While the official PCA Notes for ACI 318-14 are typically paid publications, several related official and academic resources are available online:
The publication is designed to help users bridge the gap between the literal "letter of the law" in the ACI 318-14 code and the "spirit" or engineering philosophy behind its provisions. pca notes on aci 31814 pdf link
Some users have accessed older versions of PCA Notes (like ACI 318-11) through the PCA website by signing up for a free membership and using specific access codes. Significant Changes in ACI 318-14 While the official PCA Notes for ACI 318-14
Requirements are now organized by member type (e.g., Chapter 9 for Beams, Chapter 10 for Columns) rather than by legal or material requirement. Chapter 9 for Beams