GB2428699A

GB2428699A - Attachment of a structure to a ground anchor

Info

Publication number: GB2428699A
Application number: GB0515727A
Authority: GB
Inventors: Peter Dunn
Original assignee: Screwfast Foundations Ltd
Current assignee: Screwfast Foundations Ltd
Priority date: 2005-07-30
Filing date: 2005-07-30
Publication date: 2007-02-07
Also published as: GB0515727D0

Abstract

A connection assembly (10) comprises a hollow body having first and second open ends, a flange (12) projecting laterally from the body at a position intermediate those ends and abutment means internally of the body intermediate those ends, which abutment means may be provided by the flange (12) projecting inwardly of the body. In use, the assembly is typically embedded within a concrete slab (30) to enable the slab to be connected to a ground anchor such as a pile (20). The hollow body provides a passageway from an upper surface to a lower surface of the slab (30). A first engagement member, such as a threaded stud (24), is provided at an upper end of the ground anchor (20) and the slab (30) is mounted onto the ground anchor (20) so that the hollow body overlies this member (24). A second engagement member, such as nut (28), is then secured to the first engagement member to hold the latter relative to the internal abutment, and settable material (44), such as grout, is poured into the hollow body.

Description

ATTACHMENT OF A STRUCTURE TO A GROUND ANCHOR

This invention concerns a connector, a connection assembly and a method of attaching a structure, particularly but not exclusively a concrete slab, to a ground anchor or a plurality of ground anchors, such as one or more screw piles.

The applicant's earlier GB 2390128 describes how a mast or other structure may be mounted upon a plurality of piles which have been driven into the ground. Such mounting is by way of a rectangular foundation frame which has connection boxes at its corners. The positions at which the piles are driven into the ground correspond to the corners of the frame and the connection boxes are used to secure the frame to the upper ends of the piles. A threaded stud typically projects from the upper end of each pile into the respective connection box where it is engaged by a nut and later embedded in grout. Before the grout is poured into the box, a plate having a radially open slot, termed a C-plate, is positioned over the threaded stud, and is supported within the connection box for the nut to bear against. The radially open slot of the C-plate makes allowance for slight misalignment of the position of the upper end of the respective pile relative to the foundation frame corner.

An object of the present invention is to enable connections to be made quickly and cost effectively between the tops of one or more piles and any structure which it is desirable to mount upon same. The term "pile" as used herein is interchangeable with the term "anchor" or "ground anchor". The piles concerned are typically screw piles, which have a helical fin and are driven into the ground by rotation. However, the invention is equally applicable to the mounting of structures upon other types of pile, such as those which are driven percussively into the ground by hammer action.

It is not practical or even possible to position piles in the ground to the same accuracy that is usually required for the structures which are to be mounted upon them.

Accordingly, it is a further object of the present invention to provide a connector assembly which will make allowance for inaccuracies of horizontal alignment between the upper ends of the pile or piles and the structure being mounted thereon.

Inaccuracy in level and angular alignment can always be compensated for by positioning packers between the upper end of the pile and the structure being mounted thereon.

Yet another object of the present invention is to provide a connector which can be readily embedded into a pre-cast concrete structure, such as a concrete foundation or base slab, to enable connection of same to the upper end of an embedded pile, and which will enable the effective transmission, not only of a compression load, but also of a tension toad from the structure, once so mounted/connected, to the said pile.

With these objects in view, the invention provides a connector comprising a hollow body having first and second open ends, a flange projecting laterally from the body at a position intermediate those ends, and abutment means internally of the body intermediate those ends.

When embedded in a concrete slab, the hollow body provides a passageway from an upper surface to a lower surface of the slab.

Taking a wider view, the invention also provides a connector assembly for attaching a structure to a ground anchor, which assembly comprises, in addition to the aforesaid connector, a first engagement member attached or attachable to the ground anchor, and a second engagement member engageable with the first engagement member to hold the first engagement means relative to the abutment means of the connector and thereby secure the structure to the ground anchor.

