Design for Multi-Hazard (MH) Resilient Highway Bridgessp.bridges.transportation.org/Documents/2015...
Transcript of Design for Multi-Hazard (MH) Resilient Highway Bridgessp.bridges.transportation.org/Documents/2015...
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Presentation to T-1
on
Design for Multi-Hazard (MH) Resilient
Highway Bridges
by
George C. Lee(1)
and
Thomas P. Murphy(2)
April 21, 2015
(1) University at Buffalo
(2) Modjeski and Masters
2015 AASHTO SCOBS ANNUAL MEETING
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OUTLINE
• Examples of Current Needs
• Multi-Hazard Bridge Design
• Multi-Hazard Survey
• Framework Development
• Current Multi-Hazard Bridge Design
Study
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EXAMPLES OF CURRENT
NEEDS
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Examples of Current Needs
• γEQ in Extreme Event I
• What loads to evaluate stability under
check scour
• Are all Extreme Events treated equally
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Live Load + EQ
• Load factor on Live Load
– 0.0, 0.5, 1.0 ???
– “This issue is not resolved”
– Two time variable loads need to be combined
– Dynamic interaction of live load and structure
• May be important
• Need baseline
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Examples of Current Needs
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Scour
• Design flood for design conditions
• Check flood for “stability”
– “The consequences of changes in foundation
conditions due to scour resulting from the
check flood for bridge scour and from
hurricanes shall be considered at the extreme
event limit states”
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Examples of Current Needs
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Scour (cont’d)
• No other guidance appears to be provided
• How much scour for seismic checks?
• For vessel collision?
• For wind?
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Examples of Current Needs
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Extreme Event Compatibility
• Service limit state calibration
• Should a uniform Beta be the goal for extreme
events?
• Should there be a goal?
• What are the Betas now?
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Examples of Current Needs
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Points of Current Study
• Focus on areas where guidance is mostly
needed
– Not necessarily new limit state equations
• Utilize framework developed in previous
MCEER project funded by FHWA
• Lay the groundwork for common treatment of
extreme events on the same platform
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Examples of Current Needs
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MULTI-HAZARD BRIDGE
DESIGN
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What?
Why?
How?
Where to?
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Multi-Hazard Bridge Design
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What?
– Risk-based design
– Straightforward implementation
– Consistent with current LRFD
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Multi-Hazard Bridge Design
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Why?
– Need more consistent safety
– Need less waste in over-design
– Need ease of future development
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Multi-Hazard Bridge Design
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How?
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Multi-Hazard Bridge Design
WSD
LFD
LRFD
• LRFD design formula:
𝜂𝑖 𝛾𝑖𝑄𝑖 ≤ 𝜙𝑅𝑛
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How?
1. Framework: Development of principles for multi-
hazard (MH) bridge design principles
(completed—MCEER)
2. Trial Calibration: Multi-hazard bridge design
(current project)
3. Future deployment: Adoption of MH-LRFD
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Multi-Hazard Bridge Design
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Where to?
