WO2001040585A1

WO2001040585A1 - Foundation structure and erection of towers

Info

Publication number: WO2001040585A1
Application number: PCT/ZA2000/000234
Authority: WO
Inventors: Paul Michael Brosnihan
Original assignee: Brosnihan, Gail, Anne
Priority date: 1999-11-30
Filing date: 2000-11-27
Publication date: 2001-06-07
Also published as: AU2302101A

Abstract

A foundation structure which includes a reinforced concrete base (72), a plurality of bolts (74) extending upwardly from the base, and a plurality of anchors (12), upper ends of which are fixed to the base and lower ends of which extend downwardly, being embedded in a settable material in respective holes in the ground.

Description

FOUNDATION STRUCTURE AND ERECTION OF TOWERS

BACKGROUND OF THE INVENTION

This invention relates generally to the erection of a tower and more particularly is

concerned with a foundation structure for a tower. The invention is described hereinafter

with particular reference to a tower which is suitable for use in a cellular communications

network, but this is only by way of example, and the scope of the invention is not limited

to this application.

A tower for use in a cellular network is, to the applicant's knowledge, normally erected on

a massive reinforced concrete slab which is cast in a suitable hole formed in the ground.

The amount of concrete required is substantial and a time penalty is incurred while the

concrete sets to a hardness which is sufficient to allow the erection of a tower on the slab.

SUMMARY OF THE INVENTION

The invention provides a foundation structure for a tower which includes a plurality of piles,

each pile including a passage which extends into the ground and which is filled with a

settable material and at least one anchor located in the passage and embedded in the settable material, and a base which is secured to the anchor.

The settable material is preferably concrete. Each anchor may have a respective fastener secured to it and the fastener may be used

to secure the base to the respective anchor.

The base may be made of any suitable material and in any appropriate way but,

preferably, includes opposed spaced lower and upper steel plates with a plurality of ribs

or similar reinforcing or bracing members between opposing surfaces of the plates.

Fixing means may extend from an upper surface of the upper steel plate and the fixing

means may be secured to a leg of a tower.

In an alternative form of the invention the base is made from concrete, which is precast or

cast in situ, and the concrete is reinforced. Fixing means may extend from the concrete

base.

The anchor may be a rod or a cable or any appropriate elongate member which possesses

adequate properties of strength. Where use is made of a cable the cable may have a

ground engaging member secured to it. The ground engaging member may provide an

initial anchor to the ground and the cable may thereafter be embedded in concrete (ie. the

settable material), in the manner described.

The invention also extends to a tower which has at least three legs, each leg being fixed

to a foundation structure of the kind described hereinbefore.

In one form of the invention a container or housing is straddled by the legs of the tower. In a different form of the invention the tower legs extend from within a container or

housing. Preferably the legs are an integral part of the housing.

The housing may contain communications apparatus of any suitable kind used for making

the tower operational.

Thus, in a preferred arrangement, the invention provides a communication structure which

includes a housing which contains communication equipment, at least three tower legs

which are an integral part of the housing, at least three foundation structures, each

structure being of the aforementioned kind, each tower leg being fixed to a respective

foundation structure, and a tower which is supported by the said legs.

The invention also extends to a method of forming a foundation structure for a tower which

includes the step of forming an elongate passage into the ground, locating at least one

anchor in the passage, embedding the anchor in a settable material which is placed in the

passage, and securing a base to a protruding upper end of the anchor.

Preferably a plurality of substantially parallel or relatively inclined passages are formed

into the ground with each passage having a respective anchor located therein, embedded

in the settable material.

