FR3096382A1 - Method of strengthening a structure. - Google Patents

Abstract

Method for strengthening a structure Method for strengthening a structure (10) comprising a cementitious material (14), the method comprising the steps of: a) placing, in a groove (30) made in the structure (10) , at least one shape memory frame (40) made of a material that can go from an initial configuration to a stretched configuration, then resume the initial configuration by being brought from room temperature to a sufficient temperature, preferably between 160 and 300 ° C, b) the frame (40) being in its stretched configuration, anchoring the ends (41) of the frame (40) to the structure (10) while leaving a free portion (42) of the reinforcement (40) without adhesion to the structure (10) within the groove (30), c) raising the temperature, at least of the free portion (42), to a value, preferably between 160 and 300 ° C to cause the reinforcement (40) to return to its initial configuration and generate a preco stress in the structure (10). Figure for the abstract: Fig. 7

Description

Description Title of the invention: Process for reinforcing a structure.

Technical area

The present invention relates to repair work and / or reinforcement of concrete structures in the field of construction.

More particularly, the invention relates to processes for repairing and/or reinforcing structures using shape-memory reinforcements.

Prior technique

[0002] It is known to use shape-memory reinforcements in the repair of a cracked structure using the techniques mentioned below.

[0003] One of the known methods consists in sealing the shape memory reinforcement in a groove which is filled with a sealing mortar after installation of the reinforcement.

The assembly consisting of the reinforcement and the sealing mortar is then put under mechanical tension by raising the temperature of the reinforcement.

A disadvantage of this method is that the mechanical tensioning of the reinforcement embedded in the sealing mortar is highly energy consuming due to the heat dissipation generated by conduction due to the contact of the reinforcement with the sealing mortar. .

In addition, during the mechanical tensioning of the reinforcement, the concrete is locally subjected to a high temperature due to the heating of the reinforcement, risking to generate local cracks which can be detrimental to the long-term resistance. of structure.

[0004] A second known method consists in placing shape memory reinforcements of flattened section on the facing of the structure and in maintaining them by fixings at the ends, such as steel nails driven into the concrete by means of a explosive cartridge pistol.

A disadvantage of this technique lies in particular in its incompatibility with the use of an additional external reinforcement.

Indeed, such a reinforcement is either placed over the previously stretched shape memory reinforcement and therefore not adherent to the structure, or placed beforehand to be in contact with the structure.

In the latter case, the risk is that the reinforcement will be damaged by the temperature of the reinforcement during its activation.

[0005] In addition, in repair, it is rare for the need for reinforcement of the structure to be limited to a single direction and one is often confronted with needs for multiaxial reinforcements, therefore calling on such additional external reinforcements.

[0006] There is therefore a need to improve the structural reinforcement methods using shape-memory reinforcements, in particular to make these methods compatible with the use of complementary reinforcement systems such as fabric reinforcements. of carbon fibers fixed by gluing.

Disclosure of Invention

The invention aims to meet this need and has as its object, according to one of its aspects, a reinforcement method (one structure comprising a cementitious material, this method comprising the steps consisting in: a) placing , in a slot made in the structure, at least one shape-memory reinforcement made of a material that can pass from an initial configuration to a stretched configuration, then resume the initial configuration by being brought from room temperature to a sufficient temperature, preferably between 160°C and 300°C, for example 250°C,

[0008] h) the reinforcement being in its stretched configuration, anchoring the ends of the reinforcement on the structure while leaving a free portion of the reinforcement without adherence to the structure within the groove,

[0009] c) raising the temperature, at least of the free portion, to a value, preferably between 160 and 300° C., to cause the reinforcement to return to its initial configuration and generate a prestress (a force of compression) in the structure.

[0010] The invention, by reducing the heat transfer between the shape-memory armature and the structure because the activation takes place before relining the bleeding, facilitates the rise in temperature of the armature and limits the dissipation dc heat within the structure, reducing energy loss and the risk of heat embrittlement upon activation.

[0011] Preferably, the shape-memory armature passes from its initial configuration to its stretched configuration by a traction exerted on the armature at room temperature.

