BACKGROUND OF THE INVENTION Mobile phone services and other telecommunication services are often carried on towers of a particular construction. These towers are currently approaching the limit of their capability to be further loaded by other antenna structures while maintaining the service within required limits. For example, the antennae for mobile phone transmissions are required to maintain less than a one degree tilt in order for the service to be properly receivable or for a transmission to carry without substantial loss between successive relay towers.

Poles, masts and towers for carrying telecommunications or similar equipment are constructed of a variety of different materials and forms.

A particularly widely used and versatile type of such structure is the spun, prestressed concrete pole, hereafter called a concrete monopole. These are manufactured in a variety of sizes and types to suit a wide range of height and strength requirements.

The poles are manufactured in lengths suitable for transportation with longer poles comprising two or more lengths joined together by bolted joints. Installation normally involves concreting the base section of the pole into a pre-drilled hole in the ground with the required height of the pole protruding above ground. The various pieces of equipment are then attached to the pole i. e. mounts, antennas, cable trays etc.

Due to changing demands and other such factors, owners or users of concrete monopoles at times find the need to increase the type, size or amount of equipment

which is to be carried on an existing pole. The existing pole may or may not have spare structural capacity to cope with the additional requirements.

Where the structural capacity of the pole in question is inadequate for the new requirements then current practice is to remove the existing pole and replace it with a new, larger capacity pole.

This is not only very expensive but also has a very disruptive effect on existing pole users including partial or even complete loss of service while the new installation is taking place. Other problems associated with this solution include requirements for council approval; possible landowner approval of the new installation; the possible need to acquire more land for installation of the new pole in a location clear of the existing pole on restricted sites and/or demolition and disposal of the redundant, existing pole.

SUMMARY OF THE INVENTION The present invention relates to a method whereby the strength and rigidity of a pole may be increased in situ to allow greater carrying capacity, that is, greater weight of equipment upon the existing structure. The present invention involves the alteration of a pole in situ whereby it may be upgraded to carry more antennae without substantially disrupting the local community or the telecommunication services provided by the pole. The present invention enables the strength of a pole to be increased by up to 50% thereby increasing the carrying capacity of the pole by a similar level.

It is thus the object of the present invention to provide a means of strengthening the existing pole installation without the need for removal and replacement while not causing damage or interference to the structural integrity of the existing pole and not causing disruption or loss of service to the present pole user (s).

In accordance with the present invention a strengthened pole can be achieved which meets all the requirements and is superior to any other options by affixing fibre

composite strips to the pole in conjunction with a reinforced concrete collar at the base.

According to one aspect of the invention there is provided a method of strengthening an existing pole, said pole having a root and a trunk, the trunk ascending above ground and the root descending below ground, said method including: fixing a plurality of reinforcing fibre strips about said trunk, each strip extending from at least the ground to a given height, said given height being in the range of substantially 30- 50% of the height of the trunk, and fixing a reinforced collar at at least the interface between the trunk and the root. Preferably, the reinforcing fibre strips are carbon fibre composite strips. Preferably the reinforced collar extends above ground to a height necessary to provide the required stiffening of the pole and to anchor the strips.

In a first embodiment of the invention, the particular pole to be strengthened consists of one section having a uniform taper along its length. The fibre composite strips are applied along its length from ground level up to a height and in number, spaced around the poles'circumference, to achieve a given increase in strength. In conjunction with this a reinforced concrete collar is constructed at ground level of a height and plan dimension to provide a required stiffness and fixity at the pole base foundation to suit the strengthened pole and also to provide an anchorage zone for the fibre composite strips.

According to a further aspect of the invention there is provided a method of strengthening an existing pole, said pole having a root and a trunk, the trunk ascending above ground and the root descending below ground, the trunk having at least a first and a second section joined at joining means, the method including smoothing the trunk at said joining means to provide a transitional pole surface between said first and said second sections, fixing a plurality of reinforcing fibre strips about said trunk, each strip extending from at least the ground to a given height, said given height extending to at least greater than the height of said joining means, said height being in the range of substantially 30-50% of the height of the trunk, and fixing a reinforced collar at at least the interface between the trunk and the root. Preferably, the reinforcing fibre

strips are carbon fibre composite strips. Preferably the reinforced collar extends above ground to a height to provide the required stiffening of the pole and to anchor the strips.

