AU778630B2 - A formwork component - Google Patents

Description

P/00/011 Regulation 3.2

AUSTRALIA

Patents Act 1990

ORIGINAL

COMPLETE SPECIFICATION STANDARD PATENT Invention Title: A formwork component The following statement is a full description of this invention, including the best method of performing it known to us: Freehijis Carter Smith Beadle Meiboume~uua~o~a Printed 7 August 2001 (13:10) page 2 Freehiis Carer Smith Beaie Mieibourne\00362658 Printed 7 August 200 1 13:1 U- page 2 CD/0038.34109v12.doc 1A A FORMWORK COMPONENT Field of the Invention This invention relates to the assembly of formwork for pouring a concrete building foundation, although the invention would equally apply to the pouring of any other generally planar structure or slab.

An example of the type of building foundation to which the invention is applicable is described in Australian patent 584769 in the name Koukourou and Partners Pty Ltd. The contents of that specification are incorporated in full by reference into this specification. The invention has a particular, but not exclusive, application to the construction of concrete "waffle" raft slabs for domestic dwellings.

The term "box" is used in this specification to describe box-shaped elements and is not limited to box elements having six sides. The box elements typically employed by the invention are rectilinear quadrilaterals and have five 15 sides, so defining a closed void when placed with the open side facing down.

Often the box, or formwork for a void, is made from expanded polystyrene or cardboard.

oeeoo Background to the Invention Concrete slabs have been used as foundations for domestic dwellings for many years. For example, the waffle raft slab has been used in Australia as the foundation of a dwelling for over 10 years. One example of such waffle rafts is shown in the Koukourou patent no. 584769 (referred to above), where it is shown to construct such a slab by locating the boxes in rows so that the channels between them extend substantially the length of the concrete slab. The boxes used in the formwork are usually made from either cardboard or expanded polystyrene and have been separated by various mechanisms in the past. In the earlier stages of the use of waffle raft slabs, bricks, such as the CelltexTM bricks, CD/003834109v12.doc 2 were used to hold quadrilateral boxes apart so as to create channels between them. These channels form the ribs on the underside of the concrete slabs creating the "waffle" effect, hence the name "waffle raft slabs".

When preparing the formwork, once the boxes are in position, steel reinforcing bars are laid on top of the spacers which hold the boxes apart. It is desirable that the bars are located approximately in the centre of the concrete ribs of the slab which will ultimately be poured. Additional steel reinforcing is usually located on top of the boxes and the concrete is then poured and compacted into the channels and on top of and around the boxes, the concrete around the boxes forming the ribs of the slab.

Different spacers have been developed which are intended to be located at the intersection of the channels, for example, the spacer described in Australian patent specification 591816 in the name of N Leonardis. It provides a lighter means of holding boxes apart while providing adequate concrete flow around it so 15 that the strength of the poured slab is comparable with using bricks. This spacer has four right-angled "brackets", each of which abuts a corner of each of four boxes which define the intersection of the channels between the boxes. This spacer relies upon other means to hold the box against the spacer as the spacer does not positively engage the boxes. During the initial set-up of the box arrangement, there is nothing to prevent boxes moving away from a spacer in position, unless the box is surrounded on all four sides. This results in continual re-positioning of the boxes until the entire "lattice" is in place. Because there is no "positive" or rigid connection between the spacers and the boxes, a small bump can separate a box from a spacer and thus require the re-positioning of a large number of boxes.

Another problem with the current arrangement is that the boxes may rise up during the pouring of the concrete. The concrete inevitably cannot be poured simultaneously across the entire slab and the differing pressures from uneven pouring cause the boxes to rise. iii this case, concrete may flow under the lower edges of the boxes, which partly defeats the purpose of having boxes there.

CO/003834109v12.doc 3 Although the boxes do support some steel reinforcing (which holds the boxes down to some extent), they are very light objects in the context of a concrete slab construction and are thus prone to rising up upon concrete flowing into them, unless firmly held down.

Further, there has been found some difficulty in locating the reinforcing steel rods into the "U"-shaped receptors on spacers, such as those described in Australian patent specification no. 591816 (referred to above). Similar "U"-shaped holders have been used on a variety of "bar chairs" in the past. The difficulty in placing the steel rods in these holders adds significantly to the time taken to assemble the formwork prior to the pouring of concrete. In particular, all of the spacers, or other supports for the rods, must be exactly in line for the straight, heavy rods to be properly located. This adds significantly to the overall cost, as well as increases the risk that the steel rods will not be properly located and may thus not be central in the underneath ribs of the resulting concrete slab. This may have structural implications and weaken the slab, but any deficiencies will not be visible.

