# 17.4.2 *Concrete Breakout Strength of Anchor in Tension*

**of a single anchor or**

*N*_{cb}**of a group of anchors, shall not exceed:**

*N*_{cbg}(a) For a single anchor

(17.4.2.1a) |

(b) For a group of anchors

(17.4.2.1b) |

Factors **ψ _{ec,N}**,

**ψ**,

_{ed,N}**ψ**, and

_{c,N}**ψ**are defined in 17.4.2.4, 17.4.2.5, 17.4.2.6, and 17.4.2.7, respectively.

_{cp,N}**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**

*A*_{Nc}**1.5**from the centerlines of the anchor, or in the case of a group of anchors, from a line through a row of adjacent anchors.

*h*_{ef}**shall not exceed**

*A*_{Nc}**, where**

*nA*_{Nco}**is the number of anchors in the group that resist tension.**

*n***is the projected concrete failure area of a single anchor with an edge distance equal to or greater than**

*A*_{Nco}**1.5**

*h*_{ef}A = 9_{Nco}h _{ef}^{2} | (17.4.2.1c) |

**, shall not exceed**

*N*_{b}(17.4.2.2a) |

where ** k_{c} = 24** for cast-in anchors and 17 for post-installed anchors.

The value of ** k_{c}** 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. ≤ h_{ef} ≤ 25 in.**,

**shall not exceed**

*N*_{b}(17.4.2.2b) |

**1.5**from three or more edges, the value of

*h*_{ef}**used for the calculation of**

*h*_{ef}**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**

*A*_{Nc}**(**and

*c*)/1.5_{a,max}**, where**

*s*/3**is the maximum spacing between anchors within the group.**

*s***ψ**, shall be calculated as

_{ec,N}(17.4.2.4) |

but **ψ _{ec,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

**for use in Eq. (17.4.2.4) and for the calculation of**

*e*'_{N}**according to Eq. (17.4.2.1b).**

*N*_{cbg}In the case where eccentric loading exists about two axes, the modification factor **ψ _{ec,N}** shall be calculated for each axis individually and the product of these factors used as

**ψ**in Eq. (17.4.2.1b).

_{ec,N}**ψ**, shall be calculated as

_{ed,N}If C ≥ 1.5_{a,min}h, then ψ_{ef}_{ed,N} = 1.0 | (17.4.2.5a) |

If C < 1.5_{a,min}h, then _{ef} | (17.4.2.5b) |

(a) **ψ**_{c,N} **= 1.25** for cast-in anchors

(b) **ψ**_{c,N} **= 1.4** for post-installed anchors, where the value of ** k_{c}** used in Eq. (17.4.2.2a) is 17

Where the value of ** k_{c}** 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

**and**

*k*_{c}**ψ**shall be based on the ACI 355.2 or ACI 355.4 product evaluation report.

_{c,N}Where the value of ** k_{c}** 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,

**ψ**shall be taken as 1.0.

_{c,N}When analysis indicates cracking at service load levels, **ψ _{c,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.

**ψ**, shall be calculated as follows using the critical distance

_{cp,N}**as defined in 17.7.6**

*c*_{ac}If C ≥ _{a,min}C, then ψ_{ac}_{cp,N} = 1.0 | (17.4.2.7a) |

If C < _{a,min}C, then _{ac} | (17.4.2.7b) |

but **ψ _{cp,N}** determined from Eq. (17.4.2.7b) shall not be taken less than

**1.5**, where the critical distance

*h*/_{ef}*c*_{ac}**is defined in 17.7.6.**

*c*_{ac}For all other cases, including cast-in anchors, **ψ _{cp,N}** shall be taken as 1.0.

**1.5**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.

*h*_{ef}**ϕ**. A strength reduction factor of 0.75 shall be used in the design of the anchor reinforcement.

*N*_{n}### Related Code Sections

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