Anchorage of Granite Base

[SkiisAndBikes]

I have several granite bases (30"x30"x30") subject to overturning due to wind loads on sculptures supported by the granite bases. The granite bases are typically dowelled into a reinforced concrete footing. I have attached a sketch.

Normally I would propose anchoring the granite base using threaded stainless steel rods and an epoxy type adhesive (I would typically specify Hilti HY-150). Anchorage into the concrete footing is not a problem, however, Hilti does not recommend or support their products when drilled into granite. I am not sure how I can justify a minimum design value for the dowels without some idea of the capabilities of the adhesive in a core drilled (and roughened) hole in the granite base.

Any suggestions for anchoring to the granite bases? i.e. alternate products, alternate methods, testing, etc..

 

[flight7]

My first thought is to do pull-out load testing using the same granite blocks. The test location would be hidden on the underside of the block. Drawbacks to this method include cost (I doubt it would be cheap) and damage to the granite if the failure mode turns out to be shear failure of the stone.

 

[CTW]

See if Williams Form Engineering has a solution.

http://www.williamsform.com/

 

[born2drill]

You could run the steel bar all the way through the granite block and anchor it with a plate and hex nut connection on the face of the granite.

 

[hokie66]

If it is competent granite, it would be stronger than the concrete, so although Hilti doesn't specifically recommend it, it would work. But if you are looking for a manufacturer to lean on, I doubt you will find it.

 

[dhengr]

Ask the granite supplier or any granite supplier for that matter, this can’t be an entirely new question for them. Maybe they have some other ideas, mechanical means, undercut notches, or some such. I would assume the big issue is the material hardness, lack of porosity and potential smoothness of the bore, as relates to epoxy bonding. Could you use some sort of an expansion bolt in the granite, without splitting it, and then epoxy its extension into the conc. ftg.? Can you core right through the granite blocks to match the sculpture feet?

 

[ishvaaag]

I certainly remember the egyptiN Aswan dam removed sculptures and recently saw a scheme of some sawn part being lifted by partial penetration (not through) dowel anchors, surely every part several tons to lift. Hence the solution is feasible even in moderately dynamic environments.

 

[SkiisAndBikes]

Thanks for the ideas. The granite bases are premium, very competent blocks. I can't through bolt for asthetic reasons. I will ask the granite supplier as well. They have informed me that they can drill 12" into the granite relatively easily. I think surface prep of the core holes will be important (roughen/clean).

I think I am going to either A) look for an combo undercut/adhesive anchor to dowel into the granite, then epoxy it's extension into the concrete or B) install conservatively designed adhesive anchors into the granite and proof load by having the contractor lift the granite base up by the dowels, i.e. use the self weight of the base itself for the load.