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Multi-Hazard Bridge Design
WSD
LFD
LRFD (non-extreme loads)
MH-LRFD (all loads)
MH-LRFD (performance-based)
Sustainability Design
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MULTIPLE-HAZARD
SURVEY
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Objectives • Record professional opinion of experienced bridge engineers on the
importance of various hazards and load combinations
• To stimulate discussion
• To identify needs in the practical application of existing specifications and guidelines
• To identify variations in extreme load usage
• Intuitive answers based on:
– Experience and precedence
– Geographical variation—terrain, weather, seismicity, …
– Bridge site conditions—navigability, urbanization
– Professional judgment
– Budget constraints
– Risk management: life cycle cost, consequence measurement
– Public expectation
Multi-Hazard Survey
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1=No, 2=Consider, 3=Always
Multi-Hazard Survey
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Part 1. Single Extreme Event
(scour, vessel collision, vehicular collision,
fire, earthquake, surge, wind, debris)
or
Combination of Events
(two or three concurrent events)
Part 2. Cascading Events
(e.g. vehicular collision fire)
(e.g. wind surge + vessel collision)
Part 3. Comments
(explanation or concern over other hazards)
Standard Special
Multi-Hazard Survey
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Survey Results
• Data were numerically and graphically
analyzed
• Comments were studied
• An MCEER Report was published
• 35+ states responded
Multi-Hazard Survey
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Multi-Hazard Survey
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Standard Bridges Special Bridges
Earthquake
Multi-Hazard Survey
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Fire
Multi-Hazard Survey
Standard Bridges Special Bridges
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Vehicular Collision
Multi-Hazard Survey
Standard Bridges Special Bridges
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Storm Surge + Wind (Concurrent)
Multi-Hazard Survey
Standard Bridges Special Bridges
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Single Event - Typical Bridges
Multi-Hazard Survey
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Multi-Hazard Survey
Single Event & Concurrent Events
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River and Coastline Issues
Multi-Hazard Survey
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5 Vessel Collision
Don ’ t Consider
Possibly Consider
Always Consider
Don ’ t Consider
Possibly Consider
Always Consider
6 Storm Surge
Don ’ t Consider
Possibly Consider
Always Consider
Don ’ t Consider
Possibly Consider
Always Consider
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1 Scour + Debris Flow
Don ’ t Consider
Possibly Consider
Always Consider
Don ’ t Consider
Possibly Consider
Always Consider
Standard - 1
.
No
Possibly
Yes
2. Possibility of Two Concurrent Extreme Events
2.5 Scour + Debris FlowSpecial - 28
Multi-Hazard Survey
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Potential Socio-economical Factors
(Consequence of Damage)
Multi-Hazard Survey
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3 Vehicular Collision
Don ’ t Consider
Possibly Consider
Always Consider
Don ’ t Consider
Possibly Consider
Always Consider
Standard - 1
4 Earthquake
Don ’ t Consider
Possibly Consider
Always Consider
Don ’ t Consider
Possibly Consider
Always Consider
Standard - 1
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Potential Boundaries
I: High seismicity, non-hurricane coastal wind II: Long-term high seismicity, Inland wind III: Inland wind IV: Hurricane zone V: Long-term high seismicity, hurricane zone
Multi-Hazard Survey
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Preliminary Observations
• Regional patterns were revealed.
• Consequence seems to be built into the assessment of risk. – Potential fatalities & economic disruption rather than
just potential for structural failure
– Population density and traffic volumes are indicators
• Hazards – Scour ranks high in survey and in lists of failures
– Collision ranks high in survey and in lists of failures
– Fire is not ranked high but is a significant cause of bridge failure
– Wind ranks high but has not been a cause of failure
Multi-Hazard Survey
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FRAMEWORK
DEVELOPMENT
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Quantified “Safety”—Reliability Index
• Kulicki et al. (1991): Calibration for dead load and live load
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AASHTO Standard Specifications Proposed LRFD Specifications
