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Old 10-11-2018, 10:17 AM
AstroApprentice (Jason)
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Steel pier - gussets or not?

Hi guys,
I'm still trying to come up with a pier design for my site with limited vehicle access on top of a hill covered by 2 m tall shrubs. My plan is to use a 2 m steel pier bolted to a pad footing in a clearing and surround it by a 1 m deck so I can see above shrubs. I've read that pipe diameter is key, but the weight of large diameter 2 m pipes is huge. I have a 2 m, 140 mm D, 5 mm wall pipe that weights 35 kg - about as much as I can manage up the hill. I realise it's narrower & thinner than ideal, but wondering if I weld 4 full-length gussets on will that help, or will that potentially create lines of weakness? (see pic)
I'm willing to wheel barrow in concrete for footing, but want to minimise how many loads, so I'm not keen on a 2 m concrete pillar. I don't plan on putting a big load on pier, likely 20 kg max for mount & scope.
As usual, any criticisms of my plan are welcome as I don't want to waste my time and energy if it's unlikely to work.
Thanks.
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Old 10-11-2018, 10:35 AM
AstroApprentice (Jason)
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steel pier design

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Old 10-11-2018, 01:17 PM
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tempestwizz (Brian)
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Does your pier need to be removable? If not you could make it longer and set into the concrete. I think the gussets would be a good idea given the length of the pier.
One pier I have made was/is relatively long also. When digging the hole for the concrete, I also drove Star pickets into the bottom of the hole at angles with the ends in the mass of concrete at the base of the pier. In my case I found some old heat shield tubing from old slow combustion heater in recycle yard. It was about 225mm diameter and pieced together provided plenty of length. I used that as the former for the concrete pier on top of where the concrete base was to be set. I tied 4 more star pickets to the ends of the pickets already in the ground to my (yet to be poured) concrete base and set these pickets inside the relatively flimsy tubing. I also welded some threaded rod onto the top ends of the pickets that would protrude through the top of the pier. This allowed attaching a plate for the mount so sit on. I then filled with hand mixed concrete.
Maybe a bit of effort to get the makings up the hill in your case, b ut the cost was minimal and the result excellent.
One thing I missed with my first attempt was installing a conduit inside the pier to allow cabling to be run inside, rather than strapped to the outside.
For my latest pier, built on a concrete ‘deck’ at roof level attached to my new house, I managed to find som 8” diameter pvc tubingused for storm water drain. I used that as the former and again put reo bars inside with threaded rod attached to the top and a utilities conduit before filling with that concrete. It too seems to work well enough, certainly for visual.
Just hope you don’t have too much trouble with the greenies if you need to trim your shrubs when they develop!
HTH BRIAN
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Old 10-11-2018, 04:31 PM
Imme (Jon)
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Remember one thing.....there are people out there that get amazing shots on a tripod placed on grass and uncompacted soil out in paddocks.

......no need to over engineer it, youíre only placing fairly light loads on it in relative terms......a 140mm x 5mm pipe will hold tons of weight. Youíre isssue is lateral movement and vibration. I think what you have, with gussets and filled with sand will be more than enough
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Old 11-11-2018, 02:10 AM
StuTodd
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Doesn't matter how much the base measures or the pier weighs, fill it with 3/4 sand and vibrations vanish...
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Old 11-11-2018, 06:15 AM
AstroApprentice (Jason)
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Flexure

Thanks for the advice, I like the longer pipe embedded in footing, and sand filled options. However, Iíve been advised that the 5 mm walls are too thin to avoid flexure over 2 m length. Iíll see if I can source thicker walled pipe or might have to explore concrete pier options.
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Old 11-11-2018, 08:35 AM
Imme (Jon)
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Quote:
Originally Posted by AstroApprentice View Post
Thanks for the advice, I like the longer pipe embedded in footing, and sand filled options. However, I’ve been advised that the 5 mm walls are too thin to avoid flexure over 2 m length. I’ll see if I can source thicker walled pipe or might have to explore concrete pier options.
Mine is around 1.8m high, no sand for vibrations, carries an eq6 and 13.5kg of gear and has 4mm walls.
Bolted to a concrete shed floor......goes fine

Last edited by Imme; 16-11-2018 at 11:13 PM.
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Old 11-11-2018, 08:52 PM
assbutt94
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Welding to it wont weaken it. Even if you blew a hole though it here or there it wont make it flex much more.

