Anchorage design in Seismic Design Category D

[ajw771983]

Hello everyone,

I'm in the process of designing post-installed anchors to connect the columns of a steel storage rack to a existing slab. Due to seismic loading, the anchors are subjected to tensile loads from uplift in the columns.

The owner hired a company to perform testing on the existing slab and they provided the concrete strength for a number of cores throughout the slab.

My question is, are there any ACI provisions when dealing with aged concrete in high seismic zones? Can I use the concrete strength from testing directly to design the anchorage per ACI318-19 Chapter 17?

Thank you for any suggestions

 

[driftLimiter]

If the testing is from an approved agency and your comfortable it will be reflective of the concrete beneath your anchorage I don't see why not. I'm not sure if I would try to just much more beyond 4.5ksi anyway. I don't think you will see that much of a benefit from increasing beyond that too much.

 

[ajw771983]

Thank you driftLimiter - testing was done by a geotech consultant based on ASTM C39. They reported concrete break strength of 24 cores, and they average around 7000 psi.
This value seems high, that's why I was wondering if I should be taking extra reduction factors for aged concrete in a high seismic zone (SDC = D)

 

[le99]

Do you have access to the original design documents? Note that concrete strength increases with age, so if you use the strength stated in the original design and the proposed scheme works, it equals to have a build-in reduction factor.

 

[JLNJ]

You might look into "core" strength versus specified compressive strength (f'c). They are not necessarily equivalent.

 

[ajw771983]

@le99 : Good point - I don't have that information but I'll request it
@JLNJ : Based on your suggestion, I was able to find ACI 318-19 section 26.12.6 "Investigation of strength tests"

Thank you all for your input!