Mode Addition Method in Time Domain

4.8.3. Earthquake Calculation with Mode Addition Method in Time Domain

4.8.3.1 - In the Mode Addition Method , if it is taken into consideration that the earthquake acts simultaneously in two horizontal directions perpendicular to each other, the modal behavior magnitudes of each vibration mode are calculated by the modal calculation method in the time domain . Simultaneous modal behavior magnitudes calculated for sufficient vibration modes are then collected directly in the time history area , and the maximum values ​​of the behavior magnitudes are obtained based on time and design . Details of the method are given in ANNEX 4B . 

4.8.3.2 - In the Adding Mode Method : 

(a) Since the   modal contributions are directly accumulated in the time history, there is no need to apply statistical modal combination rules.

(b) Since   horizontal ground motion components perpendicular to each other can be taken into account at the same time, it is not necessary to apply the approximate direction joining rules defined in 4.4.2 .