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Published byAubrey Chambliss Modified about 1 year ago

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1 AustPADS Finite Element Method Based Pavement Response to Load Model

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Outline Introduction Finite Element Method Material characterisation APADS - Austpads & Hosted service Worked examples Making sense of the results 2

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INTRODUCTION 3

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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 4

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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 5

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Schedule 6 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 7

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Pavement model: what for? 8 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

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Finite Element Method: Quick Overview 9 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

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Linear vs nonlinear analysis 10 Stress State Modulus E 1 Linear elastic material Stress State σ Modulus E(σ) Nonlinear elastic material 1 E(σ) Linear analysis Stiffness matrix is CONSTANT Stiffness matrix varies with the stress state (i.e. load) Iterative process Nonlinear analysis

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LABORATORY MATERIALS CHARACTERISATION 11

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Presumptive model parameters 12 Austroads project TT1452 developed presumptive model parameters: Report AP-T (Austroads, 2012) – Base materials (High and normal quality crushed rock) – Subbase materials – Typical subgrades MaterialCBR (%) Silt (ML) ………… Highly plastic clay (CH) ………… Silty/sandy-clay (CL/SC) ………… Sand (SW, SP) ………… Material Upper granular subbase Lower granular subbase Material High quality base Normal quality base220

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Overview of the GUI

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Load definition Traffic & Performance relationships Pavem t structure Layer characteristics Thickness Material parameters Critical strain location

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WORKED EXAMPLE 15

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Sprayed sealed surfaced unbound granular pavement Subgrade design CBR = 5% Unbound granular pavement: inputs MaterialThickness (mm) Sub-layers thickness (mm) Design modulus (Mpa)Poisson’s ratio V = H (-) EvE V /E H Sprayed seal surface -na--- Unbound granular SubgradeSemi-infinitena

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Unbound granular pavement: inputs ThicknessesModuliPoisson’s ratio Linear elastic

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Unbound granular pavement: outputs The calculation is running in the background

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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

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MAKING SENSE OF THE OUTPUTS LINEAR-ELASTIC 20

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Unbound pavement 21

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Asphalt surfaced unbound 22

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Asphalt surfaced unbound 23

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MAKING SENSE OF THE OUTPUTS NONLINEAR-ELASTIC 24

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Full depth asphalt 25

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Analysis types Linear–elastic – Results very similar to CIRCLY Nonlinear-elastic – Results different to CIRCLY – Need updated/calibrated performance relationships 26

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Further information Seek me out today. 26 th ARRB Conference paper (Bodin et al). Austroads Report AP-T Thank you

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