Seismic Considerations Seminar | Portland, Oregon

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In this presentation you will learn about:
Past Earthquakes that have Affected Oregon
Oregon Structural Specialty Code History (OSSC)
City of Portland Seismic Code Requirements - Title 24.85
Seismic Upgrade Triggers and Evaluations

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Seismic Considerations Seminar | Portland, Oregon

  1. 1. Seismic Upgrades Designing Structures to Withstand Earthquakes April 16, 2014
  2. 2. SERVICES & EXPERTISE • Project Management • Structural & Seismic Design • Structural Modeling (BIM) • Construction Engineering • Structural & Seismic Evaluations • Seismic Retrofits • Peer Reviews • Value Engineering • Planning / Feasibility Studies Seismic Considerations Series 2
  3. 3. Earthquakes Affecting Oregon Date Location Magnitude (1) Damage (2) 1700 Coastal Oregon ±9 1949 Olympia 7.1 Minor 1962 Portland 5.5 Minor 1964 Alaska 9.2 Tsunami 1996 Scotts Mills 5.6 Minor 2001 Tacoma 6.8 Negligible Notes: (1) Moment Magnitude (2) Damage relative to Oregon Seismic Considerations Series 3
  4. 4. Earthquakes Affecting Oregon Seismic Considerations Series 4 Last 12 months >M2.5
  5. 5. of Seismic Design in Oregon History Seismic Considerations Series 5
  6. 6. Oregon Structural Specialty Code History • 1956 City of Portland Adopts the 1955 UBC • 1974 State of Oregon Adopts the 1973 UBC • 1995 Portland City Council Adopts, Interim Seismic Requirements • 2004 Interim Seismic Requirements incorporated in the City of Portland Title 24.85 • 2010 State Adopts the 2009 IBC – Current Code • July 1, 2014 State Scheduled to adopt the 2012 IBC Seismic Considerations Series 6
  7. 7. 1958 UBC • Western Oregon 1. Zone 2 • Eastern Oregon 1. Zone 1 • Lateral Bracing - Appendix F = C W Where, C = 0.15 / N + 4½ For locations in Zone 2, “C” shall be doubled Seismic Considerations Series 7
  8. 8. 1970 UBC • NW Oregon 1. Zone 2 • SW Oregon 1. Zone 1 • Eastern Oregon 1. Zone 1 • Base Shear V = Z K C W Where, Z = ½ C = 0.05 / ∛T Seismic Considerations Series 8
  9. 9. 1976 UBC • ALL of Oregon 1. Zone 2 • Base Shear V = Z I K C S W Where, Z = ⅜ C S ≤ 0.14 C = 1 / 15 √T Seismic Considerations Series 9
  10. 10. 1988 UBC • ALL of Oregon 1. Zone 2B • Base Shear V = (Z I C / Rw) W Where, Z = 0.2 (Zone 2B) C = 1.25 S / T2/3 Seismic Considerations Series 10
  11. 11. 1991 UBC • Western Oregon 1. Zone 3 • Eastern Oregon 1. Zone 2B • Base Shear V = (Z I C / Rw) W Where, Z = 0.3 (Zone 3) C = 1.25 S / T2/3 Seismic Considerations Series 11
  12. 12. 1997 UBC • Western Oregon 1. Zone 3 • SW Coastal 1. Zone 4 • Eastern Oregon 1. Zone 2B • Base Shear V = (Cv I / R T) W Not exceeding V = (2.5 Ca I / R) W Where, Z = 0.3 (Zone 3) Cv = Ca = 0.3 (SB) Seismic Considerations Series 12
  13. 13. Increasing Base Shear Seismic Considerations Series Page 13 2x 3.5x
  14. 14. 2003 IBC 0.2 Sec Accelerations 1.0 Sec Accelerations Seismic Considerations Series 14
  15. 15. 2003 IBC 1997 USGS MAP VALUES Seismic Considerations Series 15
  16. 16. 2009 IBC 16Seismic Considerations Series SS = 0.987 g S1 = 0.347 g Max per City Code SS = 1.0 g S1 = 0.36 g
  17. 17. Seismic Considerations Series Page 17 Where Did Seismic Zones Go?
  18. 18. City of Portland Code Requirements Existing Buildings Seismic Considerations Series 18
  19. 19. Existing Buildings 19Seismic Considerations Series Seismic Strengthening of Existing Buildings
