Any resources on allowable stresses or other design methods for attaching metal to stone? 1

[FiniteMatt]

I'm working on a project for a client involving a statue that we are developing an internal steel frame to support it during CNC milling, and eventually to be used when transporting the statue. The frame would be tubes and plates, and would attach to points in the interior of this hollowed out Belgian Black marble statue. The plan is to use threaded epoxied anchors in the stone. They have tests that the epoxy is as strong/stronger than the stone. We have a couple of ideas of how to sort of verify the connection points via FEA by treating the statue as perfectly rigid and measuring the reaction forces at the mounting points and just making sure the load is more or less distributed evenly. We're debating whether we need to put thin plastic/rubber/wood or shims between the steel and the stone.

That said, does anyone know of any resources for methods of designing attachment points in stone like this? I've done a little poking around the internet, and cant find anything, or I'm not coming up with the right keywords.

 

[EdStainless]

I would suggest that you repost a version of this question on the Civil Engineering forum.
You likely don't want the connection stiffer than the stone, that can result in high local stress concentrations.
Maybe you'll get a geotech commenting on this for you.

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P.E. Metallurgy, consulting work welcomed

 

[dvd]

Hilti could be interested in discussing.

 

[JStephen]

Sounds a lot like putting lifting points, etc. into precast concrete.
Thermal movements may be the controlling force, the more stiff your structure is, the higher the forces.
I'd be concerned on liability on a sculpture like that, as it's doubtful anyone actually has a good handle on strong that particular block of rock is. More to the point, if it splits in half at some point, who pays for it?

 

[Tmoose]

Is the statue one piece of stone, and already hollowed out?

 

[chicopee]

Your best information may come from quarry operators particularly those operators providing stones for jetties. If you look at some of the beach jetties you'll notice holes in many of the stones probably these holes were the lifting points.

 

[MintJulep]

Or people who do marble facades for buildings.

https://www.dedalostone.com/en/marble-facade-cladding/

 

[FiniteMatt]

The statue is made up of 5-6 layers of ~18" wire sawn slabs that are epoxied together to build up the structure, with some of the middle cut out during the wire sawing. So the customer has had the chance to inspect each layer and minimize any imperfections.

We don't have specific thermal expansion numbers for this rock, but the general thermal expansion coefficient for marble is 6-14 (10^-6 m/m°C) compared to steel which is 11-12 (10^-6 m/m°C), so they're at least both in the same range.

 

[Tmoose]

laminated like this ?

https://artemest.mo.cloudinary.net/...LU-00320200522-48-11s3p18.jpg?tx=q_auto,w_750

 

[FiniteMatt]

Tmoose: Yes, except the layers are parallel with the floor in a big stack.

 

[Tmoose]

So every layer is a complete "circle" ? What is the minimum wall thickness ?

 

[Peedge]

There are some really good design references available from ASTM (and other sources), which provide guidelines in design and testing of stone anchorages/fixings. I have listed a few:

* ASTM STP 996
* ASTM MNL 21 by Lewis
* ASTM C 1242
* ASTM C 1354
* Stone Cladding Engineering by Camposinhos

I hope it helps.