I am analyzing a tower of 16 levels using a spectral dynamic analysis, I read about the correction of missing mass and I understand the theory, my question is, how it integrates the analysis and to what extent it is valid to consider this?, I have obtained 90% participation by the flexible modes. I am considering 300 modes vibrate but the base shear resulting in the analysis is a very low shear, I've added the command "MIS" with value 0, which according to theory this adds the shear corresponding to the modes below 33 hrz (rigid modes). add this to my base shear increases significantly, about 30%, this consideration is correct? or should I reach the value of shear that tell me the code design without considering the missing mass?.
there is significant variation in the values of the mechanical elements (moments and shears), I knowing this application of this tool, so I ask for help, to know what might be the appropriate guide for proper interpretation.