Torsion Irregularity Coefficient, which expresses the ratio of the maximum relative displacement at any story to the average relative displacement in the same direction at that story for any of the two earthquake directions perpendicular to each other, is automatically controlled.

The calculation of the relative story drifts is made automatically according to equivalent lateral force method, taking into account the effects of 5% additional eccentricity.


Δavg = Average reduced relative storey displacement on i'th floor of the building
Δmax = Maximum reduced relative storey displacement on i'th storey of the building
Δmin = Minimum reduced relative storey displacement on i'th storey of the building

1a - Torsion Irregularity

This type of irregularity affects the Selection of Linear Calculation Method described in Section 12.6 of ASCE 7-16. However, ideCAD Static have already used Linear Dynamic Analysis (Modal response analysis and modal superposition method in time domain) specified in Section 12.9.

1b. Extreme torsional irregularity

Extreme torsional irregularity requirements in the reference sections apply only to structures in which the diaphragms are rigid or semirigid.

According to Table 12.3-1, the calculation of the relative storey drifts is made according to the Equivalent Earthquake Load Method, taking into account the + - 5% eccentricity effects. While linear dynamic analysis are used in the earthquake calculation of the building, Equivalent Earthquake Load Method is used in1a and 1b type irregularity control.