EP2356292A1 - Procede de realisation d'une piece en beton arme et piece ainsi realisee - Google Patents
Procede de realisation d'une piece en beton arme et piece ainsi realiseeInfo
- Publication number
- EP2356292A1 EP2356292A1 EP09801519A EP09801519A EP2356292A1 EP 2356292 A1 EP2356292 A1 EP 2356292A1 EP 09801519 A EP09801519 A EP 09801519A EP 09801519 A EP09801519 A EP 09801519A EP 2356292 A1 EP2356292 A1 EP 2356292A1
- Authority
- EP
- European Patent Office
- Prior art keywords
- bar
- concrete
- crack
- increase
- zones
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Granted
Links
- 239000011150 reinforced concrete Substances 0.000 title claims abstract description 21
- 238000004519 manufacturing process Methods 0.000 title claims abstract description 7
- 239000004567 concrete Substances 0.000 claims abstract description 154
- 230000000903 blocking effect Effects 0.000 claims abstract description 57
- 230000003014 reinforcing effect Effects 0.000 claims abstract description 42
- 238000000034 method Methods 0.000 claims abstract description 35
- 238000004873 anchoring Methods 0.000 claims abstract description 13
- 230000002787 reinforcement Effects 0.000 claims description 46
- 238000007789 sealing Methods 0.000 claims description 23
- 238000009826 distribution Methods 0.000 claims description 21
- 239000011248 coating agent Substances 0.000 claims description 20
- 238000000576 coating method Methods 0.000 claims description 20
- 230000000694 effects Effects 0.000 claims description 16
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- 238000005259 measurement Methods 0.000 claims description 2
- 238000012546 transfer Methods 0.000 claims description 2
- 238000006073 displacement reaction Methods 0.000 claims 1
- 239000000853 adhesive Substances 0.000 abstract description 3
- 230000001070 adhesive effect Effects 0.000 abstract description 3
- 238000012360 testing method Methods 0.000 description 45
- 229910000831 Steel Inorganic materials 0.000 description 39
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Classifications
-
- E—FIXED CONSTRUCTIONS
- E04—BUILDING
- E04B—GENERAL BUILDING CONSTRUCTIONS; WALLS, e.g. PARTITIONS; ROOFS; FLOORS; CEILINGS; INSULATION OR OTHER PROTECTION OF BUILDINGS
- E04B1/00—Constructions in general; Structures which are not restricted either to walls, e.g. partitions, or floors or ceilings or roofs
- E04B1/18—Structures comprising elongated load-supporting parts, e.g. columns, girders, skeletons
- E04B1/20—Structures comprising elongated load-supporting parts, e.g. columns, girders, skeletons the supporting parts consisting of concrete, e.g. reinforced concrete, or other stonelike material
- E04B1/22—Structures comprising elongated load-supporting parts, e.g. columns, girders, skeletons the supporting parts consisting of concrete, e.g. reinforced concrete, or other stonelike material with parts being prestressed
-
- E—FIXED CONSTRUCTIONS
- E04—BUILDING
- E04C—STRUCTURAL ELEMENTS; BUILDING MATERIALS
- E04C5/00—Reinforcing elements, e.g. for concrete; Auxiliary elements therefor
- E04C5/01—Reinforcing elements of metal, e.g. with non-structural coatings
- E04C5/02—Reinforcing elements of metal, e.g. with non-structural coatings of low bending resistance
- E04C5/03—Reinforcing elements of metal, e.g. with non-structural coatings of low bending resistance with indentations, projections, ribs, or the like, for augmenting the adherence to the concrete
-
- E—FIXED CONSTRUCTIONS
- E04—BUILDING
- E04C—STRUCTURAL ELEMENTS; BUILDING MATERIALS
- E04C5/00—Reinforcing elements, e.g. for concrete; Auxiliary elements therefor
- E04C5/01—Reinforcing elements of metal, e.g. with non-structural coatings
- E04C5/06—Reinforcing elements of metal, e.g. with non-structural coatings of high bending resistance, i.e. of essentially three-dimensional extent, e.g. lattice girders
- E04C5/0604—Prismatic or cylindrical reinforcement cages composed of longitudinal bars and open or closed stirrup rods
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
- Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
- Y10T428/00—Stock material or miscellaneous articles
- Y10T428/249921—Web or sheet containing structurally defined element or component
- Y10T428/249923—Including interlaminar mechanical fastener
Definitions
- the subject of the invention is a method for producing a reinforced concrete part and also covers the reinforcements used for this purpose and the concrete parts thus produced.
- the invention particularly relates to the production of beams, slabs or floors subjected to bending forces but can also be applied to other pieces of reinforced concrete, for example thin shells or sails of various shapes.
- the invention applies especially but not limited to the construction of structures that can undergo earthquakes or accidental actions.
- the reinforced concrete industry has grown significantly in the 20 th century but this technique while undergoing very extensive scientific studies, has changed little.
- reinforced concrete results, as we know, from the combination of two materials with different properties, concrete which is essentially resistant to compressive forces and a reinforcement cage embedded in concrete and made of metal bars which resist pulling forces, at least if these are oriented in the direction of the rebar.
- the prestressed concrete invented by Freyssinet, is based on the same principles of operation by simply giving the armature under tension, a prestressing role of the part in the opposite direction of the tensile forces due to the load, which allows increase the resistance to bending forces.
- a reinforced concrete part on which a load is applied comprises, on either side of a neutral line, a compressed part and a part stretched under tensile stresses under the effect of the load and therefore tends to elongate.
