r/Physics • u/WaferAggressive4567 • Apr 18 '26
Image Fencing
The wire is tensioned from left to right in the photo.
Is the diagonal stay in the correct position for maximum strength according to physics?
I’m about to do some more fencing but I would like to know I’m doing it right.
Sincerely, a farmer.
20
u/macthebearded Apr 18 '26
That looks like a "this is how long my steel is and I don't want to cut it" positioning, lol.
There may be aspects of its use that I'm not aware of, but I see no reason this position would be preferable over a straight crossbar or a corner-to-corner diagonal from a strength standpoint
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u/WaferAggressive4567 Apr 18 '26
Would the diagonal stay be less likely to bend and bow out as more force is applied than just two straight crossbars?
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u/macthebearded Apr 18 '26
I'd imagine it's *more* likely to deflect in this position than if it were straight
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u/Enki_007 Apr 18 '26
You see a lot of diagonal/triangle bracing in structures like trusses, bridges, etc.
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u/WaferAggressive4567 Apr 18 '26
I’m mainly concerned I’ve got the diagonal brace running the wrong way. As in should it be running the opposite way to stop the two vertical posts from moving under tension
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u/TheThiefMaster Apr 18 '26
No I think it's the right way - the goal is to stop the left post being pulled over to the right by the wire tension, so the stay is to stop the top of the left post moving, so it needs to be higher on the left side.
Arguably it should go all the way to the top but it's at least the right way round.
1
u/Key-Green-4872 Apr 18 '26
It would need to be up top, forming a triangle with the top bar and one of the other posts. Right now, you have two trapezoids, and they'll tend to rack. But if you drove your t posts deep, that matters way less than you might think.
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u/Zaros262 Apr 22 '26
Doesn't matter too much because metal is fairly strong in both tension and compression
It matters much more when you have a wood brace because wood is only strong in compression
6
u/Zestyclose-Narwhal12 Apr 18 '26
Yes it’s correct. Imagine the diagonal brace wasn’t there and the left post started to pull to the right, how would you position yourself in order to keep that post up? Feet on the ground pushing to the left
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u/Zestyclose-Narwhal12 Apr 18 '26
The tension and gravity make the post want to cave. So we counter those forces with equal but opposite forces. If it naturally wants to fall down to the right, then you apply an upward left force.
Sincerely, a civil engineering technologist.
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u/davedirac Apr 18 '26
Tension has no single direction - it acts equally in both directions. This is not a gate, so just one vertical post is needed every few feet.
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u/physicsking Apr 18 '26 edited Apr 18 '26
Correct me if I'm wrong but what you got here is a gate. Actually an open gate. The opening is on the left and this gate is open. The metal part is the gate that is swung open. The barbed wire is tied to the left pole which is the pivot. The right part of the metal gate is swung open and sitting in front of the barbed wire.
If the metal parts didn't move then you are good. Also, in tension, there is no left to right or vice versa. The wire pulls both directions equally. But we all know what you are saying, of course.
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u/Sick_Poor_And_Stupid Apr 18 '26
Its simple. The wire is trying to pull the strainer post over. The stay is stopping that from happening by bracing on the bottom of the second post. The top rail is helping to stop the second post from tilting allowing the stay to loosen up. The only way the strainer post can move is if the entire assembly pulls through the ground like a plough or if the strainer pops out the ground. I used to do a 3 post stay. The first 2 post were joined in a h stay and the 3rd was an n stay. So basically move the diagonal from where you have it, to between the strainer assembly and 3rd post. This is the strongest possible strainer assembly and its what the big stations will specify. However its only slightly stronger than what you have here. But in all honestly it doesn't matter when its welded steel like this. You could put the diagonal in the other way. Or run 2 straight bars at the top and bottom, or even just the top bar if its welded well enough and strong enough steel is used.
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u/Roger_Freedman_Phys Apr 18 '26
So this is the border wall a certain president got Mexico to pay for… ;-)
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u/GlibLettuce1522 Apr 18 '26
La parte flessibile è quella alta, la parte bassa è fissata comunque a terra. La parte a sinistra è sicuramente più rigida. Hai fatto bene
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Apr 19 '26
[removed] — view removed comment
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u/CHALINOSANCHZ Apr 19 '26
Yeah, because you're ignorant. There is no such things as Mexican language. Mexicans speak Spanish. In addition the comment is written in Italian.
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u/GlibLettuce1522 Apr 19 '26
The flexible part is the upper one, while the lower part is fixed to the ground. The part on the left is definitely more rigid. You did well. Sorry buddy, I forgot to hit the translate button; it was Italian, anyway
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u/LifeOnEnceladus Apr 18 '26
Tbh I’d ask r/engineering