The transition to the stretched configuration can be done in the factory, for example, before the reinforcement is delivered to the site.

[0012] Preferably, the armature is in the form of a toothed bar.

This may have a cross section of substantially circular or rectangular shape.

As a variant, the reinforcement is in the form of a dish.

In general, any shape-memory armature capable of being stretched when activated and generating a prestress (a compressive force) in the structure may be suitable.

[0013] For example, the material of the shape memory reinforcement is an alloy comprising a base alloy consisting of manganese, silicon, chromium and nickel as well as an additional mass proportion of iron.

[0014] Shape memory reinforcements that can be used are, for example, those described in European patent application EP 2 141 251 A1 and marketed by the company RE-3 FER.

[0015] Preferably, the method according to the invention comprises the step consisting in injecting a filling product around the reinforcement in the groove, after the return of the reinforcement to its initial configuration.

The filling product can be a resin or any other filling material, for example a cement grout.

[0016] The invention makes it possible to use materials which would be incompatible with the activation temperature of the reinforcement if the activation took place when the kerf is already sealed.

The plugging of the groove makes it possible in particular to ensure surface continuity allowing the subsequent fitting of one or more additional external reinforcements, these reinforcements being able to adhere perfectly to the structure.

[0017] The method can thus advantageously comprise the laying, above the groove, of at least one reinforcement transverse to the reinforcement, preferably a reinforcement comprising one or more strips of fabric, in particular a Carbon Fiber Fabric (TFC) or more generally a Fiber Reinforced Polymer (FRP) fabric.

Preferably, the transverse reinforcement is applied to the filler material, after the latter has hardened.

The transverse reinforcement(s) provide additional tensile and shear resistance to the structure.

[0018] During step c), the rise in temperature in the free portion is advantageously obtained by passing an electric current therein, but other methods can be used to heat the shape-memory framework, such as exposing the framework to radiation from a UV light source.

The electric current flows between points spaced from the zones of the reinforcement anchored in the structure, and this avoids excessive heating of the anchored zones.

[0019] The anchoring of the ends of the reinforcement in the structure can be carried out in many ways, in particular by passive anchoring, for example by sealing at least one end in the structure, for example using a sealing resin.

[0020] The method may thus comprise the drilling of the structure to form at least one housing for receiving one end of the armature, in which the latter is then sealed.

[0021] The drilling may be perpendicular to the direction of the armature in which case the armature may be bent, in particular at right angles, to extend outside the housing in the desired direction.

Thus, at least one end of the frame can be bent, preferably substantially at a right angle.

Preferably, the two ends of the armature are each bent, in particular both bent at right angles.

Each of these ends can then be received in a respective perpendicular housing.

The anchoring of at least one end can be obtained other than in a housing obtained by drilling in said structure.

[0023] The anchoring of one end of the armature can for example be effected by sealing in a surface housing coming into contact with a surface of the structure.

The sealing can be obtained by applying sealing resin around the end of the armature in the housing.

This makes it possible to immobilize the reinforcement in the structure, thus making it possible to diffuse the mechanical prestressing forces in the structure.

[0025] The anchoring of the ends can also be carried out other than by sealing, for example by anchoring techniques similar to those used for active anchoring.

[0026] The anchoring of one end of the reinforcement can thus be carried out, for example, using a force distribution element bearing against a surface of the structure, in particular a force distribution plate. 'effort.

Such anchoring may in particular prove useful when reinforcing a cantilevered balcony slab, the force distribution element bearing against the free edge of the slab.

[0027]Preferably, retaining means are provided to improve the anchoring of the ends of the shape memory armature to the structure in the anchoring zones.

[0028] At least one of the ends of the armature, better both ends, can thus be fitted with an anchoring sleeve.

This sleeve is preferably metallic and fixed by crimping on the armature.

The use of anchoring sleeves makes it possible to ensure retention of the reinforcement despite a relatively low sealing depth and makes it possible to adapt the method to thin structures.

[0029] Preferably, the sleeve has a rough internal surface, in particular covered with carborundum grains.

This ensures strong friction between the sleeve and the armature.

[0030] The method may include the production of at least one housing with a width greater than that of the groove, for receiving an electric current supply clamp.

