17.4.2 Concrete Breakout Strength of Anchor in Tension
(a) For a single anchor
(b) For a group of anchors
Factors ψec,N, ψed,N, ψc,N, and ψcp,N are defined in 18.104.22.168, 22.214.171.124, 126.96.36.199, and 188.8.131.52, respectively. ANc is the projected concrete failure area of a single anchor or group of anchors that shall be approximated as the base of the rectilinear geometrical figure that results from projecting the failure surface outward 1.5hef from the centerlines of the anchor, or in the case of a group of anchors, from a line through a row of adjacent anchors. ANc shall not exceed nANco, where n is the number of anchors in the group that resist tension. ANco is the projected concrete failure area of a single anchor with an edge distance equal to or greater than 1.5hef
|ANco = 9hef 2||(184.108.40.206c)|
The value of kc for post-installed anchors shall be permitted to be increased above 17 based on ACI 355.2 or ACI 355.4 product-specific tests, but shall not exceed 24.
but ψec,N shall not be taken greater than 1.0. If the loading on an anchor group is such that only some anchors are in tension, only those anchors that are in tension shall be considered when determining the eccentricity e'N for use in Eq. (220.127.116.11) and for the calculation of Ncbg according to Eq. (18.104.22.168b).
In the case where eccentric loading exists about two axes, the modification factor ψec,N shall be calculated for each axis individually and the product of these factors used as ψec,N in Eq. (22.214.171.124b).
(a) ψc,N = 1.25 for cast-in anchors
Where the value of kc used in Eq. (126.96.36.199a) is taken from the ACI 355.2 or ACI 355.4 product evaluation report for post-installed anchors qualified for use in both cracked and uncracked concrete, the values of kc and ψc,N shall be based on the ACI 355.2 or ACI 355.4 product evaluation report.
Where the value of kc used in Eq. (188.8.131.52a) is taken from the ACI 355.2 or ACI 355.4 product evaluation report for post-installed anchors qualified for use in uncracked concrete, ψc,N shall be taken as 1.0.
When analysis indicates cracking at service load levels, ψc,N, shall be taken as 1.0 for both cast-in anchors and post-installed anchors. Post-installed anchors shall be qualified for use in cracked concrete in accordance with ACI 355.2 or ACI 355.4. The cracking in the concrete shall be controlled by flexural reinforcement distributed in accordance with 24.3.2, or equivalent crack control shall be provided by confining reinforcement.
|If Ca,min ≥ Cac, then ψcp,N = 1.0||(184.108.40.206a)|
|If Ca,min < Cac, then||(220.127.116.11b)|
but ψcp,N determined from Eq. (18.104.22.168b) shall not be taken less than 1.5hef/cac, where the critical distance cac is defined in 17.7.6.
For all other cases, including cast-in anchors, ψcp,N shall be taken as 1.0.