Formulas: Multiplier $B_{2}$ for $P-\Delta$ Effects

Equation A-8-6

The $B_{2}$ multiplier for each story and each direction of lateral translation is calculated as follows:

B_{2}=\frac{1}{1-\frac{\alpha P_{\text {story }}}{P_{e \text { story }}}} \geq 1

where

$\alpha \quad=1.0$ (LRFD); $\alpha=1.6$ (ASD)
$P_{\text {story }}=$ total vertical load supported by the story using LRFD or ASD load combinations, as applicable, including loads in columns that are not part of the lateral force-resisting system, kips (N)
$P_{e \text { story }}=$ elastic critical buckling strength for the story in the direction of translation being considered, kips (N), determined by sidesway buckling analysis or as given in Equation A-8-7.

R_{M}=1-0.15\left(P_{m f} / P_{\text {story }}\right)