a way that the upper average fiber A3 extends 4 centimeters above the upper face of the body 31 of the slab 30, 40.
  • This slab 40 can be pre-stressed using the first tensioners 1 with a compression force equal to 140 tonnes. We can also temporarily prestress this slab 40 using the second tensioners 2 with a compression force equal to 60 tonnes.
  • this hollow core slab 40 will be able to support loads twice as heavy as a hollow core slab which would not have been equipped with second tensioners 2. It is in fact designed to support a prestress of 140 tonnes which is much greater than the prestress that could not have been applied in the absence of second tensioners (which would have been approximately 82 tonnes).
  • This slab 30 can be pre-stressed using the first tensioners 1 with a compression force equal to 192 tonnes. We can also temporarily prestress this slab 30 using the second tensioners 2 with a compression force equal to 96 tonnes.
  • this solid slab 30 will be able to support loads three times heavier than a hollow core slab which would not have been equipped with second tensioners 2.
  • a solid slab can store more prestress than a hollow core slab.
  • Beams 10 and slabs 40 are prefabricated in the factory.
  • Their manufacturing process consists of placing the first and second tensioners 1, 2 in molds (the second tensioners here already being sheathed and equipped with their frustoconical sleeves 3), applying tension to these tensioners, pouring concrete into the molds , and wait for the concrete to completely set. After drying the concrete, the first and second tensioners 1, 2 are released, thus putting the bodies 11, 31 of the beams and slabs in eccentric longitudinal compression.
  • the beams 10 and slabs 40 are then taken out of their respective molds. Due to the forces exerted by the first and second tensioners 1, 2, the bodies 11, 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 avoids the appearance of cracks in the concrete.
  • the first operation will then consist of installing two beams 10 in parallel and at a distance from each other, each cantilevered between two supports 50 spaced apart from each other. For this, the ends of each beam 10 will be placed on edges 51 provided on these supports 50.
  • the second operation will consist of gradually loading the two beams 10 by installing slabs 40 on them, the ends of each slab 40 resting respectively on the two beams 10.
  • the release of second tensioners makes it possible to obtain an effect similar to a second phase of prestressed by post tension.

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Description

DOMAINE TECHNIQUE AUQUEL SE RAPPORTE L'INVENTIONTECHNICAL FIELD TO WHICH THE INVENTION RELATES

La présente invention concerne de manière générale la fabrication d'éléments de structure, notamment de poutres, de dalles ou d'ourdis en béton.The present invention generally relates to the manufacture of structural elements, in particular beams, slabs or concrete moldings.

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.It relates more particularly to a prefabricated structural element comprising an elongated body, and at least a first tensioner which is fixed in the elongated body in such a way that it compresses and bends 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 structure, for example buildings, bridges, dams, etc.

ARRIERE-PLAN TECHNOLOGIQUETECHNOLOGICAL BACKGROUND

Il 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 with concrete is that, although it resists compressive forces well, it cracks quickly when subjected to tensile forces. It is estimated that concrete resists 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 reinforce the concrete with 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, although reinforced concrete has certain advantages, its use becomes counter-productive when the stresses exerted on the structure become significant, due to the increased weight of the reinforced concrete section.

La solution alors envisagée est d'utiliser du béton dit précontraint.The solution then considered is to use so-called prestressed concrete.

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 idea is then to ensure that the concrete always works in compression and never (or only slightly) in tension. To do this, tensioners are placed in the concrete (generally steel bars or metal cables) on which traction is exerted 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 tensile 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.Currently, we know two processes for manufacturing beams in 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 process, called pre-tensioning, consists of applying tension to the tensioners before the concrete has completely set. After the concrete has dried, the tensioners are released, thus putting the beam in compression by simple adhesion effect.

Ce procédé est simple à mettre en oeuvre. 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-centered relative to the neutral fiber of the beam in such a way that they allow the beam to be bent upwards (we speak of counter-deflection), opposite to the load that the beam will receive (once loaded, the beam will then find itself little deformed).

Ce procédé présente toutefois deux inconvénients.This process, however, has two drawbacks.

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 when the beam is unmolded and the tensioners are released, the latter cause excessive forces on the beam which have the effect of bending the latter quickly, with the risk that these tensile or compressive forces generate cracks in the concrete. It is therefore advisable to wait until the concrete has dried well 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 bending generates tensile stresses in the concrete (at the level of the convex face of the beam) as well as particularly strong localized compressive stresses (at the level of the concave face of the beam). The prestress generated by the first tensioners must therefore not exceed a threshold beyond which the beam bends too much and 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 process, called post-tensioning, consists of placing tensioners through straight or curved sheaths incorporated into the concrete of the beams. After the concrete has set, the beam is placed in the structure (building, bridge, etc.) before the tensioners are tensioned. Once the beam is in place, it is gradually loaded (for example by placing slabs on top). It is during this loading stage that the tensioners will be gradually put in tension so as to compress and bend the beams as they are put under load.

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 gradually compensate for the forces exerted on the beam when it is loaded. It then makes it possible to achieve the limits of concrete resistance to compression, so that the beam obtained by this technique can be more loaded than that obtained by pre-tension.

Cette technique, relativement complexe, est en revanche généralement réservée aux grands ouvrages puisqu'elle nécessite la mise en oeuvre 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 technique, relatively complex, is however generally reserved for large works since it requires the use of bulky tensioning machines. It also turns out to be expensive not only because of the use of these machines, but also because the tensioners are threaded through special and expensive sheaths into which a special coating is injected which makes it possible to transmit the forces to the beam.

