h i = height of the i'th storey
Δ i (x) = (X) for any column or wall in the earthquake direction, reduced relative storey drift expressing the displacement difference between two consecutive floors
η ki = Stiffness Irregularity Coefficient defined at the i'th storey

B2 - Stiffness Irregularity Between Neighboring Stories (Soft Stories): For any of two earthquake directions perpendicular to each other, except for basement floors, the average relative storey drift ratio in any i'th storey is divided by the average relative storey drift ratio in the upper or lower storey. Stiffness Irregularity Coefficient η ki is greater than 2.0.
η ki = (Δ i (X) / h i ) ort / (Δ i + 1 (X) / h i + 1 ) ort > 2.0 or
η ki = (Δ i (X) / h i ) ort / (Δi-1 (X) / h i-1 ) ort > 2.0
The calculation of the relative storey displacements will be made according to 4.7 , taking into account the effects of ± 5% additional eccentricity . - A1 and B2 type irregularities are the irregularities that are effective in the selection of the earthquake calculation method according to 4.6 .