End assemblies are the most important part of any fence. They are reponsible for holding up and taking the strain of your wire or mesh and stronger is always better. No matter the length of your fence line, you need an end assembly on either side of a gate, as well as at every end or corner.
If a fence contractor does not place an emphasis on building strong end assembilies then I would recommend finding another contractor!
Strainer posts, positioned at the end or start of the fence are indispensable posts in a fence line. These posts shoulder the strain of the fence and offer support for any required gates.
To construct a strong and robust end assembly, it is essential to use solid strainer posts. As a general rule for strainer posts, you should aim for a height double that of the fence, ensuring half of the post is below the ground and half remains above.
When choosing steel strainers, contractors frequently exceed the double height rule because the diameter of steel posts is generally smaller than that of wooden strainer posts. Steel is generally more expensive, however offers superior longevity compared to wood, being resistant to rot and decay. Smaller diameter steel presents another advantage in being drivable by smaller post drivers, given favorable ground conditions. However, steel strainers also lack the impact absorption features of wood, which may result in the mushrooming or bending of posts when driving in rocky terrain. For a typical 1.2m high rural fence, we prefer to use 2.4m 150-200mm koppers pine posts.
There are several popular types of end assemblies.
Boxes or H-Braces are the most common type of end assembly in Australia, consisting of two vertical posts and one horizontal post with a wire or threaded rod brace running from the bottom of the strainer post to the top of the stay post.
Similar to the double height rule, Box assemblies adhere to specific rules and optimised ratios to ensure optimal strength and load capacity. The horizontal or top rail should always be at least twice the height of the fence, and the wire or threaded rod should maintain a close-to-30-degree angle for optimal performance. Unfortunately, many H-braces are constructed with incorrect ratios or unnecessary wires running in the wrong direction, which only promote strainer posts lifting and subsequent lean.
Box Assemblies can be constructed with both steel or pine and when working with pine we recommend a 2.4m strainer, 3m horizontal rail and a 2.1m stay post.
NZ-type stays are less prevalent in Australia, but, as the name suggests are the preferred end assembly for fencers in New Zealand. Thanks to advancements in post rammers, NZ stays are now able to outperform box assemblies and are gaining popularity in other countries.
In the past, stay posts were referred to as 'stay blocks' which had to be hand-dug. However, modern post rammers can drive stay posts to full depth while maintaining an important 45-degree angle to the strainer post. This makes NZ-type end assemblies arguably stronger than the common H-brace or box end where the typical 2.1m stay post is only driven 40% into the ground in a box end assembly. Box Strainers rely on brace wires to maintain tension, while NZ stays directly transfer force into the stay post.
NZ-type stays offer a couple of other advantages, including a better range of adjustment for dealing with significant slopes and eliminating the need for brace wire, which reduces the risk of catching the foot of livestock or interfering with tying off or gate hinges. However, mastering NZ-type stays is more difficult due to the precision required in morticing the post, which leaves no room for error.
Prefabricated stays typically consist of steel pipe which connects the strainer post to a foot plate, with a wire or threaded rod running along the ground to maintain tension. They can be used with both steel and wood strainer posts, offering quick assembly as the footplate eliminates the need for ramming a second post. Another advantage of prefabricated stays is that they are 100% reusable, making them a good choice if you think you might need to relocate your fence at a later date.
Another less common type of stay is the breastblock which is incredibly difficult to see because once finished it remains entirely underground! Breastblocks work by preventing movement of the strainer post below ground and are used for corners where you don't want an end assembly getting in the way.
The way we do breastblocks involves ramming a strainer post as per usual but then digging space for half a post to sit against the strainer horizontally on the opposite side of strain. Next we lock the half pine against the strainer by driving two posts as deeply as possible.
Studies indicate that for every 150mm increase in depth, the total load-carrying capacity of a post doubles. Consequently, the deeper a post is set into the ground, the greater the load it is able to support. The strain on strainer posts increases with each wire on a fence, and there are minimum requirements to maintain proper tension in a fence. A strainer post that is too short lacks the necessary strength and is prone to lifting out of the ground over time. It's worth noting that if there's a need to cut corners, opting for a longer post is more advisable than choosing a shorter and thicker one, given its impact on overall fence strength.
When constructing a box end assembly, the length of the rail directly influences the angle of the brace wire or threaded rod responsible for maintaining tension. If a rail is too short, it creates a steep angle, leading to an upward pull on the strainer post, thereby encouraging it to lift out of the ground. For optimal stability, an angle of around 30 degrees from the ground is considered the most desirable.
Both box end assemblies and diagonal stays adhere to the principles of physics and follow an optimal range of angles or ratios to ensure effective support. Placing a diagonal too high will only promote lifting of the strainer post, weakening the end assembly and fence. Conversely, positioning the diagonal too low fails to provide sufficient support to the strainer post, rendering it ineffective. Therefore, it is critical to maintain optimal angles to ensure the proper functioning of the end assembly.
Driven posts consistently exhibit a higher holding capacity and are less susceptible to vertical and horizontal movement. Furthermore, augering or digging a hole disrupts the soil responsible for supporting the strainer post, emphasising the importance of thoughtful installation practices.
In practice, digging a hole and then setting a post with concrete is not only more labour intensive but also provides no real benefit. Therefore, it is preferable to drive posts and reserve augering or digging holes for situations where it is absolutely necessary.
There used to be a widespread belief that a larger post diameter would result in a stronger hold in the ground. However, this notion is not entirely accurate, as the key factor for post hold is depth in the ground. Studies show that for every 150mm increase in depth, total load-carrying capacity is doubled.
Consequently, a post's ability to bear weight is significantly boosted by increasing its depth in the ground. This is a critical consideration when choosing strainer posts, as opting for a longer post instead of a wider one proves to be more effective. The sole difficulty lies in attaining considerable depth for strainers, involving a substantial investment in a post rammer, recognising that not all are alike!
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