] [Thread] [Date] [Author]

["Jake Watson" <jwatson(--nospam--at)utahisp.com>]

I am glad to see someone else wrestling with the impacts of this provision.
My issue is that it is next to impossible to get a ductile failure in
tilt-panel design.  If you place a bearing plate on top of the wall, you end
up with approximately 3" of edge distance in a standard 6" panel.  If you
need 8" panels for tall walls, you still only get 4" edge distance.  If you
put the embed on the side of the panel, you can probably get the ductile
provision to work, but not with an anchor strong enough to support the roof
joist.

Are we going to start through bolting new construction?  Does anyone know if
there are plans to provide an out to this provision?  Can we increase the
force by 50% and then design it as brittle?  Are any manufacturers going to
make new anchors which better satisfy the criteria?

Jake Watson, P.E.
Salt Lake City, UT

-----Original Message-----
From: Rick.Drake(--nospam--at)Fluor.com [mailto:Rick.Drake(--nospam--at)Fluor.com]
Sent: Wednesday, July 02, 2003 2:17 PM
To: seaint(--nospam--at)seaint.org
Subject: CCD Method Of Anchorage Design


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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