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The PTI released addendum No. 1 to the 3rd Edition of Design of Post-Tensioned Slabs-on-Ground. AT THIS TIME, SLABWORKS HAS NOT BEEN UPDATED AND IS NOT COMPLIANT WITH THIS ADDENDUM. The addendum has three important changes that impact SlabWorks:

Previously the cracked section capacity was required to be equal to 90% of the uncracked section capacity. Addendum No. 1 has changed this requirement to 50% of the uncracked section capacity [SlabWorks work-around: Multiply the SlabWorks required post-cracking capacity by 0.56 to get the Addendum No. 1 required post-cracking capacity].
Previously, the contribution of the concrete to shear capacity was equal to 1.7 times SQRT(f’c). Addendum No. 1 has changed the contribution of the concrete to 2.4 time SQRT(f’c) [SlabWorks work-around: Increase the shear capacity calculated by SlabWorks by 0.7*SQRT(F’c)].
The required slab stiffness was been reduced by 33% [SlabWorks work-around: Multiply the SlabWorks required stiffness by 0.67 to get the Addendum No. 1 required stiffness].

As can been seen, all of these changes reduced strength or stiffness requirements. Thus, SlabWorks will currently provide a conservative solution for PTI slabs compared to the requirements of Addendum No. 1. I am currently modifying the program to incorporate these changes and hope to have this completed in the near future. Until this time, these modifications can be manual incorporated if you desire to design according to the Addendum No. 1 requirements.

The addendum does have many additional changes that are not directly applicable to the SlabWorks program but do impact the designer. If you design post-tensioned foundations, you should obtain and read the addendum, available at the PTI website at:

http://www.post-tensioning.org/info_technical.asp