ACI 318-02 Versus ACI 318-05 - 2 way PT Slabs

[DEL2000]

In ACI 318-02, section 18.3.3, it defines the different classifications of PT Slabs, with type U being the typical uncracked PT slab with the tension stress limit equal to 7.5 (f'c^0.5) (which is increased from the 1999 and earlier codes which put the limit at 6 (f'c^0.5)). At the bottom of that section of the code, it says that all two way slabs should be designed to Class U.

In the new ACI 318-05, they still have class U with a tension limit of 7.5, but the words at the bottom of section 18.3.3 says that all 2 way slabs should be designed as Class U with tension stresses limited to 6.

The problem I have is that I am using software that is tailored to the ACI 318-02 code, but we don't want to go to the 7.5 limit since it seems like a mistake in the 02 code. Anybody run across this code issue? Is the 02 code a mistake that has been corrected with some erratta? Or did they just rethink the tension stress limits?

 

[DEL2000]

To the top. Has anybody run across this?

 

[rapt]

DEL2000,

I was told by someone close to the ACI committee several months after the release of the 02 code that the committee had admitted they had made a mistake and there was an amendment released limiting the tension stress in 2way slabs to .6f'c^.5. I do not think I have ever actually seen a copy of the amendment.

Actually, in negative moment regions of 2way slabs this limit is still very unconservative as it does not recognise the stress concentration near the column compared to the average stress that ACI designers actually calculate.