EP1689951A1

EP1689951A1 - Method for production of a block of concrete and reinforcing cage for a block produced thus

Info

Publication number: EP1689951A1
Application number: EP04805843A
Authority: EP
Inventors: Marcel Matiere
Original assignee: Societe Civile de Brevets Matiere
Current assignee: Societe Civile de Brevets Matiere
Priority date: 2003-11-18
Filing date: 2004-11-18
Publication date: 2006-08-16
Anticipated expiration: 2024-11-18
Also published as: AU2004291708A1; WO2005049934A1; ES2338235T3; DE602004024707D1; TNSN06144A1; EP1689951B1; AU2004291708B2; FR2862323A1; MA28165A1; ATE452255T1; PT1689951E; FR2862323B1; EP2141300B1; KR20060129218A; JP4709767B2; JP2007511689A; EP2141300A2; DK1689951T3; EP2141300A3

Abstract

The method involves casting a cement mass (2) in a casing after setting a reinforcing housing (3) in the mass, to fabricate a slab (1). The housing has lower longitudinal frameworks (31) and upper longitudinal frameworks (31) connected with each other. Each framework (31) has locking parts (43, 43) supported in the mass at respective locking zones (B, B) formed inside the slab, in direction opposite to absorbed tensile stress. An independent claim is also included for a reinforced concrete piece comprising a reinforcing housing.

Description

PROCESS FOR PRODUCING A CONCRETE PART AND REINFORCING CAGE FOR A PART THUS PRODUCED

The subject of the invention is a method of producing a concrete part and relates more specifically to the use of a new type of reinforcement having multiple advantages and making it possible, in particular, to considerably increase the level of stress to from which damaging cracks may form. We know that the principle of reinforced concrete is based on the association of two materials with complementary properties, concrete which has a high compressive strength, but a very low tensile strength, and steel, which has an excellent tensile strength and is protected from air corrosion when it is embedded in concrete. The two materials having, moreover, similar expansion coefficients, their association makes it possible to produce composite parts having the qualities of durability of concrete and which can, however, withstand moments or bending forces. Such a part indeed comprises, under the effect of the applied stresses, two parts situated on either side of a neutral axis, respectively a compressed part subjected to compression forces absorbed mainly by the concrete and a part tensile subjected to tensile forces absorbed mainly by at least one tensile longitudinal reinforcement of the reinforcement cage embedded in the concrete. To remain sheltered from air and to prevent corrosion, the reinforcements must be located at a minimum distance from an external face of the part, called "coating distance". However, under the effect of the stresses, it is not possible to avoid deformation of the part with an elongation of the stretched part which causes the appearance of cracks in the coating concrete. These cracks, inevitable in practice, can be allowed as long as their width is small enough, for example less than 3/10 of a millimeter, to prevent the penetration of air and water until contact with the frame. As long as the applied stresses do not exceed a certain limit, a reinforced concrete part therefore behaves like a composite part deforming in block with transfer of forces between the two components. For this, it is usually sought to improve the transfer connection between the reinforcement and the concrete, for example by using so-called high adhesion bars, which are notched over their entire length. On the other hand, the ends of these bars are usually bent to form anchor brackets which increase the length of reinforcement embedded in the concrete and, consequently, the length of transfer of internal forces between the reinforcement and the concrete. . However, if the load exceeds a certain limit, the cracks widen and the free part, of short length, of the tensile reinforcement which extends between the opposite faces of a crack, supports only the elongation corresponding to l thickness of this crack, while the neighboring parts are blocked in the concrete. The tendency of the stretched face to elongate under the effect of the applied stresses therefore concentrates on the free parts of the reinforcement and, because of their short length, the applied elongation can cause the elastic limit of the metal to be exceeded, which causes the necking of the frame and the ruin of the work. The subject of the invention is a new method for producing concrete molded parts which makes it possible to solve such problems thanks to the use of a new type of reinforcement frame, making it possible, in particular, to reduce the risk of cracking at equal demands. In addition, the process makes it possible to considerably improve the resistance to extreme stresses, the concrete parts thus produced being able to have a very great flexibility and to benefit from a great coefficient of safety between the appearance of the first cracks and the complete ruin of the 'work. Such advantage is particularly interesting for the construction of structures or buildings in regions subject to seismic risk. The invention therefore applies, in general, to the production of a concrete part provided with a reinforcement cage entirely embedded in the concrete during the casting thereof and comprising, when is subjected to a stress, two parts located on either side of a neutral axis, respectively a compressed part subjected to compression forces absorbed mainly by the concrete and a stretched part subjected to tensile forces absorbed mainly by at least one tensile longitudinal reinforcement of the reinforcement cage which extends at a short coating distance from a tensed longitudinal face of the part. In accordance with the invention, at least each stretched longitudinal reinforcement consists of at least one flat strip of rectangular section, with a wide face and a narrow face, and is shaped so as to spare, inside the part, at least two blocking zones spaced from one another, in which a part of said tensioned reinforcement bears on the concrete, in the direction opposite to the absorbed tensile force, and at least one sliding zone between the blocking zones, in which a corresponding part of the tensioned frame is free to lengthen over its entire length, under the effect of the forces absorbed. As will be seen in more detail later, while the purpose of the reinforced concrete technique is, in general, to secure each reinforcement over its entire length with the concrete which surrounds it, in order to achieve a composite part deforming as a block under the effect of stresses, the idea of the invention is, on the contrary, to produce spaced apart blocking zones, in which the armature, because it consists of a strip flat, is supported in the concrete by a wide face without risk of exceeding the admissible limit of compression of the concrete and, from a certain level of stress, to leave the part of the reinforcement comprised between two compression zones, free to slip slightly with respect to the concrete which surrounds it, after detachment of the latter, so that the elongation effect of the reinforcement resulting from the applied tensile forces is always distributed over the entire length between two blocking zones, which avoids stress concentrations which can lead to a rupture of the reinforcement in the event of extreme stresses. In a particularly advantageous manner, each blocking zone is produced by deflection of the corresponding part of the tensioned armature in the form of a strip, with a gradual and continuous variation of the orientation of its wide face relative to the tensioned longitudinal face of the room. In a first embodiment, each blocking zone is produced by twisting the strip over a certain length, with a progressive rotation of its wide face around its longitudinal axis, over at least a quarter of a turn. However, the twisted part of the strip can also turn a full turn or more, so as to rest on the concrete over a greater length. In another embodiment, each blocking zone is produced by the curvature of the flat strip around a transverse axis, so as to form an anchoring stick bearing on the concrete by a wide face. But it is also possible to produce a blocking zone by fixing on the flat strip, at the desired location, at least one section of rigid bar extending transversely so as to bear in the concrete on either side of the flat strip. This crossbar can be made up of a distribution strip. In fact, conventionally, the reinforcement cage usually comprises several longitudinal sectors linked together by distribution struts made up of bars perpendicular to the main longitudinal bars, the assembly constituting a sheet of reinforcement. These distribution ribbons can be welded to the longitudinal bars, whose flat strip shape allows particularly strong welds to be produced. Each welded junction can constitute a blocking zone, the distribution stringer bearing in the concrete on either side of the longitudinal bar.