- the reinforcement cage usually comprises two layers of longitudinal bars extending respectively in the compressed part and in the tensioned part and connected by a transverse reinforcement frame consisting of stirrups making it possible, on the one hand, to resist the forces cutting edges and / or vacuum thrusts and, secondly, to join together the two sheets so as to form a cage that can be made in advance and then introduced into the formwork.
- the reinforcement cage When the part extends over a certain width, for example a slab, the reinforcement cage comprises several longitudinal sections connected by transverse reinforcement distribution.
- the reinforcing bars are secured to the concrete by a binding bond determining, along each longitudinal bar, a tangential stress of adhesion which varies as a function of the tensile stresses applied.
- the assembly thus forms a composite part having a stretched part in which the concrete and the reinforcement bars, joined by adhesion, elongate together until a limit value at which the tensile stresses exceed the tensile tensile stress of the concrete, resulting in the appearance of at least one crack in a part of the part, with an increase in stress and therefore elongation of the rebar on which the concrete discharges from the appearance of the crack.
- Figure 2 is a moment-arrow diagram indicating, on the abscissa, the elongation of the stretched part resulting from the deformation of the part under the effect of the bending moment indicated on the ordinate.
- Figure 2 is a moment-arrow diagram indicating, on the abscissa, the elongation of the stretched part resulting from the deformation of the part under the effect of the bending moment indicated on the ordinate.
- the part OA corresponds to the linear elastic behavior of the composite part with a simultaneous elongation of the concrete and the reinforcement.
- Part AB corresponds to the establishment of cracking with an instantaneous increase in the deflection corresponding to the elongation of the stretched part with the steel-concrete adhesion being put into play. From point B, the tensile stresses are absorbed by the steels which are progressively loaded, over the BC range, up to their elastic limit, the mechanism of the adhesion leading to a relative sliding of the two materials , with a progressive increase of the deflection to the point C from which the steel reaches its elastic limit, with a progressive lamination of the two materials.
- Bonding is a phenomenon of chemical adhesion between steel and concrete.
- the phenomenon of friction which occurs after detachment of the bar, is due to the fact that an increase in the tensile force causes the appearance of cracks inclined relative to the axis of the bar and forming, in the concrete, trunks of cones that get stuck on the frame by working like ratchets or some kind of connecting rods.
- the high-adhesion bars are thus provided, along their entire length, locking locks arranged obliquely to the longitudinal direction of the bar, so as to achieve a continuous blocking along the entire length thereof.
- the reinforcements may, for example, be twisted cold, or provided with oblique impressions made by cold rolling on the outer face of the bar.
- FIG. 3 is a so-called Tassios diagram representing the evolution of the tangential stress of adhesion ⁇ as a function of the slip local S of the bar relative to the concrete that enrobe.
- the frame elongates slightly with the concrete which is still in its range of elastic behavior.
- the adhesion is then in a phase of resistance to the detachment of the reinforcement whose tendency to elongation is greater than that of the concrete which coats it.
- the tangential stress of adhesion ⁇ A at point A corresponds to the tensile tensile stress of concrete, from which, as indicated above, transverse microcracks appear.
- the smooth rebar behaves in the same way as the high-adhesion bars up to the point B from which the stop action of the locking notches comes into play. From the corresponding point B, for the smooth bars, at the steel-concrete bond failure, the tangential stress of adhesion decreases rapidly and the sliding increases, as shown by the part BE shown in dashed lines in FIG. In general, the cracking that occurs when the tensile strength of the concrete has been locally exceeded, occurs in the most stressed parts of the room.
- the object of the invention is to solve such problems by means of a new technique for producing reinforced concrete parts.
- the invention therefore relates generally to a method for producing a reinforced concrete part comprising, on either side of a neutral line, a compressed part and a tensioned part subjected to tensile stresses. and having a tendency to elongate under the effect of the load supported by the workpiece, and in which is embedded a reinforcement cage comprising, in the stretched portion, at least one stretched longitudinal bar secured to the concrete by a connection d determining adhesion, along said bar, a tangential stress of adhesion varying according to the tensile stresses applied, respectively on the bar and on the concrete of coating, an increase of the tensile stress in the concrete above a limit value resulting in the opening of at least one crack with a transfer of the tensile stress on the bar and a corresponding elongation thereof, in which process, at least in the portion When subjected to the workpiece, said tensioned bar is provided with a plurality of spaced anchoring means forming abutments bearing on the coating concrete.
- the means for anchoring the bar are distributed in a discontinuous series of spaced locking zones each comprising a plurality of means anchors (23) and separated from each other by sliding zones without anchoring means, in each of which a local increase in the traction differential between the bar and the concrete above a limit value, causes a detachment of the bar relative to the concrete which coats it, over at least a part of the length of said sliding zone between two blocking zones, said unhooked part being able to elongate without any disorder in the coating concrete under the effect of the tensile stresses applied to the tensioned bar.
- the part has, in the concrete, randomly distributed zones of weakness, at which an increase in the tensile stresses applied above the tensile strength of the concrete causes, in the most stressed part of the part, the appearance of at least one crack localized at least in line with one of said weak areas, the opening of said crack determining, at this level, the cancellation of the stress of traction in the concrete and a local correlative increase of the tensile force applied to the reinforcing bar, with a corresponding increase in the tendency to elongation thereof under the effect of the constraints applied.
- the local increase of the tractive force on the bar, at a crack determines a stall of the bar relative to the concrete, at least in the zone of sliding closest to said crack and over a length such that the stall force of the bar relative to the concrete at least partially offsets the traction differential between the two materials when this differential causes the stress to be exceeded. adhesion on the length considered.
