ACI-349 Approval for KB-TZ2 Expansion Anchor

Applicability of the KB-TZ2 Anchor
5
August 2021
Method used to calculate the effectiveness factor, k
Both ACI 355.2-01 and ACI 349-01 require that the k-factor (effectiveness factor, whose value depends on the type of anchor)
reported for the anchors be calculated from the 5% fractile of the test data. ICC-ES AC 193 allows the mean values to be used as
an alternative to the 5% fractile, albeit the required calculated k factor is much higher than what is published (for example: to have
a calculated k of 17 for cracked concrete, the calculated k of the mean values must be at least 22). When mean values are too
low to establish the k value, 5% fractile values are calculated to checked against the published value to determine if a k value can
be established via 5% fractile values or if a pullout load must be published (this is only possible because the calculated k values
required via mean method are higher than the published values).
Resolution: The published data is based on the AC 193 criteria which utilizes both the mean and 5% fractile methods instead of
just the 5% fractile method. In general, the results should be about the same, with a few notable exceptions. It is possible for the
5% fractile method to be less conservative when the COV is small, resulting in a higher 5% fractile value that may obtain a higher k
factor than what would have been calculated for the mean method. Similarly, it is possible for the mean method results to be less
conservative for test series that have a high average, but also a high COV resulting in a lower 5% fractile value that would have lead
to a lower calculated k factor. In regard to the KB-TZ2 evaluation, there are examples of both of these instances occurring. While
there are instances of the mean method resulting in higher k factors compared to the 5% fractile method, it should be noted that
the mean method results are significantly more stagnant once established, whereas 5% fractile values, and thus k factor derived
from them, can be easily influenced and possibly improved by increasing the number of tests performed. While there are subtle
differences between these two methods, in general, the mean method of AC 193 typically results in the more conservative value.
The intent of the ACI codes is to provide a k factor that will result in an anchor design load that will be met or exceeded by 95% of
all anchors with a 90% assurance. It is our belief that the k factors published meet the intent of the code.
Question on measurement of ductility of the KB-TZ2 anchor steel
ACI 355.2-01 does not contain criteria for establishing the ductility of mechanical anchor steel. ACI 318-14 (Chapter 2 – Notation
and Terminology) define it as, “steel element, ductile – element with a tensile test elongation of at least 14 percent and reduction in
area of at least 30 percent…”
Similarly, ACI 349-01 (Appendix B – Anchoring to Concrete) defines it as, “Ductile steel element – An element with a tensile test
elongation of at least 14% and reduction in area of at least 30%...”
Resolution: AC 193 has incorporated a method for determination of anchor steel element ductility. Chapter 6 of AC 193 defines the
tests required for steel classification. Table 6.3 of AC 193 similarly requires steel testing to result in elongation of at least 14% and
the reduction in area of at least 30% to be considered ductile.
Steel testing was performed at Element Material Technology in conformance with AC 193. Both carbon and stainless steel anchors
of every diameter were tested and all were classified as ductile.