Where the sections are of matching taper the transitional zone is also formed of the same taper. Where the sections are of dissimilar taper, producing a step at the joining means, the transitional zone is tapered so as to join the respective tapers of the sections and reinforcing carbon fibre composite strips may be added in a circumferential direction, at each change of direction of the taper.

In a second embodiment of the invention, the particular pole to be strengthened consists of two or more sections coupled together by bolted or similar connections consisting of lugs, studs, connecting plates or similar mechanisms. The overall pole has a uniform taper along its length. The application of the fibre composite strips and the construction of the concrete collar remain the same as for the first embodiment but additional treatment is required at the connection zone (s). This consists of infilling any voids around bolts, connecting plates and the like with a suitable high strength mortar or similar to match the adjoining pole surfaces. This enables the subsequent application of the fibre composite strips in the required uniform manner up the pole.

In a third embodiment of the invention, the particular pole to be strengthened consists of two or more sections coupled together as was the case for the second embodiment but with one or more of the connections involving a stepped or abruptly tapered cross sectional transition i. e. the pole no longer has a uniform taper along its length. The application of the fibre composite strips, the construction of the concrete collar and the infilling at the standard connection points remain the same as for the second embodiment but additional treatment is applied to the transition zone (s). This consists of forming a maximum 1: 10 tapered transition using high strength patching mortar in this zone prior to applying the longitudinal fibre composite strips. After the longitudinal fibre composite strips are installed two layers of fibre composite strip are applied around the circumference of the pole at each change of direction of taper at each transition zone.

While this invention will mainly be applied to conventional pole installations with poles supported by burying a significant proportion of its length under the ground and poles being of tapered, hollow, circular cross section manufactured in spun, prestressed and reinforced concrete it can be applied equally to variants of the above within the knowledge of a person skilled in the art. These could include poles attached to a separate foundation, solid poles, reinforced concrete only poles, poles of non- circular cross section, non-tapered poles, stepped poles and combinations of such variants.

Fibre composite strips manufactured by Sika Pty Ltd called the CarboDur (registered trade mark) system can be used for the reinforcing fibre strips. Other carbon fibre systems or products may also be used. The application of the fibre composite strips usually involves between 4 and 16 fibre composite strips equally spaced around the pole circumference depending on the increase in strength required and any constraints to strip placement as a result of attachments, cut-outs and similar items on the existing pole. Fibre composite strips are generally spaced to miss obstructions and some localized shifts in position of individual fibre composite strips can be made to assist in avoiding obstructions without substantially adversely affecting the relevant stiffening.

According to yet a further aspect of the invention there is provided a pole having a root and trunk, said root extending below ground and said trunk extending above ground, said trunk further having a treated surface to which is affixed a plurality of reinforcing strips about said trunk, each strip extending to a given height, said height being in the range of 30-50% of the height of said trunk, and further including a base about said trunk at said ground. Preferably, said strips are carbon fibre composite strips and said base is of reinforced concrete. The trunk may be continuous or made up of a number of joined sections. The transition at each join is made smooth by infill with a patching mortar with said strips affixed thereover.

Fibre composite strips are manufactured in a variety of widths (commonly around 100mm), thicknesses (commonly 1.2mm) and compositions which allow different

requirements for strength and elastic modulus to be accommodated for a particular pole requiring strengthening. Fibre composite strips are not restricted in what lengths they can be applied. The maximum height of strips required above ground level is usually around 10-13 metres for a pole of height 25-30 metres. This is normally the most stressed zone and hence the region requiring strengthening but this can vary according to the particular pole. In some instances it may not be necessary to continue all the strips to the same height to achieve the necessary strength as there is a progressive diminution of bending moment with increased height up the pole.

The application of the invention requires a knowledge of the existing poles'design and construction i. e. the dimensions, the concrete strength, the quantity and layout of any steel reinforcement and any prestressing strands. With this information a new stronger pole section can be made by adding the fibre composite strips as additional tensile reinforcement to the surface of the pole which then allows the pole to be analyzed as a new composite section with enhanced strength characteristics. In conjunction with a stronger and more highly loaded pole the existing foundation requires stiffening and strengthening. The design of the reinforced concrete base collar achieves this by increasing and changing the application of the increased foundation loading, increasing the pole stiffness by a large increase in effective pole cross section within the depth of the collar, which is especially required to limit pole tip deflection as well as providing an anchorage zone for the strips so that the loads in them can be effectively transferred.

