(a) Deflections due to service-level gravity loads (24.2)

(b) Distribution of flexural reinforcement in one-way slabs and beams to control cracking (24.3)

(c) Shrinkage and temperature reinforcement (24.4)

(d) Permissible stresses in prestressed flexural members (24.5)

- Beams ......................................30
- One-way slabs .........................40
- Two-way floor slabs ................40
- Two-way roof slabs .................44

These ratios should be decreased for special conditions such as heavy loads and simple spans.

Maximum deflection criteria shall be in accordance with ACI 318 Section 24.2.2.

**Table 24.2.2—Maximum permissible calculated deflections**

Member | Condition | Deflection to be considered | Deflection limitation | |
---|---|---|---|---|

Flat roofs | Not supporting or attached to nonstructural elements likely to be damaged by large deflections | Immediate deflection due to maximum of L, _{r}S, and R | ℓ/180^{[1]} | |

Floors | Immediate deflection due to L | ℓ/360 | ||

Roof or floors | Supporting or attached to nonstructural elements | Likely to be damaged by large deflections | That part of the total deflection occurring after attachment of nonstructural elements, which is the sum of the time-dependent deflection due to all sustained loads and the immediate deflection due to any additional live load^{[2]} | ℓ/480^{[3]} |

Not likely to be damaged by large deflections | ℓ/240^{[4]} |

^{[1]}Limit not intended to safeguard against ponding. Ponding shall be checked by calculations of deflection, including added deflections due to ponded water, and considering time-dependent effects of sustained loads, camber, construction tolerances, and reliability of provisions for drainage.

^{[2]}Time-dependent deflection shall be calculated in accordance with 24.2.4, but shall be permitted to be reduced by amount of deflection calculated to occur before attachment of nonstructural elements. This amount shall be calculated on basis of accepted engineering data relating to time-deflection characteristics of members similar to those being considered.

^{[3]}Limit shall be permitted to be exceeded if measures are taken to prevent damage to supported or attached elements.

^{[4]}Limit shall not exceed tolerance provided for nonstructural elements.

**, shall be calculated by Eq. (24.2.3.5a) unless obtained by a more comprehensive analysis, but**

*I*_{e}**shall not be greater than**

*I*_{e}**.**

*I*_{g}(24.2.3.5a) |

where ** M_{cr}** is calculated by

(24.2.3.5b) |

**in accordance with Eq. (24.2.3.5a), where**

*I*_{e}**is calculated as:**

*M*_{cr}(24.2.3.9) |

**λ**

_{Δ}(24.2.4.1.1) |

**ρ'**shall be calculated at midspan for simple and continuous spans, and at the support for cantilevers.

**ξ**, shall be in accordance with Table 24.2.4.1.3.

**Table 24.2.4.1.3—Time-dependent factor for sustained loads**

Sustained load duration, months | Time-dependent factor ξ |
---|---|

3 | 1.0 |

6 | 1.2 |

12 | 1.4 |

60 or more | 2.0 |

**is the least distance from surface of deformed or prestressed reinforcement to the tension face. Calculated stress in deformed reinforcement,**

*c*_{c}**, and calculated change in stress in bonded prestressed reinforcement,**

*f*_{s}**Δ**, shall be in accordance with 24.3.2.1 and 24.3.2.2, respectively.

*f*_{ps}**Table 24.3.2—Maximum spacing of bonded reinforcement in nonprestressed and Class C prestressed one-way slabs and beams**

Reinforcement type | Maximum spacing s | |
---|---|---|

Deformed bars or wires | Lesser of: | |

Bonded prestressed reinforcement | Lesser of: | |

Combined deformed bars or wires and bonded prestressed reinforcement | Lesser of: | |

**in deformed reinforcement closest to the tension face at service loads shall be calculated based on the unfactored moment, or it shall be permitted to take**

*f*_{s}**as**

*f*_{s}**(2/3)**.

*f*_{y}**Δ**, in bonded prestressed reinforcement at service loads shall be equal to the calculated stress based on a cracked section analysis minus the decompression stress

*f*_{ps}**. It shall be permitted to take**

*f*_{dc}**equal to the effective stress in the prestressed reinforcement**

*f*_{dc}**. The value of**

*f*_{se}**Δ**shall not exceed 36,000 psi. If

*f*_{ps}**Δ**does not exceed 20,000 psi, the spacing limits in Table 24.3.2 need not be satisfied.

*f*_{ps}**determined in accordance with Table 24.3.2.**

*s***. If the effective flange width exceeds**

*ℓ*/10_{n}**, additional bonded longitudinal reinforcement shall be provided in the outer portions of the flange.**

*ℓ*/10_{n}**shall be considered in accordance with 5.3.6.**

*T***Table 24.4.3.2—Minimum ratios of deformed shrinkage and temperature reinforcement area to gross concrete area**

Reinforcement type | f, psi_{y} | Minimum reinforcement ratio | |
---|---|---|---|

Deformed bars | < 60,000 | 0.0020 | |

Deformed bars or welded wire reinforcement | ≥ 60,000 | Greater of: | |

0.0014 |

**5**and 18 in.

*h***in tension.**

*f*_{y}(a) Precast members are not wider than 12 ft

(b) Precast members are not mechanically connected to cause restraint in the transverse direction

(c) Reinforcement is not required to resist transverse flexural stresses

(a) Strains vary linearly with distance from neutral axis in accordance with 22.2.1.

(b) At cracked sections, concrete resists no tension.

**in the precompressed tension zone calculated at service loads assuming an uncracked section.**

*f*_{t}**Table 24.5.2.1—Classification of prestressed flexural members based on f_{t}**

Assumed behavior | Class | Limits of f_{t} |
---|---|---|

Uncracked | U^{[1]} | |

Transition between uncracked and cracked | T | |

Cracked | C |

^{[1]}Prestressed two-way slabs shall be designed as Class U with *.*

**Table 24.5.3.1—Concrete compressive stress limits immediately after transfer of prestress**

Location | Concrete compressive stress limits |
---|---|

End of simply-supported members | 0.70f'_{ci} |

All other locations | 0.60f'_{ci} |

**Table 24.5.3.2—Concrete tensile stress limits immediately after transfer of prestress, without additional bonded reinforcement in tension zone**

Location | Concrete tensile stress limits |
---|---|

Ends of simply-supported members | |

All other locations |

**Table 24.5.4.1—Concrete compressive stress limits at service loads**

Load condition | Concrete compressive stress limits |
---|---|

Prestress plus sustained load | 0.45f'_{c} |

Prestress plus total load | 0.60f'_{c} |