GB2144479A

GB2144479A - The casting of concrete shells

Info

Publication number: GB2144479A
Application number: GB08418060A
Authority: GB
Inventors: Winston Griffith Jones; Ian Kenneth Massey
Original assignee: CMGM Pty Ltd
Current assignee: CMGM Pty Ltd
Priority date: 1983-07-18
Filing date: 1984-07-12
Publication date: 1985-03-06
Also published as: GB8418060D0; FR2549513A3; FR2549513B3; DE8421064U1

Abstract

A shutter assembly and method for casting an axisymmetrical concrete shell (14). The shutter assembly consists of a plurality of cantilever beams (24), means (32, 22) for anchoring each beam to the upper surface of a concrete ring (18) of the shell (14) to extend in a substantially radial direction towards the centre of the shell (14), single face shutter decking (40) and means (34, 36) for suspending the decking (40) from the beams (24) to lie against the under surface of the shell ring (18) and extend therefrom in substantially radial direction so that the subsequent ring (54) of the shell may be cast on the shutter against the edge of the ring (18). The method includes the steps of sequentially casting and connecting the rings in a radial a direction to complete the shell (14). <IMAGE>

Description

SPECIFICATION The casting of concrete shells This invention relates to a method of casting a concrete shell which is domed, conical, pyramidal or outwardly flared onto shuttering which supports the poured concrete only on its upper face.

Domed concrete roofs for reservoirs and like structures are conventionally cast over the structure on a continuous or substantially continuous deck which is supported by a plurality of temporary columns which are erected in the structure. A problem with this method of construction is, particularly with large diameter reservoirs, that a vast amount of shuttering and support structure is required to cover the reservoir to provide the deck onto which the concrete is to be poured. This false work is expensive and time consuming to erect and dismantle and contributes significantly to the cost of constructing the reservoirs.

It is the object of this invention to provide a method of casting a concrete shell which will minimize the amount of decking required for casting the shell and eliminate supports from the ground for supporting the decking.

A method of casting an axisymetrical concrete shell according to the invention includes the steps of sequentially casting and connecting in a substantially radial direction a plurai- ity of concrete rings on a single face shutter.

Preferably the shutter is a cantilever shutter and the method includes the step of supporting and extending the shutter in a substantially radial direction from a previously cast ring of the shell and casting the subsequent ring on the shutter. The shutter may include a plurality of radially directed beams which are located on the upper surface of at least one cast shell ring and shutter decking which is suspended from the beams with the method including the steps of locating anchor elements in the shell rings as they are cast and anchoring the beams to the elements in the cast rings.

Further according to the invention the method includes the steps of locating reinforcing material in each ring of t;he shell so that a portion of the material projects in a radial direction from the ring when cast and casting the adjacent ring over the projecting reinforcing material.

If the shell is to form a roof over a walled structure the method may include the step of casting the initial ring of the shell integrally with a ring beam at the upper end of the structure wall.

A shutter assembly for the casting of concrete shells according to the invention includes a plurality of beams, means on each beam for anchoring it to the upper surface of a concrete ring of the shell to extend in a substantially radial direction towards the centre of the shell, single face shutter decking and means for suspending the decking from the beam to lie against the under surface of the shell ring and extend therefrom in a substantially radial direction so that the subsequent ring of the shell may be cast on the shutter. Conveniently each beam carries an adjustabie levelling jack on each side of the anchor means so that the angle of inclination of the beam may be varied relatively to the upper surface of the ring to which the beam is anchored.

Further according to the invention the anchor means on each beam is a rod which is threadedly engageable in an anchor element which is cast into the shell ring.

Still further according to the invention the assembly includes a scaffold which is suspended from the underside of the shutter decking in use.

An embodiment of the invention is now described by way of example only with reference to the drawings in which: Figure 1 is a quarter section perspective view of the reservoir including a domed shell roof which has been constructed by the method of the invention, Figures 2 and 3 are sectional side elevations of fragments of the Fig. 1 reservoir roof while being constructed by the method of the invention, and Figure 4 is a partially schematic end elevation of the shuttering and supports structure of Figs. 1 and 2 as seen from the right hand end of the dravvings.

The reservoir of Fig. 1 is shown in the drawing to consist of a base 10, a cylindrical wall 1 2 and a domed axisymmetrical roof 14.

The base and wall of the reservoir are constructed in the conventional manner. The roof is constructed by first constructing a ring beam 1 6 on the upper edge of the wall 1 2.

The ring 1 6 may be and preferably is, particu larly if the reservoir is of a large diameter, post-tensioned and is made to include an inwardly and upwardly directed lip 1 8.

A plurality of reinforcing rods 20 are anchored in the beam 1 6 and extend radially from the end of the lip 1 8. The lip 1 8 additionally carries a plurality of circumferentially spaced rod anchors 22.

When the concrete of the ring beam 1 6 and its lip 1 8 has cured sufficiently, a plurality of radially directed cantilever beams arrangements 24 are located, as shown in Fig. 2, on the lip. The beam arrangements each include a beam 26 which carries two levelling jacks 28 and 30, locating means for at least two anchor rods 32 and 34 and a downwardly depending end support 36. The beam 26 preferably carries slings, not shown, on or near their free ends for supporting the free ends of the reinforcing rods 20 and whatever other reinforcing material may be necessary in the construction of the roof 14.