- the excess traction remaining applied to the bar can be absorbed, at least in part, by the neighboring blocking zone extending beyond the first sliding zone, the opposite side to the crack.
- the reinforcing bar is detached from the concrete coating in at least a first slip zone, the closest to said crack and an increase in applied tensile stresses successively determines the opening of at least one secondary crack in another weakness zone of the concrete part and the stall of the bar in at least another sliding zone, the closest to said secondary crack, and so on as and when an increase in tensile stresses applied, the sum of the thicknesses of the first crack and secondary cracks open at a given instant , being a function of the increase in the elongation of the bar resulting from the increase in the stresses applied at this instant and this increase in the elongation spread over all of the slip zones, as the secondary cracks appear.
- cracks can occur in areas of weak concrete that are randomly distributed.
- the local increase of the tensile stress applied to the tensioned bar resulting from the opening of the crack causes a stall of the bar of share and else of said crack over a total length for which the stall work of the bar relative to the concrete compensates for at least a portion of the traction differential between the two materials.
- the number and distribution of the locking zones and the corresponding lengths of the sliding zones can be determined according to the distribution and the foreseeable values of the tensile stresses along each tensioned bar, taking into account the loads applied. so that the thickness of each crack does not exceed a given limit.
- each locking zone extends over a length at least equal to a so-called sealing length of the reinforcing bar determining an adhesion stress at least equal to the maximum stress of allowable traction by said bar, and not more than twice that length of seal.
- the invention also covers the parts thus produced and the reinforcing bars used for the implementation of the method and comprising a discontinuous series of locking zones separated from each other by sliding zones.
- each sliding zone of a stretched longitudinal bar has a smooth outer surface in the longitudinal direction.
- each stretched longitudinal bar having, in cross section, the area necessary for the desired tensile strength, the profile of said bar in each sliding zone can advantageously be adapted to give it the perimeter necessary for the contact area between the bar and the concrete provides a frictional connection to achieve the desired limit value of the tangential stress of adhesion in said sliding zone.
- each stretched longitudinal bar may have, in cross section a flattened profile with a width greater than the thickness, so as to increase the perimeter relative to that of a circular bar having the same transverse area.
- each stretched longitudinal bar has, in cross-section, a corrugated profile with longitudinal, recessed and projecting portions, extending parallel to the axis of the bar, along the entire length of each sliding zone.
- each sliding zone comprises a layer of particles releasably attached to the outer surface of the bar and protruding into the coating concrete so as to increase the bonding adhesion.
- these particles are gradually detached one after the other, the bar remaining embedded in the concrete, as and when increasing tensile stresses, which allows to maintain the stress of adhesion to its limit value over a range of increase of said tensile stresses.
- These particles may consist of grains of sand or gravel bonded to the outer surface of the bar or sprinkled and applied under pressure thereon at high temperature at the outlet of the rolling mill.
- These particles may also consist of metal balls or filings fixed on the outer surface of the bar by electrofusion in contact.
- the particles thus fixed on the outer surface of each sliding zone of the bar have various dimensions so as to become progressively detached according to the size of the fixed part, as and when the stresses of applied traction.
- Figure 1 is a perspective diagram of a reinforced concrete part such as a beam.
- FIG. 2 is a moment-strain diagram illustrating the constitutive law of a part subjected to bending stresses.
- FIG. 3 is a stress-strain diagram indicating, according to the type of reinforcement, the evolution of the tangential stress of adhesion as a function of the elongation of the reinforcement.
- Figure 4 is a diagram of a bending machine on a beam.
- Figure 4a is a diagram showing, for such a beam, the variations of the applied tractions, respectively, on a tension bar and on the concrete coating.
- FIG. 5 is a schematic detail view, at a crack and in longitudinal section, of a beam armed with conventional high-adhesion bars.
- FIG. 5a is a diagram indicating, in the case of FIG. 5, the evolution, at the level of a crack, of the tractions applied on a tensioned bar and on the concrete.
- FIG. 6 is a detail view in longitudinal section, of an armed part of rebar according to the invention, in the case of the formation of a crack in the right of a sliding zone.
- FIG. 6a is a diagram showing, in the case of FIG. 6, the variations of the tractions applied on a tensioned bar and on the concrete.
- Figure 7 shows two cross-sectional views of a test beam, left in the vertical midplane and right at a blocking area.
- Figure 8 illustrates the process of crack formation on several beams subjected to a first series of bending tests.
- FIG. 9 is a diagram showing, for the various beams, the arrows obtained during this first series of tests, during the progressive increase of the applied load.
- Figure 10 is a diagram indicating, for the various beams, the number of open cracks according to the arrow.
- FIG. 11 is a diagram indicating, for the various beams, the cumulative opening of the cracks as a function of the arrow.
- Figure 12 is a detail view, in longitudinal section, of an armed part of reinforcing bars according to the invention, in the case of the formation of a crack at a blocking zone.
- FIG. 12a is a diagram showing, in the case of FIG. 12, the variations of the pulls applied on a tensioned bar and on the concrete.
- Figure 13 is a schematic view of a tear test device on a metal bar embedded in a concrete specimen.
- Figure 14 shows schematically, in longitudinal section and in cross section, a second type of test beam provided with reinforcing bars according to the invention.
- FIG. 15 is a table showing the results of a second series of bending tests carried out on beams of the type of FIG. 14.
- FIG. 16 is a table indicating, for a test beam, the order of appearance of the cracks, their location and their thicknesses as a function of the load applied.