Preferably, two housings are made with a width greater than that of the groove for receiving two current supply clamps, in particular in the vicinity of each anchoring zone.

This makes the activation step easier, by allowing easy connection of the power supply used for activation.

[0031] Step a) can be preceded by making the kerf, which is done using a grinder or groover.

[0032] The method may include the step consisting in measuring a stress in the armature, at least after the armature has returned to its initial configuration, using a suitable measuring device.

This makes it possible to verify the mechanical tensioning of the shape memory reinforcement and the creation of a corresponding prestress in the structure.

[0033] The measuring device used can thus comprise one or more strain gauges (extensometers), a crossbow dynamometer, a long base extensometer, a fiber optic extensometer, a vibration analysis device by wave measurements with transmitter /receiver, a sensor sensitive to the magnetostriction of the reinforcement or a device for local measurement of the compression of the concrete, this list not being exhaustive.

Preferably, the measuring device is a crossbow dynamometer.

The method may include measuring the temperature of the free portion of the shape memory armature during step c), in particular by means of a contactless infrared thermometer.

The electric current in the armature can be adjusted according to the temperature measured in order to bring the armature to a temperature, preferably between 160 and 300 C, without however bringing the armature to an excessive temperature.

The method is advantageously applied to the reinforcement of a cantilevered slab, in particular a balcony slab.

[0036] A further subject of the invention is a reinforced structure comprising a cementairc material, the reinforcement having preferably been obtained by implementing the method according to the invention as defined above, the reinforced structure comprising at least a groove in which is placed at least one shape-memory armature made of a material that can pass from an initial configuration to a stretched configuration and then return to the initial configuration by being brought from room temperature to a sufficient temperature, preferably between 160 and 300°C, the reinforcement having its ends anchored in the structure and inducing by its mechanical tension a prestress in the structure, the reinforcement comprising at least one bent end sealed in a borehole of the structure and/or at least one end anchored using a force distribution element resting on the structure.

As mentioned above, the two ends of the armature can be bent, in particular both bent at a low angle.

As indicated above, in order to improve the anchoring of the reinforcement in the structure, at least one end of the shape memory reinforcement can be equipped with an anchoring sleeve.

The two ends can thus each be equipped with an anchoring sleeve.

The sleeve is preferably fixed by crimping on the armature.

The sleeve preferably comprises a rough internal surface, in particular covered with grains of carborundum.

[0039] A filling product advantageously surrounds the frame in the groove, coming into contact with it.

This allows on the one hand the sealing of reinforcement in the structure, and on the other hand ensures the continuity of the plane of the reinforced structure.

[0040] At least one transverse reinforcement to the frame can be placed above the groove.

The reinforcement is preferably a reinforcement comprising one or more strips of fabric, in particular of a carbon fiber fabric.

6 100411 The structure is advantageously a cantilevered slab, in particular a balcony slab.

Brief description of the drawings

The invention can be better understood on reading the detailed description which follows, non-limiting examples of implementation thereof, and on examining the appended drawing, in which:

[0043] [fie.11 is a schematic and partial section of a structure awaiting reinforcement,

[0044] [fie.21 illustrates the drilling in the structure,

[0045] [fie.31 illustrates the realization of the housings for receiving the electrical current supply clamps,

[0046] [fig.41 illustrates the execution of bleeding,

[0047] [fig.51 illustrates the injection of a sealing resin into the housings defined by the boreholes,

[0048] [fig.61 represents the shape memory reinforcement,

[0049] [fig.71 illustrates the installation of the reinforcement in the groove,

[0050] [fig.81 illustrates the activation of the armature,

[0051] [fig.91 illustrates the measurement of the mechanical stress in the shape memory reinforcement,

[0052] [fig.101 illustrates the filling of the groove,

[0053] [fig.11] illustrates the installation of an additional transverse reinforcement dc carbon fiber dc fabric,

[0054] [fig.121 represents in isolation, in perspective, an anchoring sleeve,

[0055] [fig.131 represents an alternative embodiment of anchoring the armature, and

[0056] [fig.141 represents an alternative embodiment of anchoring the armature.

