[BS] 503A.4 Existing Structural Elements Carrying Lateral Load
Except as permitted by Section 503A.13, where the alteration increases design lateral loads in accordance with California Building Code Section 1609A or 1613A, or where the alteration results in a prohibited structural irregularity as defined in the California Building Code, or where the alteration decreases the capacity of any existing lateral load-carrying structural element, the structure of the altered building or structure shall be shown to meet the requirements of California Building Code Sections 1609A and 1613A.
Exceptions: For incidental and minor alterations:
- 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.
- Drift limits based on original design code shall be permitted to be used in lieu of the drift limits required by ASCE 7.