WO2013135292A1

WO2013135292A1 - Mast

Info

Publication number: WO2013135292A1
Application number: PCT/EP2012/054574
Authority: WO
Inventors: Thomas Scheidegger
Original assignee: Simex Group Ag
Priority date: 2012-03-15
Filing date: 2012-03-15
Publication date: 2013-09-19

Abstract

A mast is described for use in mobile communications networks. The mast body is a light-weight, tubular body made of reinforced composite material, adapted to support wind or solar energy sources for charging batteries accommodated in ballast containers which form the base assembly of the mast. Lateral forces due to the wind acting on the mast body and the wind- turbine or solar panels result in increased tension forces in the reinforcing fibres of the composite material, which are directed down through the fibres to a tubular rigid reinforcement element (10) which, in turn, is rigidly mounted to the base assembly (2, 3). The fibres are rigidly secured, preferably by being woven through perforations, to the reinforcement element (10), which is rigidly secured to the base assembly (2, 3) in order to achieve increased rigidity of the whole structure from ballast containers to wind-turbine mounting.

Description

Mast

The invention relates to masts for communications networks and in particular, but not exclusively, to the field of light-weight, quickly-erectable communications masts which require little or no assembly or site preparation.

Communications networks such as cellular mobile telephone networks have been rapidly expanding in extent and network density, and require the installation of many masts, often in remote locations, for mounting the antennae or dishes which convey the network traffic.

Hitherto, masts have usually been constructed as steel towers mounted on a concrete foundation. Wire stays may also be used to improve the stability of the mast. Where a mast is to be constructed in a remote location, therefore, several construction stages are required: the site must be prepared using excavating equipment, concrete must be delivered and the foundation cast, the tower must be assembled, the antennae must be mounted on the tower using a crane or lifting gear, and the stays must be attached, anchored and tensioned. Power cables must then be laid to the mast from the nearest point on the electricity grid. This process may take many days, require many deliveries of heavy parts and equipment, and may result in a cumbersome mast which occupies a significant land area.

It is possible to prefabricate the body of such a mast as a hollow, tubular body, for example from a composite material such as fibreglass.

Fibreglass masts are relatively light and strong, and have the additional advantage of being transparent to electromagnetic radiation in the frequencies which are commonly used for network communications. Antennae, dishes and such equipment can be enclosed within the upper part of the mast body such that they are protected from the elements. In order to facilitate access, the equipment can be mounted, using a lifting mechanism, from an access door in a lower region of the mast.

Many communications devices, such as antennae or dishes, are highly directional, and require a stable mounting and a rigid mast which does not sway or rotate. In practice, sway cannot be completely eliminated, but it is important to minimize the amount of sway as far as possible. Sway can be substantially reduced by means of stays fitted to the mast, but stays require firm ground-anchor points located some distance away from the base of the mast. Such anchor points are sometimes difficult to achieve (in regions of deep sandy soil, for example); they require significant installation work, and enlarge the mast's terrain footprint.

Sway amounts of 1 ° or more may be observed in some traditional masts, but this is too large for some communications applications, and 0.5° may be specified as an upper limit. By means of the present invention, it is possible to reduce this sway to 0.15° or less, even in high winds of up to 100 mph, without resorting to stays or other costly installation options.

In developing countries and remote regions, it is often the case that a mobile telephone network is one of the first systems of widespread

infrastructure to be set up - even before electricity transmission grids, road and rail networks, or water pipelines are established. In such regions, therefore, the provision of a network of masts may present significant practical challenges. Masts must be easy to transport over difficult country, and easy to erect without special equipment or engineering staff. The erected mast should also be well protected against adverse weather conditions such as sandstorms, high winds, blizzards, drifting snow, ice build-up or monsoon rains.

Ideally, masts in remote locations should be able to operate autonomously, and should not be dependent on any continuous external supply of energy or other services. The general reliability of a wireless

communications network depends on the mast density of the network (i.e. the separation distance between the masts) and the transmission power of the individual masts. High-power masts are typically connected by cable to a power grid or other source of electrical power. These power lines are themselves a source of potential failure, and a mast outage which occurs in a widely-spread network of masts is likely to have widely-spread failure consequences. Lower- power masts arranged in a more dense network, on the other hand, may be powered by local power sources such as diesel generators, and/or by renewable energy sources such as wind turbines or solar panels, and the network is less susceptible to major widespread failure as a result.