While this invention is particularly designed around using a reinforced concrete stiffening collar constructed above ground, square in plan and up to approximately 1.5 metres in height this applies equally to collars or similar stiffening mechanisms cast below ground, non-square collars and other variants within the knowledge of a person skilled in the art.

The application of the strips to a pole is carried out to the manufacturer's recommendations and involves a number of steps. Firstly, the concrete pole surface which is to receive the strips has to be suitably roughened by scabbling or similar

technique and the resulting surface thoroughly cleaned. The fibre composite strips are then bonded to this prepared substrate using an epoxy adhesive paste specifically formulated by the manufacturer for this purpose, typically Sikadur-30. The epoxy is applied to both the substrate and the strip to the recommended thickness of approximately lmm and 2mm respectively, then the strip is firmly and evenly bedded onto the pole. Following installation of all the strips the surface of the pole including the strips has a protective epoxy paint coating applied to prevent ultra violet degradation of the fibre composite strips.

The concrete stiffening collar is typically constructed on a suitable subgrade which provides the stability and bearing capacity necessary to resist the loads from the strengthened pole. This involves geotechnical assessment of the ground then, normally, subgrade compaction and, if necessary, improvement of the foundation conditions by removal of low strength materials and replacement with higher quality materials or similar treatment. An integral connection between the pole and the collar is achieved by scabbling the pole surface (excluding the strips) in contact with the collar or similar means. The reinforced concrete collar is then conventionally constructed with the hollow section of the pole from ground level to at least the top of the collar also infilled with concrete. The collar not only strengthens and stiffens the foundation of the pole so that it can resist the increased loads from the strengthening, it also provides the necessary anchorage zone for the fibre composite strips.

BRIEF DESCRIPTION OF THE DRAWINGS Preferred embodiments of the invention will now be described with reference to following drawings wherein: Figure 1 is a perspective view of a single section strengthened, concrete monopole inserted into the ground according to a first embodiment of the present invention; Figure l (a) is a perspective view of a two section strengthened, concrete monopole inserted into the ground according to a second embodiment of the present invention;

Figure 2 is the section through 2-2 as shown in figure 1, 1 (a) or 4; Figure 3 is the section through 3-3 as shown in figure 1, 1 (a) or 4; Figure 4 is a perspective view of a multiple section strengthened concrete monopole with a stepped or tapered transition, according to a third embodiment of the invention, with the pole inserted into the ground as shown in figure 1; Figure 5 is an exploded perspective view of the bolted connection plate of the pole illustrated in figure l (a) which connects the lower and upper pole sections together ; Figure 6 is an exploded perspective view of the stepped or tapered transition of the pole illustrated in figure 4; Figure 7 is an exploded cross sectional view of the reinforced concrete collar of the poles illustrated in figures 1, 1 (a) or 4; Figure 8 is the section plan through 8-8 as shown in figure 7; Figure 9 is a perspective view of a four sectioned strengthened concrete monopole inserted into the ground according to a further embodiment of the present invention; Figure 10 and Figure 11 show the reinforced concrete collar in cross sectional plan and elevation respectively; Figure 12 shows the transition zone between the first and second sections of the pole of Figure 9; and Figures 13,14 and 15 show cross sections of the pole of Figure 9 at various heights.

PREFERRED MODES FOR PERFORMING THE INVENTION In Figure 1 there is illustrated a one piece concrete monopole 10. The pole 10 is conventionally supported in the ground, the surface of which is indicated by a dashed line 11, with the buried portion 15 of the pole 10 backfilled with concrete 16 up to ground level 11. The surface of the pole 10 is of a continuous taper. The pole 10 may extend 15-50 metres, although the pole would typically extend 20-35 metres. Large poles may be made in sections as will be described below with reference to Figures 1 (a) or 4.

