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C_s = The seismic response coefficient
W = The effective seismic weight
S_DS = The design spectral response acceleration parameter in the short period range
R = The response modification factor in Table 12.2-1
I_e = The Importance Factor
S_D1 = the design spectral response acceleration parameter at a period of 1.0 s
T = The fundamental period of the structure(s)
T_L = The long-period transition period(s)
S₁ = The mapped maximum considered earthquake spectral response acceleration parameter
N = Number of stories above the base
C_q =0.0019 ft (0.00058 m)
A_B = area of base of structure [ft² (m²)];
A_i = web area of shear wall i [ft² (m²)];
D_i = length of shear-wall i [ft (m)]; and
x = number of shear walls in the building effective in resisting lateral forces in the direction under consideration.
F_i = The portion of the seismic base shear (V) [kip (kN)] induced at level i
C_vx = vertical distribution factor
V = total design lateral force or shear at the base of the structure [kip (kN)];
w_i and w_x = portion of the total effective seismic weight of the structure (W) located or assigned to level i or x;
h_i and h_{x= height [ft (m)] from the base to level i or x; and
k = an exponent related to the structure period}

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The equivalent Lateral Force Method is based on the principle that the dynamic behavior of the building in the direction of the earthquake considered in buildings with low height is represented by the behavior of the structural system in the dominant vibration mode, and the shape of this mode is considered as an approximately inverted triangle. The Equivalent Lateral Force Method is only used to determine structural irregularities.

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The fundamental period, T, does not exceed the product of the coefficient for the upper limit on the calculated period (C_u) from Table 12.8-1, and the approximate fundamental period, T_a, is determined in accordance with ASCE 7-16 Section 12.8.2.1.

Approximate Fundamental Period

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