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Performance‐Based Seismic Bridge DesignWhat Is It and How Is It Different from Today’s
Practice
Lee Marsh PhD PE President/CEO
BergerABAM, Inc
June 12, 20172017 AASHTO SCOBS Meeting
Spokane, WA
Presentation Outline
• Review of Current AASHTO Methods• NCHRP 12‐106 and Performance‐Based Seismic Design
• Fragility and Probabilistic Considerations• Developments in the Practice• Possible Structure to the Methodology
Operational Classification – AASHTO LFRD
Critical Bridges•Open to all traffic after 1000‐yr event• Open to emergency vehicles after 2500‐yr event
Essential Bridges•Open to emergency vehicles after 1000‐yr event
Other Bridges•No collapse, significant damage, disruption in service
Spec 3.10.1 and Commentary C3.10.5
Seismic Design Options ‐ AASHTO
Performance(OperationalClassification)
AASHTO
Seismic Design
LRFD Seismic
Critical
Essential
Other
Seismic Guide Spec(SGS)
Other
Critical or Essential
Project‐Specific Critiera
R‐factor Force‐based Approach
Displacement‐based Approach
LRFD Force-Based Method (FBM)
F
FElastic
F
Elastic Response
Elastic System
FYield
R (based on ductilityPlastic Hinge
Focus of Force Based Method Is Primarily Design Forces
Yielding System
Displacement Capacity Is NotDirectly Checked. Instead PrescriptiveDetailing Is Required.
Capacity
LRFD Response Modification Factors, R
SubstructuresOperational Classification
Critical Essential OtherWall-type piers - larger dimension 1.5 1.5 2.0
Reinforced concrete pile bents• Vertical piles only• With batter piles
1.51.5
2.01.5
3.02.0
Single columns 1.5 2.0 3.0Steel or composite steel and concrete pile bents• Vertical piles only• With batter piles
1.51.5
3.52.0
5.03.0
Multiple column bents 1.5 3.5 5.0
§ 3.10.7 16‐7
SGS Displacement-Based Method (DBM)
F
FElastic
F
Elastic Response
Elastic
FYieldFnon‐Seismic
Plastic Hinge
Yielding System
Capacity
Only Minimum Required Force, But No Unique Force Required
Displacement Capacity IsDirectly Checked, Based on Actual Provided Detailing. (Confinement)
Ensured
Example: Unequal Resistance Piers
30 ft15 ft
Col. A
Col. B
F
6.6”
demand
Designed using DBM where designer has control over column strength selected
Note different damage states of the two columns
400
5 10 15
(column A)
(column B)
(full frame)
200
Displacement (inches)
F(kips)
yield
failure
NCHRP 12‐106 Project
• Synthesis 440 (2012)– Reviewed work to date– Identified knowledge gaps– Recommendations
• NCHRP 12‐106 builds off Synthesis 440
• Objective –– Develop AASHTO Guidelines
for implementing Performance‐Based Seismic Design (PBSD)
– Propose extensions of the AASHTO Guide Specifications for LFRD Seismic Bridge Design
– Design Examples
• Completion March 2019
NCHRP 12‐106 Project Team
• Tom Murphy, Maria Lopez, Modjeski and Masters• Lee Marsh, Stuart Bennion, BergerABAM• Don Anderson, CH2M• Ian Buckle, Independent Consultant• Mervyn Kowalsky, North Carolina State University• Jose Restrepo, UCSD/Advanced Analysis LLC
Performance‐Based Seismic Design ‐ PBSD
Seismic Hazard
Structural Analysis
Damage Analysis
Loss Analysis
Rational process to link decision making to seismic input, facility response and potential
damage
(Spectral Acceleration)
(Strains, Displacements)
(Immediate Use, No Collapse)
($, Downtime)
PBSD vs AASHTO
PBSD – Start with desired performance and work to a design which will deliver desired performance
AASHTO Code – Start with an operational classification and work through design methodology, but no direct assessment of performance
What is Performance Based Seismic Design (PBSD) ?
Must Consider Both Capacity and Demand –Deterministic vs Probabilistic Approaches
Upper EQDemand
Lower EQDemand
• Direct control of the bridge system seismic performance for distinct seismic input.
• PBSD typically strives to go beyond the performance outlined in the design codes.– Additional or Enhanced
Criteria– Better “control” of design
outcome– Applies to both the
demand and capacity– Directly estimates/checks
performance
Visual Catalogs from Cyclic TestingSpalling Condition at
3.7% Drift
Bar Buckling & Spiral Fracture5.6% Drift
Spalling Onset2.2% Drift
Possible Reinforcing Steel Strain LimitsAllowable Tensile Strain
Main Bars Buckle, Then Rupture
Thus Use ReducedStrain Limit, suRas an AllowableTensile Strain
Onset of Strain Hardening
Necking Begins
ExpectedProperties
ye sh suR su
fye
fue
ParabolaC? E?