The pole 10 shown in Figure 1 is strengthened, according to the invention, by fibre composite strips 17 and 18 and a reinforced concrete collar 19. The fibre composite strips 17,18 are installed in two different lengths alternatively. The shorter set 17 extend from ground level to a height determined by the most heavily stressed portion of the pole, typically ten metres above ground level for a pole of 20-35 metres'height and shown here as six in number. The longer set 18 extend again from ground level but to a greater height, such additional height determined by the progressive reduction in stress in this upper zone until the fibre composite strips are no longer required.

Typically the longer strips would extend three metres higher than the shorter strips and be equal in number i. e. six. The collar 19 is constructed at ground level after completing the strips and typically would be four metres square and one to one and a half metres high (see Fig. 7).

In Figure l (a) there is illustrated a strengthened two section concrete monopole 21.

Pole 21 is supported in the ground, the surface of which is indicated by a dashed line 11. The existing concrete monopole is a two section pole 21 and includes a lower first section 12 connected to an upper section 13 by a bolted connection plate 24. The buried portion 15 of the lower (existing) pole section 12 is backfilled with concrete 16 up to ground level 11.

In the embodiment of Figure 1 (a), as for the embodiment of Figure 1, the pole 21 is strengthened by the fibre composite strips 17 and 18 and the reinforced concrete collar 19. As for Figure 1, the fibre composite strips are installed in two different lengths

alternatively. The shorter set 17 extends from ground level to a height determined by the most heavily stressed portion of the pole, typically ten metres above ground level and, as shown here, comprise six in number. The longer set 18 extends again from ground level but to a greater height, such additional height being determined by the progressive reduction in stress in this upper zone as the fibre composite strips are no longer required. Typically the longer strips would extend three metres higher than the shorter strips and be equal in number. A protective coating may be applied over the strips and concrete pole surface as will be further described below.

The collar 19 is constructed at ground level after completing the strips and typically would be four metres square and one to one and a half metres high (see Fig. 7).

Figure 2 illustrates in cross section the lower pole section 12 and the two sets of fibre composite strips 17 and 18 which are bonded to the external surface of the pole 21 at an even spacing around the circumference. Also shown by a dotted line 20 is the protective coating applied to the pole 21 over all the strips and the adjacent concrete surface for the full extent of the strips. Typically this coating will be Sikagard-670W, a one component, water borne acrylic anti-carbonation coating.

Figure 3 illustrates, in cross section, the upper pole section 13, to which has been fixed the longer set of fibre composite strips 18 as well as the protective coating 20.

In Figure 4 there is illustrated a strengthened concrete monopole 31 with all aspects the same as the pole illustrated in Figure l (a) except that this pole 31 has a stepped or tapered transition 32 as part of its construction. The items in common for the two poles are shown by the same reference number.

The exploded view, Figure 5, of the connection detail for the pole in Figure 1 (a) shows the lower pole section 12 connected to the upper pole section 13 via the fabricated steel plate and bolt assembly 24. The bolts 23 usually comprise projecting studs, embedded in the adjacent pole section 12,13, which pass through holes in the connection plate and are then secured by a nut and washer. The connection assembly

24 consists of an upper and a lower horizontal plate 25,27, connected by a series of welded spacer plates 28, far enough apart to permit the nuts to be installed. The space between the upper and lower plates 25,27 and around all the bolts is completely filled with a high strength patching mortar 30 e. g Sika MonoTop 615 HB, a one part, polymer modified, cementitious patching mortar. The mortar infill 30 is finished to a smooth line 29 with the adjacent pole sections 12,13. Figure 5 also shows the fibre composite strips 17 and 18 bonded continuously across the joint 24.

Referring to Figure 6, which shows the exploded view of the stepped or tapered transition for the pole in Figure 4, the lower pole section 12 is connected to the upper pole section 13 via a stepped or tapered transition 32. The connection is usually a similar fabricated plate and bolted connection to that shown in Figure 5 but can also be an integral stepped or tapered transition contained within a particular pole section itself.

In Figure 6 the full details are not shown for clarity but the treatment by mortar infilling remains the same as for a straight connection (Figure 5) if this applies. In addition to the infilling of any connection the taper or step has additional buildup or wedge applied to the joint and the upper pole section using the same mortar to create a smooth extended taper with a maximum 1: 10 slope 33. This tapered wedge is constructed prior to installing any fibre composite strips 17 and 18.