The first engagement member is preferably a threaded member which is attached or attachable to a plate, which in turn is attached to an upper end of the ground anchor, while the second engagement member is preferably a further threaded member adapted to engage threadedly with the first engagement member. Typically, the first engagement member is in the form of a threaded rod, while the second engagement member is a nut which is engageable theron. However, the first engagement member could be a nut which is welded to the plate at the upper end of the ground anchor, while the second engagement member could be a bolt which is screwed down into the nut. Alternatively, the plate attached to the upper end of the ground anchor could itself provide a threaded aperture for direct attachment of a second member in the form of a bolt.

Conveniently, the flange of the connector also projects inwardly of the hollow body to provide the abutment means.

Preferably, the assembly includes specific means to compensate for horizontal misalignment of the first engagement member relative to the structure being attached to the ground anchor. Such means may be a plate having an elongate slot therein which is locatable within the hollow body of the connector between the second engagement member and the abutment means.

As regards the connector, the flange, externally of the hollow body, may be provided with apertures to enable connection of reinforcement means whereby the connector can be more securely embedded within a concrete slab or other pre-cast structure. Additionally or alternatively, at least one elongate reinforcement element may be secured to the flange, externally of the hollow body.

A further aspect of the invention is a method of attaching a concrete slab to a ground anchor comprising the steps of casting the slab to embed a connector which comprises a hollow body having first and second open ends, a flange projecting laterally from the body at a position intermediate those ends, and abutment means internally of the body intermediate those ends, so that the hollow body provides a passageway from an upper surface to a lower surface of the slab, attaching a first engagement member to an upper end of the ground anchor, mounting the slab onto the ground anchor so that the hollow body overlies the first engagement member, securing a second engagement member to the first engagement member to hold the first engagement member relative to the abutment means, and pouring settable material, such as grout, into the hollow body.

The connector is typically made of metal for necessary strength and rigidity. However, in many applications it will be desirable to avoid the metal of the connector being exposed at the surface of the concrete structure in order to reduce or delay corrosion of the embedded metal. To deal with this requirement, an insert may be fitted into the first end of the hollow body, so as to project therefrom. The first end should then be selected as the upper end of the connector when positioned for casting of the concrete structure therearound. Then, when the concrete slab is cast, it is cast to a level above the first end of the hollow body, as defined by the projecting end of the insert.

The insert may be a metal cylinder with a section cut away to make it springy. This allows it to be inserted readily and also to be removed after casting by means of a tool, such as a screwdriver. Alternatively, the insert may be a cylinder of plastics material, which can be left in place after casting, or which can be subsequently removed by being dissolved in a suitable solvent. For example, a polystyrene insert can be dissolved in petrol.

The invention will be described further, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a schematic, exploded, and fragmentary view showing how a practical embodiment of a connector assembly of the invention is attachable to the upper end of a pile; Figure 2 is a schematic cross-section showing the same embodiment cast into a concrete slab and mounting same to the upper end of the pile; and Figures 3 and 4 are schematic cross sections showing two modified versions of the connector of the invention embedded into respective concrete slabs.

Referring to Figures 1 and 2, a preferred embodiment of a connector 10 of the invention is formed by welding respective pieces 11, 13, of steel tube to opposing surfaces of a flange plate 12, which is a circular plate having a central aperture 16. The tubular pieces 11, 13 may be sections of the same tube, each about 150 mm diameter and 3 mm wall thickness. The flange plate 12 may have a diameter of 250 mm and a thickness of 12 mm. These dimensions are only by way of example, of course. In this way a hollow body is provided having first and second open ends 15, 17. The flange plate 12 provides an annual flange 14 extending radially externally of the body and intermediate those first and second ends 15, 17. As the aperture 16 is of smaller diameter than the tubular pieces 11, 13, the flange plate 12 also provides an annual flange internally of the body which serves as abutment means when the connector 10 is used to make a connection in accordance with the method of the invention.

