P-Delta analysis including stress stiffening effect of the KG matrix. With this option the global stiffness is adjusted with every iteration.

A regular STAAD.Pro P-Delta Analysis performs a first order linear analysis and obtains a set of joint forces from member/plates based on the large P-Delta effect.  These forces are added to the original load vector.  A second analysis is then performed on this updated load vector (5 to 10 iterations will usually be sufficient).

In the new P-Delta KG Analysis, that is, with the Kg option selected, the effect of the axial stress after the first analysis is used to modify the stiffness of the member/plates.  A second analysis is then performed using the original load vector.  Large & small P-Delta effects are always included (1 or 2 iterations will usually be sufficient).

Select this option to include both P-small and large Delta effects (recommended), sometimes referred to as P-δ & P-Δ. Leave this box uncheck to only include the "PlargeDelta" effects (P-Δ only).

Without the Small Delta option (i.e., a default STAAD.Pro P-Delta analysis), STAAD.Pro performs a first order linear analysis and obtains a set of joint forces, from members/plates based on the large P-Delta effect, which are then added to the original load vector. A second analysis is then performed on this updated load vector.

With the Small Delta option selected, both the large & small P-Delta effects are included in calculating the end forces, (5 to 10 iterations will usually be sufficient).