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Anchor Bolt Design for Vessel/Stack

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Been awhile since I looked at this topic, and especially not in light of 
ACI 318 App. D.

Observations:

1. Pretensioning bolts is a good idea. The benefits include lessening the 
possibility of bolt loosening and fatigue, and creating a sort of composite 
 behavior between the concrete foundation and the anchor bolts. This  is 
commonly done for anchoring tall slender structures such as highway light 
standards.

2. If pretension is sufficiently applied, the base ring will be in 
continual compression against the concrete (or grout).

3. Pretension to 70% of Fu appears ideal for this purpose.

Questions raised:

- How does ACI 318-11 App. D apply? I can't seem to find anything there 
regarding pretension of anchors. I assume the following:

- It seems like only the "net tension" from lateral loads would pertain as 
far as concrete breakout is concerned, since the pretension is opposed by 
the pressure on the base ring.

- Bear in mind it's a base RING. The concrete breakout "effective area" is 
modeled with anchor boys in nice rows and columns. My thought is to look at 
 the circular arc of Anchors in net tension, and bound it by a parallel arc 
 inside and parallel arc outside the anchor arc, at the appropriate 
distance (1.5*hef max.) The "sides" would be max. 1.5*hef from the "last" 
anchor. The resultant tension c.g. and the geometric c.g. are calculated 
from the anchor locations on the arc, and their difference is the value for 
 e-sub-Nc.

- Pullout would however be affected by the total tension (pretension + 
tension from lateral loads).

- Anchor steel strength would also be calculated using total force 
(pretension + tension from lateral loads).

I'd love some comments on my thinking.

Thanks.

William L. Polhemus, Jr. P.E.

5

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