CONSTRUCTION OF ANNULAR WALLS

Abstract: In one aspect the present invention provides an apparatus and a method for constructing an annular wall (10), for example a cylindrical concrete water tank, the apparatus comprising a mould (26) attached to a support assembly (20) mounted on a pivot (16). The mould (26) being rotatable about the pivot (16) in a substantially horizontal plane. In use, the mould (26) is positioned at selected angular locations and a hardenable composition is applied to the mould surface (28) to form the wall. In another aspect a frame arrangement is provided for use in the construction of a reinforced wall (10), the arrangement comprising a plurality of substantially upright supports (37), a first layer of reinforcement (40a) secured to the supports (37) and a second layer of reinforcement (40b) secured to the truss members (38) such that the second layer (40b) is generally parallel to, but laterally spaced from, the first layer of reinforcement.

Description: CONSTRUCTION OF ANNULAR WALLS This invention relates to the construction of annular walls as may be used, for instance, in large water storage tanks. Currently the normal technique for constructing a large tank involves the provision of a large number of preformed concrete panels in the form of segments which are often constructed off-site and transported to the location at which the tank is to be constructed, and the segments are sealed edge to edge to form the wall of the tank. The construction of such a tank is time-consuming and transportation of large pre-cast segments to remote sites is difficult. An alternative technique requires an internal framework to be erected on-site and the outer surface of the framework is sprayed with a concrete matrix to produce a tank. A still further technique requires concentric inner and outer shells to be constructed into which concrete is poured to form a unitary circular wall. It will be apparent that maintaining the structural integrity of such an internal framework or concentric inner and outer shells, prior to application of the matrix is difficult in large scale applications and necessitates construction of the full circular internal framework or concentric shells prior to commencing spraying or pouring of the concrete. It is an object of the present invention to provide a technique and apparatus able to quickly and conveniently erect annular walls or segments thereof. In accordance with one aspect of the present invention there is provided an apparatus for constructing an annular wall, the apparatus comprising a mould having a substantially upright mould surface defining a surface of a segment of the wall to be constructed, the mould being attached to a support assembly mounted on pivot means located substantially on the central axis of the wall such that the mould is rotatable about the axis in a substantially horizontal plane, the arrangement being such that in use, the mould is positioned at a selected first angular location relative to the pivot means and a hardenable composition is applied to the mould surface to form a first wall segment, after which the mould is moved to an adjacent location and the hardenable composition is applied to the mould surface to form an adjacent wall segment. In accordance with another aspect of the present invention there is provided a method of constructing an annular wall using the above-described apparatus, the method comprising: forming a first wall segment by applying a hardenable composition to the mould surface and allowing the composition to harden, at least partially; moving the mould surface to an adjacent location; and applying the hardenable composition to the mould surface at the adjacent location to form an adjacent wall segment. In accordance with a further aspect of the present invention there is provided a frame arrangement for use in the construction of a reinforced wall, the arrangement comprising: a plurality of substantially upright supports positioned at spaced locations along a side of the wall to be constructed; a first layer of reinforcement secured to the supports such that the layer is parallel to the side of the wall and extends along the wall; a plurality of vertically spaced elongate truss members secured at one lengthwise edge to the supports such that the truss members extend laterally along the wall and such that they each lie in a substantially horizontal plane; and a second layer of reinforcement secured to the free lengthwise edge of each of the truss members such that the second layer is generally parallel to, but laterally spaced from, the first layer of reinforcement. By the use of the present invention an annular tank can be cast in situ without requiring extensive scaffolding or other framework to define a complete mould surface. Furthermore, the rotation of the mould surface around the pivot means enables the wall to be cast continuously or in a stepwise, or semi-continuous manner, thereby avoiding a difficulty encountered in the prior art in which the alignment of individual adjacent