# Which beam is stronger?



## mae-ling (Dec 9, 2011)

Yes what you are proposing would be stronger than a 4X6. would not be as strong a 4-2X10's.
Beams are much stronger in depth then width.


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## cortell (Nov 27, 2010)

I suspect you could also considerably stiffen the beam by laminating (glue-n-screw) exterior-grade plywood (10" nominal continuous strips) to the 2x10s in your design. It will only increase the beam width by 1" or 1.5" but make a big difference.


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## D270 (Mar 27, 2011)

Wouldn't it be difficult to precisely drill thru a 2x10 for a carriage bolt with a handdrill and typical drill bits?
Or am I fretting over nothing?

Wouldn't 4, 2x10s be as strong (vertically) as 6, 2x10s or 2, 2x10s??
I thought the vertical dimension was the important part?

My purpose is to get typical available lumber, i.e. a 4x6, and not need to buy a specialty drill bit to go thru a 2x10. Plus make it a strong beam.

Would the plywood strips help because they are sheets with opposing grain laminated together?

Thanks!


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## ninjahero (Apr 10, 2012)

D270 said:


> Wouldn't it be difficult to precisely drill thru a 2x10 for a carriage bolt with a handdrill and typical drill bits?
> Or am I fretting over nothing?
> 
> Wouldn't 4, 2x10s be as strong (vertically) as 6, 2x10s or 2, 2x10s??
> ...


Your idea will work due to mass because u cant precisely drill through a 2x10 n by the way u can never over do a project especially if it for your kid(s) cuz u obviously want to keep them safe but just a tip if u do go through with it finish boxing it up with plywood or something jus do it covers the bolt and makes it look nice ya no


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## joecaption (Nov 30, 2011)

A simple cheap 1/2" paddle bit would do the job and for what your doing it does not to be precise as you suggested.


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## Joe Carola (Apr 14, 2006)

D270 said:


> Hi,
> For my kids playset I am trying to overbuild the swingset portion.
> I see many designs with 4x6 as a swing beam. I saw a DIY swingset with 4, 2x10's bolted and glued together.
> 
> ...


How is 4-2x10s...10"?


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## ninjahero (Apr 10, 2012)

Joe Carola said:


> How is 4-2x10s...10"?


Because he building a swing he's goin to bolt it so he wanted to drill it upward not through you understand so his idea of sistering 2 2x10s on each side of a 4x6 is good enough cuz it will be solid and hold a good amount of weight n will last for his kids for a long time to come


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## ninjahero (Apr 10, 2012)

joecaption said:


> A simple cheap 1/2" paddle bit would do the job and for what your doing it does not to be precise as you suggested.


Ya but me personally would use 1/4" because some of the hook or whatever you would call it I can't really find a huge selection But 1/2" would to if you can find one


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## cortell (Nov 27, 2010)

D270 said:


> Wouldn't it be difficult to precisely drill thru a 2x10 for a carriage bolt with a handdrill and typical drill bits?
> Or am I fretting over nothing?


You don't need to drill precisely through the 9-1/4" of distance in _one_ single 2x10. Think of the four fastened 2x10s as a single block of wood. All that matters is that you start drilling through the top (or bottom) and you come out the other side, and that the resulting hole is mostly vertical. You're going to have a washer and nut holding the through-bolt in place.



> Wouldn't 4, 2x10s be as strong (vertically) as 6, 2x10s or 2, 2x10s??
> I thought the vertical dimension was the important part?


Absolutely not. You're getting confused with the fact that increasing the depth of a joist or beam is more effective than doubling up. E.g., a 2x12 makes a stronger and more rigid joist than two 2x10s.



> My purpose is to get typical available lumber, i.e. a 4x6, and not need to buy a specialty drill bit to go thru a 2x10. Plus make it a strong beam.


You just need a long bit. That's not too difficult to find, especially in the age of the internet.


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## Joe Carola (Apr 14, 2006)

ninjahero said:


> Because he building a swing he's goin to bolt it so he wanted to drill it upward not through


Ok....all he has to do is buy a long drill bit.


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## D270 (Mar 27, 2011)

I do appreciate all the feedback. Lots of good perspectives. I mis-spoke when talking about 10" to drill through...all lumber is smaller, of course.

My thought about the lamination was what if I drill through the one 2x10 crooked and come through a seam? 

Maybe it doesn't really matter??



Would adding anything to the width strengthen a beam in the downward deflection? I'm still confused...below is what I was talking about.
Thanks, lots to think about.

