GB2399133A - Demolition apparatus and method - Google Patents

Abstract

Apparatus for supporting demolition equipment for use in demolition of walls 7 of concrete or masonry comprises a rig 1 suitable for carrying demolition equipment such as a winch, derrick and crushing unit (Fig 5, not shown) and rig support means 6 attached to the side of a wall 7 being demolished, such that the load of the apparatus is borne by the wall 7. Rollers 4 act on rail 6 to support the rig, and depending members 2,3 on each side of the wall 7 carry rollers 5 which bear against the wall for lateral stabilisation. For demolition of a circular body such as a cooling tower or chimney, rail 6 is helically disposed so that one circumferential pass of the equipment continuously reduces wall height from level 8 to level 9. A multi start helix may be used with a corresponding number of apparatus 1; pieces of rail 6 may be removed from behind apparatus 1 and replaced in front of it.

Description

DEMOLITION APPARATUS AND METHOD

This invention relates to apparatus and a method for demolishing walls and similar structures. It is particularly applicable, but in no way limited, to the demolition of masonry or concrete wall structures such as chimneys, cooling towers and silos.

Industrial chimneys are up to 300 metres in height. Natural draught cooling tower shells are up to 200 metros tall. These structures comprise reinforced concrete walls of thickness mm to 600 mm and diameters from 4 m to 120 m. The greater part of these structures is beyond the reach of ground level demolition plant.

In the past, hand-held pneumatic tools were used to demolish reinforced concrete wall structures such as industrial chimneys, cooling towers and silos. More recently larger pneumatic tools have been available for mounting on the arms of mechanical excavators and other civil engineering plant. These tools are only suitable for walls up to a height that is within reach of the machine from ground level.

Work on tall structures, including demolition of industrial chimneys and natural draught cooling tower shells, is therefore normally carried out by steeplejack operatives using hand held tools. These operatives have the qualifications and skills necessary to work safely at height. Access to the top of the structure is normally by steeplejack ladder. A powered cradle may subsequently be installed. A fixed personnel access platform is assembled around the top of the structure at the working level. The access platform is normally a lightweight modular structure that is capable of carrying operatives, hand tools and other small items. As the wall of the concrete structure is demolished, the access platform is lowered in stages to maintain access at the required height.

The personnel access platform is not wide enough or strong enough to carry bulky and heavy demolition equipment. Furthermore, all equipment used by the steeplejacks for demolishing the structure has to be raised from the ground. The lifting equipment normally available is a small powered winch with a capacity of a few hundred kilograms. The winch capacity places a limit on the weight of any component used in the demolition process.

Health and safety legislation will in future severely curtail the time that an operative can spend during each working shift using a hand-held pneumatic tool for breaking concrete. In future it will no longer be acceptable or economic to continue with hand-held tools for the demolition of reinforced concrete.

Concrete can be broken and removed from a reinforced concrete wall using hydraulically operated proprietary concrete crushing equipment. This equipment takes the form of a set of jaws that are closed under hydraulic power. This type of equipment does not require an applied force from the support system and can be loosely suspended from an excavator arm or a tower crane. However, it is not practical to use a heavy excavator at height and the provision of a tower crane is expensive. For the economic demolition of tall reinforced concrete structures an alternative support system is required.

According to a first aspect of the present invention there is provided apparatus for supporting demolition equipment, for use in the demolition of concrete or masonry walls or similar structures, said apparatus comprising a rig suitable for carrying demolition equipment such as a winch, derrick and concrete crushing unit, and rig support means, wherein, in use for the demolition of a wall, the rig support means are attached to a side of the wall being demolished, such that the load of the said apparatus is borne by the said wall.

This apparatus advantageously supports the concrete crushing equipment at the working level, using a rig that is itself supported by the wall structure that is being demolished. Thus, by virtue of the present invention, steeplejacks are not required to use hand-held tools to demolish high wall sections, and demolition equipment that is too heavy to operate by hand can be used at height without the need for a tower crane.

