AU1950100A

AU1950100A - Method and device for reinforcing a concrete structure

Info

Publication number: AU1950100A
Application number: AU19501/00A
Authority: AU
Inventors: Khelil Doghri; Sebastien Lardy; Christian Tourneur
Original assignee: Freyssinet International STUP SA
Current assignee: Freyssinet International STUP SA
Priority date: 1999-03-01
Filing date: 2000-02-28
Publication date: 2000-09-07
Also published as: FR2790500B1; JP2000248690A; FR2790500A1; EP1033455A1

Description

51534 GEH:HM P/00/011 Regulation 3.2

AUSTRALIA

Patents Act 1990 COMPLETE SPECIFICATION FOR A STANDARD PATENT

ORIGINAL

Name of Applicant: FREYSSINET INTERNATIONAL STUP Actual Inventors: Khelil DOGHRI Christian TOURNEUR Sebastien LARDY Address for Service: COLLISON CO., 117 King William Street, Adelaide, S.A. 5000 Invention Title: METHOD AND DEVICE FOR REINFORCING A CONCRETE STRUCTURE The following statement is a full description of this invention, including the best method of performing it known to us: .f la METHOD AND DEVICE FOR REINFORCING A CONCRETE

STRUCTURE

The present invention relates to the field of structural reinforcement for construction work.

In this field, it is common practice to bond reinforcements onto the parts of a structure to be reinforced by means of appropriate resins.

In the case of one conventional process commonly used, known as the Lhermite process, the reinforcement consists of a steel sheet bonded onto the concrete after preparing the bonding surface. This conventional method has undergone various changes, in particular to keep pace with developments in the technology used to make the materials and more especially changes that have led to an alternative to the sheeting, which is often difficult to handle and requires special precautions to combat corrosion.

Accordingly, the last few years have seen the arrival of reinforcement 15 techniques involving the use of composite materials in the form of bonded plates (see FR-A-2 594 871, for example), and then in the form of bonded fibres (see US-A-5308430) and bonded fabrics. The latter types of reinforcement offer numerous advantages, in particular their ease of use and So the fact that they can be applied to surfaces of various shapes.

20 Those various types of bonded reinforcement significantly improve the static and dynamic behaviour of the reinforced structure. Moreover, it is very rare that a rupture occurs in the reinforcement itself. Figure 1 shows a schematic illustration of the cross section of a reinforced concrete beam 8 resting on two supports 9 adjacent to its ends, the bottom face.of which is 25 provided, between these two supports 9, with a bonded reinforcement withstanding traction in the longitudinal direction of the beam. The bonded reinforcement 10 improves the behaviour of the beam 8 when subjected to a force F which tends to make it bend between its two supports 9. If the force F is great enough to cause the structure of the beam to rupture, this rupture is likely to occur in the "overlapping" concrete, i.e. in the thickness of non-reinforced concrete between the surface provided with the bonded reinforcement 10 and the reinforcing rods 11 underneath. Typically, the rupture 12 starts in the vicinity of one of the ends of the bonded reinforcement 10 due to the tearing effort E resulting from the reaction R of one of the supports 9 and the traction force T exerted by the reinforcement 10, after which it propagates along the -2reinforcing rods 11. In other words, it is the concrete of the structure which gives way in an area where it is not working under compression (the desired type of stress) but shear stress.

As a result, the properties of the bonded reinforcement are not used to full advantage.

In order to increase the breaking strength of a beam such as that illustrated in figure 1 and reinforced by metal sheeting, it has been suggested that additional pieces of sheeting, referred to as "locks", should be bonded to the sides of the beam to withstand the shearing of the concrete. The disadvantage of this method is that it can only be used with a beam whose sides are accessible. In practice, reinforcements are often bonded onto slabs or walls, thereby making it impossible to fit locks.

Patent application FR-A-2 754 556 describes a method of strengthening a reinforced concrete structure by means of a bonded composite reinforcement with a carbon fibre base, whereby rovings of carbon fibre and a bonding resin are placed in holes bored obliquely through the structural concrete so as to produce a mechanical link based on carbon fibre between the bonded reinforcement and the reinforcing members of the concrete. This imparts resistance to shear stress.

Patent application W096/21785 describes a method of anchoring the ends of a bonded composite reinforcement onto a concrete structure, which consists in forming a recess having an inclined edge in the structural concrete, along which the end part of the reinforcement is bonded. A wedge-shaped insert is then placed above this end part to restore surface continuity. This :25 insert may be bonded to or anchored in the concrete by means of bolts or pegs.

