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Small P-delta is included in frame elements, to the extent that it can be represented by a cubic curve. The frame small P-delta effect is very accurate for a single element with effective-length factor of 2 (cantilever), and moderately accurate for an effective-length factor of 1 (pinned or sway condition). When When accurate small P-delta effects are important for analysis or design of a member, it is generally recommended to auto-mesh frame objects into 2 elements, especially for axial loads close to buckling. For most other purposes, small P-delta effects as they impact the overall structure are adequately considered with a single frame object between connections.
P-Δ effect, or P-"big-delta", is associated with displacements relative to member ends. Large P-delta effect is important for overall structure behavior under significant axial load. As indicated intuitively by Figure 2, gravity loading will influence structural response under significant lateral displacement.
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