nz guide to pavement evaluation and treatment design · nz guide to pavement evaluation and...
TRANSCRIPT
![Page 1: NZ Guide to Pavement Evaluation and Treatment Design · NZ Guide to Pavement Evaluation and Treatment Design ... Thickness limits for AC – using DESA . Traffic loading - discussion](https://reader035.vdocument.in/reader035/viewer/2022070719/5ede9fd5ad6a402d6669f3c7/html5/thumbnails/1.jpg)
NZ Guide to Pavement Evaluation and Treatment Design Rehabilitation guide
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Traffic loading – design values
• Not addressed in either of the Guides
• Austroads Part 2 is due for imminent release
• New Zealand specific design methodology in Part 2 should be used
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Loading Calculations in AGPT Part 2 2017
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Learning outcomes
• AGPT Part:2 – New loading calculations for ME Design
• Why we are changing
• What are we changing to
• How is that different to old SAR/ESA
• What you will need to do
• Empirical designs keep old ESA approach.
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Why - history
• 2012 approach considers relative damage between axle groups to be independent of Pavement Structure
• Current approach developed by Scala (1970a), simply compared axle group loads using surface deflections.
• Scala (1969, 1970b) – Noted that deflection axle group load equivalencies would change with pavement structure
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Why - research
Moffet 2015: PhD Thesis
Austroads 2015: The influence of multiple-axle groups loads on flexible pavement design (AP-R481-15)
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Why - summary
Basically – to get better axle group equivalency
• Old approach: Same Group Deflection = Same Damage
• i.e. 53 kN SAST = 80 kN SADT = ….. = 226 kN QADT
• New Approach: Same Strain = Same Damage
• i.e. 53 kN SAST ≠ 80 kN SADT ≠ ….. ≠ 226 kN QADT
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The details
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The details - outline
• Common Elements to calculations
• The Empirical Approach (Deflection / ESA)
• The new ME Strain Approach
• New limits for AC loading calculations
• Loading Discussion
• Learning Outcomes - check
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Common elements to traffic calculations
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Common elements – initial daily heavies
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Common elements – design heavies
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Specific elements to traffic calculations
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Empirical ESA approach
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Empirical standard on axle groups
• Austroads Reference Load - Single axle with two sets of dual wheels that carries a load of 80 kN.
• The loads on other axle groups that cause the same damage as a Standard Axle are:
Axle Configuration Load (kN)
Single Axle Single Wheels 53
Single axle Dual Wheels 80
Tandem Axle Single Wheels 90
Tandem Axle Dual Wheels 135
Triaxle 181
Quad axle 221
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Empirical ESA approach
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Empirical Approach is easy
45
90
4
26
53
4
+
± ±
Equivalent Standard Axles =
26𝑘𝑁 45𝑘𝑁 Axles Loads =
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Empirical design loading
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Empirical design loading
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ME approach – 2017 AC fatigue equation
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2017 AC fatigue equation in practice
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ME approach – calculate strains for all cases
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ME approach – all case calculations
• Requires response to load calculation for each load and axle type
• Using layered linear-elastic modelling
• Can linearly scale response from model
• Demonstrated not to significantly affect outcome
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2017 AC fatigue equation – in use
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ME damage caused by an axle group
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ME Summing up the TLD damage
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ME allowable HV axle groups
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Converted back to allowable ESA
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Mechanistic Empirical approach not that hard
26
1 𝜇𝜀𝑆𝐴𝑆𝑇,53
53 ,
45
2 𝜇𝜀𝑆𝐴𝑆𝑇,53
53
± ±
Allowable groups is Sum of
Critical Strains
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Thickness limits for AC – using DESA
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Traffic loading - discussion
NZ Transport Agency has
• 1600 Traffic Counting site – 1 site per 7 km
• 390 Continuously – 1site per 28 km
• 6 Weigh in Motion Site – 1 site per 1800 km
• Data averaged across sites
• Can estimate loading from AADT and %HCV
• Best estimates in RAMM
Australia has 200 Weigh in Motion Sites
• ESA/HCV ranges from 1 - 7
Questions also around “power laws”, reference loads/width and axle group equivalency.
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Learning outcomes - check
• Austroads Guide to Pavement Technology Part:2 –New loading calculations for ME Design
• Why we are changing?
• What are we changing to?
• How is that different to old SAR/ESA?
• What you will need to do?
• Empirical designs keep old ESA approach.