WO2006021152A1

WO2006021152A1 - Wrap-around centraliser for a reinforcing bar

Info

Publication number: WO2006021152A1
Application number: PCT/CN2005/001322
Authority: WO
Inventors: Noriman Sai Chi Mak; Ngai Leung Ho
Original assignee: Hong Kong Fiberglass Technology Limited; Ove Arup & Partners Hong Kong
Priority date: 2004-08-25
Filing date: 2005-08-24
Publication date: 2006-03-02

Abstract

A centraliser for wrap-around attachment to a reinforcing bar, includes a flexible open sheath having one face for bearing against an outside surface of a reinforcing bar an opposed face having a number of spaced apart lengthwise fins projecting from it. The centraliser includes a retainer by which it cam be fixed closed around a reinforcing bar in such manner that the fins radiate outwardly from the sheath in use.

Description

Wrap-around Centraliser for a Reinforcing Bar

Background of the Invention

The present invention relates to the centralisation of reinforcing bars (also known as retaining rods or anchor rods) in drilled boreholes. Such reinforcing bars might be used to stabilise landslip areas, or to back-anchor retaining walls for example. Such bars might also be used in the underground mining industry in retaining mine roofs for example.

More particularly, although not exclusively, the invention relates to a wrap-around centraliser for attachment around a reinforcing bar to maintain the bar centralised within a borehole so that cementacious grout can be injected along the borehole to evenly surround the bar and pass by the centraliser with minimal hindrance to grout flow being caused by the centraliser.

It is known to centralise reinforcing bars in pre- drilled boreholes in soil and/or rock using centralisers that slide upon the bar from one end of the bar to a desired longitudinal position thereon. Such centralisers are formed somewhat like an old- fashioned Chinese paper lantern having radially expanded longitudinal arches. Such centralisers have been known to be formed from a short length of PVC pipe having a plurality of longitudinal slots cut therein to define separated longitudinal strips of PVC material that are deformed outwardly under heat to form the arches.

The above type of centraliser presents a number of significant problems. Firstly, in order to position the centraliser upon the reinforcing bar, the centraliser must be slid along the bar from one end. Secondly, small stones and other debris can become lodged underneath the arches and against the surface of the bar thereby forming an obstacle to the flow of grout lengthwise past the bar in situ in the borehole,

As a result, grout that is injected into the borehole around the bar does not fill the entire annular cavity. A third problem is in achieving and/or maintaining a firm grip between the centraliser and the bar. The centralisers have a fixed internal diameter, yet the bars can vary slightly in diameter and sometimes it is necessary to tighten the centraliser down upon the bar by makeshift methods. Another problem with the known centralisers is in their inability to be packaged densely for transportation purposes. Moreover, the large volume of each centraliser and their inability to be reconfigured or folded flat means that large shipping cartons can contain only a very limited number of centralisers.

Objects of the Invention

It is the object of the present invention to overcome or substantially ameliorate at least one of the above disadvantages and/or more generally to provide an improved centraliser for a reinforcing bar.

Disclosure of the Invention

There is disclosed herein a centraliser for wrap¬ around attachment to a reinforcing bar, comprising: a flexible open sheath having a first face for bearing against an outside surface of a reinforcing bar and a second opposed face having a plurality of spaced apart lengthwise fins extending therefrom, and a retainer by which the sheath can be fixed closed around a reinforcing bar in such manner that the fins radiate outwardly therefrom in use.

Preferably, the retainer comprises a tiedown strap - A -

extending from the sheath and a clamp upon the sheath to which the strap attaches.

Preferably, the strap has a plurality of serrations therealong and the clamp comprises an aperture through which the serrations can pass in one direction only.

Preferably, the fins have opposed ends that taper in toward the sheath.

Preferably, the sheath comprises a plurality of apertures situated between the fins.

Preferably, the fins are hollow and comprise a plurality of internal strengthening ribs.

Preferably, the centraliser further comprises a pair of segmented in the from the the rails along the first face of the sheath for bearing frictionally against the reinforcing bar in use.

Brief Description of the Drawings

A preferred form of the present invention will now be described by way of example with reference to the accompanying drawings, wherein: Fig. 1 is a schematic perspective illustration of a wrap-around centraliser closed around a reinforcing bar,

Fig. 2 is a schematic perspective illustration of the wrap-around centraliser of Fig. 1 in an open configuration prior to installation,

Fig. 3 is a schematic perspective illustration of the rap-around centraliser in a closed configuration, but not mounted upon a reinforcing bar -- the figure being included for illustration purposes only,

Fig. 4 is a schematic perspective illustration of the centraliser in the configurations of Fig. 2 showing the back of the centraliser, and

Fig. 5 is a schematic side elevation of the centraliser in the configurations of Figs. 2 and 4.

