performance‐based seismic bridge design · 2017 aashto scobs meeting ... aashto seismic design...

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


Fragility Function (typ)

Probabilistic Basis for Performance Level Definition

Δ

F









DISPLACEMENT

PRO

BA

BIL

ITY

OF

OC

CU

RR

EN

CE 1.00

0.75

0.50

0.25



50% Probability of Occurrence


Δ

F









DISPLACEMENT

PRO

BA

BIL

ITY

OF

OC

CU

RR

EN

CE 1.00

0.75

0.50

0.25



FULLY OPERATIONAL



Δ

F









DISPLACEMENT

PRO

BA

BIL

ITY

OF

OC

CU

RR

EN

CE 1.00

0.75

0.50

0.25



FULLY OPERATIONAL

OPERATIONAL



Δ

F









DISPLACEMENT

PRO

BA

BIL

ITY

OF

OC

CU

RR

EN

CE 1.00

0.75

0.50

0.25



FULLY OPERATIONAL

OPERATIONAL

LIFE SAFETY



Δ

F









DISPLACEMENT

PRO

BA

BIL

ITY

OF

OC

CU

RR

EN

CE 1.00

0.75

0.50

0.25



FULLY OPERATIONAL

OPERATIONAL

LIFE SAFETYCOLLAPSE


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!

performance‐based seismic bridge design · 2017 aashto scobs meeting ... aashto seismic design...

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