NZ243822A - Concrete slab with angular crack control element - Google Patents

Description

24 3 82 2 Patents Form #5 NEW ZFAf.ANT) Patents Act 1953 COMPLETE SPECIFICATION Vy* ft y/ AFTER PROVISIONAL NO : 243822 DATED: 3 August 1992 TITLE; Element for Forming Controlled Cracks in Concrete Slabs We,: Steel Products Limited Address: 4th Floor, Ronald Trotter House, 583 Great South Road, Penrose, Auckland, New Zealand Nationality: New Zealand company hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: PF05JWP FEE CODE -1050 24 3822 This invention relates to an element for controlling the formation of cracks in concrete slabs and facilitating the production of a slab with a screeded level surface.

When concrete slabs are cast they have a common tendency to crack. To help reduce the disadvantageous results of uncontrolled or random cracking, a technique has been developed to cause a slab to crack along a predetermined line. This technique involves the placement in the slab of an elongate element which creates a line of weakness in the slab along which the slab will crack. The element may be cast into a slab at the time 10 when the slab is first made; or it may be placed in a channel cut out of an existing slab.

In the past these elements have been constructed of both concrete and steel. Elements of concrete known to the applicant have a shape resembling a railroad rail; i.e. they have a flat base on which they rest and an upstanding portion which is narrower than the base.

Concrete elements of this type have been used in the casting of a slab which is levelled by a vibrating screeding beam. In this technique the concrete elements are set up in spaced parallel rows on the ground and concrete is cast between the elements. The vibrating screeding beam is mounted between two of the concrete elements and moved 20 along the elements to level the concrete before it has set.

Concrete elements of this type are heavy and rather cumbersome to work with. They must be cut with an abrasive disc which is a dirty and time consuming job. Furthermore, they have relatively wide upper faces which makes it difficult to finish off 25 neatly a joint in the slab where such an element is located. There is also a tendency for the slab to crack away from the concrete eleme nts in use.

On the other hand the elements which are made of steel are substantially lighter and easier to work with. Those known to the applicant which are intended to be used in 30 newly cast slabs must be supported above the ground in their working position either prior to casting of the slab or placed in the concrete after the slab has been cast but before the concrete has set. The former version is illustrated in US patent #4455104 (Weisbach). As disclosed in this patent, the element is supported on pegs driven into the ground at intervals along the line of the working position. This has a number of 35 disadvantages. In the first place the pegs will pierce the plastics film which is 243822 weight which the pegs can support will be relatively limited. Also, accurate location of the pegs may be difficult.

It is an object of the invention to provide an alternative design which enables the elements to be used to support a vibrating screeding beam for levelling the slab.

According to the invention there is provided an element of sheet steel or other laminar material which is cast into a slab of cementitious material having upper and lower faces, 10 the element comprising a longitudinally extending flat base on which the element rests and which is located adjacent the lower face of the slab, and an upwardly projecting portion which arises from the base and separates portions of the slab located one on either side of the upwardly projecting portion, the upwardiy projecting portion having an upper edge which is located adjacent and substantially parallel to the upper face of 15 the slab and opposing side faces which are in contact with the respective portions of the slab, the base having spaced apart longitudinally extending first and second edges, the upwardly projecting portion being joined to the base along the first edge and being shaped so that it is located substantially completely on one side of a plane which passes through the first edge and is perpendicular to the base and the upper edge of the 20 upwardly projecting portion is located between and above the two edges.

Advantageously, substantially the whole of the upwardly projecting portion is located between and above said first and second edges. This has the advantage that the centre of gravity of the upwardly projecting portion is brought closer to the longitudinal centre of 25 the base. The element is thus likely to rest more securely on the base with less propensity to tip when the weight of the vibrating screeding beam is applied to the upper edge of the upwardly projecting portion.

The element can be supported on supports located at intervals along the length of the 30 element. It is an advantage of the invention that these supports can comprise piles of concrete put down on the plastic film vapour barrier. The element can be laid on the concrete piles and levelled before the concrete sets. The base of the element, being usually flat and relatively wide, helps the element to stay in place until the concrete is set. In addition, the concrete can flow over the free edge of the base, helping to hold the 35 element in place and to further prevent any propensity to tip undej-^ Wfy^ht of the vibrating screeding beam.

The upwardly projecting portions may advantageously be provided with a longitudinally extending fold or channel-like formation which serves to provide lateral stiffness and/or to key the element into the slab.

According to another aspect of the invention the base is provided along its second said edge with an upstanding flange or similar formation. This has two advantages. In the first place said formation is keyed into the concrete of the aforementioned supporting piles adding further security to the positioning of the element. Furthermore said formation permits two of the elements which are butted up to one another to be joined together by a cap or similar device which fits over the formations and which has a recess in which the formations are held captive and in mutual alignment.