US 6 668 412 B1 divulgue les caractéristiques du préambule de la revendication 1. US 6,668,412 B1 discloses the features of the preamble of claim 1.

OBJET DE L'INVENTIONOBJECT 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 remedy 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 support higher loads.

Plus particulièrement, on propose selon l'invention un élément de structure selon la revendication 1 et un procédé de construction d'un ouvrage selon la revendication 14. En particulier, on propose 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, according to the invention, we propose a structural element according to claim 1 and a method of constructing a structure according to claim 14. In particular, we propose a structural element as defined in the introduction, in which there is provided at least a second tensioner which is fixed at two distinct points to said elongated body such that it compresses and flexes the elongated body, and in which there is provided deactivation means for releasing the compression and flexing exerted on the body elongated 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 oeuvre que le procédé de précontrainte par pré-tension.The first and second tensioners will then be put in tension during the molding of the body (beam, slab, etc.) of the structural element in the factory. The process for manufacturing the structural element will therefore be as easy to implement as the prestressing process by pre-tension.

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 deflection of the structural element (the counter-deflection exerted by the first tensioner will be compensated by the deflection 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.We thus understand that this structural element can be demolded earlier since there will be no risk of cracking when the tensioners are released and demolded. Its manufacturing will therefore be faster, to the benefit of its production cost.

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 tensioner(s) will make it possible to compress and flex the body temporarily. After the release of the second tensioners, the structural element will behave like a structural element obtained by a pre-tensioning process by pre-tension.

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 only slightly, 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.In fact, as long as the second tensioners are taut, the structural element will be little or not bent. We can then plan 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.Consequently, as the bending will be less significant, the risks of cracks appearing will be less, so that it will be possible to further tighten the first tensioners (and the second tensioners) until approaching the strength limits of the concrete at the compression.

Il 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 move the first tensioners as far as possible from the neutral fiber of the body so that after extracting the second tensioners from the body, the first tensioners exert a strong bending moment on the body which opposes the bending. generated by the body's own weight and by the loads resting 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 support 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 savings in weight, size and costs.

D'autres caractéristiques avantageuses et non limitatives de l'élément de structure conforme à l'invention sont les suivantes :

  • le corps allongé présentant deux abouts et chaque second tendeur présentant deux extrémités noyées dans les abouts du corps allongé;
  • 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 ;
  • 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 ;
  • ladite partie amovible est fusible ;
  • ladite partie amovible est démontable ;
  • au moins une partie centrale du second tendeur est accessible depuis l'extérieur du corps allongé pour être découpée ou cassée ;
  • 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 ;
  • chaque second tendeur est adapté à être entièrement ou partiellement extrait dudit corps allongé ;
  • chaque second tendeur comporte un fil, un câble ou une barre métallique;
  • au moins une partie centrale du second tendeur est enfilée librement dans une gaine fixée au corps allongé ;
  • au moins une partie centrale du second tendeur est située à l'extérieur du corps allongé ;
  • chaque premier tendeur comporte un fil, un câble ou une barre métallique, noyé dans le matériau du corps allongé ; et
  • le corps est formé par une poutre en béton ou par une dalle en béton.
Other advantageous and non-limiting characteristics of the structural element according to the invention are as follows:
  • the elongated body having two ends and each second tensioner having two ends embedded in the ends of the elongated body;
  • the second tensioner being fixed to said elongated 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 each other by a fixing means, this fixing means comprises a removable part which forms said means deactivation;
  • said removable part is fuseable;
  • said removable part is removable;
  • at least a central part of the second tensioner is accessible from outside the elongated body to be cut or broken;
  • the second tensioner being fixed to said elongated body by its ends, the deactivation means are only adapted to release the compression and the bending exerted on the elongated body by the central part 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 part of the second tensioner is threaded freely into a sheath fixed to the elongated body;
  • at least a central part 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; And
  • the body is formed by a concrete beam or by a concrete slab.

L'invention propose également un procédé de construction d'un ouvrage, comportant des étapes :

  1. a) d'installation d'une structure initiale,
  2. b) de fixation d'un élément de structure tel que précité à ladite structure initiale,
  3. c) d'installation d'une structure postérieure sur ledit élément de structure, de telle sorte que ledit élément de structure est mis en charge,
  4. 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, en supprimant cette compression et cette flexion.
The invention also proposes a method of constructing a structure, comprising steps:
  1. a) installation of an initial structure,
  2. b) fixing a structural element as mentioned above to said initial structure,
  3. c) installation of a posterior structure on said structural element, such that said structural element is loaded,
  4. d) deactivating each second tensioner of said structural element to release the compression and flexion exerted by the second tensioner on the elongated body of said structural element, eliminating this compression and this flexion.

Préférentiellement, les étapes c) et d) sont opérées de manière concomitante.Preferably, steps c) and d) are carried out 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 :

  • e) d'ajout d'une chape ou d'une table de compression ou d'une charge de poids permanente sur ladite structure postérieure, et
  • 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.
Advantageously, said posterior structure comprising at least one structural element conforming to the invention, steps c) and d) are followed by the steps:
  • e) adding a screed or a compression table or a load permanent weight on said posterior structure, and
  • f) deactivating each second tensioner of the structural element of said posterior structure to release the compression and flexion exerted by the second tensioner on the elongated body of said structural element.

