For use in Equation 2-4, the value of T shall be calculated using one of the following methods:
Method 1. The value of T may be taken to be equal to the approximate fundamental period of the building (Ta) determined as follows:
- As an alternate for concrete and steel moment-resisting-frame buildings of 12 stories or fewer with a minimum story height of 10 feet, the equation Ta = 0.10N, where N = the number of stories, may be used in lieu of Equation 2-6a.
Method 2. The fundamental period T may be estimated using the structural properties and deformational characteristics of the resisting elements in a properly substantiated analysis. This requirement may be satisfied by using the following equation:
The values of fi represent any lateral force, associated with weights wi, distributed approximately in accordance with the principles of Equations 2-8, 2-9 and 2-10 or any other rational distribution. The elastic deflections, di, should be calculated using the applied lateral forces, fi. The period used for computation of Cs shall not exceed CaTa, where Ca is given in Table 220.127.116.11.