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RE: Anchoring to Concrete

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I am not as familiar with the background on ACI 318 Appendix D as I would
like to be, but I am familiar with previous anchor bolt design procedures
such as Appendix B of ACI 349-97 and similar procedures described in the
article "Guide to the Design of Anchor Bolts and Other Steel Embedments"
from Concrete International, July 1981. 

The general intent in those documents was that the concrete tension capacity
be developed such that it exceeds the yield strength of the anchor bolt,
such that the ductile behavior will occur. Thus an anchor bolt embedded deep
enough in mass concrete should have adequate concrete pullout capacity to
initiate bolt yielding prior to concrete failure. 

In a pier of limited dimensions, reinforcing steel can be used to resist
pullout where there is not adequate concrete area for a ductile design. The
commentary for the above noted documents discusses how this can be done. In
essence, a 45-degree cone is drawn towards the failure surface from the head
of the anchor bolt, and the reinforcing steel must be developed both within
and outside of the failure cone. 

Similar procedures are described for lateral shear failure, using a
semi-circular failure cone initiated at the top of the anchor bolt.
Reinforcing steel anchored on each side of that half-cone failure can be
used to resist lateral loads in lieu of only using concrete strength. 

William C. Sherman, PE 
(Bill Sherman) 
CDM, Denver, CO
Phone: 303-298-1311
Fax: 303-293-8236
email: shermanwc(--nospam--at)cdm.com
 

> -----Original Message-----
> From: Michael Bryson [mailto:mbryson(--nospam--at)NYASE.com] 
> Sent: Saturday, October 16, 2004 4:26 PM
> To: seaint(--nospam--at)seaint.org
> Subject: RE: Anchoring to Concrete
> 
> I think the intent of the code here is that the addition of 
> reinforcement is only meant to control cracking, not to 
> increase the capacity of the anchorage in tension. Once a 
> crack forms, the stresses in the concrete (hoop stresses) 
> change and the anchorage capacity is reduced. 
> 
> Now having said that, if more reinforcing means you have 
> smaller cracks, and since there is a correlation between 
> crack size and anchor capacity, then technically additional 
> reinforcing does increase the capacity. But I don't think the 
> code allows for this.
> 
> -----Original Message-----
> From: Rlabbe [mailto:rlabbe(--nospam--at)cadeidepe.cl]
> Sent: Saturday, October 16, 2004 6:49 AM
> To: seaint(--nospam--at)seaint.org
> Subject: Anchoring to Concrete
> 
> List,
> 
> I will require some help to see if we are correctly 
> interpreting the codes in the referenced matter.
> ACI 318-02, ( App. D ) is determining the anchoring capacities 
> in concrete, based on the concrete breakout strength in 
> tension ( failure cone of the concrete mass ).
> It also allows to increase this capacity, when there is no 
> cracking in the anchoring region.
> The question is, since this capacity is based only in the 
> concrete failure, can it be increased with the addition of 
> adequate reinforcement ? i.e. enough rebar, and properly 
> placed, in the ( would be ) failure cone mass, as to take the 
> full pull-out load.
> Appreciate your opinions.
> 
> Best Regards,
> 
> Raul Labbé  S.E.
> M. ASCE.

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