WO1999064695A2

WO1999064695A2 - Formation and attachment of tilt-up concrete panels

Info

Publication number: WO1999064695A2
Application number: PCT/NZ1999/000075
Authority: WO
Inventors: Clegg James Hollings
Original assignee: Clegg James Hollings
Priority date: 1998-06-08
Filing date: 1999-06-08
Publication date: 1999-12-16
Also published as: AU4535099A; NZ330593A; WO1999064695A8

Abstract

A void former (10) for the placement of reinforcing bars (11) in a pre-cast concrete panel for tilt-up construction has a base (23) for attachment to a casting surface, and a pair of tapered legs (22), the total height (24) of the void former being equivalent to the thickness of the desired pre-cast panel, with each leg having a flexible tell-tale (25) capable of protruding from the top surface of the panel during the casting process. After the concrete panel has hardened, the void formers can be removed leaving a U-shaped void. A U-shaped bar or fastener (11) can then be driven into the void, with its ends protruding from the surface of the panel, so that the bars (11) can be connected to reinforcing bars forming part of the building structure.

Description

FORMA TIONΛND A TTACHMENT OF TILT-UP CONCRETE PANELS

TECHNICAL FIELD OF THE INVENTION

This invention relates to construction and has particular though not sole application to the preparation of pre-cast concrete elements such as tilt-up panels and the construction of tilt-up concrete panel structures.

BACKGROUND

In tilt-up panel structures, pre-cast panels are typically cast on the building site, although in some cases where smaller panels are required the smaller panels can be pre-cast in a factory situation and transported to the building site.

Pre-cast panel elements typically have thicknesses in the range of 100 to 250 mm. On some sites, a foundation pad is cast on the ground, and used as the casting surface for the casting of panels by placing the appropriate form work on the casting surface. Such panels are then cast with apertures for doors or windows.

If space permits such panels may be cast with starter bars in place. However on many sites there is insufficient space to cast panels side by side and typically panels will either be cast one on top of the other in the form of a stack, or panels will be cast, and then stacked one on top of the other until required. Where space is limited, it is not practical to cast starter bars directly into the panels. One solution is to cast a threaded socket into the panel and then attach a threaded rod to the socket after the panel has hardened. However the strength of the connection between the new vertical tilt-up panel and a cast floor depends on the strength of the panel concrete. OBJECT

It is an object of this invention to provide an improved method of construction using pre-cast concrete panels and/or a novel void former for use with such panels.

STATEMENT OF INVENTION

In one aspect the invention provides a void former adapted to be cast into and subsequently removed from a pre-cast concrete element to leave a shaped void for the location of a shaped connector, wherein said void former has a base portion having a lower surface for attachment to a casting surface, and a leg extending from the base, the void former having a thickness which is greater than the thickness of the connector, the base portion has a height which is greater than the height of that portion of the connector to be located in the base void, and the combined height of base portion and the leg is equivalent to (or just slightly less than) the required thickness of the concrete element to be cast on the casting surface.

Preferably the concrete element is a tilt-up panel and the void former is to be used to create a void for the insertion of a U-shaped metal bar bent from a 410 MPa (or similar) steel bar having ribs on the surface thereof to assist in embedding it in a concrete floor or the like. Although other shapes of bars or fasteners will be described, as will different shapes of void formers.

Preferably the lower surface of the base portion is provided by a base plate.

In its most preferred form a second leg extends from the base portion substantially parallel to the first leg.

Preferably each leg has locating means extending or protruding from the end of the leg, so that in use the locating means can protrude from the cast concrete element.

Preferably each locating means is a flexible and/or resilient member of lesser cross-section than the cross-section of its leg.

Preferably each leg tapers from the base portion of the former towards its top to facilitate removal of the former from a cast concrete element.

Preferably the interface between the base portion and the leg or legs has an internal curvature corresponding to the shape of a connector designed to be inserted into the pre-cast element after removal of the void former.

Preferably the void former is moulded from a plastics material.

Preferably the void former is injection moulded and the flexible or resilient tail is provided by the moulding sprue.

In another aspect the invention provides a method of construction using a pre-cast concrete element, wherein the element is cast with a number of void formers (as described above) in place, the void formers being removed prior to connection of the element to part of a building structure, and shaped connectors are inserted into the voids left by the removal of the void formers, so that the connectors can be connected to part of a building structure.