O
C – Critical, E – Essential, O ‐ Other
Possible Concrete Strain Limits
Spiral Rupture
co = 0.002sp = 0.005
cu normally ranges from 0.008 to 0.025
Confined Concrete
co sp cc cu
f’ce
f’cc
Unconfined Concrete
O
E?
C?
SpallingOnset
Limit States for RC Column
Actual First Yield
EIeff Mp = 58,200 kip‐in (= 1.16 Mne)
effective yield
yield= 0.00
0111
5 rad/in
cu controls over suRto define ultimate curvature, u
u= 0.00
0794
rad/in
Curvature Ductility, = u/y = 7.0
Mne = 50,100 kip‐in(ACI =0.003)
OE?C?
Databases Feed Specification DevelopmentSGS Implicit Displacement Capacity – SDC C
0.00
1.00
2.00
3.00
4.00
5.00
6.00
0.1 0.15 0.2 0.25 0.3
Drif
t Cap
acity
(%)
D/H
Experimental (C1)Yield (C2)Spalling (C3)Ductility 4 (C4)SDC C (C6)
SDC C
Analytical Yield
Analytical = 4
ExperimentalSpalling ‐ Database
Analytical Spalling
SDC C was set as theAverage of Analytical = 4 and Experimental
Spalling.
, Column Width to Height
Dam
age
Des
crip
tors
Damage Level I II III IV V
Classification None Minor Moderate Life Safety Near Collapse
Damage Description None Minimal Repairable Significant Near Collapse
Physical Description
(RC Elements)
Hairline cracks
First yield of tensile
reinforcement
Onset of spalling
Wide cracks extended spalling
Bar buckling bar fracture confined concrete crushing
Displacement Ductility μΔ ≤ 1 μΔ = 2 μΔ = 4 to 6 μΔ = 8 to 12
Repair Reparability None/no interruption
Minor repair/ no closure
Repair/limited closure
Repair/weeks to months closure Replacement
Perf
orm
ance
D
escr
ipto
rs Availability Immediate
Open to All Traffic
Open to Emergency
Vehicles Only Closed
Performance Level Fully Operational Operational Life Safety Collapse
Retrofit Manual PL3 PL2 PL1 NA
Fully Operational
PL3
Operational
PL2
Life Safety
PL1
Collapse
N/A
Comparison of Damage vs Performance
Example Performance vs Hazard Pe
rfor
man
ce
Des
crip
tors
Availability Immediate Open to All Traffic
Open to Emergency
Vehicles Only Closed
Performance Level Fully Operational Operational Life Safety Collapse
Retrofit Manual PL3 PL2 PL1 NA
Agency or Project-Specific Criteria is shown below
Seis
mic
Haz
ard
Ret
urn
Peri
od
100-yr RP RM-E RM-S
300-yr RP VTR SFOBB-WA
500-yr RP SC-OC I SC-OCII ODOT CRC
1,000-yr RP
LRFD-C LRFD-E SGS B/C*
RM-E
LRFD-O SGS-D RM-S
CA-SDC ODOT*
VTR Antioch SR520*
SFOBB-WA*
2,500-yr RP I-40 MR (isolated) LRFD-C
SC-OC I SC-OC II SC-OCI II
CRC
Fully OperationalPL0
Fully OperationalPL0
OperationalPL1
OperationalPL1
Life SafetyPL2
Life SafetyPL2
Life SafetyPL3
Life SafetyPL3
Concept of Fragility
Δ
F
Δyield Δbar bucklingΔspall
Overstrength (1.7f’c, 1.3fy)
Expected Strength (1.3f’c, 1.1fy)
Design Strength (f’c, fy)
Distribution of Onset of Spalling
Distribution of First Yield
Distribution of Strength
Distribution of Bar Buckling
DISPLACEMENT
PRO
BA
BIL
ITY
OF
OC
CU
RR
EN
CE 1.00
0.75
0.50
0.25
Δyield Δbar bucklingΔspall
Fragility Function (typ)
Probabilistic Basis for Performance Level Definition
Δ
F
Δyield Δbar bucklingΔspall
Overstrength (1.7f’c, 1.3fy)
Expected Strength (1.3f’c, 1.1fy)
Design Strength (f’c, fy)
Distribution of Onset of Spalling
Distribution of First Yield
Distribution of Strength
Distribution of Bar Buckling
DISPLACEMENT
PRO
BA
BIL
ITY
OF
OC
CU
RR
EN
CE 1.00
0.75
0.50
0.25
Δyield Δbar bucklingΔspall
Fragility Function (typ)
50% Probability of Occurrence
Probabilistic Basis for Performance Level Definition
Δ
F
Δyield Δbar bucklingΔspall
Overstrength (1.7f’c, 1.3fy)
Expected Strength (1.3f’c, 1.1fy)
Design Strength (f’c, fy)
Distribution of Onset of Spalling
Distribution of First Yield
Distribution of Strength
Distribution of Bar Buckling
DISPLACEMENT
PRO
BA
BIL
ITY
OF
OC
CU
RR
EN
CE 1.00
0.75
0.50
0.25
Δyield Δbar bucklingΔspall
Fragility Function (typ)
FULLY OPERATIONAL
50% Probability of Occurrence
Probabilistic Basis for Performance Level Definition
Δ
F