Accordingly, investigations have been carried out to ameliorate these disadvantages and develop a spacer which, at least partly, overcomes these difficulties and provides for a relatively rigid formwork lattice of boxes and spacers over which the concrete can be poured.

Summary of the Invention The invention generally provides a spacer for locating boxes forming part of a building foundation formwork arrangement, the spacer including: an engaging surface adapted to abut a box adjacent a corner area of the box, and an engagement means adapted to releasably engage a cooperating receiving means on the box to prevent, once engaged, the corner area rising vertically with respect to the spacer in situ.

CD/003834109v12.doc 4 Preferably, the engaging surface includes two parts perpendicularly disposed with respect to each other for abutting the corner area. Also, preferably the engagement means extends from the engaging surface.

In a preferred embodiment, the engagement means includes: a web extending outwardly from a junction of the two parts of the engaging surface, and a downwardly depending locking flange along the web's outward edge, the flange being adapted to engage an upwardly open receiving means on the box.

Desirably, there is provided a spacer for locating boxes in a grid arrangement, the spacer having four engaging surfaces which are disposed equidistantly around the spacer's perimeter so each engaging surface engages, in use, a corner of each of four boxes when the spacer is located at the intersection of perpendicular channels defined between the boxes. The spacer is thus in the 15 form of a cross or"cruciform".

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In another preferred embodiment, together with or instead of the above feature, there is provided a spacer in which the central portion of the spacer is adapted to receive two rods, which are perpendicular to each other. Preferably, the adaptation of the central portion includes "U"-shaped openings in the spacer to accommodate a rod in situ. More preferably, the spacer includes guiding members, each located between an engaging surface and the central portion, adapted to guide a reinforcing rod, in use, to the central portion by providing an upper surface of the guiding member downwardly inclined towards the central portion along which a rod may slide. In addition, there is provided a spacer in which each of the downwardly inclined guiding member's upper surfaces is shaped so that the outermost point, relative to the central portion, of its upper surface is higher than the innermost point of its upper surface. Preferably, the spacer includes bridging members extending from the inner end of each guiding member to the "U"-shaped openings, each bridging member being disposed at a CD/00834109v12.doc guiding member's inner end, an upper surface of the bridging member being at its highest point at the junction with the inner end of the guiding member and the maximum height of the bridging member being no more than the minimum height of the guiding member, the bridging member's upper surface being adapted for a rod to slide on it from a guide member to a "U"-shaped opening.

In another preferred embodiment, the spacer further includes a crossmember extending between two adjacent engaging surfaces to reinforce those engaging surfaces. Preferably, the cross-member comprises four elements in the form of a rectangle, connected to and located between parallel parts of the adjacent engaging surfaces.

A further preferred spacer further includes two central reinforcing members extending from each end respectively of a cross-member towards the centre of the spacer, the ends of the two central reinforcing members distant from the crossmember being connected.

*o The invention also provides a spacer in which at least one of the engaging surfaces is supported above a supporting level surface by a support member, or an element of a cross-member, which extends downwardly from a lowermost edge of the engaging surface.

Preferably, the support member or cross-member element is connected to the base of the engaging surface which it supports such that it is spaced horizontally from the engaging surfaces so that the spacer nests with an identical spacer when stacked.

oooo S° In another form of the invention there is provided a spacer adapted such that its upper surface is inclined downwardly to its centre facilitate a rod placed on top of the spacer sliding into the "U"-shaped opening.

The invention also generally provides a spacer for locating boxes in a building foundation formwork arrangement, the boxes being used to create voids CD/003834109v2.do 6 in a structure formed by the formwork, the spacer including: a pair of first engaging surfaces, each surface adapted to abut a box adjacent a corner of the box, and a second engagement means to engage a cooperating protuberance at the corner of the box to prevent, once engaged, the box rising vertically with respect to the spacer.

Preferably in this embodiment, the pair of first engaging surfaces are perpendicularly disposed with respect to each other. More preferably, the second engaging means is a web between the pair of first engaging surfaces. Most preferably, this web extends from the joint of the pair of first engaging surfaces and extends outwardly therefrom, desirably with a locking flange along its outward edge. In one preferred embodiment, the box has a vertically open groove at its corner which receives the locking flange from above to form the second engaging means. Preferably, the outer edge of the groove is inclined downwardly to 15 facilitate the flange being lifted into the groove upon the spacer being moved towards the corner of the box.

