1613.3.5.1 Alternative seismic design category determination.
BC § 1613.3.5.1
The seismic design category is permitted to be determined from Table 11.6-1 of ASCE 7 alone, except for Risk Category IV structures for which Table 1613.3.5 of this code shall be used, when all of the following apply: 1. In each of the two orthogonal directions, the approximate fundamental period of the structure, T a , in each of the two orthogonal directions determined in accordance with Section 12.8.2.1 of ASCE 7, is less than 0.8 T s determined in accordance with Section 111.4.6 of ASCE 7.
2.In each of the two orthogonal directions, the fundamental period of the structure used to calculate the story drift is less than T s .
3.Equation 12.8-2 of ASCE 7 is used to determine the seismic response coefficient, C s .
4.The diaphragms are rigid or are permitted to be idealized as rigid in accordance with Section 12.3.1 of ASCE 7 or, for diaphragms permitted to be idealized as flexible in accordance with Section 12.3.1 of ASCE 7, the distances between vertical elements of the seismic force-resisting system do not exceed 40 feet (12 192 mm).
