My SACS output file contains the warning message:

*** WARNING-PGU SECTION IRREGULAR. 

The section found to be modeled as below:

 

What does this message mean?

Regular PGU means the plastic or elastic centroid lies within the web. Irregular PGU means the centroid lies within the flanges. Irregular PGU section is not supported by SACS Post for code checks. Hence it prints out the warning message about the PGU section being irregular.