Transcript 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.

AustPADS Finite Element
Method Based Pavement
Response to Load Model
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Outline
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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
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linear-elastic materials
cross-anisotropy
nonlinear-elastic materials
simple interface
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Schedule
• Transitioning from CIRCLY to FEM
– The journey started
• Official implementation
– Not before some years
• Staged implementation
1. Linear elastic
2. Nonlinear elastic
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FINITE ELEMENT METHOD
OVERVIEW
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Pavement model: what for?
Objective: calculate the critical responses to be used for
performance prediction (performance relationships)
Pavement model = multi-layered structure + axle load
Critical strains
locations
Current pavement model
• Multilayered
• Infinite in plane
• Subgrade semi-infinite
• Wheel-load = circular
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Finite Element Method: Quick Overview
• Finite element method (FEM) in pavement engineering
– Available finite element packages (ABAQUS, …) are very general
– Program developed by academics (Universities, Research organisations…)
E
D
Asphalt
2D-axi. FEM pavement model
UGM
Part 1
Symm
etry pla
ne
Subgrade
Part 4
O
Part 4
Part 3
C
m
et
ry
pla
ne
O
is
Symmetry Ax
Sy
m
Subgr
ade
Part 2
z
Asphalt
Part 3
y
A
x
UGM
Part 2
Subgrade
Part 1
A
B
3D FEM pavement model
z
T
R
B
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Linear vs nonlinear analysis
Nonlinear analysis
Nonlinear elastic
material
Modulus
Modulus
Linear analysis
Linear elastic
material
E(σ)
E
1
1
E(σ)
1
E(σ)
1
1
1
Stress State
𝐹=𝑲𝑈
Stiffness matrix is CONSTANT
E(σ)
Stress State σ
𝐹=𝑲 𝝈 𝑈
Stiffness matrix varies with the
stress state (i.e. load)
 Iterative process
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LABORATORY MATERIALS
CHARACTERISATION
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Presumptive model parameters
Austroads project TT1452 developed presumptive model
parameters: Report AP-T199-12 (Austroads, 2012)
– Base materials (High and normal quality crushed rock)
Material
High quality base
Normal quality base
– Subbase materials
– Typical subgrades
Material
Upper granular subbase
Lower granular subbase
Material
Silt (ML)
Highly plastic clay (CH)
Silty/sandy-clay
(CL/SC)
Sand (SW, SP)
CBR (%)
2
…
5
2
…
5
3
…
10
10
…
15
𝒌𝟏 (MPa)
250
220
𝒌𝟏 (MPa)
175
150
𝒌𝟏 (MPa)
10
…
35
10
…
35
15
…
70
70
…
85
𝒌𝟐
𝒌𝟑
1.0
-0.25
𝒌𝟐
0.9
0.8
𝒌𝟐
0.0
…
0.10
0.0
…
0.10
0.0
…
0.15
0.15
…
0.15
𝒌𝟑
-0.25
𝒌𝟑
-0.50
…
-0.35
-0.50
…
-0.35
-0.50
…
-0.35
-0.35
…
-0.35
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Overview of the GUI
Overview of the GUI
WORKED EXAMPLE
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Unbound granular pavement: inputs
Sprayed sealed surfaced unbound granular pavement
Subgrade design CBR = 5%
Material
Sprayed seal surface
Unbound granular
Subgrade
Thickness
(mm)
Sub-layers
thickness (mm)
-
475
Semi-infinite
Design modulus (Mpa)
Poisson’s ratio
V = H (-)
Ev
EV/EH
na
-
-
-
95
500
95
314
95
198
2
0.35
95
125
95
79
na
50
2
0.45
Unbound granular pavement: inputs
Linear elastic
Thicknesses
Moduli
Poisson’s ratio
Unbound granular pavement: outputs


The calculation is running in the background
Unbound granular pavement: outputs
Critical strain (CIRCLY output +/- 0.3%)
Thicknesses
Moduli problem
(being fixed)
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 OUTPUTS
LINEAR-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 OUTPUTS
NONLINEAR-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
www.arrb.com.au
Thank you