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Characterizing the Load Environment ofWashington State Ferries & Alaska Marine

Highway Ferry Landings

Andrew T. Metzger, Ph.D., P.E.

Jonathan Hutchinson, E.I.T.

December, 2010

GoTo Meeting


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Scope

Project overview

Assess design criteria for vessel loads on Ferry

Dolphins (AKDOT&PF) and Wingwalls (WashDOT)

Long-term in situ monitoring of active ferry landings

Collect a sample of structure response to vessel loading

Determine design load criteria based on sample

statistics


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Auke Bay Study

Auke Bay Study - dolphins


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Auke Bay Study

Study of loads from vessels

Model fender pile with available geotechnical

information

Measure compression of side-loaded cylinders

Axial strain in tripod piles

Measurements collected at 5Hz

Identify maximum load for event

Collect sample over approx. 1 year of operation


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Auke Bay Study

Study of vessel berthing energy

Distance measurements at 5 Hz during vesselapproach and impact

Estimate impact velocity from distancemeasurements

Energy is estimated with displacementmeasurements and SAP model

Statistics for Vessel impact velocity

Impact energy

Mass + added Mass at impact


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Dolphins monitored:

70 complete berthing events have been collected for Five different vessels.

Monitoring will continue into July, 2011

W2 and E4 monitor Mooring Loads

E1 and E3 monitor Berthing loads

E2 monitors both Berthing and Mooring loads


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Motion Sensors on E1 and E2 Two motion sensors located 10 from

dolphins E1 and E2

Used to measure approach of

berthing vessels at E1 and E2


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LMTs (linear motion transducers) One LMT located adjacent to each

cylindrical fender


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Tide Gage: at E1

Monitors tide

Used to estimate elevation of

ship sponson.

i.e., point of application of load


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Strain Gages on Piling

Gages placed on dolphins:

E1, E2, and E3

Oriented to measure

Axial Strain in piling

Axial force is calculated real-time

and stored in datalogger


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Mooring Instrumentation: Original method: determine mooring forces by

measuring bending stresses in bollards.

Assumption that the primary

stress in the bollards, from

mooring loads, are bending

stresses.


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Data

Data has been collected for 70 berthing events

Datalogger takes measurements continuouslybetween events

Begins to store data when vessel is with ~ 20of E1 motion sensor


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Data

For each event:

Data collection for 10 minutes (3,000 records)

Each day, data is downloaded from Juneau to

Fairbanks via digital cellular modem

For each event:

Data collection for 10 minutes (3,000 records) Each day, data is downloaded from Juneau to

Fairbanks via digital cellular modem


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Vessel Approach Profile: E1

Typical Malaspina

position vs time

Graph for E1

Used to determine

approach velocityNormal to dock for

each per berthing

event.


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Bollard Data for E2

Shows the mooring line

effect on the force in

the Piles


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Time history for:

Malaspina, August 23, 2010on Dolphin E1

LMT

Pile Force

Vessel Motion


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Time History Pile Data: E2

Pile Reaction (Kips)

from Impact

and Springline


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Time History Pile Data: E2

Pile Reaction (Kips)

from Impact


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Berthing Energy

Impact Energy is needed for design vessel

berthing structures

Cannot measure energy directly

Can be inferred from structure response:

2 2

2 2

mv kxE = =


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Berthing Energy

We are directly measuring

Velocity, v

Fender displacement

Using a structural analysis software (SAP) +

available geotechnical information

Related fender displacement to dolphin

displacement


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Berthing Energy

Relating fender displacement to dolphin displacement

Fender stiffness taken from manufacturer data

Tri-pod stiffness modeled with SAP model; accounting for data frompile driving logs

Fender support piles notes from driving logs piles went to bedrock under self weight

Driven another 1-2 feet

soil is poor and likely deformed from previous displacements

Given poor soil condition and relatively long length of piling

Chosen to ignore lateral stiffness probably small compared to fender andtripod stiffness

Personally observed that ANY wave action causes movement in fendersupport piles

E1 Force vs Deflection


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y = 27.66x y = 7.375x y = 5.822x

0

20

40

60

80

100

120

0 5 10 15 20

Force

(Kips)

Deflection (inches)

E1: Force vs Deflection

Tripod

Fender

Combined (Fender +Tripod)

y = 0.3766x2

y = 0.3072x2

y = 0

0

10

20

30

40

50

60

70

80

0 2 4 6 8 10 12 14 16

EnergyAbsorbedbyS

tructure(ft-kips)

Fender Deflection (inches)

E1: Energy vs Fender Deflection

Combined (Fender + Tripod)

Fender

Tripod

1 1 1

2dolphin tripod fender

k k k= +


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Ksys

0

20

40

60

80

100

120

140

160

0 2 4 6 8 10 12 14 16 18 20

FORCE(K

IPS)

TOTAL DEFLECTION (INCHES)

Force vs Fender Displacement

Kt


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Time history for:

Malaspina, August 24, 2010on Dolphin E1

Recall our Extreme Event:

Vessel Motion

Pile Force

LMT


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Fender supportpiling probablycontacted tripod

platform

Evidence of this

occurring (gougesin toe-kick plates;bent cap plates)


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Evidence of this occurring (gouges in

toe-kick plates; bent cap plates)

S d l f l hi 2


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Sap Model of Dolphin E2:

Energy from a berthing vessel is

absorbed by both the fender

AND the tripod structure

Determining Berthing Energy:


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Results

Histograms

Normal Approach Velocity

Berthing Energy


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E1 histograms


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Results

Histograms Berthing Factor, Cb

from

We can represent the kinetic energy as

Where c is a factor representing uncertainty associated with Added mass

Mass of cargo

Other uncertainties

A multiplier applied to the mass to account for uncertainties inberthing energy

( ) 2 2

2 2

am m v kx

Energy+

= =

( )2

2

b vC m v


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Results

Histograms A correction factor histogram will also be constructed

(presently, in the works)

Consistent with heavy shipping industry

Presently, correction factors are hard to find for ferry classvessels

Result is a probability distribution for the correction factor(histogram)

2

2f n e m c s

ME V C C C C=


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Implementation

Statically description of relevant design

parameters

Description of the uncertainty for:

Normal velocity

Impact energy

Correction factor


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Implementation

Any of these parameters can be used for

design end user will have options

Design Energy

Specify acceptable deflection,x

design structure with necessary stiffness

2

2E

k x=


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Implementation

Reliability-based design

Method to account for uncertainty in design

Result is a structure with quantified degree ofreliability

Probability of not failing LRFD approach in structures


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Implementation

Reliability baseddesign

Fit a distribution tohistogram

Identify demandvalue with lowprobability ofexceedance

This will be thedesign value

Implementation


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p

Reliability baseddesign

Design pointchosen forspecified reliability

index

Our new designpoint(s) will becompatible withexisting designcodes:AISC, ACI, NDS

Implementation


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p

Reliability based

design

Reliabilitybased

design criteria formarine structuresdo notexist, presently

Implementationtimeframe:immediate


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Characterizing the Load Environment of

Washington State Ferries & Alaska Marine

Highway Ferry Landings

Thank you so much!