Equivalent earthquake force procedure; it is used to control irregularities as indicated in Table 12.3-1 and 12.3-2.

Seismic calculation is done automatically with the Modal Response Spectrum Analysis.

Seismic loads acting on buildings; the floor level, which is assumed to accumulate the story masses, is accepted as the horizontal load acting on the floors. Seismic effects determined for two perpendicular directions are combined as specified in the regulation. The total equivalent lateral force is known as the base shear force and is used in the earthquake resistant design of structures.

The equivalent lateral force method is a method that takes into account only the effect of the 1st mode. For this reason, there are limitations in using the method.