Thus, the anchoring of the end of the reinforcement results from -a certain penetration of this end into the concrete structure.

Another approach is to apply tensile pre-stressing to a composite reinforcement whilst the bonding resin is setting (see FR-A-2 594 871 or US-A- 5 617 685). This will improve the load behaviour of the structure. At the same time, the pre-stressed reinforcement applies compressive force to the overlapping concrete, which reduces the occurrence of the problem outlined above.

An object of the present invention is to propose a different solution that will limit the shear stress to which the overlapping concrete on the reinforced surface of the structure is subjected.

-3- Accordingly, the invention proposes a device for reinforcing a concrete structure, comprising a reinforcement bonded onto the structural concrete and means for anchoring at least one portion of the reinforcement to the structure.

The reinforcement comprises reinforcing fibres extending in at least one main direction. The anchoring means comprise at least one anchoring plate fixed to the structural concrete in a position so that an external surface of the anchoring plate is flush with a surface of the structure receiving the reinforcement. The anchored portion of the reinforcement is bonded onto the external surface of the anchoring plate.

The plate fixed to the concrete takes up the shearing force generated by the reinforcement when bonded in its anchored portion, which typically (but not necessarily) will be adjacent to an end of the reinforcement.

Mounting the anchoring plate flush will ensure that the composite reinforcement remains in a continuous bonding plane, free of any geometric 15 disruption which might otherwise generate bulging.

The anchoring plate is fixed to the concrete by means of connecting S: members which might be of any known structure. As a typical example, they might be arranged so as to extend into the areas of the bulk concrete provided with reinforcing members so that the forces are continuously taken up these oooo areas and the surface stressed by the bonded composite reinforcement.

A preferred embodiment of the device has means for maintaining a tension in the reinforcement parallel with the main direction. These means advantageously comprise a system for locking the anchoring plate in a seating provided in an anchoring support fixed to the concrete.

25 Another aspect of the present invention relates to a method of reinforcing a concrete structure, comprising the steps of forming at least one recess on a surface of the structure; bonding a reinforcement comprising reinforcing fibres onto said surface of the structure, at least some of the reinforcing fibres being aligned along a main direction of said surface of the structure, the reinforcement being arranged so that at least one portion thereof is bonded to an external surface of an anchoring plate fixed in a recess so that the external surface of the anchoring plate is flush with said surface of the structure.

Other features and advantages of the present invention will become clear from the description given below of examples of embodiments, which are not restrictive, and with reference to the appended drawings, in which -4- -figure 1, described above, is a schematic view of a reinforced concrete beam provided with a bonded reinforcement, which is breaking under the effect of bending stress -figure 2 is a front view of a reinforcing device as proposed by the invention; -figure 3 is a view of the device in cross section, along the plane II1-111I marked in figure 2 -figure 4 is a view similar to that of figure 3, showing a different embodiment of the device figure 5 is a front view of another embodiment of the device, in which the anchoring plate is provided with means for tensioning the reinforcement -figures 6 to 8 are views in longitudinal section, from the front and in cross -section, respectively, of another embodiment of a reinforcing device proposed by the invention, the sectional planes VI-VI and VIII-VIII of figures 6 and 8 being marked in figure 7; -figures 9 and 10 are front are views from the front and in cross section of another embodiment of the device, the sectional plane X-X of figure being marked in figure 9; figures 11 and 12 are views in longitudinal section and from the front of an *ooo embodiment of the anchoring plate, the sectional plane XI-XI of figure 11 being marked in figure 12; and -figures 13 and 14 are views in longitudinal section and from the front of another embodiment of the anchoring device, the sectional plane XIII-XIII of figure 13 being marked on figure 14.

25 Figures 2 and 3 provide an illustration of the invention as applied to a concrete structure made from reinforced concrete, one surface 15 of which is provided with a bonded reinforcement 16.

The reinforcement 16 is designed to withstand traction in a main direction A of the surface 15. By preference, it consists of a strip of treated carbon fibres aligned parallel with the direction A, or alternatively a carbon fibre fabric, the warp yarns of which are aligned with direction A, the carbon fibres being impregnated with a resin which sets at ambient temperature. In particular, the reinforcement 16 may be laid as follows: the surface 15 is coated with an epoxy resin in liquid state, capable of setting at ambient temperature; the strip or fabric is then applied to the coated surface so that the resin impregnates the fibres and provides the bonding action. The strip or fabric may be applied by a simple pressihg action which does not require the application of prolonged pressure.