In addition, usually, each sector of the reinforcement cage comprises at least two longitudinal bars respectively compressed and tensioned and connected to one another by connecting stirrups. Preferably, the compressed reinforcements also consist of flat strips. Similarly, according to another advantageous arrangement, the connecting stirrups can each consist of at least one flat strip secured to the reinforcements by weld beads or glued parts extending over a length equal to the width of the strip , and therefore, particularly resistant. In addition, each strip constituting a stirrup is inclined relative to the direction of the tensioned bar and the whole of the welded junction between these two flat strips of different orientation, forms a sort of wedge resting on the concrete. Therefore, each blocking zone between the tensioned reinforcement and the concrete can be constituted by a joining junction between this tensioned reinforcement and a strip-shaped connecting stirrup. However, the use of flat strips to produce at least the tensile reinforcements gives still other possibilities. Thus, to form a blocking zone, the armature stretched in the form of a strip can be split axially over a certain length, the two strip parts thus formed being spaced from one another to form a transverse passage opening d '' at least one rigid bar section likely to bear on the concrete on either side of the longitudinal strip, in the opposite direction to the tensile force applied to the longitudinal reinforcement. This rigid bar can be a distribution streak crossing the longitudinal strip in the plane of the latter, or a simple section of bar crossing the longitudinal strip perpendicular to its plane. Furthermore, the use of flat strips allows multiple possibilities for implementing the method according to the invention. In particular, each longitudinal reinforcement may comprise at least two contiguous strips extending longitudinally, substantially in the extension of one another and subjected to tensile forces in opposite directions, the two contiguous strips overlapping on a certain length and ending respectively, on either side of the overlap, by two hooks facing one another, which thus tend to approach under the effect of opposite tensile forces applied to the two corresponding bands, by inducing the compression of a concrete core between the two sticks, over said covering length. In the usual case where the reinforcement cage consists of parallel sectors connected by distribution struts, the latter can pass inside the sticks of two neighboring sectors, so as to transmit to the part of the concrete comprised between said sectors, the compression forces induced, in each sector, by the tendency to approach opposite sticks. According to a particular arrangement, the two adjoining strips form the longitudinal reinforcement of each sector of the cage, can constitute two strands of a single strip ending in opposite hooks and forming a loop between two spaced apart levels, so as to surround a concrete core in compression by tightening said loop under the effect of the tensile forces applied in opposite directions on the two strands of the longitudinal reinforcement. In a particularly advantageous manner, in each sector, the longitudinal reinforcement may consist of a series of consecutive strips each having two ends curved in the shape of a stick, the adjacent sticks of two consecutive strips being placed one next to the another by partially overlapping so as to limit a passage space, in the transverse direction, of at least one bar section forming a connecting key between the two consecutive strips. The longitudinal reinforcement then behaves like a taut chain made up of a series of links each formed of a band and connected two by two by pairs of adjacent hooks keyed together. In another equally advantageous embodiment, in each sector, the longitudinal reinforcement comprises a stack of flat strips, arranged on at least two superposed levels, respectively a first level, the closest to a stretched longitudinal face of the part. comprising a strip, with two ends in the form of hooks facing the interior of the part and at least a second level comprising at least two substantially parallel flat strips arranged side by side with, each, two ends in the form of hooks, respectively internal and external, and said bands of the second level overlap over a certain length, so that their internal ends in the form of hooks are turned towards each other. The part thus comprises at least one part forming a core comprised between the internal sticks of the two bands and put in compression by the tendency towards each other of said internal sticks under the effect of the tensile forces applied in directions. opposite on the corresponding bands, and two extreme parts each included between the external sticks of the bands of the first and second level and put in compression by the tendency to approximation towards the inside of each external stock of the strip of the first level under the effect of the tensile force supported by said strip. It is thus possible to compress all of the concrete in the room. However, the invention also allows other arrangements and covers numerous advantageous characteristics which will appear in the following description of certain embodiments given by way of nonlimiting examples illustrated by the appended drawings. Figure 1 is a schematic view, in longitudinal section, of a concrete part made according to the invention. Figure 2 is a partial cross-sectional view along l-ll of Figure 1. Figure 3 is a perspective view of a twisted part of the frame. Figure 4 is a sectional view, along a transverse median plane, of the twisted part. Figure 5 is a partial perspective view of a portion in the form of a butt. Figure 6 is a partial side view of a double butt. Figure 7 is a view in longitudinal section of a part produced according to a variant of the invention. Figure 8 shows, in perspective, a twisted part applied to the embodiment of Figure 7. Figure 9 shows, in longitudinal section, a part made according to another variant of the invention. Figures 10 and 1 1 show, in longitudinal section, other variants of the invention, with several layers of reinforcements. Figure 12 shows, in longitudinal section, a part of the type shown in Figure 1 0, with a closed loop frame. Figure 13 is a perspective view of a closed loop frame. Figure 14 shows, in longitudinal section, another variant of the invention, with a chain-shaped frame. Figure 15 shows, in perspective, the junction between two elements of the reinforcement of the type shown in Figure 14. Figures 16, 17, 18 show, in perspective, other embodiments of a blocking area . Figure 19 shows, in perspective, a stick-shaped blocking zone. FIG. 20 shows, in perspective, another embodiment of a butt end of a butt-shaped frame. In Figures 1 and 2, there is shown, respectively in longitudinal section and in cross section, a concrete part made according to the invention. As usual, this concrete part 1 which constitutes, in the example shown in the drawings, a slab having two flat faces, respectively lower 20 and upper 21, is a molded part produced by pouring a mass of concrete 2 in a formwork, after installation, in the latter of a reinforcement cage 3 comprising two reinforcing plies, respectively lower 30 and upper 30 ', substantially parallel to the two faces 20, 21 of the slab 1. The