bwf fwd harmony v090610d

7/27/2019 BWF FWD Harmony v090610d

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Insert the title of yourpresentation here

Presented by Name Here

Job Title - Date

Different loads and load pulses

make comparisons between LWD,

FWD, HWD and SHWD difficult

Brian Ferne and Peter LangdaleTRL 10 June 2010

EUROFWD10

(6th

European FWD Users Group Meeting)

BRRC, Brussels10 and 11 June 2010,


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Insert the title of yourpresentation here

Presented by Name Here

Job Title - Date

or Harmonising FWDs?

Brian Ferne and Peter LangdaleTRL 10 June 2010

EUROFWD10

(6th

European FWD Users Group Meeting)

BRRC, Brussels10 and 11 June 2010,


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Page 3

Table of contents

A short history of harmonisation

Introduction to FWDs, L(F)WDs, H(F)WDs and SH(F)WDs

History of harmonisation

Crow/COST336

UK HA correlation trials

1

23

4

5

LWD use and comparisons

HWD use and comparisons

Summary and questions to be answered

6

7

8

USA SHRP procedure


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History of measurement

Pulse loads

- 1963 Bretonniere France

- 1964 Finsen/Ullidtz/Gautier Denmark

- 1966 Isada USA

- 1968? First Phoenix FWD, Denmark

- 1968? First Dynatest FWD, Denmark- 1976 First KUAB FWD, Sweden

- 1987 First JILS FWD, USA

- 19?? First Komatsu FWD, Japan


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What is an FWD? (1)


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d1

d5

d3

d4

d2

d6 d7

Applied load

Falling Weight Deflectometer Schematic

Geophones

Deflection bowl

Loading plate


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Types of FWD

FWD (Falling Weight Deflectometer)Peak load = 25 to 100 kN

HWD (Heavy Weight Deflectometer)

Peak load = 50 to 250 kN

LWD (Light Weight Deflectometer)

Peak load = 1 to 10 kN


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How do we use FWDs onpavements?

To assess the structural properties of

New pavements

In-service pavements

Rehabilitated pavements

Structural properties can include layer stiffnesses and loadtransfer at joints or cracks


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Therefore :

Vital that:

Measurement

InterpretationIs

Accurate

Consistent


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Therefore :

Vital that:

Measurement

InterpretationIs

Accurate ?

Consistent


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First overall assessment

1989

Comparison of Falling Weight Deflectometer systems available inthe United Kingdom


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Four Survey Contractors


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QuestionHow should we test our FWDs?

Main Options:

USA SHRP-LTPP

- emphasis on calibration of

components

Dutch CROW protocol- emphasis on correlation of

whole systems


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Main Options:

USA SHRP-LTPP

Dutch CROW protocol



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Main Options:

USA SHRP-LTPP

Dutch CROW protocol

Preliminary trial held in November 1998 sponsored by

the Highways Agency with support from the UK andIreland FWD Group



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Six machines from five companiesSix machines from five companies

-- FiveFive FWDsFWDs, one HWD (all, one HWD (all DynatestDynatest))

All machines similarly configuredAll machines similarly configured

(Load, geophones, plate size, 5 drops, smoothing)(Load, geophones, plate size, 5 drops, smoothing) Machines inspectedMachines inspected

modelmodel

weight and buffer configurationweight and buffer configuration plate typeplate type

load attainment methodload attainment method

geophone locationsgeophone locations

calibration detailscalibration details

PreliminaryPreliminary

1998 FWD1998 FWD

Correlation TrialCorrelation Trial


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How do we use the results?

Pass/fail criteria

FCF (mean) >0.95 and 0.90 and


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Trial Development

1998 - preliminary trial (6 machines)

1999 - second trial (also looked at rigid pavements,mid slab and joints)

(7 machines)

2000 - First mandatory trial!

(9 machines)

2000 First mini trial

Now annual exercise with 16 machines in 2005

20 machines in 2010


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HA requirements for measurement

All machines operating on trunk road network must:

Take part in and pass annual correlation trial

Be retested following any major maintenance


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FWD Correlation 2009 - FCF


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FWD and LWD test equipment

Comparison of foundation stiffness


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Comparison of foundation stiffnessmeasurements by LWD and FWD

Repeatability of FWD : Low stiffness foundation

1

10

100

1000

10000

0 50 100 150 200 250 300 350

Foundationstiffn

ess(MPa)

PRIMA FWD


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LWD and FWD test methods

Is the relationship between an LWD and a

FWD dependent on the foundation typetested?

Comparison of LWD and FWD on an


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Comparison of LWD and FWD on anunbound granular foundation

0

100

200

300

400

0 50 100 150 200 250 300Surface stress (kPa)

Surfacemo

dulus(MPa

PRIMA FWD

Comparison of LWD and FWD on a


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Comparison of LWD and FWD on abound foundation

0

100

200

300

400

0 100 200 300 400 500Surface stress (kPa)

SurfaceModulus(MP

a)

PRIMA FWD

Comparison of LWD and FWD on


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Comparison of LWD and FWD onunbound and bound foundations

Foundation stiffness (MPa) by:Foundation

typeLWD FWD

Proportionaldifference*

(%)

167 210 -20

204 244 -16

110 138 -21

98 115 -15

Unbound

38 78 -53Weakly bound 89 108 -18

335 321 5Bound

1055 1125 -6

*{(LWD-FWD)*100 / FWD}

Potential LWD/FWD adjustment and


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Potential LWD/FWD adjustment andtest procedure

Test Demonstration Area with LWD and FWD

Calculate factor to adjust LWD test results

Confirm precision of calibration is adequate

Use LWD on Main Works with results adjustedby factor.