Detailed description 100571 Will be described with reference to Figures 1 to 11 an example of a method of reinforcement according to the invention, applied to a cracked structure 10 in concrete 14, in particular in reinforced concrete.

The structure 10 may correspond to a balcony slab extending cantilevered from a load-bearing structure, for example a floor slab (not shown).

100581 The method comprises a first step of delimiting the zone to be prestressed, followed by the realization of boreholes 33 using a drill 37 as illustrated in L figure 2.

100591 In the example considered, the boreholes 33 are for example made to a depth pi-, between 50 and 100mm, for example around 75mm.

The diameter of the boreholes cp is for example between 10 and 20mm, for example 714mm.

The center distance LI between the boreholes 33 minus a constant b substantially corresponds to the length over which it is desired to exert a prestress, the constant b being of the order of 10 to 20mm, for example 14mm.

The boreholes 33 define receiving housings 34 for the ends of the shape memory armature 40, as described below.

The housings 34 have a depth pf3 which is preferably at least 10 times the diameter of the armature.

The depth pf3 can be between 40mm and 100mm, for example approximately 60mm.

Once the boreholes 33 have been drilled, housings 35 can be made for receiving clamps 61 for supplying electric current, as illustrated in FIG. 3.

These housings 35 are for example made by coring with a substantially circular cross-section, for example of diameter (R) of between 20 and 50mm, for example of approximately 40mm and over a depth pf2 of between 10 and 30mm, by example of about 15mm.

The method then comprises the execution of a groove 30 in the concrete 14 by means of a groove 39, as illustrated in Figure 4.

The groove 30 is delimited axially by the boreholes 33.

The groove 30 is for example made with a substantially rectangular cross section, for example about 8 mm to 10 mm wide and 15 mm deep, as shown in Figure 4.

The preparation of the shape memory reinforcement 40 can be carried out in parallel, or alternatively the reinforcements are delivered to the site already prepared.

The shape memory armature 40 is preferably in the form of a toothed bar.

It has for example a diameter comprised between 5mm and 20mm, for example 6 rmin and an ability to restore a force by returning to its initial configuration for example of approximately 1000 to 1400 daN.

The length of the armature corresponds for example to the center distance LI of the boreholes 33, to which is added a constant c of between 100mm and 200mm, for example of around 145mm.

[0067] This shape memory reinforcement 40 is made of an alloy that can pass from an initial configuration to a stretched configuration, in particular by traction exerted on the material at room temperature, then resume the initial configuration by being worn from the temperature ambient at a temperature between 160 and 300°C, for example 250°C.

[0068] Shape memory reinforcements that can be used are, for example, those described in European patent application EP 2 141 251 A1 and marketed by the company REFER.

In the illustrated embodiment, the frame 40 is placed in the groove 30 in its stretched configuration. 8

As illustrated in Figure 6, the ends 41 are bent over a radius re between 10mm and 20mm, for example around 15mm.

The armature 40 thus has two ends 41 bent at right angles.

The ends 41 of the reinforcement 40 are advantageously provided with anchoring sleeves 50, making it possible to ensure the sealing of the reinforcement over relatively shallow depths.

The anchor sleeves are preferably hard steel hollow cylinders approximately 28mm in length.

The external diameters cp, and internal p', of each sleeve 50 are for example approximately 10 mm and 7 mm respectively.

The sleeves 50 are preferably fixed by crimping on the ends of the reinforcements 40.

The crimping operation consists of crushing the sleeve 50 between two treated steel jaws of a suitable crimping press (not shown).

The crushing pressure can be between 5 and 8 tons.

Each sleeve 50 preferably has a rough internal surface 52 .

Such an internal surface is obtained, in the illustrated embodiment, by covering the internal surface with carborundum grains with a gauge of about 0.3mm to 0.5mm.

Prior to the application of the carborundum grains, the sleeves are preferably degreased and the internal surface 52 is coated with a thin layer of resin of between 0.1 mm and 0.4 mm, for example 0.2 mm.

[0075] After the resin has hardened, the excess carborundum is preferably removed and the sleeves are blown with compressed air.

