GRIP REINFORCING BAR AND METHOD OF PRODUCING SAME

Abstract

A reinforcing bar with improved adherence for reinforced concrete component, consists of a metal profile section (1) in the form of a flattened strip of rectangular cross section with two opposite wide faces (10, 10′) on which longitudinally separated projecting anchoring portions are formed.

Description

The invention has for object a reinforcing bar with improved adherence for a reinforced concrete component, in particular a beam, a slab or a column, and also covers the reinforcing cages using such bars and the methods of producing same.

It is known that the principle of the reinforced concrete consists in combining the quality of compression strength of concrete with that of tensile strength of metal reinforcements. A reinforced concrete construction element indeed performs as a composite component in which the reinforcing bars and the concrete, which have close expansion coefficients, are deformed in the same way under the applied stresses, at least up to a limit load.

In the case, for example, of a reinforced concrete component subjected to flexion forces, it is usually considered, for the calculation of the reinforcements, that this component includes, on either side of a neutral axis, two portions subjected to respectively compression forces supported by the concrete and tensile forces supported essentially by the longitudinal reinforcing bars. It is hence determined by calculation the cross-section that it is advisable to give to each bar in tension to resist to the forces applied, taking into account the distance between the facing of the compressed portion and the centre of gravity of the bar.

Generally, the whole reinforcement of a reinforced concrete element has the form of a cage consisting in two webs of longitudinal bars, respectively active and passive, connected to each other by transverse stirrups that allow the handling and positioning of the whole cage and that, on the other hand, resist to the shearing stresses.

As the external forces that act upon a reinforced concrete element are generally applied to the concrete, it is the adherence link at the level of the steel-concrete interface, i.e. the concrete sheath surrounding each bar, which allows placing under load the reinforcements, necessary for normal functioning of the structure. The transfer capacity of the loads between the concrete and the reinforcing bar, thus, depends upon the quality of this adherence link.

It is known that, when the tensile force applied in the portion under tension of a reinforced concrete component increases, it is firstly observed an almost linear phase during which the tensile force is transferred in each bar by the steel-concrete interface that progressively degrades up to appearance, in the concrete, of microcracks caused by small displacements between the bar and the concrete that surrounds the latter. If the tensile forces continue to increase, this first almost-linear phase is followed by a non-linear phase during which the microcracks localize into macrocracks, less numerous and larger, which form a “fishbone” network, with a loss of adherence and stiffness of the interface.

These macrocracks allow the penetration of humidity and aggressive agents in contact with the reinforcement. As they firstly appear on the side where the coating is less important, it is necessary to leave a minimal distance of coating between a reinforcing bar and the corresponding facing of the component to avoid corrosion of the bar and bursting of the concrete. This distance of coating imposed by the Regulation may be, for example, of 30 mm.

A long time ago, it has already been proposed, in the document FR-A-765,943, to improve the strength of a reinforced concrete beam by replacing the round bars of circular cross-section commonly used as reinforcements by flat bars in the form of rectangular cross-section metal strips, while keeping this imposed minimal distance.

Indeed, in such an arrangement, the width and the thickness of each flat bar may be chosen so as to have the cross-section usually determined by calculation to resist to the forces applied. Such flat reinforcing bars are hence, with a same cross-section, equivalent to the round bars usually used but, for a same distance of coating, the axis of the flat bar is more distant from the centre of gravity of the beam than that of the round bar of same cross-section and the strength of the beam may then be improved.

Likewise, for a same strength, the use of flat reinforcing bars allows to reduce the whole thickness of the reinforcing cage and, hence, of the concrete component, while keeping the same lever arm between the bars in tension and the opposite facing.

However, to prevent the concrete from sliding with respect to the bar, it has been provided, in the document FR-A-765,943, to form, on one face of the bar, a series of recesses made by rolling and each corresponding to a projecting boss on the other face. These bosses and cavities formed on the two wide faces, respectively, of the bar have a significant height, of the same order as the thickness of the strip, so as to realize a perfect link between the bar and the concrete, while preventing any sliding one over the other.

However, to allow the formation of such bosses, these latter have to be spaced apart from each other by a distance of the same order as the width of the flat bar and hence exert on the coating concrete punctual stop forces, separated from each other, which, beyond a certain level of tension, may cause the appearance of more open macrocracks, with a risk of bursting of the concrete.

Such an arrangement hence allows no progressivity in the transmission of the forces between the bar and the concrete sheath, which remain perfectly cohesive up to a limit tensile force, beyond which the bar risk to brutally come away from the concrete.

