Seismic base shear for each direction is calculated automatically according to Equation 12.8-1.
Cs = The seismic response coefficient
W = The effective seismic weight
SDS = The design spectral response acceleration parameter in the short period range
R = The response modification factor in Table 12.2-1
Ie = The Importance Factor
SD1 = the design spectral response acceleration parameter at a period of 1.0 s
T = The fundamental period of the structure(s)
TL = The long-period transition period(s)
S1 = The mapped maximum considered earthquake spectral response acceleration parameter
Equivalent Lateral Force Method considered in buildings with low height can be represented by the behavior of the load-bearing system in the dominant vibration mode and the shape of this mode can be considered as approximately the inverted triangle. Also, the procedure is valid only for structures without significant discontinuities in mass and stiffness along the height, where the dominant response to ground motions is in the horizontal direction without significant torsion.
The base shear force is calculated by the above equation. The mass and Cs used in this calculation and the base shear force determined as a result of the calculation are tabulated in the Dynamic Analysis report.