// CODE SNIPPET

# 22.9 Shear Friction

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The required area of shear-friction reinforcement across the assumed shear plane,

**, shall be calculated in accordance with 22.9.4. Alternatively, it shall be permitted to use shear transfer design methods that result in prediction of strength in substantial agreement with results of comprehensive tests.***A*_{vf}The value of

**used to calculate***f*_{y}**for shear friction shall not exceed the limit in 20.2.2.4.***V*_{n}Surface preparation of the shear plane assumed for design shall be specified in the construction documents.

Factored forces across the assumed shear plane shall be calculated in accordance with the factored load combinations defined in Chapter 5 and analysis procedures defined in Chapter 6.

Design shear strength across the assumed shear plane shall satisfy:

ϕV ≥ _{n}V_{u} | (22.9.3.1) |

for each applicable factored load combination.

If shear-friction reinforcement is perpendicular to the shear plane, nominal shear strength across the assumed shear plane shall be calculated by:

V _{n}= µA _{vf}f_{y} | (22.9.4.2) |

where *A _{vf}* is the area of reinforcement crossing the assumed shear plane to resist shear, and µ is the coefficient of friction in accordance with Table 22.9.4.2.

**Table 22.9.4.2—Coefficients of friction**

Contact surface condition | Coefficient of friction µ^{[1]} | |
---|---|---|

Concrete placed monolithically | 1.4λ | (a) |

Concrete placed against hardened concrete that is clean, free of laitance, and intentionally roughened to a full amplitude of approximately 1/4 in. | 1.0λ | (b) |

Concrete placed against hardened concrete that is clean, free of laitance, and not intentionally roughened | 0.6λ | (c) |

Concrete placed against as-rolled structural steel that is clean, free of paint, and with shear transferred across the contact surface by headed studs or by welded deformed bars or wires. | 0.7λ | (d) |

^{[1]}λ = 1.0 for normalweight concrete; λ = 0.75 for all lightweight concrete. Otherwise, λ is calculated based on volumetric proportions of lightweight and normalweight aggregate as given in 19.2.4, but shall not exceed 0.85.

If shear-friction reinforcement is inclined to the shear plane and the shear force induces tension in the shear-friction reinforcement, nominal shear strength across the assumed shear plane shall be calculated by:

V _{n}= A(µsinα _{vf}f_{y}+ cosα) | (22.9.4.3) |

where **α** is the angle between shear-friction reinforcement and assumed shear plane, and µ is the coefficient of friction in accordance with Table 22.9.4.2.

The value of

**across the assumed shear plane shall not exceed the limits in Table 22.9.4.4. Where concretes of different strengths are cast against each other, the lesser value of***V*_{n}**shall be used in Table 22.9.4.4.***f*'_{c}**Table 22.9.4.4—Maximum V_{n} across the assumed shear plane**

Condition | Maximum V_{n} | ||
---|---|---|---|

Normalweight concrete placed monolithically or placed against hardened concrete intentionally roughened to a full amplitude of approximately 1/4 in. | Least of (a), (b), and (c) | 0.2f'_{c}A_{c} | (a) |

(480 + 0.08f')_{c}A_{c} | (b) | ||

1600A_{c} | (c) | ||

Other cases | Lesser of (d) and (e) | 0.2f'_{c}A_{c} | (d) |

800A_{c} | (e) |

Permanent net compression across the shear plane shall be permitted to be added to

**, the force in the shear-friction reinforcement, to calculate required***A*_{vf}f_{y}**.***A*_{vf}Area of reinforcement required to resist a net factored tension across an assumed shear plane shall be added to the area of reinforcement required for shear friction crossing the assumed shear plane.

Reinforcement crossing the shear plane to satisfy 22.9.4 shall be anchored to develop

**on both sides of the shear plane.***f*_{y}### Related Code Sections

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