GB2170239A - Security fencing - Google Patents

Abstract

Security fencing comprises a plurality of rigid vertical bars 5 secured together by cross members 9,10 and a chain link mesh 1, each bar being engaged with a respective run of wire of the mesh, successive portions of the run being disposed on alternate sides of the bar, the runs engaged to respective bars being separated by two runs not engaged to bars. <IMAGE>

Description

SPECIFICATION Security fencing This invention relates to security fencing particularly but not exclusively to security fencing used to prevent unauthorised access to enclosures.

The construction of security fencing is dictated by considerations which are quite different from simple boundary fencing, or decorative fencing or windbreaks.

The minimum time in which an intruder can penetrate security fencing is important in the arrangement of a security system. Closed circuit television cameras or other means of detection of an attempt to cut fencing must scan the whole fence with a frequency equivalent to this minimum time. Back-up security, such as patrolling guards, must be able to respond within this minimum time in order to prevent an intruder from penetrating beyond the interior of the fencing.

Cost effectiveness of fencing may be determined by use of the following formula:- Cost of Fence = per second Penetration time 100 cost e.g. =1 per second 100 seconds 40 cost or =2 per second 20 seconds Thus an expensive fence which is difficult to penetrate may be more economical than a cheaper fence.

In addition the lifespan of a fence is important. A fence lasting for 10 years is clearly more economical than a fence of half the cost but which lasts for only two years.

Chaih -link wire mesh is generally used for fencing. This comprises successive runs of wire, each bent to zig zag or spiral formation and interlinked at the angles with the next adjacent run of wire. It has been found that a person using bolt cutting shears can penetrate such a fence in as little as one minute and twenty seconds. Use of such fencing imposes a heavy burden on the supporting security system, particularly where there is a large fenced perimeter. Welded mesh has also been used but this is much more expensive and affords iittle greater impediment to a person using heavy shears.

The weakness of security fencing constructed from chain link or welded mesh is that once it has been cut, the cut edges may be unravelled or pulled back without difficuity.

According to the present invention security fencing comprises a plurality of rigid vertical bars secured together by cross members and a chain link mesh, the mesh being composed of successive runs of wire each angled to form a zig zag formation and interlinked at the angles with adjacent runs of wire, the runs of wire extending vertically, each bar being engaged with a respective run whereby successive portions of the run between the angles are disposed on alternate sides of the bar, the runs engaged to respective bars being separated by two runs not engaged to bars.

The bars are preferably generally flat and of rectangular cross section, although round, oval, square or ótherwise shaped cross-sectioned bars may be employed.

Engagement of each bar with a single respective run of wire makes it necessary for each angle of the run to be cut in order to force the mesh from the bar. Unravelling of mesh is impossible, in contrast to previously known fencing in which chain link mesh is secured at a few points to supports.

Disposition of the bars at every third run of the wire, leaving two free runs between each bar, results in the bars being separated by a single aperture of the mesh. Spacing the bars moreclosely together, for example, at alternate runs of the wire, is uneconomical and does not enhance the cost effectiveness of the fence. However, more distant separation of the bars may allow a person to squeeze between them, possibly with use of a crowbar, jack or the like. For example, conventional chain mesh wherein the distance between angles of a run is 5 cm, has horizontally adjacent links separated by an aperture of 7 cm. The space between adjacent bars in fencing according to this invention would be 8 cm.Location of the bars with three unengaged runs between them would result in a separation about 12 cm, a dimension which could be easily increased by a crowbar or jack to a size through which a person may pass.

The lower ends of the bars and mesh are preferably secured into the ground, for example, by embedment to a depth of 60 cm in concrete.

The upper ends of the bars may extend above the mesh to form upwardly or outwardly directed spikes.

The invention is further described by means of example and not in any limitative sense, with reference to the accompanying drawings, of which: Figure 1 shows fencing in accordance with this invention; Figure 2 is a cross-section of the fence shown in Fig. 1-; and Figure 3 is a detailed view of a portion of the fencing.

The fencing shown in the Figures comprises conventional chain link mesh 1 suspended between supporting uprights 2 located e.g. 3m apart. The mesh comprising successive runs of wire, each bent to zig zag or spiral formation and interlinked at the angles with the next adjacent row of wire. The runs 3, 4 extend vertically of the fence. The mesh may be composed of wire having a gauge of 2mm to 5mm as may be convenient. The wire may be galvanised mild steel, plastics coated bright steel, plastics coated galvanised steel or any other suitable material.