preformed wall segments requires sophisticated surveying or precision framework. In a preferred form of the invention, the annular wall is cylindrical, in which case the central axis constitutes the axis of curvature of the wall, and means are provided for adjusting the orientation of the mould surface relative to the support assembly such that the axis of curvature of the mould surface may be inclined relative to the axis of curvature of the wall and/or the axis of curvature of the mould surface may be moved such that it is slightly offset relative to the pivot means. In some applications, after a wall segment has been formed and has dried, or has commenced to dry, upon the mould surface it may be necessary to physically remove the mould surface by a radially inward movement of the mould surface prior to rotation of the mould surface to an adjacent location. It is therefore desirable that the support assembly is telescopic and includes driving means for moving the mould radially in a plane substantially normal to the axis of curvature of the wall. It is also desirable that the support assembly further comprises means for raising and lowering the support assembly to facilitate the insertion of means for preventing the apparatus from rotating when the hardenable composition is to be applied. Adjacent wall segments may be post-tensioned, for instance, by disposing circumferentially extending conduits adjacent the outer surface of the mould surface and then spraying the hardenable composition onto and around them. After the annular wall has been cast, cables or other tensioning means disposed within the conduits can be tightened to post-tension the wall. Alternatively, external tensioning means can be disposed around the circumference of the hardened wall. Additionally, or alternatively, vertically extending conduits can also be disposed such that they extend vertically through the wall to receive vertically, extending tensioning means to assist in stressing of the wall. If it is desired to form the wall in a non- continuous manner, the individual hardened wall segments can be locked together by the circumferential tensioning means after a sealant has been interposed between adjacent wall segments. In general the fluid hardenable composition will comprise a concrete such as CSR "Readymix" Super Spray Concrete with "Micropoz". Other construction materials appropriate for moulding/casting onto the mould surface such as organic polymers will also be known to those skilled in the art. Conveniently the fluid composition is sprayable although other application techniques such as trowelling will also be appropriate in some circumstances. The lateral extent (degrees of arc) of the mould surface is not particularly limited - for a cylindrical tank, a circumferential length of the order of 8.5 metres is convenient when constructing walls of 10 to 15 metres radius and 6.5 metres high. With both the method and apparatus aspects of the invention, the mould surface may define an arcuate cross- section such that the internal surface of the completed annular wall is a smooth circular surface. However, the invention is not limited to this and other configurations of the mould surface are also appropriate. For instance a flat mould surface will produce a polygonal internal surface of the wall. It will be apparent, for instance, that the apparatus could be used to produce conical walls by providing an inwardly directed sloping mould surface. It is also envisaged that the method and apparatus are also adaptable to the construction of structures such as channels. An embodiment of the apparatus and method incorporating the invention will now be described, by way of example only, with reference to the accompanying drawings in which: Figure 1 shows a perspective view of an embodiment of the apparatus of the present invention prior to spraying of the construction material; Figure 2 shows a cross-section of a wall under construction and the embodiment of Figure 1; Figure 3 shows a plan view of the wall and apparatus of Figure 2 ; Figure 4 shows a part sectional view of a frame arrangement for the wall; and Figure 5 shows a perspective view of a detail of Figure 4. In the drawings a vertically extending wall 10 is shown under construction footed on a circular slab 12. Apparatus 14 in accordance with the invention comprises a pivot 16 in the form of a post located at the centre of the circular slab 12. A radially extending support assembly 20 is rotatably mounted on the post and rides on swivel wheels 24. Extending radially from the support assembly 20 is an arcuate sheet 26 having a radially outer surface defining a mould surface 28 with a horizontal cross-section corresponding to the internal diameter of wall 10 and extending vertically the height of the wall 10. A typical height of the mould surface is 7.5 metres. The support assembly 20 is of telescopic form and has, intermediate the pivot 16 and the mould surface 28, an hydraulic mechanism 30 serving to displace the arcuate sheet 26, and thus the mould surface 