reinforcement cage 3 normally consists of several sectors S1, S2, ... centered, respectively, in planes P1, P2 ... parallel to a longitudinal axis of the part 1, that is to say in the plane of FIG. 1, and each comprising a lower longitudinal reinforcement 31 and an upper longitudinal reinforcement 31 ′ which are connected together, in the plane P1, P2 of the sector S1, S2 by transverse reinforcements called stirrups, which are not not shown in FIGS. 1 and 2. In addition, the different sectors S1, S2, etc. of the cage are interconnected by transverse struts 32, 32 'perpendicular to the plane of FIG. 1. As is known, under the effect, for example, of a vertical load M applied to its upper face 20 ′, the part in concrete 1 can be divided into two parts located on either side of a neutral axis 10 respectively a compressed part 1 1 'between the neutral axis 10 and the face 21 on which the forces are applied and a stretched part 1 1 extending to the face 20 opposite the forces. All these provisions are conventional and do not require a detailed description. However, the reinforcement cage 3 differs from the cages usually produced by the fact that, according to an arrangement described in patent application FR-A-2 814 480 by the same inventor, at least the longitudinal reinforcements 31 located in the part te ndue 1 1 of the part and extending at a small coating distance from the lower face 20, consist of flat metal bars 4 of rectangular section, with a wide face 41 and a narrow face 42, each flat bar thus being consisting of a metal strip having a width I substantially greater than its thickness e. Preferably, the compressed frames 31 ′ also consist of flat bars but, for economy, one could also use conventional round bars. As indicated in the previous patent FR-A-2,814,480 by the same inventor, the cross section (I xe) of the strip 4 is calculated, in a conventional manner, as a function of the tensile forces to be supported, taking account of the stresses applied to the part. 1. Indeed, under the effect of the load M, the part 1 tends to bend slightly, each longitudinal reinforcement 31 of the lower ply 30 being subjected to a tensile force which tends to lengthen it. In the conventional reinforced concrete technique, notched reinforcing bars are generally used in order to improve the transfer connection between the reinforcement and the concrete, and a composite part is thus produced, the aim of which is usually to increase rigidity to avoid the appearance of damaging cracks. However, one cannot avoid a deformation even minimal of the part with an elongation of the tensile reinforcement as well as of the concrete which coats them, whose tensile strength is minimal. This therefore results in the appearance of cracks from a certain charge. In the invention, on the contrary, we do not seek, as usual, to secure the reinforcement with the concrete over its entire length, but, on the contrary, we house in the concrete 2, along each tensioned longitudinal reinforcement 31, two blocking zones B, B 'spaced on either side of the transverse median plane Q of the part, between which extends a central zone C in which the armature 31 is free to lengthen under the effect of the forces applied, sliding in relation to the concrete that surrounds it. Due to the fact that flat strips are used as longitudinal reinforcement, each blocking zone B, B ′ can be produced simply by deflecting the corresponding part of the tensioned reinforcement 31, which is gradually varied and continuously the orientation of its wide face with respect to the taut longitudinal face 20 of the part so that, in this zone, the strip 4 forming the frame 31 is supported in the concrete, mainly, by its wide side 41, in the opposite direction to the absorbed tensile force. In the embodiment shown in FIGS. 1 to 4, each blocking zone B, B ′ is produced by twisting the strip 4 over a certain length L1, with a progressive rotation of its wide face 41 around its longitudinal axis 40. In the case shown in FIG. 3, the strip is twisted over one complete revolution. If we consider a horizontal strip 4 subjected to a tensile force T directed to the right and having a part 43 twisted on a complete revolution on either side of a median plane P, the tensile force T applied on the strip 4 determines, as in a corkscrew, a support of this strip 4 in the concrete by its two faces 41, 41 '. Because the strip is flat and rests on the concrete on two sides wide, the concrete does not risk shearing, the compressive stress being weak. Moreover, the width I of the strip 4 can be determined as a function of the stresses applied, so that the compressive stress applied to the concrete remains below an admissible limit. The reinforcing strip 4 thus secured to the concrete by its two twisted parts 43, 43 'which constitute blocking zones B and B' can, however, freely extend in its central part 44 between the two twisted parts 43, 43 '. Admittedly, after concreting, there is an adhesion bond between the concrete and the reinforcement over the entire length of the latter. However, unlike the usual technique, this is avoided to improve this adhesion, for example by means of notches. In the invention, in fact, each strip 4 constituting a longitudinal reinforcement 31 is secured to the concrete only in the two blocking zones B, B 'which are spaced from one another and the tendency to elongation of the reinforcement under the effect of the applied voltage can be distributed evenly over the entire length L₂ of the central part 44 between the two twisted parts 43, 43 ′, this central part 44 being able to come off the concrete from a certain level of stress. Certainly, concrete 2 cannot be deformed in the same way as reinforcement and one cannot therefore avoid the appearance of cracks, but this risk of cracking is distributed uniformly over the entire length L₂ of the central part 44 and the more numerous cracks may have a width reduced enough not to be prejudicial. In this way, it is no longer necessary, as before, to increase the rigidity of the concrete part in order to reduce its deformation and, on the contrary, relatively flexible concrete parts can be produced. When the applied stresses remain low, the part behaves, as usual, like a part composite, concrete deforming in the same way as reinforcement. From a certain level of stress, the reinforcement remains solidified with the concrete only in its blocking parts 43, 43 ′ and its central part 44 can, on the contrary, peel off from the concrete which surrounds it and slide slightly relative to this one. The tension and, consequently, the tendency to elongation of the reinforcement, is therefore distributed in a substantially uniform manner over the entire length L₂ of the central part 44. This avoids a concentration of the tensile stress over a short length of the reinforcement and, consequently, the risk of rupture of the reinforcement at a crack is reduced, under the effect excessive demands. By way of example, the slabs produced according to the invention were subjected to bending tests with progressive increase in the applied load and it was found that a slab thus produced could, surprisingly, admit a very deflection. important before the slab breaks and with relatively small width cracks. It should also be noted that, as indicated in patent application FR-A-2 814 480, the use, as reinforcements, of flat strips makes it possible to reduce the overall thickness