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1
Remaining Life of Concrete Sleepers: A
Multifaceted Approach
A/Prof Alex RemennikovSchool of Civil, Mining and Environmental
EngineeringUniversity of Wollongong, NSW, Australia
University of Wollongong
Introduction
2
This project will give track owners methods of more accurately assessing the dynamic capacity of in-track concrete sleepers.
As commercial pressures drive up axle loads and train speeds, deferring large-scale sleeper replacement through higher sleeper capacity rating has the potential for very large savings in capital expenditure for owners.
To establish better methods of sleeper rating, the method is based on in-track and laboratory-based studies of the static, dynamic and impact behaviour of sleepers, of the actual loading regimes experienced by sleepers in-track, and detailed material characterization of the concrete.
2
Three-Pronged Characterisation Approach
Strength
Loading
Materials
• Static tests• Impact tests• Fatigue tests• Prestressing tests• Processing of WILD
data• Spectral analysis of
WILD• Forecasting for next
5-10 years• Limit states design
checks• Concrete strength• Cement content/w/c ratio
• Ultrasonic Pulse Velocity
• Concrete carbonation• Sulphate Attack and Delayed
• Ettringite Formation
3
Loading Characterisation for Railway TrackCollection and Processing of Wheel Impact Detectors Data
Spectral Analysis of Data from WILD
Extrapolation of data for next 5-10 years period
Limit States Design Checks
Impact load, forecasting
9
Return period (years) 1 10 50 100 2000 Maximum likely incremental impact force (kN)
320 370 385 415 475
Strength Characterisation for Concrete Sleepers
Static bending testing
Dynamic impact testing
Fatigue testing
Prestressing tests
STATIC TESTS
11
Rail seat vertical load tests – Negative and Positive Bending Moments
Centre Negative and Positive Bending Moment Tests
11
DYNAMIC TESTING
12
Concrete Sleepers Impact Load Testing Facility at UoW
Characteristics:• Height of impact = 6 m• Weight of anvil = 600 kg• Max impact velocity = 10
m/s• Max impact energy =
10,000 J• Max impact load = 2000
kNMonitoring equipment:• Dynamic load cell• Laser displacement
sensors• Accelerometers• Strain gauges• High-speed camera
12
DYNAMIC TESTING
13
Impact tests setup
Falling anvil 600 kg
Shock absorbers
Strong floor
Tested concrete sleepers
Sleeper support system
Optical trigger
13
DYNAMIC TESTING
14
Impact tests setup – sleepers support systems for different track moduli
Moderate track modulus (20-70 MPa)
Very soft track (8 MPa) Very hard track (120 MPa)
Ballast (200 mm)
Sand-rubber Mix (200 mm)
Strong Concrete Floor (1.5 m deep)
Strong Concrete Floor (1.5 m deep)
Ballast (150 mm)
Shock mat (10mm) Shock mat
(10mm)
14
VERIFICATION OF PRESTRESSING
15
Test arrangement and instrumentation
Specimens prepared for dynamic relaxation tests at sleeper centre
Strain gauges attached to steel wires
Wire cutting and data recording procedure
15
TYPICAL RESULTS – STATIC TESTING
16
Rail Seat Bending Strength
Displacement (mm)
Tota
l loa
d (k
N)
0 4 8 12 16 200
100
200
300
400
500
600UOW5UOW6
Displacement (mm)
Tota
l loa
d (k
N)
0 4 8 12 16 200
100
200
300
400
500UOW7UOW8
16
TYPICAL RESULTS – STATIC TESTING
17
Centre Bending Strength
Displacement (mm)
Tota
l loa
d (k
N)
0 10 20 30 400
20
40
60
80
100
120UOW1UOW2
Displacement (mm)
Tota
l loa
d (k
N)
0 10 20 30 40 500
30
60
90
120
150UOW3UOW4
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TYPICAL SUMMARY OF STATIC TEST RESULTS
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Type of test Sleeper marks
Cracking load (kN)
Cracking moment (kN.m)
Ultimate load capacity (kN)
Ultimate moment capacity(kN.m)
Design moment capacity (kN.m)
1 Centre positive moment (MC+)
UOW1 78 30.0 99 3838
UOW2 85 32.6 99 38
2 Centre negative moment (MC-)
UOW3 85 32.6 104 4040
UOW4 110 42.2 138 52
3 Rail seat positive moment (MR+)
UOW5 350 57.8 575 9595
UOW6 350 57.8 580 96
4 Rail seat negative moment (MR-)
UOW7 150 24.8 420 6958
UOW8 150 24.8 350 58
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RESULTS – IMPACT TESTING
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Hard Track Support Condition
Experimental setup
High-speed camera for recording short duration impact event
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RESULTS – IMPACT TESTING
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Hard Track Support ConditionImpact testing program (based on predicted impact load from spectral analysis of WILD data)
Test No
Drop height (mm)
Maximum load (kN)
Loading duration (msec)
Observed damage
1 910 606 14 no damage2 910 570 15 no damage3 915 615 13 no damage4 915 625 14 first minor
crack
5 915 580 14 crack propagation
6 915 590 14 no additional damage
7 915 637 13 no additional damage
8 915 613 13 no additional damage
9 915 630 13 no additional damage
10 915 630 14 no additional damage
11 1025 700 13 no additional damage
Time (sec)
Impa
ct lo
ad (k
N)
0 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08 0.09 0.10
50100150200250300350400450500550600650
Time (sec)
Slee
per v
ertic
al d
ispl
acem
ent (
mm
)
0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.45-15
-10
-5
0
5
10
15
20
25
Residual displacementdue to ballast crushing
Sleeper deformation from image processing
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RESULTS – IMPACT TESTING
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Hard Track Support Condition
Cracking at rail seat
Ballast crushing due to high impact loads
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RESULTS – LEVEL OF PRESTRESS
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Dynamic relaxation tests
Level of prestress for undamaged sleeper is
Time (sec)
Stra
in (
stra
in)
0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5-6000
-5500
-5000
-4500
-4000
-3500
-3000
-2500
-2000
-1500
-1000
-500
0
500Initial state - wire intact
Final relaxed state
Inertial effects
Prestressing Tendon 1Prestressing Tendon 2
Sleepers with damaged end and exposed steel wires
Time (sec)
Stra
in (s
trai
n)
0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5-4000
-3500
-3000
-2500
-2000
-1500
-1000
-500
0
500
Initial state - wire intact
Final relaxed state
Inertial effects
Prestressing Tendon 1Prestressing Tendon 2
Level of prestress for damaged sleeper is
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Material Characterisation for Concrete Sleepers
Concret
e Strength a
nd Modulus
of Elasticity
Cement Conte
nt and W/C
Ratio
Ultrasonic Pulse Velocity
Concrete Carbonation
Chloride Content Analysis and more
Material Characterisation for Concrete Sleepers
Concrete Strength
Ultrasonic Pulse Velocity Carbonation testing
Material Characterisation for Concrete SleepersLevel of Chloride at strand depth
Alkali Silica Reaction
Delayed Ettringite Formation/Sulphate Attack
Future Research Objectives:
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To revise current acceptance standards for prestressed concrete sleepers based on results of impact testing for fatigue and ultimate limit state conditions.
To revise current sleeper loading prediction methodology to reflect findings from the measurement and analysis of in-track data.
To develop a sleeper acceptance framework for sleepers.
To establish a methodology for capacity rating of concrete sleepers.
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