In another aspect the invention provides a method of casting concrete panels for use in tilt-up building construction wherein a plurality of void formers are placed at intervals on a casting surface and are cast into a concrete panel, so that the void formers can be removed from the panel to leave voids for the reception of shaped connectors.

In another aspect the invention provides a concrete panel for use in tilt-up building construction wherein the cast concrete panel has a plurality of substantially U-shaped voids left for the reception of U-shaped connecting bars.

In another aspect the invention provides a building formed from concrete panels wherein the cast concrete panels are connected to a floor by a plurality of U-shaped connecting bars located in said voids with the ends of the bars protruding from the panels and being connected to said floor.

In another aspect the invention provides a void former for placement of a reinforcing bar in a pre-cast concrete element, wherein said void former is substantially U-shaped and has a base for attachment to a casting surface, and a pair of legs extending from the base, the combined height of base and a leg being equivalent to the required thickness of the concrete element to be cast on the casting surface, and wherein each leg has locating means extending or protruding from the end of the leg, so that in use the locating means can protrude from the cast concrete element.

Preferably the locating means is a flexible or resilient tail.

Preferably each leg tapers from the base of the former towards its top to assist in the removal of the former in use from the cast concrete element.

Preferably the pair of legs has an internal curvature corresponding to the radius of a U-shaped bar designed to be inserted into the pre-cast element after removal of the void former.

Preferably the void former is formed of a water resistant material.

Preferably the void former is moulded from a plastics material.

These and other aspects of this invention, which shall be considered in all its novel aspects, will become apparent from the following description which is given by way of example only with reference to the accompanying drawings. DRAWINGS

Figure 1 illustrates a front elevation of a preferred void former, onto which is superimposed the position of a U-shaped reinforcing bar.

Figure 2 is a side view of the preferred void former of Figure 1.

Figure 3 shows the placement of three such void formers on a casting surface, preparatory to casting a pre-cast tilt-up panel.

Figure 4 illustrates a pre-cast panel and then being moved into a vertical position, at which point the void formers can be removed, and replaced by U-shaped bars.

Figure 5 is a three dimensional cut away view of the void resulting from the removal of the void former, with a reinforcing bar placed in the void.

Figure 6 is a cross sectional view through a concrete panel showing the relationship between the concrete around the do welling bars, and the location of the U-shaped bar within the void.

Figure 7 is a cross sectional view through a concrete panel showing the relationship between the concrete around the dowelling bars, and the location of a J-shaped threaded fastener bar within the void.

Figure 8 is a cross sectional view through a concrete panel showing an L-shaped void close to a portion of a welded metal mesh, and the location of an L-shaped threaded fastener bar within that void.

Figure 9 is a three dimensional view of an L-shaped void former for use with the fastener of Figure 8. Figure 10 is a three dimensional view of a U-shaped void former without a tell-tale.

Example 1

A preferred void former 10 is manufactured to a standard size for a particular pre-cast panel thickness. This void former 10 is formed from a water resistant material, and typically will be formed from a robust plastics material, either injection moulded as a substantially solid unit (it may have one or more cavities in it to save on material), or blow moulded as a hollow unit, with sufficient stiffness that the void former can be physically removed from the concrete panel.

A prototype void former has been created from a solid block of industrial grade nylon, of the shape shown in Figures 1-3.

The void former 10 has a base 23 with a base plate 20, which is wide enough to enable the void former to stand upright on a casting surface, and has sufficient width 28 to enable it to be cemented in place to the casting surface.

The void former 10 has a pair of legs 22, which conveniently are tapered, being narrower at the top than at the bottom, and in this example they are substantially rectangular in cross section (although other shapes could be used) and have substantially smooth outer surfaces (to aid in removal from the cast panel). There is an internal radius 26 where the base 23 meets a leg 22. This internal radius 26 on each of the internal corners, corresponds to the radius of the bends in a U-shaped reinforcing bar which can be positioned in the void after removal of the void former.

In Figure 1 such a U-shaped reinforcing bar 11 is superimposed on the void former 10 to show the relationship between the curvature of the U-shaped bar 11 and the internal radius 26 of the void former 10.

Each leg of the void former has a flexible tell-tale 25 protruding from the top thereof, which flexible tell tale 25 is preferably formed from a plastics material, but is small enough and thin enough that it can protrude from the surface of the cast panel, in such a way that it will not interfere with the stacking of another panel on top of the first panel.

The void formers 10 will be mass produced, typically by injection moulding or blow moulding, and made to a size to suit a particular panel thickness.