- FIG. 17 shows, in cross section, a round bar and a flat bar, provided with directional imprints.
- FIG. 1 shows schematically, in perspective, the conventional arrangement of a molded concrete part 1, inside which a reinforcement cage 2 is embedded.
- the part 1 is a beam with rectangular cross section, extending between two supports spaced apart by a distance L and having two facing faces, respectively lower 11 and upper 1 1 ', and two vertical side faces, respectively 12, 12'.
- the reinforcement cage 2 comprises two layers of longitudinal bars, respectively a lower sheet of bars 21 called bending, and an upper layer of bars 22 said mounting respectively parallel to the two faces of facing 11, 11 of the beam 1 and extending at a minimum distance of coating thereof.
- the two layers of longitudinal bars are connected by transverse reinforcements forming rectangular stirrups spaced apart from each other and distributed over the length of the beam.
- FIG. 2 is a classical moment-strain diagram, illustrating the behavior of the part 1 when it is subjected to a progressively increasing bending moment, indicated on the ordinate and causing an arrow, indicated on the abscissa, which increases with the applied load , causing a corresponding elongation of the stretched portion T and the lower facing face 1 1.
- the tensioned bars 21 and the concrete which coats them are joined by adhesion and simultaneously elongate up to a curvature C1, corresponding to the point A, to from which the tensile stresses generated by the curvature of the part reach the tensile stress limit of the concrete. It then discharges on the tensioned bars 21 which only take up the tensile stresses. This results in an almost instantaneous increase in the curvature of C1 to C2, corresponding to the AB bearing, with an extension of the tensioned lower bars 21 and a beginning of cracking.
- the piece then follows a moment-deformation law corresponding to the section BC whose slope depends on the mechanism of the adhesion which imposes a relative sliding of the tensioned bars with respect to the concrete with, correlatively, a variation of the position of the neutral axis.
- the slope of the line OA corresponds to the flexional stiffness E c l of the part, E 0 being the modulus of elasticity of the non-cracked concrete and I its inertia.
- the slope of the line OB corresponds to the stiffness E c l f , where f is the inertia of the part after the first cracking.
- the inventor has deduced from this that the phenomenon of armature failure, which sometimes occurs in the event of an excessive increase in stresses, for example due to seismic shocks, could be related to the mode of operation of the high-strength reinforcing bars that it is usually used to increase the tangential stress of adhesion.
- the inventor has therefore analyzed the behavior, in the case of bending under the effect of a load, of the stretched part of a reinforced concrete part such as a beam or a slab resting on two supports. , in which is embedded a reinforcement cage having a lower layer of high-adhesion bars which are provided, along their length, transverse locks oriented obliquely to the longitudinal axis of the bar, to ensure a solidarization continues with the concrete of coating.
- a reinforcement cage having a lower layer of high-adhesion bars which are provided, along their length, transverse locks oriented obliquely to the longitudinal axis of the bar, to ensure a solidarization continues with the concrete of coating.
- the inventor has sought to solve such problems and has specifically studied the conditions under which reinforcement and concrete work together to resist the stresses applied.
- FIG. 4 shows, for example, a frame-shaped bending test machine 4 having a cross member 41 fixed at its ends to two columns 42 between which is placed a test beam 5 resting on two spaced apart supports. 43 via ball joints 44, 44 '.
- the beam 5 is subjected, in its central part, to a progressively increasing load by means of a jack 45 bearing in one direction in the center of the cross member 41 and, in the other direction, on the beam 5, by the intermediate of a spreader resting on two ball bearings 46, 46 'apart, for example, a distance of 1 m.
- the jack 45 By means of the jack 45, it is thus possible to subject the beam 5 to a gradually increasing bending moment.
- the stretched portion T of the workpiece tends to lengthen, and in the OA portion of the diagram of Figure 2, the tension bars and the concrete lengthen. the same way.
- the resulting tensile stresses apply differently on tension bars and on concrete which are subjected to T1 and T2 pull-ups in a ratio of approximately 1 to 15, respectively.
- FIG. 5 is a schematic detail view showing, in longitudinal section, the behavior, in its most stressed part, of a reinforced concrete beam 1 comprising, in its stretched part, a sheet of reinforcing bars 21 at high adhesion provided, therefore, ribs 23 along their entire length and in which a crack 3 opens.
- FIG. 5a is a diagram indicating on the ordinate the tensile stresses applied, respectively, on a tensioned bar 21 and on the concrete of FIG. 'coating.
- the crack width 3 can be enlarged, e.g., 1/10 th to 2/10 th and 3/10 th of a millimeter, which means that the free steel length 24 in the crack will be brought to double and then triple, the sealed portions 21a, 21 'remaining locked in the concrete.
- an excessive increase in the stresses causing a widening of the crack and, consequently, an excessive elongation of this short length of the bar will cause, by necking, the sudden rupture thereof with a risk of collapse of the structure.
- the inventor therefore thought that it would be interesting to allow the concrete to drop in the vicinity of the crack, so that the bar could lengthen the length necessary under the effect of applied tractions, without causing disorder in the concrete coating or necking of the steel.
- the notches or ribs 23 are arranged in spaced apart locking zones 25 each having a length I and separated from each other by a zone 26 having a smooth surface and extending over a distance d.
- the forces applied on the reinforced concrete part 1, for example a bending moment, cause the extension of the stretched portion T of the part and, consequently, the placing in tension of each tension bar 21 and the concrete 16 which enrobe, with the appearance of at least one crack primer 3 when the tensile strength of concrete 16 is exceeded.
