Diseño por aashto
• Highway Pavements
AASHTO The Asphalt Institute Portland Cement Association
• Airfield Pavements
FAA The Asphalt Institute Portland Cement Association U.S. Army Corps of Engineers
Objectives of Pavement Design
To provide a surface that is:
• Strong
Surface strength Moisture control
• Smooth • Safe
Friction Drainage
• Economical
Initial construction costRecurring maintenance cost
Pavements are Designed to Fail !!
Pavement Design Methodologies
• Experience • Empirical
Statistical models from road tests
• Mechanistic-Empirical
Calculation of pavement stresses/strains/deformations Empirical pavement performance models
• Mechanistic
Calculation of pavement stresses/strains/deformations Mechanics-based pavement performance modelsEmpirical vs. Mechanistic Design P d Wood Floor Joist
L
Empirical “Rule of 2”: d in inches= (L in feet / 2) + 2
Mechanistic: σbending =
PL ≤ σ allowable 4S
1993 Version
AASHTO Pavement Design Guide
• Empirical design methodology • Several versions:
1961 (Interim Guide) 1972 1986
Refined material characterization Version included in Huang (1993)
1993
More on rehabilitation Moreconsistency between flexible, rigid designs Current version
2002
Under development Will be based on mechanistic-empirical approach
AASHO Road Test (late 1950’s)
(AASHO, 1961)
One Rainfall Zone...
(AASHO, 1961)
One Temperature Zone...
(AASHO, 1961)
One Subgrade...
A-6 / A-7-6 (Clay) Poor Drainage
(AASHO, 1961)
Limited Set of Materials...
• One asphalt concrete3/4” surface course 1” binder course
• One Portland cement concrete (3500 psi @ 14 days) • Four base materials
Well-graded crushed limestone (main experiment) Well-graded uncrushed gravel (special studies) Bituminous-treated base (special studies) Cement-treated base (special studies)
• One uniform sand/gravel subbase
1950’s Construction Methods...
(AASHO, 1961)
(AASHO, 1961)1950’s Vehicle Loads...
Limited Traffic Volumes...
1.1M Axles 1.1M Axles
Axle Loads (Thousands)
2 Years 2 Years
Time (Months)
(AASHO, 1961)
1950’s Data Analysis...
(AASHO, 1961)
Some Failures...
(Some pavements too!)
(AASHO, 1961)
AASHTO Design Based on Serviceability Decrease
(AASHTO, 1993)
What is Serviceability?
• Based upon Present
Serviceability Rating(PSR)
• Subjective rating by
individual/panel
Initial/post-construction Various times after construction
• 0 < PSR < 5 • PSR < ~2.5: Unacceptable
(AASHO, 1961)
Present Serviceability Index (PSI)
• PSR correlated to physical pavement measures via Present
Serviceability Index (PSI):
PSI = 5.03 − 1.91log(1 + SV ) − 1.38 RD − 0.01(C + P)1/ 2 SV = slope variance (measure of roughness) RD= average rut depth (inches) C + P = area of cracking and patching per 1000 ft 2 PSI ≈ PSR
2
Empirical!
AASHTO Design Guide (1993)
Part I: Pavement Design and Management Principles • Introduction and Background • Design Related to Project Level Pavement Management • Economic Evaluation of Alternative Design Strategies • Reliability
AASHTO Design Guide (1993)
Part II: Pavement DesignProcedures for New Construction or Reconstruction • Design Requirements • Highway Pavement Structural Design • Low-Volume Road Design
AASHTO Design Guide (1993)
Part III: Pavement Design Procedures for Rehabilitation of Existing Pavements • Rehabilitation Concepts • Guides for Field Data Collection • Rehabilitation Methods Other Than Overlay • Rehabilitation Methods With Overlays
DesignScenarios Included in AASHTO Guide
(AASHTO, 1993)
AASHTO Design Based on Serviceability Decrease
(AASHTO, 1993)
Flexible Pavements
Design Equation
log10 (W18 ) = Z R So + 9.36 log10 ( SN + 1) − 0.20 ∆PSI log10 4.2 − 1.5 + 2.32 log M − 8.07 + 10 ( R) 1094 0.40 + 5.19 ( SN + 1)
W18 = design traffic (18-kip ESALs) ZR = standard normal deviate So = combined standard error...
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