This procedure may be used for:

1. Regular/Irregular structures (Table208-9 and 208-10) under Occupancy Categories (Table 103-1) in Seismic Zone 2 (Figure 208-3, Figure 208-4);

2. Regular structures less than 75 m in height with lateral force-resisting systems listed in Table 208-11;

3. Irregular structures less than five (5) stories or 20 m in height;

4. Structures having a flexible upper portion supported on a rigid lower portion where both portions of the structure considered separately can be classified as being regular, the average story stiffness of the lower portion is at least 10 times the average story stiffness of the upper portion and the period of the entire structure is not greater than 1.1 times the period of the upper portion considered as a separate structure fixed at the base.

DESIGN BASE SHEAR:

                         V need not exceed      

where: 

C_a : acceleration-controlled coefficient (see Table 208-7)

C_v : velocity-controlled coefficient (see Table 208-8)

I: Importance Factor (see Table 208-1)

W : Total Seismic Dead Load

R : numerical coefficient representative of the inherent overstrength and global ductility capacity of lateral-force resisting systems (see Table 208-11)

T : elastic fundamental period of the structure in the direction under consideration

Lower limits for V:

                    (for all structures)

              (additional limit for Seismic Zone 4)

OTHER FACTORS AND PARAMETERS USED TO OBTAIN THE DESIGN BASE SHEAR:

Seismic Zone Factor Z (see Table 208-3 & Table 208-4)

Near-Source Factors N_a and N_v (see Table 208-4 and Table 208-5)

Soil Profile Type (see Table 208-2)

Seismic Source Type (see Table 208-6)

Vertical Irregularities (see Table 208-9)

Horizontal Irregularities (see Table 208-10)