A wind turbine mounted on top of a mast may be able to generate a significant proportion of the energy required to power the communications equipment mounted in the mast. Such a wind-turbine, however, can add significantly to the lateral, sway-inducing forces acting on the mast. For this reason, it is particularly important to improve the rigidity and stability of the mast when the mast is intended for autonomous operation in remote areas.

In order to achieve at least some of the above aims, and to overcome at least some of the above problems with existing masts, the invention aims to provide a mast for accommodating an antenna of a communications network, the mast comprising a substantially hollow, tubular mast body and a base comprising a base mounting element for securing to a mast foundation, and one or more ballast container elements for providing a mast-stabilising weight of the base, wherein: the mast body is constructed of reinforced composite material to the extent that the structural rigidity of the mast body derives principally from the reinforced composite material of the hollow, tubular mast body, the reinforced composite material comprises reinforcement fibres in a binding matrix, the mast body comprises a rigidised lower section for securing to the base mounting element, the rigidised lower section being constructed at least partially from the reinforced composite material, the lower section comprises one or more rigid reinforcement elements moulded into the reinforced composite material of the lower section, the or each rigid reinforcement element is provided with fibre- securing means for bonding the reinforcement fibres to the or each rigid reinforcement element, and the rigid reinforcement element comprises a plurality of attachment points for attaching the mast body to the base mounting element. Because the rigidised lower section is rigidly (i.e. inelastically) secured both to the base and to the reinforcement fibres of the mast body, tension in the reinforcement fibres can be directed substantially inelastically from the upper region of the mast, where the antennae may be mounted, through the rigid reinforcement element(s) to the base. The lateral forces experienced by the upper part of the mast can thus be rigidly directed into the base of the mast, thereby increasing the overall rigidity of the mast, and reducing the amount of sway of the part of the mast where the antennae are mounted. This is of particular advantage in the case where a wind generator or solar panels, which significantly increase the lateral forces due to incident wind, are mounted on the mast.

According to a variant of the mast of the invention, the fibre-securing means may comprise an adhesion binding agent for bonding the reinforcing fibres to the rigid reinforcement element. The fibre-securing means may comprise one or more textured and/or perforated regions of the rigid

reinforcement element. Perforations may advantageously be provided in the rigid reinforcement element such that at least some of the reinforcement fibres pass through the perforations. The reinforcement fibres may for example be woven through the perforations of the rigid reinforcement element. By weaving or drawing the fibres into perforations of depressions in the rigid reinforcement element, a stronger inelastic bond between the fibres and the rigid

reinforcement element can be achieved when the binding matrix is applied to the fibres.

According to a further variant of the mast of the invention, the mast body comprises, in an upper region, first mounting means for a wind turbine and/or second mounting means for solar panels, and moreover the said rigid reinforcement element, said reinforced composite material, said attachment points and said fibre-securing means are arranged such that said structural rigidity extends at least from the base mounting element to the upper region. The ballast container elements of the base may be adapted to contain fuel, energy storage elements (such as batteries for storing energy generated by the wind or solar devices) and/or thermal transfer liquid, such that the weight of the fuel, energy storage elements and/or thermal transfer liquid acts to ballast the base, whereby the said rigid reinforcement element, said reinforced composite material, said attachment points and said fibre-securing means are arranged to transmit lateral forces on the upper region of the mast body substantially inelastically to the base. The reinforcement fibres may comprise glass fibres, at least in a radio-transparent region of the tubular mast body. In a further variant, the reinforcement fibres may comprise carbon fibres, in at least a region of the tubular mast body below said radio-transparent region of the tubular mast body.

According to a further variant of the mast of the invention, the securing means comprise one or more fibre-diverting elements, the or each fibre-diverting means being arranged to divert one or more of the reinforcement fibres into or through one or more of the perforations, and/or to secure two or more bundles of fibres together at or through one or more of the perforations.

