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  1. #1
    Join Date
    Oct 2003
    Location
    melbourne
    Age
    63
    Posts
    936

    Default Question on post arrangment

    I want to put up hail netting 5m high 90m wide some I can do with bed logs but I can't next to my drive.
    I was going to use 6m posts 1m in ground with a 3.6m post between them braced with cable like box fencing setup.
    It will have about a 1.5 tonne pull on it.
    My question is does the distance between the posts affect the strength greatly?
    Would I be better off having one vertical and a brace?

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  3. #2
    Join Date
    Aug 2011
    Location
    Murrumbateman
    Posts
    62

    Default

    Your options will be dictated a lot by soil type. Both angled stays and box strainer assemblies will convert horizontal forces into vertical ones and will try to lift your strainer posts out of the ground. Especially a problem with lightweight treated pine. At the other end of the scale, using steel strainers with deformed ends concreted in holes with belled out bottoms won't lift out unless in sand. Box assemblies with 3 metre plus top rails are generally a lot stronger but they are also more expensive.

    1.5 tonnes is a lot of tension. And presumably it will be even more if there is hail sitting on the net. If you add more light weight intermediate posts then you shouldn't need as much tension. What design are others in the district using?

    What is the crop? 5 metres is a lot higher than standard fruit picking ladders.

    Uplift forces in high winds need to be accounted for as well.

  4. #3
    Join Date
    Oct 2003
    Location
    melbourne
    Age
    63
    Posts
    936

    Default

    My soil is sandy, and I am growing blueberries it will also cover some existing fruit trees. I need the hight as I may run a mechanical harvester in the future. We get very little hail and the storms are mild compared with most places. The main reason is to stop birds and we have lots of those. Here is my proposedstrainer.PNG design a 6m post and a 5.4m with a 3.6 horizontal. I read that the major trouble with these H frames is the front post sinking. So I decided a base plate and a not so deep hole, so less digging and cheaper post. I thought a piece of wood nailed to the strainer would help hold it down and stop it from twisting.
    I will be running 7.1mm cable in a 12m grid over 90m with no internal supports. We have one next door that spans 300m at 20m spacing but it sagged a little so we put in an internal row of posts.
    One problem is the cables cutting into the pine posts, not sure if this is expansion and contraction or wind or perhaps the posts soaking in water and getting soft. Not sure what to do about that, it has cut in a long way in 8 years. These posts are supported by bed logs which I can't do in places.

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