NZ711053A - Load spreading device for hollow core concrete - Google Patents

Abstract

load spreading device for use in suspending loads from hollow core concrete comprises a plate, a plurality of spaced apart holes in the plate, each hole sized to allow a hollow core concrete anchor to pass through for attaching the plate to the hollow core concrete, and a substantially central area of the plate adapted to allow connection to a suspended ceiling load. rea of the plate adapted to allow connection to a suspended ceiling load.

Description

COMLPLETE SPECIFICATION TITLE LOAD SPREADING DEVICE FOR HOLLOW CORE CONCRETE FIELD OF INVENTION The invention relates to the field of fastenings for attaching to hollow core concrete in buildings.

BACKGROUND Prefabricated concrete is used for construction in many multi-storey buildings.

Prefabricated concrete slab floors can be quickly laid to form the ceilings/floors of a multi- storey building. One type of concrete used in construction of multi-storey buildings is hollow core concrete. A hollow core concrete slab has a series of hollow cores extending along the length of the slab. Pre-stressed metal strands are provided along the length of the slab in areas between the hollow cores. When the slabs are in place services are hung from the slabs. These services may include suspended ceiling systems, cable trays, light fittings, pipework and air-conditioning ducts. To hang services from the slab fastenings or anchors are needed. The fastenings must be spaced away from the pre- stressed strands so the function of the strands is preserved. This means that the fastenings are positioned into or through the hollow cores of the slab or in the joins between the slabs.

A variety of fasteners have been used to hang services and ceilings from Hollowcore slabs. A more common way of hanging MEP&F (Mechanical, Electrical, Plumbing and Fire Services) from the hollow core slab is to use threaded rod. Often the rod is fastened to a drop in anchor or other anchor not designed for use in hollow core slabs but into solid concrete. In many instances "due to the thin concrete available at the core" loading capacities of the fasteners are unknown. In the event of seismic activity, extra stresses can be placed on the fasteners causing failure. Depending on the severity of the earthquake the anchor may pull out of the hollow core concrete slab leaving the services attached to the anchor with less support than previously. In some cases the rod may bend at the point at which it enters the concrete slab developing extra shear load on the anchor or anchoring method. In a severe earthquake failure by a number of anchors can lead to services falling from ceilings and causing further damage to buildings and occupants of the buildings.

It is an object of a preferred embodiment of the present invention to go at least some way towards providing a load spreading device suitable for use with hollow core concrete slabs. While this object applies to the preferred embodiment, it should be understood that it is not intended to limit the scope of the claims. This is because the object of the invention per se is simply to provide construction professionals with a useful choice.

The term “comprising” and derivatives thereof, e.g. “comprises”, if and when used herein in relation to a combination of features should not be taken as excluding the possibility that the combination may have further unspecified features. For example, a statement that an arrangement “comprises” certain parts does not mean that it cannot also, optionally, have additional parts.

SUMMARY OF THE INVENTION In broad terms in one aspect the invention comprises a load spreading device for use in suspending loads from hollow core concrete comprising: a plate, a plurality of spaced apart holes in the plate, each hole sized to allow a hollow core concrete anchor to pass through for attaching the plate to hollow core concrete, and a substantially central area of the plate adapted to allow connection to a load.

Optionally the central area and the spaced apart holes are in different planes.

Optionally the planes are substantially parallel.

Optionally the holes are provided on end tabs of the plate.

Optionally the plate comprises side walls that extend between the plane of the plate and the plane of the tabs.

Optionally the load spreading device further includes a substantially central slot in the plate through which a fitting can be attached for a suspended load and a captive plate/gate shaped to fit across the slot to prevent the fitting from being remove through the slot when the captive plate/gate is in place.

In broad terms in another aspect the invention comprises a method for spreading a load suspended from a hollow core concrete slab, the method comprising: providing a load spreading device comprising a plate, a plurality of spaced apart holes in the plate, each hole sized to allow an hollow core concrete anchor to pass through for attaching the plate to the hollow core concrete slab, and a substantially central area of the plate adapted to allow connection to a load, attaching a fitting to the load spreading device onto which a ceiling load may be suspended, or encompassing a threaded rod attached to the hollow core concrete slab attaching the load spreading device to the hollow core concrete by placing anchors through at least two of the spaced apart holes and connecting the anchors to the hollow core concrete and the load spreading device, and attaching a load to the fitting.

