Development of Innovative Mechanistic Empirical Fatigue Analysis for

Development of Innovative Mechanistic Empirical Fatigue Analysis for

Development of Innovative Mechanistic Empirical Fatigue
Analysis for Jointed Plain Concrete Pavements
Jacob E. Hiller
Graduate Student at the University of Jeffery
IllinoisRoesler
at Urbana-Champaign

RESULTS

MOTIVATION

Numerous statistical distributions of input parameters were developed for the analysis including the following:

Traditional mechanistic analyses suggest that bottom-up mid-slab
transverse cracking is the only failure mode possible

Geometry

MOR

Trans. joints
20 to 90%
Long. joints
50%
Lateral Wander Distribution

MECHANISMS

The built-in curl can be significant enough for the slab to always
remain curled up even at the highest positive temperature gradients
The magnitude of EBITD effectively changes the Free
baseline
of
edge
support conditions at no temperature differential
from
the assumption
T=-6
C
T=-3many
C
of a fully-supported slab to one with
unsupported
areas
T=-11 C
o

o

o

T=-22oC
T=-33oC

0.46 to 0.76m
0.25m

Single axles
Tandem axles
Axle spacing
CA Regions

Class 5
Class 6
Class 7
Class 8
Class 9

23.03%
5.18%
0.28%
6.66%
50.63%

Class 10
Class 11
Class 12

0.63%
8.78%
1.06%

Class 13
Class 14

0.10%
2.52%

Final Position

4.3m

a) EBITD = 0F
1
0.8
0.6
0.4
0.2
0
-0.2
-0.4
-0.6
-0.8
-1

b) EBITD = -30F
1
0.8
0.6
0.4
0.2
0
-0.2
-0.4
-0.6
-0.8
-1

3.6m

ISLAB2000 software was used to analyze over 1.3
million cases using a static moving wheel approach to
assess changing stresses in the slab for a variety a
geometries, load levels, load positions, load transfer levels,
etc. Results for up to 178 nodes for each of these finite
element runs were trained into a neural network scheme
for use in the resulting software

max
1 1 R log10 N
MOR

Utilizing the above fatigue transfer function but
ignoring the residual stress effects (R = 0) for a typical
rigid pavement section in the San Francisco Bay Area, the
figure on the left shows the expected damage profiles with
a EBITD of a.) 0oF and b.) -30oF

TRAFFIC

When the EBITD case of -30oF (from b above) is analyzed
using R-values determined from minimum residual stresses
and maximum stresses incurred at each point along the
transverse joint and longitudinal edge, the resulting damage
profile (on the right) shows a multitude of potential fatigue
cracking locations.

1
0.8
0.6
0.4
0.2
0
-0.2
-0.4
-0.6
-0.8
-1

These critical damage areas are widely affected by geometry, restraint conditions (shoulders,
widened lanes, dowels)

0.8
0.7
0.6
0.5
0.4
0.3
0.2

Residual Temperature Stress (MPa)

0.9

By varying both the climatic region, EBITD level, and lateral wander within reasonable limits, the critical damage location
was found to be widely variable using the stress range approach. Using only maximum stress in the fatigue transfer
functions yielded a more finite number of critical damage locations that agree well with the NCHRP 1-37A design software.

Maximum Stress

Stress Range

0.1
0

Transverse Joint

Nodal
Points of
Interest on
Design Slab

DISCUSSION
1

Longitudinal Edge

Starting Position

While RadiCAL can employ a variety of fatigue transfer functions, most of the work
has been focused on incorporating Tepfers stress range (R = min / max) into the
analyses to assess the effects of residual stresses on damage level predictions

Doweled Joint

EBITD levels have been
measured to -40oF in
extreme conditions and
depends on factors such
as geometry, restraints,
construction conditions,
cement type, etc.

53 to 107kN
125 to 196kN
2.7 to 6.4m
7

Avg. CA Vehicle Class Distribution
Class 4
1.14%

Relative Damage Level

Cyclical temperature gradients also influence the curling magnitude

Relative Damage Level

Moisture gradients
Differential drying shrinkage through the slab
depth
Built-in temperature curl from gradients during
concrete setting

In most cases, the
longest slab edge incurs
higher residual stresses,
creating a higher
baseline than the
shorter dimension

4.0 to 5.0 MPa

E
27.6 GPa
COTE
9*10-6 / oC

0.15
k-value
68 kPa/mm
EBITD
0 to -50oC
Load Transfer Efficiency

This project aims to provide a better understanding to the mechanisms
behind longitudinal and corner cracking phenomenon so that the
potential for such distresses can be accounted for in design

Jointed plain concrete pavements have long been observed to have a
wide variety of cracking locations induced through fatigue mechanisms

Load Specifications/Climate

Joint spacing
3.6 to 4.6m
Slab width
3.7 to 4.3m
h
203 to 305mm
PCC Materials / Support

NCHRP 1-37A mechanistic-empirical design guide provides a means
to analyze top-down transverse cracking, but does not account for
either top-down or bottom-up longitudinal or corner cracking
mechanisms

The inclusion of built-in curling effectively causes an equivalent
negative temperature difference in the slab due to the following factors
which are grouped together termed the linear effective built-in
temperature difference (EBITD) and expressed in units
of temperature:

CONCLUSIONS

Relative Damage Level

Concrete pavements in California exhibit longitudinal and corner
fatigue cracking in similar magnitude as transverse cracking

Tied lane

Faculty Advisor: Dr.

Asphalt Shoulder

Tied Shoulder

Widened Lane

Typically the critical damage location flipped from
bottom-up to top-down around an EBITD level of -20
to -25oF due to unsupported areas of the slab, axle
spacing effects, etc.
These predicted fatigue failure modes
and locations correspond well to the wide
variety of observed fatigue cracking
patterns on existing California rigid
pavements

Using assumptions for slab stress predictions which
were set forth by H.M. Westergaard in the early 20th
Century have led to a limited focus on the critical
fatigue
cracking
location
(bottom-up
mid-slab
transverse cracking) which does not necessarily match
observed fatigue distresses in many parts of the world
While these and similar analyses show that traditional
bottom-up transverse cracking is still very prevalent in
designing against fatigue, utilizing newer technologies
such as finite element modeling and achieving a better
understanding of rigid pavement behavior (pre-load
residual stress conditions from built-in curling, stress
ranging, axle spacing effects, etc.) can provide a clearer
picture of stress states and eventually lead to more
reliable designs in the future.

FUTURE WORK

Implementation of non-linear temperature predictions
profiles into the RadiCAL analysis software to account
for self-equilibrating axial forces which tend to promote
higher stress at the top of the slab due to the high nonlinearity of the temperature near the surface

Total
Temperature
Distribution
Function, T(z)

a.) Uniform
Axial
Stress
axial

b.) Linear
Curling
Stress
linear

c.) Self-equilibrating
Non-linear
Stress
nl

Accommodation of size-effect, boundary effects, and
shrinkage cracking in concrete slabs using fracture
mechanics principles to scale beam flexural strength to
the slabs bending resistance
Development of a limit state design methodology for
jointed concrete pavements to circumvent the use of
Miners Law calculations using calibration data and
safety factors to account for multiple fatigue locations
Rigid Pavement Analysis for Design in California

SPONSORED BY:

Caltrans
Pavement Research Center at UCBerkeley
FHWA NHI Eisenhower Fellowship
Program

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