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AustPADS Finite Element Method Based Pavement Response to Load Model

Outline

• Introduction• Finite Element Method• Material characterisation• APADS - Austpads & Hosted service• Worked examples• Making sense of the results

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INTRODUCTION

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Background

• Current designs use CIRCLY to calculated critical strains

• CIRCLY is a – layered linear-elastic modelling of

materials– cross-anisotropy– GUI actively developed

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Background

• Austroads PTF want greater flexibility– future design tasks– non-linear modelling of materials

• Finite Element Method framework– provides headroom to grow– start a journey

• Austroads developed FEM tool– linear-elastic materials– cross-anisotropy– nonlinear-elastic materials– simple interface

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Schedule

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• Transitioning from CIRCLY to FEM– The journey started

• Official implementation– Not before some years

• Staged implementation1. Linear elastic 2. Nonlinear elastic

FINITE ELEMENT METHOD OVERVIEW

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Pavement model: what for?

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Objective: calculate the critical responses to be used for performance prediction (performance relationships)

Pavement model = multi-layered structure + axle load

Current pavement model• Multilayered • Infinite in plane• Subgrade semi-infinite• Wheel-load = circular

Critical strains locations

Finite Element Method: Quick Overview

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• Finite element method (FEM) in pavement engineering– Available finite element packages (ABAQUS, …) are very general– Program developed by academics (Universities, Research organisations…)

3D FEM pavement model

2D-axi. FEM pavement model

RT

z

Part 1Part 2

Part 3

Part 4

A

B

O

Asphalt

UGM

Subgrade

Part 1

Part 2

Part 3

Part 4

x

yz A

B

C

D

O

E

Asphalt

UGM

Subgrade

Linear vs nonlinear analysis

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Stress State

Mo

du

lus

E

1

Linear elastic material

=

Stress State σ

Mo

du

lus

E(σ)

1

1

1

1

Nonlinear elastic material

1

E(σ)

E(σ)

E(σ)

Linear analysis

Stiffness matrix is CONSTANT

=

Stiffness matrix varies with the stress state (i.e. load) Iterative process

Nonlinear analysis

LABORATORY MATERIALS CHARACTERISATION

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Presumptive model parameters

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Austroads project TT1452 developed presumptive model parameters: Report AP-T199-12 (Austroads, 2012)

– Base materials (High and normal quality crushed rock)

– Subbase materials

– Typical subgradesMaterial CBR (%) (MPa)

Silt (ML)2 10 0.0 -0.50… … … …5 35 0.10 -0.35

Highly plastic clay (CH)2 10 0.0 -0.50… … … …5 35 0.10 -0.35

Silty/sandy-clay (CL/SC)

3 15 0.0 -0.50… … … …10 70 0.15 -0.35

Sand (SW, SP)10 70 0.15 -0.35… … … …15 85 0.15 -0.35

Material (MPa)Upper granular subbase 175 0.9 -0.25Lower granular subbase 150 0.8

Material (MPa)High quality base 250 1.0 -0.25Normal quality base 220

Overview of the GUI

Overview of the GUI

Load definition

Traffic &

Performance

relationships

Pavemt structure

Layer characteristics

• Thickness

• Material parameters

• Critical strain location

WORKED EXAMPLE

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Sprayed sealed surfaced unbound granular pavementSubgrade design CBR = 5%

Unbound granular pavement: inputs

Material Thickness (mm)

Sub-layers thickness (mm)

Design modulus (Mpa) Poisson’s ratio V = H (-)

Ev EV/EH

Sprayed seal surface - na - - -

Unbound granular 475

95 500

2 0.35

95 314

95 198

95 125

95 79

Subgrade Semi-infinite na 50 2 0.45

Unbound granular pavement: inputs

Thicknesses Moduli Poisson’s ratio

Linear elastic

Unbound granular pavement: outputs

The calculation is running in the background

Unbound granular pavement: outputs

Thicknesses Moduli problem(being fixed)

Critical strain (CIRCLY output +/- 0.3%)

Austroads method (AGPT Part 2 – Appendix K.1)Critical strains from CIRCLY output:• Subgrade 906 μm/m midway between the loaded wheels

MAKING SENSE OF THE OUTPUTSLINEAR-ELASTIC

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Unbound pavement

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Asphalt surfaced unbound

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Asphalt surfaced unbound

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MAKING SENSE OF THE OUTPUTSNONLINEAR-ELASTIC

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Full depth asphalt

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Analysis types

• Linear–elastic– Results very similar to CIRCLY

• Nonlinear-elastic– Results different to CIRCLY– Need updated/calibrated performance

relationships

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Further information

Seek me out today.

26th ARRB Conference paper (Bodin et al).

www.arrb.com.au/ARRB-

Conferences

Austroads Report AP-T199-12

Thank youwww.arrb.com.au