Page 319 - Planning and Design of Airports

Structural Design of Airport Pavements 277

FIGURE 7-9 Example output of FAARFIELD software for rigid pavement design.

elastic design theory in that it takes into account the Young’s modu-
lus of the subgrade and the materials used in the slab and subbase
courses, and considers a cumulative damage factor in its analysis.
3D-FE design modeling, however, considers the pavement in discrete
sections, rather than a continuous material. This perspective allows
for more accurate estimation of stresses and strain on the edges of the
rigid pavement slabs, which compared to the transverse stress near
the center of the slab, is more critical in rigid pavements.

Joints and Joint Spacing
Slabs of PCC rigid pavement are connected by joints to permit expan-
sion and contraction of the pavement, thereby relieving flexural stresses
due to curling and friction and to facilitate construction. There are three
types of joints: isolation (type A), contraction (type B, C, or E), and
construction (type E) joints. The locations of these joints are illustrated
in Fig. 7-10, with details as to their specifications found in Fig. 7-11.
The function of type A isolation joints is to isolate adjacent pave-
ment slabs and provides space for the expansion of the pavement,
thereby preventing the development of very high compressive
stresses which can cause the pavement to buckle.
Contraction joints are provided to relieve the tensile stresses due to
temperature, moisture, and friction, thereby controlling cracking. If
contraction joints were not installed, random cracking would occur
on the surface of the pavement. The spacing between contraction
joints is dependent on the thickness of the slab, the character of the