Determination of Barge Impact Probabilities for
Bridge Design
5th Annual FDOT Structures Research Update (Aug. 4-5, 2015)
Source: Oklahoma Department of Transportation (ODOT)
FDOT project: BDV 31-977-21
Project manager: Will Potter
University of Florida
Principal investigator: Gary Consolazio
Graduate research assistant: George Kantrales

Background
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Past UF/FDOT research
• More accurate structural analysis procedures
• Coupled dynamic (barge and bridge together)
• Simplified dynamic (impact force-time history)
• Equivalent static (load cases)
• Barge impact load-prediction model
• Revised probability of collapse expression (based on reliability analysis)
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Current Work
• No previous research on predicting the frequency of barge-bridge impacts
• Current AASHTO impact probability expressions developed in late 1980's
• Changes in vessel technology and operator training
• Advances in GPS accuracy (within 300 ft to within 40 ft)
• Lack of available barge-bridge accident data (other vessel casualties also used)
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Objective
• Propose revisions to AASHTO specifications which predict the frequency of barge-bridge collisions
• Recent barge traffic and accident data for Florida waterways (approach applicable nationwide)
• Concentrate solely on barge-bridge collision events
• Operate within existing AASHTO framework (recalibrate specific values based on collected data)
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Project Tasks
• Task 1 ( completed ): Literature review
• AASHTO, Eurocode, related research
• Task 2 ( completed ): Methodology
• Selection of data sources and analysis procedures
• Task 3 ( nearly complete ): Data collection
• Collection of all data required to perform statistical analyses
• Task 4 ( underway ): Data analysis
• Analysis of collected data, formulation of revised probabilities, and preparation of risk assessment examples
• Task 5 (outstanding): Final report
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Task 1: Literature review
( completed )

Literature Review
1.
AASHTO specifications
2.
Eurocode provisions
3.
Related research
Source: Oklahoma Department of Transportation (ODOT)
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AASHTO Bridge Design Spec. (2014)
• Default design methodology for vessel impact: comprehensive risk assessment
• Compute the Annual Frequency of Collapse ( AF ) for each bridge element :
Probability of Impact (PI)
AF
     
N - Number of vessel transits per year
PA - Probability of vessel aberrancy
PG - Geometric probability of collision
PC
PF
- Probability of collapse
- Protection factor
•
AF values compared against permissible limits (0.001 for typical bridges, 0.0001 for critical/essential bridges)
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AASHTO Bridge Design Spec. (2014)
• Probability of Aberrancy ( PA ):
PA
    
R
XC
  
BR - Base aberrancy rate (0.00006 [ships], 0.00012 [barges])
R
B
R
C
R
XC
- Bridge location modification factor
- Current (water velocity) modification factor
- Cross-current (water velocity) modification factor
R
D
- Vessel traffic density modification factor
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AASHTO Bridge Design Spec. (2014)
• Geometric Probability ( PG ):
• Mean corresponds to centerline of vessel transit path
• Standard deviation is the overall vessel length (LOA)
• Any bridge elements outside of 3 x LOA from the centerline need not be considered in the risk analysis
(AASHTO 2014)
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AASHTO Bridge Design Spec. (2014)
PF
 
Protection Provided /100) source: https://www.flickr.com
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Eurocode 1: Actions on Structures
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Related Research and Findings
• Relevant research reviewed: Friis-Hansen and Simonsen
(2003); Gucma (2003); Hutchinson et al. (2003); Kunz
(1998); Larsen (1993); Wang and Wang (2014); Zhang
(2013); Zhou (2011)
• Findings
• No study focused specifically on quantifying barge-bridge collision probabilities
• Many variables not readily characterized probabilistically (e.g., human error, current conditions)
•
Most prominent existing empirical method (AASHTO) was developed with limited data
• Remains a need for a revised empirical approach focused specifically on barge-bridge collisions
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Task 2: Methodology
( completed )

