|
The contraction joint spacing used by WSDOT is based on dowel bar use for load
transfer. A reasonable joint spacing when dowels are used is 3.7 m (12
ft.); however, contraction joint spacings up to 4.5 m
(15 ft.) can be used and are specified in the
WSDOT Standard Plans.
These contraction joint spacings are, in part, based on prior rigid pavement
performance in Washington State and elsewhere and
slab
stress calculations. For example:
- Contraction joint spacings of 3.7 - 4.5 m (12 to 15 ft.) result in
lower slab stresses due to thermal gradients.
- A contraction joint spacing of about 3.7 m (12 ft). conforms to the
FHWA L/l = 5.0 criterion for "thinner"
slabs of about 228 mm (9 in.) on stiff subbases. A spacing of
about 4.5 m (15 ft.) conforms to the same criterion for "thicker" slabs
of about 330 mm (13 in.) on stiff subbases.
- In general, annual joint openings should be limited to no more than
0.6 - 0.9 mm (0.025 - 0.035 in.) to insure long term joint performance.
Using the slab shrinkage/expansion equation and PCC slabs on stabilized
base for annual temperature ranges estimated for eastern and western
Washington, the resulting joint movements are:
- 3.7 m (12 ft.) slab in Eastern Washington: 0.79 mm (0.031 in.)
- 3.7 m (12 ft.) slab in Western Washington: 0.53 mm (0.021 in.)
- 4.5 m (15 ft.) slab in Eastern Washington: 0.99 mm (0.039 in.)
- 4.5 m (15 ft.) slab in Western Washington: 0.66 mm (0.026 in.)
|