First adopted in 1994, Portland City Code Chapter 24.85 “Seismic Design Standards for Existing Buildings” contains requirements for upgrade to the lateral systems of existing buildings when the buildings are undergoing change of use or occupancy or are being altered. In addition, for Unreinforced Masonry Buildings (URM’s) undergoing alterations or repair, Title 24.85.065 has triggers associated with the cost of repair or alteration which, if exceeded, would require mandatory seismic strengthening.
In 2004, Title 24.85 underwent a major revision. This revised version adopted in October 2004, serves as the governing code for seismic design for existing buildings.
Based on feedback received over years of use of these provisions, the following are some common clarifications and City ofPortlandpolicies.
1) What is meant by ASCE 31 Seismic Improvement standard ?
Some provisions of Title 24.85 requires buildings be upgraded to ASCE 31 standards. This refers to a limited upgrade of buildings where deficiencies identified by an ASCE 31, Tier 2 analysis for Life Safety Performance Level criteria are required to be mitigated or upgraded. The upgrade shall meet or exceed one of the following three standards:
- The requirements of ASCE 41. When upgrading using ASCE 41, BSE-1 Earthquake hazard level with performance levels as follows shall be used. For buildings in occupancy category I and II, the performance level shall be Life Safety (LS). For buildings in occupancy category IV, the performance level shall be Immediate Occupancy ( IO). For occupancy category III, the acceptance criteria shall be halfway between acceptance criteria for category II and IV buildings. The design spectral response acceleration parameters Sxs and Sx1 specified in ASCE 41 shall not be less than 75% of the respective design spectral parameters Sds and Sd1 as defined in OSSC.
- The requirements of ASCE 31 using the detailing requirements from the latest edition of the Oregon Structural Specialty Code (OSSC)
- The requirements of the latest edition of the Oregon Structural Specialty Code (OSSC) with reduced force levels. The reduced force shall not be less than 75% of the prescribed forces in OSSC. In order to use this option the lateral system for the entire structure shall be defined and allowed by OSSC.
It is not acceptable to mix different standards when designing the upgrade. Each standard must be used in its entirety.
2) When an existing building undergoing a change of occupancy or change of use is required to be seismically upgraded due to provisions of section 24.85.040, and this change involved multiple or mixed occupancies, what seismic improvement standard is required by Title 24.85.040?
In general, the relative hazard classification ( see table 24.85-A) that corresponds to the occupancy classification with the majority of the occupants added to the building determines the seismic improvement standard required for change. However, if the change in occupancy includes areas which are changing to occupancies that are classified into hazard levels 4 and 5 in table 24.85-A of Title 24.85 and if these occupancies add more than 150 people or take up more than 33% of the net floor area then, the seismic improvement standard shall be current code as defined in Title 24.85. This is irrespective of whether these occupancies constitute a majority of the occupant load or not.
3) When Title 24.85 underwent a revision in 2004, it incorporated monetary triggers associated with the cost of repair or alteration of URM buildings which, if exceeded, would require mandatory seismic strengthening. Furthermore, these dollar figures are required to be adjusted annually. What are the current monetary triggers?
When revised in 2004, Title 24.85 established cost triggers which if exceeded would require mandatory seismic strengthening. These triggers were set at $40 per square foot for a single story URM building as $40 per square foot and $30 per square foot for two stories or greater. For URM buildings with special hazards, the limit is set at $30 per sq.ft regardless of the size. These triggers are usually adjusted annually in January each year using the RS means construction cost index.
4) Section 24.85.065(B) states “....When the cost of alteration or repair work which requires a building permit in a 2 year period exceeds the following criteria, then the building shall be improved to resist seismic forces such that the entire building conforms to the ASCE 31 improvement standard.” When does the two-year period to determine the costs of permits begin and end, and what permits need to be counted?
At the time an application is submitted for a permit (any permit) on a Unreinforced Masonry Building, the valuation of all “issued” permits from two years prior to the date of application of the current permit, including the valuation of the current permit, shall be added up to determine the total cost. These costs minus any costs allowed to be deducted per section 24.85.065B(3) shall be used to determine if any of the triggers in section 24.85.065 are exceeded. If revision permits are part of the issued permits in the two-year period described above and these revision permit valuations add to the value of the original permit, then, in addition to the valuation of the revision permit, the valuation of the original permit shall be included in the costs for the purpose of determining if any seismic triggers are exceeded.
5) Can exclusions allowed under section 24.85.060 like mechanical, electrical, plumbing work be excluded from the costs used to determine if seismic upgrade is required under section 24.85.065
No. Exclusions listed in section 24.85.060 do not apply to seismic triggers when determining if seismic strengthening of URM buildings is required under provisions of 24.85.065. Mechanical, electrical and plumbing work can not be excluded from the cost calculations. The only exclusions are listed in 24.85.065B(3). Exclusions listed in section 24.85.060 apply only to costs used to determine if a seismic evaluation of a building is required.
6) How is the valuation of the work confirmed for the purposes of determining if seismic strengthening is required by section 24.85.065(B)?
For all work in unreinforced masonry buildings that requires a permit, a cost estimate for the proposed work maybe required to confirm the valuation. The estimate must provide a detailed estimated cost for the entire scope of work proposed including cost for the work that can be excluded per section 24.85.065B (3) of Title 24.85. The final valuation will be the total value minus the excluded costs. The valuation should reflect the fair market value of all labor and material costs. At the discretion of the Bureau Director or his designee, the Bureau of Development Service may require confirmation of the estimate by an independent third party cost estimator.
If there are questions or further clarifications required, please contact AmitKumar, Sr. Engineer, Bureau of Development Services, City of Portlandvia email at firstname.lastname@example.org.