CT4860 STRUCTURAL DESIGN OF PAVEMENTS

surface, only touches the substructure at the four corners and in the centre of
the slab. The critical slab length can be calculated by means of the equation:
long slab: (L/W > 1.2 or L/W < 0.8): lcrit = 200 h E α ∆t
(14a)
square slab: (0.8 ≤ L/W ≤ 1.2): lcrit = 228 h E α ∆t
(14b)
where: lcrit = critical slab length (mm)
h = thickness (mm) of the concrete slab
E = Young’s modulus of elasticity (N/mm²) of concrete
α = coefficient of linear thermal expansion (°C -1 )
∆t = positive temperature gradient (°C/mm)
L = slab length (mm)
W = slab width (mm)
Furthermore Eisenmann takes into account that near the edges the concrete
slab is supported over a certain distance, the ‘support length’ C. This means
that the span L’ of the concrete slab is always less than the slab length L:
' 2
L = L − C
(15)
3
The support length C is approximately:
h
C = 4.5 if C 1.1 lcrit (17)
where: υ = Poisson’s ratio of concrete
h = thickness (mm) of the concrete slab
∆t = positive temperature gradient (°C/mm)
α = coefficient of linear thermal expansion (°C -1 )
E = Young’s modulus of elasticity (N/mm 2 ) of concrete
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