Hinges for Domes

[Ajay Ajay]

Adam / Paul(Krantz).... 

Thankx for the image using Hinges on a Dome, even though it uses Hexgaons in place of Triangles and the Hinges are ON the Struts, rather than at the Ends/Corners.

This is an interesting modification to the "typical Fuller Dome" specially if all the Struts are of the Same Size and Shape, and so are the Hinges, as it can support "mass-production" with subsequent lower Costs.

The Dome in the image also has has large gaps on the outer surfaces and would have to be "sealed" .... somehow...

Perhaps Adam can comment on this... specially with respect to the Strut Dimensions, Shapes, and Sealing the Joints on the Outer Surfaces... 

Ajay Goyal 

Gurgaon 

[Dx G]

Interesting discussion regarding "hinges".  I would add that we should expand our concept of just what a hinge is.

- A typical hinge is designed to support a moving component in a rotational direction.

- Some hinges come with removable pins. These are excellent tools for assembly and disassembly

- Consider that for the use under discussion, there is little need for rotation.  

   As such, other materials could be used in place of a "hinge". Even bent plates, or even sheet metal plates or strips, could be used to connect panels where we see hinges used in these examples.  There are also polymer versions of "living hinge" which are inexpensive, light weight, not prone to corrosion and very tough.  These other materials can bend to accommodate various axial angles while providing strength with flexibility to allow axial angles to be "self adjusting" for different dome configurations.   There are even some caulking-like materials that may perform the same function adequately. Actually, some domes that have been on the market for many years use bent plates or strips to connect panels, essentially where struts would be, at the seams of the panels.  One I've seen uses bent, thick aluminum plates to join multiwall polycarbonate panels.

  Others are invited to comment on some expansion of thinking on this approach to dome construction.  The list of features provided earlier for the USconn (universal strut connector) can be reviewed for the various options.

As we say in the research business, the reach should exceed the grasp. 

Dx G

[Charles Lasater]

Seems ideal for greenhouse vinyl.

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[Eric Marceau]

About DxG's statements

Consider that for the use under discussion, there is little need for rotation. 
As such, other materials could be used in place of a "hinge".

If the hinge is being used in the context of assembly/attachment of adjacent struts, as demonstrated in the provided example,

the use of lower-cost, mass-produced hinges for this un-intended application is a clear case of out-of-the-box thinking and design ingenuity which results in a very elegant solution, as applied, which addresses the issue of simplifying assembly/disassembly, and allowing for substituting any panel, at a later date, with an alternative structure that could potentially protrude ... or connect with an adjacent dome of similar structure, all without having to perform "major structural surgery" to make it happen!

HOWEVER,  that design concept did not address what I considered excessive flexibility of hinges in the arrangement that was presented in this example.

where, in my view, 

• there is to much "swivel" freedom of action in the plane in which adjacent hinges are bolted together (black bolts),
• which leads to freedom of alignment displacement during intermittent loading events,
• which, at higher dome frequencies (guessing 8ν+), could lead to an excess of such displacements,
• which, in turn, could lead to joint "prolapse" into the dome, the beginnings of dome collapse.

... and maybe, my imagination is working overtime. 🙂

For sure, at frequency of 4ν or less, that joint configuration is likely stable enough.

I would be much less certain or categorical for any configuration using a frequency value between those two.

That is a gut feeling!

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[Eric Marceau]

Charles,

Depending on how big or solid or permanent your structure needs to be, and materials being used, you could consider what is being presented on this site:

Zip-tie Domes

Eric

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[Dx G]

Eric,

 Your reasoning is sound, but consider, if you will, that there are already lots of examples of "hinges" allowing rotation, but then are locked in place.  Paul pointed this out earlier.

  So consider the example of almost any folding table.  The legs are on a hinge or pivot of some sort.  After opening, the "third" leg of the triangle locks the other two sides in place, preventing any further rotation between the table and leg.  If its something like a flexible cable, this third leg would prevent opening any further, if solid, could be used for both compression and tension.

  As I said in my comments earlier, there are likely over a dozen ways to "lock" a hinge, or even fit it with springs of sorts (like a torsion spring) to resist a given limit of force.  It does not look like the panels in the photo utilize a brace or lock for their hinges, but it would not take much to add such a feature.  Some of those folding locks they use on folding tables are typical examples of what you can buy off the shelf for lighter applications, but there are many such options.  The hinge concept offers many opportunities. 

Dx G

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[Charles Lasater]

Eric,

Thanks.

I enjoyed the simple aesthetics and open spaces. Very unindustrial.

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[Eric Marceau]

I'm sorry but, from my perspective, unless you weld the rotary joints into a "locked" rotary position, that hinge is free to move, allowing for un-planned (not unpredictable) rotary motion, resulting from varying tension/compression/vibration "impulses".  

Positional "pinning" of struts is not the same as "force-clamping" that a solid plate offers. Using hinges can never replicate the force/torsion transmission that a single-piece solid bolted plate would. But, I recognize that some configurations don't need that extreme solidity, given the low-risk applications where some structural designs are used.

It is my gut instinct that tells me, as I stated before, that the "sensitivity" of the structure is less at lower frequencies, and greater at higher frequencies.  I would not hazard a guess as to where, specifically, the threshold for categorical "safe zone" would be, for applying the hinges in that configuration which is making me "run away in the opposite direction".  I leave it to the experts with more mathematical skill to show the extent to which those deviations can lead to catastrophic collapse, again depending on the frequency of the dome's structure.

Eric

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[Dx G]

Eric,  
 Perhaps I am misunderstanding your issues with the hinge. Let me suggest a few things that my lead you to some angles on this that may not be apparent.

 I think technical society became very enamored with strength and power after we won world war 2.  It took decades for technical society to depart from the blow-it-out-of-the-way-with-a-bulldozer mentality, and try to work with and within systems rather than trying to dominate and subdue them.

Two items that may be of related interest.
 Firstly, look at how floor and roof trusses are engineered. Many of them use connected points in a locked configuration, similar to triangular dome panels. Many of those points are single pin types which could pivot, just like a hinge, if they were disconnected from the assembly. They are designed to manage compression and extension, and do move.

 Second, take a look at seismic building code. It has changed a lot in the last few decades.  Engineering finally woke up and realized you can't erect buildings that can overpower an earthquake.  If you want the building to survive, it has to be designed to move without collapsing.  Steel plates? They tried it. Buildings collapsed. Stress cracks and various other issues make that approach beyond our current technical know-how.  You don't always want to transmit forces, often dampening is just as, or more, important.  However, what does work are the systems developed in Asia over 1000 years ago that have been recreated for seismic testing.  You can watch some very well done records of this on youtube.  The performance, and track record, are quite striking.  

https://www.youtube.com/watch?v=w78Yb_aotH0

Dx G