Anchoring for Wind Loads in Concrete Member No Longer in Tension 1

[P1VPEng]

I understand that cracked concrete must be assumed when designing anchorage per ACI 318 Appendix D when anchoring in tension zones of members or when sited in Seismic Design Categories C-F. I have a ring-shaped foundation stemwall for a grain bin that has a hoop-tension force (and is therefore cracked) when loaded with grain but will have a negligible hoop-tension force when the anchors are seeing loads due to wind. Must cracked concrete be assumed when considering only the net wind reactions?

I know the conservative thing to do in always assumed "cracked", and that is what I normally do, but the wind tension reactions are large enough that nothing will work (from a calculation standpoint) if I assume cracked concrete.

The anchors will be either cast-in-place headed anchors or post-installed adhesive anchors. Any input would be appreciated. Thanks.

 

[sbouvia]

You would have to verify that the concrete is not cracked in a service loading state, which could include both wind loads and your grain loading. The concrete not being cracked would allow you to use section D.5.2.9 (ACI 318-08) to get higher strengths. Also the factor will vary based on whether you use cast-in or post installed anchors, and could vary again whether you use the ACI 318-08 values or the values based on the evaluation report which should be based on ACI 355.2.

Hope this helps.

 

[structSU10]

Unless you can prove that cracking will never occur you are stuck. According to what you stated, once the silo is filled with grain the concrete will crack. These cracks don't just heal themselves after the load is gone.

 

[P1VPEng]

Thank you sbouvia and structSU10 for your responses.