Seismic UpgradesDesigning Structures to Withstand

EarthquakesApril 16, 2014

SERVICES & EXPERTISE

• Project Management • Structural & Seismic Design• Structural Modeling (BIM)• Construction Engineering• Structural & Seismic Evaluations• Seismic Retrofits• Peer Reviews• Value Engineering• Planning / Feasibility Studies

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Earthquakes Affecting Oregon

Date Location Magnitude (1) Damage (2)

1700 Coastal Oregon ±91949 Olympia 7.1 Minor1962 Portland 5.5 Minor1964 Alaska 9.2 Tsunami1996 Scotts Mills 5.6 Minor2001 Tacoma 6.8 Negligible

Notes:

(1) Moment Magnitude

(2) Damage relative to Oregon

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Earthquakes Affecting Oregon

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Last 12 months >M2.5

of Seismic Design in OregonHistory

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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

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1958 UBC• Western Oregon

1. Zone 2

• Eastern Oregon1. Zone 1

• Lateral Bracing -AppendixF = C WWhere,

C = 0.15 / N + 4½For locations in Zone 2,

“C” shall be doubled

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1970 UBC• NW Oregon

1. Zone 2

• SW Oregon1. Zone 1

• Eastern Oregon1. Zone 1

• Base ShearV = Z K C WWhere,

Z = ½C = 0.05 / ∛T

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1976 UBC

• ALL of Oregon1. Zone 2

• Base ShearV = Z I K C S WWhere,

Z = ⅜C S ≤ 0.14C = 1 / 15 √T

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1988 UBC

• ALL of Oregon1. Zone 2B

• Base ShearV = (Z I C / Rw) WWhere,

Z = 0.2 (Zone 2B)C = 1.25 S / T2/3

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1991 UBC

• Western Oregon1. Zone 3

• Eastern Oregon1. Zone 2B

• Base ShearV = (Z I C / Rw) WWhere,

Z = 0.3 (Zone 3)C = 1.25 S / T2/3

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1997 UBC• Western Oregon

1. Zone 3• SW Coastal

1. Zone 4• Eastern Oregon

1. Zone 2B• Base Shear

V = (Cv I / R T) WNot exceedingV = (2.5 Ca I / R) WWhere,

Z = 0.3 (Zone 3)Cv = Ca = 0.3 (SB)

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Increasing Base Shear

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2x

3.5x

2003 IBC

0.2 Sec Accelerations 1.0 Sec Accelerations

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2003 IBC

1997 USGS MAP VALUES

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2009 IBC

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SS = 0.987 gS1 = 0.347 g

Max per City CodeSS = 1.0 gS1 = 0.36 g

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Where Did Seismic Zones Go?

City of Portland Code Requirements

Existing Buildings

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Existing Buildings

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Seismic Strengthening of Existing Buildings

Existing Buildings

• When are seismic evaluations required; and

• What triggers when seismic strengthening needs to occur.

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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”)

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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.

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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

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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;

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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.

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Seismic Upgrade Triggers

Seismic Strengthening

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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

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Seismic Strengthening

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• Seismic Upgrade Triggers1. OSSC Chapter 34 –Current Code Upgrade2. Title 24.85 Triggers –ASCE 31 (or ASCE 41 / OSSC)

• Voluntary Seismic Upgrade1. Identify standard basis

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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.

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Seismic Strengthening Costs

• Varies greatly.• Usually combined with other architectural

improvements.• Cost Ranges:

o $15 to $50 / sfo Lower for simple URM roof upgradeo Higher for complex Code upgrade

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Code vs. ASCE 31

• ASCE 31 is 75% of Code• ASCE 31 allows for some non-Code compliant

materials

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Questions?

Edwin T. Dean, PE, SEManaging Principal(503) 445-8685 ped.dean@nishkian.com

Robert A. Aman, PE, SE, LEED APAssociate(503) 445-8687 prob.aman@nishkian.com

PK Park, Eugene, Oregon Home of U of O Baseball Video & Scoreboard Towers

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