Preferably the rig support means comprise a support rail, and the rig comprises: a plafform suitable for carrying the demolition equipment; and conveying means attached to the plafform, the conveying means being adapted to move along the support rail and to transfer the load of the plafform to the support rail and thence to the wall; wherein, in use, the support rail is attached to the said side of the wall and the plafform is supported by the rail using the conveying means, such that the rig can move along the rail and demolition equipment on the plafform can demolish a region of the wall above the rail.

The term 'plafform' as used herein should be interpreted broadly, to mean any structure attached to or integral with the rig suitable for bearing the demolition equipment. The plafform may be a closed boarded region, or alternatively it may be a more open framework of structural members on which the demolition equipment may be mounted.

The term 'support rail' should also be interpreted broadly, to encompass any rail, track, cable, wire or other support that may be attached to the side of the wall and supports the rig, and that the rig can travel along by virtue of the conveying means.

S The term 'conveying means' should also be interpreted broadly, to encompass any arrangement which transfers the load of the rig to the support rail and which enables the rig to travel along the rail. The conveying means may be, for example, a wheel, caterpillaritrack or a toothed wheel.

The ability for the rig to travel along the rail greatly facilitates and expedites the demolition of the entirety of the wall.

Preferably the rig further comprises a vertical support member extending between the support platform and the conveying means, the support member being arranged such that the platform is positioned over the top of the wall in use. This has the advantage that the demolition equipment can operate effectively on the top of the wall, and that the personnel access platform is not restricted.

Preferably the rig further comprises a stabilising member attached to the support platform, the stabilizing member being arranged to pass down the opposite side of the wall to the support rail in use.

Preferably the vertical support member and/or the stabilizing member further comprise horizontal restraining means arranged to act against the wall in use. These horizontal restraining means advantageously provide horizontal stability to the rig.

Particularly preferably the horizontal restraining means comprise one or more wheels. The wheels are preferably oriented to rotate such that their direction of travel is parallel to that of the rig along the rail. The wheels thereby facilitate the rig's travel whilst providing horizontal stability.

Preferably the conveying means comprise a wheel arranged to act on the upper surface of the support rail in use. Particularly preferably the conveying means further comprise a wheel arranged to act on the underside of the support rail in use. The use of a pair of wheels, one above and one below the rail, provides vertical stability to the rig.

Preferably the conveying means are operable to secure the rig onto the support rail in use.

Particularly preferably the rig is shaped and configured such that, if it were inadvertently to fall in use, the rig would locate around the top of the wall and not fall to the ground. This is an important safety consideration. Such a configuration is provided, for example, by a rig having a vertical support member on one side of the wall, the platform above the top of the wall, and a stabilising member extending down the opposite side of the wall to the vertical support member.

Preferably the width of the rig is adjustable to enable it to be used on walls of different thickness.

Particularly preferably the support rail is shaped and configured to receive the conveying means such that the rig cannot become inadvertently detached from the support rail during use. For example, the cross-section of the support rail may have a 1-l profile, i.e. having recesses into which the conveying means locate.

Preferably, for use in the demolition of a circular structure such as a cooling tower, the support rail follows a helical path down the structure. By the rail following such a path, the rig can travel round and down the structure, thereby enabling the demolition equipment to demolish the entire structure from top to bottom. The pitch of the helix of the support rail is preferably such that when the rig makes one circumferential circuit of the structure, the support rail has descended by a distance equal to the height of concrete removed in one pass of the rig.

The apparatus may comprise a plurality of rigs for use in the demolition of a common structure. The use of a plurality of rigs advantageously reduces the time for the structure to be demolished. Each of the plurality of rigs is preferably supported in use by a separate support rail.

