Basis of ACI Reduction Factors (phi) for columns

[Pororo]

Hello! I am currently generating the P-M interaction diagram of a confined concrete column using Mander's model for confined concrete, Hognestad's model for unconfined concrete, and Priestley's model for steel. The problem is, when generating my ϕP-ϕM diagram, the trend deviates from the original trend of the P-M diagram (without the reduction factors).

My question now is what are the basis of ACI in using 0.002 and 0.005 as the limits for compression and tension controlled regions.

Thank you!

 

[dik]

The change in material reduction reduction factors reflects the proportion of M to P, which have different phi factors.

Dik