Scaffold tube based pier

[powerlord]

Hi chaps. I've been teaching myself to weld for something to do,  and it got me thinking about a scaffold tube based pier.

Perhaps 3 or 4 scaffold tubes as central pillar. Might need a bit joining them together half way up for rigidity.

Old poles are cheap -  3 quid a meter. I was thinking if I got a good solid design I could start making these for people at a reasonable cost rather than the £500+ cost of commercial ones.

Stu

[powerlord]

A rough mock up. Each tube is in compression even with sideways forces. Welding where they meet you end up with all triangles. I'd have though this would be very strong? Obviously not to scale here or pier would be 3m high, but you get the idea...

Edited July 25, 2022 by powerlord

[Rusted]

In my narrow universe, your design is inherently weak in the middle.
It suffers from poor stiffness due its greatly reduced beam dimensions.
It is the exact opposite of a Serrurier truss.

A triangulated, parallel pier has maximum beam dimensions.
A tapered pier with triangulation is stiffest.
The large base provides automatic triangulation with a smaller top plate.

Triangulation is most easily achieved by plating over the upright tubes.

I used a simple, four sided pyramidal pier 4m/ 14' / high.
Timber 10x10cm/4"x4 " uprights with ply cladding.
Legs splayed to just fit within the 3m/ 10' circle of the observatory.

 

 

[powerlord]

thanks Rusted. Understood, but most people require a pier to not take up too much room - which limits the base size.

So I suppose the question is, a basic triangular pier (aka pyramid) vs my 'opposite of a Serrurier' ?

And you are saying basically that the pyramid is better. Fair enough.

I'm not a mechanical engineer (I'm an electronic one). My thought was smaller triangles, and through reduced rigidity in the middle - it's still 3 x 50mm tube welded together at that point, and in my head it felt like in the real world for what we need stability wise, that would be better than the pyramid. But you are saying it isn't correct ?

So then, my question is (as you know more than me by miles here|), do you think that simple pyramid - steel based, 3 x 50mm steel poles, angling in to a smaller top plate has a chance of being rigid enough ?

stu

 

[Cosmic Geoff]

I suggest looking at what has been used elsewhere. Tripods work.  Steel tube piers work.  Tri-piers (free standing tube with support feet) also work. 

[Peter Drew]

The "Todmorden" pier is the easiest and cheapest to make but they are a DIY item, you won't be posting one!    😀 

[powerlord]

Oh I know what works before, I just want a project to play with welder, and with 2nd hand scaffolding cheap, it seemed a good opportunity. large diameter pipe is too expensive - steel prices are through the roof.

I don't need a pier myself, so no interest in Todmorden style ones to be honest. If you follow Luke on youtube you'll know he went even simpler - breeze blocks. and is happy with it.

I've seen folk happy with a single scaffolding tube upright, filled with cement/sand. So 3 feels like it would be solid enough to almost be overkill.

I'm not one to copy others (see my observatory) - I'd rather do something individual and innovative. And learn through the process, even if it fails. 😀

 

[ollypenrice]

I'd beware of solutions which are looking for a problem, a quip once aimed at Vincent motorcycles.  A simple, thin-gauge but large diameter steel tube has good strength in compression, plus high resistance to bending and twisting.  It can be triangulated against tilt by using cables in tension (as per Astro-Physics) which require less metal and less volume than struts in compression. Since this design ain't broke, I wouldn't try to fix it.

The exercise is interesting, though.

Olly

[powerlord]

I hear you. But as I say - look up the cost of large (10-12") diameter steel tubing. You are talkng 100s of pounds per meter.

Here's for 6": https://www.metals4u.co.uk/materials/mild-steel/mild-steel-pipe/pipe-galvanized/8694-p

Hence the need for an alternative solution. So it's not looking for a problem - the problem is the cost of steel. That is real I'm afraid.

[Steve Ward]

Try a local scrapyard ... 😉

[CraigT82]

Could try a simple arrangement like this, add in three 'guylines' made with steel rope and turnbuckles and it should be nice and stiff whilst very low cost?

[scotty38]

At £3 per metre how many scaffold poles to create an equivalent 6-8" diameter steel tube pier, not £500 worth I'd guess? What about if you used formers and just had the outer "ring" of tubes with judicious welding. Couple of ideas there?

[powerlord]

aye, I think that's overkill though. I need to find a local source of used scaffolding. all the ones on ebay are too far away.

[Rusted]

 The Norton "Featherbed" motorcycle frame used beam stiffness by widely separating the tube members. [Search!]
The two tubes replaced a single down tube which was commonplace until then. Flexible!

 A tripod spreads the feet wide into a pyramid. Yet it is often pitifully weak because of using thin tubes.
Or, the tops of the tubes are poorly connected to the top plate.
The Berleback tripod is a well designed geometrical exercise. [Search!]

 The portable piers use a series of very clever geometry measures to remain stiff yet light: [Search!]
Widely spaced hinge points at the top plate and wide, tapered legs for example.
Do an image search for portable pier and use your three scaffolding tubes as spaced uprights.
Then find a way to use short lengths of scaffolding pole for your legs.