Besides, the making of a series of bosses on one face and of cavities on the other face provides the flat bar, in the central portion thereof, with a corrugated profile including, in the longitudinal direction, a succession of thickness narrowings that constitute weakness points harmful to the tensile strength and liable to cause a rupture of the bar for a force that is much lower than the theoretically applicable limit force. Moreover, the arrangements provided in this patent, published in 1934, have never been applied in practice.

The invention has for object to solve such problems and to therefore avoid the drawbacks of this prior technique while however benefiting from all the advantages offered by the use of flat bars with improved adherence as reinforcements for reinforced concrete.

The present invention hence generally relates to the production of a reinforcing bar with improved adherence for a reinforcing concrete component, consisting in a metal section extending in a longitudinal direction, having the form of a flattened strip of substantially rectangular cross-section, with two opposite wide faces extending between two lateral sides and including a plurality of projecting anchoring portions which are longitudinally separated from each other and bearing on the concrete in a direction opposite to a tensile force applied to the bar.

According to the invention, each of the two wide faces of the strip is provided with a series of anchoring portions in the form of elongated locks separated from each other by hollow portions in the form of grooves and extending transversally over the whole width of the strip, substantially up to the lateral sides thereof, and each of said elongated locks extends in projection over a small height, not exceeding a quarter of the thickness of the strip, and has, in cross-section, a substantially trapezoidal profile, with an embossed face of small width with respect to its length and two inclined flanks for connection with the elongated bottom of the adjacent grooves that constitute, for each lock, two inclined faces that bear, each in one direction, on the coating concrete, said inclined faces each having an elongated shape extending between the two sides of the strip, so as to distribute the bearing forces over all the width thereof.

Thanks to such arrangements, it becomes possible to ensure an excellent distribution of the bearing forces over the whole rectangular perimeter of the bar, without risk of brittleness of the latter and with the maintaining, over its whole length, of a cross-section as constant as possible, to resist in the best conditions to the tensile forces applied.

In a particularly advantageous manner, the elongated locks formed on each face of the strip are spaced apart from each other by a constant pitch that do not exceed half the width of the strip and, preferably, comprised between one and three times the thickness of the strip.

Preferably, the locks formed on the two wide faces, respectively, of the strip, are parallel to each other, and the locks formed on one face are longitudinally shifted by a half pitch with respect to the locks of the opposite face, in such a manner that the bottom of each groove of a first face is substantially opposite to a lock of the second face.

In a preferential embodiment, the elongated locks formed on the two faces, respectively, of the strip, extend transversally in directions inclined by a non-zero angle with respect to the longitudinal axis of the strip.

According to another preferential characteristic, the elongated locks formed on the two faces, respectively, of the strip, are symmetrically inclined, in opposite directions, with respect to the longitudinal axis.

Advantageously, on each face of the strip, the angle 13 of inclination of the locks with respect to the axis is comprised between 35° and 75°.

In a particular embodiment, the anchoring locks formed on each wide face of the strip have the shape of imbricated V-shaped chevrons, with two rectilinear portions symmetrically inclined on either side of the longitudinal axis of the strip.

In another embodiment, the anchoring locks have a corrugated shape, symmetrical with respect to the longitudinal axis of the strip.

According to another preferential characteristic, the locks formed on each wide face of the strip extend up to a small distance from each of the lateral edges of the latter, so as to leave, along each of said edges, a smooth flat of small width, of the order of 0.2 e, e being the average thickness of the strip.

Advantageously, on each of the two wide faces of the strip, the embossed faces of the elongated locks and the bottoms of the grooves are located in two parallel planes, respectively, extending on either side of a mean plane in which are placed the two flats extending along the two lateral edges, respectively, of the strip.

Preferably, the two planes in which are located the embossed faces of the locks and the bottoms of the grooves, respectively, are spaced apart by a height h that can be from 0.08 e to 0.24 e, e being the average thickness of the strip.

Besides, the connecting flanks between the embossed faces of the locks and the bottom of the corresponding grooves, which constitute, for each lock, two elongated faces that bear, each in one direction, on the concrete, are inclined by an angle of at least 45°, with respect to the embossed face of said lock.

The invention also covers a reinforcing cage for a reinforced concrete component, including two webs of reinforcing bars connected by stirrups and extending at a small distance of coating from two spaced-apart facings, respectively, of the component.

