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Re: CCD Method Of Anchorage Design

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Rick,

Per table R1.1.8.3 of ACI 318-02, moderate/intermediate seismic level
(in ACI terms) corresponds to SDC/SPC C while high seismic level
corresponds to SDC D, E, F (IBC 2000+ & NEHRP 1997+) or SPC D, E (BOCA,
SBC, ASCE 7 1993 to 1998, and NEHRP 1991/1994).

That answers you first question...although from the strict "law of the
land" view it does not as table R1.1.8.3 is in the commentary so it has no
real legal force.

As to your second and third questions...they are good, but unfortuately
point out the problem with anchorage design...it kind of falls in the "no
man's (or woman's) land" between concrete design and steel design.  I
would say that the "solution" provided by the "concrete folks" is
typically consistant with prevailing structural thinking...that is that we
tend to want the "weak" link in the structural system that is the location
of the expected failure at the failure load to be in a ductile manner.
Thus, when you look at anchorage to concrete as a small structural
sub-system, it would make sense to have the failure mechanism of that
sub-system be in a ductile manner.  Now, you could certainly argue that we
don't want the concrete anchorage sub-system to be the weak link in our
overall structural systems, thus the concrete anchor anchorage sub-system
could be designed to fail in a non-ductile systems since we would have the
overall structural system failing in a ductile manner elsewhere.  If so,
then the answer to the last question would be that the EOR should be
making the decision or the code could still do it in terms of the entire
structural system (after, the codes "force" engineers to make the beams
the ductile element in moment frame systems by requiring the strong
column-weak beam methodology and designing the connections for a large
load than what actually may come from the beam).

HTH,

Scott
Ypsilanti, MI

On Wed, 2 Jul 2003 Rick.Drake(--nospam--at)Fluor.com wrote:

> A similar question came up on the list server recently, with little
> discussion.  I thought I'd try again.
>
> The CCD Method for concrete anchor design can be found in Section 1913 of
> the 2000 IBC and Appendix D of ACI 318-02 (part of code as referenced by
> both NFPA 5000 and 2003 IBC).
>
> If you are in regions of moderate or high seismic risk (undefined), you
> must size the anchors for a reduced tensile strength defined as
> 0.75(phi)(F-sub-u)(A-sub-net), which is approximately 75% of what you would
> get from LRFD design.  You will probably end up with larger anchor bolts.
>
> Then, with your probably larger anchor bolts, you need to provide a
> "ductile design", ensuring that the strength of all concrete limit states
> (pullout, breakout, burstout) be larger than the full anchor bolt tensile
> strength (phi)(F-sub-u)(A-sub-net).  (Note the lack of the 0.75 factor.)
> This results in some combination of large embedments and supplemental
> reinforcing steel.
>
> 1st Question:  Should regions of moderate or high seismic risk be
> considered equivalent to Seismic Design Categories C, D, E, and F, as
> defined by the 2000 IBC and later codes?
>
> 2nd Question:  Why should the requirements for sizing the steel anchor
> bolts be prescribed by the "concrete people" to be more conservative than
> that prescribed by the "steel people"
>
> 3rd Question:  Should the decision for "ductile design" of the anchor bolts
> be made by the EOR, considering the required system performance of the
> structure above?
>
> Whether we like it or not, if you are using the 2000 IBC in regions of
> moderate or high seismic risk, you will probably be using larger bolt
> diameters, deeper concrete embedments, and more supplemental reinforcing
> steel than you are used to.
>
> Have a nice day.
>
> Rick Drake, SE
> Still in 1997 UBC country.
> *********
>
>
>
>
>
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