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The City of Portland, Oregon

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24.85.050 Building Additions or Structural Alterations.

(Amended by Ordinance Nos. 178831 and 187192, effective July 17, 2015.)  An addition that is not structurally independent from an existing building shall be designed and constructed such that the entire building conforms to the seismic force resistance requirements for new buildings unless the following two conditions listed below are met.  Furthermore, structural alterations to an existing building or its structural elements shall also meet the following two conditions:

A.  The addition or structural alteration shall comply with the requirements for new buildings; and

B.  Any existing lateral load-carrying structural element whose demand-capacity ratio with the addition(s) or structural alteration(s) considered is no more than 10 percent greater than its demand-capacity ratio with the addition(s) or structural alteration(s) ignored shall be permitted to remain unaltered. For purposes of this paragraph, comparisons of demand-capacity ratios and calculation of design lateral loads, forces, and capacities shall account for the cumulative effects of additions and structural alterations since original construction.