CHAPTER 5 CONCRETE PAVEMENTS - TU Delft

Next a fatigue damage analysis is carried out for the locations VR and ZR by
calculating the allowable number of load repetitions Ni for each combination of wheel
load Pi and temperature gradient ∆ti. In the damage analysis the following concrete
fatigue relationship (50% fatigue curve, so an average relationship) is used:
12.
903 ( 0.
995 − σ max / fbtg)
i
= with 0.
5 ≤ σ / fbtg ≤
1.
000 − 0.
7525 σ / fbtg
log N i
max
min
where:
i
0.
833
(5.12)
Ni = allowable number of repetitions of wheel load Pi i.e. the traffic load
stress σvi until failure when a temperature gradient stress σti is present
σmin i = minimum occurring flexural tensile stress (= σti)
σmaxi = maximum occurring flexural tensile stress (= σvi + σti)
fbtg = average flexural tensile strength (N/mm 2 ) of unreinforced (plain)
concrete under loading of short duration:
fbtg = 1.4 (1.6 – h/1000) (1.05 + 0.05B) (5.13)
where: h = thickness (mm) of the concrete slab
B = characteristic cube compressive strength (N/mm 2 ) after 28
days (see table 5.1)
The design criterion (i.e. cracking occurs) is the cumulative damage law of Palmgren-
Miner:
n
i
∑ = 1.0 (5.14)
i N i
where:
ni = occurring number of repetitions of wheel load Pi i.e. the traffic load
stress σvi during the pavement life when a temperature gradient stress
σti is present
NI = allowable number of repetitions of wheel load Pi i.e. the traffic load
stress σvi until failure when a temperature gradient stress σti is present
5.4.5 Stiffness criterion:
To prevent longitudinal unevenness (joint faulting) at the transverse joints in the plain
concrete pavement the deflection of the transverse edge in the wheel track (location
VR in figure 5.12) due to the traffic loading should be limited. According to
Westergaard the deflection of the transverse edge is (2,13):
⎛ W ⎞ ⎛ P ⎞
wl = λ ⎜1
− ⎟ ⎜ 2 ⎟
(5.15)
⎝ 200 ⎠ ⎝ kl ⎠
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