The resin used is, for example, the dual-component epoxy resin made up on the one hand of the resin base sold under the brand name "CECA XEP 3935/A", and on the other of the curing agent sold under the brand name "CECA XEP 2919/B", these two components being made and sold by CECA 12 place de I'lris, La Defense 2, Cedex 54, 92062 PARIS LA DEFENSE

(FRANCE).

When applied in the liquid state, this resin has a viscosity of between 1,000 and 10,000 mPa.s at ambient temperature.

Once set, this resin exhibits -a resistance to shearing that is compatible with that of the material from -which the structure is made, -a tensile strength ranging between 5 and 100 MPa, with an elongation at break ranging between 0.5 and -and an ultimate crushing strength of between 5 and 100 MPa, with a ••:shortening at break of between 0.5 and The bonded carbon fibres forming the strip or fabric 16 have a tensile strength in excess of 1,500 Mpa and a modulus of elasticity of between 200 o* o and 400 GPa.

The carbon fibre strip or fabric 16 extends beyond the area of the structure to be strengthened so that its ends can be anchored in the concrete of the structure. In order to provide such anchoring of an end, a plate 17 is :*:mounted so that its external surface lies flush with the surface of the reinforced •i *25 concrete 15 and the end of the reinforcement 16 is bonded onto it.

The length L (measured parallel with the direction A) of the portion of the reinforcement 16 bonded onto the anchoring plate 17 is typically at least cm, which will ensure that shear stress is efficiently taken up. This plate 17 is advantageously made from steel which is at least 5 mm thick so as to impart sufficient strength to withstand shearing. The specific dimensions and materials of the plate 17 and the characteristics of the means used to anchor them into the concrete are parameters whose values will be adjusted to cope with the different types of stress which each structure to be strengthened must withstand and the characteristics of the composite reinforcement.

These anchoring points for the reinforcements 16 are made as follows.

Before bonding the reinforcement 16, an recess 19 is formed at the level of the end of this reinforcement td be anchored. The bottom of the recess 19 is treated with a rendering mortar to make it smooth. Holes 20 are then bored into the concrete to receive the connecting members 18 of the plate.

These holes 20 extend down as far as the reinforcing rods (not shown) in the concrete structure so as to form a suitable link between these reinforcing rods and the reinforcement 16. The plate 17, prepared beforehand to receive the bonded reinforcement (by sanding), is placed in the recess and anchored by means of connectors 18 located in the holes 20. Typically, the connectors 18 are steel rods located in the holes 20 where they are chemically or mechanically sealed. They might also be made from another material which has the requisite properties to work under shearing stress and traction. These connectors may be active (pre-stressed) or passive.

Once set in place and anchored, the external surface of the plate 17 is flush with the surface 15 of the structure on which the reinforcement 16 is to be ".15 bonded. The reinforcement 16 can now be bonded on in the manner described S: above so that its end covers the anchoring plate 17. Depending on the applications, a protective and/or decorative treatment may be applied to the reinforced surface.

In the embodiment illustrated in figure 4, the reinforcement 16 is retained between the anchoring plate 17a to which it is bonded and a second plate 17b. The second plate 17b may be of a design similar to that of the plate 17a. It is clamped against the reinforcement 16 and the anchoring plate 17a by stress exerted on the connecting members 18, by means of nuts for example.

In the embodiment illustrated in figure 5, supports 24 are welded onto the external surface of the anchoring plate 27 to bear the shaft of a roller perpendicular to the direction A. The roller 25, which may or may not be mobile, is used to tension the strip of reinforcement fabric 16 while it is being bonded.

For example, the strip of fabric may be wound onto the roller 25 and tensioned by the actuation thereof. Alternatively, traction may be exerted on the strip 16 beyond the rollers 25, in which case these will act as a deviator to guide the strip along the surface of the structure to be reinforced and align the traction parallel with this surface.

Figures 2 to 5 illustrate the invention in a situation where an anchoring is provided for the end of a bonded reinforcement. Any portion of the reinforcement could be anchored in a similar manner by covering an anchoring plate appropriately fixed to the structure by means of connectors. Generally -7speaking, the reinforcing method roposed by the invention offers an advantage in that it can be used with very different types of reinforced surface.

In the embodiments illustrated in figures 6 to 14, the anchoring plate onto which the end of the composite reinforcement 16 is bonded is not anchored directly to the concrete. An anchoring support 30, 40, 60 (not shown in the example illustrated in figures 11 and 12) is fixed into each recess, formed in the concrete structure beforehand, by means of connecting members 18, for example, similar to those described above. This anchoring support 30, 40, is provided with a seating 31, 41, 61 which is open toward the exterior of the structure and designed to receive the anchoring plate 32, 42, 62.