Compare running mean averages of 5 testresults and individual values with targetstiffness values


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Two questions were posed:

-Is it essential to use a Heavy WeightDeflectometer when assessing airfields?

-How should we interpret the results from

FWD/HWD?

FWD HWD C i


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FWD - HWD Comparison

The study:

FWD (TRL) and HWD (Dynatest UK)

Simultaneous testing Range of airfields and constructions

Load transfer testing (joints)

Stiffness testing (mid-slab)

Effect of load

Effect of plate size

FWDFWD HWD C iHWD C i R lt ( idR lt ( id l b)l b)


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FWDFWD -- HWD ComparisonHWD ComparisonResults (midResults (mid--slab)slab)

Scampton Slab B6 Central Deflections (D1)

0

100

200

300

0 50 100 150 200 250 300

Load (kN)

Deflection(microns)

FWD 300mm plate

FWD 450mm plate

HWD 300mm plate

HWD 450mm plate

FWDFWD HWD ComparisonHWD Comparison Results (midResults (mid slab)slab)


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Marham Slab E1 Cent ral Def lectio ns (D1)

0

100

200

300

400

0 50 100 150 200 250 300

Load (k N)

De

flection(m

icrons)

FWD 300mm plateFWD 450mm plate

HWD 300mm plate

HWD 450mm plate

FWDFWD HWD ComparisonHWD Comparison Results (midResults (mid slab)slab)


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Cottesmore Slab G1 Central Deflections (D1)

0

100

200

300

400

0 50 100 150 200 250 300

Load (kN)

Deflection(microns)

FWD 300mm plate

FWD 450mm plate

HWD 300mm plate

HWD 450mm plate

FWD HWD Comparison Conclusions


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No systematic differences between the FWDand HWD test results

Generally good agreement in the mid-slab

results between test machines and platesizes

However more recent work has suggestedthat there can be significant differences oncertain airfield pavement constructions

FWD - HWD Comparison Conclusions


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Introduction of Super Heavyweight FWD - SHWD

Page 36

Alternative calibration approach?


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(1)

Use independent deflectionmeasure e.g.accelerometer?

C o m p a r i so n o f F WD a n d A c c e l e r o m e t e r : 3 0 0 m m o f f

-100

-50

0

50

100

150

200

250

51.41 51.42 51. 43 51.44 51. 45 51.46 51. 47 51.48 51.49

t i m e ( s e c s )

Ac cel er ometer

FWD

-200

-150

-100

-50

0

50

100

150

200

250

300

0 10 20 30 40 50 60

Time [s]

Deflection[m]

Alternative calibration approach? (2)


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But an accelerometer confirms just the response of partof the system the deflection measuring part

What about the correctness of the loading system?

For rolling wheel loading, pavement response dependson load configuration and speed the load configurationis can be defined fairly easily but will the response of thetyres remain the same over time?

For FWD impulse loading the response also depends onthese parameters what is the correct loading pulse?

how well defined is this?

Varying load pulse on one FWD


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Varying load pulse on one FWD

-100

0

100

200

300

400

500

600

700

800

900

0 10 20 30 40 50 60

Time (s)

Pressure(kPa)

Test 1

Test 2

Test 3

Test4

-100

-50

0

50

100

150

200

250

300

0 20 40 60 80

Time (s)

Deflection

@D

1

Test 1_d1

Test 2_d1

Test 3_d1

Test4_d1

FWD pulse with different durations

Deflection response at Geophone 1

FEM modelling of FWD pulse


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FEM modelling of FWD pulse

-0.2

0

0.2

0.4

0.6

0.8

1

1.2

0 0.01 0.02 0.03 0.04

Time (s)

Normalisedpulse

-0.00001

-0.000005

0

0.000005

0.00001

0.000015

0.00002

0.000025

0.00003

0 0.02 0.04 0.06 0.08

Time (s)

Verticaldeflection(m)

Pulse 0

Pulse 1

Pulse 2

Normalised pulse shapes used in

some Finite Element analyses

Effect of FWD pulse on the vertical

deflection under the centre of the

plate

Extracts from :Staring at Deflection Traces: Lookingor the Truth in Time Histories by David P Orr


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or the Truth in Time Histories by David P Orr,Cornell LRP

-700

-600

-500

-400

-300

-200

-100

0

100

200

0 10 20 30 40 50 60

Time (mSec)

Deflection

(m

icrons)

-400

-300

-200

-100

0

100

200

300

400

500

600

0 10 20 30 40 50

Time (mSec)

Deflection(

m

ic

rons)

-300

-200

-100

0

100

200

300

0 20 40 60 80 100 120

Time (mSec)

Deflection(

microns)

-150

-100

-50

0

50

100

150

200

250

0 20 40 60 80 100 120

Time (mSec)

Deflection

(mic

rons)

Brand Average Rise Time

(mSec)

Carl Bro 13.2

Dynatest 13.1

JILS 18.4

KUAB 14.5



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Could we compare/calibrate all deflection measuringdevices with the deflection response under a standardaxle at traffic speed?


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Some questions for discussion? (1)

Page 43

Can we define a specification for a standard FWD for each main

purpose?

Is calibration of the individual components adequate or do we needto check the whole system?

If we use the fleet mean as the reference, how many machinesand of what type are needed?

If so, how do we prevent a steady change in the mean of the

fleet?


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Some questions for discussion? (2)

Page 44

Since, ultimately, we are using FWD measurements to predict thestructural condition of the pavement, and its response to rolling wheelloads:

Should we therefore also be referencing all measurements topavement responses under a standardised rolling wheel load?


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Thank you!

Presented by Brian Ferne 10 June 2010Tel: +44-1344-770668Email: [email protected]

bwf fwd harmony v090610d

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