Δyield Δbar bucklingΔspall
Overstrength (1.7f’c, 1.3fy)
Expected Strength (1.3f’c, 1.1fy)
Design Strength (f’c, fy)
Distribution of Onset of Spalling
Distribution of First Yield
Distribution of Strength
Distribution of Bar Buckling
DISPLACEMENT
PRO
BA
BIL
ITY
OF
OC
CU
RR
EN
CE 1.00
0.75
0.50
0.25
Δyield Δbar bucklingΔspall
Fragility Function (typ)
FULLY OPERATIONAL
OPERATIONAL
50% Probability of Occurrence
Probabilistic Basis for Performance Level Definition
Δ
F
Δyield Δbar bucklingΔspall
Overstrength (1.7f’c, 1.3fy)
Expected Strength (1.3f’c, 1.1fy)
Design Strength (f’c, fy)
Distribution of Onset of Spalling
Distribution of First Yield
Distribution of Strength
Distribution of Bar Buckling
DISPLACEMENT
PRO
BA
BIL
ITY
OF
OC
CU
RR
EN
CE 1.00
0.75
0.50
0.25
Δyield Δbar bucklingΔspall
Fragility Function (typ)
FULLY OPERATIONAL
OPERATIONAL
LIFE SAFETY
50% Probability of Occurrence
Probabilistic Basis for Performance Level Definition
Δ
F
Δyield Δbar bucklingΔspall
Overstrength (1.7f’c, 1.3fy)
Expected Strength (1.3f’c, 1.1fy)
Design Strength (f’c, fy)
Distribution of Onset of Spalling
Distribution of First Yield
Distribution of Strength
Distribution of Bar Buckling
DISPLACEMENT
PRO
BA
BIL
ITY
OF
OC
CU
RR
EN
CE 1.00
0.75
0.50
0.25
Δyield Δbar bucklingΔspall
Fragility Function (typ)
FULLY OPERATIONAL
OPERATIONAL
LIFE SAFETYCOLLAPSE
50% Probability of Occurrence
Damage Analysis ‐ Caltrans
COMPONENT vs. SYSTEM Fragility
• Fragilities typically determined from experimental research on individual components orsubassemblies
• Component/subassembly fragility often does not equal the global system fragility
• System fragility dependent on:– Structural system– Redundancy– Configuration– Boundary conditions– Articulation
Unique to each bridge implementation
COMPONENT vs. SYSTEM Fragility
Courtesy: NISEE, EERC UC Berkeley
Developments in the Practice
• Seismic Hazard• Evolution of Structural Analysis• Innovative Materials and Systems• Public Involvement and Expectations• Organization‐specific Criteria• Building Industry
Future of Seismic Hazard Representation
Nico Luco (USGS) Presentation Excerpt –AASHTO T‐3 and TRB AFF50 2016
Directional Ground Motion Effects
Kowalsky, 2017
• RotD50 is median motion
• Nearly equal to GeoMean
• RotD100 is maximum• Period dependency• Not clear how
directional combination interfaces
• Should be investigated
Structural Analysis Techniques Are More Powerful
UBC ‐ Vancouver, CAN
• High Performance Computing– Solid modeling, SSI, NLTH,
Parallel Computing (Open Sees, ABAQUS, FLAC, ANSYS, SAP2000, etc)
Improved Performance –Innovative Materials and Systems
• Seismic Isolation• Shape Memory Alloy (SMA)• Engineered Cementitious
Composites (ECC) • Use of prestress in columns• Grade 80 steel• Ultra‐High Performance
Concrete (UHPC)• Fiber‐Reinforced Polymer
(FRP) wraps• Alternative connection
technologies
SMA Constitutive Relation
Public and Engineering Expectations
Washington State Targets of Recovery
City of Seattle Recovery Continuum
Organization‐Specific Criteria
• Caltrans– Developing SDC 2.0– Ordinary, Recovery, Important– Safety (SEE) and Function
(FEE) seismic hazard– Both damage and service
addressed
• Oregon– Essential, Important and
Other– Two‐level criteria– 1000‐yr Life Safety– CSZ deterministic ‐
Operational
• South Carolina– Operational Category I, II, III– Two‐level criteria– FEE (475 yr)– SEE (2,475)– Modifying geotechnical
design manual• Others
– Utah– Japan Road Assoc– FEMA – Bldgs (including work
by NIST)
Loss Analysis ‐ ODOT REDARS System Study for Retrofit Prioritization
ODOT Bridge Maintenance Conference – Oct. 2011
Resilience‐based Earthquake Design Initiative (REDi)Downtime Assessment Methodology
• Similar curves are created for engineering mobilization, review & design, repair financing, contractor mobilization, permitting, long‐lead items.
