How ideCAD defines linear dynamic analysis for two earthquake directions according to ASCE 7-16?
Seismic load is determined automatically according to the selected Modal response spectrum analysis method.
Modal Response Spectrum Analysis
In the Modal Response spectrum analysis, mode shapes are taken as the basis for the distribution of the total earthquake force. This method evaluates the equations that give the behavior of multi-degree of freedom systems separately for each mode shape. Unlike the equivalent lateral force method, in determining the total earthquake strength, the number of vibration modes depends on the mass participation ratio, and many modes affect the behavior.
Calculation methods can be selected from the Analysis settings - general settings tab.