When a plurality of rigs are used on helical support rails, the pitch of the helix of each support rail is preferably such that, when each of the plurality of rigs completes one circumferential circuit of the structure, each support rail has descended by a distance equal to the product of the height of concrete removed in one pass by one rig and the number of rigs in use. For example, if two rigs are used, the pitch of the helix of each support rail is preferably such that when each of the two rigs completes one circumferential circuit of the structure, each support rail has descended by a distance equal to twice the height of concrete removed in one pass by one rig. The two rail helices are in effect similar to a 'two start thread' of a common screw and, during operation, the two rigs are likely to be at the same level at locations diametrically opposite one another.

Preferably the support rail comprises a plurality of short rail sections in mutual alignment.

This facilitates the assembly and attachment of the support rail to the wall, and also enables rail sections to be readily removed from the wall behind the rig, as the demolition equipment demolishes the wall and the rig travels along the rail. The short rail sections may comprise an alignment arrangement to ensure that the rail presents a uniform level at joints. The short rail sections may also be fixed one to another, although this is by no means necessary.

For the avoidance of any ambiguity, references to 'behind' and 'in front of' (or 'ahead of') the rig are with respect to the direction of motion of the rig along the support rail (or equivalent rig support means).

According to a second aspect of the present invention there is provided a method of demolishing a concrete or masonry wall or a similar structure, the method comprising: attaching apparatus to a side of the wall to be demolished, the apparatus comprising a rig for carrying demolition equipment and rig support means for bearing the load of the rig, the rig support means being attached to the said side of the wall such that the load of the said apparatus is borne by the said wall; and operating demolition equipment on the platform to demolish a region of the wall.

Preferably the step of attaching the apparatus to the said side of the wall comprises attaching a support rail to the side of the wall, the load of the rig being borne by the support rail and thence the wall.

Preferably the step of operating the demolition equipment comprises demolishing a region of the wall above the support rail.

Preferably the rig comprises a platform for carrying the demolition equipment and conveying means attached to the platform, the conveying means being adapted to move along the support rail and to transfer the load of the platform to the support rail, and the method further comprises advancing the rig along the support rail as required to demolish further regions of the wall. This facilitates and expedites the demolition of the entirety of the wall.

Preferably the step of attaching the support rail to the wall comprises attaching a plurality of short rail sections to the wall in mutual alignment. This facilitates the construction of the support rail, particularly when working at height.

Preferably the method further comprises removing a short rail section from the wall behind the rig after a region of the wall above the rail has been demolished. The ability to do this is a benefit of constructing the rail from a plurality of short rail sections, and this also means that the demolition equipment itself does not demolish any of the rail left behind after the rig has moved on. The removed short rail section may be attached to the wall in front of the rig, thereby enabling a limited number of short rail sections to be used to complete what may be a large demolition job.

When preparing the apparatus for use, the rig may be raised to the working level in pieces and assembled in situ. The rig may first be placed astride the top of the wall, then lifted clear of the top of the wall using temporary support means. The conveying means can then be introduced to the support rail for use, and then the temporary support means removed such that the rig is supported by the support rail, ready for use.

Preferably the conveying means comprise a first wheel arranged to act on the upper surface of the support rail and a second wheel arranged to act on the underside of the support rail, and accordingly the step of introducing the conveying means to the support rail preferably comprises passing the support rail between the first and second wheels.

Preferably the step of operating demolition equipment comprises operating a concrete crushing unit supported by the rig.

The step of advancing the rig along the support rail may be performed by hand or with the aid of hand operated tools such as tirfors (industrial devices for pulling on a steel rope), or alternatively, if the conveying means are motorised, by driving the conveying means.

Embodiments of the invention will now be described, by way of example, and with reference to the drawings in which: Figure 1 illustrates a schematic cross section of a demolition equipment support rig in use around a concrete wall being demolished; Figure 2 illustrates a corresponding elevation from outside the wall; Figure 3 illustrates a corresponding elevation from inside the wall; Figure 4 shows details of the support wheel orientation; Figure 5 illustrates a typical arrangement of the rig with proprietary demolition equipment installed; Figures 6a and 6b show, in cross-section and from the side respectively, a first possible arrangement by which the support rail may be secured to a wall, using fixings and rail stabilising lugs; and Figures 7a and 7b show, in cross-section and from the side respectively, a second possible arrangement by which the support rail may be secured to a wall.