BRIEF DESCRIPTION OF DRAWINGS Figure 1A shows a cross section of one embodiment of a hollow core concrete slab, Figure 1B shows a cross section of another embodiment of hollow core concrete slab, Figure 2A shows a side view of a load spreading device, Figure 2B shows a top view of a load spreading device with side plates extended; and Figure 2C shows a top view of a captive plate/gate used with the load spreading device.

DETAILED DESCRIPTION Figures 1A and 1B show the cross sections of two different hollow core concrete slabs.

Both slabs have an upper surface 1, lower surface 2, a plurality of hollow cores 3 and a plurality of pre-stressed strands 4. Both the hollow cores and pre-stressed strands extend the length of the slab. The pre-stressed strands are made of metal.

Hollow core concrete slabs are made in a variety of different thicknesses. The thicker the hollow core concrete slab the larger the hollow cores. In addition more strands 4 are provided in thicker slabs.

To preserve the strength of the hollow core concrete slab loads suspended from the ceiling cannot be suspended within 30mm of a strand. In practical terms this means that anchors securing the loads must extend into or pass through a hollow core or be placed between slabs.

Figure 2A is a side view of an embodiment of load spreading device. The load spreading device shown in figure 2A has a plate 5, tabs 6, and side panels 9. The load spreading device is suited for attaching ceiling and /or suspended services to hollow core concrete slabs.

Figure 2A also shows a side view of a captive plate/gate 10 used to help secure a fitting to which loads are attached.

Figure 2B shows a top view of the load spreading device of figure 2A. In figure 2B the side panels 9 are shown flat. In use these side panels extend between the plane of plate and the plane of tabs 6. Figure 2B shows slot 7 though which a fitting can be attached to support a load or retrofitted to an existing rod supporting a suspended load. Holes 8 allow the load spreading device to be attached to a hollow core slab. Holes 11 are provided to allow attachment of captive plate/gate 10 to the load spreading device to hold the fitting, which may be a threaded rod, (not shown) in place.

The plate 5 has a substantially central slot 7 from which services can be suspended or can be slotted. These services include, but are not limited to, suspended ceiling systems, cable trays, light fittings, plumbing and air-conditioning ducts. Any suitable fitting may be used to attach the services to the plate through the central hole. One commonly used fitting is the threaded rod. The fitting can be slid into place in the central slot 7. Once in place, captive plate/gate 10 is attached to the plate. Holes 11 in the captive plate/gate 10 match holes 11 in plate 5 to allow bolts to extend through the captive plate/gate holes and into the corresponding plate holes 11. In one embodiment these holes are threaded.

When the captive plate/gate 10 is in place the fitting can no longer be slid through slot 7.

Tabs 6 provide holes 8 to allow the load spreading device to be attached to a hollow core slab. At least two holes 8 are provided to attach the load spreading device to the hollow core slab. The load that is suspended from the device is spread over the two or more attachment points. In some embodiments more than two attachment points may be provided. Holes 8 allow an anchor to pass through the hole for anchoring the device to a hollow core slab. There are many known anchors and any suitable anchor may be used.

In preferred embodiments the load spreading device is fitted across two cores of the hollow core slab. In a load spreading device with two attachment points to the hollow core slab these attachments are made across two cores of the hollow core slab. Alternatively the load spreading device may be installed along one core of a hollow core slab.

In the load spreading device shown in figure 2, the tabs 6 are in a plane parallel to the plate 5. This spacing allows for a bolt or other device to be used to secure the fitting through slot 7 without interfering with distance between the tabs and the hollow core slab.

The load spreading device shown in figure 2 may also have side walls 9. The sidewalls 9 help to maintain the spacing between the tabs and the central aperture.

In preferred embodiments the load spreading device is formed from metal.

In one example, the load spreading device and captive plate/gate are made from 6mm thick mild steel. In this example the plane of the plate is parallel to the plane of the tabs and separated from the plane of the tabs by 13mm. There is a 276 mm distance between the anchor holes 6 in the tabs. Holes 11 for attachment to the captive plate/gate have a centre to centre distance of 48 mm. Slot 7 extends 40mm into central plate 5 at a central point.