The invention also envisages a method of constructing a mast as described above, the method comprising the steps of: a) arranging the reinforcing fibres and the at least one rigid reinforcing element in or on a mould, b) securing, using the attachment means, the reinforcing fibres to the rigid reinforcing element, and c) injecting, pouring or applying the binding matrix, as a liquid, to the reinforcing fibres and to the rigid reinforcing means. As described above, the securing of the rigid reinforcement element to both the fibres and the base gives rise to a more stable mast with significantly less sway. The step of securing may comprise weaving the reinforcement fibres through the perforations of the rigid reinforcement element, thereby giving a highly rigid connection between the rigid reinforcement element and the fibres. The step of securing may comprise using diverting elements to draw bundles of the reinforcement fibres into or through one or more of the perforations, and/or to secure two or more bundles of fibres together at or through one or more of the perforations, during the injecting, pouring or applying step.

The invention will now be described with reference to the attached drawings, in which: Figure 1 shows in perspective view an example of a mast according to an embodiment of the invention.

Figures 2a and 2b show in sectional and perspective view a lower section of a mast according to the invention.

Figures 3a to 3c show in schematic sectional view three fibre- securing methods for a mast according to the invention.

Figures 4a to 4c show in schematic, cut-away and close-up view a fibre and perforation arrangement for a mast according to the invention.

Note that the drawings are provided for explanatory purposes only, and are intended merely to indicate an example of how the invention can be implemented. The drawings should not be taken as limiting the scope of protection, which is set out in the accompanying claims. The use of the same reference numbers in different drawings is intended to indicate that the references refer to the same features. The use of different references for similar features in different drawings does not indicate that the features referred to are also different.

Figure 1 shows a mast comprising a hollow tubular mast body 1 . The illustrated mast body has a circular cross section, but the cross section could be elliptical, oval or polygonal. A round cross section is preferred for strength and for minimizing wind-resistance and the amount of material required for construction. The illustrated mast body 1 is constructed, for example, from a composite material such as fibreglass, with many of the fibres running in a substantially vertical orientation. The mast is surmounted by a wind-turbine 20, and fitted, at least on its south side, with solar panels 15. The solar panels 15 preferably comprise flexible panel arrays of cells which can be adhered to the external surface of the mast body 1 . Energy generated by turbine 20 and/or panels 15 can be stored in batteries stored in the base element 3.

Communications equipment 4, such as antennae or dishes, may be mounted within the tubular body. Lifting means 9, such as rails and wires, can be used to raise these into position from the lower part 8 of the mast, where they are introduced to the interior of the hollow mast body 1 through closable opening 5. As can be seen from figure 1 , the outside of the lower region 8 of the mast body 1 is slightly fatter than the rest of the mast body 1 . The inner space of the mast, on the other hand, can have substantially the same cross- sectional profile from the bottom to the top, so as to permit an unimpeded lifting or lowering of antennae or dishes through substantially the whole height of the mast body 1 . The lower section 8 of the mast body 1 , as will be seen in figures 2 to 4, is provided with a rigid reinforcement element, which may for example be a steel tube of substantially the same cross section as the mast body. The rigid reinforcement element serves to direct tension forces from the reinforcing fibres in the upper mast body through to the base assembly 2, 3. To this end, the rigid reinforcement element is securely fixed to a base plate 2, which may comprise adjustment means for adjusting a vertical orientation of the mast, and to the base element 3, which preferably comprises ballast container elements.

Figures 2a and 2b show an example of how a flanged tubular reinforcement element can be used to direct the tension forces in the fibres 1 1 down to the base 2, 3. The flange 17 of the rigid reinforcement element 10 is fixed to a base mounting element, which is in turn fixed to a foundation 3.