According to the invention, at least one of the two webs of the cage consists in such flat bars with improved adherence and the stirrups are also formed of flat metal strips, alternately welded on the embossed faces of the elongated anchoring locks formed on each of the wide faces of said flat bars.

But the invention also covers a method of producing such reinforcing bars with improved adherence. According to the invention, it is firstly made a metal bar in the form of a flattened strip with two opposite wide faces and centred on a longitudinal axis, then this flattened strip is subjected to a rolling pass between two cylinders rotating about axes parallel to each other and orthogonal to the longitudinal axis of the strip, said cylinders being provided, over their periphery, with spaced-apart recesses for the formation, by rolling, of elongated locks separated by parallel grooves, on each of the two wide faces of the strip.

These two rolling cylinders are each provided, over their periphery, with an alternation of recesses and teeth intended to form the locks and the grooves, respectively, on each of the wide faces of the strip and extending between two smooth portions of small width, for the formation of two flats along the two lateral sides of the strip.

Normally, these lock formation recesses are regularly spaced apart along the periphery of each of the rolling cylinders, so as to form locks spaced apart by a constant pitch. But, in some cases, the recesses may be distributed along the periphery of each of the rolling cylinders in such a way to vary periodically the spacing between the locks made on each wide face of the strip.

But the invention will be better understood by the following detailed description of some preferential embodiments, given by way of simple examples and shown in the appended drawings.

FIG. 1 schematically shows, in perspective view, a reinforcing bar according to the invention, provided with locks orthogonal to its longitudinal axis.

FIG. 2 schematically shows, in two embodiments, the effect of a tensile force applied to such a bar.

FIG. 3 is a partial perspective view of a reinforcing bar provided with locks inclined with respect to its longitudinal axis.

FIG. 4 is a schematic sectional view of such a bar according to a plane orthogonal to its longitudinal axis.

FIG. 5 is a top view of a bar provided, on its two faces, with locks inclined in opposite directions.

FIG. 6 is a sectional view of a bar of FIG. 5 according to a plane orthogonal to its longitudinal axis.

FIG. 7 is a detail sectional view of this bar according to a plane parallel to its longitudinal axis.

FIG. 8 is a detail sectional view of a reinforcing cage using longitudinal bars according to the invention.

FIG. 9 shows, in top view, two alternative embodiments of a reinforcing bar according to the invention.

FIG. 10 schematically shows the steps of production of a reinforcing bar.

FIG. 11 is a detail sectional view of rolling cylinders according to the line I-I of FIG. 10.

FIG. 12 is a cross-sectional view of another embodiment of a flattened bar.

In FIG. 1, which is a half detail, longitudinal sectional view, it has been shown, in a perspective view, a first embodiment of a reinforcing bar according to the invention, consisting in a flat metal strip 1 centred on a longitudinal axis x′ x and having a rectangular cross-section with two opposite, respectively upper 10 and lower 10′, wide faces extending between two lateral sides 11.

Each of the two wide faces 10, 10′ of the strip 1 is provided with a series of regularly spaced apart, elongated projecting portions 2, 2′, separated from each other by hollow portions in the form of grooves 3, 3′.

Each projecting portion 2, 2′ hence forms an elongated lock that has, in cross-section with respect to its direction, a substantially trapezoidal profile with an embossed face 21 and two inclined flanks 22, 23 of connection with the rectangular bottom 31 of two grooves 32, 33 extending respectively on either side of the lock 2. These locks 2 extend transversally over almost the whole width I of the strip 1, substantially up to the lateral sides 11 of the latter and are relatively close to each other, the pitch c of spacing between two successive locks being at most equal to half the width I of the strip.

For a reinforcing bar of reinforced concrete, the ratio of the nominal width to the nominal thickness is normally comprised between 4.5 and 6. Preferably, the spacing pitch of the locks will hence be comprised between one and three times the thickness of the strip.

The so close-together locks 2, as well as the grooves 3 that border them, have hence an elongated rectangular shape, with an embossed face 21 of very small width with respect to its length.

Such a reduced spacing pitch between the locks allows to form three or four parallel locks over a strip length corresponding to the width thereof, whereas, in the prior arrangement of the document FR-A-765,943, the locks were spaced apart by a distance of the order of the strip width.

This multiplication of the number of locks hence allows, for equivalent bearing forces, to considerably reduce the height of the locks and, hence, the risk of fracturing of the coating concrete.

In practice, the height of the locks, i.e. the space between the level of the embossed faces 21 and that of the bottom 31 of the grooves 3, shall not exceed the quarter of the thickness e of the strip and will preferably be comprised between 0.08 e and 0.25 e.

