Spectral response analysis procedure

For each spectral load case, the analysis procedure is as follows:

1. Calculates the mass participation factor (MPF) for each mode in each global axis direction and the vector direction.
   
2. Determines the dominant mode for each direction based on the largest MPFs.
   
3. Calculates the excitation factor for each direction.
   
4. Gets the acceleration for each mode based on its period and the spectral curve being used.
   
5. Calculates the code-specific spectral curve multiplying factor and scales the accelerations accordingly.
   
6. Calculates the total static force in each direction based on the mass and the scaled accelerations.
   
7. Calculates the amplitude factor for each mode based on its frequency and the scaled accelerations.
   
8. Calculates the deflections for each mode by multiplying each mode shape by the amplitude factor and the user scaling factor.
   
9. Calculates the element forces, moments and reactions for each mode based on the deflections.
   
10. Calculates the reactions and sum of reactions for each mode based on the residual forces and moments.
    
11. Combines the deflections, forces, moments and reactions for all the modes using SRSS or CQC.
    
12. Combines the sums of reactions for all the modes using SRSS or CQC to give a total reaction in each direction. These total reactions are taken as the base shear in each direction and are used to scale the results if horizontal base shear scaling is turned on. They are also reported in the "Reac" line at the end of the reactions report.
    
    Note that because of the SRSS or CQC mode combination step, the sum of the individual reactions shown in the reactions report will rarely be equal to the total reactions shown in the "Reac" line at the end of the reactions report.
    
13. Applies base shear scaling if the total reaction in the vector direction is less than the total static force or user defined percentage of the total mass. The base shear scaling is applied equally to all deflections, forces, moments and reactions.
    
14. Saves the results and then moves onto the next spectral load case.
    

For a detailed explanation of the dynamic spectral response analysis results, refer to "Spectral response analysis results".