Figure 6 shows the strips bonded continuously along this tapered section and it also shows additional fibre composite strips applied as horizontal bands at the changes of section of the taper 34,35. These bands 34,35 consist of a double wrap of fibre composite material bonded around the pole 31 over the vertical strips 17,18. These strips 34,35 counteract any transverse forces generated in the vertical strips 17, 18 due to the deflections of these strips 17,18 at the taper 32.

The collar and pole base detail is shown in Figure 7. The existing lower pole section 12 has the lower portion 15, usually around five metres, buried below ground 11, in a hole 45. The hole 45 is usually a bored hole larger in diameter than the pole 10,21, or

31 with the hole around the pole, after its installation, backfilled with concrete 16. As well as this concrete 16, the hollow core 40 inside the pole is infilled with concrete 41 up to ground level 11.

The construction of a reinforced concrete collar 19, according to the invention, is at ground level 11 on a compacted sound subgrade having a required bearing capacity, typically 200 kPa. The collar 19 is constructed after the strips 17,18 are installed typically comprising a square block of formed and poured in situ concrete reinforced with a cage 36 of reinforcing steel all cast around the existing pole 10,21, or 31. In addition, the hollow core section 40 of the pole 10, 21, or 31 is infilled with concrete from the existing concrete infill 41 to above the top 43 of the collar 19 at 38.

Figure 8 is the plan cross section of the collar showing the reinforcing cage 36, the strips 17, 18 within the collar 19 and the concrete infill 41 to the pole 10,21, 31 up to point 38.

The embodiments described above with respect to Figures 1-8 have employed a pole having two sections with the join between the sections being of different forms. It is equally contemplated that a pole may be made up of a plurality of sections joined together by any one of the types of joins or transitions as described with respect to these figures.

In Figure 9 a pole 100 made up of four sections 50,52, 54 and 56 is shown. The join 60 between the first and second sections 50,52 is of a type as shown in more detail in Figure 6 above, namely, involving sections 50,52 of dissimilar taper. As shown in Figure 6, and as also shown in Figure 12, the join 60 comprises a fill 33,70 of mortar joining the sections 50,52 in a smooth 1: 10 taper. In addition, the reinforcing fibres 17,18, 68,72 are fixed to the circumference of the transition zone 32,60 while bands 34,35 or 74,76 of reinforcing carbon fibre strips encircle the pole 100 at each boundary between the respective pole section 50,52 and the join or transition zone 32, 60.

The sections 52,54 are of similar taper and hence, the join 80 between these sections is smooth. The join 80 between such sections 52,54 or 54,56 is of a type as shown and described with respect to Figure 1 (a) or Figure 5.

While the join 82 between the upper sections 54,56 is also a join between sections of similar taper, the join 82 does not require reinforcing according to the invention due to its location at more than 50% along the height of the pole 100.

At the base of the pole a reinforcing collar 90 comprises a reinforced concrete slab resting above the ground level 92 on a base or foot of stabilised sand 94 to a depth of 600mm below the ground level. Additionally or alternatively, as shown in Figure 7, the reinforcing concrete collar may also include a reinforcing concrete annulus formed about the pole and extending above and below ground. In Figure 11 the annulus 96 is shown extending below the ground level 92. The reinforcing fibres 68 (72) terminate at the ground level 90 as shown in Figure 11, and extend to a height approximately 50% above the ground level 90 of the height of the pole. Figures 15,14 and 13 show respective cross sections through the first, second and third sections 50,52, 54 of the pole 100. In the first section 50,12 fibre composite strips of dissimilar length 68,72 extend longitudinally with 12 strips arranged about the circumference of the pole 100.

In the second section 52 also, 12 longitudinally extending fibre composite strips 68, 72 are arranged about the circumference of the pole 100. In the third section 54, fewer strips 68, in this case 6, being the longer strips, extend longitudinally, evenly arranged, about the circumference of the pole 100, as has been described with respect to Figures 1 and 4.

Although the invention has been described above with respect to preferred embodiments thereof variations therein are contemplated within the knowledge of a person skilled in the art.