In the case of a pre-cast concrete panel of 150mm thickness, the height of the void former 10, shown by line 24 in Figure 1 will be 150mm corresponding as closely as possible to the thickness of the pre-cast panel. An acceptable tolerance would be + 0mm, - 4mm, as it is preferable that the legs of void former are cast flush with top surface of the panel (or just below the top surface). The tell-tale 25 will typically be 25mm in length, i.e. just enough to protrude from a pre-cast panel to enable the void former to be seen but without interfering with the stacking of the panels.

The width 27 of the void former 10 in Figure 1 can be of any convenient size, however typically this will be of a width sufficient to accommodate the spacing of the dowelling bars 40 laid within the panel (or the bars in a welded metal mesh if that is used in place of orthogonal dowelling bars). In this example the void former 10 has a width of 150mm to provide a void sufficient in width to accommodate a U-shaped reinforcing bar 1 1 which can be fitted around a pair of dowelling bars 40 as shown in Figure 1.

Nevertheless it will be appreciated that the size of the void former will depend upon the thickness of the desired panel, and to some degree the reinforcing requirements for that size of panel.

It is envisaged that void formers will be made to standard sizes for most panels, and used in the manner described below.

In use, a panel can be cast using the void formers 10 of this invention by placing the void formers 10 on the casting surface in the required positions where reinforcing bars are to protrude from the surface of the pre-cast panel. For example as shown in Figure 4, the void formers 10 may be aligned with the dowelling bars 40. In such a case the void formers 10 would be cemented to the casting surface, and the dowelling bars placed on top of the void formers. Other reinforcing bars would be laid out as required on the casting surface, on spacers known as "bar chairs". The form work will be laid on the casting surface. The concrete can be poured into space defined by the form work, and the panel allowed to harden.

As the void formers 10 correspond to the thickness of the cast panel, their legs will be flush with or just below the top surface of the panel but the tell-tales 25 will protrude above the surface of the cast panel. Some of the tell-tales may be bent over by the float as the cement surface is levelled.

If a number of panels are stacked one on top of the other prior to use in the building structure, the remaining tell-tales may be flattened by the pressure of the subsequent panels, but when the panels are tilted up for use in the structure, at least some of the tell-tales will be visible.

As shown in Figure 4, a panel can be lifted off the stack by a crane, using conventional anchor points cast into the panel, and once the panel has been lifted clear of the stack, the void formers can be removed from the panel.

The visible tell-tales enable a worker to locate the centre of each of the legs 22 of a void former 10, so that he can then drive the void former out of the panel by a suitable tool. Typically the worker would use a club hammer and a drift made from an off cut of a reinforcing bar. As shown in Figure 4 a hammer 42 is used with a drift 43 to push out a void former 10A. Alternatively the removal tool might be a substantially U-shaped driving tool also made from reinforcing bar or the like, or maybe a pre-cast metal drift having two legs corresponding to the legs of the void former so that both legs can be driven out at once.

Once the void former has been removed as shown in Figure 4, the worker can then drive into place a much longer U-shaped reinforcing bar 1 1 from the other side of the pre-cast panel. Once all of the void formers have been removed and replaced by the reinforcing bars 1 1, the reinforcing bars 1 1 can be grouted or cemented in place. Typically a U-shaped bar would protrude a distance of 600mm from the surface of the panel. In Figure 6 such a bar has a protrusion length 70 represented by a break line.

In Figure 4, the tell-tales protrude from the front face 35 of the panel 30, and when the void formers have been removed they are pushed out of the rear face 36 of the panel 30, leaving a pair of apertures 37 passing right through the panel, and a substantially rectangular cavity 38, corresponding to the main portion 23 of the void former, and a smaller but wider rectangular cavity 39 corresponding to the base plate 20 of the void former.

Conveniently, the rectangular voids 38 and 39 on the rear face 36 of the panel is filled with a special cement filler compound. A suitable compound would be SIKA - "MONOTOP 612" (trade mark) which is a high strength non-shrink cement-base plate 20d compound with properties better than most concrete. This provides a substantially waterproof seal against the rear face of the panel. Alternatively, a specially shaped plastic, or other patch may be used on the rear face of the panel to cover the voids 38, 39 left by removal of the void former.

Preferably site concrete is placed against the front face 35 of the panel and vibrated to achieve grouting of the reinforcing bars 1 1 within the void.

