FDOT project: BDV 31-977-21Project manager: Will Potter

University of FloridaPrincipal investigator: Gary Consolazio

Graduate research assistant: George Kantrales

Determination of Barge Impact Probabilities for Bridge Design

5th Annual FDOT Structures Research Update (Aug. 4-5, 2015)

Source: Oklahoma Department of Transportation (ODOT)

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Background

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• 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)

Past UF/FDOT research

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• 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)

Current Work

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• 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 (re-

calibrate specific values based on collected data)

Objective

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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

Task 1: Literature review(completed)

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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)

AF N PA PG PC PF

N

PAPG

PC

PF

• Default design methodology for vessel impact: comprehensive risk assessment

• Compute the Annual Frequency of Collapse (AF) for each bridge element:

- Number of vessel transits per year

- Probability of vessel aberrancy

- Geometric probability of collision

- Probability of collapse

- Protection factor

• AF values compared against permissible limits (0.001 for typical bridges, 0.0001 for critical/essential bridges)

Probability of Impact (PI)

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AASHTO Bridge Design Spec. (2014)

• Probability of Aberrancy (PA):

B C XC DPA BR R R R R

BRBR

CR

XCR

DR

- Base aberrancy rate (0.00006 [ships], 0.00012 [barges])

- Bridge location modification factor

- Current (water velocity) modification factor

- Cross-current (water velocity) modification factor

- 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)

source: https://www.flickr.com

1 (% /100)PF Protection Provided

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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

Task 2: Methodology(completed)

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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

• Probability of Impact (PI): the probability that a given vessel will strike the bridge

• Expanding:

• Rearranging terms:

AF N PA PG PC PF

PI PA PG PF

B C XC DPI BR R R R R PG PF

B C XC D

PIBR

R R R R PG PF

Task 3: Data collection(nearly complete)

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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

for earlier incidents

(as early as 1992)

Pensaco la

Tam pa

Jacksonville

(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: RC; RXC

• National Oceanic and Atmospheric Administration (NOAA)• Hydraulic reports• Accident reports

Task 3: Data analysis(underway)

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Data Analysis – Probability of Impact (PI)

2014

i

t

tt t

T

BC

PIN

- Probability of impact (per vessel passage)

- Number of vessel casualties that occurred in year t

- Number of barge transits from year ti to 2014

PI

tBC

TN

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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 re-

calibration of BR

B C XC D

PIBR

R R R R PG PF

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Data Analysis – Protection Factor (PF)

source: https://www.flickr.com

1 (% /100)PF Protection Provided

• AASHTO (2014)

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Data Analysis – Modification Factors (RB)

145

BR

190

BR

• AASHTO (2014)• Within turn or bend

• Within transition region• 3,000 ft from the

end of the turn or bend

• Smallest RB value will be selected (conservative)

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Data Analysis – Modification Factors (RC ,RXC ,RD)

• AASHTO (2014)• Current and cross-current (RC,RXC)

• Calculated directly from velocity data

• Vessel traffic density (RD)• Low density (RD = 1.0)

• Average density (RD = 1.3)

• High density (RD = 1.6)

110

CC

VR

1XC XCR V

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- Vessel density factor

- Average annual barge traffic

- Width of the waterway near the bridge location

Data Analysis – Modification Factors (RD)

• Selection of RD value for each bridge location• Based on calculated VDF values and possible consultation with

industry professionals (e.g., tug operators, bridge designers, port captains)

NVDFW

NW

VDF

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Data Analysis – Re-calibration of BR

B C X C D

P IB R

R R R R P G P F

C a lcu la te va lues fo r each b ridge location :B R

A ssess va riab ility am ong pred ic tionsB Rand deve lop conf dence bounds usingicom pu ted sam p le sta tis tics

B ased on f nd ings, se lect rev ised va lue (s ) i B Rfo r ba rges tha t m ay be used in risk ana lyses o f new and exis ting structu res using curren t (A A S H TO ) p rocedures

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Thank you for your attention

Questions?