- An increase in the tensile stresses applied determines, correlatively, an increase in the adhesion stresses on either side of the portion 24 of a tensioned bar 21 corresponding to the opening of the crack 3 which, in the case of the Figure 6, is formed at the smooth zone 26 between two locking zones 25.
- the traction differential between the tensile stress of the steel T2 and that of the concrete T1 is maximum.
- the shear stress applied by this traction differential exceeds the peel strength of the steel which is lower in the smooth zone 26a of the bar, the bar will become detached from the concrete.
- these two parts 27, 27 'of the bar will be able to lie freely and the elongation corresponding to this increase in tensile stresses, will therefore be distributed over the length 2d 'of the unhooked part.
- the bar 21 can extend from 50 to 50.1 then 50.2 then 50.3 millimeters if the crack increases from 0.1 to 0.2 then to 0.3 millimeters.
- a steel bar can perfectly support such elongation distributed over a length of about 50 millimeters whereas, in the case of FIG. 4, this elongation was limited to the only free portion 24 of the bar, corresponding to the width of the crack.
- the recess will be able to extend over the entire length d of the smooth zone 26a, along which the concrete coating is therefore not subject to any tensile stress.
- the tensile stress T1 then vanishes over the entire length of the smooth zone 26a and presents a bearing at this level, on either side of the crack 3, the tensile stress T1 on the steel increasing correspondingly on a bearing of the same length.
- the resulting elongation of the bar will be distributed over this entire length of time, without any mess in the concrete.
- a reinforced concrete beam or slab will therefore better resist the passage of a load exceeding the limit for which it was calculated or localized overloads resulting from an earthquake.
- the crack is therefore less likely to widen and no other crack can appear over the length d of the unhooked zone 26a since the concrete is no longer taut.
- this reinforcement cage 2 has a triangular shape having only three longitudinal bars, respectively two lower bars 21 in the stretched portion of the beam 5 and an upper bar 22 in the compressed part, said bars being connected by triangular stirrups 20.
- FIG. 8 shows the results of FIG.
- FIG. 7 schematically shows such an arrangement on its left side which is a cross-sectional view along the line AA of Figure 8, at the central yoke.
- the lower longitudinal bars of the test beams are provided with locking zones whose number and distribution vary from one beam to another.
- tensioned bars 21 consist of smooth metal strips with a flattened section, as indicated in FIG.
- the first beam 51 diagrammatically represented in the upper part of FIG. 8, comprises a single central blockage 0 formed by the lower part 20a of the central yoke 20, welded to the two bars 21 which, in a conventional manner, are simply provided with anchor bolts at both ends.
- the second beam 52 is provided, on the other hand, with five blockages comprising the same central locking at 0 and, on either side thereof, two pairs of transverse irons welded on the bars 21, and constituting four blockages, respectively a u a 2 on one side and a ⁇ , a ' 2 on the other side. It is thus possible to vary the number and spacings of the blocking points constituted by the transverse irons placed on either side of the central blocking 20a and more or less spaced from each other, all test beams having the same scope. for example 1.5 m between the supports 44, 44 'for a distance of 0.30 m between the load application points 46, 46'.
- the four transverse irons 27 constituting, with the central iron 20a, the five blocks a ⁇ , a 2 , a 0 , a ⁇ , a ' 2 are separated one of the another from a distance of about 25 cm for a span between supports 1.5 m.
- the beam 53 has four transverse irons, each side of the central iron 20a and, therefore, nine blockages respectively bi .... b 4 , a 0 , b'i b ' 4 apart the one of the other about 14 cm.
- the beam 54 has seven transverse irons on each side of the central iron 20a, 15 blocks spaced apart by 9.4 cm.
- the beam 55 has 10 transverse irons on each side of the central iron 20a, 21 blocks spaced apart by 6.8 cm and the beam 56 comprises 30 transverse irons 31 blocks spaced 4.7 cm apart.
- the beam 52 comprises, on each side of the central locking at 0 , two locking points spaced apart by a distance of approximately 25 cm for a span of 1.5 m between the two supports 44, respectively a ⁇ , a 2 , on the left and a ⁇ , a ' 2 , on the right.
- a first crack to the left of the central lock at 0 a second crack f 2 to the right
- a third crack f 3 to the left of the first crack f 1
- a fourth crack f 4 to the right of the second crack f 2 .
- the cracks are not located perfectly symmetrically on either side of the median plane of the beam because, as indicated above, the risk of opening a crack depends on the quality of the crack. concrete that is not absolutely homogeneous.
- the four cracks observed are located in the central part of the beam, between the blocks a ⁇ and a'i, on either side of the central block at 0 .
- reinforcing bars comprising an alternating series of spaced sliding zones, separated from one another by separated blocking points, will therefore make it possible to distribute the cracking over a certain length of the beam, the appearance of a crack in a sliding zone causing the detent of the bar in this sliding zone by canceling the tensile stress on all the cut-in concrete, so that the widening of the crack is limited in this unhooked zone and that no other crack will therefore tend to form there, this part of the room being, so to speak, "vaccinated”.
- FIG. 9 is a diagram indicating, for each beam, the deflection measured during the loading tests and corresponding to the load indicated on the ordinate.
- each beam has a limit from which the curve tends to an asymptote, the beam no longer opposing resistance to deformation. As expected, this limit is the lowest for the curve 1 corresponding to the beam 51 of FIG. 8, the sudden drop in the resistance corresponding to the stall of the tensioned reinforcements which have a smooth surface, on both sides. other central locking 20a.
