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Working Out the Tension on a Screw Pile

06/03/2017 8:02 AM

Hi,

looking at foundations for an art installation. The installation is 6.0m high x 1.4m wide and weighs 11 tonne it needs a temporary steel base (assume it adds another 1.5 tonne) anchored to the ground with screw piles assuming the steel frame is 5m square with the installation in the middle with a wind loading of + or - 2.0 Kn/m2. with no wind the loading for 4 screw piles will be sum of load divide x 4 - If wind loading is applied can anyone tell me the max loading and the least loading or tension load - I am limited to 70 Kn per pile unless I increase the number.

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#1

Re: working out the Tension on a screw pile

06/03/2017 12:00 PM

What is a Kn ?

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#2
In reply to #1

Re: working out the Tension on a screw pile

06/03/2017 1:44 PM

kilonewtons, though the 'k' is properly written in lower-case and the 'n' capitalised, ie, kN.

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#17
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Re: working out the Tension on a screw pile

06/04/2017 6:33 AM

My point

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#20
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Re: working out the Tension on a screw pile

06/04/2017 12:30 PM

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#24
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Re: working out the Tension on a screw pile

06/04/2017 5:47 PM

Glaring to me as well, and quite like an initial question I would ask the OP.

I'm sorry to say that that approach doesn't seem to work all that well here, as evidenced by the lack of OPs response, or the quite different approach by other (well-intentioned) members.

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#3

Re: Working Out the Tension on a Screw Pile

06/03/2017 3:21 PM

If the shape is substantially rectangular, and the screws are 4.5m apart, I get 11.2 kN of extra down force leeward and 11.2 kN of lift windward.

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#18
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Re: Working Out the Tension on a Screw Pile

06/04/2017 7:42 AM

Hi, thanks for this info,I think that the screw piles will take the extra compression and tension and will be a viable option.

regards

Mark

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#19
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Re: Working Out the Tension on a Screw Pile

06/04/2017 7:53 AM

I suspect this is correct. If you can share any pictures of this installation, I would enjoy that.

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#25
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Re: Working Out the Tension on a Screw Pile

06/04/2017 6:10 PM

Hi,

This is the model.

http://www.cambridge-news.co.uk/news/cambridge-news/angel-north-sculptor-anthony-gormley-12264134

The installation will be erected in Trinity college in a months time.

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#29
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Re: Working Out the Tension on a Screw Pile

06/05/2017 4:12 AM

Looks to me like all the stress will be at the base of the sculpture....

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#30
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Re: Working Out the Tension on a Screw Pile

06/05/2017 7:34 AM

It seems to me the cubes should be hollow to keep the weight at a more manageable amount....

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#38
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Re: Working Out the Tension on a Screw Pile

06/06/2017 12:21 PM

Is the photo showing that the bottom tip of the (abstracted?) pile has been bent under, due to over-driving into bedrock?

Tres gauche?

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#39
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Re: Working Out the Tension on a Screw Pile

06/06/2017 7:02 PM

No, those are the clay feet of the Angel....

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#35
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Re: Working Out the Tension on a Screw Pile

06/05/2017 2:45 PM

Given that the final sculpture is 6 metres tall and weighs 11 tonnes, and considering how comparatively tiny its point of attachment is, I would very, very strongly urge you to retain the services of a professionally-recognised stress engineer/engineering company to design this base and to NOT rely on the advice of anonymous online forum exclusively. If this thing topples in strong winds, there will be hell to pay.

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#4

Re: Working Out the Tension on a Screw Pile

06/03/2017 4:48 PM
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#5

Re: Working Out the Tension on a Screw Pile

06/03/2017 11:44 PM

How long is the long-side?

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#6
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Re: Working Out the Tension on a Screw Pile

06/04/2017 12:04 AM

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#9
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Re: Working Out the Tension on a Screw Pile

06/04/2017 12:26 AM

"How obvious—how necessary—was that mathematical ratio of its sides, the quadratic sequence 1:4:9! And how naive to have imagined that the series ended at this point, in only three dimensions!"

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#12
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Re: Working Out the Tension on a Screw Pile

06/04/2017 1:54 AM

0.750" x 3.000" x 6.750" MT-185 tungsten version on ebony base (460.4 grams) for 'only' USD $1225.66

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#16
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Re: Working Out the Tension on a Screw Pile

06/04/2017 6:10 AM

Cheap at half the price...

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#7
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Re: Working Out the Tension on a Screw Pile

06/04/2017 12:23 AM

See OP for dimensions.

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#8

Re: Working Out the Tension on a Screw Pile

06/04/2017 12:23 AM

How could something like that block of wood weight 11 tons?

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#10
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Re: Working Out the Tension on a Screw Pile

06/04/2017 12:52 AM

Maybe it's ironwood....

