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Description / Abstract:
This standard applies only to post-installed adhesive anchors as
defined herein.
Adhesive anchors resist tension loads with a combination of
adhesion and mechanical bond (micro-interlock). Different anchor
designs and adhesive types may exhibit a range of performance
characteristics. In particular, the sensitivity of adhesive anchors
to variations in installation and service-condition parameters
(such as hole cleaning, installation orientation, and cracked
concrete characteristics) may vary widely from each system. ACI
318M addresses this situation by matching capacity reduction
factors to anchor performance categories that are, in turn,
established through a series of reliability tests.
This standard applies to anchors with a diameter
da of 6 mm or larger. The drilled hole shall be
approximately cylindrical with a diameter
doless-than or equal to
1.5da. This standard also applies to anchors
with an anchor embedment depth hef not less
than four diameters (4da), or 41 mm, and an
embedment depth not exceeding 20da.
The minimum diameter of 6 mm is based on practical
considerations regarding the limit of structural anchor
applications. The upper limit on the ratio of hole diameter to
anchor element diameter provides a demarcation between conditions
where a single bond strength can be used to evaluate anchor
strength and conditions where bond strengths at both the anchor
interface and concrete interface must be determined to evaluate
anchor strength. In addition, the value of 1.5da is
based on consideration of typical practice whereby most organic
adhesives are used with thin bond lines to limit both adhesive
shrinkage and creep of the anchor when under load. The design
method deemed to satisfy the anchor design requirements of ACI
318M, Appendix D, is based on an analysis of an anchor database
with a maximum diameter of 50.8 mm. While ACI 355.4M gives no
limitations on maximum anchor diameter, for anchors beyond this
dimension, the testing authority should decide if the tests
described in this standard are applicable or if alternative tests
and analyses are more appropriate. It may also be desirable to
reconsider those tests where only small, medium, and large
diameters are tested when the upper diameter is much larger than 38
mm.
A limitation on the minimum embedment length of adhesive anchors
is necessary to ensure conformance with the design method deemed to
satisfy the anchor design requirements of ACI 318M, Appendix D.