AU727660B2 - Slab construction method - Google Patents

Description

It 1

AUSTRALIA

Patents Act 1990 COMPLETE SPECIFICATION FOR A STANDARD PATENT Name of Applicant(s): Address for Service: Invention Title: INTERLOCK INTERNATIONAL PTY LTD CULLEN CO., Patent Trade Mark Attorneys, 240 Queen Street, Brisbane, Qld. 4000, Australia.

SLAB CONSTRUCTION METHOD The following statement is a full description of this invention, including the best method of performing it known to us: THIS INVENTION relates to a building method.

In particular, the invention concerns a method of making a concrete slab foundation for a building.

Slabs for building foundations are currently formed using techniques which require specialist skills and often more concrete is used than that realistically necessary for forming the slab foundation.

One known slab constructing technique involves digging a perimeter trench which, when filled with concrete, forms a footing for the slab. Digging the trench manually is time consuming and does not result in a trench of the minimum width dictated by the building plans. Digging is often carried out by a mechanical back hoe, but it is difficult to produce a trench to the 15 precise dimensions dictated by the plans and a wider and deeper trench often results and more concrete than necessary is used.

Timber formwork or bricks are then employed to define the upper level of the slab. The timber needs to be formed to match the undulations of natural ground level up to a level line which is used to form the top of the concrete slab.

If bricks are used, a footing is poured around the perimeter and bricks are laid to gain the height of the required slab.

Concrete is then poured up to the height of the formwork or bricks and the slab finished off in a known manner.

Both of these known methods are extremely time consuming and costly and are not particularly suitable for use in constructing low cost housing or where skilled labour is not available.

It is an object of the present invention to provide a method of making a slab foundation which at least minimise some of the disadvantages referred to above.

According to one aspect, the invention provides a method of making a slab foundation including the steps '.4 3 of assembling a formwork from prefabricated corner frame members and side frame members to define the periphery of a slab area and locating the formwork on the slab area, digging pier holes in the slab area at predetermined locations, positioning respective supports adjacent each of the pier holes, anchoring the supports to the ground and securing rods to ends of the supports so that a respective said rod extends into each said pier hole pouring concrete into the holes to form piers, building up an area of the slab area to a predetermined height and leaving a trench adjacent an inner periphery of the formwork, levelling the formwork relative to the ground and the rods extending from the piers, fixing the ends of the supports to the rods to maintain the levelled 15 position, laying reinforcing in the slab area, pouring concrete into the slab area and finishing the upper surface of the concrete to form the slab.

Preferably, the rods which extend into the pier holes do so to a depth of about two thirds of the depth o of the hole. These rods which may be screw threaded cyclone rated, may be used to anchor tie down rods in the building constructed on the slab.

0 The method of the invention may include the step of levelling the ground prior to placing the formwork onto the area where the slab is to be formed.

This step is only necessary where the ground is uneven.

Packing such as sand may be used and spread over the area. The sand may be compacted if desired. Preferably, the packing extends over an area approximately two metres wider and longer than the area required for the slab.

Packing sand is preferably employed within the formwork to build up the area to the desired height.

This packing sand is introduced to a height equal to the desired slab concrete thickness i.e. if the designed concrete thickness equals 100mm the packing sand beneath the slab is also 100mm and the frame depth therefore equals 200mm.

The trench may have any suitable width as .4 4 dictated by engineering considerations and has a width at least equal to the diameter of the pier holes.

A membrane moisture barrier may be laid over the slab area prior to pouring the concrete to produce the slab. A plastic film may be used. Holes may be cut in the membrane in the vicinity of the concrete piers.

The reinforcing placed in the slab area may consist of mesh and reinforcing rods. The rods may be arranged in the trench and the mesh placed over the built up slab area. The reinforcing may be supported by bar chairs.

If desired, elongate frame members may be secured to the supports and extend parallel to and inwardly of sides of the formwork. These elongate frame 15 members may be used to form a stepped rebate in the upper periphery of the slab.

According to another aspect, the invention provides a method of making a slab foundation including the steps of assembling a formwork from prefabricated corner frame members and side frame members to define the periphery of a slab area and locating the formwork on the slab area, digging a trench around the periphery of the slab area, positioning respective supports adjacent the *trench and at predetermined spacings along the trench, anchoring the supports to the ground and securing rods to ends of the supports so that the rods extend into the trench, pouring concrete into the trench to at least partially fill the trench, building up an area of the slab area to a predetermined height, levelling the formwork relative to the ground and the rods, fixing the ends of the supports to the rods to maintain the levelled position, laying reinforcing in the slab area, pouring concrete into the slab area and finishing the upper surface of the concrete to form a slab.