A consistent numbering system is used to identify rig components: 1. The rig box (equipment support platform).

2. An outer leg.

3. An inner leg.

4. An outer leg vertical support wheel or equivalent rolling/conveying means.

5. An outer or inner leg horizontal support.

6. The rig support rail.

7. The concrete wall to be demolished.

I5 8. The level of the concrete wall in advance of the current pass of the equipment.

9. The level of the concrete wall after the current pass of the equipment.

10. Rail stabilising lugs.

11. Fixings passing through the rail stabilising lugs and into the wall.

A lettering system is used to identify the proprietary equipment normally used with the rig: A. The winch used for raising and lowering the concrete crushing unit.

B. The concrete crushing unit power unit.

C. Derrick for supporting the concrete crushing unit.

D. The concrete crushing unit.

Overview A demolition equipment support rig representing a presently preferred embodiment of the invention is shown in the Figures. This rig is particularly suited for use on tall circular structures.

During the demolition of such structures the personnel access platform is normally on the outside of the structure. No access is normally provided on the inside. Debris from the demolition process is normally cleared from the platform by hand and dropped down the inside of the structure.

Rig components and support The rig is completely independent of the personnel access platform.

The rig is supported from the reinforced concrete wall that is being demolished. No loads are applied to the personnel access platform.

Vertical support of the rig is from a support rail 6. The support rail is fixed to the outside of the reinforced concrete wall 7. No support rails are used on the inside of the wall and no access is required to the inside of the wall for normal operation of the rig. Only one support rail is used. The rail provides the vertical support to the rig.

Normal tolerances for drilling of fixings into concrete are adequate for rail alignment.

The rig sits astride the wall 7 and is supported by a system of wheels 4, 5 that provide vertical and lateral restraint by running on the inside and outside of the concrete wall. The arrangement of vertical and horizontal restraints ensures that the rig cannot come off the wall or the support rail 6 when in use. Vertical support is provided by the wheels 4 acting on the support rail 6. Horizontal restraint is provided by the wheels 5, and ensure equilibrium of the rig. s

The support rail 6 is entirely supported by the concrete wall 7 being demolished, to which the support rail 6 is attached. The weight of the rig and the demolition equipment carried by the rig is entirely borne by the support rail 6, and thence by the concrete wall 7. It is important to appreciate that the rig and the demolition equipment carried by the rig are entirely supported by the wall itself, and that the wall is demolished by the demolition equipment it simultaneously supports.

For the avoidance of any ambiguity, it is to be stressed that the support rail 6 is attached to the intact region of the wall 7, beneath and ahead of the region of the wall that is being demolished by the rig. Demolition of the wall takes place in regions above the support rail 6 (or conceivably a safe distance behind the end of the support rail 6).

There are no load-bearing means between the support rail and the ground, other than the wall being demolished.

No load is applied to the top surface of the concrete wall 7 and no contact is made with the top surface of the wall during demolition. (This surface is rough and uneven.) The rig is adjustable to compensate for varying thickness of wall. For example, the rig box 1 may be varied in width to span different wall thicknesses; a narrower box may be used for thinner-walled structures such as cooling towers and smaller chimneys. Alternatively the system of attachment of the inner leg 3 to the rig box structure 1 may be adjustable This may take the form of a hinge at the top of the leg 3 with an adjuster at a lower level. For example, the hinge may be at the top of the box and the adjuster at the bottom of the box, to allow adjustment from the access platform on the outside of the structure.

Rig cross section (Figure 1) As illustrated in Figure 1, the rig box structure 1 provides anchorage for the rig legs and rigidity to the rig. It is also a convenient location for equipment such as the winch and power I O unit.