The housings 34 are filled with a sealing resin 32 using a resin cartridge 36, as shown in Figure 5.

The sealing resin 36 is for example an epoxy resin.

The ends of the frame equipped with anchoring sleeves are then anchored in the housings 34 before the resin sets, while leaving a free portion 42 of the frame 40 without adherence to the structure 10 within the bleeding 30.

Once the ends 41 have been sealed, the armature 40 is mechanically tensioned.

This is obtained by raising the temperature of the free portion to between 160 and 300°C, which causes the reinforcement to return to its initial configuration, thus generating a prestress in the structure.

As illustrated in Figure 8, the temperature rise can be obtained by Joule effect by passing an electric current using an electric current generator 60 whose terminals equipped with clamps 61 are connected to the ends of the free portion 42 in the housings 35.

[0080] The temperature in the free portion is advantageously monitored during activation, by means of a contactless infrared thermometer (not shown).

[0081] The rise in temperature to the values indicated causes the armature 40 to return to its initial configuration.

Because contact between armature 40 and structure 10 is limited, thermal losses are reduced.

It is possible to measure the mechanical stress in the armature 40 using a crossbow dynamometer 70, for example, as in Figure 9.

This makes it possible to ensure the application of the prestressing in the structure and therefore compliance with compliance.

Then, one can inject a filling product 18 around the frame 40 under mechanical tension in the groove 30, so as to seal the frame 40 over its entire length and restore continuity of the plane of the reinforced structure.

If appropriate, additional reinforcement 80 can be put in place, for example strips of carbon fiber fabric, for example Foreva® TFC (Carbon Fiber Fabric), as shown in Figure 11.

[0085] The strips 80 are preferably arranged transversely to the reinforcement.

The implementation of the reinforcement strips 80 is preferably carried out at least 24 hours after the sealing of the reinforcements 40 in the groove 30.

Of course, the invention is not limited to the example which has just been described.

For example, the anchoring of the ends 41 can be done other than by sealing in the housings 33.

As illustrated in Figure 13, the anchoring of one end 41 of the reinforcement 40 can be carried out using a force distribution element 54 bearing against a surface of the structure , this distribution element being for example a force distribution plate allowing the diffusion of the prestressing forces in the concrete 14.

The distribution plate 54 is for example a rectangular steel plate provided with a hole in its center, for the passage of the armature.

This force distribution plate 54 is preferably positioned so that the armature 40 is centered therein.

The anchoring of the ends 41 can be done other than by pressing on the distribution element.

In the example illustrated in Figure 14, the distribution plate can be replaced by a surface housing 90 arranged on the edge of a surface of the structure, and which is filled with a sealing resin .

In this embodiment, the anchoring of the armature 40 is carried out by sealing a right end of the armature 40 provided with the anchoring sleeve 50 in the surface housing 90.

The anchoring by sealing of the assembly consisting of the frame 40 and the sleeve 90 in the housing is obtained by applying the sealing resin around the end of the frame in the housing.

Thus, the reinforcement is secured to the structure, which makes it possible to diffuse the mechanical prestressing forces in the concrete 14 during the return of the reinforcement to its initial position.

The variants described in Figures 13 and 14 prove useful when reinforcing a cantilevered balcony slab, the force distribution element bearing against the free edge of the slab. 11

Claims (1)