Reinforcement fibres 1 1 of the mast body are secured to the rigid reinforcement element 10 in such a manner as to convey the tension in the fibres 1 1 inelastically to the rigid reinforcement element 10. The fibres may be sheets or mats or bundles of individual fibres, preferably with the fibres oriented substantially vertically, by which is meant that at least the majority of the fibres are oriented at an angle of greater than 60° to the horizontal, and preferably arranged to follow the wall of the mast body. The fibres may be pre-tensioned in their substantially vertical orientation for the step of moulding, casting or injection of the binding matrix, in order to give the mast body additional rigidity. In the case of glass fibres, a ratio of binder to glass of between 35% and 55% is preferred, in order to obtain a mast body which is sufficiently robust in compression, but also strong and rigid in tension. It is possible, using such ratios and the elements of the invention, to achieve a 25 m tall mast having maximum sway deflection angles of as little as 8' (eight arc minutes) or even less, even under conditions of gusty high winds. Figure 2a also shows in cross section how the ballast containers 13 may be arranged to make up the foundation 3. Lightweight, quick-assembly masts should ideally require as little ground work as possible. To this end, the foundation 3 can be comprised of multiple elements, held together in tension. Each element can serve as a container for ballast, which may for example be local ly-sourced sand, rock, water, etc. Alternatively, or additionally, some or all of the ballast container elements 13 can be given over to storing batteries, such as lead-acid batteries 14, or fuel cells, for storing or generating power for use by equipment in the mast. Alternatively, or additionally, some or all of the ballast container elements 13 can be given over to storing fuel, such as diesel or gas, for fuelling a generator for generating power for use by equipment in the mast. In some environments, such as very hot or very cold conditions, some heating or cooling may be required for the equipment inside the mast, or for maintaining the outer surface of the mast free of ice, for example. In this case, the ballast container elements may be used to store thermal transfer fluid and/or equipment, such as a heat-pump or heat-exchanger, for providing such heating or cooling. The ballast container elements may be held in tension using a chain 12 or wire or similar tensionable element arranged to pull the ballast container elements together 13 on the surface of the ground. Even if the site is not perfectly even or level, the individual ballast container elements may be arranged in position on the ground, in which case they may be at different heights relative to each other. They can then be tensioned together at their respective heights. In this way, a foundation 3 can be created which fits the contours of the ground on which it rests. Additional fixing elements may also be used, if necessary, to further secure the foundation. The base mounting plate 2 may then be secured on top of the foundation 3, and may be provided with one or more adjusting means (not shown) for adjusting the height and/or the horizontal orientation of the base mounting element 2 relative to the foundation 3. The mast body can be secured by means of the flange 17 and fixing elements 6, here illustrated as bolts, to the foundation 3.

The foundation 3 may comprise a single assembly of ballast container elements 13, or it may comprise several (for example three or four) separate assemblies of ballast container elements 13. In the latter case, the base mounting plate 2 can be secured to the several foundation assemblies, for example with each corner of the base mounting plate (if it is triangular or square, for example) supported by one foundation assembly.

Figures 2a and 4a show an example of how the rigid reinforcement element 10 can be provided with perforations 16 for inelastically securing the fibres 1 1 to the rigid reinforcement element 10 when the binding matrix is applied or injected. Alternatively, the rigid reinforcement element 10 may be provided with a roughened or textured region to which the fibres 1 1 may be bonded before the binding matrix is applied or injected. The perforations 16 are illustrated as relatively large, circular holes. However, it should be understood that the perforations 16 could be any size and shape suitable for drawing the fibres 1 1 into or through. Figures 3a to 3c and 4b and 4c illustrate how the fibres 1 1 may be pulled into or through the perforations 16 by using clips 1 1 to pull fibres inwards into the perforations as shown in figures 3b and 4b. Or the fibres 1 1 can be threaded through the perforations as shown in figure 3c.

Figure 4a also shows how the reinforcement fibres 1 1 can be arranged so that at least the majority of the fibres 1 1 follow a straight course along the wall of the tubular mast body 1 . Some of the fibres run one way around the body, while others run the other way, thus ensuring the rigidity of the mast body once the binding matrix, which may be an epoxy, for example, is cured.

Claims

1 . Mast (1 ) for accommodating an antenna (4) of a communications network, the mast (1 ) comprising a substantially hollow, tubular mast body (1 ) and a base (2, 3) comprising a base mounting element (2) for securing to a mast foundation (3), and one or more ballast container elements (13) for providing a mast-stabilising weight of the base (2, 3), wherein: the mast body (1 ) is constructed of reinforced composite material to the extent that the structural rigidity of the mast body (1 ) derives principally from the reinforced composite material, the reinforced composite material comprises reinforcement fibres (1 1 ) in a binding matrix, the mast body (1 ) comprises a rigidised lower section (8) for securing to the base mounting element (2), the rigidised lower section being constructed at least partially from the reinforced composite material, the lower section (8) comprises one or more rigid reinforcement elements (10) moulded into the reinforced composite material of the lower section (8), the or each rigid reinforcement element (10) is provided with fibre- securing means (16, 18) for bonding the reinforcement fibres (1 1 ) to the or each rigid reinforcement element (10), and the rigid reinforcement element (10) comprises a plurality of attachment points (6) for attaching the mast body (1 ) to the base mounting element (2, 3).