of the slab because the stirrups, which also consist of a flat strip, possibly corrugated, can be welded on the internal face of each strip, the external face of which must be separated from the facing face 20 of the slab, only by the minimum coating distance imposed by regulation. In addition, in a reinforced concrete part produced in a conventional manner, the stretched longitudinal bars must be bent in the shape of a butt at their ends in order to increase the transfer length between the reinforcement and the concrete. However, given the hardness of the steel used, the curvature that can be given to a bar is necessarily limited and the regulations require, moreover, to give the sticks a diameter of at least 10 times the diameter of the bar. For this reason alone, a concrete part must have a minimum thickness of twelve times the diameter of the tension bars to which it is necessary to add twice the minimum coating thickness. If, as in the invention, flat bars are used, these can also be provided at their ends with hooks 5, as shown in perspective in FIG. 5, but these hooks 5 can have a diameter internal D lower than in the case of one or more round bars, because the thickness e of a flat strip with rectangular section is less than the diameter of one or even several round bars of the same equivalent section. In addition, even if steels with a high elastic limit are used, the use of flat strips makes it possible to further reduce the diameter D of the curved part because it can be more easily bent around an axis 50 parallel to the plan of the wide face of the strip. In addition, as shown in Figure 20, it is possible to rotate the stick around a vertical axis in order to further reduce the thickness of the slab 1. For this reason, it is possible, with the same weight of reinforcement, to produce parts thinner than the parts produced in the conventional manner in reinforced concrete. Furthermore, each butt 5 also constitutes a blocking zone B1 in the concrete 2. Since, according to the invention, the longitudinal reinforcement is, in a way, attached to the concrete in the blocking zones 43, 5 while the central part 44 is free to lengthen, the stresses applied by the reinforcement to the concrete are greater than in the case of a conventional reinforcement where it is sought to make a connection over the entire length of the reinforcement . Of course, this results, in the blocking zones, in a more compressive force. important in concrete but, specifically, concrete has excellent compressive strength. In addition, there is nothing to fear as in the case of a round bar, a shearing effect of the concrete, because the width I of each flat bar can be determined according to the forces applied so that the co Compression stress of concrete does not exceed a given limit. Because the strip 4 is subjected to a significant tensile force T which is absorbed by the blocking zone B1 situated inside the butt 5, the latter may tend to unwind if the adhesion between the bar 4 is concrete is not enough. To avoid such an effect, it is possible to add to the stock 5 an auxiliary stock 51 turned in the opposite direction and having a slightly smaller diameter, in order to avoid this unwinding effect. It should be noted, moreover, that in the preferred embodiment shown in FIG. 1, each tensioned bar 31 consisting of a late strip 4 is oriented so that its wide face 41 is substantially parallel to the face stretched 20 of the piece. Such an arrangement increases the flexibility of the slab because the bar 4 thus oriented has only a low resistance to flexion and the bending of the part simply results in an elongation of the reinforcement. It is possible, however, if it is desired to increase the resistance to deflection, to use strips 4 oriented as shown in FIG. 7. In this case, in fact, each reinforcement strip 4 is twisted in two parts 43, 43 'spaced from each other, but only on a quarter turn so that, in the central part 44' and over the entire length of the latter, the wide side 41 of the strip 4 is located in a plane orthogonal to the stretched face 20 of the part. In this case, the blocking of the strip 4 in the concrete is carried out essentially at the level of the zones B1, B'1, inside the brackets 5, 5 ', formed at the ends of the strip 4, the blocking effect of the twisted parts 43, 43 ′ being reduced. On the other hand, each oriented reinforcement strip 4, in its central part 44 ', perpendicular to the tensioned face 20, brings by itself a certain resistance to bending which makes it possible to increase the rigidity of the part and to decrease the deflection resulting from the applied forces. As usual, the longitudinal bars 31, 31 'of the two plies, respectively lower 30 and upper 30' can be connected by stirrups which, as described in document FR-A-2 814 480, are advantageously made up of flat strips corrugated 13 secured to the longitudinal reinforcement, at the top of the corrugations, by welding or gluing. However, as shown in FIG. 9, for the implementation of the method according to the invention, it is preferable that the welds between the corrugated strips 13 and the strips 4 constituting the tensile reinforcements 31, be carried out only near the two ends of the part 1 so that the central part 44 of each strip 4 can extend freely. On the other hand, the stirrups can be welded or glued to the compressed bars 31 'at the top of each corrugation. For this, it is preferable that each compressed bar 31 'also consists of at least one flat strip, in order to produce a weld bead over the entire width of the corrugated strip 13. It should be noted that each welded or glued junction 34 between a bar 4 and the corresponding part of the stirrup 13 which forms an angle with this bar 4 constitutes, by wedge effect, a blocking zone B. It is therefore unnecessary, in this case, to provide the strip 4 with verified parts. On the other hand, it is advantageous to bend the ends in the form of sticks 5 in order to provide, as previously, blocking zones B1, B'1 at the two ends of the frame 31. However, the invention can be the subject of other variants, in particular by taking advantage of the support forces exerted in the concrete by the blocking zones of the longitudinal reinforcements, for example as shown diagrammatically in FIGS. 10 to 20 which illustrate various variants. For simplicity, the compressed frames 31 'have not been shown in these figures. In a first variant shown in FIG. 10, the lower ply 30 of the reinforcement cage 3 has two superposed levels. At the lowest level, closest to the taut lower face 20 of the part, each sector of the reinforcement cage has a longitudinal reinforcement 31 made up of a flat strip which extends over the entire length of part 1 and the ends 5, 5 'of which are curved in the shape of a stick as indicated above. However, these longitudinal bars 31 are associated with a second level of longitudinal bars offset upwards and comprising, in each sector of the cage, two bars 33, 34 each formed by a flat strip and placed side by side, each of these bars 33, 34 being provided with curved ends in the form of sticks 51, 51 ', 52, 52'. In addition, the two adjoining strips 33, 34 of the same sector are offset longitudinally with respect to each other so that the two sticks 51, 51 '(52, 52') formed at the ends of each strip 33 (34) are placed at different distances from the transverse median plane Q of the part 1, on