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THIS INVENTION relates to a fixture for providing an anchorage for the lower end portion of an upright pole and is particularly, although not exclusively, concerned with providing such an anchorage on loose or particulate material such as sand or soft earth.
State of the Art
Poles for supporting overhead screens above head height at predetermined positions often have a length exceeding two metres and are subjected to lateral loading from the structure supported at their upper end. When the lower end-portion of the pole is fixed in a concrete base buried in the ground, it will normally provide the necessary rigidity for supporting an overhead structure. However, if the lower end-portion of the pole is simply buried in the ground, it may be necessary to utilise guy lines and/or other rigging in order to prevent the pole from tilting over a period of use. The presence of guy lines around a pole present a hazard to those in the vicinity of the pole. They also occupy space beneath the supported structure which might otherwise be usefully employed.
An object of this invention is to provide a fixture for supporting a lower end-portion of a pole.
In accordance with the present invention a fixture for anchoring the lower end-portion of an upright pole in the ground, comprises a post having a longitudinally-extending radial fin, and a screen attachable to an intermediate portion of the post beneath ground level so as to extend horizontally for a sufficient distance around the post to provide lateral stability when the lower end-portion of a pole is attached to it. The fin may spiral around the post axis. This configuration allows the post to be screwed into the ground if desired. More than one radial fin may be provided on the post.
Preferred Features of the Invention
The screen may be bolted or otherwise rigidly attached to the post, preferably by way of the longitudinally-extending fins. Suitably, these fins extend radially from the post for a distance which exceeds the post diameter. A central opening may be provided in the screen to allow the finned post to pass through it before the screen and post are attached to one another. The screen is conveniently constructed as a grid. However it may also be formed as plate having on its periphery on upstanding rim flange to prevent or reduce horizontal movement.
The lower end of the post may be open. Preferably the fin adjacent its lower end taper towards the post to provide it with a relatively pointed lower end to enable it to be driven more easily into soft earth or sand.
The upper end of the post may be rigidly attached to a radially-extending, cap plate to which a correspondingly-shaped radial flange attached to the base of the pole can be connected by bolts or in some other way to unite the pole with the fixture.
Introduction to the Drawings
The invention will now be described in more detail, by way of a preferred embodiment, with reference to the accompanying drawings in which:—
FIG. 1 shows a fixture in elevation;
FIG. 2 is a plan view of a screen formed as a grid used to stabilise an intermediate portion of the fixture; and,
FIG. 3 is a cross-section through FIG. 1 taken on the line and in the direction of the arrow III-III in FIG. 1.
The fixture shown in FIG. 1 comprises a post formed by a tube 1 having a cap plate 2 which is welded to the upper end of the tube 1 and the upper ends of four longitudinally-extending fins 3 which are welded to the outside of the tube 1 and are arranged symmetrically around it as shown in FIG. 3. The radial length of each fin is preferably rather larger than the external diameter of the tube 1. The lower ends of the fins 3 taper toward the lower end of the tube 1 to facilitate the fixture being driven into soft ground such as sand or a friable soil. The lower end of the tube 1 is open and the fins, tube and top plate 2 are made from galvanised steel.
A reticulated grid-like screen 5 made from welded-together flat steel bars as shown in FIG. 2, has a rectangular outline and a central rectangular opening 6 which enables it to be mounted at an intermediate position on the finned tube 1 in close contact with the fins, as shown in FIG. 3. Brackets 4 of the same shape and also made from steel, are welded to the portions of the bars of the screen around the opening 6 and these are attached to the upper and undersides of the screen 5 to facilitate its rigid attachment to the fins by bolts or other forms of connection.
The fixture is used as follows:—
A post hole having a depth at least equal to the length of the tube and of matching diameter is first dug in the sand or friable soil by a suitable post-hole digger tool at a position where a lower end-portion of a pole is to be mounted. The upper end-portion of the hole is then dug out laterally to provide a horizontally extending rectangular seat to receive the screen 5 which is then placed on the seat so that its opening 6 is concentric with the post hole axis.
The finned tube is then inserted downwardly through the opening 6 and into the post hole. The screen 5 is then fixed by its brackets to the fins 3 at the desired position along the length of the tube 1. The stiffness of the screen 5 and its resistance to horizontal movement after the hole has been filled up with sand or friable earth thereafter locates the tube.
The circular cap plate 2 is located at or just beneath ground level so that it does not form an obstruction.
The lower end of the pole which is to be mounted on the tube has a steel flange welded to it and this flange fits over the circular cap plate 2. The flange and cap plate are then bolted together by circumferentially spaced bolts so that the pole and fixture are rigidly united with one another.
The fins 3 ensure that the tube 1 will not bend and the attachment of the screen 5 to the tube 1 beneath ground level ensures that the tube cannot tilt. It is convenient, although not essential, to have the lower ends of the fins tapered as shown, as this helps the fixture to be hammered into the ground.
In one example of the embodiment of the invention illustrated, the screen is 1,043 millimetres long and 1,003 millimetres wide. The central rectangular opening is 317 millimetres long and 290 millimetres wide. The bars making up the screen are of rectangular cross-section and are 40 millimetres wide and 5 millimetres thick. The screen is placed about 200 millimetres beneath ground level.
The external diameter of the tube is 80 millimetres and the radial length of each fin is 85 millimetres. The length of the tube is 1,200 millimetres and its wall thickness is 3.6 millimetres. The cap plate at the top of the fixture is 390 millimetres in diameter and its thickness is 16 millimetres.
In practice, although a reticulated structure for the screen is preferred it could equally well be constructed as a continuous or perforated plate having around its periphery an upstanding rim flange to restrict horizontal movement. The screen can also be made up of individual segments which are attached to one another at the site of use and may, for example, be bolted together when the fixture is being assembled.
In some cases enhanced stability of the fixture may be obtained by providing the post with two or more vertically spaced and horizontal screens of identical construction and similarly attached to the finned post. In the embodiments of the invention the screen should be of fairly rigid construction so that when buried in the ground its rigidity and dimensions are sufficient to resist tilting of the pole when in use and subjected to sideways forces.
An advantage of the ground mounting fixture specifically described, is that it can be fairly easily dismantled and moved to another site where it can be re-erected. This should be contrasted with the conventional method of mounting a lower end of a pole in a concrete block provided with side bars to give support to withstand lateral loading of the pole. Re-location of the pole involves breaking the concrete block out of the ground and then smashing it up. It cannot be re-used and is difficult to handle. The presence of the radiating side bars also has to be dealt with by cutting them off. As these are usually steel bars, they cause additional complications and costs.