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RE: Shear Stud Tensile Strength

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Gentleman,

In regard to the anchor capacities predicted by the Concrete Capacity Method
reflected in ACI 318-02, Appendix D:

1.	Allowable values for tension and shear of post-installed expansion
anchors was based on testing by the individual manufacturers.  In tension
tests, manufacturers set the anchors into concrete away from a free edge or
adjacent anchors and pulled them to failure.  Some testing agencies
collected data on load and displacement, others did not.  Shear tests were
also conducted away from free edges and adjacent anchors.  This testing
occurred through the mid 1980s.  The 10 diameter spacing and edge distance
criteria that we used back then was based on the Expansion Anchor
Manufacturers Institute.  As far as I know, there was no rational basis,
i.e., tests for these values.

2.	Circa 1976, the Tennessee Valley Authority (TVA) sponsored testing
at the University of Tennessee, Knoxville for tests on headed studs
subjected to tension and shear loads.  These tests confirmed the 45 degree
cone that was the basis of the method many of us have used to date.  The
methodology of the "Cone Method" was first codified in ACI 349-80, Appendix
B for use in nuclear safety related structures.

3.  In 1979, the Nuclear Regulatory Commission issued Bulletin 79-02 which
addressed the design of anchors for safety related pipe supports.  This
bulletin required utilities to verify their anchor designs and assure that
all wedge anchors (post-installed torque controlled anchors) had factors of
safety of 4.0 and all shell anchors (post-installed displacement controlled
anchors) had a factor of safety of 5.0.  Utilities were to account for base
plate flexibility for load distribution from the attachment to the
individual anchors.  The NRC also recommended site-specific testing.

4.  In 1988, Hilti, Inc. reported that the published edge distances for some
of their anchors were unconservative and need to be increased to the
distances now reflected in the ICBO ES reports.  During hearings on how
these revisions affected the nuclear industry, the NRC first acknowledge the
existence of the testing that was proceeding in Europe, particularly at the
University of Stuttgart by Fuchs and Eligehausen.

5.  Subsequent to this meeting, Sub-Committee 3 of ACI 349 began to review
and evaluate the existing domestic test data and, thanks to the
participation of Rolf Eligehausen, the data from Stuttgart.  The reviewed
data included all anchors, not merely post-installed.  I know this because I
did some of the data reviews.  This process took more than several years and
the subcommittee worked carefully to assure that a change to the
requirements was reasonable.

6.  Parallel to the Sub-Committee 3's efforts, the NRC began a series of
tests at the University of Texas, Austin.  These tests looked at all anchor
types.  The results of these tests were also considered by Sub-Committee 3.

7.  Sub-Committee 3 looked at the overall levels of safety and reliability
of the Concrete Capacity Method versus the Cone Method and determined the
Concrete Capacity Method was superior overall.

8.  Running behind the efforts of Sub-Committee 3 were the efforts of the
committees for ACI 318 and 355.  Committee 355 reviewed the overall approach
to anchor behavior and specifically addressed the specific requirements for
anchor testing in their document ACI 355.2-01.  ACI 318 reviewed the work of
Sub-Committee 3 and adopted it as required for inclusion into Appendix D of
ACI 318-02.

In regard to the "conservative" approach to anchor designs, I think you must
review what the basis of how we designed before versus what we know now.  I
too thought that something was wrong when the sub-committee first thought of
changing to the Concrete Capacity Method, but I can tell you the studies
bear out its superior representation of anchor behavior.

Please call or email if you wish to discuss this issue further

John Russ
Diablo Canyon Power Plant
805-545-6615
jprh(--nospam--at)pge.com

-----Original Message-----
From: Jim Getaz [mailto:jgetaz(--nospam--at)shockeyprecast.com]
Sent: Friday, September 06, 2002 7:22 AM
To: seaint(--nospam--at)seaint.org
Subject: Re: Shear Stud Tensile Strength


	Eric,
		ACI-318-02 Appendix D, Anchoring to Concrete is the most
recent comprehensive document on stud strength in concrete. Equation D-3,
which is simple, gives the strength of the steel. The next section gives the
strength of the concrete which has all sorts of factors and conditions.
		There are claims that Appendix D is too conservative because
it is based on mostly post-installed bolt tests and few cast-in stud tests,
so more research is being done. But I understand that the 45 degree shear
cone and the group action of a number of studs with intersecting shear cones
was based on even less research.
		All that notwithstanding, I design with the modified shear
cone model in the PCI Handbook 5th Edition and confinement. If studs are
near a concrete edge, it is prudent either to weld a tail bar onto the plate
that extends away from the edge or provide some other reinforcing that will
cross a crack from the edge to the most distant studs of the plate. However,
some of the researchers dismiss that latter because the concrete has
cracked, so it has failed. No amount of pointing out that this is the basis
of reinforced concrete design budges them from this position, so I keep it
in mind.
	Regards,
	James L. Getaz, III
	Winchester, Virginia

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