In one form of the invention a longitudinally extending capping piece is mounted on the upper edge. Advantageously, the capping piece has an upper face which is substantially flush with the upper face of the slab.

The invention is further discussed with reference to the accompanying drawings in which Figure 1 is a sectional view showing a first element in end profile cast into a concrete slab; Figure 2 is a perspective view of a short length of the element shown in Figure l; Figure 3 is a side view (on Arrow A in Figure 1) a short length of the element; and Figure 4 is a sectional view similar to Figure 1 showing a second element in end profile; Figure 5 is a cross-sectional view in full scale of a third element; »7CS2.7»\lv 24 3 82 2 Figuie 6 is a view on Arrow Bin Figure 5; Figure 7 is a cross sectional view, twice full size, of a capping piece which can be used with any of the elements shown in Figures 1 to 6; Figure 8 is a cross sectional view, four times full size, of a second such capping piece; and Figure 9 is a diagrammatic illustration of a vibrating screed beam supported on a pair of the elements shown in Figure 5.

Referring to Figures 1 to 3 there is shown an element 10 placed in a cast concrete slab 12.

The element 10 is produced from steel strip having a thickness of, for example, between 0.9S mm and 1.85 mm although it is not necessarily restricted to this range. The thickness is limited by cost considerations and also by the fact that the element must be stiff enough for the service for which it is intended. The element comprises a flat base 14 extending the full length thereof. An upwardly extending portion or "upstand" 16 is formed in the element. The upstand also extends the full length of the element. The upstand joins the base along one edge 17 thereof. A longitudinally extending channel 18 is formed in the upstand. This channel stiffens the upstand laterally and also provides a key for securing the element to the slab. The channel comprises upper and lower flat walls 18a, 18b disposed at right angles one to the other. A vertically disposed lip 20 is formed in the upstand above the channel 18. The lip has a straight upper edge which extends the full length of the element and is parallel to the plane in which the base lies.

Holes 22 of, for example, 22 mm diameter are punched in the lower wall 18b of the channel at intervals of, say, 300 mm. Reinforcing bars 23 for reinforcing the slab may pass through selected ones of these holes. An advantage of the holes is that they locate the reinforcing bars accurately relative to the upper face of the slab.

A longitudinally extending flange 24 is formed along the free edge of the base. This flange helps to stiffen the base and also provides a seat for a capping piece 26 by means 5l»7C»2.7»3Uv 243822 of which two of the elements which are butted up to one another can be held together in mutual alignment.

The upstand slopes backwardly from the edge 17 towards the free edge of the base to carry the centre of gravity of the upstand and, more particularly, the upper edge of the lip 20 closer to the longitudinal centre of the base than it would be if the upstand rose perpendicularly from the base.

In use the ground 28 on which the slab is to be cast is levelled and, in one method of casting a slab, a bed of compacted fill 30 is laid down at least along the lines where the elements are to be laid. A vapour screen 32 in the form of a plastics film is laid over the ground and the gravel bed. Parallel rows of elements 10 are placed on the bed along lines where controlled cracking of the slab is required. Reinforcing is next located in 15 position where required, being passed through the holes 22 where necessary. If reasonable care is taken to level the fill 30, the upper edges of the lips 20 will be level enough for most purposes. Piles of concrete 34 are put down at intervals along the length of the elements, partly on the base 14 and partly on the plastics film so that the flange 24 is keyed into the pile. This helps to hold the element 10 in place. The piles are 20 allowed to set and the slab is then cast. After the concrete for the slab is cast but before it has set a vibrating screeding beam can be supported on two adjacent elements 10", as illustrated in Figure 9, in which the screeding beam is indicated at 50 and the slab at 46. The beam is moved along the elements to level the upper surface of the slab. It is this function in particular which determines how stiff the elements must be. However the 25 provision of the flat base in the elements and the sloping of the upstands substantially increases both the rigidity and the positional stability of the elements and facilitates the production of a level slab.

A capping piece 31 can be placed on the lips 20 of the elements prior to casting the 30 slab. This capping piece provides a bearing edge for the screeding beam. Two capping pieces are shown in detail in Figures 7 and 8 and are described in more detail below.

The shape of the element 10 is suited to forming the element in a folding machine. A modified element 10' is shown in Figure 4. The function thereof is substantially 35 identical to that of the element 10. However the shape of the element 10' is more suited to roll forming.

