CT4860 STRUCTURAL DESIGN OF PAVEMENTS

3. STRESSES AND DISPLACEMENTS IN CONCRETE
PAVEMENT STRUCTURES
3.1 General
In concrete pavement structures, especially the concrete top layer, stresses
(and displacements) are introduced by:
- shrinkage during the hardening process of the concrete
- variation of the moisture content of the concrete
- a temperature change which is constant over the thickness of the concrete
layer
- a temperature gradient in the concrete layer
- the traffic loadings
- unequal subgrade settlements.
The stresses and displacements due to the hardening shrinkage of the
concrete and due to the regular temperature change are (practically spoken)
eliminated by dividing the concrete layer into slabs (plain concrete pavements)
or by the application of a continuous longitudinal reinforcement (reinforced
concrete pavements).
Variation of the moisture content of the concrete (more specific drying out of
the upper part of the concrete layer) is only relevant in very extreme climatic
conditions (short period of heavy rainfall, followed by long hot dry periods). In
moderate climates drying out of the concrete is not a serious problem, and
therefore no further attention is paid to this phenomenon.
The (flexural tensile) stresses (and displacements) in concrete pavement
structures due to traffic loadings, temperature gradients and unequal
subgrade settlements are discussed in 3.3, 3.4 and 3.5 respectively.
Next in 3.6 in general terms the applicability of the finite element method for
concrete pavement structures is discussed.
However, first in 3.2 some attention is paid to the amount of support that the
substructure can give to the concrete top layer. This support, usually
expressed as the modulus of substructure reaction, influences the flexural
tensile stresses and especially the vertical displacements of the concrete top
layer due to the above mentioned external loadings (traffic, temperature
gradient, settlements).
3.2 Modulus of substructure reaction
One of the input parameters in the design of concrete pavement structures is
the bearing capacity of the substructure (base plus sub-base plus subgrade).
Generally the complete substructure is modeled as a dense liquid, which
means that in the substructure no shear stresses can occur. The bearing
capacity of the substructure thus is expressed as the ‘modulus of substructure
reaction’ k, which is defined as (figure 6):
k = p/w (9)
where: k = modulus of substructure reaction (N/mm 3 )
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