GB2470377A

GB2470377A - A connection device for attaching a structure to a ground anchor

Info

Publication number: GB2470377A
Application number: GB0908684A
Authority: GB
Inventors: Peter Dunn
Original assignee: Screwfast Foundations Ltd
Current assignee: Screwfast Foundations Ltd
Priority date: 2009-05-20
Filing date: 2009-05-20
Publication date: 2010-11-24
Anticipated expiration: 2029-05-20
Also published as: GB2470377B; GB0908684D0

Abstract

A base plate (12) and upstanding walling (14) define an upwardly open enclosure for reception of grout or similar. In use, the base plate (12) is attached to a ground anchor, such as pile (20), eg. by bolts (26). The upstanding walling (14) is configured so that the enclosure has a cross-section area at its open upper end which is smaller than its cross-section area adjacent to the base plate, eg. by between 10% and 15%. This may be by at least a part of the upstanding walling (14) extending obliquely from adjacent the base plate to its open upper end, or by the upstanding walling (14) being crimped or pressed inwardly or by each opposing side wall having an inwardly directed fold in its upper margin. A lower end of a levelling bolt (30) of a structure (32) to be supported is inserted into the enclosure of the connection device to contact the base plate (12) and after making any levelling adjustments the enclosure is filled with grout to retain the levelling bolt.

Description

A connection device for attaching a structure to a ground anchor This invention concerns means of attachment of a structure to a ground anchor. It is particularly, but not exclusively, concerned with such means of attachment suitable for relatively light weight structures which may also be intended as temporary structures.

The applicant's earlier GB 2390128A 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.

Individual connection boxes, commonly referred to as grout boxes, which are hollow or upwardly open enclosures, typically of rectangular cross-section, are also known more widely, typically for mounting/supporting foundation frames or other foundation elements of buildings and other structures which are supported upon a plurality of individual piles.

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.

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, but which is intended to be temporary, said connection thus being in a manner which will facilitate later disconnection, yet which is still sufficiently robust to support the structure in the long term if necessary.

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 requirement of the connection device of the present

I

invention that allowance is made for height adjustment of structure support as well as for inaccuracies of horizontal alignment and angular alignment between the upper ends of the pile or piles and the structure being mounted thereon.

In accordance with the present invention a connection device for attaching a structure to a ground anchor comprises a base plate and upstanding walling defining an upwardly open enclosure for reception of grout or similar, the base plate having means whereby it may be attached to the ground anchor and the upstanding walling being configured so that the enclosure has a cross-section area at its open upper end which is smaller than its cross-section area adjacent to the base plate.

In preferred embodiments the cross-section area at the open upper end of the enclosure is between 10% and 15% less than the cross-section area of the enclosure adjacent the base plate.

There are various ways in which this structure of connection device can be fabricated. Usually the side walling will be welded onto the base plate. In many embodiments in accordance with the invention at least a part of the upstanding walling of the connection device will extend obliquely from adjacent the base plate to its open upper end. Thus, in most common embodiments in which the upstanding walling has a substantially rectangular cross-section, each side wall or only two opposing side walls may extend obliquely in this manner. Additionally or alternatively the upstanding walling may be crimped or pressed inwardly from an initial substantially upright alignment in order to achieve the desired reduction in cross-sectional area at the open upper end of the enclosure.

In one specific practical embodiment wherein the upstanding walling has a substantially rectangular cross-section adjacent the base plate, each of its side walls (or only two opposing side walls) may be formed to have an inwardly directed fold in a substantially central location of its upper margin.

The advantage of this configuration of connection device compared to a conventional grout box with upright walling is that, while it does not impede reception of a lower end of a levelling bolt, and allows for filling with grout and attendant horizontal and angular misalignment compensation, because of the un-constricted open upper end, transmission of forces to the side walling is sufficiently improved to avoid the need for additional bolted connections, as would be necessary with a conventional form of grout box.

