UFC 3-260-02
30 June 2001
CHAPTER 11
LAYER ELASTIC DESIGN OF FLEXIBLE PAVEMENTS
1. DESIGN PRINCIPLES. The structural deterioration of a flexible pavement caused by traffic is
normally evidenced by cracking of the bituminous surface course and development of ruts in the wheel
paths. The design procedure handles these two modes of structural deterioration through limiting values
of the strain at the bottom of the bituminous concrete and at the top of the subgrade. Use of a
cumulative damage concept permits the rational handling of variations in the bituminous concrete
properties and subgrade strength caused by cyclic climatic conditions. The strains used for entering the
criteria are computed by the use of Burmister's solution for multilayered elastic continua. The solution of
Burmister's equations for most pavement systems will require the use of computer programs and the
characterization of the pavement materials by the elastic constants of the modulus of elasticity and
Poisson's ratio.
2. FLEXIBLE PAVEMENT RESPONSE MODEL. The computer code recommended for computing
the pavement response is the JULEA code. When the code is used, the following assumptions are
made.
a. The pavement is a multilayered structure, and each layer is represented by a modulus of
elasticity and Poisson's ratio.
b. The interface between layers is continuous; i.e., the friction resistance between layers is greater
than the developed shear force.
c. The bottom layer is of infinite thickness.
d. All loads are static, circular, and uniform over the contact area.
3.
DESIGN DATA.
a. Climatic Factors. In the design system, two climatic factors, temperature and moisture, are
considered to influence the structural behavior of the pavement. Temperature influences the stiffness
and fatigue of bituminous material and is the major factor in frost penetration. Moisture conditions
influence the stiffness and strength of the base course, subbase course, and subgrade.
(1) Pavement temperature. The design procedure requires the determination of a design
pavement temperature for consideration of vertical compressive strain at the top of subgrade and
horizontal tensile strain at the bottom of cement- or lime-stabilized layers and a different design
pavement temperature for consideration of the fatigue damage of the bituminous concrete surface. In
either case, a design air temperature from Figure 11-1 is used to determine the design pavement
temperature. Temperature data for computing the design air temperatures are available from the
National Oceanic and Atmospheric Administration (NOAA) "Local Climatological Data Annual Summary
with Comparative Data." These data may be obtained by requesting it from personnel at NOAA's web
site: http://www.noaa.gov/. With respect to subgrade strain and fatigue of cement- and lime-stabilized
base or subbase courses, the design air temperature is the average of the average daily mean
temperature and the average daily maximum temperature during the traffic period. For consideration of
the fatigue damage of bituminous materials, the design air temperature is the average daily mean
temperature. Thus, for each traffic period, two design air temperatures are determined. Normally,
11-1
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