• Utility disruption curves are also developed. • Once delays are characterized total downtime and losses can be estimated.
Delay or “Impeding Curve” for post‐EQ inspectionDeveloped by
Arupfor Buildings
Technology Readiness and Knowledge Gaps
TRL Description 0-25 25-50 50-75 75-1001 PBSD Concept exists2 Seismic Hazard deployable3 Structural Analysis deployable 4 Damage Analysis deployable 5 Loss Analysis deployable 6 Owners willing and skilled in PBSD 7 Design guidelines8 Demonstration projects9 Proven effectiveness in EQ
Technology Readiness Level (TRL) % of development complete
?
• Gaps related to Engineering:– Not all materials and construction
types covered evenly– Link between damage levels and
return to service– Probabilistic data for all four steps
• Gaps related to decision makers:– Tools for decision makers and
public– Regional differences vs concensus– Funding– Other hazards combined with
seismic
General Observations
• Innovative technology is moving quickly and broadly– This will continue into the
future• Full probabilistic
approaches not likely for some time
• Education is key• Continued development is
key
• Guidelines should be flexible to permit new approaches and technology
• Possible to capture where we are today, but need an open approach
• Owners and Design Professionals must work at a higher level – “Higher Bar”
2015 ICC Performance Code
ICC‐PCFlowchart
• Performance Code used in Building Industry
• Sits “above” IBC requirements• Owner and Design Professional
(DP) agree on performance and criteria
• DP coordinates with Building Official
• Peer review typically used• Extensive control and
documentation requirements
2015 ICC Performance Code
• Damage levels suggested for natural hazards and technological hazards
• Performance Group– PG I – Low hazard bldgs.,
farm/storage/temp– PG II – Those not in I, III, or IV– PG III – Substantial hazard to human life:
More than 300 people in one area, schools, health, jails
– PG IV – Essential: Hospitals w/ emergency care, fire and police stations, power plants, fuel and hazard storage, water storage, air traffic control
• Earthquake– Small – 25 years– Medium – 72 years– Large – 475 years– Very Large – 2,475 years
• Damage Levels specified for:– Structural, Nonstructural, Occupant
hazard, Overall extent of damage, Hazardous material release
Possible PBSD Design Methodology
• Use current AASHTO operational categories
• Relate damage limit states to engineering design parameters (EDPs)
• Multi‐level approach• Post‐earthquake
inspection and expected performance documentation
• More design and detailed cost comparisons at TS&L
• Onus on engineer to relate damage to EDPs
• Open‐ended for customization and to take advantage of new developments
• Not fully probabilistic in near future
Operational Category – Performance Level
GroundMotion
Bridge Operational Category
Critical Essential Other
Lower Level(100 year)
PL3 – FullyOperational
PL3 – Fully Operational
PL2 –Operational
Upper Level (1000 year)
PL3 – Fully Operational
PL2 –Operational
PL1 – Life Safety
2500 year? PL1 – Life Safety?
PBSD Flowchart – 1 of 2
• Changes from a typical design procedure:– Determine
Performance Level, inclusive of damage
– Additional lower level motions
– Additional SDC’s– Consideration of
performance vs. cost
PBSD Flowchart – 2 of 2
• Two demand analyses required
• Displacement or force check replaced with EDP check –similar to displacement check
• Design is complete when performance and damage matches EDPs
• Loss could be assessed on a case‐by‐case with cost data and situational assumptions
Performance‐Based Seismic Design ‐ PBSD
Seismic Hazard
Structural Analysis
Damage Analysis
Loss Analysis
Rational process to link decision making to seismic input, facility response and potential
damage
(Spectral Acceleration)
(Strains, Displacements)
(Immediate Use, No Collapse)
($, Downtime)
Questions
Thank you!
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