DESCRIPTION DETAILLEE D'UN EXEMPLE DE REALISATIONDETAILED DESCRIPTION OF AN EXAMPLE OF WORK

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 description which follows with reference to the appended drawings, given as non-limiting examples, will make it clear what the invention consists of and how it can be carried out.

Sur les dessins annexés :

  • les figures 1A et 1B sont des vues schématiques de côté et en coupe d'une poutre de section rectangulaire conforme à l'invention,
  • la figure 1C est un diagramme des efforts et moments s'exerçant à vide sur le corps de la poutre représentée sur les figures 1A et 1B,
  • la figure 1D est un diagramme des efforts et moments s'exerçant sous charge sur le corps de la poutre représentée sur les figures 1A et 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 1A et 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,
  • les figures 4A et 4B sont des vues schématiques de côté et en coupe d'une dalle conforme à l'invention, et
  • les figures 5A et 5B sont des vues schématiques d'un ouvrage utilisant des poutres et des dalles conformes à l'invention.
On the attached drawings:
  • THE Figures 1A and 1B are schematic side and sectional views of a beam of rectangular section according to the invention,
  • there Figure 1C is a diagram of the forces and moments acting empty on the body of the beam represented on the Figures 1A and 1B ,
  • there Figure 1D is a diagram of the forces and moments acting under load on the body of the beam represented on the Figures 1A and 1B ,
  • THE Figures 2A, 2B and 2C are detailed views, in section, of three embodiments of the means for deactivating a second tensioner of the beam shown on the Figures 1A and 1B ,
  • THE Figures 3A and 3B are schematic side and sectional views of an I-section beam according to the invention,
  • THE Figures 4A and 4B are schematic side and sectional views of a slab according to the invention, and
  • THE Figures 5A and 5B are schematic views of a structure using beams and slabs conforming 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 generally made using prefabricated structural elements, which are assembled together on the 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 in relation to this work once 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.On the figures 1A, 3A , 4A and 5A , four types of prefabricated structural elements 10, 20, 30, 40 are shown. On the Figures 1A and 3A , these are beams 10, 20. On the Figures 4A and 5A , these are slabs 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.The points common to these different 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 presentation.

Chaque élément de structure 10, 20, 30, 40 comporte tout d'abord un corps 11, 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 elongated body 11, 21, 31, 41. This body gives the structural element 10, 20, 30, 40 its general shape. It also incorporates reinforcements allowing it to be pre-stressed.

On considérera ici le cas où le corps 11, 21, 31, 41 est réalisé en béton. En variante, un autre matériau pourrait être utilisé.We will consider here the case where the body 11, 21, 31, 41 is made of concrete. Alternatively, another material could be used.

On considérera en outre le cas où le corps 11, 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).We will also consider the case where the body 11, 21, 31, 41 is designed to be placed horizontally in the structure, to be fixed there by its two ends, and to be loaded (that is to say to support 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.We understand 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. Usually, we can subdivide this load into two components: a permanent component and a variable component.

Sous l'effet de ces deux efforts, le corps 11, 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 efforts, the body 11, 21, 31, 41 will naturally tend to deform, bending downwards (the body is then said to have an “arrow”). This flexion will generate compressive stresses in the upper part of the body, and tensile stresses in the lower part of the body. The risk would then be that, due to these tensile or compressive stresses, the concrete would crack on the lower face or on the upper face of the body.

Pour éviter l'apparition de telles fissures, les éléments de structure 10, 20, 30, 40 sont équipés chacun d'au moins un premier tendeur 1 qui est fixé dans le corps 11, 21, 31, 41 de telle manière que ce dernier s'en trouve comprimé.To prevent the appearance of such cracks, the structural elements 10, 20, 30, 40 are each equipped with at least a first tensioner 1 which is fixed in the body 11, 21, 31, 41 in such a way 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 11, 21, 31, 41 est donc ainsi précontraint par chaque premier tendeur 1.The compression obtained will then make it possible to compensate for the aforementioned tensile stresses, so as to avoid the appearance of cracks. The body 11, 21, 31, 41 is therefore 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 11, 21, 31, 41 de l'élément de structure 10, 20, 30, 40 considéré.Generally, several first rectilinear tensioners 1 will be used. These first tensioners 1 could be formed by wires, by metal cables or by high-capacity steel bars. They will preferably be embedded in concrete, so as to gradually transmit the forces to the body of the structural element 10, 20, 30, 40. They are also eccentric with respect to the neutral fiber A1 of the body 11, 21, 31, 41 of the structural element 10, 20, 30, 40 considered .

Comme le montrent bien les figures 1B, 3B, 4B et 5, ces premiers tendeurs 1 sont préférentiellement répartis sous la fibre neutre A1 du corps 11, 21, 31, 41 de l'élément de structure 10, 20, 30, 40 considéré.As clearly shown by the figures 1B, 3B , 4B and 5 , these first tensioners 1 are preferentially distributed under the neutral fiber A1 of the body 11, 21, 31, 41 of the structural element 10, 20, 30, 40 considered.

Comme le montrent bien les figures 1A et 1B (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 11 de la poutre 10, et ils sont régulièrement répartis autour d'une fibre moyenne inférieure A2.As clearly shown by the Figures 1A and 1B (and it is the same for the other structural elements 20, 30, 40), the first tensioners 1 extend in length parallel to the neutral fiber A1 of the body 11 of the beam 10, and they are regularly distributed around 'a lower middle fiber A2.