Framework Development
𝛽 =𝜇𝑅 − 𝜇𝑄
𝜎𝑅2 + 𝜎𝑄
2
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Steps for Calibration of LRFD (DL+LL)
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Framework Development
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LRFD and Supporting Guide-
specifications/Guidelines for Extreme Loads
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Not all risk-based and not calibrated
consistently
Dead Load Live Load
Strength limit states
Service limit states
Fatigue limit states
(LRFD)
Earthquake Surge Collision Flood
Strength/Extreme event limit state
(Coastal Guidespec)
Check flood
(HEC-18)
Extreme event
limit state
(Seismic
Guidespec)
Extreme event limit
state
(Vessel Collision
Guidespec)
Framework Development
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MH-LRFD (DL+LL+ Extreme Loads)
MCEER Framework for the Development of
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Risk-based and consistently
calibrated
Dead Load Live Load Earthquake Surge Collision Flood
MH-LRFD Framework
Framework Development
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The MCEER Framework
• Reliability-based platform including load (and
equivalent load) effects of all hazard that may
cause structural damage / failure of bridges
(components)
• Systematic approach for handling multiple time-
variable loads
• Method to derive design limit state equations
(DLSE’s) from calibration data
• Calibrating with loads and other effects (such as
scour)
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Framework Development
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Accomplishment of required reliability
• Considering two time-variable loads, the effect
cannot be a direct summation
• Potentially decreased load factors
representing the less-likely
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Framework Development
𝜇𝑄 ≠ 𝜇𝑄1+ 𝜇𝑄2+ 𝜇𝑄3+ ⋯ 𝛽 =𝜇𝑅 − 𝜇𝑄
𝜎𝑅2 + 𝜎𝑄
2
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Inte
nsi
ty
TimeIn
ten
sity
Time
Inte
nsi
ty
Time
Somewhat increased risk of
high intensity
Load 1 Load 2
Framework Development
Combined time-variable loads without concurrence
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Load Combinations of Interest
Important frequent-infrequent load combinations based on
input from SCOBS (responses from 35+ states in 2010),
FHWA and selected Bridge Engineers:
• DL+LL+EQ
• DL+LL+SC+EQ
• DL+LL+SC+CV
• DL+LL+EQ+Wind (more significant for Signature Bridges)
• DL+LL+CT+ Subsequent Fire
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Framework Development
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Combinations of Dead Load, Live Load
and Earthquake: A case study
Development of Future MH-LRFD (A Case Study)
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Framework Development
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Target Bridge Reliability
Bridge Failure Probability
Design Limit State Equations
Load and Resistant Factors
Load Distribution Models
Load Combinations Bridge Capacity
Model
Dead Load Truck Load
Infrequent, Extreme Loads and Effects
(earthquake, wind, scour, vessel collisions, etc.)
1
2
3
4
5
6 Experience and
Judgment
STEP
Framework Development
A Case Study (Cont’d)
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Step 1. Selection of representative bridges.
♦ One typical example
Three spans are 100, 120, 100 ft in length, respectively
Superstructure is one continuous cast-in-place concrete
box girder
Two 4ft diameter columns at each bent, with clearance
height of 20 ft
This bridge is located in
San Francisco, CA
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Framework Development
A Case Study (Cont’d)
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Step 2. Establish the statistical data base for load and resistance
parameters
Live loads
Normal distribution (Moses*)
• Mean value: 68 kips
• Standard deviation: 18 kips (COV = 26.5%)
Rate: 5,000 / day
Earthquake
USGS Hazard Map
0 0.5 1 1.5 2 2.50
0.05
0.1
0.15
0.2
PGA (g)P
DF
* Moses, F. (2001). NCHRP Report 454: Calibration of Load Factors
for LRFR Bridge Evaluation, Transportation Research Board of
the National Academies, Washington, DC.
Framework Development
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A Case Study (Cont’d)
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Step 3. Development of load and resistance models
Resistance Model
The nominal value of resistance is calculated based on
the current LRFD. Resistance follows a lognormal
distribution with the COV of 0.13.
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Framework Development
0 0.5 1 1.5 2 2.5 3
x 10 4
0
0.5
1
1.5
2
2.5
3
3.5 x 10
-4 PDF in 75 years
Bending Moment (kip-ft)
PD
F in 7
5 y
ears
