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/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


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)


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


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


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


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


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


Experimental set upConventional instrumentation

• Strain gages on lateral faces• LVDT on the top face, at the interface and under loads


Experimental set up« Innovative » instrumentation: NDT with P- and S-wave propagation


Ultrasonic tools MesurementsThe arrival time: velocities Cp and CsThe maximum amplitude


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


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


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


ResultsConventional instrumentation at +10°C

• Strain amplitude• Linear regression• Good repetability• Strain limit

Crack at the intersection of 2 straight lines

1500 µstrains


Results: Conventional instrumentation at -10°C

Crack at the intersection of 2 straight lines

1000 µstrains


Results NDT at +10°CQuick decrease

Material’s heating

Slow evolution

Fatigue behavior

Quick decrease -

Cracks influences waves transmission(delay and amplitude)


Results Fracture photographs

bubbles with soapy water

Cracking in the section of the welded stiffener


HOUEL Adrien – ARNAUD Laurent

Results Test on UHPConcrete


Results NDT on UHPC concrete


– 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


Results UPP - Cylindrical cores at -10°C


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

Thank you

for your attention …

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