Building Official Determination 25-02: Seismic Benchmarking

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BOD 25-02: Seismic Benchmarking

City of Portland Title 24.85, ASCE-41, OSSC Table 1604.5

QUESTION:Title 24.85 requires seismic improvements based on cumulative changes from the legal building occupancy as of October 1, 2004. If a building was built under modern codes or has completed a seismic upgrade in the past, are additional seismic improvements required?

RESPONSE:Where structural improvements to the lateral system are not required by Chapter 34 of the building code based on the scope of an alteration or addition, the following options are available. See Additional Notes at the end of this document for more information.

1. For structures built to conform to the 2004 or later edition of the Oregon Structural Specialty Code (OSSC), no further seismic upgrades are required, provided theproposed change of occupancy/use does not result in the building being assigned a higher Risk Category in OSSC Table 1604.5.  

2. For structures that have been previously seismically upgraded, and a seismic upgrade is triggered again by Title 24.85.065 applicable to unreinforced masonry buildings or by Title 24.85 due to additional changes in use or occupancy that result in more occupants or more of the building area changing to a higher relative hazard occupancy classification in Table 24.85-A, additional improvements will not be required under the following conditions.

   1. Where the required improvement standard triggered by the current alteration is ASCE 41-BPOE, additional improvements will not be required if it can be demonstrated that the previous seismic upgrades met the Life Safety performance standard at BSE-1E of the benchmark building codes listed in Table 3-2 or Table 3-3 of ASCE 41-17.

      In order to demonstrate compliance with the benchmark standards, as required by section 3.3 of ASCE 41-17, the design professional shall complete all of the following: 

      1. Review the approved drawings for previous seismic upgrades of the structure to confirm that the design was in accordance with the requirements of the applicable standards for the building type listed in Table 3-2 or Table 3-3 of ASCE 41-17. The review shall not be limited to review of the design criteria but shall be of sufficient depth to verify that the design was intended to meet all the requirements of the applicable standard.

      2. Conduct a field verification to confirm the building was constructed in general conformance with the record drawings. 

      3. Conduct a condition assessment to confirm that significant deterioration of the structural materials has not occurred. 

      4. Confirm that no geologic site hazards are present at the site or if present, hazard has been mitigated.

      The design professional shall provide a stamped letter confirming that the required investigations were conducted and that the structure meets the requirements outlined in the preceding paragraph and therefore qualifies as a Benchmark building per ASCE 41-17.

   2. Where the required improvement standard triggered by the current alteration is ASCE 41-BPON or OSSC, additional seismic improvements will not be required if all the following conditions are met: 

      1. The building was seismically upgraded to meet the requirements of the 2004 (or later) edition of the OSSC or ASCE 41-BPON standard.

      2. The proposed change of occupancy/use does not result in the building being assigned a higher Risk Category in OSSC Table 1604.5.

      3. The Design Professional shall complete all of the following: 

         1. Review the approved drawings for previous seismic upgrades of the structure to confirm that the structure and the detailing were intended to be designed to meet or exceed ASCE 41-BPON or 2004 (or later) OSSC. The review shall not be limited to review of the design criteria but shall be of sufficient depth to verify that the design was intended to meet all the requirements of the applicable standard. 

         2. Conduct a field verification to confirm the building was constructed in general conformance with the record drawings. 

         3. Conduct a condition assessment to confirm that significant deterioration of the structural materials has not occurred. 

         4. Confirm that no geologic site hazards are present at the site or if present, the hazard has been mitigated. 

         The design professional shall provide a stamped letter confirming that the required investigations were conducted and that the structure meets the requirements outlined in A-D.

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