In service, a locking system secures the anchoring plate 32, 42, 52, 62 in its seating 31, 41, 61, so as to maintain a pre-stressing force in the composite reinforcement 16 along the main direction A.

In the embodiment illustrated in figures 6 to 8, the support 30 and the 15 anchoring plate 32 are provided with orifices 33, 34 opening at the exterior face Sof the structure, designed to receive a system for placing the strip 16 under tension. The tensioning system may comprise one or more telescopic jacks having one end connected to the orifices 33 and an opposite end connected to the orifice 34. When energised, these jacks tension the strip 16, the end of which is bonded to the anchoring plate 32 beforehand, by sliding the plate 32 within the seating 31. A wedge 35 is then located in the seating 31 in order to o• *.*firmly hold the anchoring plate 32 during and after setting of the bonding substance applied to the surface of the concrete.

In the example illustrated, the side edges of the seating 31 have two S.i 25 respective longitudinal grooves 36A, 36B formed in the thickness of the anchoring support 30, one 36A receiving a matching ridge 37A provided on a side edge of the anchoring plate 32 and the other 36B receiving a matching ridge 37B provided on the side edge opposite the wedge 35. The plate 32 and the wedge 35 are in reciprocal contact along a surface 38 parallel with the direction A and inclined relative to the surface of the structure so that the wedge 35 prevents the plate 32 from coming out of its seating 31. Furthermore, the wedge 35 bears on the support 30 along a ramp 39 subtending an angle with the direction A, so that when the tensioning system is energised, the wedge 35 simply has to be pushed within the seating 31 in the direction of the strip of fabric 16 to lock the plate 32 in the seating 31, which maintains the prestressing force in the strip 16 during and after setting of the bonding substance.

-8- Figures 9 et 10 illustrate a different embodiment in which the side edges of the anchoring plate 42 are provided with respective ridges 47 cooperating with matching grooves 46 provided in the side edges of the seating 41. The grooves 46 are interrupted at a front part 43 of the seating 41, across a length at least equal to that of the plate 42. In this front part 43, the seating 41 is wider than the anchoring plate 42 to allow it to be inserted. The plate 42 can then slide rearwards when the composite reinforcement is tensioned, being guided and held in place by the grooves 46. Two wedges 44, 45 may be used for tensioning purposes, being inserted in the front part 43 of the seating 41, bearing one against the other along an oblique surface, the wedge 44 being applied against the front edge of the plate 42 and the wedge 45 being applied against the front edge of the seating 41. The composite reinforcement, bonded onto-the anchoring plate 42 beforehand, is tensioned by pushing the wedges, ~44, 45 one against the other, as indicated by the arrows P in figure 9.

15 In the embodiment illustrated in figures 11 and 12, the anchoring plate 52 has a slot 53 perpendicular to the direction A, slightly longer than the width °of the strip of fabric 16. The strip 16 is inserted into the slot 53 and wound around the portion 54 of the plate 52 located in front of the slot 53, before being C "bonded onto this portion 54. This increases the strength of the connection 20 between the reinforcement 16 and the anchoring plate 52. Once this connection has been made, the plate 52 can be fitted on an anchoring support, previously fastened in the concrete surface to be reinforced. This anchoring o support may be of the same type as those described above with reference to figures 6 to 10, for example.

25 In the embodiment illustrated in figures 13 et 14, the anchoring plate 62 also has a slot 63 perpendicular to the direction A. References 62A and 62B denote respectively the portions of the plate 62 located to the front and rear of the slot 63. In this embodiment, the strip of fabric 16 is wound in an S shape around the two portions 62A, 62B of the anchoring plate 62, as illustrated in figure 13. The end of the strip 16 is applied to the external face of the rear portion 62B, from where the strip 16 is turned around the rear edge of the plate 62 along the internal face of the portion 62B, passed through the slot 63 along the external face of the portion 62A, turned around the front edge of the plate 62, along the internal face of portions 62A and 62B, turned back around the rear edge of the plate 62 and then back along the external face of portions 62B and 62A before being brought into contact with the concrete face to be -9reinforced.