  20. 20. Existing Buildings • When are seismic evaluations required; and • What triggers when seismic strengthening needs to occur. 20Seismic Considerations Series
  21. 21. Local Design Requirements • Oregon Structural Specialty Code. • Chapter 34 Existing Structures • ASCE 41-06 “Seismic Rehabilitation of Existing Buildings” • Existing buildings within city limits fall under chapter 24.85 of Title 24 “Building Regulations, Seismic Design Requirements for Existing Buildings” • ASCE 31-03 “Seismic Evaluation of Existing Buildings” • (ASCE 41-13 “Seismic Evaluation and Retrofit of Existing Buildings”) Seismic Considerations Series 21
  22. 22. City of Portland Code Requirements (Title 24.85) • Public Safety; • Owners planning to modify their existing buildings; and • Purchasers of a building need to understand the possible costs. Seismic Considerations Series 22
  23. 23. Seismic Triggers • Permitted Work Threshold • Seismic Evaluation • Change of Use or Occupancy Classification • 1/3 or more of the floor area • 150 person occupant load increase Seismic Considerations Series 23
  24. 24. Required Seismic Evaluation • Intended for the oldest and highest-risk buildings in Portland; • For buildings permitted by the City prior to 1974 with renovations exceeding $243,000; Seismic Considerations Series 24
  25. 25. Required Seismic Evaluation • All trigger costs are updated annually; • Certain costs are excluded from building renovation totals, including: MEP, Equipment, Painting, Fire Protection, Site improvements, and Eco-roofs. Seismic Considerations Series 25
  26. 26. Seismic Upgrade Triggers Seismic Strengthening Seismic Considerations Series 26
  27. 27. Seismic Upgrade Triggers • Change of Use or Occupancy that may require a higher hazard level. • Additions or Modifications must be in compliance with current code. • Special URM Building Requirements Seismic Considerations Series 27
  28. 28. Seismic Strengthening Seismic Considerations Series • Seismic Upgrade Triggers 1. OSSC Chapter 34 –Current Code Upgrade 2. Title 24.85 Triggers –ASCE 31 (or ASCE 41 / OSSC) • Voluntary Seismic Upgrade 1. Identify standard basis 28
  29. 29. Required Seismic Upgrades • URM buildings will require seismic upgrades for: • Roof repair or replacement of 50% or more over a 5 year period; or • When cost of work, requiring a building permit, exceed $41.63 per ft2 for buildings two or more stories and $55.50 per ft2 for single story buildings, in a two year period. • Certain costs are excluded from URM building renovation totals, including: Site improvements, Eco-roofs and mandatory ADA and Elevator improvements. Seismic Considerations Series 29
  30. 30. Seismic Strengthening Costs • Varies greatly. • Usually combined with other architectural improvements. • Cost Ranges: o $15 to $50 / sf o Lower for simple URM roof upgrade o Higher for complex Code upgrade Seismic Considerations Series 30
  31. 31. Code vs. ASCE 31 • ASCE 31 is 75% of Code • ASCE 31 allows for some non-Code compliant materials Seismic Considerations Series 31
  32. 32. Questions? Edwin T. Dean, PE, SE Managing Principal (503) 445-8685 p ed.dean@nishkian.com Robert A. Aman, PE, SE, LEED AP Associate (503) 445-8687 p rob.aman@nishkian.com PK Park, Eugene, Oregon Home of U of O Baseball Video & Scoreboard Towers Seismic Considerations Series 32

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