An easier way to reduce flexure might be to fill it with concrete once you set it up and bolt it down.
Wont want to move it again though.
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Old 16-11-2018, 11:09 PM
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Jason, my gut feel is that a pier 2 metres tall at 140 dia is a bit slender unless it is gusseted. I would use tapered gussets on the lower 2/3 of the pier. To keep the weight off the top half, I would avoid filling the pier with sand or concrete past the half-way mark, if at all. The 5 mm wall thickness should be okay. It's the pipe diameter that gives it most of its strength - not the wall thickness. Having too much mass up the pier lowers the vibration frequency, which is what you don't want.

Cheers, Chris
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Old 17-11-2018, 06:31 AM
AstroApprentice (Jason)
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Thanks Chris,
Iím now considering a pier with a greater diameter - just trying to figure out the logistical challenges of moving and placing a heavy pipe. Plus the necessary footing...
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Old 17-11-2018, 09:39 AM
Wilso (Darren)
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It's sounds like your on the right track Jason.
+1 for gussets even if you stop at the underside of the deck, should make a stronger/sturdier pier.
I made a pier couple of yrs ago 1300h X 160d x5mm thick and added an access hatch. Very strong.
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Old 17-11-2018, 05:35 PM
AstroApprentice (Jason)
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Wow Wilso,
That’s a work of art! Is that a lockable hatch?!...
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Old 17-11-2018, 06:06 PM
Wilso (Darren)
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No just superglued rare earth magnets on the inside corners.
Works surprisingly good.

You might want to consider going to 180mm dia. depending on your mount etc.
You will need a helping hand to carry the load though, quite awkward carting a cylinder!

Enjoy!

Last edited by Wilso; 17-11-2018 at 06:39 PM.
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Old 18-11-2018, 11:13 AM
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Quote:
Originally Posted by ChrisM View Post
Jason, my gut feel is that a pier 2 metres tall at 140 dia is a bit slender unless it is gusseted. I would use tapered gussets on the lower 2/3 of the pier. To keep the weight off the top half, I would avoid filling the pier with sand or concrete past the half-way mark, if at all. The 5 mm wall thickness should be okay. It's the pipe diameter that gives it most of its strength - not the wall thickness. Having too much mass up the pier lowers the vibration frequency, which is what you don't want.

Cheers, Chris
+1 on the tapered gussets to 2/3 height. Diameter is much more important than wall thickness.

A nice thick base plate, 16mm at least, with the gussets welded along the diagonals and a bolt or preferably 2 bolt in each corner of the plate either side of the gussets and as close as possible to the gusset.

I have seen many good piers spoiled by thin base plates with poorly located bolt holes...
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Old 18-11-2018, 01:00 PM
AstroApprentice (Jason)
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BIG diameter pipe!

