The B₂ factor is an amplifier to account for the P-Δ effects (large P-delta, second order effects caused by relative displacement of the member ends). The B₂ factor is calculated for each rigid diaphragm, and differs for each combination. B₂ is given as:

where

α	=	1.0 for LRFD 1.6 for ASD
ΣPnt	=	total vertical load supported by story using LRFD or ASD load combinations, including gravity column loads
ΣPe2	=	the "elastic critical buckling resistance for the story"; it is permitted to use:

where

RM	=	1.0 for braced-frame systems 0.85 for moment-frame and combined systems
ΣH	=	the story/diaphragm shear (calculated per load combination)
L	=	he story height
ΔH	=	the interstory drift (calculated per load combination) and it is based on the drift at the center of diaphragm masses

The B₂ factors are found in such a way that diaphragm shear forces and story drift values are first resolved along member local system and then the B₂ factors are calculated according to Eq. (C2-3). Note that these factors are applied to the axial loads and moments from the lateral load cases.