In a further preferred embodiment, the spacer includes guiding frame members located between the perimeter of the spacer and the centre of the spacer. Each guiding frame member is shaped so that the outermost point of its upper surface is higher than the innermost point of its upper surface. This facilitates an item, such as a reinforcing rod, sliding down the member towards the centre of the spacer. A steel rod placed on top of the spacer to one side of its medial area will slide down the upper surfaces of the guiding members into the groove defined by the inner edges of the four members. The guiding members may have two portions, being an outer portion and an inner portion, in which the outer portion is disposed generally along part of a radius from the centre of the spacer, and the inner portion is disposed perpendicularly to the outer portion at its inner end, the upper surface of the inner portion beinn at it- highest nnpoint at the junction with the inner end of the outer portion, the maximum height of the inner CD/003834109v12.doc 7 portion being the same as the minimum height of the outer portion. So that the guiding members do not obstruct the steel rods when in position, they may be located on radii at 450 to the rods, ie between the central portion and the pair of first engaging surfaces. As such, a steel reinforcing bar placed on the upper surface of the outer portion (with which it forms an acute angle of around 450) may slide under the effect of gravity to the inner end of the outer portion where it will continue to slide along the upper surfaces of the inner portion into the groove which is defined by the edges of the inner portion.

Preferably, the spacers nest upon being stacked for transport) to minimise volume in transit. Thus, the lower parts of the spacer are disposed so as to rest between the upper parts of a second spacer placed underneath the first.

Similar spacers may also be formed as would be appreciated by one skilled in the art for use at the ends of channels between rows of boxes. For example, such a spacer may only have two engaging surfaces, adjacent to each other for 15 use at a intersection (eg, at an edge of a slab). A spacer may also usefully have one or three engaging surfaces. The spacer may also be adapted by *addition of an arm disposed opposite the two engaging surfaces in order to support reinforcing rods on the external perimeter of the formwork used to reinforce the external beams of the slab or structure formed by the formwork.

The invention also provides a formwork arrangement for a concrete slab o.o including a spacer according to any one of claims 1 to 18 and a plurality of boxes located so as to form a grid of channels between the boxes, each box having a receiving means comprising a substantially horizontal groove, open along its top longitudinal side, at each of its corners to receive the engagement means.

It will be understood that the term "comprises" or its grammatical variants as used in this specification and claims is equivalent to the term "includes" and is not to be taken as excluding the presence of other elements or features.

CD/003834109v12.doc 8 Description of a preferred embodiment of the Invention A preferred embodiment of the invention will now be illustrated by way of example only with reference to the accompanying drawings in which: Figure 1 shows an isometric view of a spacer according to one embodiment of the invention; Figure 2 shows a plan view of a spacer according to the embodiment of the invention shown in Figure 1; Figure 3 shows a side view of a spacer according to the embodiment of the invention shown in Figure 1; Figure 4 shows a bottom view of a spacer according to the embodiment of the invention shown in Figure 1; g* Figure 5 shows a perspective view of a spacer according to the embodiment of the invention shown in Figure 1 when engaged with two adjacent boxes.

15 Figure 6 is an isometric view of a complete box.

Figure 7 is a cross-sectional view of a corner of the box illustrated in Figure 6.

For convenience only, in the drawings illustrating the invention, like numerals refer to like components.

Figure 1 illustrates a spacer 1 for locating boxes in a building foundation formwork arrangement.

Spacer 1 comnrises a central portion 2 and four symmetrically disposed outer portions 3. In each of outer portions 3, there is a pair of supporting arches CD/003834O1v 12.doc 9 4a and 4b. Each arch 4a is connected to a corresponding arch 4b of the adjacent outer portion by a web 5. Web 5 supports a guiding flange, comprising outer portion 6 and inner portion 7. The outer end of web 5 forms engagement means 8, which also acts as a web between the parts of engaging surface 9a and 9b.

The cruciform structure can be seen particularly in Figure 2.

