dr. mostafa abo-hashema - uacg.bg · dr. mostafa abo-hashema . 5/28/2014 . advanced topics in...

Dr. Mostafa Abo-Hashema 5/28/2014

Advanced Topics in Highway Engineering Fayoum University

Fayoum University

Cultural Exchange Program between

Egypt and Bulgaria 25-31.05.2014

New Technologies and Material Considerations in Pavement Design

Course Topics

1. Introduction

2. Stress-Strain Analysis of Flexible Pavements (Software)

3. Material Characterization for Pavement Analysis and Design

4. Pavement Design (State-of-the-Art)

5. Asphalt Institute Methods

6. Design for Stage Construction

7. Introduction to LTPP PROFESSOR MOSTAFA A

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Types of Pavement Design Approaches

Empirical methods based on Strength test (CBR)

Classification (soil classification)

Regression methods based on Road Tests

Mechanistic-Empirical (M-E) methods Mechanistic model predicts stresses, strains, deflections

Regression models to predict pavement life


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AASHTO Method

The Asphalt Institute Method for Flexible Pavements

Portland Cement Association (PCA) Method for Concrete Pavements

Texas DOT Method

Other methods

Current Design Methods

PROFESSOR MOSTAFA A

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AASHTO Road Test (late 1950’s)


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Current Design Methods, continued…

AASHTO Design Equation:


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Current Design Methods , continued… The current design methods in most countries in the

world have relied mostly on:

Empirical correlations with past performance,

Index-value-based characterization of material properties such as the layer coefficient,

R-value or the California Bearing Ratio (CBR-value),

Engineering judgment for design strategy selection. PROFESSOR MOSTAFA A

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Current Design Methods, continued… Generally,

Empirical approach requires a number of observations to be made in order to ascertain the relationships between input variables and outcomes. It is not necessary to firmly establish the scientific basis for the relationships between variables and outcomes. It is not prudent to use empirically derived relationships to describe phenomena that occur outside the range of the original data used to develop the relationship.


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Current Design Methods, continued…

These limitations make the empirical design approach obscure and difficult to apply.

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Mechanistic-Empirical Design Approach

A M–E design method for a flexible pavement means application of the principles of engineering mechanics to evaluate the response of pavement structures to traffic loading and much improved design methods to carry out distress prediction or how performance changes with time.


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M-E Design Approach

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Pavement Performance Today, pavement performance is largely defined by evaluation in the following categories

Roughness (often called "smoothness")

Surface distress

Structural evaluation

Skid resistance (Safety)


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Performance Prediction Models

Fatigue Cracking Model

Rutting Model

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ff

tf EfFSFN

The factor f1 for actual pavements should be much greater than that for laboratory specimens due to the fact that wheel loads on actual pavements are not applied at the same location and there are longer rest periods between load applications, both of which increase the fatigue life.

5

4

f

vf fN


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Fatigue and Rutting Coefficients Used

by Various Agencies

Fatigue Coefficients Rutting Coefficients

No. Procedures (Models) f1 f2 f3 f4 f5

1 Arizona DOT 9.33E-07 3.84 0 (Not Available) (Not Available)

2 Austin Research Engineers (ARE) 9.73E-15 5.16 0 (Not Available) (Not Available)

3 Belgian Road Research Center (BRRC) 4.92E-14 4.76 0 3.05E-09 4.35

4 CHEVRON (Not Available) (Not Available) (Not Available) (Not Available) 1.34E-09 4.484

5 Federal Highway Administration 7.56E-12 4.68 0 (Not Available) (Not Available)

6 Illinois DOT 5.00E-06 3 0 (Not Available) (Not Available)

7 SHELL Research 0.0685 5.671 2.363 6.15E-07 4

8 The Asphalt Institute (AI) 4.32E-03 3.291 0.854 1.37E-09 4.477

9 Transport and Road Research Laboratory 1.66E-10 4.32 0 1.13E-06 3.57

10 U.S. Army Corps of Engineers 497.156 5 2.665 1.81E-15 6.527

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M-E Design Process

Environmental Factors

Axle Loadings

Material Properties

Analysis Pavement Structure

Distress Prediction


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Flexible Pavement Response

Two-Dimensional Layered Elastic Model Example of Computer Programs:ELSYM5, KENLAYER, WESLEA, CHEVRON, JULEA, and BISAR

Three-Dimensional Finite Elements Model Example: EverFlex Program

Mechanistic Models

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H1

H2

H3

P

En , nn

E3, n3

E2, n2

E1 , n1

Layered Elastic Model, Inputs


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Layered Elastic Model, Outputs

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Damage Analysis

For Fatigue

For Rutting

4

1 )(

)(0.1

i iallow

ifuture

futureN

NSDR

14

1 )(

)(

i iallow

ifuture

ruttingN

NSDR


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Environmental Effects

Asphalt Bound Materials

Unbound Materials, Subgrade Soil, Granular Base & Subbase

Temperature and Moisture

The effect on Elastic Modulus value of an unbound layer

may be represented by a multiplying factor, called Seasonal

Adjustment Factor (SAF). PROFESSOR MOSTAFA A

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Effective Subgrade Resilient Modulus in AASHTO 1993

Resilient Modulus (Mr) for subgrade is the main

factor in pavement design. It changes with

surrounding environment changes such as moisture

and temperature. It is important to address the

seasonal moduli in the design process. Mr

Season

Winter

Spring

Summer Fall

Freezing

(Snow)

Raining

Mre = Effective


Effective Subgrade Resilient Modulus - Cont’d

Mre is an equivalent modulus that would result in the

same damage of seasonal modulus values.

32.28

f 1018.1u reM

Month Jan. Feb. Mar. Apr. May June July Aug. Sept. Oct. Nov. Dec.

Mr(subgrade),

psi

(uf = relative damage)

15900 27300 38700 50000 900 1620 2340 3060 3780 4500 4500 4500

0.02 0.01 0.00 0.00 16.52 4.22 1.80 0.97 0.59 0.39 0.39 0.39 Relative

Damage (uf)

Example

30.25 fu 11.212

30.25)( fuAverage

32.281018.111.2 reM )log(32.2)1018.1

11.2log(

8 reM

Mre = 2185 psi PROFESSOR M

OSTAFA ABO-H

ASHEMA




Effective Subgrade Resilient Modulus - Cont’d

32.28

f 1018.1u reM (uf = relative damage)

Example

Yu f 56.012

)( Y

uAverage f

32.281018.156.0 reM Mre = 3870 psi

Season Mr uf Period Uf * Period

Fall 5000 0.3 3 0.3*3

Winter 30000 0.005 4 0.005*4

Spring 2000 2.6 2 2.6*2

Summer 6000 0.2 3 0.2*3


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Traffic Data

No more ESAL’s!

Traffic input will be number of axles by type and weight

Same type and quality of raw traffic data currently used to compute ESAL’s


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Thank You

PROFESSOR MOSTAFA A

BO-HASHEMA

dr. mostafa abo-hashema - uacg.bg · dr. mostafa abo-hashema . 5/28/2014 . advanced topics in...

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