Torsional Irregularities per ASCE 7-16 with ideCAD
How does ideCAD control the torsional Irregularities, according to ASCE 7-16, for two earthquake directions?
The 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 relative story drifts are calculated automatically according to the equivalent lateral force method, considering the effects of 5% additional eccentricity.
SYMBOLS
Δavg = Average reduced relative story displacement on i'th floor of the building
Δmax = Maximum reduced relative story displacement on i'th story of the building
Δmin = Minimum reduced relative story displacement on i'th story of the building
1a - Torsion Irregularity
The case where the Torsional Irregularity Factor, which is defined for any of the two orthogonal earthquake directions as the ratio of the maximum story drift at any story to the average relative story drifts at the same story in the same direction, is greater than 1.2. Maximum story drift, computed including accidental torsion with Ax =1.0. Torsional irregularity requirements in the reference sections apply only to structures in which the diaphragms are rigid or semirigid.
This type of irregularity affects the Selection of Linear Calculation Method described in Section 12.6 of ASCE 7-16. However, ideCAD Static has already used Linear Dynamic Analysis (Modal response analysis and modal superposition method in time domain) specified in Section 12.9.
1b. Extreme torsional irregularity
The case where the Torsional Irregularity Factor, which is defined for any of the two orthogonal earthquake directions as the ratio of the maximum story drift at any story to the average relative story drifts at the same story in the same direction, is greater than 1.2. Maximum story drift, computed including accidental torsion with Ax =1.0.
Extreme torsional irregularity requirements in the reference sections apply only to structures where the diaphragms are rigid or semirigid.
According to Table 12.3-1, the relative story drifts are calculated according to the Equivalent Earthquake Load Method, considering the + - 5% eccentricity effects. While linear dynamic analysis is used in the earthquake calculation of the building, Equivalent Earthquake Load Method is used in 1a and 1b type irregularity control.
