AU651026B2

AU651026B2 - Anchoring device for a bundle of fibrous bars

Info

Publication number: AU651026B2
Application number: AU31987/93A
Authority: AU
Inventors: Bruno Renoud-Lias; Roland Stenne
Original assignee: SIF ENTREPRISE
Current assignee: Sondages Injections Forages SIF Enterprise Bachy
Priority date: 1992-01-31
Filing date: 1993-01-25
Publication date: 1994-07-07
Anticipated expiration: 2013-01-25
Also published as: EP0554161A1; FR2686916A1; AU3198793A

Description

AUSTRALIA

Patents Act 61, :3" 026 COMPLETE SPECIFICATION

(ORIGINAL)

Class Int. Class Application Number: Lodged: Complete Specification Lodged: Accepted: Published: Priority Related Art: S Name of Applicant: Sondages Injections Forages "SIF" Entreprise Bachy Actual Inventor(s): ~lr Bruno Renoud-Lias Roland Stenne Address for Service: o*n Invention Title: PHILLIPS ORMONDE FITZPATRICK Patent and Trade Mark Attorneys 367 Collins Street Melbourne 3000 AUSTRALIA ANCHORING DEVICE FOR A BUNDLE OF FIBROUS BARS Our Ref 316951 POF Code: 1149/52667 The following statement is a full description of this invention, including the best method of performing it known to applicant(s): -1- 6006 The invention relates to a device for anchoring a bundle of bars formed from substantially parallel fibres bound by a synthetic resin.

Bars formed from substantially parallel glass fibres bound by a synthetic resin, such as an epoxy resin, are well known. It is often necessary for applications involving large loads to have recourse to a bundle of several bars. For this purpose, it is necessary to anchor the ends of the bars to terminal elements which serve to fix the ends of the bundle of bars in the intended application. However, on account of their highly ,o oanisotropic nature, these bars pose a problem of fixing at their ends. The known anchoring system, consisting in setting the ends of the bars into a hollow cylindrical 15 metal sleeve, then in casting a mass of resin, possibly *J:o -filled or reinforced, into the sleeve so that it embeds the ends of the bars, is not entirely satisfactory as, in such a system, the anchoring of each bar in the mass of resin is ensured by pure adhesion. This limits the 20 usefulness of this anchoring system to bars of small diameter and relatively low mechanical strength.

A known improvement to this system consists in using a metal sleeve, the internal part of which is no longer cylindrical but has the shape of a truncated cone 0 25 or of a plurality of successive truncated cones, so as to create a "wedge" effect generating compressive forces normal to the bars when the bundle of bars is under tension, these normal compressive forces increasing as the tension applied to the bars increases. However, taking into account the deformation characteristics of the resin, which is possibly filled or reinforced, compared to those of the bars, the said compressive forces induce an axial elongation of the cast resin, which, in turn, causes tensile overloads in the bars. This phenomenon limits the effectiveness of the anchoring.

In order to avoid excessive tensile overloads prejudicial to the bars, EP-A-0,025,856 and US-A-4,448,002

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2 have proposed limiting the clamping force on the bars by providing a compressible element between the mass of resin embedding the bars and a closure plate solidly joined to the sleeve, this compressible element limiting the axial elongation of the mass of resin, as, for example, Figure 9 of these prior patents shows. According to an embodiment illustrated by Figures 11 and 12, the bars, instead of Sbeing directly embedded by the mass of resin, are housed in metal sheaths having longitudinal slits. According to another embodiment illustrated in Figure 16, the mass of resin embedding the bars is divided into a cylindrical *:to central part butting up against the closure plate, and a ot peripheral part forming a wedge and butting up against the compressible element, a cylindrical element made from thin 15 metal, for example steel, provided with longitudinal slits, being interspersed between these two parts in order to make it easier for the peripheral part to slide with respect to the central part. Furthermore, the bars located in the peripheral part are not extended in the same manner as the bars of the central part.

Although the anchoring described in EP-A-0,025,865 and US-A-4,448,002 is interesting on paper, its practical realisation poses a problem as regards the choice of the compressible element. If this is too compressible, the clamping force on the bars will be excessive and, if not compressible enough, the clamping force will be too limited, with the result that the anchoring has a low effectiveness. Moreover, EP-A-0,025, 856 and US-A-4,448, 002 gives practically no indications on the manner of calculating the compressible element.

