(a) Deflections due to service-level gravity loads (24.2)
(c) Shrinkage and temperature reinforcement (24.4)
(d) Permissible stresses in prestressed flexural members (24.5)
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 Lr, S, and R||ℓ/180|
|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||ℓ/480|
|Not likely to be damaged by large deflections||ℓ/240|
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.
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.
Limit shall be permitted to be exceeded if measures are taken to prevent damage to supported or attached elements.
Limit shall not exceed tolerance provided for nonstructural elements.
where Mcr is calculated by
|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:|
|Reinforcement type||fy, psi||Minimum reinforcement ratio|
|Deformed bars||< 60,000||0.0020|
|Deformed bars or welded wire reinforcement||≥ 60,000||Greater of:|
(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
Table 220.127.116.11—Classification of prestressed flexural members based on ft
|Assumed behavior||Class||Limits of ft|
|Transition between uncracked and cracked||T|
Prestressed two-way slabs shall be designed as Class U with .
|Location||Concrete compressive stress limits|
|End of simply-supported members||0.70fci'|
|All other locations||0.60fci'|
|Location||Concrete tensile stress limits|
|Ends of simply-supported members|
|All other locations|
|Load condition||Concrete compressive stress limits|
|Prestress plus sustained load||0.45fc'|
|Prestress plus total load||0.60fc'|