photo standards for seismic design of piers and …...photo photo photo photo presented by: gayle...
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PHOTO
PHOTO
PHOTO
PHOTO
Presented by:
Gayle JohnsonHalcrow, Inc.Oakland, CA
New Performance-Based Standards forSeismic Design of Piers and Wharves
November 9, 2007
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AgendaAgenda
Background / history of standards
Why we had to go this route
What to expect
Technical issues / political drama
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ASCE Standards CommitteeASCE Standards Committee
Formed in 2005
National committee of > 40 professionals
Owners, consultants, and academics
Geographically diverse
Heavy geotechnical emphasis
Funding by US Navy
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What will these new standards do?What will these new standards do?
Codify current practice of performance-based seismic design– National consensus document
Build on work done by others specifically for the marine industry– Port of Los Angeles– California State Land Commission (MOTEMS)– PIANC
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Why is this necessary ?Why is this necessary ?
Billions of dollars of construction in seismic regions– Performance-based design being used routinely on
a project basisExisting marine codes have limited standing
Conventional building codes still often take precedence– Enforcement by local building officials
Conventional code development controlled by building designers– Major changes to those codes
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Code HistoryCode History
Through 1997: – Three model building codes adopted by building
officials in US• Note: Not all ports subject to local building
official jurisdiction– Dominated by UBC / SEAOC “Blue Book”– “Nonbuilding structures” added in 1988– No specific reference to piers and wharves
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““World domination” by building designersWorld domination” by building designers
Post 1997: – Consolidation of 3 US Model Building Codes
into IBC– FEMA Sponsored National Earthquake Hazards
Reduction Program (NEHRP) – ASCE 7
– Different sponsoring organizations– Similar, but not identical, documents– Many of the same authors
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Major changes to codes Major changes to codes –– not benignnot benign
Some due to “lessons learned”, many change for the sake of change
Huge expansion of “nonbuilding structures”– Conflicts with existing industry practices and
standards (not just piers and wharves)
Major changes to ground motion definitions– Biggest effect outside of California
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2000 NEHRP2000 NEHRP
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2003 NEHRP2003 NEHRP
Task Committee of industry engineers
Attempt to add performance-based design
Crashed and burned
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2003 NEHRP2003 NEHRP
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ASCE 7ASCE 7--0505
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Why was performanceWhy was performance--based design rejected ?based design rejected ?
Two level performance criteria
Levels of shaking / return periods viewed as “unconservative”– Consistent risk vs. life-safety
Displacement based design not understood
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UBC / IBC / ASCE Performance CriteriaUBC / IBC / ASCE Performance CriteriaHistorically was single earthquake– 475 year return period– Life safety only
Now Maximum Considered Earthquake (MCE)– 2,500 year RP with deterministic cap– Collapse Prevention
Design Earthquake– 2/3 MCE
• (800-1000 year)– Life Safety
Really a single-level earthquake design for 2/3 MCE
Performance at higher level is presumed due to implied factors of safety for buildings
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Why change the 475 year return period ?Why change the 475 year return period ?
Increase ground shaking in Eastern US– 2% in 50 years
Keep actual design values for California about the same– 2/3 factor – Justified by inherent 1.5 factor of safety
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New York, NYSite Class D
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5
Period (sec)
Spec
tral
Acc
eler
atio
n (g
)
2/3 NEHRP USGS-10% in 50 Years
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Charleston, SCSite Class D
0.0
0.2
0.4
0.6
0.8
1.0
1.2
0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0
Period (sec)
Spec
tral
Acc
eler
atio
n (g
)
2/3 NEHRP USGS-10% in 50 Years
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Seattle, WASite Class D
0.0
0.2
0.4
0.6
0.8
1.0
1.2
0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5
Period (sec)
Spec
tral
Acc
eler
atio
n (g
)
2/3 NEHRP USGS-10% in 50 Years
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San Diego, CASite Class D
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5
Period (sec)
Spec
tral
Acc
eler
atio
n (g
)
2/3 NEHRP USGS-10% in 50 Years
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Oakland Outer Harbor Wharf, CASite Class D
0.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0