Finally, it should be pointed out that the prior anchoring device is rather complex to realise, hence a rather high anticipated cost.

There is therefore a need for a device for anchoring a bundle of fibrous bars which ensures an improved binding between the bars and the terminal sleeve, whilst being simple to realise and inexpensive.

The invention aims to form just such an improved anchoring device.

The anchoring device of the invention, contrary to the devices which are des,-ibed by EP-A-0,025,856 and US- A-4,448,002, is not base- on a limitation of the clamping force by use of a compressible stop, but on a limitation of the axial elongation of the mass of resin under the compressive forces, by virtue of the incorporation of one or more reinforcing elements bound to the mass of resin.

More precisely, the invention relates to a device for anchoring a bundle of bars formed from substantially parallel fibres bound by a synthetic resin, which comprises a metal sleeve surrounding the end of the bundle S* and a mass of resin, possibly reinforced or filled, cast S 15 into the said sleeve and solidly joining the bars together and to the sleeve, the internal surface of the sleeve forming at least one truncated cone, the cross-section of which decreases in the direction of the tensile force to which the said bundle will be subjected in service, S 20 characterised in that it comprises, furthermore, reinforcing elements extending inside the sleeve, substantially parallel to the bars, these elements being constituted by a material having a tensile modulus greater than that of the bars and being bound to the bars and to the sleeve by the said mass of resin.

According to one embodiment, the reinforcing elements consist of a central cylindrical core and the bars are arranged in an annular space made between the said core and the sleeve. The central core may be solid or provided with a central bore.

According to another embodiment, the reinforcing elements consist of a plurality of rods distributed, in the sleeve, between the bars.

According to yet another embodiment, the reinforcing elements consist of a plurality of rods arranged between the bars and the sleeve.

Any combination of the previously described te t 44 it #44 embodiments may be envisaged.

It should be noted that the sleeve used in the present device comprises neither a base plate nor a plate forming a stop intended to receive or support all or part of the tensile force applied to the bars. However, it is not excluded for the sleeve to be able to comprise a terminal wall of low mechanical strength, the purpose of which would simply be to act as a mould during the filling of the sleeve with the resin when casting the latter.

The anchoring device of the invention may be used for bars formed from glass fibres, aramid fibres (Kevlar fibres, for example), carbon fibres, etc.

The synthetic resin cast into the sleeve may be, for example, an epoxy resin possibly filled or reinforced 15 with glass fibres or the like.

The reinforcing elements are normally made of steel, but the use of any material having a tensile modulus greater than that of the bars may be envisaged.

The description which will follow, made with reference to the attached drawings, will make the invention well understood. In the drawings: Figures 1 and 2 are longitudinal and transverse sectional views, respectively, of an anchoring device according to the invention; 25 Figures 3 and 4 are longitudinal and transverse sectional views, respectively, of another anchoring device according to the invention, and Figures 5 and 6 are longitudinal and transverse sectional views, respectively, of yet another anchoring device according to the invention.

The anchoring device, illustrated by Figures 1 and 2, is constituted by a central cylindrical core 1, which may be solid or hollow, acting as reinforcing elements, and by a sleeve 2, open at its two ends, the profile of the internal surface 3 of which is formed from three successive truncated cones 4. The internal diameter of the sleeve 2 is greater than the external diameter of the core

A

I 4 449 4 1 so as to make, between them, an annular space 5 into which the bars 6 of the bundle of bars to be anchored are inserted. The bars 6 are bound together, to the core and to the sleeve, by a solid mass 7 of epoxy resin for example, possibly filled or reinforced with glass fibres, thermally cured, obtained by casting, into the annular space 5 between the bars 6, of a thermosetting epoxy resin composition for example, possibly filled or reinforced with glass fibres.

Figures 3 and 4 show another embodiment of the anchoring device of the invention. In this mode, the bundle of bars 6 is inserted into the sleeve 2, but the core 1 is omitted and replaced by a plurality of metal rods 8, for example made from steel, acting as reinforcing elements, which rods are distributed between the bars, parallel to them. Here too, a solid mass 7 of epoxy resin, for example, possibly filled or reinforced with glass fibres, is used in order to bind the bars and the rods 8 It together and to the sleeve.