Moreover, as the locks have a length substantially equal to the width of the strip, the connection flanks 22, 23 have also the shape of elongated rectangles, of very small width with respect to the length thereof.

The so-constituted bearing faces hence allow, on the one hand, to reduce the individual stop forces applied by each lock on the coating concrete and, on the other hand, to distribute these forces over the whole width of the strip.

In the embodiment illustrated in FIGS. 1 to 3, the elongated locks 2 are directed perpendicular to the longitudinal axis x′ x of the strip 1 and are regularly spaced apart by the pitch c, whereas the locks 2′ of the opposite face 10′ are longitudinally shifted by a half-pitch. The bottom 31′ of each groove 3′ of the lower face 10′ is hence located opposite to the embossed face 21 of a lock 2 of the upper face 10.

As indicated above, in the prior technique described in the document FR-A-765,943, it is made, in the central portion of one of the wide faces of the flat reinforcing bar, a series of cavities each determining the formation of a projecting boss on the other face. The cavities and the bosses having a height of the same order than the thickness of the bar, it results therefrom a corrugated profile with a succession of points of lesser strength.

On the other hand, in the invention, due to the fact that the locks 2′2′ are formed on the two faces 10, 10′ of the strip and that they have a very small height, the thickness of the active portion resisting to the tensile forces remains of the same order than the nominal thickness of the reinforcing bar and is almost kept over the whole length thereof, in the direction of application of the tensile force.

It is to be noted that, for more clarity, it has been given a maximal height to the locks represented in FIGS. 2 and 3.

As schematically shown in FIG. 2, when the grooved flat bar 1 embedded in the concrete is subjected to a tensile force T, the front inclined flank 22 of each lock 2 exerts on the concrete, in the longitudinal tensile direction, bearing forces F, distributed over the whole length of the inclined bearing face 22 and substantially perpendicular to the latter. Hence, if the flanks 22 are inclined by an angle α with respect to the plane of the upper face 10 of the strip, the bearing forces F are substantially inclined by the complementary angle α1.

It is to be noted that, as shown in the two schemes of FIG. 2, it is possible to vary the inclination angle α of the flanks 22, 23 with respect to the mean plane of the strip and, hence, the complementary inclination angle α1, α′1 of the bearing forces F, F′. However, the inclination angle α1, α′1 must not exceed 45° so as to avoid a risk of cleaving of the concrete by wedge effect.

Taking into account that the locks 2 are rectilinear and extend almost over the whole width I of the strip 1, each of said locks 2 exerts on the concrete, through its front face 22, bearing forces directed following a mean plane P inclined by the angle α1 with respect to the wide face 10 of the bar 1.

Likewise, each of the locks 2′ of the lower face 10′ of the strip 1 exerts on the concrete, through its front face 22′, bearing forces that are directed following a mean plane P′ inclined by an angle α′1 with respect to the lower face 10′ of the strip 1.

Hence, when a reinforcing bar in the form of a strip 1 is subjected to a tensile force T, all the parallel grooves 2, 2′ formed on the two wide faces 10, 10′, respectively, of this strip 1, exert on the coating concrete bearing forces substantially directed following two series of parallel planes P, P′ symmetrically inclined with respect to the two faces 10, 10′ of the strip 1.

Moreover, due to the trapezoidal profile of the locks 2 and the grooves 3, the inclined flanks 22, 22′ of the grooves 2, 2′ that extend over almost the whole width of the strip, have a substantially constant height, such that the forces applied by each by each lock on the concrete, when the bar is subjected to a tension, are uniformly distributed over the whole length of the lock, i.e. over the whole width of the bar 1.

Furthermore, as each bar has, in cross-section with respect to its axis, a rectangular profile of small thickness with respect to its width, the projection of the locks in the longitudinal direction of the tensile force, which corresponds to the stress transmitted by the bar to the concrete, may extend over at least 75% of the perimeter of the bar, calculated from the nominal cross-section of the latter. It results therefrom a lesser risk of shearing of the junction.

Besides, the longitudinal spacing of the mean planes P, P′ of the bearing forces on the concrete corresponds, on each face 10, 10′ of the strip, to the reduced pitch c of spacing of the elongated locks 2, 2′, which, as indicated above, is smaller than half the width of the strip 1. Therefore, the stop stresses that are exerted along two directions symmetrically inclined on either sides of the mean plane of the strip, along two series of parallel planes P, P′, not much separated from each other, are hence distributed in a substantially uniform way over the whole width and the whole length of the bar 1.

