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CE  461  Roadway  and  Pavement  Design  

  A  model  that  defines  the  response  of  the  pavement  to  loading  in  terms  of  stresses,  strains,  and  deflections  

P

L/2 L/2

δmax

EIPL48

3max =δ

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  Differ  in:    Capabilities    Complexity   Material  Input  Requirements    Underlying  Assumptions  

  Provide  σ,  ε,  δ  anywhere  and  in  any  direction  in  the  pavement  structure  

  Handle  dynamic  loading    HMA  modeled  as  visco-‐elastic    PCC  modeled  as  linear-‐elastic    Base  and  subgrade  modeled  as  non-‐linear  inelastic    Consider  temperature  stresses  

  DOES  NOT  EXIST    Would  require  tremendous  material  properties  inputs  

  Significant  progress  has  been  made  

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  Multilayer  elastic  theory    Finite  element  methods    Visco-‐elastic  theory    Dynamic  analysis    Thermal  models  

  Complexity  of  model    Material  property  input  requirements    Computational  time    Relative  accuracy  

  Flexible  pavements    Fatigue  cracking    Rutting    Thermal  cracking    Others  

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  Alligator  cracking  in  asphalt  layer    Horizontal  tensile  strain  at  the  bottom  of  the  asphalt  layer  

  Base  material  will  not  take  tension    Limit  tensile  strain  in  asphalt  layer  

Base  Course  

HMA  

Subgrade  

Compression  

Tension  

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Base  Course  

HMA  

Subgrade  

σc

Base  Course  

HMA  

Subgrade  

Thermal  Contraction  

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  Rigid  pavements    Fatigue  cracking    Pumping/erosion    Others  

  Stress  at  mid-‐slab    Temperature  differential  

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Ttop  >  Tbottom  

Ttop  <  Tbottom  Day  

Night  

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  Loss  of  fines    Corner  breaks    Faulting  

Travel  Direction  

Rebo

und  

Defl

ectio

n  

Loss  of  fines  Fines  Deposited  

Trailing  Slab   Leading                Slab  

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  Many  cannot  be  addressed  in  pavement  design   Materials  problems  

  One  must  develop  an  understanding  of  the  stresses  involved  in  order  to  design  the  material  and  the  thickness