Post on 18-Dec-2015
Considering multiple-axle group loads in mechanistic design of bound pavements
Michael Moffatt
Source: Department of Planning, Transport and Infrastructure, South Australia
80 kN
Standard Axle
equivalent Standard Axle Repetitions
Axle type Standard group load [kN]
single axle – single tyres 53
single axle – dual tyres 80
tandem – dual tyres 135
triaxle – dual tyres 181
quad-axle – dual tyres 221
Failure mechanism LDE
asphalt fatigue 5
cemented material fatigue 12
total deformation 7
Fatigue testing
flexural fatigue testingusing trapezoidal beam
displacement controlduring testing
no rest periods
simulated axles had equal peaks
8
non-linear elastic support materials
localised stress/modulus states
superpositioning of responses
3D FEM
Asphalt
Crushed rock
Subgrade
Pavement structures
1000 MPa 3000 MPa5000 MPa
High quality crushed rockLower subbase
Highly plastic clay (CBR 3%)Sand (CBR 15%)
50 100 200 300 mm
200 400 600 mm
• Equating damage by strain (+ superposition) varies withpavement structure
• thicknesses
• modulus
• Single load equivalency values unsuitable
• Model traffic spectrum, and assign damage to each combination of axle group and load
• same as for concrete design
Implementation in the guide
Design processAustroadstraffic load distribution + HVAG count
SAR5
Model candidate structure with Standard Axle
Allowable loading cf. SAR5
Summed peakstraffic load distribution + HVAG count
Model candidate structure with axle types/loads in TDL
Sum damage (want ≤ 100 %)
Austroads Summed peaks
pulse width rest
250 ms250 ms
(a) Haversine
(b) Single axle
(c) tandem
(d) tri-axle
(e) quad-axle
• conclude that relative damage is the same as number of axles in group
• same procedure as for asphalt
FindingsGroup damage relative to single axle
Groups Relative damage
2 2.4
3 2.8
4.1
Design example
1 x 108 HVAG
Asphalt
Crushed rock
Subgrade
Candidate structure
3000 MPa
CBR 7 %
340 mm
300 mm
Reference load: 135 kN
XX YY
58.2 43.0XX YY
60.7 44.2
XX YY
58.2 43.0XX YY
60.7 44.2
Further information
Seek me out today.
26th ARRB Conference paper.
www.arrb.com.au/ARRB-
Conferences
Research Report for Austroads in press.
PhD thesis in pre-pre-press.Thank youwww.arrb.com.au