O Level Notes : Agriculture - Fencing
Fencing refers to construction of a structure that provides a boundary or demarcation between two or more areas. Fencing involves the use of anchors that serves the purpose of keeping the fence intact.
Anchors are structures that are constructed in order to support the straining posts and corner posts so as to withstand the straining effect. Anchors contribute a number of advantages to fencing as well as a few disadvantages. Also in fencing some mathematical calculations are required in order to determine the quantities of material required per given perimeter.
The role of anchor
- To hold the corner posts at the same position ﬁrmly so as to withstand force of pull or push.
- They are also used to hold the straining posts in order to overcome the pulling effect of fence.
- They assist in keeping the strands of wire at an intact position.
- Anchors increase durability of the fence as it prevents the poles from falling.
- They are also used to keep the gate posts intact and strong at a ﬁxed position.
Types of anchors
Corner post wire anchor
The anchor is put at every corner post. It consists of two wires that are tied at the uppermost part of the corner post. These wires are stretched far apart on the outside of the fenced area. Large rocks are tied at the end of each wire and are then buried dip enough to keep the pulling force on the corner pole. The rock is called the dead man. It is buried at approximately 1.8 metres from the corner posts.
- There are durable due to wire material which is strong.
- Cost effective due to less material required.
- Saves the purpose of holding the corner posts ﬁrmly.
- The wire may rust with time.
- More caution should be observed in working with large rocks to avoid accidents.
- Only suitable at a corner post.
Double wire anchor
It is used to support the straining posts so that it stand ﬁrm on one position. Two wires are used at a straight angle opposite to each other. The wires are 1.8m away from the straining post to the point of burial into the ground. A large stone (dead man) is tied at the end of each wire and is buried into the ground to keep the pulling force exerted on the post.
- Requires less material to construct.
- It is more durable as compared to wooden anchors.
- Wire cannot be attacked by pests.
- Iron wires may rust over time due to air and moisture exposure.
- They are not suitable for corner posts straining.
Can be called strut anchor. It is used to keep the straining post intact at one position. It supports so that the posts will not move due to pulling force of wire strands along the fence line. A wooden post is used whereby it is put at an angle to be inclined to the post whereas the other side is buried ﬁrmly into the ground.
- Cheap to construct since wooden material are easily accessible.
- It can be constructed so easily.
- They may decay quickly due to moisture and microbe activities.
Double box anchor
The anchor forms a box structure at the corner post of the fence. It serves a purpose of withstanding the pulling force of wire strands in the two directions formed by the angle used on construction.
- It is cheap to construct since the wooden materials are easily accessible.
- It is a very strong anchoring system.
- It makes it possible to strain wires into two different directions.
- It is difﬁcult to erect thereby it require a skilled personnel.
- Wood may rot starting from the part buried in the ground with time.
Wire and wooden struts anchor
This structure consists of two posts being spaced at 1.8m from each other and are held together by a horizontal strut or stay at the top. Two wires are tied between the two posts at an inclined angle so that they cross each other at the centre to form an x shape. It is used along the wire strands.
- Requires less material to construct it.
- It can withstand the pulling force in either direction.
- Not suitable for use at the corner.
- Expertise required to put the strut and wire strongly.
High gate post anchor
It is used to hold the two gate posts at the top. This will pull the gate posts to the opposite directions of the wire strands pulling direction.Awire is used as the anchor.
- Easy to construct.
- Cheap as it requires less material.
- Is suitable for use on gates.
- Not applicable at the corners.
Determining quantity of fencing material
It is of utmost importance to calculate the amount of material that are required to fence the concerned area. Most farmers prefer to make use of calculated ﬁgures when purchasing fencing material.
Importance of determining fencing material
- It enables the farmers to purchase the right quantities that is no unwanted material will be purchased.
- It saves time in procurement when the material and their quantities are already listed.
- Unnecessary expenditure is avoided when the materials are determined prior to purchasing.
Worked example on calculating fencing materials
Calculate number of droppers, standards, anchors and bundles of wire required to fence a farm paddock of perimeter 2000m given the following information; 5 strands of wire are to be used, spacing between standards is 14m, spacing between straining posts is 400m and spacing between droppers is 3.5m.
- Number of bundles of wire given that 1 bundle can hold 1000m of wire.
Perimeter to be fenced = 2000m
For 5 strands of wire = 5 x 2000m = 10000m
Number of bundles =10000/1000 = 10 bundles
- Standard posts
The spacing between standards = 14m
For 1000m = 1000/14 = 71
For 2000m = 71 x 2 = 142
= 142 - 2
= 140 standards
- Straining posts
The spacing between straining posts = 400m
For 2000m = 2000/400 = 5
= 5 + 1 = 6 straining posts
The spacing of droppers = 3.5m
Droppers between 2 standards = 14/3.5 = 4
= 4 - 1 = 3
For 2000m = 142 x 3 = 426 droppers
Here is what we discussed in this topic
- Anchors are structures that are constructed in order to support the straining posts and corner posts against the straining effect.
- They hold the corner posts ﬁrmly to overcome pulling force.
- Anchors are used to hold straining posts to overcome the pull effect.
- They are also used to keep the gate posts intact.
- Types of anchors that are used in fencing are; corner post wire anchor, double wire anchor, stay anchor, double box anchor, wire and wooden strut anchor and high gate post anchor.
- Stay or strut anchors are used for keeping straining posts intact at one position.
- Their advantages are that, they are cheap and easy to construct.
- One of their disadvantages is that if wooden poles are used they may decay over time.
- Corner post wire anchors consist of two wires that are tied at the top part of corner post and are stretched apart to be buried in the ground at approximately 1.8m away from corner post.
- Their advantage is that, they are cost effective due to less material required.
- They are used to hold corner posts ﬁrmly.
- Their disadvantages are that, they are only suitable for corner posts and also the wire may get rust over time.
- Double box anchors are constructed forming a box structure at the corner post of the fence.
- They are cheap to construct, very strong and durable.
- They make it possible to strain posts and wire into two different directions.
- The disadvantages are that, they are difﬁcult to construct and poles may rot over time.
Definition of terms used in this topic
- Anchors –these are structures that are constructed in order to support corner posts and straining posts against straining forces.
- Straining –it is the pulling force that is experienced by an object.
- Strands – refers to the wires that runs horizontally and parallel to each other during fencing.
- Dead man – a large stone on which anchoring wire is tied and buried to give it more strength.