This uniform distribution of the stop stresses in all the concrete sheath surrounding the bar favours, from a limit tensile force, the progressive formation of a set of microcracks, the opening of which remains acceptable and, in case of increase of the tensile force, the number of microcracks increases, which allows to avoid their localization into macrocracks of harmful opening.

This uniformization, along a reinforcing bar in tension, of the distribution of the bearing forces on the concrete hence allows to also distribute, over a greater length, the tensioning of the concrete, and hence the risk of cracking. Therefore, when the tensile force transmitted to the concrete exceeds the strength of the latter, this force may be distributed over a certain length of the bar, by forming progressively multiple cracks of small width, allowing to avoid an excessive widening of a localized crack.

Besides, as mentioned above, the locks 2′ of the lower face 10′ of the bar are shifted by a half-pitch with respect to the locks 2 of the upper face 10 and are hence placed substantially opposite to the grooves 3 between these latter. It results therefrom that the cross-section of metal on which is applied the tensile force T remains substantially constant over the whole length of the strip, which hence participates in totality to the strength whereas the resistance of a conventional circular cross-section reinforcing bar has to be calculated only as a function of its nominal diameter, without taking into account the volume of metal corresponding to the anchoring portions.

It is to be further noted that the production of elongated locks and grooves extending over the whole width of the strip allows to keep all the advantages offered by the use of a flat strip as a reinforcing bar.

In particular, due to the fact that the perimeter of a rectangular cross-section flat bar corresponds to about 1.5 times the circumference of a round bar of same cross-section, the use, as reinforcements, of flat bars provided, according to the invention, with elongated locks that are close to each other, allows to increase the adherence link on the embossed faces 21 of the locks 2 and the bottoms 31 of the grooves 3.

Moreover, it is known that, in a round bar provided with projecting circular locks, the sudden variations of cross-section of the material may lead to a certain brittleness at bending of the bar. On the other hand, the use of reinforcing bars according to the invention, including a great number of nearly spaced apart and small height locks, allows to reduce this risk of brittleness at bending of the bar, for example to form anchoring hooks at the ends or to adapt the profile of the bar to the shape of the component or to the distribution of stresses in the concrete component.

However, as the locks 2 and the grooves 3 extend almost over the whole width I of the strip, their ends risk to form sharp angles harmful for the handling of the bar and able to facilitate a cracking of the concrete at the tensioning of the bar.

That is why, as shown in the drawings, the locks 2 and the grooves 3 extend transversally over only a width that is a little smaller than that of the flat strip 1, so as to leave, along each of the two lateral edges of the latter, a smooth flat 12 having a small width, for example of the order of 0.2 e, e being the thickness of the strip at each of its sides 11.

In the embodiment of FIGS. 1 and 2, the elongated locks 2, 2′, formed on the two faces 10, 10′, respectively, of the strip, and separated from each other by the grooves 3, 3′, are directed perpendicular to the longitudinal axis x′, x of the bar. It is however more advantageous, in another embodiment of the invention, shown in perspective view in FIG. 3, that the elongated locks 2, 2′ of the two faces 10, 10′ of the strip are inclined by a certain angle 13 with respect to the longitudinal axis x′, x of the strip 1.

It is hence the same for the planes P, P′ in which are located, as above, the bearing forces exerted by all the locks 2, 2′ on the coating concrete.

That way, as shown in FIGS. 3 and 4, each of the two faces 10, 10′ of the bar 1 has, in a direction perpendicular to the longitudinal tensile force T, an alternation of projecting portions and of recessed portions corresponding to several inclined locks 2a, 2b, 2c, whose bearing faces 22 cross the cross-sectional plane. It results therefrom a better uniformization, along the longitudinal axis x′ x, of the bearing forces exerted on the concrete by the two grooved faces 10, 10′ of the bar 1, when the latter is subjected to a longitudinal tensile force.

The inclination angle β of the locks may be the same on the two faces 10, 10′, which are then provided with parallel locks 2, 2′, which, as above, may be shifted by a half-pitch, so that each lock on a face corresponds to a groove on the other face.