Resistance
A Case Study (Cont’d)
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R =RRn
RnRD
Ln
Design load and resistance
Pro
babili
ty D
ensity F
unctio
n
LD
L=LLn
L
Nominal load Nominal resistance
Mean Value
Mean resistance
R
Intensity
fL(x)
fR(x)
Maximum Load
Distribution
AASHTO LRFD Bridge Design Specifications
Framework Development
48
A Case Study (Cont’d)
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Step 3. Development of load and resistance models (Cont’d)
Live Load Effect Model: Obtained using structural
mechanics principles
49
Framework Development
0 200 400 600 800 1000 1200 0
1
2
3
4
5
6 x 10
-3 PDF for one Truck
Bending Moment (kip-ft)
PD
F
Live Load
A Case Study (Cont’d)
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Step 3. Development of load and resistance models (Cont’d)
Earthquake Load Effect Model: Obtained using time-
history analysis
Obtain the PGA (peak ground acceleration)
distribution from USGS
Discretize the PDF (probability density function) for
one earthquake using an specified interval (0.01g)
Use a series of earthquake ground motion records for
each level of PGA to analyze the time-history
response of the column
50
Framework Development
A Case Study (Cont’d)
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Step 3. Development of load and resistance models (Cont’d)
Earthquake Load Effect Model: Obtained using time-history analysis
Record the maximum load responses in abscissa of PMF (probability mass function)
•
Maximum response
51
Framework Development
0 10 20 30 40 50 60 -1
0
1 x 10
4 Earthquake Time-history
Be
nd
ing
Mo
me
nt (k
ip-f
t)
Time (s)
0 0.5 1 1.5 2 2.5 3
x 10 4
0
0.2
0.4
0.6
0.8
1
1.2 x 10
-5 PMF in 75 years
Bending Moment (kip-ft)
PM
F in 7
5 y
ears
Corresponding
probability of
PGA
A Case Study (Cont’d)
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Step 3. Development of load and resistance models (Cont’d)
Earthquake Load Effect Model : Obtained using time-
history analysis
Modify the PMF (discretized PDF) to ensure the sum
of probability equals to 1
52
Framework Development
0 1 2 3 4 5
x 10 4
0
1
2
3
4
5 x 10
-3
Moment (kN-m)
PM
F
A Case Study (Cont’d)
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Step 3. Development of load and resistance models (Cont’d)
Combined Load Effect Model
Maximum response
EQ
LL
53
0 10 20 30 40 0
100
200
300
Time (s)
Mo
me
nt(
kip
-ft)
+
0 10 20 30 40 50 60 -1
0
1 x 10
4 Combined Time-history
Be
nd
ing
Mo
me
nt (k
ip-f
t)
Time (s)
Framework Development
0 10 20 30 40 50 60 -1
0
1 x 10
4 Earthquake Time-history
Be
nd
ing
Mo
me
nt
(kip
-ft)
Time (s)
0 0.5 1 1.5 2 2.5 3
x 10 4
0
0.2
0.4
0.6
0.8
1
1.2 x 10
-5 PMF in 75 years
Bending Moment (kip-ft)
PM
F in 7
5 y
ears
Corresponding
probability of
PGA
A Case Study (Cont’d)
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Step 3. Development of load and resistance models (Cont’d)
Combined Load Effect Model
Modify the PMF (discretized PDF) to ensure the sum of
probability equals to 1
54
0 1 2 3 4 5
x 10 4
0
0.5
1
1.5
2
2.5
3 x 10 -3
Moment (kN-m)
PM
F
Framework Development
A Case Study (Cont’d)
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Step 4. Development of the reliability analysis procedure
• Partial and total failure probabilities
• Principle of Comprehensive Reliability
Earthquake Combined Live load (disregarded)
55
Framework Development
𝑝𝑓𝐸 = 4.78 × 10−6 𝑝𝑓
𝐸𝐿 = 7.72 × 10−4 𝑝𝑓𝐿 = 3.50 × 10−22 ≈ 0
A Case Study (Cont’d)
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56
Target Bridge Reliability
Bridge Failure Probability
Design Limit State Equations
Load and Resistant Factors
Load Distribution Models
Load Combinations Bridge Capacity
Model
Dead Load Truck Load
Infrequent, Extreme Loads and Effects
(earthquake, wind, scour, vessel collisions, etc.)
1
2
3
4
5
6 Experience and
Judgment
STEP
Framework Development
A Case Study (Cont’d)
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Step 5. Selection of the target reliability index
• Parametric Study (selection of different bridges)
70’
120’
200’
57
Framework Development
57
A Case Study (Cont’d)
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20’ 35’ 50’
Step 5. Selection of the target reliability index (Cont’d)
• Parametric Study (selection of different bridges)
58
Framework Development
58
A Case Study (Cont’d)
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0
1
2
3
4
5
0 50 100 150 200
b
Side Span (ft)
Current EQ
Step 5. Selection of the target reliability index (Cont’d)
Determine the reliability of current design
Average
b = 2.5
59
Framework Development
A Case Study (Cont’d)
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Step 5. Selection of the target reliability index (Cont’d)
• Determine the reliability of current design
♦ Why b = 2.5 ?