I 3B97NZCS.095/JW/iv / N "ML'., 24 3 8 2 Figure 4 also shows an alternative means of locating the element 10'' in position. Here, the plastic film vapour barrier 32 is laid on the ground. Thereafter, piles 34' of concrete are put down at selected intervals of, typically, 1 metre along the lines on 5 which the elements 10' are to be located. Before the concrete sets, the elements 10' (or any of the other elements described herein) are laid on the piles and levelled by any suitable means such as a laser. Advantageously, some of the concrete in each pile flows around the flanges 24' as shown at 36 or more concrete can be added to achieve this. The broad flat base of each element 10' ensures that the element will sit securely on the 10 piles and the flange 24' keys the base into the pile. After the concrete has set the slab is cast. As mentioned before, a vibrating screeding beam can be supported on the^ elements for levelling the upper face of the slab.

The modified profile of an element 10", also suitable for fabrication in a folding 15 machine, is shown in Figure 5. Typically, for incorporation in a slab of 100 mm nominal thickness, this element 10" may be about 80 mm high and about 70 mm wide. It is advantageously made from galvanised sheet steel, 1.15 mm thick. Similar profiles may be used for slabs up to 200 mm thick. For a 150 mm thick slab, for example, the element 10" would be about 125 mm high and about 100 mm wide and be fabricated 20 from 1.55 mm thick galvanised sheet steel. The element 10" is provided with square holes 22".

Similar elements can be used to cast slabs of any thickness which would normally be required. 200 mm thick slabs have been cast. The profile of such elements would be 25 substantially similar to that of the element 10" but the dimensions would be increased in proportion to the thickness of the slab.

One of the advantages of the use of capping pieces 31 is that they provide spacers for lifting the vibrating screeding beam above the level of the upper edges of the elements 30 10,10' and 10". The upper face of the slab is thus located well above the top of the element in each case. The capping pieces can be left in place or removed. Figure 8 shows a plastics capping piece which is intended to be left in place. To this end it is provided with downwardly depending limbs terminating in longitudinally extending lugs 40 which key into the concrete of the slab. These lugs are omitted from the capping 35 piece 42 shown in Figure 7 which is intended to be removed after the slab is cast The capping piece 42 is tapered to assist removal. Furthermore, removal is facilitated by the 9l97CS2.793\iv 24 3 82 provision of the longitudinally extending cavity 44. This is best achieved by inserting any suitable hooked implement in the cavity at the end of the capping piece and simply lifting the capping piece out of the slab. The recess left by removal of the capping piece can be filled with a suitable flexible filler of known type.

It may be noted that in no case is it necessary for the plastics film vapour barrier to be perforated.

It is not intended that the scope of a patent granted in pursuance of the application of which this specification forms a part should exclude modifications and/or improvements to the embodiments described and/or illustrated which are within the scope of the claims or be limited by details of such embodiments further than is necessary to distinguish the invention from the prior art 5l»7C»2.7»3Uv

Claims (8)

1. WHAT WE CLAIM IS: -9- 243822 1.
2. An element of sheet steel or other laminar material which is cast into a slab of cementitious material having upper and lower faces, the element comprising a longitudinally extending flat 5 base on which the element rests and which is located adjacent the lower face of the slab, and an upwardly projecting portion which arises from the base and separates portions of the slab which are located one on either side of the upwardly projecting portion and are in contact with opposing side faces of said sheet steel or said other laminar material of which the upwardly projecting portion is constructed, the base having spaced apart longitudinally extending first 10 and second edges, the upwardly projecting portion being joined to the base along the first edge and being shaped so that it is located substantially completely on one side of a plane which passes through the first edge and is perpendicular to the base the upwardly projecting portion having an upper edge which is located adjacent and substantially parallel to the upper face of the slab and is disposed between and above the first edge and the second edge. 15 2_ An element according to claim 1, in which the upwardly projecting portion is shaped so that it is located substantially completely between and above the two edges. 20
3. 3. An element according to claim 1 or claim 2, in which the upwardly projecting portion is provided with a longitudinally extending fold or channel-like formation which serves to provide lateral stiffness and/or to key the element into the slab. 25
4. 4. An element according to any one of claims 1 to 3, in which the base is provided along the second said edge with an upstanding flange or similar formation.
5. 5. 30 An element according to any one of claims 1 to 4, in which the upwardly projecting portion is provided with at least one hole through which a reinforcing bar passes which is cast into the slab.
6. 6. ^ 35 An element according to any one of claims 1 to 5, in which a longitudinally extending capping v j. .Vy;* - •- piece is mounted on the upper edge. -^ " 'i, ' " - , * i, , 5897ICSl.D95/i7W/£v 1Q ■$ ' , ~ ~ " ■ V * < 243822
7. 7. An element according to claim 6, in which the capping piece has an upper face which is substantially flush with the upper face of the slab. 5 8. An element, substantially as herein described with reference to any one of the examples shown in the accompanying drawings. 10 JAMES W PIPER & CO. Attorneys for the Applicant 15 STEEL PRODUCT
8. S LIMITED 01 20 25 30 35 5897NZCS.095AWiv