To locate the beam arrangements 24, the rods 32 are passed through the beams and anchored in the anchors 22 in the lip 18. The jacks 28 and 30 are then adjusted to the design inclination of the beams 26 and the rods 32 are tensioned and held to the beams by suitable anchor clamps 38. Deck shutters 40 are engaged with and between the end supports 36 on adjacent pairs of beams and pulled up against the underside of the lip 1 8 by the anchor rods 34 which are engaged with captive nuts 42 on the underside of the shutters. To enable this simply to be done the deck is pivotally connected to the support 36.

The anchor rods 34 carry threaded anchor sleeves 44 which are positioned on the rods to be located in the ring to be cast on the annular deck. With the shutters 40 located between spaced pairs of beams 26 tapered decking sheets 46 are layed on tubes 48 which, as is more clearly seen in Fig. 4, span the gaps between the pairs of beams which carry the deck shutters 40. A scaffold 50 is slung from the underside of the deck shutters for accessibility to the underside of the annular deck. Concrete is now poured onto the suspended deck between the free end of the lip18 and stops 52 on the deck shutters to form an annular concrete ring 54.

When the concrete of the ring 54 has cured sufficiently the anchor rods 34 are withdrawn from the deck shutters and the concrete of the ring 54 to free the shutters from the underside of the cast concrete. The ring 54, when free of its supporting shutter, is held in position by the reinforcing and the shell effect provided by its upward inclination.

The beam arrangements 24 are extended or replaced by the longer beams illustrated in Fig. 3 which are now advanced radially inwardly over the previously cast ring or rings to a position in which the following rings 56 and 58 may sequentially be cast on the deck shutters 40 and 46 against the free edges of the previously cast rings. The beam arrangements are held in the advanced position by engagement of the anchor rods 32 with the sleeve anchors 44 in the ring which for the time being are to anchor the deck. The deck is again adjusted to the design inclination for the particular ring to be cast by adjustment of the jacks 28 and 30, which as seen from Fig.

3, may be moved to any desired position on the beams 26.

As the diameter of the cast rings decreases towards the centre of the dome the tapered shutter elements 40 are arranged to overlap the shutters 46 progressively where this is possible. Where overlapping of the shutters is no longer possible narrower panels are used and the existing taper panels are combined to increase the effect angle.

The method and shutter arrangement of the invention is not limited to the construction of domes and could find equal application in the construction of any curved or peak shell which could for example be pyramidal in shape or be the outwardly flared base of an elevated reservoir or the like. Additionally the shutter arrangement for casting the concrete rings is not limited to that illustrated in the drawings and could consist of the any suitable cantilevered single deck apparatus capable of being anchored to the upper surface only of the cast shell rings and movably support the shutters on which the concrete rings are to be cast.

Claims

1. A method of casting an axisymetrical concrete shell including the steps of sequentially casting and connecting in a substantially radial direction a plurality of rings on a single face shutter.

2. A method as claimed in Claim 1 in which the shutter is a cantilever shutter and the method includes the step of supporting and extending the shutter in a substantially radial direction from a previously cast ring of the shell and casting the subsequent ring on the shutter.

3. A method as claimed in Claim 2 in which the shutter includes a plurality of radially directed beams which are located on the upper surface of at least one cast shell ring and shutter decking which is suspended from the beams with the method including the steps of locating anchor elements in the shell rings as they are cast and anchoring the beams to the elements in the cast rings.

4. A method as claimed in any one of the above claims including the steps of locating reinforcing material in each ring of the shell so that a portion of the material projects in a radial direction from the ring when cast and casting the adjacent ring over the projecting reinforcing material.

5. A method as claimed in any one of the above claims in which the shell is to form a roof over a walled structure and the method includes the step of casting the initial ring of the shell integrally with a ring beam at the upper end of the structure wall.

6. A shutter assembly for the casting of concrete shells including a plurality of beams, means on each beam for anchoring it to the upper surface of a concrete ring of the shell to extend in a substantially radial direction towards the centre of the shell, single face shutter decking and means for suspending the decking from the beams to lie against the under surface of the shell ring and extend therefrom in a substantially radial direction so that the subsequent ring of the shell may be cast on the shutter.

7. A shutter assembly as claimed in Claim 6 in which each beam carries an adjustable levelling jack on at least one side of the anchor means on the beam axis so that the angle of inclination of the beam may be varied relatively to the upper surface of the ring to which the beam is anchored.

8. A shutter assembly as claimed in either one of Claims 6 or 7 in which the anchor means on each beam is a rod which in use is threadedly engageable in an anchor element which is cast into the shell ring to hold the beam to the ring against movement in the direction of the beam axis.

9. A shutter assembly as claimed in any one of Claims 6 to 8 including a scaffold which is suspended from the underside of the shutter decking in use.

10. A shutter assembly as claimed in any one of Claims 6 to 9 in which the decking suspension means are supports which depend downwardly from the beams and to which the radially inner edge of the decking is pivotally connected and anchor rods which are connected, in use, between the beams through holes in the shell to the decking.

11. A method of casting a concrete shell substantially as herein described with reference to the drawings.

1 2. A shutter assembly for the casting of concrete shells substantially as herein described with reference to the drawings.