CLAIMS [Claim 1] Method for reinforcing a structure (10) comprising a cementitious material (14), the method comprising the steps consisting in: a) placing, in a slot (30) made in the structure (10), at the at least one shape-memory reinforcement (40) made of a material that can pass from an initial configuration to a stretched configuration, then return to the initial configuration by being brought from room temperature to a sufficient temperature, preferably between 160 and 300 °C, b) the armature (40) being in its stretched configuration, anchor the ends (41) of the armature (40) to the structure (10) while leaving a free portion (42) of the armature ( 40) without adhesion to the structure (10) within the groove (30), c) raising the temperature, at least of the free portion (42), to a value, preferably between 160 and 300°C, for cause the armature (40) to return to its initial configuration and generate a prestress in the structure (10). [Claim 2] A method according to claim 1, comprising the step of injecting a filling product (18) around the reinforcement (40) in the groove (30), after the Palmature (40) has returned to its configuration initial. [Claim 3] Method according to claim 1 or 2, comprising the laying, above the groove (30), of at least one reinforcement (80) transverse to the reinforcement (40), preferably a reinforcement (80 ) comprising one or more strips of fabric, in particular of a carbon fiber fabric. [Claim 4] 4. Method according to any one of the preceding claims, the rise in temperature in the free portion (42) being obtained by passing an electric current therein or by exposing the armature (40) to radiation from a UV light source. [Claim 5] Method according to any one of the preceding claims, comprising drilling the structure (10) to define at least one housing (33, 34) for receiving one end of the armature (40) in which that it is sealed. [Claim 6] Method according to any one of the preceding claims, at least one end (41) of the armature (40) being bent, preferably substantially at right angles, the two ends (41) of the armature (40 ) each being preferably bent, in particular both bent at 1-> [Claim 7] [Claim 8] [Claim 9] [Claim 10] [Claim 11] [Claim 12] [Claim 13] [Claim 14] [Claim 15 ] right angle. Method according to any one of the preceding claims, the anchoring of one end (41) of the reinforcement (40) being carried out using a force distribution element (54) coming to bear against a surface of the structure, in particular a force distribution plate. Method according to any one of the preceding claims, the anchoring of one end (41) of the armature (40) being carried out by sealing the said end (41) in a surface housing (90) coming into contact with a surface of the structure (10). 9. Method according to any one of the preceding claims, at least one of the ends (41) of the reinforcement (40), better still the two ends (41), being equipped with an anchoring sleeve (50 ), this sleeve (50) being preferably fixed by crimping on the armature (40), preferably comprising a rough internal surface (52), in particular covered with grains of carborundum. 10. Method according to any one of the preceding claims, comprising the production of at least one housing (35) of width greater than that of the groove (30), for receiving a clamp (61) for supplying current electric. 1 1 . Method according to any one of the preceding claims, step a) being preceded by making the kerf (30). 12. Method according to any one of the preceding claims, comprising the step consisting in measuring a stress in the reinforcement (40) at least after the return of the reinforcement (40) to its initial configuration, in particular using a crossbow dynamometer (70). 13. Method according to any one of the preceding claims, comprising measuring the temperature of the free portion (42) during step c), in particular by means of a contactless infrared thermometer. 14. Method according to any one of the preceding claims, being applied to the reinforcement of a cantilevered slab, in particular a balcony slab. 15. Reinforced structure comprising a cementitious material, the reinforcement having preferably been obtained by implementing the method according to any one of the preceding claims, the reinforced structure comprising at least one groove (30) in which is placed at least one shape-memory frame (40) made of a material that can change from an initial configuration to a stretched configuration, then resume the initial configuration by being brought from ambient temperature to a sufficient temperature, preferably between 160 and 300° C., the armature (40) having its ends (41) anchored in the structure and inducing by its mechanical tension during the return to the initial configuration a prestress in the structure (10), the reinforcement (40) comprising at least one bent end (41) sealed in a borehole (33) of the structure (10) and/or at least one end (41) anchored using a force distribution element (54) resting on the structure (10) and/or at least one end (41) sealed in a surface housing (90) coming into contact with a structural surface. 16. Structure according to claim 15, the two ends (41) of the armature (40) each being bent, in particular both bent at right angles. 17. Structure according to any one of claims 15 and 16, at least one reinforcement (80) transverse to the reinforcement (40) being placed above the groove (30), preferably a reinforcement (80) comprising a or several strips of fabric, in particular of a carbon fiber fabric. 18. Structure according to any one of claims 15 to 17, a filling product (18) surrounding the frame in the groove (30), coming into contact with it. 19. Structure according to any one of claims 15 to 18, at least one of the ends (41) of the frame (40), better both ends (41), being equipped (s) with a sleeve of anchor (50), this sleeve (50) being preferably fixed by crimping on the armature, preferably comprising an internal surface (52) rough, in particular covered with grains of carborundum. 20. Structure according to any one of claims 15 to 19, the structure (10) being a cantilevered slab, in particular a balcony slab.