However, in another embodiment even more advantageous and shown in top view in FIG. 5, the two series of locks formed on the two wide faces 10, 10′, respectively, of the strip are symmetrically inclined by angle β on the upper face 10 and by the opposite angle 13′ on the lower face 10′. Therefore, the possible effects of lateral shift are compensated and the strip 1 remains better centred on the longitudinal axis x′, x of application of the tensile force T. Moreover, as each of the two faces 10, 10′ includes, in cross-section, an alternation of projecting portions 2 and recessed portions 2′, shifted by a small height with respect to the thickness of the strip, the whole cross-section of the latter remains substantially constant over the whole length thereof.

As above, the inclined locks 2, 2′ and the grooves 3, 3′ are stopped at a small distance from the lateral edges of the strip 1, so as to form, along each of the sides and on each face 10, 10′ of the strip 1, a smooth flat 12, 12′ having a small width, of the order of 0.2 e.

Besides, as shown in FIG. 4, on each of the wide faces 10, 10′, the embossed faces 21, 21′ of the locks 2, 2′ and the bottoms 31, 31′ of the grooves 3, 3′ are located in parallel planes, respectively, extending on either side of a mean plane of the strip and in which are placed the smooth flats 12, 12′.

The invention also covers an original method of producing such corrugated flat bars from a commercial wire rod or, more generally, of a circular cross-section smooth bar.

In this method, as schematically shown in FIG. 10, such a round bar 4 may be firstly subjected to a first rolling pass between two cylinders 41 rotating about horizontal axes 40, so to provide it with the desired thickness e, then to a second rolling pass between two cylinders 42 rotating about vertical axes, to adjust the width I thereof. It is hence obtained a rectangular cross-section flat strip 1, which is then subjected to a third rolling pass between two opposite rolls 5, 5′ rotating about horizontal axes 50, 50′ parallel to the wide faces 10, 10′ and each provided on its periphery with an alternation of recesses 51, 51′ intended to form the locks 2, 2′ and with teeth 52, 52′ intended to form the grooves 3, 3′, as schematically shown in FIG. 11, which is a detail sectional view according to a plane I,I passing by the axes 50, 50′ of the rolls 5, 5′.

Preferably, the recesses 51 and the teeth 52 formed on the periphery of each of the rolls 5, 5′ do not extend over the whole width of these latter, so as to leave, at their ends, smooth portions 53, 53′ for the formation of the flats 12, 12′ along the lateral edges of each of the two faces 10, 10′ of the strip 1.

Moreover, to facilitate the putting in place of the concrete in the grooves 3 and to avoid sharp angles at the ends of the locks 2, the recesses 51 and the teeth 52 formed at the periphery of the rolling cylinders 5, 5′ have a trapezoidal section, both in lengthwise and crosswise, so that, on each of the faces 10, 10′ of the strip 1, the locks 2 are connected, at each end, to the corresponding flat 12, by an inclined face 24, just as the grooves 3 that are terminated, at each end, by an inclined face 34 (FIG. 3).

Such corrugated reinforcing bars provided, on their wide faces, with parallel locks and grooves with a trapezoidal cross-profile, allow to keep all the advantages offered by the use of flat reinforcing bars for the making of a reinforcing cage, for example as described in the document FR-A-2 814 480.

FIG. 8, for example, is a schematic, longitudinal sectional, detail view of a concrete component 6 such as a beam or a slab subjected to flexion forces, having two parallel facings, respectively a face 61 in tension under the effect of the forces applied and a compressed face 62, and wherein is embedded a reinforcing cage 7 including two webs of longitudinal bars 71, 72 crossing transverse bars 71′, 72′, which extend at a small distance of coating of the facings 61, 62, respectively, and are connected to stirrups 73. As described in the document FR-A-2 814 480, the longitudinal and transverse bars consist advantageously in flat strips, as well as transverse stirrups that may be consisted of a corrugated strip alternately welded, by its tops, to the two webs of bars, or of a series of flat tabs shaped so as to form, at their ends, two planar faces for the welding to the bars of the two webs, respectively.

According to the invention, the longitudinal bars 71 extending along the face 61 in tension consist in corrugated flat strips of the above-described type, comprising, on each wide face, a series of parallel anchoring locks separated by grooves. However, the transverse flat reinforcing bars 71′ as well as the stirrups in the form of corrugated strips 73 can also be easily welded to the planar embossed faces 21 of the elongated locks 2, due to the trapezoidal profile and the small width of these latter.

Moreover, the arrangement of FIGS. 3 and 4, including, on each wide face, a series of parallel locks, inclined by a same angle with respect to the longitudinal axis x′ x of the bar 1, allows to apply and weld each transverse bar 71′ to the embossed faces 21 of several neighbour locks, and it is the same for the stirrups 73, at the top of the corrugations.