The plate is 316mm long and 96 mm wide. It is bent or pressed to form turn downs on the sides and 26 mm to the end tabs to form a raised central area and add strength characteristics. In this example the side plates are 186 mm long and 23 mm wide. The plate is 185 mm long and 50 mm wide. This example is sized for a 10 mm or 12 mm threaded rod or bolt from which services can be suspended. It is intended that nuts are fitted above and below the load spreading device to lock the threaded rod in place.

Captive plate/gate 10 has a length of 72 mm and width of 25 mm. The two holes of the captive plate/gate have a centre to centre distance of 48 mm. The central slot of the captive plate/gate has a width of 11 mm and extends 16 mm into the captive plate/gate.

The load spreading device and captive plate/gate described in the example above were tested with a 200 mm hollow core slab. The dimensions can be scaled up and down for different dimensions of hollow core slabs.

In use a fitting is fixed through slot 7 and secured to the load spreading device by securing means including the captive plate/gate. Holes are drilled into the hollow core slab where anchors will attach the load spreading device to the hollow core slab. The load spreading device is then inverted so that underside of the tabs 6 will contact the hollow core slab.

Anchors are then inserted through holes 8 into the hollow core slab to secure the load spreading device to the hollow core slab. Services can then be suspended from the hollow core slab or the device itself.

In retrofit the plate is slotted over a nut on a threaded rod (previously attached to a hollow core slab) through slot 7. The rod is then held captive by the captive plate/gate and the load spreading device is then positioned so that the anchor holes are positioned over core areas of the hollow core concrete slab. Holes are drilled through the anchor holes of the device into the concrete slab and hollow core anchors are inserted and tightened. When used in a hollow core concrete slab, the load spreading device is positioned so that the holes 8 in the tabs allow anchors to be positioned in or through the hollow core(s). Ideally the attachment points for each load spreading device attached to the hollow core extend across two cores. Alternatively the load spreading device may be attached along a single core.

While some preferred forms of the invention have been described by way of example it should be appreciated that modifications and improvements can occur without departing from the scope of the appended claims.

Claims (8)

1. A load spreading device for use in suspending loads from hollow core concrete comprising: 5 a plate, a plurality of spaced apart holes in the plate, each hole sized to allow a hollow core concrete anchor to pass through for attaching the plate to the hollow core concrete, and a substantially central area of the plate adapted to allow connection to a suspended ceiling load.

2. A load spreading device for use in suspending loads from hollow core concrete as claimed in claim 1 wherein the central area and the spaced apart holes are in different planes. 15

3. A load spreading device for use in suspending load from hollow core concrete as claimed in claim 1 or claim 2 wherein the planes are substantially parallel.

4. A load spreading device for use in suspending load from hollow core concrete as claimed in any one of claims 1 to 3 wherein the holes are provided on end tabs of the 20 plate.

5. A load spreading device for use in suspending load from hollow core concrete as claimed in claim 2 or claim 3 wherein the plate comprises side walls that extend between the plane of the plate and the plane of the tabs.

6. A load spreading device for use in suspending loads from hollow core concrete as claimed in any one of claims 1 to 5 further comprising a substantially central slot in the plate through which a fitting can be attached for a suspended load and a captive plate/gate shaped to fit across the slot to prevent the fitting from being remove through the 30 slot when the captive plate/gate is in place.

7. A method for spreading a load suspended from a hollow core concrete slab, the method comprising: providing a load spreading device comprising a plate, a plurality of spaced apart 5 holes in the plate, each hole sized to allow an hollow core concrete anchor to pass through for attaching the plate to the hollow core concrete slab, and a substantially central area of the plate adapted to allow connection to a suspended ceiling load, attaching a fitting to the load spreading device onto which a ceiling load may be suspended or encompassing a threaded rod attached to the hollow core concrete slab, 10 attaching the load spreading device to the hollow core concrete by placing anchors through at least two of the spaced apart holes and connecting the anchors to the hollow core concrete and the load spreading device, and attaching a ceiling load to the fitting. 15

8. A load spreading device substantially as herein described with reference to figures 2A to 2C.