D.


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## joecaption (Nov 30, 2011)

Three 2 X 10's would be more then enough.
It does not matter if you hit a seam.
Just make sure not to drill where there's a fastner.
You will need a 12" long bit. A paddle bit would be less then $10.00 and would have a small enough shank that even a small drill will hold it. As you drilling keep back it out to clear the chips.
1/4" would not barly be strong enough for a plant hanger, use 1/2 instead.
You will need a lifting eye not a reguler eye bolt.
A lifting eye has a one piece eye, it's all cast as one piece.
A reguler eye eye bolt is just a streight rod that has been bend to form the eye and can open up over time.


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## Daniel Holzman (Mar 10, 2009)

You are confused about the definition of the word strength. The strength of a beam refers to the load the beam can carry before it fails. Strength does not refer to the deflection of the beam, that is a different item. In typical residential applications, beam strength is computed based on the maximum allowable fiber bending stress on the beam, which means how much stress the edge of the beam experiences when the beam is loaded.

The strength of the beam depends on three factors:

1. The maximum allowable fiber bending stress. This varies with the species of wood, and can be as low as 800 psi, and as high as 2,500 psi, depending on the species. For most construction grade wood, the maximum allowable bending stress is around 1,000 psi.
2. The moment of inertia of the beam. The greater the moment, the lower the fiber bending stress, and the stronger the beam. For a rectangular beam, the moment of inertia is b*d^3/12, where b is the width of the beam, d is the depth, and the ^3 means cubed. so if you double the width of the beam, you double the moment of inertia, and the beam is twice as strong. If you double the DEPTH of the beam, the moment of inertia is 8 times as big, and the beam is 8 times as strong (but see note three for the whole story).
3. The distance from the centroid of the beam to the edge of the beam. Stress is directly proportional to the distance, so a beam twice as deep carries twice the stress; however, the moment of inertia is 8 times as big, so doubling the depth of the beam increases strength four times.


Conclusion is that sistering a second beam of equal size onto the first beam doubles bending strength. Doubling the depth of the beam increases bending strength 4 times. Note that this discussion is about BENDING STRENGTH only. These conclusion DO NOT apply to vertical and horizontal shear, torsion, and tear through of the nut holding the support. But this is not a course in structural mechanics, so let's leave it at this for the moment.


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## mae-ling (Dec 9, 2011)

Doesn't need to drill at all. Notch the center 2x10's will a saw before making the beam. Nice even straight hole.


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## jklingel (Dec 21, 2008)

All this for a swing set? How much do your kids weigh? First define the span and the weight on it, THEN size the beam. If in doubt, hang a 2x6 across the desired span and YOU hang on it. If that bends greatly, try a 2x8. I think you'll find that two 2x10's and a 4x6 are gross overkill. Are you using aircraft cable to the swing seat, rope, or chain? I'd be more worried about that than whether or not you need two or four 2x10's. Something has to support this beam, remember, so beef up the legs accordingly.


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## D270 (Mar 27, 2011)

I was going to use the standard 4x4 post, A frame with 2,2x6s holding up the weight. Is that sufficient for 3, 2x10s or 2x10s (the 4x6 sandwich)?

Thanks...kids are currently 40 and 50 lbs.....


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## Alan (Apr 12, 2006)

http://www.amazon.com/Irwin-88708-2x16spade-Wood-Dril/dp/accessories/B001BZM7LS


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## jklingel (Dec 21, 2008)

D270 said:


> I was going to use the standard 4x4 post, A frame with 2,2x6s holding up the weight...


"Holding up the weight" ??? Do you mean a 4x4 post w/ 2x6 legs? I am not an engineer, but just for reference, a 2x4x9' stud, braced from lateral deflection (nailed to plywood, for ex), can support about 1750 lbs. A 4x4 will obviously carry more, probably by a factor of 2.2 or so. With 2x6 legs to keep the post from swaying, I would think the whole family could swing w/ reckless abandon. I'd make sure the 2x6 legs go well up the 4x4, and properly anchor everything into the ground. We used to get a pipe-constructed swing set to almost topple over if 3 of us swung in synch and got very high. I would surmise that the weak points will be the connections; I am not an engineer. Copy commercial swing sets' design of the A part, then go wider; overkill is our friend.


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## tony.g (Apr 15, 2012)

Daniel Holzman said:


> But this is not a course in structural mechanics


Could have fooled me!!:laughing:


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