either side of it. Thus, the external stock 51 of the bar 33 placed on the left in FIG. 10 is further from the median plane Q than the external stock 51 ′ of the same strip 31, placed on the right and the arrangement is reversed for the second longitudinal strip 34 On the other hand, the lengths of the longitudinal bars 33, 34 are determined so that the different sticks 5, 51, 52 placed on the same side of the transverse median plane Q are distributed over a certain length of the part 1 from its end 1 1. The part 1 is thus divided into several adjacent zones: - a central zone B3 comprised between the internal stock 51 'of the longitudinal reinforcement e 33 placed on the right of the transverse median plane Q and the internal stock 52 of the frame 34 placed to the left of this plane; - two lateral zones B2, B'2 placed respectively, to the left and to the right of the plane Q, the left zone B2 being between the external stock 51 of the strip 33 and the internal stock of the bar 34 and the right zone B '2 between the external stock 52' of the strip 34 and the internal stock 51 'of the band 33; - two extreme zones B 1 and B'1 included, respectively on the left and on the right, between the hooks 5, 5 'of the lower strip 31, and the external hooks 51, 52' of the upper strips 33, 34. When the part 1 is subjected to a stress which tends to cause it to bend downwards, the longitudinal reinforcements are subjected to tensile forces and are supported in the concrete by their ends in the form of sticks which are therefore stressed inwards. The longitudinal reinforcements 33, 34 which overlap in the central part of the part, are stretched in different directions and the central blocking zone B3 is therefore compressed by the tendency for the internal hooks 51 to approach one another. ', 52 of the two frames 33, 34. Likewise, the external brackets 51, 52' tend to approach the plane Q under the effect of the tensile forces applied to the bars 33, 34 and the lateral zones B2, B '2 are thus put in compression. For the same reasons, the end zones B1, B'1 are also placed in compression by the sticks 5, 5 'which oppose the tensile forces applied to the frame 31. Thus, the part 1 is put in compression practically over its entire length by the tendency towards the inward approach of the sticks of the different reinforcements and this compression effect is exerted over the entire thickness of the concrete limited by the sticks and not only, as usual, above the neutral axis 10. The risk of cracking of the part, even in the vicinity of the tensioned face 20 is therefore considerably reduced and loading tests carried out on a part thus produced have shown that such a part could withstand, before rupture, a very large and quite unusual deflection for a reinforced concrete part. In the embodiment which has just been described, the compression of the central zone B3 of the part between the internal hooks 52, 51 ′ of the two adjoining strips 33, 34 results from the overlapping of these which are stretched in opposite directions on either side of the transverse median plane Q. However, as shown in FIG. 11, the tensile reinforcement of the cage 3 can also consist of a simple stack of longitudinal strips of different lengths, respectively a first strip 35 extending over a length slightly shorter than that of the part and a second strip 36 extending over a length l₂ less than h, each strip being provided with ends in the form of hooks facing the interior of the part. In this case, too, the concrete is put in compression by the sticks 5, 5 ', 51, 51' which absorb the tensile forces applied to the strips 35, 36 due to the deflection of the part. In this regard, it may be advantageous to produce the metal strips having different mechanical characteristics so as to modulate the compression forces applied by the sticks as a function of the distribution of the forces applied to the part. It should be noted that the use of flat strips as reinforcing bars, fairly easily makes it possible to vary their modulus of elasticity because the flat strips can be produced by slitting sheets and one can find sheets on the market. of different characteristics while the possibilities of choice are more reduced for concrete reinforcing bars. Furthermore, the fact that, unlike the conventional technique, no attempt is made to secure the reinforcement with the concrete which surrounds it, it is possible to place the two superposed strips 31, 35 which are placed one against the other. then behave like a kind of leaf spring. Figures 12 and 13 show a variant of the embodiment of Figure 10 in which the two adjacent strips 33, 34 constitute two strands of a single strip forming a closed loop, the two opposite sticks 51 ', 52 being connected by a part 37 of the strip located at the upper level 30 ′ of the cage 3. Each longitudinal reinforcement thus consists of a single strip 33, 37, 34 surrounding a concrete core B3 which is put in compression by tightening the loop thus formed under the effect of the tensile forces applied in opposite directions on the two strands 33, 34 of the longitudinal reinforcement when the part 1 is subjected to a vertical load. It should be noted that in this case, the upper part 37 of each long itudinal reinforcement in the form of a loop can constitute part of the upper ply 30 ′ of the reinforcement cage 3. On the other hand in the case of FIG. 10 like that of FIG. 12, the opposite sticks 51 ′, 52 which tend to compress a concrete core B3, are not necessarily symmetrically spaced apart on either side of the transverse median plane Q of the part 1. Indeed, depending on the loading mode of the part, it is possible to determine certain parts of the part 1 in which the tensile forces induced in the concrete by the applied stresses are maximum and to lay out the reinforcements and their hooks so that the tensile forces resulting from the stresses are compensated at least partially by the compression, in the same areas, of a concrete core comprised between two stressed sticks towards each other by the tensile forces applied to the frame. In general, each of the figures described above shows a sector of the reinforcement cage centered in a vertical plane parallel to the longitudinal axis and the brackets formed on the reinforcements of two neighboring sectors are placed substantially at the same level so as to pass, in the aligned blocking zones of the sectors Si, S₂, S₃, transverse threads 32 which are also biased inward and therefore distribute over the concrete between two neighboring sectors, the compression forces applied by the sticks 5, 51, 52. These distribution threads can have a round or rectangular section , as shown in the figures. However, the use of flat bars makes it possible to facilitate the production of a weld bead between the longitudinal and transverse bars. In another embodiment shown diagrammatically in FIG. 14, each taut longitudinal reinforcement 6 of the cage 3 is made up of a series of consecutive strips 6a, 6b .... each having two curved ends in the form of hooks 5a, 5 'a, 5b, 5'b ... and these bars are arranged so that the pairs of adjacent sticks 5'a, 5b of two successive bands 6a, 6b are located substantially at the same level, slightly overlapping so as to surround a space E in which a bar 38 is passed which can constitute a transverse distribution streak. Each bar 38 passing through a space E placed in compression by the two