28, radially inward and radially outward relative to the pivot 16. Further, the apparatus 14 also comprises length adjustable props 27 which are connected to the radially inner surface of the arcuate sheet 26 and to the support assembly 20 by way of swivels (not shown) such that by adjusting the length of each prop 27, the orientation of the mould surface 28 relative to the support assembly 20 can be adjusted. By varying the length of the props, the axis of curvature of the mould surface 28 may be tilted backwardly or forwardly relative to the axis of curvature of the wall or, if the props 27 on one side of the support assembly are shortened, the axis of curvature of the mould surface may be slightly offset relative to the pivot 16. These adjustments enable the mould surface 28 to be positioned in such a way as to most closely correspond to the shape of the inner surface of a frame arrangement 36 which will be described hereinafter. Wall 10 in this embodiment is the retaining wall of a 22 metre diameter, 6.5 metre high water tank. Construction commences by pouring a reinforced concrete slab 12 in the form of a 22.5 metre circle with a deepened, reinforced circumferential rim 32. Within rim 32 is a circumferentially extending channel 34 into which wall 10 seats. Following hardening of the slab 12, the pivot 16 is installed at the radial centre of the slab 12 and the apparatus 14 is rotatably disposed thereon. The frame arrangement 36 is then constructed and comprises a number of vertically extending soldiers 37 which are spaced around the radial outer edge of the rim 32 and a number of vertically spaced, laterally extending annular trusses 38, shown in detail in Figures 4 and 5. In use, the soldiers 37 are fixed at their bottom end to the slab 12 by way of bolts, for example, and a sheet of reinforcing mesh 40a is placed against the innermost edge of each soldier 37, as shown in Figure 4. A number of the annular trusses 38 are then fixed to the soldiers 37, for example by tying securely with wire, at spaced intervals along their vertical length, thereby holding the mesh 40a in position. A number of laterally extending conduits 42a are then located adjacent the radially inner surface of the sheet of reinforcing mesh 40a and are fixed to the trusses 38 by tying securely with wire. A number of laterally spaced, vertically extending conduits 42b are then inserted lengthwise through apertures 44 in the trusses 38 such that they lie against the laterally extending conduits 42a and are likewise tied to the trusses 38. The conduits 42a, 42b will serve to carry the post-tensioning tendons as will be described hereinafter. A second, or inner, sheet of reinforcing mesh 40b is then placed against the radially innermost edge of the annular trusses 38 and is, again, tied to the other components of the frame. The vertical conduits serve to support the weight of the wall and, prior to subsequent operations, a cable is inserted into each vertical conduit such that one end of the cable extends from the bottom of the conduit and is ultimately held in position in the wall after the concrete composition has hardened. The other end of the cable is threaded, for example, to cooperate with means, such as a nut, for tensioning the wall 10 after it has fully hardened. The frame arrangement 36 stably supports the reinforcing mesh 40a, 40b and the conduits 42a, 42b such that their vibration is minimised when the concrete composition is sprayed onto them under high pressure. The soldiers 37 are ultimately removed from the tank after the tank wall has fully hardened. This frame arrangement is, of course, applicable to walls other than cylindrical walls, such as straight wall sections. The arcuate mould surface 28 of the apparatus 14 is then manoeuvred so that the arcuate outer surface of the mould surface 28 coincides with the internal diameter of channel 34 in the slab 12, the support assembly 20 is raised to facilitate the insertion of stands and is then lowered again such that the arcuate sheet 26 cannot rotate about the pivot 16. The wall segment is then formed by spraying a concrete composition such as "Super Spray with Micropoz" available from CSR Readymix Australia onto the mould surface thereby incorporating the tendon conduits and reinforcing mesh within the wall. To facilitate construction of the wall, the operator spraying the concrete composition may be positioned upon a scissor lift which can be raised and lowered, thereby enabling him, and his ancillary spray equipment, to be positioned at the most appropriate position relative to the wall. Spraying is carried out until a wall depth of approximately 20 centimetres is achieved and the concrete composition is allowed to commence hardening. After each segment of the wall has been formed and commences hardening, the support assembly 20 is retracted radially inward such that the mould surface 28 is spaced laterally from the hardening wall, thereby providing a substantial gap between the mould surface 28 and the wall surface. A formwork release agent may then