Description of the Preferred Embodiment

In Fig. 1 of the accompanying drawings there is depicted schematically a centraliser 10 wrapped around a reinforcing bar R. The reinforcing bar B is typically formed of glass fibre-reinforced resinous plastics material, but might alternatively be of any suitable material such as steel bar, depending upon application. The anchor is to be installed in a pre- drilled borehole having a diameter somewhat larger than that of the reinforcing bar itself.

The centraliser 10 is formed of moulded plastics material and comprises a sheath 16 from which there extend six fins 11. The sheath includes a number of apertures 17 in between the fins 11. Each fin 11 comprises a tapered end portion 19 extending down to the sheath's upper surface. This facilitates easy insertion of the bar [with the centraliser(s) installed thereon] into the borehole with minimal disruption to the borehole. Each fin is typically hollow in form -- open at the base and comprising a plurality of internal strengthening ribs 18 (Fig. 4) .

From each end of the sheath, there extends a tiedown 12. The sheath also includes a pair of clamps 14 positioned opposite each tiedown 12. The tiedowns and clamps together with the end portions of the sheath 16 can be likened to a cable tie. That is, each strap 12 comprises an array of serrations 13, and located within the aperture 18 of each clamp 14 there are serrations also. These serrations are configured to enable easy insertion of the strap 12 through the aperture 18, but prevent withdrawal of the strap 12 from the clamp 14 in the opposite direction.

Two segmented positioning rails 20 extend along the back face of the sheath at its end portions and in parallel aligned disposition with respect to the tiedown straps. The rail segments are located directly behind each fin and bear against the reinforcing bar B in use and provide friction against the reinforcing bar to assist in preventing the centraliser from sliding along the bar within the borehole.

In use, the centraliser 10 is wrapped around the bar B and the tiedowns 12 are pulled through the clamps 14 to tightly secure the centraliser in place upon the bar.

The outer extremities of the fins 11 approximate the borehole diameter of a pre-drilled borehole into which the bar is to be inserted. One or more centralisers can be spaced along the bar. The bar is inserted into the borehole and then cementacious grout is injected down the annulus defined between the borehole and the bar. The grout can flow smoothly along either side of the fins 11 to completely surround and encase the bar within the borehole. The centraliser presents no pockets or voids to the flow of grout into which debris or soil can be trapped. Such pockets (as is the case in the acknowledged prior art) would hinder the smooth flow of grout to thereby prevent proper encasement of the reinforcing bar.

A further advantage of the instant invention is that the centralisers can be packed densely for transportation purposes. To this end, the centralisers in the configuration depicted in Figs. 2 and 4 can be nested within one another with the fins of one centraliser fitting into the spaces provided between the fins of another (upside down) centraliser,

It should be appreciated that modifications and alterations obvious to those skilled in the art are not to be considered as beyond the scope of the present invention. For example, instead of forming cable tie-like retainers integrally upon the centraliser, metallic screw-down hose clamps might be placed around flat end portions of the sheath. Such end portions might even be provided with grooves to accommodate such clamps.

Claims

CIiAIMS ;

1. A centraliser for wrap-around attachment to a reinforcing bar, comprising: a flexible open sheath having a first face for bearing against an outside surface of a reinforcing bar and a second opposed face having a plurality of spaced apart lengthwise fins extending therefrom, and a retainer by which the sheath can be fixed closed around a reinforcing bar in such manner that the fins radiate outwardly therefrom in use.

2. The centraliser of Claim 1, wherein the retainer comprises a tiedown strap extending from the sheath and a clamp upon the sheath to which the strap attaches.

3. The centraliser of Claim 2, wherein the strap has a plurality of serrations therealong and the clamp comprises an aperture through which the serrations can pass in one direction only.

4. The centraliser of Claim 1, wherein the fins have opposed ends that taper in toward the sheath.

5. The centraliser of Claim 1, wherein the sheath comprises a plurality of apertures situated between the fins.

6. The centraliser of Claim 1, wherein the fins are hollow and comprise a plurality of internal strengthening ribs.

7. The centraliser of Claim 1, further comprising a pair of segmented rails along the first face of the sheath for bearing frictionally against the reinforcing bar in use.