Interviews
• What factors may have caused a change in BR since the early 1990s?
• Interview with lead author of existing AASHTO provisions
• Reviewed basis for existing BR expression
•
Barge-bridge accident data not readily available
• Different types of vessel casualties used (e.g., strandings)
• Interviews with tug operators
• Global positioning systems (GPS)
•
Automatic identification systems (AIS)
• Electronic chart and display systems (ECDIS)
•
Advances in mechanical technology
• Changes in operator training
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Approach
• Re-calibrate design base aberrancy rate ( BR ) for barges
•
Collect barge-bridge accident data for Florida bridges
• Collect supporting information for each bridge site (e.g., barge traffic, water current data)
• Back-calculate BR values for each bridge location
•
Determine re-calibrated design BR value(s) for barges
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Re-calibration of Base Aberrancy Rate ( BR )
• Revised BR values will be derived using current AASHTO expressions
AF
     
• Probability of Impact ( PI ): the probability that a given vessel will strike the bridge
PI
    
• Expanding:
PI
     
R
XC
    
•
Rearranging terms:
BR

   
R
XC
PI
    
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Task 3: Data collection
( nearly complete )

Data Collection – Collision Data (completed)
• Barge-bridge collision data obtained from United States
Coast Guard (USCG)
• Data collected every year from 2002-2014
•
Some data available
Jacksonville for earlier incidents Pensacola
(as early as 1992)
Tampa
(map adapted from: the United States Geological Survey [USGS])
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Data Collection – Collision Data (completed)
• Collision data sets
• Contain incident date, location of incident, vessel information, narratives
• Screened to remove events other than barge-bridge impacts
• In some cases, relevant data fields were blank (e.g., vessel dimensions were omitted)
• Collision incident reports (CG-2692 and CG-2692A)
• Original incident reports for each collision
• Obtained from the USCG through the Freedom of Information Act
(FOIA)
•
Used to obtain information left out of previously collected data and to determine the cause of each collision
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Data Collection – Barge Traffic Data (underway)
• Barge traffic data requested from the United States Army
Corps of Engineers (USACE)
• Data requested every other year from 2002-2014
•
40% of requested data sets have been obtained
• Data associated with mile marker locations near bridges
•
Traffic (trips) data organized by year, vessel characteristics (e.g., length, width) and direction of travel
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Data Collection – Barge Traffic Data (underway)
• Processing methodology
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Data Collection – Other (completed)
• Bridge plans
• Needed for: PG ; PF
• FDOT district offices
• Water current data
• Needed for: R
C
; R
XC
•
National Oceanic and Atmospheric Administration (NOAA)
• Hydraulic reports
•
Accident reports
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Task 3: Data analysis
( underway )

Data Analysis – Probability of Impact (
PI )
PI
 t

2014

 i
BC t
N
T
PI - Probability of impact (per vessel passage)
BC t
- Number of vessel casualties that occurred in year t
N
T
- Number of barge transits from year t i to 2014
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Data Analysis – Geometric Probability (
PG )
• AASHTO (2014)
• Flotilla with fewest number of rows and columns will be used
• Results in a lower calculated PG
•
Conservative recalibration of BR
BR

   
R
XC
PI
    
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Data Analysis – Protection Factor (
PF )
• AASHTO (2014)
PF
 
Protection Provided /100) source: https://www.flickr.com
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Data Analysis – Modification Factors (
R
B
)
•
AASHTO (2014)
• Within turn or bend
R
B
 


45

•
Within transition region
• 3,000 ft from the end of the turn or bend
R
B
 


90

• Smallest R
B value will be selected
(conservative)
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Data Analysis – Modification Factors (
R
C
,R
XC
,R
D
)
• AASHTO (2014)
• Current and cross-current ( R
C
, R
XC
)
• Calculated directly from velocity data
R
C


1
V
C
10 
• Vessel traffic density ( R
D
)
• Low density ( R
D
= 1.0)
• Average density ( R
D
• High density ( R
D
= 1.3)
= 1.6)
R
XC

V
XC

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Data Analysis – Modification Factors (
R
D
)
• Selection of R
D value for each bridge location
• Based on calculated VDF values and possible consultation with industry professionals (e.g., tug operators, bridge designers, port captains)
VDF


N
W
VDF

N
- Vessel density factor
- Average annual barge traffic
W - Width of the waterway near the bridge location
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Data Analysis – Re-calibration of
BR
Calculate BR values for each bridge location:
BR

  
R
XC
PI
   
Assess variability among BR predictions computed sample statistics
Based on f ndings, select revised BR value(s) for barges that may be used in risk analyses of new and existing structures using current
(AASHTO) procedures
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Thank you for your attention
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