Design criteria for thin plates of natural stone (granite). 1

[azrom]

Hi! This is my first post to this community.

At present I am designing a product which have unsupported shelves in natural stone (or wood). The shelves have a thickness of 27mm (~1"), and a maximum free span of 1m (~40").

I have searched the net for design criteria for thin plates made of natural stone, and I have diffuculty finding conclusive results. I see some mention of a deflection criteria of L/720 or L/360, but am unsure of those criteria have some dependencies.

I have access to the general material properties like modulus of rupture and compressive strength. But I am unsure how to implement them against a safe design criteria. My best guess is that the maximum load for each shelve is to be about 50kg (~110lb), which I think these shelves should carry with ease. But I would like to know whats the safe limits of the shelve loading.

I am most concerned with the design criteria of natural stone (most often granite), but similar criteria for wood is also welcome.

 

[GeoPaveTraffic]

The wood shelves will be deflection controlled, whereas the natural stone will be strength controlled. Wood will tend to deflect and bow over time.

The biggest issue with the stone will be fractures or weak planes in the rock. You will not be able to model this and will require good quality control and testing of the cut shelves. However, for 110lbs I would not expect many problems with the stone.

 

[azrom]

I agree that the uncertainty regarding fractures is an important issue. But I cannot see that it is practical to test every shelve. There must be some criteria with enough built-in safety.

If there isnt any 'rule of thumb' or criteria in (like the L/720), I find that hard to believe. I am sure architects and engineers that use thin plates of stone in floor or wall designs, have some understanding of how much load their plates can withstand.

I realise that some types of natural stone have anisotropic material properties, but even that can be implemented in FEM-analysis for instance (if those properties are available).

Does anyone know if there is any deflection critera for plates of cement that I can have a look at?

I am looking for a good site for stone engineering. I am thankful for any help or advise!

 

[SlideRuleEra]

Perhaps "Dimension Stone Design Manual" or "Stone Selection and Stone Testing", from the Marble Institute of America will help. Here is the link

http://store.marble-institute.com/merchant.mvc?Screen=CTGY&Store_Code=MB&Category_Code=ts

For wood see, the American Wood Council

http://www.awc.org/index.html

They publish the "National Design Specification (NDS) for Wood Construction" which forms the basis for many building codes on this subject.

http://www.SlideRuleEra.net