The two shorter outside legs 2 of the rig carry the weight of the rig to the vertical supports 4.

These vertical supports 4 comprise wheels that run on a rail 6, although other conveying means such as rollers or caterpillar tracks are also possible. The arrows show the direction in which these wheels act on the support rail, thereby providing vertical restraint to the rig.

The two inner legs 3 do not carry vertical loads. They provide horizontal restraint to the rig.

These legs are adjustable to cater for different wall thickness.

Horizontal restraint and overturning resistance for the rig is provided by a system of horizontal supports 5 on the inner and outer legs. These supports are positioned to prevent overturning of the rig.

The concrete wall is represented by (7).

Rig outside and inside elevations (Figures 2 and 3) The elevations in Figures 2 and 3 show the location of the inner and outer legs and their supports at each end of the rig box structure. The direction of travel of the rig is indicated on each elevation.

The support rail 6 is installed at the rig location to support the rig and also ahead of the rig to enable the rig to be advanced. The wheels 4 may or may not be motorised.

The level of the concrete wall in advance of the current pass of the equipment is shown by (8) and the reduced level of the wall after the current pass is shown by (9).

Support wheel orientation (Figure 4) Figure 4 shows the arrangement of the vertical support wheels 4 and the support rail 6. One wheel runs on the top surface of the rail and provides resistance to gravity loads. The other wheel runs on the underside of the rail and provides resistance to uplift loads.

The horizontal support wheel 5 runs horizontally on the concrete wall.

The concrete wall is again represented by (7).

Arrangement of rig with equipment (Figure 5) This shows the typical arrangement of the proprietary equipment to be used with the rig.

The winch (A) is used to raise and lower the demolition tool (D). The derrick supports the winch rope. The power unit (B) supplies hydraulic power to the concrete crushing unit (D).

The concrete crushing unit (D) reduces the level of the concrete wall.

Demolition equipment The bulky components used for the demolition process, such as the power unit (B), are supported above the top of the wall 7 so that the personnel access platform is not restricted.

The concrete crushing unit (D) is suspended above the wall.

The rig has provision for a derrick (C) with a winch (A) to carry the concrete crushing unit.

The rig also has space to accommodate the power unit (B) for the concrete crushing unit (D) and the winch (A) for lifting and lowering the concrete crushing unit (D). In a preferred embodiment, the power unit delivers hydraulic power to the concrete crushing unit, although compressed air or electric power may alternatively be used.

The derrick (C) supports the concrete crushing unit (D) to the rear of the rig, over the section of wall that is to be lowered in height. The rig has already travailed over this location. This section of wall is reduced in height by the concrete crushing unit without affecting the section of wall that is supporting the rig.

The rig is locked in place on the rail during operation of the concrete crushing unit.

Example Dimensions and Materials The dimensions of the rig will vary according to the size and weight of the equipment to be carried. It is envisaged that the length of the rig will be between two and three metros, and the width around one metro. The length of the outer leg 2 would be around 1.5 metres and that of the inner leg 3 would be around 2.5 metros. These dimensions and the sizes of structural members used in the fabrication of the rig would depend on the size and weight of the equipment to be carried. A rig for a small diameter chimney would need to be short; a rig for a cooling tower could be longer.

The rig can be constructed from mild steel, mostly from rolled steel sections. Most rig members can be fabricated from angle sections. Some members may be structural hollow sections, particularly where torsional stiffness is required. These are all common steelwork sections used in the construction industry.

Alternatively the rig could be constructed from aluminium sections in order to save weight.

Similar sections are available in aluminium. The lighter weight would be offset by greater cost.

The rail may also be fabricated from mild steel. It is likely to be around 60 mm in width between the flanges in order to give lateral clearance to a 40 mm wide steel wheel. The lateral clearance is necessary because, when demolishing curved structures such as cooling towers, for economy the rail is likely to be in short straight sections rather than a smooth curve.

