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Strength of a 4x4

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Forum topic by Alexp08 posted 04-23-2016 01:33 AM 866 views 0 times favorited 22 replies Add to Favorites Watch
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Alexp08

6 posts in 229 days


04-23-2016 01:33 AM

Hello, so im here for a quick question. Im looking to build a hammock stand. Im hoping to use pressured treated pine 4×4s and im wondering if anyone know the breakibg point of such wood. It will be like the one in the picture. And im trying to determine the weight capacity of it.
 photo 805766_19747_raw_zpsh7ra7g0t.jpg

Thanks.


22 replies so far

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conifur

955 posts in 617 days


#1 posted 04-23-2016 01:42 AM

Way too many variables, the longer/higher you would put the 45* supports easier to break at that point, any flaws in the 4×4 supports, ect. How much weight do you want it to hold?

-- Knowledge and experience equals Wisdom, Michael Frankowski

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Alexp08

6 posts in 229 days


#2 posted 04-23-2016 01:46 AM

The 45* supports will be almost right where theyre at in the picture unless someone can recommend a better place for them. Ideally i would like it to hold 500lbs.

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BurlyBob

3692 posts in 1731 days


#3 posted 04-23-2016 02:31 AM

Alex, Pressure treated has only one useful purpose, being in contact with ground or bare concrete. PT lumber is general the poorest quality lumber milled. It’s stored wet and once dry will assume all sorts of wonderful contortions. Perhaps adding a cross piece at the top would be the best solution for this project. Just looking at the design there seems to be a lot of weak points that will give with time, weight and stress.

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Alexp08

6 posts in 229 days


#4 posted 04-23-2016 02:39 AM

The only reason i was looking at pressure treated was due to the fact that this stand will be outside. I can easily go with another. And realistically it only has to last me for a year or two till I can build a more permanent one or spend a few hundred on a metal one. Right now im just looking to see if it’ll hold up to the weight

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conifur

955 posts in 617 days


#5 posted 04-23-2016 03:18 AM

Will the hammock netting hold 500lb?

-- Knowledge and experience equals Wisdom, Michael Frankowski

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Alexp08

6 posts in 229 days


#6 posted 04-23-2016 03:20 AM

The hammock netting will hold 650lbs

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alittleoff

296 posts in 742 days


#7 posted 04-23-2016 03:24 AM

It might work better if you were to raise the two end braces up as much as possible without getting in the way. You could also run a small aircraft cabler over the top and down the back of the 4×4, then anchor it on the bottom.
Gerald

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DirtyMike

461 posts in 367 days


#8 posted 04-23-2016 03:26 AM

alex, i have worked with pt pine for similar outdoor projects and construction. If you were to follow that design i would use 4×6 ’s for the main supports. 4×4’s are really meant to support vertical weight as opposed to being fulcrumed. a 4×6 should give your more support and not twist and bow after drying. proper bracing is the most vital part of the whole build for rigidity. good luck

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Rick M

7923 posts in 1845 days


#9 posted 04-23-2016 03:34 AM

The wood will hold, the joinery is the question. The posted picture appears to be bolted together, so that or another strong form of joinery. If you don’t want to use bolts maybe look at timber framing joinery.

-- http://thewoodknack.blogspot.com/

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Alexp08

6 posts in 229 days


#10 posted 04-23-2016 03:37 AM

Im fine with bolts, that was ths initial plan. As far as wood should i not use PT?

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Rick M

7923 posts in 1845 days


#11 posted 04-23-2016 04:13 AM

The problem with pressure treated is it is very wet when you buy it and tends to warp, even more than regular construction pine; otherwise, it’s fine.

-- http://thewoodknack.blogspot.com/

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Alexp08

6 posts in 229 days


#12 posted 04-23-2016 04:16 AM

So should i buy nonPT lumber? And how well will it then stand up to the elements?

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Lazyman

695 posts in 853 days


#13 posted 04-23-2016 04:30 AM

Personally, I would use PT only if it is in contract with the ground.

If you find after building this that the 4×4s have more flex that you feel comfortable with you could always add a 2×4 brace between the tops of the 2 4×4s to add more strength. Also, moving the angle braces higher up will also help. Because the weight will be partially directed downward in compression, it seems like it should be plenty strong.

-- Nathan, TX -- Hire the lazy man. He may not do as much work but that's because he will find a better way.

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clin

514 posts in 461 days


#14 posted 04-23-2016 04:30 AM

I think 4×4 would be plenty strong in this application. They aren’t going to break. And a little bow isn’t going to hurt anything. If it bowed too much, the person in the hammock will start dragging they’re hind end on the ground, but it’s not going to fail in some spectacular fashion.

Look at that photo. I’d estimate that 2/3 of the force on the uprights is straight down ( compression), leaving about 1/3 pulling inward (bending load). Assume 500 lbs (3 adults?), that’s 250 lbs per side and perhaps 80 to 100 lbs pulling inward. A 4×4 about 8 ft long could hold 100 lbs at the end of it with no issue at all.

Keep in mind that if the net were strung very tightly across (like a tight rope), then you could create bending forces greater than the applied weight. Point being you do want the netting to sag so the net is pulling down a lot (as seen in the photo). In other words keep the angle between the net and upright as small as possible.

The forces at the joint will be significant. But as mentioned, with strong joints (like the bolted one in the photo) you won’t have any issues.

Like any outdoor wooden furniture or structure, you have to keep an eye out for rot that will weaken it. But that won’t happen fast.

I also agree to avoid pressure treated wood, except perhaps the two bottom pieces that might touch the ground. Put a good exterior paint on it or other finish like Penofin, and it will last for years.

-- Clin

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Neilswoodcraft

9 posts in 233 days


#15 posted 04-23-2016 04:42 AM

I think 4×4 is the bare minimum. I would do some jointery as suggested above.

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