Five bar gates

[ebee]

Five bar gates or similar.
Lots of those who should know tell be that the bar (The diagonal ) should be the correct way round .
That is low (say near the bottom hinge) at the hinged side and high at the open end to give the strength of a traingular shape.
The say that the opposite will not achieve that strength and the gate will drop.
I can`t see the logic of this because both options still give the triangle shape for strength and the only difference I see is that one way the diagonal is in tension and the other way it is in compression.
Unless the stregth of the material (wood usually) is different under these conditions of course.
Am I missing something?

 

[big-all]

with the diagonal at the bottom hinge you have 2 joints under compression and one under tension

with the diagonal the opposit way round the weight will try and open 2 joints instead of one

so it depends on your thought on wether a compressed join is better than one under tension

 

[ebee]

Yes Agreed the Tension versus Compression but is one always superior to the other?
Either are a basic One Triangle shaped basis so it can only be tension V compression that decides it. Has wood more concerns than metal as a consideration in this?

 

[Jurassicspark]

Yes Agreed the Tension versus Compression but is one always superior to the other?
Either are a basic One Triangle shaped basis so it can only be tension V compression that decides it. Has wood more concerns than metal as a consideration in this?

Were you waiting for this day just to post that? Wow.

 

[freddiemercurystwin]

I've set my diary for his next tantalising follow-up in 2041.

 

[ebee]

Were you waiting for this day just to post that? Wow.

No not at all, any day any year would do! Is it Triangle Day Today or something I am unaware of?

 

[ebee]

To be honest, the only reason I asked the question in the first place is that in conversation some joinering types have stated to me that "It must be the correct way around and if it is the wrong way around then it will not work as intended" I just wondered if that was true and if so then why? Am I missing something?

 

[Jurassicspark]

No not at all, any day any year would do! Is it Triangle Day Today or something I am unaware of?

Not really.

It’s just how bizarre it looks.

If I have a question, or if I’m genuinely curious about something, I will try to get the answer as soon as possible - not wait years.

 

[ebee]

So far I have not had an answer from those who insist it is/is not the correct way.
To my mind it is the triangle that is important - unless someone has a good reason for there being only one correct orientation. I have asked the question several times over the years, and had no answer, I have not lost any sleep over it but I merely noticed it on here once more so I added to the thread, one day I might get y answer or I might never do so.

 

[freddiemercurystwin]

There is much less stress on the fixings when a strut is employed, as opposed to a tie. So a tie will work just fine if the fixings are strong enough. It's not an issue for say a roof with meaty timbers or a steel structure where you can employ bolts or other solid fixings but a gate typically has a few nails or some screws which are far less strong. It's really not complicated.

 

[ebee]

Thank you Fred, could you elaborate on struts and ties please?

It's really not complicated - To those that know, but to those with alternative disciplines it might be best to explain

 

[Harry Bloomfield]

Thank you Fred, could you elaborate on struts and ties please?

Would you feel more long term stable, standing on the floor, or hanging by your hands from a support?

Standing, your body is in compression. Hanging from your hands you are in tension, relying on your grip on the support (nails/screws)

 

[ebee]

Yes Harry but a plank of wood would not care, as long as it is securely fixed then it is in tension or compression, so you might stand or hang from that plank, is the plank more stable in one or tother? and if so then why?

 

[Harry Bloomfield]

Yes Harry but a plank of wood would not care, as long as it is securely fixed then it is in tension or compression, so you might stand or hang from that plank, is the plank more stable in one or tother? and if so then why?

It's the same principle - suspended by fixings, is always weaker than under compression.

 

[freddiemercurystwin]

So when the gate has a strut like in this excellent diagram, the red being the strut, the joints (and strut) is in compression (the red arrows), which means any fixings that hold the bits of wood together at these junctions be they screws, nails, proper timber joints or whatever don't need to do an awful lot, just keep the thing held together, the strut is doing all (most) of the work.

Whereas when a tie is employed like in this equally excellent diagram the forces are in the opposite direction - they're pulling away from each other, the tie is in tension and the fixings need to be much stronger because you're gaining little from the tie.

Of course this is simple timber gates we're talking about, so these rules go out the window when you start talking about much more beefy structures like roof trusses or steel frames etc as previously mentioned. Or if you engineered a timber gate differently so that the tie was suitably fixed in each corner.