La traction totale exercée sur les premiers tendeurs 1 permet donc de comprimer le corps 11 de la poutre 10 selon la fibre moyenne inférieure A2.The total traction exerted on the first tensioners 1 therefore makes it possible to compress the body 11 of the beam 10 along the lower middle fiber A2.

Comme le montre la figure 1C, ces premiers tendeurs 1 exercent donc un effort de compression E1 sur le corps 11 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 11.As shown in the Figure 1C , these first tensioners 1 therefore exert a compressive force E1 on the body 11 of the beam 10. This compressive force E1 generates compressive stresses distributed homogeneously over the entire section of the body 11.

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 the Figure 1A , the lower average fiber A2 is here located under the neutral fiber A1, at a distance from it denoted difference D1.

Comme le montre la figure 1C, du fait de cet écart D1, les premiers tendeurs 1 exercent un moment de flexion M1 sur le corps 11 de la poutre 10. Ce moment de flexion M1 permet de faire fléchir le corps 11 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 11, des contraintes de traction. Il génère en outre des contraintes de compression dans la partie inférieure du corps 11.As shown in the Figure 1C , due to this difference D1, the first tensioners 1 exert a bending moment M1 on the body 11 of the beam 10. This bending moment M1 makes it possible to bend the body 11 upwards, that is to say in a direction opposite to that in which it tends to deflect under the effect of its own weight (the beam is then said to have a “counter-deflection). This bending moment M1 generates, in the upper part of the body 11, tensile stresses. It also generates compressive stresses in the lower part of the body 11.

Lorsque le corps 11, 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 11, 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 11, 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 installation of the structural element 10, 20, 30, 40 in the structure, the bending moment M1 is not compensated and tends to bend the body 11, 21, 31, 41 (especially when the structural element is stored vertically and its own weight no longer causes the body to bend towards the down).

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 deviation D1 and/or the tensile force exerted on the first tensioners 1 remains less than a threshold, the tensile stresses generated by the bending moment M1 are compensated by the compressive stresses generated by the compressive force E1: the stresses remain within admissible limits. There is therefore 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 then that the bending moment M1 then remains limited due to this difference D1, so that the loads that the structural element 10, 20, 30, 40 can support are also limited.

L'invention propose alors une méthode permettant d'accroître cet écart D1 et/ou d'accroitre 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.The invention then proposes a method making it possible to increase this gap D1 and/or to increase the forces exerted on the first tensioners in order to be able to further load the structural element 10, 20, 30, 40, without risking damage. see cracks appear 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 11, 21, 31, 41 par deux moyens de fixation 3 de telle sorte qu'il comprime et fléchit le corps 11, 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 11, 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 11, 21, 31, 41 by two means fixing means 3 such that it compresses and bends the body 11, 21, 31, 41 downwards, and there is provided a deactivation means 3B to release the compression and bending exerted on the elongated body 11, 21, 31, 41 by this second tensioner 2.

En pratique, chaque second tendeur 2 est situé sur le corps 11, 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 11, 21, 31, 41 off-centered relative to the neutral fiber A1 so that, when the structural element is not yet placed in the work and is not yet loaded, the compression it exerts on the structural element helps prevent the appearance of cracks.

Préférentiellement, chaque second tendeur 2 est situé au-dessus de la fibre neutre A1 du corps 11, 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 11, 21, 31, 41, so that it exerts on the body a bending moment which at least partially opposes the bending moment M1.

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.We will generally use several second straight tensioners 2. These second tensioners 2 may be formed by wires, by metal cables or even by metal bars, preferably made of suitable steel.

Comme le montrent bien les figures 1B, 3B, 4B et 5, ces seconds tendeurs 2 sont préférentiellement répartis au-dessus de la fibre neutre A1 du corps 11, 21, 31, 41 de l'élément de structure 10, 20, 30, 40 considéré.As clearly shown by the figures 1B, 3B , 4B and 5 , these second tensioners 2 are preferably distributed above the neutral fiber A1 of the body 11, 21, 31, 41 of the structural element 10, 20, 30, 40 considered.

Comme le montrent par exemple les figures 1A et 1B (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 11 de la poutre 10 et sont régulièrement répartis autour d'une fibre moyenne supérieure A3.As shown, for example, by Figures 1A and 1B (and it is the same for the other structural elements 20, 30, 40), these second tensioners 2 are here elongated parallel to the neutral fiber A1 of the body 11 of the beam 10 and are regularly distributed around an average fiber superior A3.

La traction totale exercée sur les seconds tendeurs 2 permet donc de comprimer le corps 11 de la poutre 10 selon la fibre moyenne supérieure A3.The total traction exerted on the second tensioners 2 therefore makes it possible to compress the body 11 of the beam 10 along the upper middle fiber A3.

Comme le montre la figure 1C, ces seconds tendeurs 2 exercent un effort de compression E2 sur le corps 11 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 11.As shown in the Figure 1C , these second tensioners 2 exert a compressive force E2 on the body 11 of the beam 10, which is added to the compressive force E1. This compressive force E2 generates compressive stresses distributed homogeneously over the entire section of the body 11.

Comme le montrent par exemple les figures 1A et 1B, 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, by Figures 1A and 1B , this upper average fiber A3 is located above the neutral fiber A1, at a distance from it denoted difference D2.

