Barbed Wire Fencing

Barbed Wire Fencing

Barbed wire, also known as barb wire (and frequently in dialect form spelled Bob or Bobbed), is a type of fencing wire constructed with sharp edges or points arranged at intervals along the strand(s). It is used to construct inexpensive fences and is used atop walls surrounding secured property. It is also a major feature of the fortifications in trench warfare (as a wire obstacle).

A person or animal trying to pass through or over barbed wire will suffer discomfort and possibly injury. Barbed wire fencing requires only fence posts, wire, and fixing devices such as staples. It is simple to construct and quick to erect, even by an unskilled person.

Barbed wire was the first wire technology capable of restraining cattle. Wire fences were cheaper and easier to erect than their alternatives. When wire fences became widely available in India in the late 20th century, they made intensive animal husbandry practical on a much larger scale.

Agricultural and Forest Usage

Barbed wire fences remain the standard fencing technology for enclosing cattle in most regions of the India, but not all countries. The wire is aligned under tension between heavy, braced, fence posts (strainer posts) and then held at the correct height by being attached to Wooden posts, Granite posts or Steel posts. The gaps between posts vary depending on terrain. On short fences in hilly country they may be placed every 3 Mtrs, while in flat terrain with long spans and relatively few stock they may be spaced up to 5 to 6 Mtrs. Wooden or Granite posts are normally spaced at 3 Mtrs in any case with 4 or 5 battens in between. Many farmers place posts 2 meters apart as battens can bend causing wires to close in on one another.

Barbed wire for agricultural and forest fencing is typically available in two varieties — "Soft" or mild-steel wire and "High-Tensile (HT)". Both types are galvanized for longevity. High-Tensile wire is made with thinner but higher-strength steel. It’s greater strength make fences longer lasting because cattle cannot stretch and loosen it. It copes with the expansions and contraction caused by heat and animal pressure by stretching and relaxing within wider elastic limits. It also supports longer spans, but because of its "Springy" nature it is hard to handle and somewhat dangerous for inexperienced fencers. Soft wire is much easier to work but is less durable and only suitable for short spans such as repairs and gates, where it is less likely to tangle.

Human-Proof Fencing

Most barbed wire fences, while sufficient to discourage cattle, are passable by humans who can simply climb over the fence, or through the fence by stretching the gaps between the wires using non-barbed sections of the wire as hand holds. To prevent humans crossing, many Prisons and other High-Security installations construct fences with barbed wire along with razor blade wire, a variant which instead of occasional barbs features near-continuous cutting surfaces sufficient to injure unprotected persons who climb on it. A commonly seen alternative is the placement of a few strands of barbed wire at the top of a chain link fence. The limited mobility of someone climbing a fence makes passing conventional barbed wire more difficult. On some chain link fences these strands are attached to a bracket tilted 45 degrees towards the intruder, further increasing the difficulty.

Installation of Barbed Wire

The most important and most time-consuming part of a barbed wire fence is constructing the corner post and the bracing assembly. A barbed wire fence is under tremendous tension, often up to half a ton, and so the corner post's sole function is to resist the tension of the fence spans connected to it. The bracing keeps the corner post vertical and prevents slack from developing in the fence.

Brace posts are placed in-line about 3 Mtrs from the corner post. A horizontal compression brace connects the top of the two posts, and a diagonal wire connects the top of the brace post to the bottom of the corner post. This diagonal wire prevents the brace post from leaning, which in turn allows the horizontal brace to prevent the corner post from leaning into the brace post. A second set of brace posts (forming a double brace) is used whenever the barbed wire span exceeds 200 feet (61 Mtrs. approx).

When the barbed wire span exceeds 650 ft (200 Mtrs. approx), a braced line assembly is added in-line. This has the function of a corner post and brace assembly but handles tension from opposite sides. It uses diagonal brace wire that connects the tops to the bottoms of all adjacent posts.

Line posts are installed along the span of the fence at intervals of 3 to 5 Mtrs. An interval of 5 mtrs is most common. Heavy livestock and crowded pasture demands the smaller spacing. The sole function of a line post is not to take up slack but to keep the barbed wire strands spaced equally and off the ground.

Once these posts and bracing have been erected, the wire is wrapped around one corner post, held with a hitch often using a staple to hold the height and then reeled out along the span of the fence replacing the role every 400 Mtrs. It is then wrapped around the opposite corner post, pulled tightly with wire stretchers, and sometimes nailed with more fence staples, although this may make readjustment of tension or replacement of the wire more difficult. Then it is attached to all of the line posts with fencing staples driven in partially to allow stretching of the wire.

There are several ways to anchor the wire to a corner post

The wire is wrapped around the corner post and knotted by hand. This is the most common method to attaching wire to a corner post. A steel hitch works well as it stays better with wire than with rope.

The wire is wrapped around the corner post and bound to the incoming wire using metal sleeves which are crimped using lock cutters. This method should be avoided because while sleeves can work well on repairs in the middle of the fence where there is not enough wire for hand knotting, they tend to slip when under tension.

The wire is passed through a hole drilled into the corner post and is anchored on the far side.

The wire is wrapped around the corner post and wrapped onto a special, gritted helical wire which also wraps around the incoming wire, with friction holding it in place.

Barbed wire for general usage is typically double-strand 12 gauge, zinc-coated (galvanized) steel and comes in rolls of 400 Mtrs (approx) length. Barbed wire is usually placed on the inner (pasture) side of the posts. Where a fence runs between two pastures livestock could be with the wire on the outside or on both sides of the fence.

Galvanized wire is classified into three categories; Classes I, II, and III. Class I has the thinnest coating and the shortest life expectancy. A wire with Class II coating will start showing general rusting in 8 to 10 years, while the same wire with Class III coating will show rust in 15 to 20 years. Aluminum-coated wire is occasionally used, and yields a longer life.