Maximum SDS Value in the Determination of Cs and Ev

ASCE 12.8.1.3 allows you to limit the value of the short-term design response parameter S_DS to 1.0 under a number of conditions, one of which is that the structure has no irregularities at all. This limitation applies only to the use of S_DS in

• calculation of seismic response coefficient C_S in Eqn. 12.8-2 and its lower limit in 12.8-3, which are used to calculate base shear V
• calculation of vertical earthquake force E_v in Eqn. 12.4-4a

The limit is not applied to the use of S_DS for

• determination of Seismic Design Category (11.6)
• min. and max. diaphragm design forces (12.10.1.1)
• wall out-of-plane (12.11.1) and anchorage (12.11.2) forces
• calculation of T_S for the exception to the use of site-specific ground motion analysis for Site Class D (11.4.8).

If rigid diaphragm design is set to be performed, if any irregularity is entered in the Site Dialog, the limit on S_DS is suppressed. If only flexible diaphragm design is set, it is suppressed for any irregularity except horizontal Torsional Irregularities 1a and 1b. If upon design the program detects irregularities that were not set in the site dialog, the program warns you about it. If a limit was suppressed only because of torsional irregularities, it suggests you do load generation and design for rigid and flexible diaphragms separately.