Externally of the connector body 11, 13, the flange plate 12 is provided with further smaller apertures 18 and, as shown, additional elongate reinforcement elements, such as steel rods 19, maybe inserted through these apertures 18. The rods 19 may be bent into a U shape, as shown, or indeed into any other shape, to provide additional anchorage when the connector 10 is embedded in concrete. Such rods 19 or other similar elements may be tied to other conventional reinforcement 29 which is embedded within the concrete 30, as indicated in figure 2. They can also, when required, be bent quite tightly so as not to protrude from the concrete when the connector 10 is embedded near the edge or a corner of a concrete slab, as is likely to be the case.

A typical situation in which a plurality of the aforesaid connectors 10 will be used is for mounting a concrete foundation slab 30 (see figure 2) upon a plurality of piles which have been driven into the ground. To achieve this, a number of connectors 10 corresponding to the number of mounting piles are cast into the concrete slab 30 at positions corresponding to the tops of the piles such that the hollow bodies provided by the tubes 11, 13 define passageways between the upper and lower surfaces of the slab 30. Only one such pile 20 and connector 10 are shown in figures 1 and 2.

The upper end of each pile 20 has a standard drive plate 22 welded thereto with a threaded central aperture into which a first engagement member in the form of an upwardly projecting threaded rod or stub 24 is engaged.

The levels of the upper ends of the respective piles 20 are checked carefully at this stage. As required, a grout pad 32 and/or a steel washer (not shown) may be located over each stud 24, with additional such pads and/or washers to make up for any discrepancy in the height of any of the pile heads relative to the others, so that they all have packing up to a substantially equal level. A grout pad (32) is an envelope of porous material containing grout and having a central zone where little grout is present which can readily be penetrated by the stud 24. Such a pad has already been disclosed in the applicant's earlier application GB 050734.5. The use of grout pads as packing in this position also allows any angular misalignment of the pile heads to be compensated for.

The pre-cast concrete slab 30 incorporating the appropriately positioned connectors 10 is then lowered onto the tops of the piles 20. Grout or other suitable settable material 44 (see figure 2)is then poured into each connector 10 up to the level of the flange plate 12. A C-plate 34 having an open elongate, a radial slot 36 is then positioned over the stud 24 to rest on the internal annual abutment provided by the flange plate 12.

Obviously the position of the slot 36 is selected so that the C-plate fits irrespective of any slight horizontal misalignment of the position of the stud 24 relative to the central axis of the connector 10. A washer 38 is then fitted above the C-plate and a second engagement member in the form of a nut 28 is screwed down onto the stud 24 and tightened to secure the stud 24 relative to the abutment of the flange plate 12 thus securing the slab 30 to the pile 20. Further grout may then be poured into the top of the connector 10 up to the level of the top of the slab 30, or else this opening may be filled with particulate material such as sand or screed.

Figures 3 and 4 show how in modified embodiments the external flange l4may be provided at a position closer to the top of the connector body (figure 3) for enhanced ability to transmit tension load or at a position closer to the bottom of the connector body (figure 4) for enhanced ability to transmit compression load Provision of the external flange 14, as provided by the flange plate 12 in the illustrated embodiments, is particularly important in transmission of tension load from the slab 30 and any structure constructed above the same to the piles 20. In other embodiments the external flange 14 does not need to be continuous and need not project exactly radially of the connector. Indeed, the connector need not be cylindrical, although that is obviously the most typical configuration.

Connectors may be produced in a few standard lengths (heights) to match standard thicknesses of pre-cast foundation slabs.

A single connector could be used to mount a relatively small slab or other pre-cast structure to a single pile in exactly the same way as already described by being embedded in the pre-cast concrete structure. In most cases, however, a slab or structure will be mounted on plural piles using a corresponding number of appropriately positioned connectors.

In a development of the invention an insert 40 may usefully be employed during the casting of the slab 30, as indicated in both figures 1 and 2. This is a measure to avoid the metal of the connector 10 being exposed at the surface of the concrete slab 30. The insert 40 is effectively a temporary former. It can be made from the same thin gauge steel tube as the pieces 11, 13 of the connector 10, but having a short vertical strip cut away so that the cut edges can be squeezed together to enable it to be fitted inside one tubular piece 11 of the connector 10, but projecting from the open end 15. The end 15 is chosen as the upper end when the connector 10 is positioned for casting of the concrete slab 30. The slab is then cast up to the level of the top of the projecting insert 40. After the concrete has hardened the insert 40 can be removed quite simply with a small lever tool, such as a screwdriver 42, so that there is no metal extending to the top of the slab 30.