Period (sec)
Spec
tral
Acc
eler
atio
n (g
)
2/3 NEHRP USGS-10% in 50 Years
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Port industry issues with changesPort industry issues with changes
Hard to distinguish between damage states for life-safety and collapse prevention– Inherent 1.5 FS is only for buildings – doesn’t
make sense for portsAccelerations / forces can be scaled, displacements are not linearMassive ground failures occur in 2,500 year event that don’t occur at 500 years– Can’t just scale those events by 2/3
Life safety hasn’t been an issue
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1989 Loma 1989 Loma PrietaPrieta EarthquakeEarthquake
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1989 Loma 1989 Loma PrietaPrieta EarthquakeEarthquake
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1995 Kobe Earthquake1995 Kobe Earthquake
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1995 Kobe Earthquake1995 Kobe Earthquake
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1995 1995 ManzanilloManzanillo, Mexico Earthquake, Mexico Earthquake
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1995 1995 ManzanilloManzanillo, Mexico Earthquake, Mexico Earthquake
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1999 Turkey Earthquake1999 Turkey Earthquake
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1999 Turkey Earthquake1999 Turkey Earthquake
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2004 Indonesia Earthquake / Tsunami 2004 Indonesia Earthquake / Tsunami
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New StandardsNew StandardsSeismic Hazard Level and Performance Level
Operating Level Earthquake (OLE)*
Contingency Level Earthquake (CLE)*
Design Earthquake (DE) Design
Classification Ground Motion
Probability of Exceedance
Performance Level
Ground Motion
Probability of Exceedance
Performance Level
Seismic Hazard Level
Performance Level
High
50% in 50 years
(72 year RP)
Minimal Damage
10% in 50 years
(475 year RP)
Controlled and
Repairable Damage
as per ASCE-7
Life Safety Protection
Moderate n/a n/a
20% in 50 years
(225 year RP)
Controlled and
Repairable Damage
as per ASCE-7 Life Safety
Protection
Low n/a n/a n/a n/a as per ASCE-7 Life Safety
Protection
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Does higher RP = more conservative ?Does higher RP = more conservative ?
ASCE 7– 2,500 year return period– Non-collapse / life-safety
ASCE Piers and Wharves– Lower return periods– Controlled and repairable damage– “Failure” is more functional and economical– Life-safety and collapse not such a big issue
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Why is displacement based design an issue ?Why is displacement based design an issue ?
Displacement based not done for buildings– Force based– R factors to reduce the load accounting for
ductility and inelastic deformations
Force based doesn’t work well for piers and wharves– Judgment needed– Assign a building system or non-building
structure
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CLE Strain Limits Top of pile In-ground
0.005≤ εc ≤0.020c 0.005≤ εc ≤0.008c,d Solid Concrete Piles - Doweled εsd = 0.050 ? 0.6εsmd εp = 0.015b
εc = 0.004 εc = 0.006 Hollow Concrete Pilesa - Doweled εsd = 0.025 εp = 0.015
0.005≤ εc ≤0.020c 0.005≤ εc ≤0.008c,d Solid Concrete Piles - Fully Embedded εp = 0.040 εp = 0.015b
εc = 0.004 0.006 Hollow Concrete Pilesa - Fully Embedded εp = 0.015 εp = 0.015
εc = 0.025 See Fully Embedded Steel Pipe Piles (concrete plug doweled connection) εsd = 0.050 ≤ 0.6εsmd ?
εs,c = 0.025 εs = 0.025 Steel Pipe Piles (hollow steel section) - Fully Embedded
εs = 0.035 εs = 0.035 Steel Pipe Piles (concrete filled) - Fully Embedded
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Tests at Oregon State UniversityTests at Oregon State University
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Tests at University of WashingtonTests at University of Washington
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Tests at University of WashingtonTests at University of Washington
9% Drift
1.75 % Drift
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Advantages to industry specific standardsAdvantages to industry specific standardsStructural configurations– “Irregularities”– Sloping foundations– Battered piles– Strong beam / weak column
Loading– Kinematic– Mooring and berthing
Code developers who work in the industry– Building guys won’t listen to us
Standing as “ASCE Mandatory Standard”
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What’s next ?What’s next ?
Standard to be balloted in 2008
Hopefully published 2009
Over time – gain national standing and acceptance by building officials
Continued application by marine industry
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AcknowledgementsAcknowledgements
Stu Werner – Seismic Systems and Risk Engineering
Martin Eskijian – California State Lands Commission
Peter Yin - Port of Los Angeles
Scott Ashford – Oregon State University
Amanda Jellin - University of Washington
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Questions ?Questions ?
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