Of course, the invention is not limited to the embodiments described above by way of simple examples but also covers all the variants using equivalent means and remaining in the same protective framework.

In particular, if it is advantageous that the locks 2, 2′ are spaced apart by a constant pitch c, along each face 10, 10′ of a bar 1, it would be possible, in certain cases, to adjust the distribution of the recesses 51 and the teeth 52 over the periphery of the rolling cylinders 5, 5′, to vary periodically the spacing of the anchoring locks. For example, it could be made, on each face 10, 10′ of the strip 1, an alternation of blocking areas provided with locks and of areas left smooth, as described in detail in the document WO 2010/067023 A1, so as to distribute the risk of cracking over le length of the component, by reducing the opening of the cracks under a certain load.

On the other hand, the elongated locks 2, 2′ formed on the two faces of the strip, do not necessarily extend in straight line between the two sides 11a, 11b of the strip 1.

FIG. 9, for example, shows two variants of the invention. The upper portion shows, in top view, a flat bar 1 provided, on its upper face 10, with anchoring locks 2 in the form of imbricated chevrons, centred on the longitudinal axis x′, x of the strip. The opposite face 10′ is also provided with imbricated-chevron locks that may be rotated in the same direction or in the opposite direction, so as to better resist to alternated tensile forces.

The lower portion of FIG. 9 shows another variant in which the locks 2a, 2b are arranged in two lines that extend only over half the width of the strip 1 and are alternately inclined toward the right or toward the left of the longitudinal axis x′, x.

Moreover, it is more advantageous that the flanks of the locks are rectilinear, so that the bearing forces are exerted following a succession of parallel planes, but corrugated locks could also be made.

Furthermore, if it is preferable to subject the round bar to two successive rolling passes, as shown in FIG. 10, to adjust precisely the thickness and the width of the flat strip, it is however not necessary that the latter has a strictly rectangular cross-section. Indeed, in a simpler embodiment, it would be possible to subject the round bar to a single rolling pass to obtain an oblong cross-section strip, as shown in FIG. 12, wherein such a strip can also be provided with elongated locks on each of its wide faces.

Finally, the grooves of the wide faces of the strip could be eliminated at certain places and over a small length, for example for marking the bar.

Claims

1. A reinforcing bar with improved adherence for a reinforced concrete component, consisting in of a metal section (1) extending in a longitudinal direction, having the form of a flattened strip of substantially rectangular cross-section, with two opposite wide faces (10, 10′) extending between two lateral sides (11, 11′) and including a plurality of projecting anchoring portions which are longitudinally separated from each other and bearing on the concrete in a direction opposite to a tensile force applied to the bar (1), characterized in that each of the two wide faces (10, 10′) of the strip is provided with a series of anchoring portions in the form of elongated locks (2, 24) separated from each other by hollow portions (3, 3′) in the form of grooves and extending transversally over the whole width of the strip (1), substantially up to the lateral sides (11, 11′) thereof, and each of said elongated locks (2) extends in projection over a small height, not exceeding a quarter of the thickness of the strip (1), and has, in cross-section, a substantially trapezoidal profile, with an embossed face (21) of small width with respect to its length and two inclined flanks (22, 23) for connection with the elongated bottom (31, 31′) of the adjacent grooves (3, 3′) that constitute, for each lock (2), two inclined faces (22, 23) that bear, each in one direction, on the coating concrete, said inclined faces (22, 23) each having an elongated shape extending between the two sides of the strip (1), so as to distribute the bearing forces over all the width thereof.

2. The reinforcing bar according to claim 1, characterized in that, on each face (10, 10′) of the strip (1), the elongated locks (2, 2′) are spaced apart from each other by a constant pitch (c) that do not exceed half the width (1) of the strip (1).

3. The reinforcing bar according to claim 1, characterized in that, on each face (10, 10′) of the strip (1), the embossed faces (21, 21′) of the elongated locks (2, 2′) have a width lower than half the width (1) of the strip (1).

4. The reinforcing bar according to claim 1, characterized in that the elongated locks (2, 2′) extend transversally in directions inclined by a non-zero angle with respect to a longitudinal axis of each face (10, 10′) of the strip (1).

5. The reinforcing bar according to claim 4, characterized in that the elongated locks (2, 2′) formed on the two faces (10, 10′), respectively, of the strip (1) are symmetrically inclined, in opposite directions, with respect to the longitudinal axis X′, X of the strip (1).