This S-winding ensures that the strip 16 is firmly secured onto the anchoring plate 62 so that the strip 16 can be bonded onto the anchoring plate 62 at the same time as the strip is bonded to the concrete face. In addition, the strip of fabric 16 can be tensioned by applying the front edge of the plate 62 against the front edge 61 of the seating 61 provided in the anchoring support and folding back the rear edge of the plate 62 as illustrated by the dotteddashed lines in figure 13. Once tensioned, the plate 62 is immobilised in its seating 61, for example by screwing it to the support 60 through orifices 64 provided in the anchoring plate 62 on either side of the strip 16. As illustrated in figure 14, so as not to damage the fabric 16, the front edge of the anchoring plate 62 does not bear against the front edge of the seating 61 except on either side-of the width of the strip 16.

a

Claims

1. A device for reinforcing a concrete structure, comprising a reinforcement bonded onto the structural concrete and means for anchoring at least one portion of the reinforcement to the structure, the reinforcement comprising reinforcing fibres extending in at least one main direction characterised in that the anchoring means comprise at least one anchoring plate fixed to the structural concrete in a position such that an extemrnal surface of the anchoring plate is flush with a surface of the structure receiving the reinforcement and in that said portion of the reinforcement is bonded onto the external surface of the anchoring plate. *oe

2. A device as claimed in claim 1, wherein the reinforcement covers the ~extemrnal surface of the anchoring plate across a length of at least S•measured parallel with the main direction

3. A device as claimed in claim 1 or 2, wherein the anchoring plate has a 15 shear strength higher than 1.5 MPa. al

4. A device as claimed in claim 3, wherein the anchoring plate is made from S•steel with a thickness of at least A device as claimed in any one of claims 1 to 4, wherein the external surface of the anchoring plate has supporting means for a system of tensioning the 20 reinforcement in the main direction

6. A device as claimed in any one of claims 1 to 5, wherein the reinforcement is retained between the anchoring plate and a second plate, said plates being fixed to the concrete by common connecting members.

7. A device as claimed in any one of the preceding claims, comprising means to maintain a tension in the reinforcement parallel with the main direction

8. A device as claimed in claim 7, wherein the means for maintaining a tension in the reinforcement parallel with the main direction comprise a system for locking the anchoring plate in a seating provided in an anchoring support -11- secured to the concrete.

9. A device as claimed in claim 8, wherein the locking system comprises at least one wedge member arranged between the anchoring support and the anchoring plate so as to withstand the tension exerted in the reinforcement. A device as claimed in claim 8 or 9, wherein the anchoring plate has a slot substantially perpendicular to the main direction and wherein the reinforcement is provided in the form of a strip having an end portion wound around the anchoring plate and passing through said slot.

11. A method of reinforcing a concrete structure, comprising the steps of: forming at least one recess on a surface of the structure; bonding a reinforcement comprising reinforcing fibres onto said surface of oooo *the structure, at least some of the reinforcing fibres being aligned along a main direction of said surface of the structure, the reinforcement being arranged so that at least one portion thereof is bonded to an extemrnal surface of an anchoring plate fixed in a recess so that the extemrnal surface of the anchoring plate is flush with said surface of the structure. go

12. A method as claimed in claim 11, wherein an anchoring plate is fixed in each recess by means of connecting members before bonding the reinforcement. 20 13. A method as claimed in claim 12, comprising placing the reinforcement between the anchoring plate and a second plate secured by means of the connecting members.

14. A method as claimed in claim 13, comprising exerting a stress on the connecting members in order to clamp the second plate against the reinforcement and the anchoring plate. A method as claimed in any one of claims 11 to 14, comprising arranging the reinforcement so that it covers the external surface of the anchoring plate across a length of at least 10cm measured parallel with the main direction 12-

16. A method as claimed in any one of claims 11 to 15, comprising arranging the reinforcement so that it is interrupted, parallel with the main direction on the extemrnal surface of the anchoring plate.

17. A method as claimed in any one of claims 11 to 16, comprising tensioning the reinforcement while the reinforcement is being bonded onto said surface of the structure.

18. A method as claimed in claim 17, wherein the tensioning is applied by means of a system mounted on the anchoring plate. 10 19. A method as claimed in claim 17 or 18, comprising fixing an anchoring ooo° support in the recess provided on said surface of the structure, and locking the anchoring plate in a seating provided in said anchoring support in order to maintain the tension applied when the reinforcement is being bonded to said surface of the •structure. 15 20. A method as claimed in any one of claims 17 to 19, wherein the ooo* reinforcement is bonded onto said surface of the structure after said portion has been bonded to the anchoring plate, the reinforcement being tensioned by traction .o applied to the anchoring plate.

21. A method as claimed in any one of claims 17 to 19, comprising bonding 20 the reinforcement onto said surface of the structure at the same time as said portion is bonded to the anchoring plate.

22. A device for reinforcing a concrete structure substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings. Dated this 28th day of February 2000 FREYSSINET INTERNATIONAL STUP By their Patent Attorneys COLLISON CO.