2. Mast according to claim 1 , wherein the fibre-securing means (16, 18) comprise one or more textured and/or perforated regions (16) of the rigid reinforcement element (10).

3. Mast according to claim 1 or claim 2, wherein the fibre-securing means (16, 18) comprise an adhesion binding agent for bonding the reinforcing fibres (1 1 ) to the rigid reinforcement element (10).

4. Mast according to one of claims 1 to 3, wherein the fibre-securing means (16, 18) comprise perforations (16) in the rigid reinforcement element (10), and wherein at least some of the reinforcement fibres (1 1 ) pass through the perforations (16).

5. Mast according to claim 4, wherein at least some of the reinforcement fibres (1 1 ) are woven through the perforations (16) of the rigid reinforcement element (10).

6. Mast according to one of claims 1 to 5, wherein the mast body (1 ) comprises, in an upper region, first mounting means for a wind turbine (20) and/or second mounting means for solar panels (16), and wherein the said rigid reinforcement element (10), said reinforced composite material, said

attachment points (6, 17) and said fibre-securing means (10, 16, 18) are arranged such that said structural rigidity extends at least from said base mounting element (2) to the upper region.

7. Mast according to claim 6, wherein the ballast container elements (13) are adapted to contain fuel, energy storage elements (14) and/or thermal transfer liquid, such that the weight of the fuel, energy storage elements and/or thermal transfer liquid acts to ballast the base (2, 3), whereby the said rigid reinforcement element (10), said reinforced composite material, said

attachment points and said fibre-securing means are arranged to transmit lateral forces on the upper region of the mast body substantially inelastically to the base (2, 3).

8. Mast according to claim 7, wherein the energy storage elements (14) comprise batteries for storing electrical energy generated by said wind turbine (20) and/or solar panels (15).

9. Mast according to one of the preceding claims, wherein the reinforcement fibres (1 1 ) comprise glass fibres (1 1 ), in at least a radio- transparent region of the tubular mast body 1 .

10. Mast according to claim 9, wherein the reinforcement fibres (1 1 ) comprise carbon fibres, in at least a region of the tubular mast body (1 ) below said radio-transparent region of the tubular mast body (1 ).

1 1 . Mast according to one of the preceding claims, wherein the securing means (18, 16) comprise one or more fibre-diverting elements (18), the or each fibre-diverting element (18) being arranged to divert one or more of the reinforcement fibres (1 1 ) into or through one or more of the perforations (16), and/or to secure two or more bundles of fibres (1 1 ) together at or through one or more of the perforations (16).

12. Method of constructing a mast according to one of claims 1 to 1 1 , the method comprising the steps of: securing the rigid reinforcing element (10) to the base mounting element (2), arranging the reinforcing fibres (1 1 ) and the at least one rigid reinforcing element (10) in or on a mould, securing, using the securing means (16, 18), the reinforcing fibres to the rigid reinforcing element (10), and injecting, pouring or applying the binding matrix, as a liquid, to the reinforcing fibres (1 1 ) and to the rigid reinforcing means (10).

13. Method according to claim 12, wherein the step of securing comprises weaving the reinforcement fibres (1 1 ) through the perforations (16) of the rigid reinforcement element (10).

14. Method according to claim 12 or 13, wherein the step of securing comprises using a bonding agent to adhere the reinforcement fibres (1 1 ) to a textured surface of the rigid reinforcement element (10).

15. Method according to one of claims 12 to 14, wherein the step of securing comprises using diverting elements (18) to draw bundles of the reinforcement fibres into or through one or more of the perforations (16), and/or to secure two or more bundles of fibres together at or through one or more of the perforations (16).