Flat bars 5 or other rigid members arranged vertically in parallel relation are supported by horizontal cross member 9, 10. Each bar 5 is engaged to a respective run of the wire mesh, successive portions of the row between the angles 7,8 being disposed on alternate sides of the bar 5. Every third run is engaged with a respective bar. Each bar is therefore separated from the adjacent bars by two runs which do not have bars threaded through them.

The bars 5 are secured by means of rivets 11, bolts or other fastenings to cross members 9, 10. These are spaced by a distance selected to impede forcing of the bars apart. A distance of 1.4m has been found to be adequate for most purposes. Adjacent bars are preferably disposed on opposite sides of the mesh.

In alternative embodiments of this invention the bars or other members may be arranged diagonally of the mesh either in addition to the vertical bars. Horizontal bars may also be employed but this is not preferred since these facilitate climbing over the fence.

Plastics coating of bars and mesh enables the fence to be provided in a variety of colours.

The bars may be differently coloured to the mesh. In addition diagonal bars may be differently coloured to vertical bars. This provides a wide variety of decorative warning or camouflage effects.

The bars 5 extend beyond the top of the mesh to form spikes 6, alternate spikes 15 being cranked to support coiled barbed wire or razor tape 16. The cranked spikes 15 may be inclined horizontally or may be inclined at an angle of 45" to the vertical. Any other convenient angle may be employed. The vertical spikes preferably extend to half of the height of the roll of barbed wire. Provision of the plurality of bars in fencing in accordance with this invention confers the advantage that a spiked top may be provided by simple extension of the bars.

Separation of the bars to a greater or lesser extent than every third run of the mesh would either cause wide spaces to be left between the spikes, or would place them- sufficiently close together to reduce the effectiveness of the spikes by distribution of a load over several of them.

The lower ends17 of the bars 5 may also be spiked but preferably extend into the ground and are embedded in concrete to prevent excavation under the fence.

Furthermore the mesh may barbed.

Fencing in accordance with this invention may incorporate one or more gates constructed in a analogous manner.

Back stops may be attached to the rear of the posts 2 to buttress the latter.

The mesh may have a distance of 50mm between consecutive angles 12, 13 of a run, affording a maximum distance of 70 mm between horizontally adjacent runs. The distance between the bars is about 80mm in this case, preventing a person who has cut the mesh from squeezing between the bars.

The posts 2 may be secured directly to bar 5 as shown in Fig. 1. Alternatively each post 2 may be located between two bars 5 but not directly attached to them. This avoids a potential source of weakness. In the latter arrangement the cross members may be secured to the post by means of bolts, clips or other secure fastenings.

The lower ends 7 of the bars 5 may not be embedded in concrete to avoid the difficultyincumbent in replacement of a damaged portion of the fence if the concrete has to be excavated. Digging under the fence of this invention is more time consuming than cutting through it.

For this reason embedment in concrete may be unnecomomical.

Claims (8)

1. Security fencing comprising a plurality of rigid vertical bars secured together by cross members and a chain link mesh, the mesh being composed of successive runs of wire each angled to form a zig zag formation and interlinked at the angles with adjacent runs of-wire, the runs of wire extending vertically, each bar being engaged with a respective run whereby successive portions of the run between the angles are disposed on alternate sides of the bar, the runs engaged to respective bars being separated by two runs not engaged to bars.

2. Security fencing as claimed in claim 1, wherein the bars extend beyond the top of the mesh the upper ends of the bars forming spikes.

3. Security fencing as claimed in claim 2, wherein alternate spiked bars are cranked.

4. Security fencing as claimed in claim 3, wherein barbed wire or razor tape is secured to spiked bars.

S. Security fencing as claimed in any preceding claim, wherein the bars are flat and rectangu lar in cross section.

6. Security fencing as claimed ih any preceding claim, wherein the lower portions of the mesh and bars are embedded in concrete.

7. Security fencing as claimed in any preceding claim, wherein the distance between consecutive angles of a run of wire is 5cm.

8. Security fencing substantially as hereinbefore described with reference to the accompanying drawings.