The foregoing it is illustrative and not limitative of the scope of the invention and many variations in detail are possible as will be readily apparent to anyone skilled in this technical field. In particular the connector may be constructed in a different manner to that shown so long as a hollow body and external flange are present.

Claims

1. A connection assembly for attaching a structure to a ground anchor, the assembly comprising a hollow body having first and second open ends, a flange projecting laterally from the body at a position intermediate those ends and abutment means internally of the body intermediate those ends, a first engagement member attached or attachable to the ground anchor, and a second engagement member engageable with the first engagement member to hold the first engagement means relative to the abutment means and thereby secure the structure to the ground anchor.

2. A connection assembly according to claim I including a plate attached to an upper end of the ground anchor.

3. A connection assembly according to claim 2 wherein the first engagement member is a threaded member attached or attachable to the plate.

4. A connection assembly according to claim 3 wherein the second engagement member is a further threaded member to be threadedly engaged with the first engagement member.

5. A connection assembly according to any preceding claim wherein the flange also projects inwardly of the body to provide the abutment means.

6. A connection assembly according to any preceding claim further including means to compensate for horizontal misalignment of the first engagement member.

7. A connection assembly according to claim 6 wherein the misalignment compensation means is a plate having an elongate slot therein which is locatable within the hollow body between the second engagement member and the abutment means.

8. A connection assembly according to any preceding claim wherein the flange, externally of the hollow body, it is provided with apertures for connection of reinforcement means.

9. A connection assembly according to any preceding claim including at least one elongate reinforcement element secured to the flange, externally of the hollow body.

10. A connection assembly as claimed in any preceding claim including an insert which is a snug fit in the first end of the hollow body and projects therefrom.

11. A connection assembly as claimed in claim 10 wherein the insert is a split tubular element.

12. A connector for attaching a structure to a ground anchor, the connector, comprising a hollow body having first and second open ends, a flange projecting laterally from the body at a position intermediate those ends, and abutment means internally of the body intermediate those ends.

13. A connector as claimed in claim 12 for attaching a pre-cast concrete slab to a ground anchor.

14. A concrete slab incorporating a connector as claimed in claim 12 such that the hollow body provides a passageway from an upper surface to a lower surface of the slab.

15. A method of attaching a concrete slab to a ground anchor comprising the steps of casting the slab to embed a connector which comprises a hollow body having first and second open ends, a flange projecting laterally from the body at a position intermediate those ends, and abutment means internally of the body intermediate those ends, so that the hollow body provides a passageway from an upper surface to a lower surface of the slab, attaching a first engagement member to an upper end of the ground anchor, mounting the slab onto the ground anchor so that the hollow body overlies the first engagement member, securing a second engagement member to the first engagement member to hold the first engagement member relative to the abutment means, and pouring settable material into the hollow body. p

16. A method as claimed in claim 15 wherein additional projecting reinforcement means are mounted on the flange before the slab is cast around the connector.

17. A method as claimed in claim 15 or 16 wherein an insert is fitted into the first end of the hollow body so as to project therefrom before the slab is cast, wherein the connector is disposed so that the first end is uppermost, and the slab is cast to a level above the first end of the hollow body, as defined by the projecting upper end of the insert.

18. A method as claimed in claim 17 wherein the insert is removed after the slab has been cast.

19. A method as claimed in any of claims 15 to 18 wherein means to compensate for horizontal misalignment is placed within the hollow body before the second engagement member is secured to the first engagement member to act between the second engagement member and the abutment means.

20. A connection assembly for attaching a structure to a ground anchor substantially as hereinbefore described with reference to and as illustrated by any of the accompanying drawings.

21. A connector for attaching a concrete slab to a ground anchor substantially as hereinbefore described with reference to and as illustrated by any of the accompanying drawings.

22. A method of attaching a concrete slab to a ground anchor substantial'y as hereinbefore described with reference to the accompanying drawings.