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Re: INSP - Special Inspection Epoxy Anchors

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At 10:28 AM 1/15/98 -0800, you wrote:
>Pringle  ... Silva ... anybody?
>
>For wedge anchors and the like, I have seen
>special inspection criteria which use torque  on
>the nut to test the anchor.  I understand that
>this is generally justified because in these types
>of anchors, the ability of the anchor to resist
>forces is intimately connected to the amount of
>torque applied during installation.
>
>What about torque testing of epoxy anchor systems,
>Like Hilti's HY150 (we are trying to anchor stuff
>in Zone 4).

Stan,
You may download  Guideline 3, "TORQUE TESTING & INSTALLATION INSPECTION OF 
DRILLED-IN ANCHORS", a City of Los Angeles document, from the Inspection
Practices Committee section of the SEAOC web page, which is pretty
thorough, but the following is more specific:
Wedge anchors are installed with the anchor capacity developed through an
amount of pressure to the sides of the hole.  Critical to this operation is
the psi of the concrete, the diameter, depth and cleanliness of the hole
once the issue of edge or interval spacing is addressed.  Wedge anchors
require that the hole depth be greater than the embedment requirement to
accommodate the withdrawal of the anchor as it is tightened and
simultaneously expanded.  Just how tight the nut is directly relates to the
amount of pressure of the actual wedge part of the anchor to the sides of
the hole. This is determined by a specific torque that is part of the
installation process.  This is generally a one time operation and is
performed by at the time of installation.  Once the anchor is installed and
properly torqued, the nut can be removed and whatever is required may be
fastened since the anchor is already well and properly set.  The fastening
of hardware or whatever has its own tightness requirements and is not part
of the anchoring capacity.  

For anchors installed through existing framing, care must be taken not to
unduly compress the member.  This can be accomplished by the use of large
steel plates and must be considered as some torque values for standard
sizes (7/8 Hilti Kwikbolt, for example) with 300# torque would surely
damage unprotected framing.

Other friction type anchors may also require torque as part of their
installation, but generally the wedge anchor has higher values and is most
frequently used for structural applications.

This torque is part of the installation process and any subsequent torquing
is not required; in fact, were you to torque an anchor, say 5 days after
the initial installation torque, you would find the anchor would require
more turns of the nut to re-achieve the torque.  This is due to some degree
of elongation or relaxation within the body of the anchor and to a concrete
compression aspect within the hole at the point of contact with the wedge
portion of the anchor.  These issues are considered by the manufacturers
and the accreditors (ICBOES for example).

The bottom line is that wedge anchors are generally supposed to be
installed with continuous inspection by a qualified Special Inspector
present.  Testing or torquing after the fact for wedge anchors is redundant
if the installation included a torque requirement.

Testing of these anchor systems is part of their Research Report approval,
but if, for whatever reason, specific anchor testing is desired, a Tension
Test per ASTM Standard using a tripod and a gauge to determine load
capacity is the preferred method.  There does exist a un quantifiable
although relatively accurate formula for the translation of torque to
tension values that can be used, but the coefficient of friction is the
variable in this formula and generally this system is used for brand new,
clean anchors. 
Hkd/12 = torque ft# where H is the load capacity, k is the coefficient of
friction (use .4 for conservative values) and d is the diameter of the
anchor, but for truly accurate requirements, the tripod test is needed.
 
Epoxy anchors have no torque requirements, only installation monitoring by
a Special Inspector since once all the installation criteria requirements
have been met you will have the same anchor that has been tested and
re-tested before the approval was ever issued.  But once again, you may
feel a specific project warrants the extra margin of verification (perhaps
the psi of the concrete is not clear).  The tripod system is preferred, but
if the expense becomes and issue and you opt to use the torque/tension
translation, the tension should be backed off once the test is complete.
Epoxy anchors are not supposed to be left under tension loads due some
element of creep.

Whew!!  I wonder how many of you will read this whole thing?


R. Sandy Pringle, Chair	       STRUCTURAL INSPECTION CONSULTANTS Inc. 
SEAOSC				 (800)598-1970  Fax (310)376-5294 
Inspection Practices Committee	 Hermosa Beach & Redondo Beach, CA   
sandyp(--nospam--at)sic-inc.com 		     	http://www.sic-inc.com

	It's not a matter of where you stand,
	 but in what direction you're headed.