Preferably the base comprises a concrete slab which may be pre-cast, under controlled factory conditions. BRIEF DESCRIPTION OF THE DRAWINGS

The invention is further described by way of examples with reference to the accompanying

drawings in which

Figure 1 is a view in perspective of a foundation structure according to one form of the

invention,

Figure 2 is a side view of the structure of Figure 1 illustrating the manner in which a leg

of a tower is attached to the structure,

Figure 3 is a view similar to Figure 2 of an alternative arrangement according to the

invention,

Figure 4 is a plan view, somewhat simplified, of foundation structures for legs of a tower,

Figure 5 shows a different foundation structure according to the invention,

Figure 6 is a perspective plan view of a housing or container used in the erection of a

communication structure,

Figure 7 is a perspective view of a communication structure according to the invention, and

Figure 8 shows a different view of a communication structure according to the invention

DESCRIPTION OF PREFERRED EMBODIMENTS

Figure 1 of the accompanying drawings illustrates a foundation structure 10 according to

the invention which is particularly suited for the erection of a tower in a cellular network

The use of the invention is however not confined to this particularly application

At a selected site four holes 12A, 12B, 12C and 12D respectively are drilled into the ground to a desired depth which depends on prevailing geological conditions and which,

by way of example, may be of the order of 8 metres. Each hole is circular in cross section

and, by way of example, may have a diameter of the order of 250mm.

Steel rods 14 of appropriate dimensions are located in the respective holes 12 and a

settable material of any suitable kind eg. a resin but preferably concrete 16 of an

appropriate mix is then placed in the holes thereby embedding the rods in the concrete.

If necessary use may be made of spacers or positioning devices to ensure that the rods

are correctly located more or less centrally inside the holes.

Each concrete filled hole with its embedded steel rod thus forms a robust pile to act as a

support and foundation for a tower leg.

A preformed base 18 is then placed over the rods. The base has a lower plate 20, an

upper plate 22, and a number of strengthening ribs 24 which extend between opposing

inner surfaces of the upper and lower plates. The plates are formed with holes 26 and the

upper ends of the rods, which are threaded, pass through the holes. Nuts 28 are engaged

with the threaded upper ends of the rods thereby to secure the base to the concrete foundations.

Figure 2 illustrates the structure of Figure 1 from the side, and a lower end of a leg 30 of

a tower, not shown, which has a plate 32 fixed to it. The plate has holes 34 and bolts 36

are passed through the holes and registering holes 38 in the upper plate thereby to fix the

leg to base. As an alternative to this arrangement the bolts 36 can be extended, as is indicated by means of a dotted line 40 so that, in each case, the bolt extends through the

upper plate and the lower plate.

The foundation structure of the invention has a number of advantages over a conventional

approach. It is formed rapidly and the amount of concrete which is used is substantially

less than in a conventional approach. Once the base has been bolted to the foundation

structure the tower can be erected. Substantial time is saved therefor in the erection of

the tower.

Figure 3 illustrates a variation of the invention. In this case a foundation structure 10A is

formed, as is the case with Figure 1 , with a plurality of concrete filled passages. In this

instance only one passage designated 50 is shown. As is the case with the arrangement

shown in Figure 1 a hole 12 is initially bored into the ground to a desired depth. A steel

cable 52, as opposed to a rod 14, is then placed in the hole. At its lower end the cable has

a wedge shaped ground engaging member 54 which is pivotally attached at a point 56 to

the cable. The member 54 can pivot in a way which allows the lower end of the cable to

move under gravity action into the hole. When an upwards force is exerted on the cable

the member 54 pivots about the point 56 and digs into the wall of the hole. The anchoring

force which is exerted in this way can be substantial and can be immediately tested. The

cable 52 is therefore stressed immediately and its upper end 58 is secured with a wedge-

type locking arrangement 60 to the base 18 which is similar to the base shown in Figure

1. Concrete 16 is then placed in the hole 12 to embed the cable in the concrete. The

approach shown in Figure 3 is twofold in that a positive anchoring force is immediately

provided without the use of concrete. The magnitude of the force is determined by means of a stressing arrangement engaged with an upper end of the cable. In addition once

concrete is placed in the hole the cable is embedded in position and the arrangement is

therefore similar to what has been described in connection with Figure 1.

The Figure 3 arrangement further shortens the time which is required before a tower can

be erected. With the Figure 3 arrangement a tower can be erected immediately even

though the concrete has not set for the restraining forces which are exerted by the

stressed cables are accurately known.

