4.8.1. Modal Calculation Methods - the modal behavior of the structural system under seismic action based Modal Analysis Methods , 4.8.2 from the computational with the seismic spectrum combine mode method and 4.8.3 'in the account in the time domain based mode summation method ' is. Detailed explanations for these methods are given in ANNEX 4B . In buildings with and without basement, 3.3.1 will be used for the definition of building base and building height . - In modal calculation methods, sufficient number of vibration modes to be taken into account , YM, 

(a) According to Annex 4B , the base shear force calculated for each mode in earthquake directions (X) and (Y) shall be determined according to the rule that the sum of the modal effective masses is not less than 95% of the total building mass .                                              

However, all modes with a contribution greater than 3% will be considered.

(b)  The largest of the YMs calculated for both directions will be taken into account in the three dimensional calculation.