danger
COVID-19 Risk Level for Multnomah County: High Risk

Structural Advisory Committee Meeting November 20, 2020

Public Meeting

Available Online

Agenda

  1. Welcome
  2. Discussion on Proposed Seismic Retrofit Requirements for Existing Wood Frame Buildings with R-3 Occupancies Undergoing a Change of Occupancy to R-1, R-2, B or M occupancies
  3. Continue discussion on the proposed simplified Alternate Method to Demonstrate Deformation Compatibility on URM Buildings with New Lateral System Using ASCE 41

DRAFT: Alternate Method to Demonstrate Deformation Compatibility on URM Buildings with New Lateral System Using ASCE 41

In lieu of rigorous structural analysis to demonstrate deformation compatibility between existing URM and a new lateral system for an ASCE 41 upgrade, the design professional may utilize the following methodology when seismically upgrading their building when required by Title 24.85. Note: If existing URM walls are being used to resist lateral load, this document does not apply and all provisions of ASCE 41 must be followed.

Buildings in Risk Category I or II

When the required upgrade standard per COP Title 24.85 is BPOE or BPON

  1. Provide back-up gravity support at all URM walls.
  2. Limit drift at existing URM walls to 0.7% or less under BSE-1E (as defined in Title 24.85), considering only the new lateral system and neglecting contribution of the existing URM walls.
  3. URM walls/piers shall meet ASCE 41-17 §11.3.3.3.1 for Collapse Prevention (i.e. h/t ratios) for out-of-plane action, or the wall/pier and spandrel shall be retrofitted with a back-up system for out-of-plane bracing
  4. For BPON or Tier 3 BPOE upgrades, additional check shall be done to verify URM walls/piers meet ASCE 41-17 §11.3.3 for Life Safety, or the wall/pier and spandrel shall be retrofitted with a back-up system for out-of-plane bracing

Exception: When a new lateral system is provided that resists 100% of lateral load, and out-of-plane bracing is provided at all URM walls/piers/spandrels, items 2 through 4 need not be checked.

Buildings in Risk Category III

When the required upgrade standard per COP Title 24.85 is BPOE or BPON:

  1. Provide back-up gravity support at all URM walls.
  2. Limit drift at existing URM walls to 0.7% or less under BSE-1E (as defined in Title 24.85), considering only the new lateral system and neglecting contribution of the existing URM walls.
  3. Provide out-of-plane bracing for all walls/piers/spandrels.

Buildings in Risk Category IV

No prescriptive provisions—must demonstrate deformation compatibility per ASCE 41-17 §7.2.3.3.

This criteria is subject to re-evaluation and is subject to change. (February 2020)