TM 5-822-13/AFJMAN 32-1018
CHAPTER 2
BASIS OF PAVEMENT DESIGN
in the bituminous concrete properties and subgrade
2-1. Design Principles.
strength caused by cyclic climatic conditions. The
a. Concrete pavements. The basic principle for the
strains used for entering the criteria are computed by
elastic layered design procedure is to limit the tensile
the use of Burmister's solution for multilayered elas-
stresses in the portland cement concrete (PCC) to lev-
tic continua. The solution of Burmister's equations for
els that are sufficiently below the flexural strength of
most pavement systems will require the use of com-
the concrete such that failure occurs only after the
puter programs and the characterization of the pave-
pavement has sustained a number of load repetitions.
ment materials by the modulus of elasticity and
The tensile stress is modeled by the use of Burmister's
Poisson's ratio.
solution for elastic multilayered continua. The com-
puted tensile stress divided into the concrete strength
2-2. Design Variables.
is the design parameter and is referred to as the de-
The prime factor influencing the structural design of
sign factor. This parameter has been related to pave-
a pavement is the load-carrying capacity required. The
ment performance through a study of test section data.
pavement thickness necessary to provide the desired
Use of a cumulative damage concept determines the
load-carrying capacity is a function of the following.
required concrete thickness. Correlations among
a. Principal variables.
theory, small-scale model studies, and full-scale accel-
(1) Vehicle wheel load or axle load.
erated traffic tests have shown that maximum tensile
(2) Configuration of vehicle wheels or tracks.
stresses in the pavement occur when the vehicle
(3) Volume of traffic during the design life of
wheels are placed at a free or unsupported edge of
pavement.
the pavement. Only interior stresses are computed
b. Additional rigid pavement variables.
using the elastic layered method while edge stresses
(1) Modulus of rupture (flexural strength) of the
can be computed with the Westergaard solution. The
concrete.
former is always less than the latter; the difference
(2) Elastic moduli and Poisson's ratios of concrete,
depends upon the load configuration and pavement ge-
base course, and subgrade soils.
ometry and properties. Stresses for the condition of
c. Additional flexible pavement variables.
the vehicle wheels placed at a longitudinal or trans-
(1) Elastic moduli of each layer of the pavement
verse joint are less severe because of the use of load-
structure and the subgrade soils.
transfer devices or aggregate interlock in these joints
(2) Poisson's ratios of each layer of the pavement
to transfer a portion of the load to the adjacent slab.
structure and the subgrade soils.
In military roads and streets, dowel bars are gener-
ally installed in the transverse joints and tie bars in
2-3. Pavement Response Model.
the longitudinal joints. Since traffic loads travel near
The pavement system is assumed to be a multilay-
the pavement (free) edges and free edge stresses gov-
ered continuum with each layer being elastic and ho-
ern the pavement design thickness, interior stresses
mogeneous. Each layer is to extend to infinity in the
computed with JULEA does not simulate the edge
horizontal direction and have, except for the bottom
stress condition. Thus the computed stress will be
layer, a finite thickness. The applied loads to the pave-
multiplied by a factor of 1.33.
ment are considered as static, circular, and uniform
b. Flexible pavements. The basic principle for the
over the contact area. The program chosen for the
design procedure is to select a pavement thickness
analysis is JULEA computer code. The program pro-
required to limit the vertical strains in the subgrade
vides different degrees of bond between interfaces.
and the horizontal strains at the bottom of the bitu-
With the program the performance criteria for rigid
minous concrete induced by design vehicular traffic
pavements are developed with the assumptions that
loads at select traffic levels. The purpose is to pre-
the interface between the PCC slab and the support-
vent shear failure in the subgrade and cracking in the
ing subgrade is considered smooth with no bond, i.e.,
bituminous surface course. Use of a cumulative dam-
there is no frictional resistance at the interface. All
age concept permits the rational handling of variations
other interfaces are considered to be completely
2-1
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