As shown in Figure 5 the U-shaped reinforcing bars 11 may be bent as shown by reference 11 A, to ensure that the reinforcing bars are locked in place within the panel during the filling or grouting of the voids.

These U-shaped reinforcing bars can then be attached to another part of the building structure, for example the connection between a vertical wall panel, and a horizontal floor panel. In such a case, the protruding bars 1 1 will be embedded in the floor 45 as it is cast on site to lock the walls to the floor. If a pre-cast floor panel is used the bars can be embedded in a site cast upper surface of the floor 45. Example 2

Figure 7 shows a cross sectional view through a concrete panel 30 with a U-shaped void created by the removal of the void former 10 of Figure 1, but this time having a J-shaped fastener 50 inserted into the void with its shorter end 51 below the surface 35, and its longer end 52 protruding from the surface with a threaded end for attachment by a nut 54 to a steel plate (not shown) or the like. This example also shows the location of the J-shaped threaded fastener fitting around the dowelling bars.

Example 3

Figure 9 shows an L-shaped void former 60 (it can be regarded as a one legged former) leaving a similar main void 38, and a void 39 corresponding to the shape of its base plate.

In this case an L-shaped threaded metal fastener 61 can be placed in the void, (see Figure 8) and then grouted in place as described in Example 1. Figure 8 also shows a cross sectional view through a concrete panel 30 having a welded metal mesh only one element of which is shown by the bar 40. Preferably the void former 60 was positioned close to a portion of the mesh, so that after removal the main portion 38 of the void will be located close to a portion of the mesh, allowing the L-shaped fastener to be located close to the mesh.

Example 4

Figure 10 shows a three dimensional view of a U-shaped void former 70 without a tell-tale. Such a void former is preferably of a colour contrasting to the colour of the concrete panel to aid in location. Although a tell-tale is preferred as in example 1, it is possible to locate the void formers 70 as their position in the panel will be known as they will typically be laid in lines as shown in figure 4. ADVANTAGES OF THE PREFERRED EMBODIMENT

The void formers of example 1, being formed of a plastics material, can be injection moulded or blow moulded using a portion of the material as the visible tell-tale, such that the tell-tale is flexible or resilient enough so as not to interfere with the float during leveling of the upper surface, or with stacking of panels, and yet sufficient of them are likely to remain and be visible, when the panels are removed from the stack, enabling a worker to locate the position of the void formers for ease of removal.

By designing the void former so that it has a thickness which is greater than the thickness of the connector bar or fastener to be inserted into the resulting void there will be sufficient space for the insertion of grout around the bar or fastener to seal the panel and embed the bar within the panel.

By designing the void former so that the base portion 23 has a height which is greater than the height (or diameter) of that portion of the connector bar 11 to be located in the base void there will be a cover space 38 deep enough to allow the insertion of weather proofing compound such as SIKA MONOTOP to completely cover and seal the embed bar in place.

By designing the void former so that the combined height 24 of base portion 23 and the leg 22 is equivalent to (or just slightly less than) the required thickness 31 of the concrete element 30 to be cast on the casting surface, the legs 22 will be flush with or just below the surface of the panel so as not to interfere with the float or with stacking.

By forming the void formers of plastics material, these can be coloured in such a way that at least the tell-tales (of Example 1) or the tops of the legs 22 (as in Figure 10) are readily visible (in a contrasting colour to that of the concrete).

By forming the void formers of a plastics material, they can be made at relatively low cost, and could for example be made from a recycled plastics material as they need only be used once, and could then be recycled. By injection moulding the void formers with the legs having a tapered shape, with a visible telltale protruding from the end of the legs, it is possible to use the moulding sprue as the tell-tale, and it is also possible to make the void formers in a tapered shape for easy removal from the injection mould, and also easy removal from the cast panel.

Unlike a prior art threaded socket the strength of the connection made with the U-bar is hardly at all dependent on the strength of the panel concrete, and the ultimate mode of failure would be by yielding of the U-bar; not pull-out of some mechanical anchorage exhibiting "shear-cone' failure.

The void formers shown in the drawings can be used to provide voids for the installation of different types of connectors, eg. threaded bars or bolts to enable steelwork to be fitted to the inner face of the panel.

VARIATIONS

Instead of using the plastics material, the void formers could be pressure dye cast from a zinc alloy or the like.

