Synthesis of design and construction practices
tải về 1.81 Mb. Chế độ xem pdf
|
[123doc] - phat-trien-nguon-nhan-luc-cua-cong-ty-co-phan-misa-doc
- Điều hướng trang này:
- Permanent Deformation (Rutting) Modeling.
| Fatigue Cracking. In order to model the fatigue cracking distress two approaches were
taken: (1) model the number of load repetitions to fatigue failure of the HMA layer, and (2) model the number of load repetitions to fatigue failure of the rigid base layer.
The modeling of fatigue failure of the HMA layer was based on the model presented by the proposed MEPDG (NCHRP 1-37A), which is based on the Asphalt Institute fatigue model.
3.291 0.854
' f 1 t 1 1 N 0.00432 k C E
⎛ ⎞ = × × ⎜ ⎟ ⎜ ⎟ ε ⎝ ⎠ ⎝ ⎠ (11)
M C 10 =
(12) b a b V M 4.84 0.69 V V ⎛ ⎞ = − ⎜ ⎟ + ⎝ ⎠ (13)
where
N f = number of load repetitions to fatigue cracking
'
k = parameter used for either bottom-up or top-down criteria
ε
= tensile strain at critical location
E = stiffness of material (HMA) V b = effective binder content (%)
V a = air voids (%)
For bottom-up cracking, the ' 1 k parameter is:
( ) ac ' 1 11.02 3.49 h 1 k 0.003602 0.000398 1 e
− × = + + (14)
18 where
h ac = total thickness of asphalt layer (in).
In the rigid layer fatigue case, the modeling was based on two criteria: (1) the MEPDG CSM fatigue failure transfer function for soil cement, CTB, and lean mix (Equation 15) and (2) the PCA concrete fatigue failure transfer function for RCC and PCC (Equations 16 through 19).
t c1 f c2 0.972
MR log N
0.0825 ⎛ ⎞ σ ⎛ ⎞ β − ⎜ ⎟ ⎜ ⎟ ⎝ ⎠ ⎝ ⎠ = β (15)
where
N f = number of repetitions to fatigue cracking of the CSM layer
σ
= maximum traffic-induced tensile stress at the bottom of the CSM layer (psi)
MR = 28-day modulus of rupture (flexural strength) (psi) c1 c2 , β β = field calibration factors; the default factor of 1 was used for this study.
SR ≥ 0.55: ( ) f Log N 11.737 12.077 SR = − × (16)
0.45 < SR < 0.55: 3.268
f 4.2577
N SR 0.4325 ⎛ ⎞
⎟ − ⎝ ⎠
(17) SR ≤ 0.45: N f = unlimited (18)
where
SR = ratio of equivalent stress to PCC flexural strength (as defined in Eq. 19) N f = allowable number of repetitions to fatigue cracking.
eq SR MR σ =
(19)
where
eq σ = equivalent stress = flexural stress in slab
MR = modulus of rupture of concrete = PCC flexural strength. 19 Permanent Deformation (Rutting) Modeling. The modeling of rutting in the HMA layer uses the relationship from the MEPDG (NCHRP, 2004), Equation 20, to obtain the accumulated plastic strain. This strain results from the sum of various plastic strain deformations inside the bituminous layer, which can be used to determine the rut depth after a specific number of load repetitions. To compute the rut depth, the HMA layer is divided into sub-layers according to the criterion described in the MEDPG, and plastic strains are computed at various points located at different depths from the surface.
3.4488 1.5606
0.479244 1 r k 10 T N − ε = × × × ε (20)
where
ε p = accumulated plastic strain at N repetitions of load (in/in) ε r
and time rate of loading (in/in)
N = number of load repetitions T = temperature (°F)
k
= parameter computed from Equation (21).
( ) depth 1 1 2 k C C depth 0.328196
= + × ×
(21) 2 1 ac ac C 0.1039 h 2.4868 h
17.342 = −
× + × − (22)
2 2 ac ac C 0.0172 h 1.7331 h
27.428 = × − × + (23)
where
k 1 = confining pressure correction factor
h
= total asphalt layers thickness (in)
depth = depth to computational point (in).
tải về 1.81 Mb. Chia sẻ với bạn bè của bạn:
|