Comme le montre la figure 1C, du fait de cet écart D2, ces seconds tendeurs 2 exercent un moment de flexion M2 sur le corps 11 de la poutre 10, de sens opposé au moment de flexion M1. Ce moment de flexion M2 permet de faire fléchir le corps 11 vers le bas, si bien qu'il permet de compenser au moins en partie la flexion du corps 11 sous l'effet du moment de flexion M1.As shown in the Figure 1C , due to this gap D2, these second tensioners 2 exert a bending moment M2 on the body 11 of the beam 10, in the opposite direction to the bending moment M1. This bending moment M2 makes it possible to bend the body 11 downwards, so that it makes it possible to compensate at least in part for the bending of the body 11 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 makes it possible to simulate a load on the beam 10 when it is not yet loaded. The means for deactivating each second tensioner 2 will then allow, 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 gaps D1 and D2 and the traction forces exerted on the first and second tensioners 1, 2 while avoiding excessive bending of the body when it is not yet loaded, which prevents the appearance of cracks in the concrete and which avoids exceeding the admissible 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 11, 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 gaps D1 and D2 and the traction forces therefore 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 11, 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 endure heavier loads than those it could have supported if the gap 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 remains the limit of the compressive strength of the concrete, which must not be exceeded. This is the reason why we will focus more on maximizing the gaps D1 and D2 than on increasing the tensile forces exerted on the first and second tensioners 1, 2.

Sur la figure 1C, la somme des efforts et moments exercés par les premiers et seconds tendeurs 1, 2 est noté C1.On the Figure 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 1D, 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 the Figure 1D , when the structural element 10, 20, 30, 40 is loaded, this load and the own weight of the structural element exert a bending moment M3 which is added to the aforementioned sum C1.

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 :

  • aucune contrainte de traction n'apparaît dans l'élément de structure, et
  • les contraintes de compression que subit l'élément de structure demeurent inférieures à la limite de compression du béton.
Then, the sum of the forces and moments exerted on the structural element, denoted C2, makes it possible to ensure that:
  • no tensile stress appears in the structural element, and
  • the compressive stresses experienced by the structural element remain lower than 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 fixed in a non-removable manner to the body of the structural element, provision can be made to release only the central parts of these second tensioners. It is thus possible, for example, 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 allow, after their cutting, to continue to exert compressive forces and bending moments at the ends of the body of the structural element. These efforts and moments will then make it possible to compensate for the forces that the first tensioners exert on these ends.

On peut maintenant s'intéresser plus en détail au cas particulier de la poutre de section rectangulaire représentée sur les figures 1A et 1B.We can now look in more detail at the particular case of the beam of rectangular section represented on the Figures 1A and 1B .

Dans ce mode, le corps 11 de la poutre 10 présente une forme sensiblement parallélépipédique.In this mode, the body 11 of the beam 10 has a substantially parallelepiped shape.

Les premiers tendeurs 1 sont entièrement noyés dans le béton du corps 11 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.The first tensioners 1 are entirely embedded in the concrete of the body 11 of the beam 10, with the possible exception of their ends which can project from the body. They are therefore immovable relative to the body of beam 10.

Les seconds tendeurs 2 sont quant à eux montés coulissants dans le corps 11 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 11. Ces gaines 4, ici en matière plastique, évitent que le béton ne vienne s'accrocher aux seconds tendeurs 2.The second tensioners 2 are mounted slidingly in the body 11 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, such that their ends open out at both ends of the body 11. These sheaths 4, here made of plastic, prevent the concrete from coming hang 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 explained above, we could however plan to embed 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 , we could not use a sheath, in which case it would be necessary to plan to move the second tensioners 2 (for example by making them pivot on themselves) during the drying of the concrete, so that the concrete does not adhere to the second tensioners 2. Again as a variant, a product could be applied to the second tensioners which prevents the adhesion of the concrete. We could also plan to place the second tensioners outside the concrete, as will for example be explained with reference to the Figure 4A .

Ici, comme le montre la figure 1B, 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 1B , 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 middle 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 are here half as numerous as the first tensioners 1 and are distributed relative to each other in substantially the same way as the first tensioners. The second tensioner 2 which is located in the center of this matrix therefore extends along the upper middle fiber A3.

La fibre neutre A1, qui passe aux centres des sections transversales du corps 11, s'étend donc entre les fibres moyennes supérieure A3 et inférieure A2, à égales distances de celles-ci.The neutral fiber A1, which passes through the centers of the cross sections of the body 11, 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 11 de la poutre 10, par deux moyens de fixation, et il est prévu un moyen de désactivation pour relâcher chaque second tendeur 2.As explained above, each second tensioner 2 is fixed at two distinct points to the body 11 of the beam 10, by two fixing means, and a deactivation means is provided to release each second tensioner 2.

En pratique, chaque second tendeur 2 est fixé par ses deux extrémités 2A aux deux extrémités du corps 11 de la poutre 10. De cette manière, ces extrémités 2A restent facilement accessibles depuis l'extérieur du corps 11.In practice, each second tensioner 2 is fixed by its two ends 2A to the two ends of the body 11 of the beam 10. In this way, these ends 2A remain easily accessible from outside the body 11.

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.This means of deactivation can be presented in various ways.

Il pourra ainsi être intégré à l'un au moins des moyens de fixation 3 des extrémités 2A des seconds tendeurs 2 au corps 11 de la poutre 10.It can thus be integrated into at least one of the fixing means 3 of the ends 2A of the second tensioners 2 to the body 11 of the beam 10.