If injection moulded or cast metal formers are manufactured they could be made as hollow shapes (with a cavity accessible from the base plate 20 of the former). Likewise if they are blow moulded as a hollow shape.

A variety of shapes could be used for the injection moulded, blow moulded or pressure dye cast void formers enabling them to be physically removed from the panel. The void formers illustrated have one or more legs which are substantially rectangular in cross section, and it will be appreciated that the legs could be circular in cross section leaving a circular tunnel of sufficient width to enable the insertion of the reinforcing bars. By matching the internal curvature of the void former to the radius of the comers of the U-shaped bars, it is possible to locate the U-shaped reinforcing bars in close proximity to the dowelling bars or metal mesh 40, within the pre-cast panel. However, in some applications it may be possible to do away with the internal curvature 26 of the void formers and use a more rectangular void former but that would require additional grouting or filling material around the U-shaped reinforcing bars after removal of the void former.

If a threaded fastener is to be used as shown in figures 7 or 8, one option is to use a bolt with a large head, and provide a void former with one leg and a substantially symmetrical base portion so that the resulting main void could be a frusto conical shape.

Although robust plastic void formers are preferred, it may be possible to produce the void formers of a material which could be destroyed in situ. For example if the void former was formed of a material having a low melting point, for example a hard wax or the like, it might be possible to position the void formers in place, cast the panel, and then remove the void formers by the application of heat to melt the void formers, however this is much less preferred than a robust void former which can be physically removed by force, as such a meltable material is likely to be damaged in transit, and far more likely to be damaged prior to the casting of the panel.

Finally, various other alterations or modifications may be made to the foregoing without departing from the scope of this invention as set forth in the following claims.

Claims

1 A void former (10) adapted to be cast into and subsequently removed from a pre-cast concrete element (30) to leave a shaped void for the location of a shaped connector, wherein said void former (10) has a base portion (23) having a lower surface for attachment to a casting surface, and a leg (22) extending from the base (23), the void former having a thickness which is greater than the thickness of the connector, the base portion (23) has a height which is greater than the height of that portion of the connector to be located in the base void, and the combined height (24) of base portion (23) and the leg (22) is equivalent to (or just slightly less than) the required thickness (31) of the concrete element (30) to be cast on the casting surface.

2 A void former (10) as claimed in claim 1 wherein the lower surface of the base portion (23) is provided by a base plate (20).

3 A void former (10) as claimed in claim 2 wherein a second leg (22) extends from the base portion (23) substantially parallel to the first leg (22).

4 A void former (10) as claimed in claim 3 and wherein each leg (22) has locating means extending or protruding from the end of the leg (22), so that in use the locating means can protrude from the cast concrete element (30).

5 A void former (10) as claimed in claim 4 wherein each locating means is a flexible and/or resilient member (25) of lesser cross-section than the cross-section of its leg (22).

6 A void former (10) as claimed in claim 1 wherein each leg (22) tapers from the base portion (23) of the former (10) towards its top to facilitate removal of the former (10) from a cast concrete element (30).

7 A void former (10) as claimed in claim 1, wherein the interface between the base portion (23) and the leg or legs (22) has an internal curvature (26) corresponding to the shape of a connector (1 1) designed to be inserted into the pre-cast element (30) after removal of the void former (10).

A void former (10) as claimed in claim 1, wherein the void former (10) is moulded from a plastics material.

A void former (10) as claimed in claim 1 wherein the void former (10) is injection moulded and the flexible or resilient tail is provided by the moulding sprue.

A method of construction using a pre-cast concrete element (30), wherein the element (30) is cast with a number of void formers (10) as claimed in claim 1 in place, the void formers (10) being removed prior to connection of the element (30) to part of a building structure, and shaped connectors (1 1) are inserted into the voids left by the removal of the void formers (10), so that the connectors (11) can be connected to part of a building structure.

A method of casting concrete panels for use in tilt-up building construction wherein a plurality of void formers (10) as claimed in claim 1 are placed at intervals on a casting surface and are cast into a concrete panel, so that the void formers (10) can be removed from the panel to leave voids for the reception of shaped connectors (11).

A concrete panel for use in tilt-up building construction wherein the cast concrete panel has a plurality of substantially U-shaped voids left for the reception of U-shaped connecting bars (11).

A building formed from concrete panels as claimed in claim 11 wherein the cast concrete panel are connected to a floor by a plurality of U-shaped connecting bars (11) located in said voids with the ends of the bars protruding from the panels and being connected to said floor.