The invention also provides a corresponding method of supporting a structure upon a ground anchor using a connection device as just defined, said method comprising the steps of securing the base plate of the connection device to a ground anchor by means of bolts, threadedly engaging a levelling bolt with the structure to be supported so that a lower end region of the levelling bolt projects, mounting a radially enlarged element to the lower end region of the levelling bolt, inserting the lower end region of the levelling bolt, together with said element, into the enclosure of the connection device so that the lower end of the levelling bolt contacts the base plate of the connection device, making adjustments as necessary to the position of the levelling bolt relative to the structure, and then filling the enclosure with grout and allowing it to harden to retain the levelling bolt.

The invention will be described further, by way of example, by reference to the accompanying drawings in which: Figure 1 is a schematic perspective exploded view showing use of a practical embodiment of a connection device in accordance with the invention in connecting a structure to a pile cap; Figures 2 and 3 are respective diagrammatic plan views of modified versions of the connection device shown in figure 1; Figure 4 is a schematic cross-sectional view corresponding generally to the arrangement shown in figure 1, but including more of the supported structure; Figure 5 is a perspective view of a known corner fitting for support of a superstructure; and Figure 6 is a plan view of the known corner fitting shown in figure 5.

Referring to figures 1 and 4, a practical embodiment 10 of a connection device in accordance with the invention is shown to comprise an oversized rectangular base plate 12 and upstanding side walling 14 of generally square cross-section (for example 15 x 15 cm at the base) welded thereto at a central location, each individual side wall of the upstanding walling 14 being crimped so as to have an inward fold or indent 16 at or near its midpoint at the open end of the enclosure. In this way, the space enclosed by the side walling 14 is of smaller cross-section, by between 10 and 15% at the upper end of the enclosure compared to the lower end thereof. Also, the central regions of each side wall extend obliquely inwards from the base plate 12 towards the upper end thereof. Each end region of the base plate 12, projecting beyond the side walling 14 is provided with a respective arcuate slot 18 for purposes of securement to the ground anchor, which in the illustrated version is a screw pile 20.

When used to provide the support for a temporary lightweight structure, such as a portable cabin or prefabricated dwelling, the sequence of construction, by reference to figures 1 and 4, is as follows: Firstly, a plurality of piles 20 are driven into the ground at predetermined locations to provide necessary support. Conventional screw piles have a drive flange 22 at their upper end providing convenient bolt hole apertures 24. Otherwise, if other types of pile are used or other ground anchors of any type, a known form of inverted top hat fitting can be installed at the top of the pile. The base plate 12 of a respective connection device 10 is then secured to the drive flange 22 or similar plate of each pile 20 by bolts 26 inserted through each slot 18 and respective apertures 24, secured by corresponding nuts 28 (figure 4).

A respective levelling bolt 30 is screwed into and through a threaded hole 42 (figures 4 and 6) in a base plate 32 of any conventional form of superstructure support, such as the known type of corner fittings 40, which are shown in figures 4, 5 and 6.

Typically, such levelling bolts 30 are 30mm diameter bolts. A radially enlarged element in the form of a respective washer 34 is fitted on to a lower end of each levelling bolt 30, being retained by nuts 36 above and below. The superstructure 50 is then offered to the multiple piles 20 on which it is to be supported. The lower ends of the levelling bolts 30, each carrying its washer 34 and nuts 36 are received into the enclosures provided by the upstanding walling 14 of the connection devices lOso that the lower ends of those levelling bolts 30 rest on the base plate 12. The bolts 30 can then be adjusted by screwing in or out of the base plates 32 in order to adjust the level of the said plates 32 and thus the level of the superstructure 50. As shown schematically in figure 4, a tube spanner 38 can be used for the purpose of rotating the levelling bolts 30.

Typically, the superstructure 50 to which the corner fittings 40 are attached will be held by a crane during the installation process. Therefore, once the levelling (height adjustment) operation is completed, the crane mounted superstructure can be raised slightly, lifting the bolts 30, and high-strength grout 46 can be poured into the enclosures provided by the walling 14 until they are adequately filled. The superstructure 50 is then lowered again into position, with final checking of horizontal alignment and levelling, before the grout 46 is allowed to set.

