Any granite experts here?

[Goochie]

Despite much google searching, I'm struggling to find a ball-park figure for the tensile strength of granite. My MD has another business designing and importing granite street furniture from China. He has asked if I could do some quick calculations to work out the maximum load that can be taken on a bench.

However, in order to do this, I need to know the tensile strength of granite.

I have found the other required figures on the web.

[ALawson]

The Structural Engineers Pocket Book by Fiona Cobb has not details for Ultimate Tensile Strength, it has Specific Weight as 26kN/m^3, E=40-70 kN/mm^2, v=0.2-0.3 and Characteristic crushing strength fcu = 70-280 N/mm^2.

I will have a look elsewhere.

[rev-erend]

This was for the star galaxy granite

Technical Specification
Compressive Strength 2777 Kg/cm2
Comp. Strength after Gelivity 2696 Kg/cm2
Ultimate Tensile Strength 274 Kg/cm2
Coeff. Thermal expansion 0.0045mm/mcº
Water Absorption 0.04%
Impact Test-Min Fall Height 68 cm
Specific Gravity 2.960 Kg/m3
Hardness (Moh's Scale) 6.5

[ratbane]

It will be very much dependent upon the exact type of rock. Granite is a very specific igneous rock, and often, other rocks such as Gabbro are sold as Granite.

The tensile strength can be determined by a Brazilian Test, which should be undertaken on samples of the actual rock taken from source.

[Goochie]

ratbane said:

It will be very much dependent upon the exact type of rock. Granite is a very specific igneous rock, and often, other rocks such as Gabbro are sold as Granite.

The tensile strength can be determined by a Brazilian Test, which should be undertaken on samples of the actual rock taken from source.

So is it going to be a waste of time calculating the theoretical maximum load (as I would if it were made from steel) ??

[cv01jw]

This might help although it does cost $34

http://www.springerlink.com/content/k75qr0v64p7707...

Alternatively this site

http://www.stone-network.com/india/granite/black_g...

lists the UTS for Black Galaxy Granite as 274kg/cm²

Or this site:

http://www.elbatal.com/products.html

gives UTS in the region of 195-200 kg/cm²

Using more common units (ie N/mm²) I would probably take a worst case of 190 kg/cm² or about 18N/mm²

[ALawson]

The problem is that it is a natural material so like timber would need to be examined and graded, as has been said above.

[mrmaggit]

Why would you want a tensile strength for any stone? Surely it would be used in compression, with some structure taking the tensile loading, as no stone is very strong in tension.

[Goochie]

mrmaggit said:

Why would you want a tensile strength for any stone? Surely it would be used in compression, with some structure taking the tensile loading, as no stone is very strong in tension.

The software needs all of the values to be completed before it even starts doing the sums

[s3fella]

About two fat blokes eating ginsters and chips!


HTH

[mrmaggit]

Goochie said:

mrmaggit said:

Why would you want a tensile strength for any stone? Surely it would be used in compression, with some structure taking the tensile loading, as no stone is very strong in tension.

The software needs all of the values to be completed before it even starts doing the sums

Ah! that explains it. Mind ewe, can you think of a use were stone of any description is used in tension, because I can't.

[Goochie]

mrmaggit said:

Goochie said:

mrmaggit said:

Why would you want a tensile strength for any stone? Surely it would be used in compression, with some structure taking the tensile loading, as no stone is very strong in tension.

The software needs all of the values to be completed before it even starts doing the sums

Ah! that explains it. Mind ewe, can you think of a use were stone of any description is used in tension, because I can't.

Nope, I cant think of any either.

[cv01jw]

Goochie said:

mrmaggit said:

Goochie said:

mrmaggit said:

Why would you want a tensile strength for any stone? Surely it would be used in compression, with some structure taking the tensile loading, as no stone is very strong in tension.

The software needs all of the values to be completed before it even starts doing the sums

Ah! that explains it. Mind ewe, can you think of a use were stone of any description is used in tension, because I can't.

Nope, I cant think of any either.

It will need it because, if you are using the granite as a bench seat, it will be spanning between two supports. In this case, the lower half (ish) of the slab will be put into tension, and this will be the part that fails first.

[ratbane]

Goochie said:

ratbane said:

It will be very much dependent upon the exact type of rock. Granite is a very specific igneous rock, and often, other rocks such as Gabbro are sold as Granite.

The tensile strength can be determined by a Brazilian Test, which should be undertaken on samples of the actual rock taken from source.

So is it going to be a waste of time calculating the theoretical maximum load (as I would if it were made from steel) ??

You could get a handle on the loadings that slabs could take, but it would be worth checking if the quarry has any test results available. Use the rev-erend tensile strength for an indication.

Natural materials such as igneous rock are heterogeneous, and thus have incipient discontinuities, and changes in mineralogy. Granite should be a medium to coarse grained rock, but I have seen rocks such as diorites, gabbros, even Larvikite called granite by laymen. Some "granites" are absolute rubbish.

Thus, unlike steel, you can never be certain of tensile strength, and thus will need to apply a sensible Fcator of Safety (as much as 3). Also, if the benches are to be used outside, there will be a reduction in properties due to weathering.

In answer to other comments here, a slab does indeed fail in tension, as (crystaline) rock is brittle, and thus "doesn't fail in bending". The Brazilian Tensile Strength test mimicks this as it is a compression test across the axis of a small cylinder of rock, which indicates tensile strength by the failure mode.

Edited by ratbane on Wednesday 25th February 11:49