chapter 3 rigid pavement - DOT On-Line Publications - Department ...

DESIGN OF LENGTH
Studies have shown that pavement thickness, base stiffness, and climate affect
the maximum anticipated joint spacing beyond which transverse cracking can be
expected [2]. Research indicates that there is a general relationship between
the ratio of slab length (L) to the radius of relative stiffness (e) and
transverse cracking. The radius of relative stiffness is a term defined by
Westergaard to quantify the relationship between the stiffness of the
foundation and the flexural stiffness of the slab. The radius of relative
stiffness has a lineal dimension and is determined by the following equation:
e - [Eh3/12k(I-r2)]0~'s
where
e - radius of relative stiffness (in.)
E = concrete modulus of elasticity
(psi.)
h - pavement thickness (in.)
l - Poisson's ratio of the pavement
k - modulus of subgrade reaction (pci.)
Research data indicates that there is an increase in transverse cracking when
the ratio L/e exceeds 5.0. Using the criteria of a maximum L/C ratio of 5.0,
the allowable.joint spacing would increase with increased slab thickness, but
decrease with increased (stiffer) foundation support conditions. The
relationship between slab length, slab thickness, and foundation support for a
L/C ratio of 5.0 is shown below.
16
200
,300
K - value (pci)
3.1-.15