2.5 = Average reliability index for 9 bridges
designed using current AASHTO LRFD
Same approach used for
establishing the LRFD
DL and LL:
Average b = 3.5
60
Framework Development
A Case Study (Cont’d)
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Step 6. Calculation of load and resistance factors
• Least Square Method (curve fitting)
L = 1.38; E = 0.74
61
Framework Development
A Case Study (Cont’d)
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Comparison between current LRFD and MH-LRFD
based on Case Study for DL+LL+EQ
LRFD: Extreme event limit-state equation
• p DL + EQ LL + 1.0 EQ (p = 0.9~1.25, EQ < 1.0 or EQ = 0.5)
• General design equations (for column, girder, bearing, etc.)
• Not yet calibrated by reliability-based design methodology
MH-LRFD
• p DL + 1.38 LL + 0.74 EQ (p = 0.9~1.25)
• Specific equation for column bending moment
• Generated by MH reliability-based design principles, need to
be further calibrated using sufficient cases
62
Framework Development
A Case Study (Cont’d)
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CURRENT MULTI-HAZARD
BRIDGE DESIGN STUDY
63
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Implementation of MCEER Framework
• Target the development of a guide document on
bridge design against extreme events suitable for
adoption by AASHTO with consistent design
principles
• Expand on the MCEER work to include work by
others
• Explore the potential of balanced design of typical
bridges between safety and cost
64
Current Multi-hazard Bridge Design Study
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Some Significant Research Challenges
– To include all important frequent and infrequent loads and their combinations to quantify their relative importance
– To study the appropriateness by approximating random processes as random variables
– To establish all-inclusive failure probability equations
– To establish design limit state equations and to extract load and resistance factors and their calibration
65
Current Multi-hazard Bridge Design Study
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Potential DLSE’s
• LL+SC (scour)
• LL+CV
• LL+EQ
• LL+Wind (WS, WL)
• LL+CV+SC
• LL+EQ+SC
• LL+SC+Wind
Note: each combination may be one or more DLSE’s
66
Current Multi-hazard Bridge Design Study
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Key Issues for Load Combination
• It does NOT always mean the consideration of
concurrent events.
• Increased risk from a single load, but not overly
conservative by directly combining high loads.
• Complex theory and development, simple
design limit state equations
67
Current Multi-hazard Bridge Design Study
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Load Combination Concurrence
68
Likely Concurrence Unlikely Concurrence
• Design flood with LL (Current
LRFD for all non-extreme
DLSEs)
• Design flood (scour with design
earthquake
• Drifting barge collision with
scour (current LRFD ½ scour
depth with empty barge weight)
• Check flood with other loads
except DL
• Earthquake with live load • Earthquake with vessel collision
Key Issues for Load Combination
Current Multi-hazard Bridge Design Study
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Some High Priority Subjects
• Critical variables in design
• Scour/foundation modeling
• Resistance modeling
• Efficient and reliable probability analysis
69
Current Multi-hazard Bridge Design Study
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Potentially Critical Variables in Design
• Element force
• Displacement
• Type of bridge component
• Hazard variation (temporal and spatial)
• Not considered:
– Human factors
– Interactive properties among different
hazards (except strayed empty barge)
70
Current Multi-hazard Bridge Design Study
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Scour/foundation modeling
• Types of foundation system
• Probabilistic characteristics of scour
• Soil failure vs. foundation element failure
• Positive and negative effect
71
Current Multi-hazard Bridge Design Study
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Future Research Challenges
• Explore cascading multiple hazard load effects for critical bridge components
• Develop approaches to establish failure probability of the bridge as a system of components
• Select and prioritize research projects to provide guidance in hazard mitigation studies
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Current Multi-hazard Bridge Design Study
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Project Execution
• FHWA funding for Multi-hazard Bridge Design
• Research Team
– Genex Systems
– MCEER
– Modjeski and Masters
– Arora and Associates
– FHWA: W. Philip Yen (COR)
73
Current Multi-hazard Bridge Design Study