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

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Jim,

Not only is it a good idea to add the additional ties at the top of
concrete columns/piers...it is typically required by code.

For example, section 1913.1.3 of the 1996 BOCA code requires that anchor
bolts at the tops of columns be enclosed with at least 2 #4 ties located
within 4 inches of the top of the column.

In the 2000 IBC, section 1910.4.3 requires 2 #4 or 3 #3 bars within the
top 5 inches for anchor bolts in the top of columns in Seismic Design
Category C or higher.

And this requirements has also been introduced into the 2002 ACI 318 code
in section 7.10.5.6.  This section requires anchor bolts placed in the top
of columns or pedestals to be enclosed by lateral reinforcment that also
surround at least four vertical bars of the column/pedestal.  This lateral
reinforcement must be within the first 5 inches of the column/pedestal and
must consist of either 2 #4 or 3 #3 bars.

HTH,

Scott
Ypsilanti, MI


On Fri, 1 Aug 2003, Kestner, James W. wrote:

> 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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