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.
For the underlined portion shown below, consistency between the original and edited versions may need verification.
Does initial P-Delta analysis should contain notional loads in addition to the gravity loads?
To fully account for P-Δ and P-δ one needs to run each design load combination individually as a nonlinear P-Delta analysis. These load combinations should include the notional loads. However, the larger P-Δ effect is fully accounted for in buildings with rigid or semi-rigid diaphragms by first using the gravity loads to do an initial P-Delta analysis and then do analysis for other loads as linear about it. This is because the total P at each story level does not change due to any lateral loads including any notional loads. This procedure is automatically implemented in ETABS where a constant P- Δ analysis is used to perform subsequent linear, modal and response spectrum analysis.