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  1. #21
    Senior Member coolkayaker1's Avatar
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    Maybe I'll put them at a 45 degree angle.

    If the 6x6s are at 45 degree angle, with the hammock line coming out at a corner of the square post, rather than just out from a flat surface, it'd be better. Excellent points about height and distance relationship, BW and J. Opie put his posts 15.5 feet apart, so that's a thought. I would like to know the height of J's when you geta chance with the measure. I may be going with a plan like yours--30 inches down, a three-post design, and 6x6s from HD or Lowes. Thanks.

  2. #22
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    Not Pretty, but free.

    Remnants of a pile of treated lumber from a deck I tore down sitting around for a few years. Decided to build a "permanent" hammock stand. Problem is nothing of the right dimensions. Longest 4x4 were ~9ft. Frost line rarely goes below a foot, but the soil is sandy. Need some bracing. Couple each of 7' & 6' lengths limited my span to ~12 ft. Scabbed together a 7' & 6' lengths per side. Dropped the posts into ~40" holes. Works, ugly but free.
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  3. #23
    in it for the naps oldgringo's Avatar
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    Quote Originally Posted by koaloha05 View Post
    Remnants of a pile of treated lumber from a deck I tore down sitting around for a few years. Decided to build a "permanent" hammock stand. Problem is nothing of the right dimensions. Longest 4x4 were ~9ft. Frost line rarely goes below a foot, but the soil is sandy. Need some bracing. Couple each of 7' & 6' lengths limited my span to ~12 ft. Scabbed together a 7' & 6' lengths per side. Dropped the posts into ~40" holes. Works, ugly but free.
    Uglee works for me. Paid for trumps just about everything else.
    Dave

    http://www.uark.edu/misc/xtimber/rna/pattonsbluff.html

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  4. #24
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    Why not reverse the pegola, get rid of the pretty bits,dig a trench and secure it with concrete, that way you will get the security and strength without blocking your view?

  5. #25
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    why

    You may not need the cross brace along the top if you use a post with a big enough cross section. The cross section perpendicular to the bending moment affects its resistance to bending [i.e why steel construction beams have an I shape, hence I-beams]

    There are forces on the posts pulling them in towards each other when you are in your hammock [lateral forces].

    There is a twisting force [torque] at the base of the post as well that is trying to bend the post and pull it down on top of you.

    And the higher up on the post you attach, the greater the moment arm which increase the torque also.

    Opie mentioned having a cross brace and still needing to add gussets.

    4x4 posts may be ok without bracing - if your hang angle is good and you haven't put too much tension in your hang and you are not too heavy - But I haven't done the math and I think the peace of mind the cross brace offers is worth having to tilt my head a few degrees to see the stars.

    PLUS it will look nicer to the Mrs. which means alot too.

  6. #26
    Senior Member coolkayaker1's Avatar
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    Great thoughts, tjm at al.

    I'm still waiting for jal to post the height of his posts, so that I can apply some of the armchair physics that you mention, tjm. Wondering how tall his post-less uprights are.

  7. #27
    kayak karl's Avatar
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    don't forget to cal 811 before you dig

  8. #28
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    In Ill. see if you can get hedge posts. They''ll be standing and strong when the next glacier arrives.

  9. #29
    the2nddeal's Avatar
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    Quote Originally Posted by coolkayaker1 View Post
    I'm still waiting for jal to post the height of his posts, so that I can apply some of the armchair physics that you mention, tjm. Wondering how tall his post-less uprights are.
    My posts are approximately 70" tall with the eye hooks about a foot below the top.

    Here's one tip that I was given after I had installed my posts: when digging your holes, make them teardrop shaped with the point facing the direction of the other post. That way, when you're adding concrete, the concrete will also be teardrop shape and the theory is that it will help secure the posts better against the forces trying to pull them over.

    I'm not sure how much better it would work since that tip was given a few days too late for me, but thought I'd pass it along anyway.

  10. #30
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    a little math

    All other things being equal, using 6x6 posts rather than 4x4 posts will make the posts "6 times more resistant to bending due to lateral loads [i.e. the hammock]"

    Deflection of post at location of hammock connection

    d = ( f * h * h * h ) / (3 * E * I)

    d = deflection of post at connection of suspension

    f = lateral force on post from suspension

    h = height of connection of suspension

    E = modulus of elasticity

    I = moment of inertia


    Moment of inertia for rectangular cross section

    I = d * b * b * b / 12

    I for 4x4 post = 12.5 inches4

    I for 6x6 post = 76.3 inches4

    76.3 / 12.5 = 6.1

    These equations also shows that

    A - using a material with a higher modulus of elasticity, E, than wood would allow for a small cross section [say a metal fence post]

    B - the lower to the ground you hang the lesser the bending moment
    Good luck.
    Last edited by tjm; 07-16-2010 at 09:03.

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