Compressive strength of existing concrete walls

[kaffy]

Good Morning guys,

How do you determine the compressive strength of existing concrete walls / concrete floor if no structural drawings or any technical data is available? Are there any code requirements stating that minimum compressive strength of concrete allowed? I need to specify the anchor bolts but since I do not know the compressive strength, how should I proceed?

Thanks

 

[phamENG]

So you're just looking for f'c, right? If the concrete is in good shape then you can probably assume 2500psi (about 17 MPa if my conversion is correct) conservatively. If it's a critical application (failure could cause serious injury or death or significant property damage), then I'd insist on having a testing lab core few samples to test it if you need anything more than that.

 

[kaffy]

Yes f'c. Thank you very much

 

[jayrod12]

I would tend to agree with pham on the 17 MPa being a good lower bound. When was the original structure built? I haven't seen any concrete strengths lower than 25 MPa going back a lot of years here in Canada.

Even when specifying 20 MPa grout for CMU walls we end up above 25 MPa on 99% of it. And that's cylinder results, the in-situ strength is likely significantly higher due to the moisture being sucked out of the mix by the block.

 

[kaffy]

It was built in 1972.I see. Thank You very much

 

[Sheer Force Engineer]

17MPa is a good lower bound assumption, agree with the posts above.

If you need to justify more or are unsure, core samples remove most doubt.

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