Description: Two new modal summation methods for response spectrum analysis are now available: the double sum combination (DSC) method and the grouping (GRP) method. The double sum combination method is the first attempt to evaluate modal correlation based on random vibration theory. The grouping method improves the response estimation for structures with closely spaced eigenvalues.

Two new directional summation methods for response spectrum analysis are now available: the 40% (R40) method and the 30% (R30) method. These methods use the rules recommended in the ASCE 4–98 standard to combine the response for all possible combinations of the three components, including variations in sign (plus/minus), assuming that when the maximum response from one component occurs, the response from the other two components is 40% (or 30%) of their maximum value.

Step module:
    StepCreate: Linear perturbation: Response spectrum; 
    Excitations: Multiple direction thirty percent rule or Multiple direction forty percent rule;
    Summations: Double sum combination or Grouping method