i (x) ) ort = Average reduced relative storey displacement on the i'th floor of the building
i (x) ) max = Maximum reduced relative storey displacement at i'th storey of the building
η bi = Torsional Irregularity Coefficient defined at i'th storey

A1 - Torsion Irregularity: The case where the Torsional Irregularity Coefficient ηbi, which expresses the ratio of the maximum relative displacement at any floor to the average relative displacement at the same direction at any floor, is greater than 1.2 for any two earthquake directions perpendicular to each other ( Figure 3.1 ).
bi = (Δ i (X) ) max / (Δ i (X) ) ort > 1.2]. The calculation of the relative storey drifts shall 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 .