 Tube diameter or rigid spacing is everything where stiffness is important.
Anybody who has used a crane to load and unload tubing will confirm this.
Even a tightly bound bundle of thin, horizontal tubes will bend like grass when lifted in the middle.
A large diameter tube will show no visible bending. [Search!]

  If you cannot afford a large diameter tube then you must space your thin ones.
Then triangulate them. So that the smaller diameter tubes do no bend under load.
Think about unsupported aerial/antenna masts. A classic example of triangulation.
As are high voltage pylons. [Search!]

 You could make a super stiff and strong pier using scaffolding poles.
All it takes is to fully understand your subject and do a lot of image searching for examples.
Beam stiffness, triangulation, stressed skin effect and pyramidal are all good [initial] search terms.
 

[Rusted]

1 hour ago, CraigT82 said:

Could try a simple arrangement like this, add in three 'guylines' made with steel rope and turnbuckles and it should be nice and stiff whilst very low cost?

 Your tubes are far too close together to gain anything from beam stiffness.
Each tube acts as a simple tube. No gain from multiples of tubes.

 Separate them and you begin to see the greatly increased stiffness. No extra weight!
 
 Now clad them with thin, pop riveted plates of aluminium.
Stiffness goes up almost exponentially. Stressed skin triangulation. [AIRCRAFT!]

 Space them at the bottom and taper them towards the top AND plate them.
Hey presto! Now you are using simple geometry to your maximum advantage. 

[Rusted]

11 minutes ago, powerlord said:

aye, I think that's overkill though. I need to find a local source of used scaffolding. all the ones on ebay are too far away.

A friendly scrap yard owner is your source here. Tell him you are looking for aluminium tube. You could be very surprised what turns up.

I have recently bought [as new] 50x200mm and 100x200mm aluminium, box section tube for peanuts in 2m lengths. 😊
 

[Rusted]

2 hours ago, Steve Ward said:

Try a local scrapyard ... 😉

What he said!

[DeanCJ]

If you are going to weld galvanised tube you should really remove the galvanising from the relevant areas, as the fumes are toxic. Just Google Galvi flu  and to be honest if you don’t, whichever process you use, mig, tig, mma, etc the quality of the weld will most likely be poor. Once welded, ideally you should paint the areas with a ‘galvafroid’ type of paint, I have used this at work and it is very good, but could be expensive to buy. 

[powerlord]

2 hours ago, Rusted said:

A friendly scrap yard owner is your source here. Tell him you are looking for aluminium tube. You could be very surprised what turns up.

I have recently bought [as new] 50x200mm and 100x200mm aluminium, box section tube for peanuts in 2m lengths. 😊
 

I don't really want ali :

1. it's nothing like as strong for a given size

2. it's a pain to weld (though I can weld it)

[powerlord]

41 minutes ago, DeanCJ said:

If you are going to weld galvanised tube you should really remove the galvanising from the relevant areas, as the fumes are toxic. Just Google Galvi flu  and to be honest if you don’t, whichever process you use, mig, tig, mma, etc the quality of the weld will most likely be poor. Once welded, ideally you should paint the areas with a ‘galvafroid’ type of paint, I have used this at work and it is very good, but could be expensive to buy. 

Yup, again though it's important to remember the application - a home pier, not an oil rig.

So yeh, it's just grinding off the area to weld which I'd be doing anyway. A coat of zinc paint base coat, then paint on top is all you'd need imho. More coats if its intended use was outside in the elements was the plan.

Im going to have a go in solidworks simulation and see if I can model a few different designs.

I do think it's important to remember that it's just trying to be rigid enough for normal use with 30kg or so of kit on there - a requirement that my existing 2" SS skywatcher tripod manages fine. As Persig said in Art of Motorcycle Maintainance, quality is not an absolute. A design fails if it has more of it that is needed. Imho most steel pier designs ignore that and build something with far far higher rigidity that is practically necessary, making them very poor designs. Or to put it another way  -

"A designer knows he has achieved perfection not when there is nothing left to add, but when there is nothing left to take away"

Antoine de Saint-Exupery

[Rusted]

 Do not forget the cosmetic issues. You hope to supply a very demanding market.
The slightest flaw in the mounting and instruments on it, will result in a return to dealer.

 Most factory scrapped items in such a market are probably due to cosmetic issues.
Ugly, exposed welding, battered [s/h] and and ground surfaces will not have a ready market!

 Welding multiple tubes together will be likely lead to thermal distortion.
The simple, finned tube "rocket" piers are nicely stiff but seem expensive for what they are. [IMHO]

 Will you advertise yours as being far worse but much cheaper?
How will you protect your complex tubing from rust? Over all surfaces?

 How will the proud [but penny pinching owner] keep your design clean and attractive?
What will it look like in a smart garden after a few months/years?

 Which common birds will want to nest in it? I've had blue tits nesting in the base of my MkIV.