Purdue University
School of Civil Engineering
CE 361 Introduction to Transportation Engineering
Wed. 23 October 2019
Lesson 1 of 4 on Pavement Design
Instructional Objectives:
By the end of this lesson,
the student will be able to ...
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Explain the differences between rigid and flexible pavements.
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List the factors that affect pavement design.
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Describe the impacts that trucks have on pavements.
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Explain Load Equivalency Factors.
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Identify truck types by axle configurations.
Prep:
Read FTE Chapter 9 Sections 1 and 2.
Theme music:
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Wheels, The String-a-Longs, 1961, 1:55 (instrumental).
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Wheels, The Foo Fighters, 2009, 4:38.
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Willin', Linda Ronstadt, 1976, 3:14.
"I've ... driven every kind of rig that's ever been made.
I've driven the back roads so I wouldn't get weighed."
Pavement(-related) courses at Purdue CE:
CE461, CE563, CE535
Outline of Likely Topics
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Pavement as a "system"
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Layers are system components.
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Factors that affect pavement design
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Traffic loads (AADT) and Vehicle classification --> ESALs
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Life cycle cost analysis
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ESALs and pavement life -- the "stored value card" analogy
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Video:
Truck Impacts on Pavements,
FHWA, 1988, 21:57
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Listen for
LEF
or ESAL values.
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Single-axle:
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Tandem:
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Tridem:
- What is an ESAL?
- A single-axle load of 18,000 lbs. applied to the pavement on two sets of dual tires
- Contact pressure of 70 psi
- All axle loads are converted to 18K ESAL.
- How are ESALs computed?
- Gross Axle Load + Axle Type -- ESAL
- Load Equivalency Factor (LEF) tables or 4th power equation
- How the ESAL values in the video were found.
- Truck Types: An "18-wheeler" is really a ...
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ESAL calculations, step by step.
(Group exercise?)
Click here for example.
(Note: The LEF for the 6K single axle load should be 0.010, not 0.034.)
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Build frequency table for N(i), the number of times axle load range i is observed.
- Calc. traffic growth factor, G(i).
- For each category i, look up LEF in table.
- Calc. ESAL for each category i: ESAL(i) = LEF(i) * N(i) * G(i) * 365
- Add up ESAL(i) for all categories.
