The seismic force to the effect on the floors for each direction is calculated automatically using Equation 12.8-11 and 12.8-12.


Symbols

Fi = The portion of the seismic base shear (V) [kip (kN)] induced at level i
Cvx = vertical distribution factor
V = total design lateral force or shear at the base of the structure [kip (kN)]
wi and wx = portion of the total effective seismic weight of the structure (W) located or assigned to level i or x;
hi and hx = height [ft (m)] from the base to level i or x; and
k = an exponent related to the structure period


The peak load is used to approximate the effect of high modes neglected in this method. The total equivalent lateral force (Base shear force) is calculated by the following equation.

The part of the total equivalent lateral force other than the peak load is automatically distributed to the building floors, including the Nth floor, by accepting the mode shape of the dominant mode as an inverted triangle.