Tel qu'il apparait sur la figure 2A, ce moyen de fixation 3 comporte une douille 3A qui est plaquée contre l'extrémité correspondante du corps 11 de la poutre 10 et qui loge intérieurement deux clavettes 3B.As it appears on the Figure 2A , this fixing means 3 comprises a socket 3A which is pressed against the corresponding end of the body 11 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 11.The socket 3A has a cylindrical outer face of revolution, and a frustoconical inner face whose top is turned towards the body 11.

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 overall have the shape of a cylinder cut in two lengthwise. They each have a frustoconical outer face with a shape corresponding to that of the inner face of the socket 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 11, permettent de bloquer rigidement l'extrémité 2A du second tendeur 2.These two keys 2B thus form a sort of jaw which, when they sink into the socket 3A towards the body 11, make it possible to rigidly block 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 on the Figure 2A , the aforementioned deactivation means is then formed by the two keys 3B. These two keys 3B in fact project outside the socket 3A, so that they are adapted to be mechanically pulled outside the socket 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 on the Figure 2B , the deactivation means is fuse. In this case, this deactivation means is formed by a layer of metal or by a non-metallic paste which covers the end 2A of the second tensioner 2 (or the internal face of the socket 3A or the keys 3B), the temperature of which melting temperature is relatively low, and which has satisfactory mechanical characteristics. It could thus be a layer of zinc or tin, since the melting temperature of these materials is low enough (less than 450°C, preferably around 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.Alternatively, the removable fixing means could be in the form of 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 screw 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 fixing means used could be in the form of a glue or a meltable paste. It could also be in the form of an easily destructible sleeve (for example by cutting), which would be slipped onto the second tensioner and which would rest 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 11 de la poutre 10.Still as a variant, 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 that it exerts on the body 11 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 case, the second fixing means, intended to block the other end of the second tensioner 2, can also be presented in various forms.

Il sera préférentiellement amovible. De cette manière, le second tendeur 2 pourra être extrait du corps 11 de la poutre 10 et pourra être réutilisé sur d'autres poutres, ce qui réduira les coûts.It will preferably be removable. In this way, the second tensioner 2 can be extracted from the body 11 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 fixing means. It can also be in the form of a sleeve which will be slipped on and fixed on the second tensioner and which will simply rest against the body.

En variante, ce second moyen de fixation pourra fixer la seconde extrémité du second tendeur 2 de manière inamovible au corps 11 de la poutre 10, auquel cas le second tendeur 2 ne pourra pas être extrait du corps 11. Ainsi, on pourrait prévoir de noyer cette seconde extrémité du second tendeur 2 dans le béton du corps 11.Alternatively, this second fixing means can fix the second end of the second tensioner 2 in an immovable manner to the body 11 of the beam 10, in which case the second tensioner 2 cannot be extracted from the body 11. Thus, one could plan to drown this second end of the second tensioner 2 in the concrete of the body 11.

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 11 de la poutre 10 de manière inamovible (ou non).As shown in the Figure 2C , it could alternatively be provided that the deactivation means is not at one of the ends of the second tensioner 2, but at a distance from them. In this variant, we can block the ends 2A of the second tensioner 2 to the body 11 of the beam 10 in an immovable manner (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 two pairs of keys 3B are housed. The 3B keys are identical to those shown on the Figure 2A . The sleeve 5A has an interior face which has two frustoconical parts facing 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 another material which represents suitable characteristics, in which a resistance wire runs.

Lorsque le second tendeur 2 est mis en traction (lors du moulage du corps 11 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 into traction (during the molding of the body 11 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 11 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 the resistance wire with electric current (from the outside of the body 11 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 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 L2 de 60 centimètres, et une largeur L3 de 40 centimètres.The beam could thus have a length of 7 meters, a height 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 11 de la poutre 10.The first tensioners 1 can be distributed in such a way that the lower middle fiber A2 extends 6.8 centimeters from the lower face of the body 11 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 11 de la poutre 10.The second tensioners 2 can be distributed in such a way that the upper average fiber A3 extends 5 centimeters from the upper face of the body 11 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.This beam 10 can be prestressed using the first tensioners 1 with a compression force E1 equal to 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.We can also temporarily prestress this beam 10 using the second tensioners 2 with a compression force E2 equal to 120 tonnes.

Sur la figure 3A, on a représenté un second mode de réalisation d'une poutre 20 selon l'invention.On the Figure 3A , we have shown a second embodiment of a beam 20 according to the invention.

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 an I-shaped cross section.

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 the Figure 3B , the body 21 of the beam 20 therefore 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, parallel to 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.Here there are 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 here again regularly distributed over the width of the beam 20. Thus, when they compress the body 21 of beam 10, they do not deform it 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 underside of the lower sole 23. Thus, when they are tensioned, they make it possible to bend the body 21 of the beam 20 such that the center of the beam moves to the top.

Il 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.Three second tensioners 2 are also provided, which are regularly distributed over the width of the beam 20. The means for fixing the ends of these second tensioners 2 to the body 21 of the beam 20 are identical to those described with reference to the figures 2B .

Sur les figures 4A et 4B, on a représenté un premier mode de réalisation d'une dalle 30 conforme à l'invention.On the Figures 4A and 4B , we have 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 therefore coincides with the central longitudinal axis of 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 have, projecting from the upper face of the body 31, flanges 32. These two flanges 32 run along the two ends of the body 31. They delimit between them a cavity 33 into which 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.The first and second tensioners 1, 2 extend over the entire length of the slab 30, parallel to each other.