The foundation provided by the piles 20, connection devices 10 and other intermediate support structures, such as corner fittings 40, will almost immediately be capable of supporting the construction load. Once the grout 46 has hardened, the washer 34 and nuts 36 near the end of the levelling bolts 30 assist in dissipating compression load. They also anchor the levelling bolt 30 into the enclosure of the box 1 0 and in doing so resist tension forces. Shear forces are transmitted through the grout 46 towards the inwardly inclined side walling 14, and finally through the bolts 26 to the pile 20.

Without the previously known direct bolted connection between the superstructure and the conventional grout box, this arrangement will only develop relatively low resistance to bending, but for lightly loaded structures this should be adequate. The advantage of this arrangement is the more rapid and simpler installation procedure and hence reduced cost, the ease of levelling and the facility to more readily remove the superstructure and the piles when no longer required at a particular site.

When it is necessary to remove the structure, the bolts 26 are undone and the superstructure is lifted off leaving the pile flange plates 22 exposed for unscrewing of the piles 20. The connection devices 10 can be removed by cutting through each levelling bolt 30 in the gap between the structure base plate 32 and the top of the walling 14.

The foregoing is illustrative and not limitative of the scope of the invention and variations in detail are possible in other embodiments. In particular, figures 2 and 3 showed two variants. Firstly figure 2 shows a variant where the base plate 47 of the connection device is circular instead of rectangular and has four equally spaced slots 48 for purposes of connection to the pile flange or similar. Secondly, figure 3 shows a variant where the cross sectional shape of the side walling 49 of the connection device at its base is generally an elongate rectangle rather than a square. Other variations in detail, for example of exact shape and configuration of the upstanding walling and its enclosure and in the form of the radial enlargement provided on the levelling bolt (which need not be a washer) and in any other component are possible within the scope of this invention. In particular, it is possible in other embodiments to make the enclosure have a cross-section area at its open upper end which is smaller than its cross-section area adjacent to the base plate by fixing additional elements to the inside of the side walling in its upper margin or to the top of the side walling projecting inwardly, for example additional pieces, plates or strips of metal welded to the side walling.

Claims

CLAIMS1. A connection device for attaching a structure to a ground anchor, the device comprising a base plate and upstanding walling defining an upwardly open enclosure for reception of grout or similar, the base plate having means whereby it may be attached to the ground anchor and the upstanding walling being configured so that the enclosure has a cross-section area at its open upper end which is smaller than its cross-section area adjacent to the base plate.
2. A connection device as claimed in claim 1 wherein the cross-section area at the open upper end of the enclosure is between 10% and 15% less than the cross-section area of the enclosure adjacent the base plate.
3. A connection device as claimed in claim 1 or 2 wherein at least a part of the upstanding walling extends obliquely from adjacent the base plate to its open upper end.
4. A connection device as claimed in any preceding claim wherein the upstanding walling is configured so that the enclosure has a cross-section area at its open upper end which is smaller than its cross-section area adjacent to the base plate by being crimped or pressed inwardly from an initial substantially upright alignment.
5. A connection device as claimed in any preceding claim wherein the upstanding walling has a substantially rectangular cross-section adjacent the base plate with opposing side walls having an inwardly directed fold in a substantially central location of its upper margin.
6. A connection device as claimed in claim 1 or 2 wherein additional elements are fixed to the side walling within the enclosure or at the mouth of the enclosure so that the enclosure has a cross-section area at its open upper end which is smaller than its cross-section area adjacent to the base plate.
7. A method of supporting a structure upon a ground anchor using a connection device as claimed in any preceding claim and comprising the steps of securing the base plate of the connection device to a ground anchor by means of bolts, threadedly engaging a levelling bolt with the structure to be supported so that a lower end region of the levelling bolt projects, mounting a radially enlarged element to the lower end region of the levelling bolt, inserting the lower end region of the levelling bolt, together with said element, into the enclosure of the connection device so that the lower end of the levelling bolt contacts the base plate of the connection device, making adjustments as necessary to the position of the levelling bolt relative to the structure, and then filling the enclosure with grout and allowing it to harden to retain the levelling bolt.
8. A connection device for attaching a structure to a ground anchor substantially as hereinbefore described with reference to and as illustrated in figures 1 and 4 of the accompanying drawings.