What is the cantilever method for approximate frame analysis?

The cantilever method assumes the frame acts as a vertical cantilever under lateral loads. Key assumptions: (1) inflection points at mid-height of columns and mid-span of beams, (2) axial force in columns varies linearly with distance from centroid of column areas (like stress in a cantilever cross-section). Column axial forces are found from overturning moment, then member forces from equilibrium. It's more accurate than portal method for tall, slender frames.