Essentially look after 3 values:
1-Squash Load = Is approximately 0.55Ac*fc
2- Pure bending Point = Calculated based on the golden ratio M/BD² (anywhere between 1.5 and 2.5) (about weak column axis)
Or by establishing Mu=0.7*d*fy*As
3- Balanced point = Roughly 1.3 of pure bending capacity
And some 0.25 of the squash load
Slenderness effects appear when the Height to column width ratio is above 10 for unbraced structures, and 12 for braced, so when the column stockey, estimated section area would be within the 0.8 of squash load (say 0.45F'c*Area)
if column is slender, then take 0.3 to 0.4 of squash load
Watch this video while on the train today (Liquid GOLD)