I'm now considering a much bigger pipe available cheap to future proof design - 355 OD with 12 mm wall! It's a whopping 200 kg, which creates some logistical challenges, plus footing considerations - although I think most I had planned to use for smaller D pipe would still apply. It would also need a smaller diameter mini-pier on top to avoid OTA hitting it.
Given the 14" diameter, I don't think gussets will be needed, but could add small ones to stiffen base plate connection.
200 kg is a bit intimidating, but I can use a pipe trolley up hill - maybe even with a winch if necessary and a gantry/chain block for positioning.
I can also get 12 mm medium steel sheet for 500 x 500 mm base plate and a 12 mm disc at 375 mm OD for top plate.
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Old 18-11-2018, 02:34 PM
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tempestwizz (Brian)
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If you are looking to get that big, the thin steel (or plastic) pipe former filled with concrete is still a more manageable option than a massive pipe: probably way cheaper too! You already have a need for concrete at the site in any case. The flue heat shields through the roof space used in slow combustion heater installations make an excellent lightweight former. Often dirt cheap at recycle yards.
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Old 18-11-2018, 09:30 PM
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Originally Posted by AstroApprentice View Post
I'm now considering a much bigger pipe available cheap to future proof design - 355 OD with 12 mm wall! It's a whopping 200 kg, which creates some logistical challenges, plus footing considerations - although I think most I had planned to use for smaller D pipe would still apply. It would also need a smaller diameter mini-pier on top to avoid OTA hitting it.
Given the 14" diameter, I don't think gussets will be needed, but could add small ones to stiffen base plate connection.
200 kg is a bit intimidating, but I can use a pipe trolley up hill - maybe even with a winch if necessary and a gantry/chain block for positioning.
I can also get 12 mm medium steel sheet for 500 x 500 mm base plate and a 12 mm disc at 375 mm OD for top plate.
Jason - that seems like overkill! Something else to consider with such a large thermal mass would be how long it would take to cool down to ambient temperature. This would especially be true if it's in a building. You would not want a lot of heat rising causing turbulence.

Cheers, Chris
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Old 19-11-2018, 07:22 AM
AstroApprentice (Jason)
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Thermal mass

Hi Chris,
This old thread on CN suggests 12Ē D or bigger best for tall pier in terms of deflection reduction https://www.cloudynights.com/article...amentals-r1236
They do not consider thermal issues. Like all these pier parameters, I guess itís a compromise. I wonder how different cool down times would be to a smaller D pipe in terms of hours?



Quote:
Originally Posted by ChrisM View Post
Jason - that seems like overkill! Something else to consider with such a large thermal mass would be how long it would take to cool down to ambient temperature. This would especially be true if it's in a building. You would not want a lot of heat rising causing turbulence.

Cheers, Chris
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Old 19-11-2018, 08:10 AM
Star Catcher (Ted Dobosz)
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Originally Posted by AstroApprentice View Post
Hi Chris,
This old thread on CN suggests 12Ē D or bigger best for tall pier in terms of deflection reduction https://www.cloudynights.com/article...amentals-r1236
They do not consider thermal issues. Like all these pier parameters, I guess itís a compromise. I wonder how different cool down times would be to a smaller D pipe in terms of hours?
My thoughts:

1) Diameter is king. My pier diameter is about 33cm across and 16mm walls.
2) Gussets are good but not essential when using large pier diameters.
3) Bolts close to tube walls centred between gussets if used
4) Thermal issues are not really relevant unless pier sits in direct sun all day. Even then, the pier sinks heat into big thermal mass (concrete) sitting in ground.
5) A cubic metre of concrete to bolt into is handy

Ted

Ted
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Old 19-11-2018, 12:03 PM
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Jason,
The time to cool will depend on the a few factors including total mass, surface area and difference in temperature between the pier and ambient. Whilst a larger diameter pier will provide a more stable pier (up to a point), unnecessary wall thickness won't make any noticeable difference to stability yet will take longer to cool down. Having said that, it will also take longer to heat up. If your pier will be out in the open where there is a breeze, this may not be an issue.

My pier (275 dia x 6 mm WT) sits on the top floor of a two-story observatory and heats up quite a bit during the day, so after the sun goes off the building I open the dome and entry door to allow a few hours of cooling, which is mainly for the chunky mirror, but also the obs in general.

Ultimately, use what pipe you have, or can get easily, then rigidly fix it via a solid base plate to the concrete foundation such that any movement comes from the pipe itself and not from the base plate or fixing. If the pipe is a bit slender, then add some gussets.

Cheers, Chris
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