be brushed or sprayed onto the mould surface 28 to assist in breaking the suction between the mould surface 28 and a subsequently formed wall surface. The mould surface 28 is then rotated about the pivot 16 until it lies laterally adjacent the hardening segment 10' just formed. The concrete composition is then sprayed onto the mould surface 28 to form a second wall segment 10' which is integral and coextensive with the previously formed and now hardening wall segment 10. This forming process allows the complete cylindrical tank to be formed continuously in one piece and avoids a problem encountered with the prior art in which individual wall segments must be locked together and sealed to waterproof the tank. After the tank has fully hardened, a rubber mastic composition is interposed between the wall 10 and the channel 34 to ensure water-tightness. In one preferred form of the apparatus, the support assembly 20 includes an upstanding support (not shown) such that the upstanding support can rotate about the pivot 12 with the support assembly 20. In use, after fixing the soldiers 37 to the slab 12 a roll of reinforcing mesh is fitted over the support so that on rotation of the apparatus about the pivot 12, a continuous sheet of mesh can be unwound from the roll. This has the advantage of reducing construction time as it eliminates the need to position and fit individual sections of mesh at each wall segment location. The steps of moving the mould surface 28 adjacent a freshly completed and hardening section of the circumference and spraying of concrete thereon is continued until a complete circle is achieved. Tensioning cables are then fed through the circumferentially extending conduits and tightened to bind the segments into a waterproof whole. Preferably two segments diametrically opposed from each other have access panels provided therein to operate these tensioning cables or rods in ways known in the stressed concrete art. If provided, the vertical conduits are also fed with cables and tensioned. Further, it is envisaged that more than one apparatus can be used to further reduce the overall construction time of a tank. In this case each apparatus would rotate about a common pivot post such that, for example, each apparatus initially forms adjacent wall segments after which each apparatus is rotated in opposite directions about the common pivot, each forming sequential wall segments, and again come together again to form the last of the wall segments, thereby completing the tank. If it is desired to construct the wall in discrete segments, rather than continuously, the lateral (vertical) edges 46, 48 of the wall segment 10 are cleanly sculpted, in this case in the form of a counter- clockwise oriented "V"-shaped formation. Adjacent wall segments have corresponding but opposed sculpting of their vertical edges to ensure that the segments key together to produce a water-tight seal. The curved outer surface of each segment, measured horizontally, is of the order of 7.5 metres. After an individual wall segment 10 has dried and is self-supporting, the hydraulic mechanism 30 is activated to displace the mould surface 28 radially inward from the now hardened wall segment, the swivel wheels 24 riding on the smooth surface of the slab 12. To form the next segment 10' of the cylindrical wall, the apparatus 14 with the mould surface 28 in its retracted (radially inward) position is rotated around the pivot post 16 until it lies laterally adjacent the hardened segment 10' . The hydraulic mechanism 30 is again activated until mould surface 28 is flush with the inner diameter of the channel 34. Once again, circumferential and vertical conduits are temporarily suspended adjacent but spaced from the mould surface and the concrete composition is sprayed to form a second wall segment adjacent and coextensive with the now hardened wall segment. The lateral edge of the new segment immediately adjacent the edge of the pre-existing hardened segment is shaped to correspond in section therewith. The above steps of placing the mould surface adjacent a fresh section of the circumference, removing the mould surface radially inward and rotating the apparatus are continued until a complete circle is achieved. Tensioning cables are then fed through the circumferentially extending conduits and tightened to bind the segments into a waterproof whole. In the above described embodiments, the mould surface 28 defines the internal wall of the completed water tank. It will also be apparent that the configuration of the apparatus can be modified so that the side of arcuate sheet 32 facing the pivot is the mould surface. In this embodiment the fluid composition will be applied from the "inside" of the wall and the mould surface will define the exterior face. Although the invention has been described using an example of a circular water tank many modifications may be made thereto without departing from the spirit and scope of the invention which includes every novel feature and combination of novel features herein disclosed.

