Dr. P. NANJUNDASWAMYDepartment of Civil Engineering

S J College of EngineeringMysore – 570 006

pnswamy@yahoo.com

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

Pavement Types

Pavement

Flexible

Rigid

Semi Rigid

Composite

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

Pumping of Rigid Pavements

Frost Action

Types of Rigid Pavements

Jointed Plain Concrete Pavement (JPCP)

Jointed Reinforced Concrete Pavement (JRCP)

Continuous Reinforced Concrete Pavement (CRCP)

Prestressed Concrete Pavement (PCP)

Types of Rigid Pavements

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 – Climate

• Rainfall

• Frost

• Temperature

Design Parameters

• Horizontal Curves

• Vertical Profile

Geometry

Subgrade

• Strength

• Drainage

Design Parameters – Subgrade

• CBR and Resilient modulus

• Marshall stability values

• Modulus of subgrade reaction

• Modulus of rupture

• Elastic modulus etc..

Thank you