Figure 4 illustrates, in plan, three foundation structures 10A, 10B and 10C respectively

which are positioned at apices of an equilateral triangle. Each foundation structure is

formed in the way which has been described in connection with Figures 1 and 2, or Figure

3. A respective base 18A, 18B and 18C is positioned at, and engaged with, each

foundation structure. Legs, not shown, generally of the type shown in Figure 2, extend

upwardly from each base and support a centrally positioned tower (not shown).

The invention is not limited to the precise constructional details shown in the attached

drawings and described hereinbefore. Details of the foundation structure can be varied

without departing from the scope of the inventive principles. Thus the number of holes

drilled in the ground can be varied and the cross sectional size, length and inclination of

each hole can be changed. The nature of the base plate can also be varied according to requirement.

Figure 5 illustrates in perspective and partly cut away a foundation structure 70 according to another form of the invention. The steel base 18 shown in Figure 1 is dispensed with

and is replaced by a concrete base 72. The concrete base is cast in situ or, preferably,

is precast under factory conditions. The base is suitable reinforced by means of a lattice

74 of reinforcing rods.

The base is anchored to the ground in the same way as what has been described in

connection with Figure 1 although, in this case, only two holes 12E and 12F are drilled into

the ground inclined to the vertical. The holes are filled with concrete and steel rods 14A

are embedded in the concrete and extend through passages in the concrete slab 72.

Protruding upper ends of the steel rods are threaded and nuts, not shown, are engaged

with the upper ends of the rods and are tightened to secure the slab to the rods.

The slab is fairly massive and typically has a mass of between 1000kg and 2000kg.

A plurality of bolts 74 are embedded in the concrete slab and extend upwardly at

predetermined locations. A base plate 76 of a tower leg 78 is directly secured to the bolts

by means of nuts 80 which are threadedly engaged with the bolts.

Although the arrangement shown in Figure 5 functions generally in the same way as the

foundation structure shown in Figure 1 the former arrangement does possess a number

of advantages. Firstly it has been found that, generally, it is only necessary to drill two

holes 12E and 12F into the ground in order to anchor the foundation slab. The bolts 14A

are sufficiently strong to give the tower which is erected over the foundation structure

adequate resistance to bending forces. Secondly the concrete slab 72, which has a

substantial ground-engaging area relatively to the base 18 shown in Figure 1 , acts as a load spreading component which reduces the effective pressure which is transmitted to the

ground by the tower structure. As the concrete slab is fairly substantial its mass also acts

as a stabilising factor.

It is of course possible to make use of cables of the type shown in Figure 3 to secure the

concrete base 72 in position, instead of making use of bolts 14A, as is shown in Figure 5.

Figure 6 illustrates, in a perspective plan view, an interior of a container or housing 90

which is used with foundation structures of the type shown in Figure 1 or Figure 5 in the

erection of a communication structure. The housing 90 is manufactured according to

requirement or, if necessary, use may be made of a standardised shipping container. The

container is filled with communication equipment under controlled conditions at a factory

site. In this example the container is divided into two compartments 92 and 94 respectively

and doors 96 and 98 are installed to provide access to the compartments. The

compartment 92, in this example, has four substantial corner structures formed, in each

case, by a lowermost component 100A, 100B, 100C and 100D respectively of legs of a

tower which is shown in further detail in Figure 7. The components 100 are formed

integrally with the side walls 102 of the container in that the side walls are attached to the

components which, as noted, form respective corners of the compartment.

In Figure 6 a roof of the container 90 has been omitted to show its internal structure. It is

to be understood that a secure roof is provided for the container in order to render the container weatherproof. Figure 7 illustrates a communication structure 110 according to the invention which

includes a mast or tower 112 erected over a container 90 of the type shown in Figure 6 which in turn is positioned over four foundation structures 70, each of the kind shown in Figure 5, although in Figure 7 only three of the foundation structures are visible.