opposite sticks 5'a, 5b constitutes a connecting key between the two consecutive strips 6a, 6b. Each longitudinal reinforcement 6 consisting of a series of bands 6a, 6b, 6c ... thus behaves like a chain whose links 6a, 6b, 6c ... are stretched under the effect of the loads applied to the part 1. However, the invention is not limited to the details of the various embodiments which have just been described, and could also be the subject of other variants, without departing from the protective framework of the invention. For example, each blocking zone could be obtained simply by means of a transverse bar passing through an orifice formed on the longitudinal reinforcing bar. Indeed, as shown in FIG. 17, the use of a flat strip 4 as a longitudinal reinforcing bar makes it possible to provide therein a median slot 45 extending over a certain length and limiting two lateral parts 46, 47 which can be separated from one another so as to open an orifice 45 ′ for the passage of a transverse bar 48. When the strip 4 is subjected to a tensile force, for example in the direction of the arrow indicated in Figure 16, it is supported on the crossbar 48 which, itself, is supported in the concrete, thereby achieving the blocking of the strip 4. In the case of Figure 16, the two parts 46, 47 of the strip are stretched while remaining in the plane of the latter, the transverse bar 48 thus being orthogonal to this plane. But it is also possible, as shown in FIG. 17, to separate the two parts 46, 47 perpendicularly to the plane S of the strip, to allow the passage of a transverse bar 48 which, in this case, is parallel to the plane of the strip. This bar could therefore constitute a transverse line 32 for distribution between several sectors of the reinforcement cage. In the case where the strip is twisted to constitute a blocking zone, this twisted part 43 could also be provided with a central slot making it possible to separate the two parts of the strip from one another in order to provide an opening. 45 ' passage of a distribution strand 32, as shown in Figure 18. Furthermore, as shown in Figure 19, one could also improve the locking effect of a stock 5 by providing the two parts of this orifice 45 'for the passage of a transverse bar 52 which, in addition, would prevent the stick from unwinding under the effect of the traction applied to the strip 4. It should also be noted , that the use of flat strips 4 to form the longitudinal reinforcing bars makes it possible to vary the orientation of the stock formed at the end of such a bar. In fact, in general, the flat strip 4 can be easily bent around an axis parallel to its plane. It would therefore be possible, as shown in FIG. 20, to twist the end of a strip 4 on a quarter turn so that the butt 5 rotates around a vertical axis 50. This would thus give the same blocking effect. by giving the stick a height limited to the width e of the strip 4. Such an arrangement could be advantageous for making particularly thin parts or, for example, for thinning the ends of a slab. In particular, the use of a flat strip 4 makes it possible, if necessary, to vary the orientation of the latter, as shown in FIG. 20, for example, in order to thin certain parts of the part. On the other hand, as already indicated, it is advantageous to also produce the compressed reinforcements 31 'in the form of flat strips, but, for economy, one could also use conventional bars. It should be noted, however, that the advantages brought by the use of flat bars largely compensate for a possible additional cost on the reinforcements. In this respect, it could even be advantageous to produce stainless steel bars due not only to the corrosion resistance which would reduce the coating thickness but also to greater ductility, which increases fatigue resistance and energy absorption capacity. Such advantages are particularly advantageous for the construction of engineering structures because they improve the resistance to differential settlement and, in certain cases, to earthquakes. Furthermore, to simplify the figures, these represent slabs or planar beams but it should be noted that the use of flat strips as rebar has many advantages for the production of curved or even left-hand parts. Indeed, a flat strip having a wide side parallel to the facing face of the part can easily follow the curved profile of the latter. In particular, it is thus possible to produce a flat reinforcement cage adapted to a curved part, such a cage can then naturally take the profile of the bottom of the mold when it is placed therein. The flat strips constituting the longitudinal and transverse reinforcements could even be curved in opposite directions so as to adapt to a left profile in the transverse direction, such as a regulated surface having non-parallel transverse generatrices. This is the case, for example, of the decking of a bridge inclined laterally by a variable angle from one end to the other and whose reinforcement is difficult to achieve by conventional methods. On the other hand, as it makes it possible to produce particularly flexible concrete parts capable of admitting a fairly large deflection, the invention is specially adapted to the production of crossing structures buried under an embankment and having a curved profile allowing them to be slightly deform under the applied load to bear by their sides on the side embankments. In addition, as indicated above, the blocking zones between which the concrete is put in compression can be placed at places, determined by calculation, in which the concrete is subjected to a tensile stress. maximum and where the risk of cracking is greatest. The invention therefore makes it possible, from a standard model, to adapt the reinforcement of each part to the foreseeable distribution of the stresses, taking into account the loads applied. For example, we know that we can distinguish, in a slab or beam loaded vertically uniformly, a central zone in which the tensile force applied to the underside is maximum, two lateral zones in which the slab is subjected to a shearing effect, and two support ends. However, as indicated above, the arrangement of the compression zones is not necessarily symmetrical with respect to the median plane of the part. Thanks to the invention it will be possible, without complication of the reinforcement, to adapt it, in each part of the part, to the main forces to be absorbed, by judiciously varying the orientation of the flat strips constituting the reinforcements so to make blocking zones in the most stretched parts, in order to compensate for this tension by a compression effect of the concrete. In addition, as indicated above, it is possible to orient the tensioned bands vertically as shown in FIG. 8, to increase the flexural strength, or to incline the bands as indicated in the figure. 20, in order to withstand the shearing forces, or to make horizontal sticks as shown in FIG. 20, in order to reduce the thickness of the part to the supports, these different variants can, moreover, be combined. In addition, as indicated above, the arrangement of the compression zones is not necessarily symmetrical with respect to the median plane of the part. The arrangements according to the invention therefore make it possible to vary the shape of the reinforcement cage so as to modulate the action of the reinforcements as a function of the stresses applied in service to the part.

