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Page 1/21Five-point bending testfor orthotropic steel decks
The five-point bending testapplied on wearing courses
laid on orthotropic steel decks
ARNAUD LaurentENTPE CNRS FRE 3237 - member of the University of Lyon
HOUEL Adrien – CETE de Lyon, LRPC
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Context : The five-point bending test
• 70’s: LCPC [Hameau, 1981]• 2003 - 09: ENTPE
• 5 Civil Engineering Masters [Laajili, 2003], [Houel, 2004], [Somda, 2007], [N’ Guyen, 2008], [Cohen Solal, 2009]
• 1 Ph. D. thesis [Houel, 2008]
• 2006: French standard method (NF P 98-286)
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Problematic
1. Design of the asphalt layer on steel orthotropic decks by means of laboratory test
• Flexibility of steel deck• High level of strain in asphalt pavement• Life time prediction
2. Monitoring of mechanical evolution of the asphalt layer throughout the fatigue tests
3. Detection of asphalt cracking
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Complementary approachs
1st experimental approachThe five-point bending test
•Device set up and instrumentation•Results
NDT based on ultrasonic wave propagation
2nd experimental approachTests on cylindrical cores UPP
•Thermal characterization•Mechanical characterization•Fatigue characterization
NDT based on ultrasonic wave propagation
Modelling
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Outline1 The experimental device : The five-point bending test
• Specimens
• Load
• Instrumentation (strain gauges, displacement sensors, temperature)
• Innovative instrumentation: NDT by wave propagation (P and S-waves)
2 Results3 Conclusions and On going works
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Experimental device Specimens Sample
(200*580mm)
=
Steel plate and stiffener (12mm)
+
Sealing sheet (3mm)
Wearing course
(65mm)
Supports
(Inferior part)
Load transmission
Hydraulic press frame
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The five-point bending test (FPBT)
Mechanical Load : Sine cycle fatigue
Frequency = 4 HzLoad amplitude = -3.2 to -32 kN after plate calibration(e.g. 12mm thick steel plate –625 µdef on upper part of steel plate)Several million cycles : 1 to 5.106 cycles
Temperature : -10°C and +10°C
Zones in compression
Zone in tension
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Experimental set upConventional instrumentation
• Strain gages on lateral faces• LVDT on the top face, at the interface and under loads
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Experimental set up« Innovative » instrumentation: NDT with P- and S-wave propagation
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Ultrasonic tools MesurementsThe arrival time: velocities Cp and CsThe maximum amplitude
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Ultrasonic tools Analysis• Propagation in an infinite elastic medium:
where M is the constrained modulus, G the shear modulus and ρ is the mass density
• Asphalt concrete = viscoelastic mediumComplex modulus M*= M’+jM’’
If , we have:
By inverse analysis , the complex modulus is obtained.
M = ρVP2 G = ρVS
2
tanδ = ′ ′ M / ′ M << 1 M ' ≈ ρVP2
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Ultrasonic tools : Precautions• Asphalt concrete = heterogeneous material (10 mm)• Appropriate excitation frequency (diffraction, multiple
scattering, attenuation,…)
λ (mm) -10°C +10°C
P-wave(50 kHz)
70 60
S-wave(10 kHz)
150 200
Size of specimens >> Wavelenght λ >> heterogeneties
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Experimental programme4 asphalt mixes: same granulometry, different
bitumen• Asphalt mix of the Millau viaduct
• « Classic » asphalt with polymer-modified binder
• Asphalt mix with pure binder
• Asphalt concrete with polymer-modified Styrelf® binder
8 specimens (5 at +10°C and 3 at -10°C)
1 test with a 35mm-thick UHPC pavement
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ResultsConventional instrumentation at +10°C
• Strain amplitude• Linear regression• Good repetability• Strain limit
Crack at the intersection of 2 straight lines
1500 µstrains
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Results: Conventional instrumentation at -10°C
Crack at the intersection of 2 straight lines
1000 µstrains
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Results NDT at +10°CQuick decrease
Material’s heating
Slow evolution
Fatigue behavior
Quick decrease -
Cracks influences waves transmission(delay and amplitude)
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Results Fracture photographs
bubbles with soapy water
Cracking in the section of the welded stiffener
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HOUEL Adrien – ARNAUD Laurent
Results Test on UHPConcrete
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Results NDT on UHPC concrete
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– UPP tests– 3 extensometers (±5.0mm)
E*(f,T,t)– 2 orthoradial stress gauges
ν*(f,T,t)– Temperature sensors– P-wave transducersdirectly on asphalt
2nd Experimental device on Cylindrical cores
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Results UPP - Cylindrical cores at -10°C
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Conclusions & On going works
• The FPBT enables the dimensioning of asphalt mix on orthotropic deck (French standard test)
• Strain measurements lead to the detection of fatigue macrocracks
• Ultrasonic wave propagation enables the monitoring of the time dependant mechanical characteristics of asphalt or UHPC pavement
• Theorical approach : modelling taking into account viscous-elastic and fatigue effects with refined parameters
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Thank you
for your attention …