Figures 5 and 6 illustrate yet another embodiment of the anchoring device of the invention. In this embodiment, the bars 6 of the bundle are arranged in the central space defined by the sleeve 2 as in the previous embodiment, but the metal reinforcing rods 8, instead of being distributed between the bars, are arranged between the bundle of bars and the sl-eve.

The presence of the reinforcing elements considerably improves the mechanical strength of the bundle of bars. The results of comparative tensile tests carried out between a bundle of bars anchored in an anchoring device in accordance with the embodiment illustrated by Figures 1 and 2 and a bundle of bars anchored in an anchoring device of the prior art, constituted by a single frustoconical sleeve, are presented hereinbelow. In both cases, the thermosetting resin cast into the sleeve in order to bind the bars was an Araldite CW2418 epoxy resin with a metal filler. Each r ww I 6

II

bundle comprises 19 bars made from glass fibres, each bar having a diameter of 10.7 mm. The instantaneous rupture p load of each bar was 125 kN and the instantaneous rupture load of the bundle was therefore 19 x 125 kN, that is 2375 I 5 kN. The table below summarises the test conditions and the results obtained.

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~1;7 -r~;Idi~R;~AtJr~_-m~~*UL COMPARATIVE TABLE Test comparative according to the invention Anchoring head: sleeve type having a single cone having 3 successive cones external diameter (mm) 180 160 internal diameter (mm) 115/157 98/115 total length (mm) 300 300 Arrangement of the bars Distribution of the Distribution of bars in bars in the mass a ring around a 1 central bar cylindrical 6 bars on a 50 mm diameter central core of a 72 mm 12 bars on a 96 mm diameter diameter Type of loading Loading by successive levels instantaneous rupture load.

approximately 30 minutes.

of approximately 10% of the Each level is held for Maximum load reached 1320 kN 1970 kN Type of rupture Rupture of the bars Rupture of the bars approximately 20 mm inside outside of the head the anchoring head

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U il--~i i i -1 II r L- i ~I 8 It may be seen that the anchoring device of the invention enables the supportable load to be considerably increased.

It should be pointed out that, on account of the viscoelastic behaviour of the bars, the instantaneous rupture load cannot be reached with the type of loading adopted for the tests.

The anchoring device of the invention is especially useful in applications where prestressing of bundles of fibre-based bars is required, for example, in the civil engineering field, for producing anchoring ties, for producing suspension-bridge stays, etc.

It goes without saying that the embodiments described may be modified, especially by substituting 15 equivalent technical means, without departing thereby from .the scope of the invention.

Claims

3. A device according to claim 1 wherein the reinforcing elements are composed of a plurality of rods distributed, in the sleeve, between the bars. 4 A device according to claim 1, wherein the 25 reinforcing elements are composed of a plurality of rods arranged between the bars and the sleeve. A device according to any one of claims 1 to 4, wherein the reinforcing elements are made of steel.
6. A device according to any one of claims 1 to wherein the bars are formed from glass fibres bound by a polymeric binding resin.
7. A device for anchoring a bundle of bars substantially as hereinbefore described with respect to any one of the embodiments illustrated in the accompanying drawings. DATED 22 APRIL 1994 PHILLIPS ORMONDE FITZPATRICK Attorneys For: SONDAGES INJECTIONS FORAGES "SIF" ENTREPRISE BACHY 77831 L- I I- 11 Device for anchoring a bundle of fibrous bars. Inventors: Bruno RENOUD-LIAS Roland STENNE i- Company called: SONDAGES INJECTIONS FORAGES ENTREPRISE BACHY 0* ABSTRACT o The invention relates to a device for anchoring a bundle of bars formed from substantially parallel fibres bound by a synthetic resin, which comprises a metal Ssleeve surrounding the end of the bundle and a mass of resin, possibly filled or reinforced, cast into the said sleeve and solidly joining the bars to the sleeve, the internal surface of the sleeve forming at least one truncated cone the cross-section of which decreases in the direction of the tensile force to which the said bundle will be subjected in service, characterised in that it comprises, furthermore, reinforcing elements 8) extending inside the sleeve, substantially parallel to the bars, which elements are constituted by a material having a tensile modulus greater than that of the bars. Application to the production of anchoring ties, as stays for suspension bridges, etc. FIGURE 1' F9l 3,gLi~ I: "Vr,