- the curve 2 which corresponds to the beam 52 with five blockages, has an upper limit and it is noted that the increase in the number of blockages gives the beam a higher resistance but only up to a certain limit. Indeed, the beam 56 having thirty-one blockages and corresponding to the curve 6 has a resistance a little lower than that of the beams 53, 54, 55.
- FIG. 10 is a diagram indicating, on the ordinate, the number of cracks that appear during the increase of the arrow indicated on the abscissa. As indicated above, for the beam 51 comprising only a central blocking, only two fi f 2 cracks appear, the width of which therefore increases progressively during the increase of the deflection.
- the curves 4 and 5 corresponding to the beams 54 and 55 show that there is an optimal spacing between blockages making it possible to obtain the greatest number of cracks with a limited cumulative opening, this spacing being a compromise between the resistance of the beam and the number of cracks.
- reinforcing bars comprising, according to the invention, a series of sliding zones separated by locking points, makes it possible to distribute the cracking over an area that can reach to 2/3 of the length of the beam and, thus increasing the number of cracks, to limit their openings. It will therefore be possible to comply more easily with the regulations which impose a maximum opening not exceeding 0.2 to 0.3 mm, at most 0.5 millimeters and, consequently, to limit the risk of corrosion over time.
- each reinforcing bar remains of the high-adhesion type over the greater part of its length, the sliding zones having a smaller length than the blocking zones between which they are arranged, as shown diagrammatically in FIG.
- sealing length depends on the quality of the concrete and the nature of the rebar. In the case of a round bar, this sealing length can be of the order of 10 to 12 times its diameter for a high-adhesion bar and 20 to 25 times the diameter for a smooth bar.
- This bar 6 is extended outside the test piece 60 by a free portion 61 on which is applied a tensile force by clamping jaws 62, by means of cylinders not shown bearing on the front face of the test tube 60.
- a measuring device 63 such as a load cell, attached to the opposite end 61 'of the bar 6, makes it possible to check whether the length L sealed in the test piece 60 exceeds the minimum sealing length (I 0 ), the traction applied to the end 61 'of the bar 6 opposite the jaws 62 being, then, zero. Indeed, the tensile stress applied by the jaws 62 on the front end 61 decreases progressively along the sealing length (I 0 ) and is zero on the remaining part of the bar 6.
- this high-adhesion part 25'b can absorb only a part of the tensile increase ⁇ t and, at its end 29, there remains an additional stress ⁇ 't which is transmitted to the adjacent sliding zone 26b, the same additional stress ⁇ 't to be absorbed by the concrete d 'coating.
- the traction differential 2 ⁇ 't between the steel and the concrete is balanced by the tangential stress of adhesion along this smooth part 26b.
- the tests show that, in the case of a smooth bar, the sealing length determining a total blockage of the bar relative to the concrete coating is of the order of 20 to 25 times its diameter.
- the length of the smooth zones 26 formed along a tensioned bar 61 must be relatively limited so as not to excessively reduce the stiffness of the part.
- the length d of the sliding zone 26b of the bar is normally less than the sealing length o of an equivalent smooth bar, and this portion 26b will therefore fall out of the concrete as a result of the traction differential 2 ⁇ 't, if it is greater than the tangential stress of adhesion of this smooth zone 26b.
- the two curves T1 and T2 then have a bearing along the entire length of the sliding zone 26b, as shown in FIG. 12a.
- each smooth zone must not exceed the sealing length of an equivalent smooth bar, so that the traction differential between the steel and the concrete allows its recess at the end of the blocking zone. previous.
- FIG. 14 shows, in cross-section on its right-hand side and in longitudinal half-section on its left-hand side, such a test beam 7 in which is embedded a reinforcement cage 2 comprising, as previously, two lower longitudinal bars 71 and an upper longitudinal bar 72 connected at both ends and in the central part of the beam by stirrups 70 of triangular shape.
- the tensioned bars 71 consist, in the tests carried out, of strips of rectangular section, having, for example, a width of 25 mm and a thickness of 3.5 mm.
- the test beams thus produced were subjected to bending tests on a machine of the type shown in FIG. 4, with a distance of 0.30 m between the points of application of the load 46, 46 'and a bearing. 1.5 m between the fulcrums 44, 44 '.
- HA high-adhesion irons
- the table in Figure 15 groups together the results of bending tests carried out on three series of five beams all having a length of 1.8 m for a support span of 1.5 m and a distance of 0.30 m between them. load application points 46, 46 '.
- the beams were divided into 10 cm wide sections in order to identify the order of appearance of the cracks and to locate them by measuring their distances from the left end of the beam, such as shown in the diagram of Figure 16.
- Each beam is marked by a number of three digits, the first two digits indicating the length, in centimeters, of the irons HA constituting each blocking zone and the third digit indicating the length, in centimeters, of the smooth zones interposed between two blocking zones. successive.
- the P061 beam has 6 cm blocking zones separated by smooth zones of 1 cm.
- the five beams of the first series therefore all comprise blocking zones having a length of 6 cm separated by smooth zones whose length varies from 1 cm for the P061 beam to 5 cm for the P065 beam.
- the table in Figure 15 groups these results by columns each corresponding to a maximum width of cracks.
- the P061 beam with 6 cm blocking areas separated by 1 cm smooth areas shows no cracks under a load of 7.5 kN while the boom is 3 cm in the median plane.
- the blocking zones are 10 cm long and are separated by smooth zones whose length varies from 1 cm for the P101 truss to 5 cm for the P105 truss.
