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Discussion Starter · #1 ·
I've googled and can't find the answer. Likely been answered a zillion times.

Is a 2x4 spanning a 24" space stronger in the midpoint placed on its edge or flat?

I'm guessing on edge but wonder by how much.

I'm installing a backup safety cable for a storage rack and want to use an eye bolt into a 2x4 running across ceiling joists. It would be easier to install the eye bolt into the flat orientation than on edge (using a threaded eye bolt with washer and nut, not screw thread).

TIA
 

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2xs are always stronger on edge, consider how a header is constructed. Obviously it's easier to drill thru the flat side. You might consider using both flat and on edge - connected together.
 

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Unqustionably as noted above.....

Sometimes when an application requires and you have to use a 2X with its flat side taking the load (force at 90 degrees).... we use a strongback........which is just another 2X attached to the flat side on its edge to give it greater streangth.... hence the idea of strong-backing.
 

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Mathematically, the strength is based on the Square of the depth of the piece of wood.
On the flat, the number is 1.5 inches squared. (1.5 x 1.5) = 2.25
On edge, the number is 3.5 inches squared. (3.5 x 3.5) = 12.25

As you can see, on edge is stronger.
 

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Actually, i need to correct the above posting.
Forgot to consider the difference widths, so multiply each of the above values by the width of the materials.

(2.25 x 3.5) = 7.875
(12.25 x 1.5) = 18.375

That's better. The original calculation would only be valid with the widths being the same. Sorry for the lack of consideration for the width in the original posting.
 

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Discussion Starter · #7 ·
Thank you all!
I've decided to forego wood and use a 3/4" square metal tube; will be more than strong enough and I won't have to find an eye bolt of the right length to go through a 2x4 on edge and my ceiling joist.
 

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If he used a 1/16" to a 1/8" in. thick wall 26 " long 3/4" x 3/4" steel tubing, I bet it will not hold as much weight over the long haul as a edge up...2"x4" will. JMO
 

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Discussion Starter · #10 · (Edited)
If he used a 1/16" to a 1/8" in. thick wall 26 " long 3/4" x 3/4" steel tubing, I bet it will not hold as much weight over the long haul as a edge up...2"x4" will. JMO
Where do I get the information on the strength of 2 x 4 wood on edge (a Daniel question)?

This will essentially be a point load since the eye bolt goes through the narrow edge and terminates on the top edge of the board. I would think metal might be stronger in this situation especially as the eye bolt will naturally weaken the wood as a hole needs to be drilled through the narrow edge for the bolt to exit for the nut: View attachment 505346
The gold blocks are 2" x 4" truss bottoms.
 

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Thank you all!
I've decided to forego wood and use a 3/4" square metal tube; will be more than strong enough and I won't have to find an eye bolt of the right length to go through a 2x4 on edge and my ceiling joist.
Might look into a piece of "unistrut". It's designed to do exactly what you're looking for--provide support for a load across a span. The spring nuts available for it are threaded in 3/8" allowing you to use shouldered eye bolts or all thread with female threaded eyes and jam nuts to hold it all together.

Sent from my mobile look-at device
 

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Discussion Starter · #14 ·
Both ideas are good; I'm still leaning to 3/4" sq tubing from HD; a bit less labor and less heavy stuff to carry to the spot in the garage attic stepping on the joists (I hate it up there).
Thanks for everyone's good ideas!
 

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An application question to this calculation. I want to install an extending TV mount (extends out 27", single stud installation, 2 lag screws) on a wall that was built over a door frame using 2x4s turned sideways — i.e., screwing into the 3.5" side rather than the 1.5" edge. The sheetrock is 1/2" and there's about 1" of air space behind the 2x4. The TV itself is only 26#. If I use the included 75mm (@3") lag screws, with the sideways stud hold the TV securely?

Actually, i need to correct the above posting.
Forgot to consider the difference widths, so multiply each of the above values by the width of the materials.

(2.25 x 3.5) = 7.875
(12.25 x 1.5) = 18.375

That's better. The original calculation would only be valid with the widths being the same. Sorry for the lack of consideration for the width in the original posting.
 

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Is a 2x4 spanning a 24" space stronger in the midpoint placed on its edge or flat?
To be accurate --- the 2x4 is the same strength regardless of how you orient it, just that it will be seeing a lower maximum bending stress if oriented on edge, when loaded as you described.
 

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I realize this is an old thread, but in the interest of providing accurate information, I'll dive in for a minute.

The bending strength (what us engineers call the section modulus=S) of a 2x4 (or any other rectangular shape) is width X height squared / 6 (for orientation - that's for vertical loading). For a 2x4 oriented edgewise S=1.5x3.5x3.5/6=3.0625 inches cubed; oriented flat, S=3.5x1.5x1.5/6=1.31 inches cubed.

Shear strength is about the same in either orientation.

Stiffness is similar, but it's width x height cubed /12. That's why a 2x6 is nearly 4 times stiffer than a 2x4, spanning the same distance.

Also, torque is force x distance, both in applied loading and resistance, so quatsch is correct for the 26 lbs at 27". To finish the loading calc, the tension on the fastener is the torque / the distance from the fastener to the edge of the base plate.
 
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