NCHRP SYNTHESIS 49-12Seismic Design of Non-Conventional Bridges
WIP Update to T-3 Subcommittee June 26, 2018
David Goodyear PE SE
Hans Lund PE
Thomas Murphy, PhD PE SE
T.Y.LIN INTERNATIONAL
NCHRP 49-12
NOTICE THE FOLLOWING MATERIAL IS PRESENTED AS AN UPDATE ON
WORK IN PROGRESS FOR THE SUBJECT REPORT. MATERIAL IS
DRAFT, AND HAS NOT BEEN REVIEWED BY THE PANEL OR THE
NCHRP PROGRAM MANAGER.
NCHRP 49-12
SCOPE
SUMMARIZE THE CURRENT STATE OF PRACTICE FOR SEISMIC DESIGN
OF NON-CONVENTIONAL BRIDGES
NON-CONVENTIONAL DEFINED TO INCLUDE:
TYPICALLY LONG SPAN
NON-TRADITIONAL GIRDER SECTIONS
CABLE-SUPPORTED
STRUCTURAL SYSTEMS NOT ADDRESSED IN CONTEMPORARY STRONG BEAM-
WEAK COLUMN CAPACITY-PROTECTED DESIGN METHODOLOGY
(SIM TO DEFINITION IN AASHTO LRFD C3.10.1)
NCHRP 49-12
Problem Statement
APPLICABILITY OF WEAK-COLUMN PLASTIC HINGE BASED
CAPACITY DESIGN FOR SOME NON-CONVENTIONAL BRIDGES
PRACTICAL IMPACT OF FOUNDATION CAPACITY PROTECTION
THROUGH COLUMN HINGINING FOR NON-SEISMIC CONTROLLED
DESIGNS OR LIMITED DUCTILITY DESIGNS
REVIEW OF PERFORMANCE LIMIT STATES FOR (HIGH VALUE) NON-
CONVENTIONAL BRIDGES OFTEN INVOLVES MORE DEFINITION
THAN SINGLE MODE DUCTILITY
1.2Fw
Fw
Fe
FR
δpδy δover
NCHRP 49-12
WORK PLAN
PREPARE QUESTIONAIRE / SURVEY OF PRACTICE FOR AGENCIES
CONDUCT LITERATURE REVIEW ON US DESIGN PRACTICES FOR
SEISMIC DESIGN OF NON-CONVENTIONAL BRIDGES
ASSEMBLE INFORMATION ON STATE DOT AND INDUSTRY PRACTICES
PREPARE REPORT WITH SUMMARY OF PRACTICE
NCHRP 49-12
SCHEDULE FIRST DRAFT REPORT JULY 6, 2018
SECOND DRAFT AND REPLY TO COMMENTS OCTOBER 1, 2018
FINAL DRAFT NOVEMBER 1, 2018
NCHRP 49-12
LITERATURE REIVEW
TRID AND WEB DOCUMENT SEARCH
PERSONAL LIBRARY
AGENCY DOCUMENTS AS PART OF RESPONSE TO SURVEY
PROJECT CRITERIA FROM NA PROJECTS
NCHRP 49-12
Summary of
Literature
MAJORITY OF PUBLISHED WORK ON NON-CONVENTIONAL
BRIDGES DEALS WITH ANALYSIS METHODS AND CORRELATION OF
ANALYSIS TO MODEL TESTING. LITTLE PUBLISHED ON THE
PRINCIPLES FOR DESIGN OF NON-CONVENTIONAL BRIDGES,
PARTICULARLY WHERE SEISMIC IS RELATED TO OTHER DEMANDS.