- the beams of the third series are provided with reinforcements having 14 cm locking zones separated by smooth zones whose length ranges from 1 to 5 cm.
- test beams are equipped with flat bars having a cross-sectional area of 25 x 3.5 mm which corresponds to that of an equivalent round bar of diameter 10.5 mm for which the sealing length is 10 to 15 cm.
- the locking zones have a length less than double the sealing length and therefore do not risk determining a total blockage in the event of formation of a crack at this level.
- the table of FIG. 15 shows that the distribution of the blocking zones and the smooth zones substantially influences the stiffness of the part, that is to say the deflection taken under a certain load, the number of cracks and their thicknesses.
- the beams P101 and P102 support a load exceeding 30 KN while, for the other beams, such a load causes the opening of cracks having a thickness of 0.3 or even 0.5 mm.
- the length of the sliding zones should be of the order of 5 to 30 mm.
- the table in FIG. 15 shows that an interesting result can also be obtained with beams P062 and P063 which combine pairs of low HA lengths and larger smooth zones.
- the table in FIG. 16 indicates the evolution of the cracking for the P102 truss, which seems to give the best results since it can withstand a load of up to 39 kN, with a deflection of 12 cm. for a maximum thickness of cracks of 0.3 mm.
- the beam is shown schematically above this table, to indicate the order of appearance and location of cracks.
- the first two columns indicate the applied load and the arrow measured in the middle of the beam, respectively, under this load.
- the other columns indicate, for each of the cracks and in their order of appearance, the thickness of this crack as a function of the load applied.
- the tests show that the cracking extends over a length of about 2/3 of the span of the beam between the supports 44, 44 'and that, from the beginning of the crack, the zone where the first cracks appear is not limited to the central part of the beam, between the points of application of the load 46, 46 '.
- the cracks f 2 and f 3 form outside this central portion 46, 46 '.
- the locking zones therefore have a length of the same order as the sealing length I 0 .
- a part of a structure such as a beam or slab, for example, may eventually undergo a relatively large deformation without breaking frames and, therefore, without risk of sudden collapse of the structure, because the distribution of cracking over practically the whole range of the room and the dissipation of energy by detachment of certain smooth zones.
- a bridge span accidentally subjected to too high a load for example, to the passage of an exceptional convoy, may be deformed with, possibly, opening of many cracks that can be repaired thereafter, but without major risk for the holding of the work.
- the strength of the tensile steels is a function of their section and their lever arm, that is to say the distance separating the center of gravity of the steel from that of the compressed part of the concrete.
- this lever arm is substantially increased by the use of flat strips instead of round bars of the same section because, as indicated in the document EP 1 191 163 cited above, the connecting stirrups between the two layers bars can be welded or glued on the inner faces thereof, which allows to place the longitudinal bars closer to the corresponding facing faces of the room, while respecting the minimum coating distance. The result is, in addition, that one can, thus, achieve thinner pieces and, consequently, lighter for the same resistance.
- the locking zones consisted of simple HA bars welded to the inner faces of the flat strips.
- these blocking zones could be realized differently.
- the flat strips used as reinforcements could be made of a slit sheet after rolling. It would then be possible, during rolling, to make embossed or recessed impressions on both sides of the sheet forming, after slitting, the broad faces of the strip.
- the invention can also be applied to all bar profiles, in particular round bars with round section.
- the bars according to the invention would differ from conventional high-adhesion bars in that, during rolling, the notches or blocking ribs are not produced in a continuous manner. , over the entire length of the bar, but only on remote blocking areas, alternating with smooth sliding areas.
- the invention has been described in the case of a beam or a slab but can be applied to all kinds of structures and to all forms of concrete parts such as beams, floors, slabs, sails, etc.
- the dissipation of energy required for the stepping of the steels relative to the concrete absorbs part of the energy causing the cracking such as a seismic shock, a movement of ground or an accidental shock and thus allows a better overall resistance of the work.
- the tests have shown that by producing locking zones having a length of the order of the length of seal, associated with rather short stall zones, not exceeding 20 mm, it was possible to increase the maximum permissible load without exceeding a maximum thickness of cracks of 0.3 mm, corresponding to the regulations.
- reinforcing bars consisting of flat strips with an oval or rectangular section makes it possible, for the same cross-sectional area, to enlarge the perimeter and therefore the contact surface and the surface area. energy required for the recess.
- FIG. 17 shows a round bar and a flat bar with a rectangular cross-section, both of which, in cross-section, have a corrugated profile with longitudinal, recessed and protruding portions 24, which are extend parallel to the longitudinal axis of the bar over the entire length of each sliding zone.
- asperities consist of particles releasably attached to the outer surface of the bar and protruding into the concrete in order to increase the adhesion bond and the limit value of the adhesion stress from which an increase in the tensile stresses causes the stall of the bar.
- these protruding particles can be detached gradually one after the other remaining in the concrete, as the tensile stresses increase, so as to maintain the adhesion stress to a limit value on a range of increase of said constraints.
- These particles could be fixed by gluing on the outer surface of the bar, for example by sprinkling on it of the large sand applied under pressure on the bar, at high temperature, at the output of the rolling mill.
- Such methods would make it possible to modulate the shear strength of the projections thus produced.
- For bonding it would be possible to use more or less resistant adhesives and vary the size of the projections and, therefore, their bonded surface brought into contact with the steel.