The rail will be attached to the wall by proprietary concrete fixings such as mechanical anchors. These comprise a steel bolt with a proprietary means of anchoring the bolt into or through the concrete in order to resist pullout and shear forces. Some types of anchor can be removed from the wall for further use. The type and size of anchor to be used would be determined by those skilled in the art, and may vary according to the type and strength of the individual wall being demolished.

As shown in Figures 7a and 7b, the arrangement of fixings 11 may be through the centre of the support rail 6, in which case stabilising lugs 10 may be required. Alternatively the fixings 11 may be through the lugs 10 themselves, as shown in Figures 6a and fib. The choice of arrangement would depend on the loading of the support rail and rig.

Operation The rig can be raised to the working level in sections and assembled in situ.

The support rail 6 is in short sections (or 'units') and designed to allow for varying curvature of the wall. The sections of rail are fixed to the wall ahead of the rig at the required height.

The rig is moved by hand or with the aid of hand operated tools such as tirfors (an industrial device for pulling on a steel rope) as required. If motorised wheels 4 are used, the rig can be driven forward by operating the motors. Sections of rail are removed from behind the rig after the rig has moved off them and are re-used ahead of the rig.

On a circular structure the support rail is fixed in a descending helix to the wall. The slope of the rail is such that when the rig makes one circuit of the structure the rail has fallen in level by a distance equal to the height of concrete removed in one pass.

Two or more rigs can be used on a larger diameter structure. A separate support rail is provided for each rig. The same rail units may used to construct each support rail. The alignment of the support rail when fixed to the wall is different for each rig. If two rigs are in use, then two rail helices are formed, in effect similar to a 'two-start thread' of a common screw. Thus the two rigs are likely to be at the same level at locations diametrically opposite one another. (A second rig cannot work over an identical section of rail to a first rig since, after the pass of the first rig, the level of the wall will already be at the lowest level that the equipment can work to for the current rail height.) Each rail is installed to cover a few metres ahead of each rig. The slope of the rail supporting each rig is adjusted to suit the number of rigs in use. s

Only minor adjustment is needed to accommodate the particular curvature of the wall.

Safety features An inherent safety feature of the rig is that in the event of inadequate fixing of a rail section to the wall and consequent failure of the fixing, the rig would drop only a few hundred millimetres and come to rest on the top surface of the wall. The rig would not come off the wall.

The support rails are designed so that the vertical support wheels cannot come off the rail during normal operation. This ensures that the rig remains clear of the top surface of the wall during demolition.

The arrangement of vertical and horizontal restraints 4,5 ensures that the rig cannot come off the wall when in use.

No heavy manual lifting is involved in operating the rig.

Particular example

This example refers to the use of the rig for the demolition of a reinforced concrete industrial chimney.

The steeplejack installs his normal personnel access to the top of the chimney. This comprises a steeplejack ladder and a personnel access platform around the outside of the top of the chimney. He may also installa powered cradle for access by personnel and for carrying light materials. The powered cradle is suitable for engineer access.

The steeplejack installs a winch to the top of the chimney. This is driven from ground level and is used to raise heavier items of equipment.

The winch is used to raise the components of the rig to the top of the chimney. The rig is assembled astride the chimney wall.

The rig is adjusted to suit the width and curvature of the concrete wall.

The rig is lifted clear of the top of the wall using a temporary support system. This may be the winch or jacks. The first sections of rig support rail are threaded through the rig support wheels and fixed to the concrete wall.

The temporary support system is removed from the rig, which now sits on the support rail and is restrained by the lateral support wheels on the concrete wall.

The rig winch and the power unit for the concrete crushing equipment are raised to the top of the chimney and installed in the rig.

The derrick arm is raised to the top of the chimney and installed on the top of the rig.

The derrick arm is aligned to suit the curvature of the chimney wall.

The concrete crushing unit is raised to the top of the chimney and lowered onto the concrete wall behind the rig. The rig winch is attached to the unit and the ground level winch disconnected.

