[BS] 503A.4 Existing Structural Elements Carrying Lateral Load

Exceptions: For incidental and minor alterations:

1. Any existing lateral load-carrying structural element whose demand-capacity ratio with the alteration considered is no more than 10 percent greater than its demand-capacity ratio with the alteration ignored shall be permitted to remain unaltered. For purposes of calculating demand-capacity ratios, the demand shall consider applicable load combinations with design lateral loads or forces per California Building Code Sections 1609A and 1613A. For purposes of this exception, comparisons of demandcapacity ratios and calculation of design lateral loads, forces, and capacities shall account for the cumulative effects of additions and alterations since original construction.
2. Drift limits based on original design code shall be permitted to be used in lieu of the drift limits required by ASCE 7.