Code Name

Bulgarian Code for Design of Buildings Structures in Seismic Regions

Issued by

Bulgarian Academy of Science Committee of Territorial and Town System at the Council of Ministers

Revision

1949, 1957, 1961, 1964, 1987

Horizontal Base Shear

C: Importance coefficient (See Table 1)
R: Response coefficient (See Table 2)
K_c: Seismic coefficient corresponding to seismic zone map (See Fig.1)
β_i: Dynamic coefficient corresponding to the i-th vibration mode, that is given in the following formula:

T_i: Natural period of i-th vibration mode
Soil category I, II, III: See Table 3

η_ik: Distribution coefficient of the design seismic forces corresponding to the i-th vibration mode at level k, that is calculated by the following formula

X_ik, X_ij: Modal displacement amplitude of the i-th vibration mode at level k or j
Q_j: Seismic weight assigned to level j calculated by the loading coefficients (See Table 4)
n: Number of levels