Claims

1. Method for producing a concrete part (1) provided with a reinforcement cage (3) embedded in the concrete (2) during the casting of the latter, said part being subjected to a stress and comprising, under the effect of the latter, two parts situated on either side of a neutral axis, respectively a compressed part under pressure put under compression forces absorbed mainly by the concrete (2) and a stretched part subjected to tensile forces absorbed mainly by at least one tensile longitudinal reinforcement (31) of the reinforcement cage (3), extending in a longitudinal direction of application of the tensile forces, at a small coating distance from one face longitudinal tension (20) of the part (1) and having a cross section determined as a function of the forces induced by the stress, characterized in that at least each tensile longitudinal reinforcement (31) consists of at least one flat strip (4) to section rectangular, with a wide face (41) and a narrow face (41 '), and is shaped so as to provide, inside the part (1), at least two locking zones (B, B') in which part (43, 43 ') of the tensioned reinforcement (31) is supported in the concrete (2), in the direction opposite to the absorbed tensile force, and at least one sliding zone (C) between the blocking zones (B, B '), in which a corresponding part (44) of the tensioned reinforcement (31) is free to lengthen under the effect of the forces absorbed, with a uniform distribution of the tension over all the length of said part (44).

2. Method according to claim 1, characterized in that, from a certain level of stress, at least a part (44) of the tensioned armature (31) comprised between two locking zones (B, B ' ) is left free to peel off the surrounding concrete, sliding slightly in relation to it.

3. Method according to one of claims 1 and 2, characterized in that the width (I) and the thickness (e) of a longitudinal armature stretched in the form of a strip (4), are determined as a function of a maximum tensile force to be absorbed, on the one hand in order to obtain a cross section sufficient for the absorption of said maximum force while remaining in the elastic range and on the other hand, so that, in each blocking zone, the part of the concrete on which the strip (4) is supported by its wide face (41), is subjected to a compressive stress not exceeding an admissible limit.

4. Method according to one of the preceding claims for producing a concrete part, characterized in that each blocking zone (B) is produced by deflection of a corresponding part (43) of the tensioned reinforcement (31 ) in the form of a strip (4), with a gradual and continuous variation of the orientation of its wide face (41) relative to the taut longitudinal face (20) of the part (1).

5. Method according to claim 4, characterized in that each blocking zone (B) is produced by twisting a part (43) of the strip (4) over a certain length (L1), with a progressive rotation of its wide face (41) around its longitudinal axis (40), over at least a quarter of a turn.

6. Method according to claim 5, characterized in that the twisted part (43) of the strip (4) rotates a full turn around its longitudinal axis (40).

7. Method according to one of claims 1 to 4, characterized in that each blocking zone (B) is produced by curvature of one end of the flat strip (4) around a transverse axis (50) , so as to form an anchor stock (5) bearing on the concrete by a wide face (41).

8. Method according to claim 7, characterized in that each blocking zone (B) comprises two successive sticks, respectively a first stick (5) having a concavity turned in the direction of the tensile force applied to the strip ( 4) and extended by a second stick (50) turned in the opposite direction posed, in order to oppose a tendency for the first stock (15) to unwind under the effect of the tensile force applied to the strip (4).

9. Method according to one of the preceding claims, in which the reinforcement cage comprises two sheets of longitudinal reinforcement, respectively 31 in the stretched part and 31 ′ in the compressed part, characterized in that the compressed longitudinal reinforcements 31 'are also made up of flat bars.

10. Method according to one of the preceding claims, for producing a concrete part (1) provided with a reinforcement cage (3) comprising at least two longitudinal sectors (51, 52) connected together by struts of transverse distribution (32) and each comprising at least two longitudinal reinforcements, respectively a compressed reinforcement (31 ') and a tensioned reinforcement (31) in the form of a flat strip (4), said compressed (31') and tensioned reinforcement (31) being connected to each other by at least two connecting stirrups (33), characterized in that the connecting stirrups (33) are in the form of strips and are joined to the tensioned reinforcement (31) by at least one junction (34 ) produced near each longitudinal end of the frame (31) so as to form a blocking zone (B) at each junction (34), the central part (44) of the tensioned frame (31) being left free to lie down.

1 1. Method according to claim 10, characterized in that the connecting stirrups (33) are secured at their upper part, with the compressed reinforcements (31 '), at points distributed over the whole length of the latter.

12. Method according to one of the preceding claims, characterized in that, to form a blocking zone (B) between a tensioned longitudinal reinforcement (31) and the concrete (2), said reinforcement (31) in the form of a strip (4) is split axially over a certain length and the two strip parts (46, 47) thus formed are spaced from one another to form an opening (45 ') for transverse passage of at least one section (48) of rigid bar capable of bearing on the concrete (2) in the opposite direction to the tensile force applied to the strip (4) constituting the longitudinal reinforcement (31).

13. Method according to one of claims 7 and 8, characterized in that each longitudinal reinforcement comprises at least two contiguous bands (33, 34) extending iongitudinally, substantially in the extension of one another, and subjected to tensile forces in opposite directions, said strips (33, 34) having internal ends which overlap over a certain length (h) and terminate respectively, by two internal hooks (51 ', 52) facing the towards each other and urged towards each other under the effect of the opposite tensile forces applied to the two corresponding strips (33, 34), inducing the compression of a concrete core (B3) included between said internal sticks (51 ', 52), on said covering length (l ₂ ).

14. Method according to claim 13, characterized in that the concrete core (B3) between two opposite sticks (51 ', 52) is located in a part of the room (1) in which the concrete is subjected to tensile forces induced by the licitation soil applied to the part (1), said tensile forces being compensated at least partially by the compression of said core (B3) between the two opposite sticks (51 ', 52).

15. Method according to one of claims 13 and 14, characterized in that the two adjoining strips (33, 34) forming a longitudinal reinforcement constitute two strands of a single strip, forming a loop between two spaced apart levels (30, 30 '), so as to surround a concrete core (B3) put in compression by tightening said loop under the effect of the tensile forces applied in opposite directions on the two strands (33, 34) of the longitudinal reinforcement .

16. Reinforcement cage (2) included in a concrete part (1) subjected to a stress and comprising, under the effect of the latter, two parts situated on either side of a neutral axis, respectively a compressed part subjected to compression forces absorbed mainly by concrete (2) and a stretched part subjected to tensile forces absorbed mainly by at least one tensile longitudinal reinforcement (31) of said steel cage (3) which s extends, in a longitudinal direction of application of the tensile forces, to a small coating distance from a taut longitudinal face (20) of the part (1) and has a cross section determined as a function of the forces induced by stress, characterized in that each tensioned longitudinal reinforcement (31) consists of at least one flat strip (4) of rectangular section, with a wide face (41) and a narrow face (41 '), and that each flat strip (4) forming a tensioned frame (31) comprises at least two separated parts (43, 43 ') having a wide face (41) whose orientation relative to the tensioned longitudinal face (20) of the part (1) varies gradually, from so as to provide, inside the room (1), two blocking zones (B, B ') apart, in which the strip (4) is supported in the concrete (2) by at least one wide face (41 ) in the opposite direction to the tensile force to be absorbed and at least one sliding zone (C) included between said blocking zones (B, B ') separated, in which the strip (4) is free to lengthen , under the effect of the tensile force, over the entire length of its part (44) between said locking parts (43, 43 ') in modified orientation.

