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Dr. P. NANJUNDASWAMYDepartment of Civil Engineering
S J College of EngineeringMysore – 570 006
Pavements – Where?
• Roads
High Volume National Highways to Low Volume Local Roads . . .
• Airports
Runways, Taxiways, Aprons . . .
• Parking Areas
• Ports and other places
Pavement Purpose
1. Load support• withstand and distribute stresses• hard wearing surface
2. Smoothness• riding quality• safety• low energy consumption
3. Drainage• impervious
Structural Response Models
Different analysis methods for AC and PCC
• Layered system behavior.• All layers carry part of load.
Subgrade
• Slab action predominates.• Slab carries most load.
Subgrade
AC
Base
Conventional Flexible Pavement
Typical Flexible Pavement Section can be idealized as a multi-layered system
Surface / Binder course
Base course
Sub-base course
Soil Subgrade
having different material properties
Seal coat, Tack coat and Prime coat
Full-Depth Asphalt Pavement
One or more layers of HMA directly on the subgrade
Generally considered cost-effective and dependable asphalt pavement for heavy traffic specially when local materials are not available Asphalt Surface
Asphalt Base
Prepared Subgrade
Rigid Pavements
Constructed of Portland Cement Concrete
Analysis – Plate theory
Base/Sub-base course
• Control of Pumping• Control of Frost Action• Improvement of Drainage• Control of Shrinkage and Swell• Expedition of Construction
Portland Cement Concrete Slab
Base or Sub-base Course May or May not be used
Prepared Subgrade
Types of Rigid Pavements
Jointed Plain Concrete Pavement (JPCP)
Jointed Reinforced Concrete Pavement (JRCP)
Continuous Reinforced Concrete Pavement (CRCP)
Prestressed Concrete Pavement (PCP)
Design Methods
Methods of designing flexible pavements
Empirical with or without a soil test
Limiting shear failure
Limiting Deflection
Regression – Pavement Performance
Mechanistic empirical
Currently, the design is largely empirical Mechanistic design is becoming more prevalent
Design Methods
Mechanistic approach requires the accurate evaluation of
StressesStrainsDeflections
in pavements due to wheel loads
Basics
Stress
Strain
Deflection/Deformation
Stiffness
Poisson’s Ratio
Hooke’s Theory of Elasticity
Principle of Superposition
Approaches
To compute Stresses, Strains & Deflections
Layered elastic methods
Two-dimensional (2D) FE modeling
Three-dimensional (3D) FE modeling
Layered Elastic Approach
Is the most popular and easily understood procedure.
In this method, the system is divided into an arbitrary number of horizontal layers
The thickness of each individual layer and material properties may vary from one layer to the next.
But in any one layer the material is assumed to be homogeneous and linearly elastic.
Layered Elastic Approach
Although the layered elastic method is more easily implemented than finite element methods, it still has severe limitations:
materials must be homogenous andlinearly elastic within each layer
the wheel loads applied on the surface must be axi-symmetric
2D Finite Element Analysis
Plane strain or axis-symmetric conditions
are generally assumed.
It can rigorously handle material anisotropy,
material nonlinearity, and a variety of
boundary conditions – more applicable to
practical situations
Unfortunately, 2D models can not
accurately capture non-uniform tire contact
pressure and multiple wheel loads.
3D Finite Element Analysis
To overcome the limitations inherent in
2D modeling approaches, 3D finite
element models are becoming more
widespread.
With 3D FE analysis, we can study the
response of flexible pavements under
spatially varying tire pavement contact
pressures.
Design Parameters
• Traffic
• Climatic Factors
• Road Geometry
• Subgrade
• Material Properties
• Environment
Design Parameters – Traffic
• Maximum Wheel load
• Contact Pressure
• Multiple Wheel Loads
• Repetition of Loads
• Position
• Impact of wheels
• Iron-tyred vehicles
Design Parameters – Subgrade
• CBR and Resilient modulus
• Marshall stability values
• Modulus of subgrade reaction
• Modulus of rupture
• Elastic modulus etc..