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#27
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Re: Working Out the Tension on a Screw Pile

06/04/2017 6:32 PM

Using the assumption that the original shape was cylindrical, (only 2 dimensional values were given):

V = 6.0m * Pi * (1.4m/2)^2 = 9.236m3.

Calculating density: ρ = 11,000kg/9.236m3 = 1191kg/m3 = 1.191g/cm3

This density is in range of several heavier-than-water woods, including lignum vitae and yes, ironwood!

Hah!

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#28
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Re: Working Out the Tension on a Screw Pile

06/04/2017 7:36 PM

You haven't been taking your iocane.

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#31
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Re: Working Out the Tension on a Screw Pile

06/05/2017 11:28 AM

They don't have any here on Ferenginar.

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#34
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Re: Working Out the Tension on a Screw Pile

06/05/2017 2:37 PM

Vizzini would probably like Ferenginar.

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#36
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Re: Working Out the Tension on a Screw Pile

06/05/2017 4:50 PM

He should: he's the Grand Nagus!

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#37
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Re: Working Out the Tension on a Screw Pile

06/05/2017 4:57 PM

That what he gets for taking too much iocane in one sitting.

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#21
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Re: Working Out the Tension on a Screw Pile

06/04/2017 1:19 PM

That thingo in S.E.'s pic is not a block of wood, it's 304 stainless steel with a coat of Cerakote Gen II Black (http://madcustomcoating.com/). About 10.4 pounds sans wooden base.

Btw 11 tonnes is not 11 tons. One tonne = 1000 kg = 1.102 (short, ie, 2000-lb) tons.

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#11

Re: Working Out the Tension on a Screw Pile

06/04/2017 1:05 AM

"The installation is 6.0m high x 1.4m wide."

What of its third dimension?

How is it shaped? A cylinder? A rectangular prism? A steel slab 163-169 cm thick? Is it asymmetric, that is, does its effective cross-section vary depending on wind direction?

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#13
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Re: Working Out the Tension on a Screw Pile

06/04/2017 2:40 AM

If it's steel it's about 6" thick...

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#14
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Re: Working Out the Tension on a Screw Pile

06/04/2017 3:17 AM

"163-169 cm" should read "163-169 mm". About 6.4 to 6.7 inches, depending on the steel used.

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#15

Re: Working Out the Tension on a Screw Pile

06/04/2017 4:09 AM

Assuming that the shape is as suggested by SE in #5, the worst case is when the wind blows directly against the flat face. A simple calculation of pressure applied to the center of the surface will provide an incorrect solution. At 6m high the wind speed profile needs to be accounted for. Wind at 6m above ground flows faster than at ground level so the pressure calculation needs to be applied to an apparent point above the center of surface. How far above depends on localized conditions. The flow will be disrupted by any object within about 100m upwind of the artwork. Generally upwind objects slow the flow but two or more objects can cause a tunneling effect that increases the flow. A flat plate with straight edges as shown will cause vortexes so a steady wind will cause a pulsed load each time the vortex sheds. Sufficiently irregular sides will disrupt vortex generation. For example the "Christ the Redeemer", the 30m tall, 28m fingertip to fingertip statue on Mount Corcovado high above Rio de Janeiro produces no significant vortex action. You also need to factor in any low pressure area created in the lee of the artwork. There is software specifically of this type of calculation. In the UK you would be required to prove your calculations before the authorities would allow you to place this artwork in a location accessed by the public, I assume it will be the same where you are planning to erect this piece. Get a qualified stress engineer to compute/sign off on the calculations.

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#22
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Re: Working Out the Tension on a Screw Pile

06/04/2017 4:08 PM

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Re: Working Out the Tension on a Screw Pile

06/04/2017 4:31 PM

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#26
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Re: Working Out the Tension on a Screw Pile

06/04/2017 6:12 PM

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#32

Re: Working Out the Tension on a Screw Pile

06/05/2017 12:21 PM

Why not just exhibit the 2-metre tall wooden model instead, and save a lot of money, in the process?...

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#33
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Re: Working Out the Tension on a Screw Pile

06/05/2017 1:26 PM

You can't put a price on art....haha, but nearly everybody does.....

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#40

Re: Working Out the Tension on a Screw Pile

06/07/2017 12:43 PM

ASCE 7-16; Soils Report (e. g. SPT values); AB Chance/Hubbell Helical Pile software. And away you go in the wonderful world of engineering.

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#41

Re: Working Out the Tension on a Screw Pile

06/29/2017 3:04 PM

Get Atelier One to design it. They did the support for the Marc Quinn sculpture.

Try to guess how it was done.

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#42
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Re: Working Out the Tension on a Screw Pile

06/29/2017 4:44 PM

Or Free4m. They do sculptures to.

http://free4mconsulting.com/projects/public-realm/merton-stag/

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