In addition to gravity load, should initial P-Delta analysis contain notional load?
Answer: To fully account for P-Δ and P-δ, each design load combination must be run as a nonlinear P-Delta analysis which includes notional load.
To fully account for P-Δ in buildings with either rigid or semi-rigid diaphragms, an initial P-Delta analysis should be performed with gravity load, then additional loads should be applied linearly. Justification is that total axial load (P) at each story level remains constant regardless of lateral and notional load. For subsequent linear, modal, and response-spectrum analyses, ETABS automatically implements this procedure when running constant P-Δ analysis.