Shear force for 2x4's?

[Stormstaff]

I have a good size tree in the backyard and have gotten permission from the boss (wife) to put a couple of "posts" up for my son and I to hang from.

I'm looking at about a 15' - 16' span (from tree to "post") I think and I was thinking of using 2x4's doubled or tripled up.

How far should I sink them? 3' - 4'? Do I need to triple them? (I'm about 270# at the moment) I'm trying to do this as cheaply as possible and even though some folks say to use gravel instead of concrete, I've always been one to use concrete.

Suggestions for attaching hammock to "post"? Maybe drill a hole with a steel bar sticking through or will the tree strap hold well enough just around the stack of 2x4's?

Thanks in advance!

Kirk

[maverick]

I would get PT 10'x4x4 posts. Dig a hole 3 and half feet,dump a bag of quickcrete in there and walk away. If it needs more support run guy lines. The tree straps will hold or you can use an eye bolt and hang with caribiners.

[Bannerstone]

I'd go with a 4x6 treated yellow pine and I'd almost certainly design a poured concrete footing 30-36" deep in such a way that I could remove the timber when not in use. Then craft a clever cover for the hole.

David

[gmcttr]

Even 4x4's have been known to break. I would recommend a 6x6 or something similar.

However, given a choice of 4x4's or 2x4's, I would use three treated 2x4's per post in an I-beam configuration, nailed together with 16d nails or screwed with 3 1/2" decking screws. Three foot plus in the ground. The I-beam will resist more force than 2x's nailed together flat or a 4x4.

You want the hammock attachment to catch all three 2x's so a tree strap would be ideal.

[quigleyman]

I am a carpenter in Michigan. DEFINITELY get a 10' 4x4 pressure treated post and sink it 4' with a 60lb bag of quickcrete in the bottom. plumb stick is always a must as well.

If you need any advice or explanation please pm me. I can get real specific. (went to college for carpentry.)

oh and by the way, if you happen to use hardware, eyes, lags and the like.......READ the weight ratings on them as well. This is easy to overlook.

good luck

[quigleyman]

Even 4x4's have been known to break. I would recommend a 6x6 or something similar.

However, given a choice of 4x4's or 2x4's, I would use three treated 2x4's per post in an I-beam configuration, nailed together with 16d nails or screwed with 3 1/2" decking screws. Three foot plus in the ground.

You want the tree strap attachment to catch all three 2x's so a tree strap would be ideal.

thats a nice concept, but i wouldn't hang from it. that thing will twist, trust me. As for the fasteners...16d nails only have about a 300-400lb shear strength and screws are way less than that. If you are determined to use this design....go get construction adhesive and glue the crap out of them when assembling.

I hang from 20+ year old 4x4's on a regular basis. Straps work just fine. Since you're only setting one post....spend the extra $2 and buy a 4x6.

[gmcttr]

thats a nice concept, but i wouldn't hang from it...

As I stated, I'd recommend a 6x6, but with 25 years experience in commercial construction, I would hang on the I-beam design without hesitation....just my .02

[Woods Walker]

I have done quite a few fences with treated 4x4 & seen them break from a stiff wind on a privacy fence. I would use 6x6 or better yet get a used utility pole from the power company & 3 feet in the ground with cement mix, seen quick-creet become crumbly & fail.

[quigleyman]

As I stated, I'd recommend a 6x6, but with 25 years experience in commercial construction, I would hang on the I-beam design without hesitation....just my .02

but what about squash blocks and bridging?? I'm teasing. I didn't mean to come on too strong. My "small business owner injury liability spider senses" were just tingling a little. It's just nice to be in one of these threads where I'm answering some questions...not asking all of them. Happy trails and I hope I didn't offend you, gmcttr.


We could just end the discussion and tell him to strategically plant a red oak tree....

[Rain Man]

However, given a choice of 4x4's or 2x4's, I would use three treated 2x4's ....

Unless things have changed, 4x4s and 6x6s are treated for "ground contact" and 2x4s are not.

Might want to treat with some creosote or something, if you use 2x4s, or else they will rot quicker.

Rain Man

.