The foundation structures 70 are constructed at predetermined positions in the manner

which has been described in connection with Figure 5. Thereafter lowermost components

78 of tower legs are fixed to the respective foundation structures. The container 90 is

positioned over the components 78 and the components are in turn bolted to the leg

components 100A to 100D which are shown in Figure 6 and which, as noted, form an integral part of the container 90.

The tower 112 which is formed from a lattice arrangement of prefabricated sections is then

erected above the housing 90 extending upwardly from the respective comers 100A to 100D of the container. The corners thus act as base portions or legs of the tower. In this example of the invention screens or bill boards 114 are attached to the tower 112 for advertising or display purposes.

The compartments 92 and 94 in the container are filled with communication equipment, standby electric generators and the like, according to requirement.

An end of the container which is remote from the compartment 92 is supported by means of concrete plinths 116 which are cast in situ depending on the terrain to ensure stability of the structure. The arrangement shown in Figure 7 possesses a number of significant advantages. The

container 90 is packed with the equipment which is necessary for erecting the tower 112 and with the communications equipment. The container, prepacked at a controlled factory

site, is then transported to the erection site at which the foundation structures 70 are rapidly constructed using the techniques which have been described hereinbefore. Once

the foundation structures have set the container is manoeuvred into position, as is shown

in Figure 7, and is then fixed to the foundation structures and the plinths 116, whereafter

the tower 112 is erected. Construction time is substantially reduced, compared to conventional construction techniques.

Figure 8 illustrates a further variation of the invention wherein a mast or tower 120 is

erected directly over a framework 122 which is constructed on top of legs 124 which, in

this example, are on an outer side of a container 126.

The legs extend from foundation structures 128 which may be of the type shown in Figure

1, Figure 3 or Figure 5. The container 126 houses communication equipment which can be accessed through a door 130.

The use of the container is of course optional although it is a preferred feature particularly

for the erection of communication towers in remote areas. On the other hand if a relatively

simple structure is required, eg. a standalone tower, then the tower can be constructed so

that it extends directly upwardly from foundation structures of the type shown in Figure 1

or Figure 5 and under these conditions there may be no need for an intermediate container structure for housing electronic or other equipment.

Claims

1. A foundation structure for a tower which includes a plurality of piles, each pile

including a passage which extends into the ground and which is filled with a

settable material, and at least one anchor located in the passage and embedded

in the settable material, and a base which is secured to the anchor.

2. A foundation structure according to claim 1 wherein the settable material is

concrete.

3. A foundation structure according to claim 1 or 2 wherein each anchor has a

respective fastener secured to it and the fastener is used to secure the base to the

respective anchor.

4. A foundation structure according to any one of claims 1 to 3 wherein the base

includes opposed spaced lower and upper steel plates with a plurality of ribs

between opposing surfaces of the plates.

5. A foundation structure according to any one of claims 1 to 3 wherein the base is made from reinforced concrete.

6. A foundation structure according to any one of claims 1 to 5 which includes fixing

means which extend from the base and which are secured to a tower leg.

7. A communication structure which includes a tower, a plurality of foundation

structures, each foundation structure being according to any one of claims 1 to 6,

and a plurality of legs, each leg being fixed to a respective foundation structure and

supporting the tower.

8. A communication structure according to claim 7 which includes a housing between

the foundation structures and an upper portion of the tower.

9. A communication structure according to claim 8 wherein each leg is an integral part

of the housing.

10. A communication structure which includes a housing which contains communication

equipment, at least three tower legs which are an integral part of the housing, at

least three foundation structures, each foundation structure being according to any

one of claims 1 to 6, each tower leg being fixed to a respective foundation structure,

and a tower which is supported by the said legs.

11. A foundation structure which includes a reinforced concrete base, a plurality of bolts

extending upwardly from the base, and a plurality of anchors, upper ends of which

are fixed to the base and lower ends of which extend downwardly, being embedded

in a settable material in respective holes in the ground.

12. A communication structure which includes a housing, a tower, an upper part of

which overlies the housing, legs which support the tower, and foundation structures

which are anchored to the ground by means of piles and which support the legs.