// CODE SNIPPET
17.4.2 Concrete Breakout Strength of Anchor in Tension
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17.4.2.1
The nominal concrete breakout strength in tension, Ncb of a single anchor or Ncbg of a group of anchors, shall not exceed:
(a) For a single anchor
 | (17.4.2.1a) |
(b) For a group of anchors
 | (17.4.2.1b) |
Factors ψec,N, ψed,N, ψc,N, and ψcp,N are defined in 17.4.2.4, 17.4.2.5, 17.4.2.6, and 17.4.2.7, 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 | (17.4.2.1c) |
17.4.2.2
The basic concrete breakout strength of a single anchor in tension in cracked concrete, Nb, shall not exceed
 | (17.4.2.2a) |
where kc = 24 for cast-in anchors and 17 for post-installed anchors.
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.
Alternatively, for cast-in headed studs and headed bolts with 11 in. ≤ hef ≤ 25 in., Nb shall not exceed
 | (17.4.2.2b) |
17.4.2.3
Where anchors are located less than 1.5hef from three or more edges, the value of hef used for the calculation of ANc in accordance with 17.4.2.1, as well as for the equations in 17.4.2.1 through 17.4.2.5, shall be the larger of (ca,max)/1.5 and s/3, where s is the maximum spacing between anchors within the group.
17.4.2.4
The modification factor for anchor groups loaded eccentrically in tension, ψec,N, shall be calculated as
 | (17.4.2.4) |
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. (17.4.2.4) and for the calculation of Ncbg according to Eq. (17.4.2.1b).
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. (17.4.2.1b).
17.4.2.5
The modification factor for edge effects for single anchors or anchor groups loaded in tension, ψed,N, shall be calculated as
| If Ca,min ≥ 1.5hef, then ψed,N = 1.0 | (17.4.2.5a) |
If Ca,min < 1.5hef, then  | (17.4.2.5b) |
17.4.2.6
For anchors located in a region of a concrete member where analysis indicates no cracking at service load levels, the following modification factor shall be permitted:
(a) ψc,N = 1.25 for cast-in anchors
(b) ψc,N = 1.4 for post-installed anchors, where the value of kc used in Eq. (17.4.2.2a) is 17
Where the value of kc used in Eq. (17.4.2.2a) 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. (17.4.2.2a) 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.
17.4.2.7
The modification factor for post-installed anchors designed for uncracked concrete in accordance with 17.4.2.6 without supplementary reinforcement to control splitting, ψcp,N, shall be calculated as follows using the critical distance cac as defined in 17.7.6
| If Ca,min ≥ Cac, then ψcp,N = 1.0 | (17.4.2.7a) |
If Ca,min < Cac, then  | (17.4.2.7b) |
but ψcp,N determined from Eq. (17.4.2.7b) 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.
17.4.2.8
Where an additional plate or washer is added at the head of the anchor, it shall be permitted to calculate the projected area of the failure surface by projecting the failure surface outward 1.5hef from the effective perimeter of the plate or washer. The effective perimeter shall not exceed the value at a section projected outward more than the thickness of the washer or plate from the outer edge of the head of the anchor.
17.4.2.9
Where anchor reinforcement is developed in accordance with Chapter 25 on both sides of the breakout surface, the design strength of the anchor reinforcement shall be permitted to be used instead of the concrete breakout strength in determining ϕNn. A strength reduction factor of 0.75 shall be used in the design of the anchor reinforcement.
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Related Code Sections
17.4.2 Anchoring to Concrete, Concrete Breakout Strength of Anchor in Tension
The nominal concrete breakout strength in tension, Ncb of a single anchor or Ncbg of a group of anchors, shall not exceed: (a) For a single anchor ...
17.4.2.3 Anchoring to Concrete,
Where anchors are located less than 1.5hef from three or more edges, the value of hef used for the calculation of ANc in accordance with 17.4.2.1 ...
17.4.2.6 Anchoring to Concrete,
For anchors located in a region of a concrete member where analysis indicates no cracking at service load levels, the following modification factor ...
17.4.2.7 Anchoring to Concrete,
The modification factor for post-installed anchors designed for uncracked concrete in accordance with 17.4.2.6 without supplementary reinforcement ...
17.4.2.8 Anchoring to Concrete,
Where an additional plate or washer is added at the head of the anchor, it shall be permitted to calculate the projected area of the failure surface ...