Classifications

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

Definitions

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

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