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I had a question about setting up hammock and tarp posts, and I’d appreciate any advice or feedback you might have.

I’m planning to install three posts in my garden using secondhand azobe wood:

  • The posts are 20x20 cm (about 8x8 inches)
  • Each one will stand 2 meters (about 6.5 feet) above ground
  • They’ll be buried 1 meter (about 3.3 feet) below ground

For the foundation, here’s what I’m thinking for each post:

  • Dig a hole 45x45 cm (roughly 18x18 inches) wide and 1 meter (3.3 feet) deep
  • Add a gravel layer at the bottom for drainage (the soil here is sandy and holds a fair bit of moisture — I’m in the Netherlands)
  • Set a PVC pipe into the hole with the wooden post inside it
  • Make sure the post is level and steady
  • Fill the hole with concrete

The questions at hand:

My main concern is making sure the posts can handle the lateral forces from the hammocks — there's definitely going to be some stress on them.

Does this sound like a solid approach?
Would it be a good idea to include rebar in the concrete for extra strength?

Any other thoughts are of course also welcome.

Jan
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1 Answers1

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This is the UBC 1997 code for posts, flagpoles, and pylons.

I've used this many times to calculate the resistance of concrete pylons against horizontal and vertical loads. And the projects I did using this formula are still standing.

In this case, the more relaxed the hammock is the less horizontal stress on the post

  • $T=\frac{T_y}{sin \theta}$

Meaning the more taut unproportionally, the more horizontal force!

Here is the UBC code.

  • $ d = \frac{A}{2} \left( 1 + \sqrt{1 + \frac{4.36h}{A}} \right) \tag{6-1} \label{eq:6-1} $

  • $A$ = $\frac{2.34P}{S_1\times b}$

  • $b =$ diameter of round post or footing or diagonal dimension of square post or footing, feet (m).

  • $d =$ depth of embedment in earth in feet (m) but not over 12 feet (3658 mm) for the purpose of computing lateral pressure.

  • $h =$ distance in feet (m) from ground surface to point of application of $P$.

  • $P =$ applied lateral force in pounds (kN).

  • $S_1 =$ allowable lateral soil-bearing pressure as set forth in Table 18-I-A based on a depth of one third the depth of embedment (kPa). \

  • $S_3 =$ allowable lateral soil-bearing pressure as set forth in Table 18-I-A based on a depth equal to the depth of embedment (kPa).

kamran
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