6. The reinforcing bar according to claim 4, characterized in that, on each face (10, 10′) of the strip (1), the elongated locks (2, 2′) are parallel and inclined by an angle β comprised between 35° and 75°.

7. The reinforcing bar according to claim 3, characterized in that the anchoring locks (2, 2′) formed on each wide face (10, 10′) of the strip (1) have the shape of imbricated V-shaped chevrons, with two rectilinear portions symmetrically inclined on either side of a longitudinal axis (X′, X) of the strip (1).

8. The reinforcing bar according to claim 4, characterized in that the anchoring locks (2, 2′) formed on each wide face (10, 10′) of the strip (1) have a corrugated shape, symmetrical with respect to the longitudinal axis (X′, X) of the strip (1).

9. The reinforcing bar according to claim 1, characterized in that, on each wide face (10, 10′) of the strip (1), the elongated anchoring locks (2, 2′) extend up to a small distance from each of the lateral edges (11a, 11b) of the strip (1), so as to leave a smooth flat (12) of small width along each of said edges (11, 11′).

10. The reinforcing bar according to claim 9, characterized in that the flats (12) formed along the two lateral edges (11, 11′), respectively, of the strip (1), on each of wide faces (10, 10′) thereof, have a width of the order of 0.2 e, e being the average thickness of the strip.

11. The reinforcing bar according to claim 9, characterized in that, on each wide face (10, 10′) of the strip (1), the embossed faces (21) of the locks (2) and the bottoms (31) of the grooves (3) are located in the two parallel planes, respectively, extending on either side of a mean plane Q of the wide face (10), in which are placed the two flats (12a, 12b) extending along the two lateral edges (11a, 11b), respectively, of the strip (1).

12. The reinforcing bar according to claim 11, characterized in that the two planes in which are located the embossed faces (21) of the locks (2) and the bottoms (31) of the grooves (3), respectively, are spaced apart by a height h that can be from 0.08 e to 0.24 e, e being the average thickness of the strip (1).

13. The reinforcing bar according to claim 1, characterized in that the connection flanks (22, 23) between the embossed faces (21) of the locks and the bottom (31) of the corresponding grooves (3) are inclined by an angle α of at least 45°, with respect to a plane in which said embossed faces (21) are placed.

14. The reinforcing bar according to claim 1, characterized in that the anchoring locks (2) are longitudinally spaced by a pitch (c) comprised between one and three times the average thickness e of the strip (1).

15. A reinforcing cage (7) for a reinforced concrete component (6) including two webs of reinforcing bars connected by stirrups and extending at a small distance of coating from two spaced-apart facings (61, 62), respectively, of the component (6), characterized in that at least one of the two webs of the cage consist in bars (71) with improved adherence according to claim 1, and in that the stirrups are formed of flat metal strips (73), alternately welded on the embossed faces (21) of the anchoring locks (2) of said improved-bond bars (71).

16. A method of producing a reinforcing bar according to claim 1, characterized in that it is firstly made a metal bar (1) in the form of a flattened strip with two opposite wide faces (10, 10′) and centred on a longitudinal axis (x′ x), and in that said strip (1) is subjected to a rolling pass between two cylinders (5, 5′) rotating about axes (50, 50′) parallel to each other and orthogonal to the longitudinal axis (x′ x) of the strip (1), said cylinders (5, 5′) being provided, over their periphery, with spaced-apart recesses (51), for the formation, by rolling, of elongated locks (2) separated by parallel grooves (3), on each of the two wide faces (10, 10′) of the strip (1).

17. The method according to claim 16, characterized in that the two rolling cylinders (5, 5′) are each provided, over their periphery, with an alternation of recesses (51) and teeth (52) intended to form the locks (2) and the grooves (3), respectively, on each of the wide faces (10, 10′) of the strip (1) and extending between two smooth portions (53) for the formation of two flats (12) along the two lateral sides (11a, 11b) of the strip (1).

18. The method according to claim 16, characterized in that the recesses (51) for the formation of the locks (2) are regularly spaced apart along the periphery of each of the rolling cylinders (5, 5′).

19. The method according to claim 16, characterized in that the recesses (51) are distributed along the periphery of each of the rolling cylinders (5, 5′) so as to periodically vary the spacing of the locks (2) obtained on each wide face (10, 10′) of the strip (1).

20. The reinforcing bar according to claim 2, characterized in that, on each face (10, 10′) of the strip (1), the embossed faces (21, 21′) of the elongated locks (2, 2′) have a width lower than half the width (1) of the strip (1).