Preferably, the trench is only approximately half filled with concrete and thus a partial trench remains adjacent an inner periphery of the formwork.

The rods may comprise of screw threaded cyclone rated rods. The threaded rods may be used to advantage in levelling the formwork and allow the supports to be attached to them once the formwork is levelled and maintained in the levelled condition.

In this aspect of the invention, the rods may extend any desired distance into the concrete poured into the trench. The rods may be used to anchor tie down rods inthe building constructed on the slab.

The built up area in this aspect of the invention may be of any suitable height by preferably is about 100mm below the formwork.

Once the slab has cured, the formwork may be disassembled and reused to form a slab at another location.

S 15 A preferred embodiment of the invention will now be described by way of example with reference to the drawings in which: Figure 1 is a plan view useful in understanding one step in the preferred method of the invention; Figure 2 is a plan view useful in understanding another step in the preferred method of the invention; Figure 3a is a plan view useful in understanding another step in the preferred method of the invention;

S.

Figure 3b is an elevational view of a support used in the view of Figure 3a; Figure 4 is a perspective view useful in understanding the preferred method of the invention; and, Figure 5 is a horizontal sectional view through a portion of a foundation slab produced according to an embodiment of the invention.

The invention may include levelling the ground on which a slab is to be formed. If the ground is level, then this step may not be necessary. Where levelling is necessary, packing material such as sand is used. The sand is spread over the entire area and compacted to suit. The area may be of any desired size, but typically is about two metres longer and two metres wider than the area required for the slab.

A frame 9 consisting of side members and corner members is erected as shown in Figure 1. This frame defines the periphery of the slab and functions as formwork to allow the slab to be cast. The frame has corner members 10, 11, 12 and 13 and side members 14, 16, 17. To ensure that the frame is assembled correctly, preformed braces 18, 19 are secured to the frame by fasteners extending through preformed holes in the members of the frame. These braces are shown in Figure 2. In this way, no skill is required to erect the frame so that it has square corners with parallel sides. The frame members may be colour coded to assist assembly.

The frame side members may be provided with 15 markings to define the position of piers which will be drilled or dug into the ground at predefined locations inside the periphery of the frame. These markings may consist of holes in the side members denoting locations adjacent to which piers are dug into the ground. The location of these piers in the slab to be formed may be determined by a structural engineer. These piers may also be formed at locations within the slab as well as along the periphery.

These piers are dug to a suitable depth, typically until solid ground is reached. A support 20 in the form of an outrigger like that shown inset in Figure 3b, is located outside the periphery of the frame and adjacent each pier hole as shown in Figure 3a. These supports are anchored to the ground and are secured to the frame. The supports 20 each have an inner portion 21 which extends over a respective pier hole. These inner ends are attached to a threaded reinforcing rod 22 (see Figure 4) which extends into the pier hole. Preferably, the inner portion 21 of each support 20 has an elongate member 23 secured to it. This elongate member 23 extends parallel to side members of the frame and inwardly of the side members. The elongate members 23 have a horizontal web 24 and an upwardly extending flange 25 which forms a rebate in the resultant slab.

As shown in Figure 4, each support 20 is anchored to the ground by a spike 26 held relative to the support by a U bolt 27. The U bolt may be selectively positioned along a slot 28 in the support 20 and locked at a desired position along the slot by the U bolt 27.

Once all of the supports have been positioned in this way with the reinforcing rod support within the pier hole as shown in Figure 4, concrete is then poured into each of the holes. The rod 22 typically extends two thirds of the way into the hole. The concrete in the holes is allowed to set.

Once that concrete sets, the locking nuts (see Figures 4 and 5) are then used to level the frame 15 and the elongate member (if present) and tightened to lock the frame in its level position.

Sand 38 is then introduced into the area defined by the frame and compacted to a height below the level of the frame. This packing sand is introduced to a height equal to the desired slab concrete thickness i.e.

if the designed concrete thickness equals 100mm the packing sand beneath the slab is also 100mm and the frame depth therefore equals 200mm. A trench 31 of a width dictated by engineering considerations, and at least equal in width to the diameter of the pier holes is allowed to remain around the interior periphery of the frame.

A membrane 32 of plastic film is then laid over the slab area and secured to the frame by adhesive tape.

Holes are cut into the film in the vicinity of the concrete piers previously formed.

As shown in Figure 5, bar chairs 33 are positioned on top of the film over the sand and reinforcing mesh 34 placed on these chairs. Additional bar chairs 35 are placed in the trench 31 and reinforcing rods 36 placed within the trench 31. The mesh may be fixed to each of the rods extending from the piers.

