Multiple anchord bolts projected concrete failure area ratio

[mojamake]

Can someone help me shed some lights on determining a protected area ratio Anc/Anco for calculating concrete breakout strenghth of anchor in tension. per aci318 appendix D d.5.2.1b, it said Anc shall not exceed NAnco (N can be neglected for multiple bolts). To me it means the ratio Anc/Anco can not be greater than 1.0. But, when I use Hilti profis anchor program, I notice they use the ratio greater than 1.0. I am I missing something?

 

[w12x40]

Anc for ONE anchor can't be bigger than Anco - Anco is the ideal anchor breakout cone, and the Anc is the actual breakout area based on edge distance. Anc can be greater than Anco when you've got multiple anchors in a group located far enough from edge influences. You're right that Anc/Anco can't exceed 1.0, but that only applies for one anchor. Anc/Anco can be greater or lesser than 1.0, depending on edge distances and spacing.

P.E.
Oratio imago animi.

 

[mojamake]

Thanx for the response, Oratio.
I understand that Anc/Anco can't exceed 1.0 only applies for one anchor.
But ACI318 doesn't specify exception for multiple anchor bolts. Any idea where I can find this exception?

 

[w12x40]

I see your problem. Anc < n*Anco is how the code tells us that the actual projected area can't exceed the theoretical for n anchors. The specific exception for multiple anchors is the n in n*Anco.

P.E.
Oratio imago animi.