CONSIDERABLE RESOURCES AVAILABLE FOR PROJECT CRITERIA
FOR NON-CONVENTIONAL BRIDGES OVER THE PAST 20+ YEARS OF
PRACTICE
NCHRP 49-12
AGENCY SURVEY
SURVEY THROUGH NAS/NCHRP ‘SURVEYGIZMO’
SURVEY SET UP TO ALLOW ’EARLY-OPT OUT’ FOR LACK OF
REFERENCE OR LACK OF APPLICABILITY TO AGENCY PRACTICE
RECEIVED 43 RESPONSES – 10 WITH NON-CONVENTIONAL BRIDGE
SEISMIC REFERENCES
RECEIVED CRITERIA DOCUMENTS FOR BRIDGE DESIGN AND
RETROFIT OVER A 20+ YEAR TIME FRAME
NCHRP 49-12
SURVEY ON STATE PRACTICE
0204060
Non-Conventional +
Seismic Experience
Total Responses
Seismic NC Bridge Experience
0
5
10
15
Project Specific Criteria
Ref Pool Project Specific Criteria
0
5
10
15
Guide Spec Only Criteria
Ref Pool Guide Spec Ref
0
5
10
15
LRFD BDS Only Criteria
Ref Pool LRFD BDS
CS'd
SusArch
Extrados
Box or
Cant
0
2
4
6
8
10
1 2 3 4 5
Bridge Type (1 or
more w/in State)
10 Responses out of 43 total, with the following breakdown
NCHRP 49-12
PRIMARY REFERENCES
CURRENT PRACTICE
AASHTO LRFD BRIDGE DESIGN SPECIFICATION
AASHTO GUIDE SPECIFICATION FOR LRFD SEISMIC BRIDGE DESIGN
ATC-32 (1996)
NCHRP 12-49 (ATC-49)
NCHRP 49-12
TYPICAL DESIGN CRITERIA
State of Practice - Bridge Seismic Analysis
Procedures - Conventional and Non-Conventional
Item LRFD BDS Guide Spec Project Specific
Scope conventional bridges conventional bridgesnon-conventional bridges (and
conventional at owner's discretion)
Seismicity Characterization Zones 1 to 4 based on Sd1 coeffSeismic Design Class A to D based on Sd1
coeff
typically project specific ground motions
based on PSHA
Typical Design Standard
Varies from elastic force based to inelastic
R-factor reduced elastic (pseudo-plastic)
forces depending on level of demand
Inelastic over-strength hinging based
capacity protection with ductility review to
level of demand displacement
Nonlinear, inelastic based evaluation
based on strain based performance
standards
Ground Motion Definition1000 year return - Site ground response
spectrum
1000 year return - Site ground response
spectrum
Spectrally matched ground motion time
histories, typically for both functional and
safety level events
Site Class Definition
(geotechnical
characterization)
Site Class A to F Site Class A to FProject specific characterization for SSI
analysis
Analysis type Elastic RSA for design forces
Elastic RSA or Elastic time history for
demand displacement for inelastic
pushover
Nonlinear time history for force, strains,
curvatures and global displacement
Foundation Modeling Lumped soil springs based on Site Class Lumped soil springs based on Site Class
Discrete foundation modeling with
nonlinear soil springs (or solid FEA) and
ground motion input with depth
NCHRP 49-12
STATE OF PRACTICE
APPLICATION OF PERFORMANCE BASED DESIGN (PBD) IS
UNIVERSAL FOR LARGE NON-CONVENTIONAL BRIDGES
APPLICATION OF PBD HAS EVOLVED WITH INCREASING
ANALYTICAL CAPABILITY
THE RIGOR OF ACCEPTANCE STANDARDS VARIES WITH LOCATION
MULTI-LEVEL GROUND MOTION (FUNCTIONAL AND SAFETY) IS
(ALMOST) STANDARD PRACTICE
MOST MAJOR BRIDGES DO NOT ADOPT THE NO-COLLAPSE
PERFORMANCE CRITERIA FOR THE EXTREME (2500 YEAR) EVENT
AND HAVE SOME MEASURE OF LIMITED DUCTILITY DESIGN
NCHRP 49-12
GENERAL CRITERIA
QUALITATIVE CRITERIA
Minimal Damage: Repairable Damage: Significant Damage:
Supplemental – No Damage: (Rarely specified for Seismic)
QUANTITATIVE CRITERIA
For reinforced concrete:o Minimal Damage: c = 0.004, ps =
0.008 and s = 0.01 o Repairable Damage: c = 0.007, ps =
0.015 and s = 0.025 o Significant Damage: c = 0.75cu, ps =
0.045 and s = 0.75su
For main span (single) pylons:o All damage stages: εc=.004 and εs=.01
For steel piles:o Minimal Damage: s = 0.002 and p =
0.002o Repairable Damage: s = 0.01 and p =
0.01o Significant Damage: s = 0.025 and p =
0.025
LEVEL OF PRESCRIPTIONS VARIES WITH LOCALEHIGH SEISMIC WEST COAST GENERALLY QUANTITATIVE
NCHRP 49-12
PRACTICAL EFFECTS FOR
NON-CONVENTIONAL
BRIDGES
FULL DUCTILITY DESIGNS FOR SINGLE PYLONS (COLUMNS) MAY
RESULT IN INADEQUATE REINFORCING FOR WIND LOADS FOR LONG
SPANS
FOR LIMITED DUCTILITY PYLON (COLUMN) DESIGNS, WHICH ARE
COMMON, DESIGN TO STRAIN-LIMITED PERFORMANCE LIMIT STATE
RESULTS IN PLASTIC SECTION CAPACITY THAT IS SIGNIFICANTLY
HIGHER THAN FOR A LIMIT STATE PLASTIC DESIGN
FOR MANY APPLICATIONS, EXTENDING SECTION OVER-STRENGTH TO
FOUNDATION DESIGN FOR STRAIN-LIMITED PYLON DESIGN IS
UNECONOMICAL, IF NOT IMPRACTICAL
STRAIN-LIMITED PERFORMANCE BASED DESIGN REQUIRES THE USE
OF NON-LINEAR DYNAMIC ANALYSIS FOR NON-CONVENTIONAL
BRIDGES
NCHRP 49-12
NONLINEAR METHODS
State of Practice for Nonlinear Analysis
Parameter Scope of Practice
Structure
Method 1 Method 2 Method 3
Kinematic model Full geometric stiffness Full geometric stiffness Full geometric stiffness
Structural Elements-
ConcreteFull moment-curvature definition
Assigned inelastic regions for
moment-curvature definitions
Assigned cracked stiffness
properties
Structure Elements-
SteelInelastic material definition
Idealized Elasto-plastic material
definitionElastic members
Structure Elements-
Cables
Full beam-column (geometric
stiffness)
Idealized cable element (catenary
or similar)
Catenary or spar with Ernst
effective modulus
Damping Rayleigh plus material (hysteretic) Rayleigh plus material (hysteretic) Rayleigh or viscous
Soils and
Foundations
Soil modelFinite difference ( FLAC) with
liquefaction triggering models
Finite element continuum with
liquefaction triggering models
Foundation substructure modeling
with support point interface
Substructure (piles
and shafts)
Full discretization as structural
members
Full discretization as structural
members
Modeled within substructure
model
Ground Motions
Depth varying discretized time
history based on firm ground free
field time history of continuum
Firm ground time historyFree field motion on substructure
modelNCHRP 49-12
TWO EXAMPLES 1-Portal Tower Response w/Limited Ductility Design
2-Full Discretization of Single Pylon
NCHRP 49-12
SUMMARYOF
PRACTICE
PERFORMANCE BASED DESIGN IS STANDARD PRACTICE FOR
SEISMIC DESIGN OF NON-CONVENTIONAL BRIDGES
NON-LINEAR DYNAMIC ANALYSIS IS STANDARD PRACTICE,
ALTHOUGH APPROACHES TO THE ANALYSIS DIFFER
LIMITED DUCTILITY DESIGNS ARE COMMON, AND RESULTS IN
PYLON OR COLUMN BASE OVERSTRENGTH MOMENTS IN EXCESS
OF THE DESIGN BASE MOMENTS AT THE DEMAND DISPLACEMENT
LIMITED DUCTILITY NON-CONVENTIONAL BRIDGE DESIGN CAN
CURRENTLY FIT WITHIN THE BROADER METHODS FORMAT OF LRFD
BDS, BUT LESS SO WITH THE DEFINITION OF CAPACITY
PROTECTION METHOD OF THE GUIDE SPEC
NCHRP 49-12
