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RE: Anchoring to Concrete, ACI 318-02 Appendix D

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Angela:

I think most engineers would not design piers with these hairpins at the top. It is my suggestion that you extend the anchor bolts sufficiently to lap with the vertical pier steel.  Also, I think it is good practice to add 3 additional ties at the top of the pier.

The hairpins at the top just make it more difficult to pour the pier. It might even be enough to cause segregation.

Make sure that they clean the cutting oil off of the embedded portion of the anchor bolt.

Jim K.
Green Bay, Wi

-----Original Message-----
From: Sherman, William [mailto:ShermanWC(--nospam--at)cdm.com]
Sent: Friday, August 01, 2003 12:56 PM
To: 'seaint(--nospam--at)seaint.org'
Subject: RE: Anchoring to Concrete, ACI 318-02 Appendix D


I'm not familiar with the three references noted in ACI 318, but I am
familiar with The Engineering Journal article from 1983. The method
presented was based on ACI 349, Appendix B; there was also an article titled
"Guide to the Design of Anchor Bolts and Other Steel Embedments" in the July
1981 issue of Concrete International which also was based on similar
concepts. And if you have access to the Second Quarter 1984 Engineering
Journal, refer to the "Discussion" of the 1983 article - it includes my
comments on the original article and with responses from the authors.
Although I did not address your specific questions regarding the steel
reinforcement provided, I did note discrepancies in the Example presented
for a Type D anchor bolt. 

In the example, the pier is increased in size to meet 'Ae', but that is not
a requirement if adequate supplementary reinforcement is provided. As per
ACI 318, Appendix D, Section D.8, supplementary reinforcement can be used to
control splitting in lieu of providing the additional concrete in the pier. 

It is not essential that the supplementary reinforcement be separate from
the pier vertical reinforcement and ties, but it is important that the
reinforcement provided to control splitting be located to cross the assumed
failure plane. The Engineering Journal article erroneously shows the
critical failure plane for tension as a horizontal plane in the pier - but
the failure surface should be shown as 45-degree cones extending upwards
from the bolt bearing heads. (Note: more recent failure surface assumptions
use an inverted pyramid with an angle as shown in Fig, RD.4.2.2(b) on ACI
318.) The #4 hairpin reinforcement was likely selected for ease in bending
and to permit accurate placement across the critical failure surfaces, but
the pier reinforcement can also be used if placed and developed properly. If
the anchor bolts extend deep enough, you should be able to develop the pier
vertical reinforcement above the failure surface to provide tensile
resistance. 

The shear must be addressed separately, with the resisting ties or U-bars
crossing the lateral failure cones. Alternately, provide adequate side edge
distance to avoid the necessity for supplementary reinforcement for shear. 


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

-----Original Message-----
From: Angie [mailto:stecksy(--nospam--at)charter.net]
Sent: Wednesday, July 30, 2003 7:11 PM
To: seaint(--nospam--at)seaint.org
Subject: Anchoring to Concrete, ACI 318-02 Appendix D


Hello:
 
I have enjoyed reading your discussions for the past few years, and hope
someone can provide me some guidance.
 
I need help clarifying and understanding the design of anchor rods with
shear and tensile loadings in a confined pier. ACI 318-02 Appendix D.8 -
(Required edge distances, spacings, and thicknesses to preclude splitting
failure) and D4.2.1 both speak about providing supplementary reinforcement
in the direction of the load, confining reinforcement, or both in the pier.
It states 3 references to help design for this reinforcement. The references
are (as stated in Reference D), "Design of Fastenings in Concrete,"
"Fastenings to Concrete and Masonry Structures," and "Effect of Reinforcing
Details on the Shear Resistance of Anchor Bolts under Reversed Cyclic
Loading."  My first question is, which one of these references could anyone
recommend to help me out the most for the following:
 
The reference I do have is the article from Engineering Journal AISC Second
quarter 1983, "Design of Headed Anchor Bolts."
If anyone uses this reference, maybe you could help me understand this.  I
am getting confused on Example #2:Type D (Bolts in a confined Pier).  The
anchors are subject to combined shear and tension loading.  If I have a
24"x24" pier that already has 8 vertical bars with ties, is this example
telling me that in addition to this steel, I would need to provide tension
lap reinforcement (the 4- #4 "U-bars")  and additional shear reinforcement
(another 4-#4 U-bars) around the anchors???  So now I would have 8-vertical
bars with ties in the pier, and surrounding the anchors  I would need 4-#4
U-bars for tension load and 4-#4 U-bars for shear load, or is the steel that
is already in the pier considered adequate confining reinforcement, and how
is this figured??  In the design example, the pier has vertical bars and
ties in it, and the additional "U"-bars.   The application is for a tall and
narrow tower-type structure with a significant amount of uplift.   I have
never seen this specified in previous designs by others, so I think I may be
missing something here.
 
Thank you,
Angela Baughman, PE
Wausau, WI
 
 
 

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