Concrete 37 is then poured into the slab area defined by the frame and trowelled off or finished off in a known manner to a height determined by the free edge of the upstanding flange of the elongate members. If such elongate members are not present, then the upper face of the frame wall define the height of the slab.

The frame may disassembled when the concrete has cured and removed. The frame may then be reassembled and used at a new location where a slab is to be formed.

The rods extending from the piers act as hold down bolts to which the building may be secured.

With the method of the invention, unskilled labour may be used to cast concrete slabs for building.

When concrete is poured into the pier holes or into the trench according to the second aspect of the invention, the rods extend from the cured concrete and secure the formwork via the supports. Height adjustment to level the formwork is achieved via locking nuts shown in Figure 5. The highest corner of the formwork is chosen and by using a spirit level or other levelling device, levels are determined and the formwork may be lifted by adjusting the nuts at attaching supports at other corners of the formwork until the formwork is level.

Claims (14)

1. A method of making a slab foundation including the steps of assembling a formwork from prefabricated corner frame members and side frame members to define the periphery of a slab area and locating the formwork on the slab area, digging pier holes in the slab area at predetermined locations, positioning respective supports adjacent each of the pier holes, anchoring the supports to the ground and securing rods to ends of the supports so that a respective said rod extends into each said pier hole, pouring concrete into the holes to form piers, building up an area of the slab area to a predetermined .9 e height and leaving a trench adjacent an inner periphery of the formwork, levelling the formwork relative to the 15 ground and the rods extending from the piers, laying reinforcing in the slab area, pouring concrete into the slab area and finishing the upper surface of the concrete to form the slab.

2. The method of claim 1 wherein the rods extend

9. 9 into the pier holes to a depth of about two thirds of the depth of the pier holes. 3. The method of claim 1 or 2 wherein reinforcing mesh is placed over the raised area and reinforcing rods are placed in the trench. 4. The method of claim 1, 2 or 3 including the step of levelling the ground prior to placing the formwork over the slab area. The method of claim 4 wherein the step of levelling the ground includes placing packing material on the ground and compacting the material. 6. The method of claim 5 wherein the packing material extends over an area greater in size than the slab area. 7. The method of any one of claims 1 to 6 wherein the building up step results in the built up area being about 100mm below the height of the formwork. 8. The method of any one of claims 1 to 7 wherein the trench has a width of about 300mm. 9. The method of any one of claims 1 to 8 including the step of laying a membrane moisture barrier over the slab area prior to the pouring of concrete over the slab area.

10. The method of any one of claims 1 to 9 including elongate members attached to the inner ends of the supports for defining a rebate around the slab.

11. The method of any one of claims 1 to 10 wherein the frame members are colour coded to assist assembly of the formwork.

12. A method of making a slab foundation including the steps of assembling a formwork from prefabricated .o corner frame members and side frame members to define the periphery of a slab area and locating the formwork on the slab area, digging a trench around the periphery of the :slab area, positioning respective supports adjacent the trench and at predetermined spacings along the trench, anchoring the supports to the ground and securing rods to ends of the supports so that the rods extend into the 00 0 trench, pouring concrete into the trench to at least partially fill the trench, building up an area of the 0400 slab area to a predetermined height, levelling the 000o formwork relative to the ground and the rods, fixing the ends of the supports to the rods to maintain the levelled position, laying reinforcing in the slab area, pouring concrete into the slab area and finishing the upper surface of the concrete to form a slab.

13. The method of claim 12 wherein the trench is half filled with concrete.

14. The method of claim 12 or 13 wherein reinforcing mesh is placed over the raised area and reinforcing rods are placed in the trench. The method of any one of claims 12 to 14 including to step of levelling the ground prior /to placing the formwork over the slab area.

16. The method of claim 15 wherein the step of levelling the ground includes placing packing material on the ground and compacting the material. 11

17. The method of claim 16 wherein the packing material extends over an area greater in size than the slab area.

18. The method of any one of claims 12 to 17 wherein the building up step results in the built up area being about 100mm below the height of the formwork.

19. The method of any one of claims 12 to 18 including the step of laying a membrane moisture barrier over the slab area prior to the pouring of concrete over the slab area. The method of any one of claims 12 to 19 including elongate members attached to the inner ends of e the supports for defining a rebate around the slab.

21. The method of any one of claims 12 to 15 wherein the frame members are colour coded to assist assembly of the formwork.

22. A concrete slab foundation produced by the method of any one of claims 1 to 21. DATED this 8th day of April 1997 INTERLOCK iTEPNATIONA PTY LTD By their Patent Attorneys q CULLEN CO. T. 19 1