The rig is now fully assembled.

The electric power supply is connected to the equipment on the rig.

For the first circle of the chimney the support rails are set horizontally. Demolition of the concrete begins from zero height reduction and increases uniformly to the full working depth of a pass during travel around the full circumference of the chimney. The rate of increase in depth of concrete removed is modified if two or more rigs are in use.

Once a single circumference has been traversed, the rig is still at its initial level, but the top of the concrete wall in front of the rig slopes down throughout the chimney circumference and the concrete wall immediately behind the rig is at a level one pass lower.

From this point on, the rail sections are set to a downward incline to give a helical path with the pitch of the helix equal to the depth of one pass of the demolition equipment. If two rigs are in use, the pitch of the helix is twice the depth of one pass of the equipment. More rigs could be used on a large diameter structure such as a cooling tower.

For each operating cycle the rig is locked in position on the support rail and the crushing unit reduces the height of the wall behind the rig by the required depth. The rig is then unlocked and moved forward on the support rail to the next operating position where the process is repeated.

Sections of support rail are fixed in place ahead of the rig and sections of rail are removed from behind the rig for re-use.

The demolition process continues until the chimney is reduced to the required level.

Once demolition using the rig has finished, the assembly procedure is reversed to dismantle the rig and remove it from the chimney.

The lowest few metres of the chimney wall, including sections of the chimney with large openings, are normally demolished by conventional excavator-mounted pneumatic breakers.

Claims (34)

1. Apparatus for supporting demolition equipment, for use in the demolition of concrete or masonry walls or similar structures, said apparatus comprising a rig suitable for carrying demolition equipment such as a winch, derrick and concrete crushing unit, and rig support means, wherein, in use for the demolition of a wall, the rig support means are attached to a side of the wall being demolished, such that the load of the said apparatus is borne by the said wall.

2. Apparatus as claimed in Claim 1, wherein the rig support means comprise a support rail, and the rig comprises: a plafform suitable for carrying the demolition equipment; and conveying means attached to the plafform, the conveying means being I adapted to move along the support rail and to transfer the load of the plafform to the support rail and thence to the wall; wherein, in use, the support rail is attached to the said side of the wall and the plafform is supported by the rail using the conveying means, such that the rig can move along the rail and demolition equipment on the plafform can demolish a region of the wall above the rail.

3. Apparatus as claimed in Claim 2, wherein the rig further comprises a vertical support member extending between the support plafform and the conveying means, the support member being arranged such that the plafform is positioned over the top of the wall in use.

4. Apparatus as claimed in either Claim 2 or Claim 3, wherein the rig further comprises a stabilising member attached to the support platform, the stabilising member extending down the opposite side of the wall to the support rail in use.

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5. Apparatus as claimed in Claim 3, wherein the vertical support member further comprises horizontal restraining means arranged to act against the wall in use.

6. Apparatus as claimed in Claim 4, wherein the stabilising member further comprises horizontal restraining means arranged to act against the wall in use.

7. Apparatus as claimed in Claim 5 or Claim 6, wherein the horizontal restraining means comprise one or more wheels.

8. Apparatus as claimed in any of Claims 2 to 7, wherein the conveying means comprise a wheel arranged to act on the upper surface of the support rail in use.

9. Apparatus as claimed in Claim 8, wherein the conveying means further comprise a wheel arranged to act on the underside of the support rail in use.

10. Apparatus as claimed in any of Claims 2 to 9, wherein the conveying means are operable to secure the rig onto the support rail in use.

11. Apparatus as claimed in any preceding claim, wherein the rig is shaped and configured such that, if it were inadvertently to fall in use, the rig would locate around the top of the wall and not fall to the ground.

12. Apparatus as claimed in any preceding claim, wherein the width of the rig is adjustable to enable it to be used on walls of different thickness.