Each part 9a and 9b of the engaging surface of the adjacent pair of engaging surfaces is reinforced by a cross-member extending therebetween formed by elements 10, 18a, 11 and 18b. As can be best seen in Figure 4, element 11 also forms a triangle with inner arms 12b and 12a, such that the three sides of the triangle are members 11, 12a and 12b. Each of the four members 12a and 12b are connected to the corresponding four arches 4a and 4b to reinforce the entire structure. The triangular structure defined by members 11, 12a and 12b rests on the supporting level surface on which the spacer and boxes are placed. This is important as it provides stability and strength to the formwork prior to the pouring of the concrete. The four triangular structures will remain at the lower surface of the slab once poured. The remainder of the spacer projects into the slab (once poured) from its lowermost surface.

:il e Inner sub-arches 28 and outer sub-arches 30 are located between each arch 4a and the arch 4b of the adjacent outer portion 3. The outer sub-arches extend between the outer edges of the hollow part of the arches 4a/4b and inner sub-arches 28 extend between the inner edges of that hollow part. Both inner and outer sub-arches are in a plane perpendicular to arches 4a/4b, and the top of arches 28 and 30 are connected to the underneath surface of web As is more easily seen in Figure 3, the upper surfaces of the guiding members 6 form a shallow "V"-shape to guide the reinforcing rods into "U"-shaped opening or slot 13 in the central portion 6 of the spacer 1. The initial guiding effect is from guiding member 6 to bridging member 7 to slot 13. The inner edges 14 of bridging members 7 form the vertical walls of slot 13. Further, the outer edge of guiding 3member 6 ic rinfrrnr a I 1 0 .guiding member 6 is reinforced by a triangular flange 5 conniecied to the outer edge of guiding member 6 and the upper surface of web 5. As such, guiding CD/003834109v12.doc flange 6 is supported along its base by web 5, at its outer end by flange 15 and at its inner end by bridging member 7.

Each engaging surface 9a/9b is affixed to the outer edges of corresponding arches 4a and 4b. Each part 9a and 9b is at an angle of approximately degrees to its corresponding arch 4a and 4b respectively. As a result, surface 9a and its corresponding surface 9b are disposed perpendicularly. This facilitates engaging the sides adjacent to a corner of a box. The engaging surface parts 9a and 9b are supported by panels 18a and 18b which extend from the base of engaging surfaces 9a and 9b respectively to the supporting level surface of the spacer. Each base of panels 18a and 18b is connected to the ends of both crossbeams 12a and 12b respectively and also opposite ends of cross-member 11.

Cross-member 10 has a web 19 extending either side of its'tbase surface to provide increased reinforcement.

The height of the lowermost surface of first cross-member 10 above second 15 cross-member 11, which rests on the supporting surface, may be sufficient to allow pieces of aggregate in concrete to pass between cross-members 10 and 11.

However, concrete ultimately located within the space defined by arches 4a and 4b, engaging surfaces 9a and 9b and cross-member 10 will generally enter that S-volume from above, and be compacted by a vibrator.

Figure 6 illustrates a corner of a suitable box 23 for use with the spacer illustrated in Figure 1. Box 23 has two perpendicular sides 24a and 24b which, in use, will abut against engaging surface parts 9a and 9b respectively. The corner where sides 24a and 24b meet has been bevelled, except in the bottom portion comprising protuberance 25, which has an upper outward surface 22 inclined upwardly to slot 21 as shown in Figure 7. Slot 21 is defined by corner surface 26 on its inner side and protuberance 25 on its outer side. Box 23 has a rounded or bevelled upper edge along the top of walls 24. The height of groove 21 above the lower-most edge of walls 24 is the same as the height of flange 8 abhove member 11 of the spacer.

CD/003834109v2.doc 11 Surface 22 slopes downwardly to the outer, rounded corner 29 of protruberance 25, the sides of which are co-planar with walls 24.

In use of the invention, the area in which the slab is to be poured will generally be levelled and marked out by edges in the ground, usually reinforced by wooden planks or the like. To build the formwork up from one edge, a first row of boxes is placed along that edge, each spaced by a spacer such as the one illustrated in Figure 1. That first row may also be held on its opposite side by "half" spacers which have only 2 first engaging surfaces pairs. At this stage, only two engaging surfaces are utilised against adjacent boxes. This is illustrated in Figure 5. As each spacer is pushed into position, locking flange 20 engages a cooperating slot 21 in the box 23 to "lock" spacer 1 into the box. The spacer 1 is then substantially prevented from moving horizontally with respect to the box.

The outer edge of web 8 contains a locking flange 20 extending *downwardly from web 8. Locking flange 20 can locate within a groove 21 in a 15 protuberance 25 from the corner of a box 23 and located in that groove to lock spacer 1 into position relative to the box.