17. Reinforcement cage according to claim 16 characterized in that each blocking zone (B, B ') is constituted by a part (43, 43') of the flat strip (4) which is twisted on a certain length (L1), with a progressive rotation of its wide face (41) around its longitudinal axis (40), over at least a quarter of a turn.

18. Reinforcement cage according to claim 17, characterized in that the twisted part (43) of the strip (4) rotates a full turn around its longitudinal axis (40).

19. Reinforcement cage according to claim 16, characterized in that each blocking zone (B) is produced by curvature of one end of the flat strip (4) around a transverse axis (50), so as to form at least one anchoring stick (5) bearing on the concrete by a wide face (41).

20. Reinforcement cage according to claim 19, characterized in that each end of a flat strip (4) is curved so as to form two successive sticks, respectively a first stick (5) having a concavity turned in the direction of the tensile force applied to the strip (4) and extended by a second stick turned (51) in the opposite direction, in order to oppose a tendency for the first stick (15) to unwind under the effect of the 'tensile force applied to the strip (4).

21. Reinforcement cage according to one of claims 16 to 20, comprising in at least one sector, two longitudinal reinforcements, respectively stretched (31) and compressed (31 '), characterized in that the compressed reinforcements (31') are also made up of flat bands.

22. Method according to one of claims 20 and 21, characterized in that the longitudinal, respectively tensioned (31) and compressed (31 ') reinforcements are connected together in each sector of the cage at least two connecting stirrups ( 33), and that each connecting bracket (33) consists of a flat strip welded by one end to said reinforcements (31, 31 ') in the form of a flat strip (4), at least near the ends of the cage , at an angle with them, so that each welded junction between a tensioned frame (31) and the stirrup (33) constitutes, by wedge effect, a blocking zone (B).

23. Reinforcement cage according to claim 22, characterized in that the stirrups (33) for connection between the tensioned reinforcement (31, 4) and the compressed reinforcement (31 ') consist of a corrugated strip and that this is welded with the tensioned reinforcement (31, 4) only near the two ends of the latter, so as to constitute two blocking zones between which the central part (44) of the tensioned reinforcement is free from lengthen.

24. Reinforcement cage according to one of claims 16 to 23, characterized in that, to form a blocking zone (B) between a tensioned longitudinal reinforcement (31) and the concrete (2), said reinforcement (31) in the form of a strip (4) is split axially over a certain length and the two strip parts (46, 47) thus formed are separated from one another to form an opening (45 ") for transverse passage of at least one section (48) of rigid bar capable of bearing on the concrete (2) in the opposite direction to the tensile force applied to the strip (4) constituting the longitudinal reinforcement (31).

25. Reinforcement cage according to claim 24, characterized in that the two parts (46, 47) of the longitudinal strip (4) formed on either side of an axial slot (45) are spaced apart while remaining in the plane of the strip, for the passage of a section (48) of the locking bar, orthogonally to said plane.

26. Reinforcement cage according to claim 24, characterized in that the two parts (46, 47) of the longitudinal reinforcement (31) formed on either side of an axial slot (45) are spaced apart. one of the other perpendicular to the plane of the strip (4), for the passage, parallel to said plane, of a blocking bar forming a distribution strand (32).

27. Reinforcement cage according to one of claims 19 to 26, characterized in that each tensile longitudinal reinforcement comprises a plurality of flat bars in the form of bands (4), arranged on at least two superposed levels, respectively a first level, closest to a tensioned longitudinal face (20) of the part (1), in which is disposed at least one flat tensioned bar (35) extending substantially over the entire length of the part (1), with two ends in the form of hooks (5, 5 ') facing inwards and at least one second level in which at least one flat bar (36) is arranged ) shorter than the strip (35) of the lower level, with two ends in the form of sticks (51, 51 '), turned inwards and spaced apart longitudinally, on either side of a transverse median plane, so as to limit an area B3 compressed between said sticks 51 and 51 'and at least two lateral areas B2, B'2 compressed by the sticks 5, 5' of the strip 35 of the lower level.

28. Reinforcement cage according to one of claims 16 to 26, characterized in that each longitudinal reinforcement consists of a stack of at least two flat bars applied one on the other along one side wide and together having a total cross section determined as a function of the stresses applied, said stack having the same tensile strength as a single bar of the same section, and resistant to bending in the manner of a leaf spring.

29. Reinforcement cage according to one of claims 27, 28, characterized in that the superimposed flat bars (35, 36) have different mechanical characteristics.

30. Reinforcement cage according to one of claims 16 to 29, characterized in that at least the tensioned longitudinal reinforcements (31) are made of stainless steel.

31. Reinforcement cage according to claim 19, characterized in that each longitudinal reinforcement consists of a series of consecutive bands (6a, 6b ...) each having two ends co-curved in the shape of a butt (5a, 5'a)

(5b, 5'b), the adjacent sticks of two consecutive bands (6a, 6b) being placed one next to the other and being partially overlapping so as to limit a space E for passage, in the transverse direction, of at least one rigid bar section (58) forming a connecting key between said consecutive strips (6a, 6b), said longitudinal reinforcement behaving as a tensioned chain made up of a series of links each formed by a band (6a, 6b ...) and connected two by two by a pair of adjacent hooks (5'a, 5b) (5'b, 5c) keyed between them.

32. Reinforcement cage according to one of claims 19 to 31, comprising at least two sectors connected by distribution beams (32), characterized in that the brackets (5, 51, 52, 6) of the reinforcements of two neighboring sectors are placed substantially at the same level inside the part (1) and that distribution threads (32) pass through said hooks (5, 51, 52, 6) so as to compress the assembly concrete (2) placed at this level.

33. Method for producing a curved part obtained by pouring concrete into a mold or formwork with a curved bottom, after the installation in the mold of a reinforcement cage according to one of claims 16 to 32, characterized by the fact that the reinforcement cage is made flat and has, due to the use of flat strips, sufficient flexibility to take, by its own weight, the curved shape of the bottom of the mold after the installation of the cage (3) in this one.

34. Concrete part (1) produced by the process according to one of claims 1 to 15.

35. Reinforced concrete part (1) comprising a reinforcement cage according to one of claims 16 to 32.