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13. Apparatus as claimed in any of Claims 2 to 12, wherein the support rail is shaped and configured to receive the conveying means such that the rig cannot become inadvertently detached from the support rail during use.

14. Apparatus as claimed in any of Claims 2 to 13 wherein, for use in the demolition of a circular structure such as a cooling tower, the support rail follows a helical path down the structure.

15. Apparatus as claimed in Claim 14, wherein the pitch of the helix of the support rail is such that when the rig makes one circumferential circuit of the structure, the support rail has descended by a distance equal to the height of concrete removed in one pass of the rig.

16. Apparatus as claimed in any of Claims 2 to 15 comprising a plurality of rigs for use in the demolition of a common structure.

17. Apparatus as claimed in Claim 16, wherein each of the plurality of rigs is supported in use by a separate support rail.

18. Apparatus as claimed in Claim 17 when dependent on Claim 14, wherein the pitch of the helix of each support rail is such that, when each of the plurality of rigs completes one circumferential circuit of the structure, each support rail has descended by a distance equal to the product of the height of concrete removed in one pass by one rig and the number of rigs in use.

19. Apparatus as claimed in any of Claims 2 to 18, wherein the support rail comprises a plurality of short rail sections in mutual alignment.

20. A method of demolishing a concrete or masonry wall or a similar structure, the method comprising: attaching apparatus to a side of the wall to be demolished, the apparatus comprising a rig for carrying demolition equipment and rig support means for bearing the load of the rig, the rig support means being attached to the said side of the wall such that the load of the apparatus is borne by the said wall; and operating demolition equipment on the rig to demolish a region of the wall.

21. A method as claimed in Claim 20, wherein the step of attaching the apparatus to the said side of the wall comprises attaching a support rail to the side of the wall, the load of the rig being borne by the support rail and thence the wall.

22. A method as claimed in Claim 21, wherein the step of operating the demolition equipment comprises demolishing a region of the wall above the support rail.

23. A method as claimed in Claim 22, wherein the rig comprises a platform for carrying the demolition equipment and conveying means attached to the platform, the conveying means being adapted to move along the support rail and to transfer the load of the platform to the support rail, and the method further comprises advancing the rig along the support rail as required to demolish further regions of the wall.

24. A method as claimed in any of Claims 21 to 23, wherein the step of attaching the support rail to the wall comprises attaching a plurality of short rail sections to the wall in mutual alignment.

25. A method as claimed in Claim 24 when dependent on Claim 23, further comprising removing a short rail section from the wall behind the rig after a region of the wall above the rail has been demolished.

26. A method as claimed in Claim 25, further comprising attaching the removed short rail section to the wall in front of the rig.

27. A method as claimed in any of Claims 20 to 26 wherein, when preparing the apparatus for use, the rig is raised to the working level in pieces and assembled in situ.

28. A method as claimed in any of Claims 23 to 27 wherein, when preparing the apparatus for use, the rig is first placed astride the top of the wall, the rig is lifted clear of the top of the wall using temporary support means, the conveying means are introduced to the support rail for use, and the temporary support means are then removed such that the rig is supported by the support rail.

29. A method as claimed in Claim 28, wherein the conveying means comprise a first wheel arranged to act on the upper surface of the support rail and a second wheel arranged to act on the underside of the support rail, and wherein the step of introducing the conveying means to the support rail comprises passing the support rail between the first and second wheels.

30. A method as claimed in any of Claims 20 to 29, wherein the step of operating demolition equipment comprises operating a concrete crushing unit supported by the rig.

31. A method as claimed in any of Claims 23 to 30, wherein the step of advancing the rig along the support rail is performed by hand or with the aid of hand operated tools such as tirfors.

32. A method as claimed in any of Claims 23 to 30, wherein the conveying means are motorised, and the step of advancing the rig along the support rail is performed by driving the conveying means.

33. Apparatus for supporting demolition equipment substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.

34. A method of demolishing a concrete or masonry wall or a similar structure substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.