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.Here there is provided a plurality of first tensioners 1 embedded in the concrete of the body 31 of the slab 30. These first tensioners 1 are here again regularly distributed over the width of the slab 30, under the neutral fiber A1. They are located near the lower face of body 31 of slab 30.

Il 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.Second tensioners 2 are also provided, which are regularly distributed over the width of the slab 30, above the neutral fiber A1. These second tensioners 2 pass through the two edges 32 of the body 31 of the slab 30 such that their ends project from either side of the body 31 of the slab 30. A central part of each of the second tensioners 2, which extends between these two edges 32, is on the other hand 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 across the edges 32 and which guarantees their protection from 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.As a variant, it could be envisaged that the second tensioners 2 are only sheathed over part of their length, that located in the cavity 33. The parts of the second tensioners which pass through the edges 32 will be coated with zinc or tin. and cast in concrete. To allow the forces exerted by these second tensioners to be released, it will then be sufficient to heat the zinc or tin coating.

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.As a variant, it could also 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 sufficiently low so that, once this screed has been cast, 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 edges 32 make it possible to offset the second tensioners 2 to a large distance from the neutral fiber A1 of the body 31. In this way, the tensile force exerted on each of the second tensioners 2 can be less than that exerted on the first tensioners 1. We can thus use here second tensioners 2 of a diameter smaller than that of the first tensioners 1 or 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 1A, 1B et 2B.The fixing means provided at the ends of these second tensioners 2 are here again identical to those described with reference to the figures 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 a variant of the slab, it could have been expected that the body (31) is devoid of rim (32), in which case the second tensioners would be located entirely 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.On the figure 5A , a second embodiment of slabs 40 according to the invention is shown. The 40 slabs represented on this figure 5A do not differ from the slab 30 shown on the Figures 4A and 4B than by the honeycombed nature 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 cellular slabs 40, that is to say slabs 40 whose body is hollowed out with longitudinal conduits called alveoli. 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 préfèrera utiliser une dalle 30 dont le corps 31 est plein (par opposition à alvéolé).However here, as shown by Figures 4A and 4B , we will prefer to use a slab 30 whose body 31 is solid (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 slab section, the full surface area of the slab section is larger here due to the absence of cells. Consequently, 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 forces 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 a 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 could 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 can be distributed in such a way that the lower average fiber A2 extends 4 centimeters 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 can be distributed in such a way that the upper average fiber A3 extends 4 centimeters 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).Let us first consider 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.This slab 40 can be pre-stressed using the first tensioners 1 with a compression force equal to 140 tonnes. We can also temporarily prestress this slab 40 using the second tensioners 2 with a compression force equal to 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).The result will be that this hollow core slab 40 will be able to support loads twice as heavy as a hollow core slab which would not have been equipped with second tensioners 2. It is in fact designed to support a prestress of 140 tonnes which is much greater than the prestress that could not have been applied in the absence of second tensioners (which would have been approximately 82 tonnes).

Considérons maintenant le cas où le corps 31 de la dalle 30 est plein (figures 4A et 4B).Let us 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 pre-stressed using the first tensioners 1 with a compression force equal to 192 tonnes. We can also temporarily prestress this slab 30 using the second tensioners 2 with a compression force equal to 96 tonnes.

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 will be able to support loads three times heavier than a hollow core slab which would not have been equipped with second tensioners 2. We understand in fact that a solid slab can store more prestress than a hollow core 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 the aforementioned beams 10 and slabs 40 are used, with reference to the Figures 5A and 5B .

Les poutres 10 et dalles 40 sont préfabriquées en usine.Beams 10 and slabs 40 are prefabricated in 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 11, 31 des poutres et dalles en compression longitudinale excentrée.Their manufacturing process consists of placing the first and second tensioners 1, 2 in molds (the second tensioners here already being sheathed and equipped with their frustoconical sleeves 3), applying tension to these tensioners, pouring concrete into the molds , and wait for the concrete to completely set. After drying the concrete, the first and second tensioners 1, 2 are released, thus putting the bodies 11, 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 11, 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 taken out of their respective molds. Due to the forces exerted by the first and second tensioners 1, 2, the bodies 11, 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 avoids 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 the 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 then consist of installing two beams 10 in parallel and at a distance from each other, each cantilevered between two supports 50 spaced apart from each other. For this, the ends of each beam 10 will be placed on edges 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 slabs 40 on them, 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 11 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 progressive installation of the slabs on the beams 10 will have the effect of gradually bending the beams 10 downwards. To stem this bending phenomenon, workers can gradually release the second tensioners 2 of the beams 10 so that these tensioners stop exerting a downward bending moment on the bodies 11 of the beams 10. We can thus plan to release the second tensioners 2 as the beams 10 are loaded, so that the beams 10 always maintain the best 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 all of the slabs 40 have been put in place, we can plan to cover them with a concrete screed (also called a “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, we can remove all or part of the second tensioners 2 present in the slabs 40. If we wish to extract part of these second tensioners 2 at the time of pouring the screed or after the concrete has set, we can then advantageously use boxes at the ends of the second tensioners 2, in order 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 in no way limited to the embodiments described and represented, but those skilled in the art will be able to make any variation consistent with their spirit.