Claims: CLAIMS : 1. An apparatus for constructing an annular wall, the apparatus comprising a mould having a substantially upright mould surface defining a surface of a segment of the wall to be constructed, the mould being attached to a support assembly mounted on pivot means located substantially on the central axis of the wall such that the mould is rotatable about the axis in a substantially horizontal plane, the arrangement being such that in use, the mould is positioned at a selected first angular location relative to the pivot means and a hardenable composition is applied to the mould surface to form a first wall segment, after which the mould is moved to an adjacent location and the hardenable composition is applied to the mould surface to form an adjacent wall segment. 2. An apparatus according to claim 1, wherein the annular wall is cylindrical and the central axis constitutes the axis of curvature of the wall. 3. An apparatus according to claim 2, wherein the apparatus further comprises means for adjusting the orientation of the mould surface relative to the support assembly such that the axis of curvature of the mould surface may be inclined relative to the axis of curvature of the wall and/or the axis of curvature of the mould surface may be moved such that it is slightly offset relative to the pivot means. 4. An apparatus according to claim 3, wherein the means for adjusting the orientation of the mould surface relative to the support assembly comprises a plurality of length adjustable props which extend from the support assembly to the mould. 5. An apparatus according to any one of claims 1 to 4, wherein the support assembly is telescopic and the support assembly includes first driving means for moving the mould radially in a plane substantially normal to the axis of curvature of the wall. 6. An apparatus according to claim 5, wherein the first driving means is fluid actuated. 7. An apparatus according to any one of claims 1 to 6, wherein the support assembly includes second driving means for raising and lowering of the support assembly whereby to facilitate the insertion of means for preventing the apparatus from rotating when the hardenable composition is to be applied. 8. An apparatus according to claim 7, wherein the second driving means is fluid actuated. 9. An apparatus according to any one of claims 1 to 8, wherein the support assembly includes means for carrying a roll of reinforcement material such that in use, the reinforcement material can be unwound from the roll as the support assembly is rotated about the axis. 10. An apparatus according to any one of claims 1 to 9, wherein the apparatus is mounted on a base arrangement on which the pivot means is located, the base arrangement having a circumferentially extending channel for receiving a bottom portion of the wall. 11. A frame arrangement for use in the construction of a reinforced wall, the arrangement comprising: a plurality of substantially upright supports positioned at spaced locations along a side of the wall to be constructed; a first layer of reinforcement secured to the supports such that the layer is parallel to the side of the wall and extends along the wall; a plurality of vertically spaced elongate truss members secured at one lengthwise edge to the supports such that the truss members extend laterally along the wall and such that they each lie in a substantially horizontal plane; and a second layer of reinforcement secured to the free lengthwise edge of each of the truss members such that the second layer is generally parallel to, but laterally spaced from, the first layer of reinforcement. 12. A frame arrangement according to claim 11, wherein the reinforced wall is arcuate. 13. A frame arrangement according to claim 11 or claim 12, wherein conduits for receiving post-tensioning means are secured to the frame arrangement. 14. A method of constructing an annular wall using the apparatus of any one of claims 1 to 10, the method comprising: forming a first wall segment by applying a hardenable composition to the mould surface and allowing the composition to harden, at least partially; moving the mould surface to an adjacent location; and applying the hardenable composition to the mould surface at the adjacent location to form an adjacent wall segment. 15. A method of constructing an annular wall as claimed in claim 14, wherein the mould surface is moved and the adjacent wall segment is formed while the first wall segment is hardening, thereby causing the adjacent wall segments to be integrally formed.

Inventors: LAZZAROTTO ANTONIO JOHN, LAZZAROTTO, ANTONIO, JOHN
Applicants: LAZZAROTTO ANTONIO JOHN, LAZZAROTTO, ANTONIO, JOHN
Application year: 1992
Main classification: E04H7
IPC codes: E04G11, E04H7