- the use, according to the invention, of reinforcing bars having an alternation of locking zones and sliding zones has multiple advantages. Firstly, the distribution of cracking over a long length of the part makes it possible, by increasing the number of cracks, to reduce their thickness, and consequently, the risk of corrosion of the reinforcements over time. It will also be possible, because of the small opening of the cracks, to protect the reinforcements from the risk of corrosion by means of a layer of paint or a suitable coating product. On the other hand, in case of excessive opening of a crack, it avoids the risk of rupture of the reinforcement by necking allowing it to unhook concrete on a length that can, so lie down.
- this recess also causes energy dissipation and it will be possible to determine the distribution and relative lengths of the locking zones and smooth areas so as to modulate the ability of the part to withstand abnormal stresses without risk of collapse of the structure as a result of an accidental breaking of the reinforcements.
- the distribution of the blocking zones and the sliding zones can be determined according to the normal operating load and the accidental loads against which it is necessary to protect oneself, so that, in normal service, the tensile reinforcement behaves in the usual way with a blocking of the bar with respect to the encasing concrete over its whole length and that, in case of accidental overload, the recess of certain sliding zones, due to the stress differential Steel / Concrete allows, on the one hand an elongation of reinforcement avoiding the risk of rupture and, on the other hand, causes a dissipation of energy able to avoid a brutal collapse of the structure.
- the invention thus provides the possibility of solving a whole set of problems without calling into question the general design and the calculation method of the reinforcement cages, using only rebar of a new type but which can be realized industrially in a simple and inexpensive way.
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Abstract
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Application Number | Priority Date | Filing Date | Title |
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FR0858407A FR2939459B1 (fr) | 2008-12-09 | 2008-12-09 | Procede de realisation d'une piece en beton arme et piece ainsi realisee |
PCT/FR2009/052468 WO2010067023A1 (fr) | 2008-12-09 | 2009-12-09 | Procede de realisation d'une piece en beton arme et piece ainsi realisee |
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EP2356292A1 true EP2356292A1 (fr) | 2011-08-17 |
EP2356292B1 EP2356292B1 (fr) | 2015-09-23 |
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EP09801519.1A Active EP2356292B1 (fr) | 2008-12-09 | 2009-12-09 | Procede de realisation d'une piece en beton arme et piece ainsi realisee |
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US (1) | US11199000B2 (fr) |
EP (1) | EP2356292B1 (fr) |
JP (1) | JP5497061B2 (fr) |
FR (1) | FR2939459B1 (fr) |
WO (1) | WO2010067023A1 (fr) |
Cited By (1)
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CN108571121A (zh) * | 2018-05-16 | 2018-09-25 | 广西大学 | 基于预定保证率确定混凝土中变形钢筋锚固长度设计值的方法 |
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WO2012131579A1 (fr) * | 2011-03-30 | 2012-10-04 | Rand York Castings (Proprietary) Limited | Barre d'acier |
FR2990710B1 (fr) | 2012-05-18 | 2015-02-20 | Soc Civ D Brevets Matiere | Barre d'armature a adherence amelioree |
CN110879177B (zh) * | 2018-09-06 | 2022-03-04 | 水利部交通运输部国家能源局南京水利科学研究院 | 一种混凝土水力劈裂测试中试件密封加固装置 |
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FR420102A (fr) * | 1910-09-06 | 1911-01-23 | Giovanni Antonio Porcheddu | Type spécial perfectionné de fers et son application dans les constructions en béton armé |
FR532620A (fr) * | 1921-03-23 | 1922-02-08 | Armature métallique perfectionnée pour poutres, colonnes ou autres éléments de construction, en béton ou ciment armé | |
FR597888A (fr) * | 1924-06-24 | 1925-12-01 | Hauts Fourneaux Et Acieries De | Profil spécial à nervures circulaires pour barres carrées laminées sernant d'armature pour le béton armé |
DE801175C (de) * | 1948-10-02 | 1950-12-28 | Deutsche Bundesbahn | Verdrehte oder verdrillte Spannbetoneinlagen mit staendigem Windungswechsel |
US3245190A (en) * | 1962-06-05 | 1966-04-12 | Gateway Erectors Inc | Metallically reinforced concrete structures |
FR1380233A (fr) * | 1964-01-22 | 1964-11-27 | S I S M A Societa Ind Siderurg | Barres en acier pour béton armé à adhérence améliorée |
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DE2430170C3 (de) * | 1974-06-24 | 1979-10-11 | Philipp Holzmann Ag, 6000 Frankfurt | Spannglied aus hxxochzugfestem Stahl für Spannbetonbauteile oder -bauwerke |
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- 2009-12-09 EP EP09801519.1A patent/EP2356292B1/fr active Active
- 2009-12-09 JP JP2011540172A patent/JP5497061B2/ja active Active
- 2009-12-09 US US13/133,555 patent/US11199000B2/en active Active
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CN108571121A (zh) * | 2018-05-16 | 2018-09-25 | 广西大学 | 基于预定保证率确定混凝土中变形钢筋锚固长度设计值的方法 |
CN108571121B (zh) * | 2018-05-16 | 2020-07-17 | 广西大学 | 确定混凝土中变形钢筋锚固长度设计值的方法 |
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WO2010067023A1 (fr) | 2010-06-17 |
JP5497061B2 (ja) | 2014-05-21 |
EP2356292B1 (fr) | 2015-09-23 |
US20110244211A1 (en) | 2011-10-06 |
FR2939459B1 (fr) | 2020-08-14 |
JP2012511647A (ja) | 2012-05-24 |
FR2939459A1 (fr) | 2010-06-11 |
US11199000B2 (en) | 2021-12-14 |
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