P-Δ effects play significant role in any building or structure,
We usually undertake P-Δ analysis in ETABS using either an iterative or non-iterative approach. The first method involves including the gravity component of the lateral load combination that results in maximum lateral sway. The second method is non-iterative, where ETABS performs the second-order analysis automatically.
For very tall buildings with a slenderness ratio greater than 5, P-Δ effects can contribute an additional sway of 5-15%, particularly if the building is not very stiff or if the mass is not well distributed (for example, when the building sets back). However, P-Δ effects generally do not impact buildings that are shear-dominated.
Australian Standard 1170.4-2007 provides recommendations as follows:
Quote from AS1170.4-2007
6.7.3 P-delta effects
6.7.3.1 Stability coefficient
For the inter-storey stability coefficient (θ) calculated for each level, design for P-delta
effects shall be as follows:
(a) For θ ≤ 0.1, P-delta effects need not be considered.
(b) For θ > 0.2, the structure is potentially unstable and shall be re-designed.
(c) For 0.1 <θ ≤0.2, P-delta effects shall be calculated as given in Clause 6.7.3.2,
θ = Storey Drift * ΣStorey Mass / (Storey Height * μ * ΣShear Load ) - See equation 6.7(2)
6.7.3.2 Calculating P-delta effects
Values of the horizontal earthquake shear forces and moments, the resulting member forces
and moments, and the storey drifts that include the P-delta effects shall be determined by-
(a) scaling the equivalent static forces and deflections by the factor (0.9/(1 -0)), which
is greater than or equal to 1; or
(b) using a second-order analysis.
End Quote