S* Steel reinforcing rods (not shown in Figure 5) can then be laid along the top of the spacer. Typically, these reinforcing rods are 20 feet or 30 feet long and are **-**difficult to manoeuvre by hand because of their weight. The rods need only be placed generally on top of the spacer, where they will be guided by the guiding flanges into slot 13 of each of the spacers. Once the rods are located in slots 13, the rods act to hold the spacers down as the rods have significant weight. By holding the spacers down, the spacers are then able to also hold the boxes down thus forming a relatively rigid structure. Typically steel rods are located that their ends slightly overlap which is achieved utilising the natural flexibility within the steel rods. From this point, the next row of boxes can be added. Each box is placed on the supporting surface and pushed towards the two spacers with which it must engage.

As shown in Figure 6, the surface 22 of the protuberance 25 of the box CD/003834109v12.doc 12 outside receiving slot 21 is inclined towards slot 21. Accordingly, as box 23 is slid towards the first engaging surfaces 9a ad 9b of the relevant spacer, box 23 is forced down onto the supporting surface so that locking flange 8 may ride up over the upper edge of surface 22 and into corresponding slot 21. In this way, the next row of boxes can be added to the rigid structure one at a time. Thus, there is no need to coordinate the addition of a whole row of boxes at the same time. The addition of each separate box to a rigid and firm structure can be achieved by one person (although typically that will not be the case). Once the new row of boxes is added, a second row of spacers can be added in much the same manner. Each spacer can be placed near the adjacent corners of boxes and pushed up so that locking flanges 8 engage corresponding slots 21 in the adjacent box. A second series of reinforcing rods can be placed across the spacers to hold them into position for the third row of boxes to be put into position. The entire formwork can be built up in this manner. Once a significant proportion of the formwork is 15 formed, the steel reinforcing rods can be placed in the channels perpendicular to S.those in which they have already been placed. Slot 13 is sufficiently deep to retain at least two thicknesses of reinforcing rods. The second series of steel reinforcing rods add further weight to the spacers to improve the rigidity with which the boxes are held into position.

As shown in Figure 5, once in position, flange 8 locks in groove 21 and surfaces 9a/9b abut walls 24a/24b respectively.

V The resulting formwork is rigid and relatively easy to construct. Moreover, the interlocking nature of the formwork adds to the reliability with which the components are located with respect to each other, thus minimising future structural faults in the slab which, by its nature, are generally undetectable once the slab has been poured. For example, if reinforcing rods are not properly located in the centre of the spacers, they perform their function less effectively.

Similarly, if boxes rise during the concrete pouring process, greater volumes of concrete are necessary, which defeats the purpose of having the boxes. Once the 3o enireu rrmwork is completed, the concrete can be poured from the top in manners known to those skilled in the art of pouring concrete slabs. In many jurisdictions, CD/003834109v12.doc 13 vibrators are required by regulations to force the concrete down into the channels between the boxes and to engulf the spacers. The use of such vibrators improves the overall density of the concrete slab and, ultimately, its strength.

Typically, steel netting sheets will be placed across the top of the boxes, usually supported above the boxes by a series of bar chairs. This provides additional reinforcing to the upper surface of the concrete slab.

Preferably, the spacers are made from a material which facilitates moulding, particularly injection moulding, of the spacers. Appropriate plastics materials will be known to those skilled in the art, including materials such as polyethylene or PVC. Spacers may also be fabricated from material such as wood and steel, although this is likely to be less convenient. Any material is suitable which is relatively rigid and is preferably inert to concrete, steel and water.

S-Typically, boxes 23 will be manufactured from a lightweight but rigid material, such as expanded polystyrene. Boxes may also be made from cardboard and wood, although this would generally be quite expensive. The methods for making such boxes are known to those skilled in the art.

Further, an advantage of the spacer illustrated in Figure 1 is that it may be stacked on other spacers of the same construction. Guiding flanges 6 and 7 locate within the space defined between the eight arches (being four arches 4a and four arches 4b) so that the spacers "nest" on top of one another significantly reducing the volume required to transport or store a given number of spacers.

This also reduces the cost of use of spacers of the invention.

It will be apparent from the preceding description that a spacer as described above will be effective for positively locating boxes relative to one another in the latticework before pouring concrete and also for holding boxes down. It will be understood that the invention disclosed and defined in this specification extends to all alternative combinations of two or more of the individual features mentioned or evident from the text or drawings. All of these different combinations constitute various alternative aspects of the invention.