RAM Connection - Column Splice Moment Connection (Flange-plated) & Single Shear Plate

AISC 360 says that the full area (of the top, smaller column) is in bearing, so we prorate the flange force based on that. Note, it's actually less conservative the way you wrote above; 180 -150 is only 30 kips

Thank you for the explanation! I now understand where the number is coming from. But why isn't the program calculating the demand flange force using the below equation?

Demand Flange Force = (Pu/2)+(Mu/moment arm between flange forces)

This calculates a more conservative flange force to compare the capacity to.

The program is coming up with the tensile flange force. In your case:

Moment: 150 kft * 12 = 1,800 k-in / 10 " (distance btw flanges) = 180 kips tension/compression per flange due to moment

Axial: 300 k * flange area/total area = 300 k * 37% = 111 kips (compression)

Max tension = 180 - 111 = 69 kips. 

For compression the section is assumed to bear directly as indicated in the AISC Spec.

Shear is entirely resisted by the other part of the joint.