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, provision may be made to place the second tensioners in the honeycombs 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, one could use, for the construction of a bridge, a beam of the type of that shown on the Figures 3A and 3B , with a length of 40 meters, a section of 2.5 meters in height, a lower heel of 70 centimeters in width, an upper heel of 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 prestressed by post tension.

Claims (16)

  1. A prefabricated structural element (10, 20, 30, 40) comprising:
    · an elongate body (11, 21, 31, 41); and
    · at least one first tensioner (1) that is fastened in the elongate body (11, 21, 31, 41) in such a manner that it is suitable to compress and make the elongate body (11, 21, 31, 41) bend in a first direction;
    • at least one second tensioner (2) that is fastened to said elongate body (11, 21, 31, 41) so that it is suitable to compress and make the elongate body (11, 21, 31, 41) bend in a direction that is opposite to said first direction;
    the structural element being characterized in that said at least one second tensioner (2) is fastened to said elongate body (11, 21, 31, 41) at two distinct points,
    in that deactivation means (3B) are provided for relaxing the compression and the bending exerted on the elongate body (11, 21, 31, 41) by said second tensioner (2) .
  2. A structural element (10, 20, 30, 40) according to claim 1, wherein the second tensioner (2) is fastened to said elongate body (11, 21, 31, 41) by fastener means (3), and at least one of said fastener means (3) includes a removable portion (3B; 3C) that forms said deactivation means.
  3. A structural element (10, 20, 30, 40) according to claim 1, wherein the second tensioner (2) is made of two portions (2C, 2D) that are situated in alignment with each other and that are connected together by fastener means (5), and the fastener means (5) include a removable portion (3B; 3C) that forms said deactivation means.
  4. A structural element (10, 20, 30, 40) according to claim 2 or claim 3, wherein said removable portion (3C) is meltable.
  5. A structural element (10, 20, 30, 40) according to claim 2 or claim 3, wherein said removable portion (3B) is detachable.
  6. A structural element according to any preceding claim, wherein at least a central portion of the second tensioner is accessible from the outside of the elongate body in order to be cut or broken.
  7. A structural element according to the preceding claim, wherein the second tensioner is fastened to said elongate body via its ends, and the deactivation means are adapted solely to relax the compression and the bending exerted on the elongate body by the central portion of said second tensioner.
  8. A structural element (10, 20, 30, 40) according to any preceding claim, wherein each second tensioner (2) is adapted to be removed from said elongate body (11, 21, 31, 41) completely or in part.
  9. A structural element (10, 20, 30, 40) according to any preceding claim, wherein each second tensioner (2) comprises a metal bar, cable, or wire.
  10. A structural element (10, 20, 30, 40) according to any preceding claim, wherein at least a central portion of the second tensioner (2) is passed freely into a sheath (4) that is fastened to the elongate body (11, 21, 31, 41).
  11. A structural element (10, 20, 30, 40) according to any preceding claim, wherein at least a central portion of the second tensioner (2) is situated outside the elongate body (11, 21, 31, 41).
  12. A structural element (10, 20, 30, 40) according to any preceding claim, wherein each first tensioner (1) comprises a metal bar, cable, or wire that is embedded in the material of the elongate body (11, 21, 31, 41).
  13. A structural element (10, 20, 30, 40) according to any preceding claim, wherein the body is formed by a concrete beam (11, 21) or by a concrete slab (31, 41).
  14. A method of building a work, the method comprising steps of:
    a) installing an initial structure (50);
    b) fastening a structural element (20) in accordance with any preceding claim to said initial structure (50), each first tensioner (1) being, at this step, fastened in the elongate body (11, 21, 31, 41) in such a manner that it compresses and bends the elongate body (11, 21, 31, 41) in a first direction, and each second tensioner (2) of the structural element (20) being fastened to said elongate body (11, 21, 31, 41) at two distinct points so that it compresses and bends the elongate body (11, 21, 31, 41) in a direction that is opposite to said first direction;
    c) installing a subsequent structure (40) on said structural element (20), so that said structural element (20) is put under load; and
    d) deactivating each second tensioner (2) of said structural element (20) so as to relax the compression and the bending exerted by the second tensioner (2) on the elongate body (21) of said structural element (20), by removing this compression and this bending.
  15. A method according to the preceding claim, wherein steps c) and d) are performed in concurrent manner.
  16. A method according to any one of the two preceding claims, wherein said subsequent structure comprises at least one structural element (40) according to any one of claims 1 to 13, and steps c) and d) are followed by steps of:
    e) adding a screed or concrete topping or a permanent heavy load on said subsequent structure; and
    f) deactivating each second tensioner (2) of said structural element (40) of said subsequent structure (40) so as to relax the compression and the bending exerted by the second tensioner (2) on the elongate body (41) of said structural element (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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EP3175057A1 EP3175057A1 (en) 2017-06-07
EP3175057B1 true EP3175057B1 (en) 2023-12-13
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Publication number Priority date Publication date Assignee Title
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

Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US6668412B1 (en) * 1997-05-29 2003-12-30 Board Of Regents Of University Of Nebraska Continuous prestressed concrete bridge deck subpanel system
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

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US6668412B1 (en) * 1997-05-29 2003-12-30 Board Of Regents Of University Of Nebraska Continuous prestressed concrete bridge deck subpanel system
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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FR3024480B1 (en) 2018-03-09
EP3175057A1 (en) 2017-06-07
US20170218628A1 (en) 2017-08-03
EP3175057C0 (en) 2023-12-13
FR3024480A1 (en) 2016-02-05

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