CIRCLY 5.0 User Manual

C I R C LY 5 User Manual

MINCAD Systems Pty. Ltd. P.O. Box 2114, Richmond South, Vic., 3121 Australia Tel.:(03) 9427 1085 Intl. +613 9427 1085 Fax:(03) 9428 1197 Intl. +613 9428 1197 Email: [email protected] Web: http://www.mincad.com.au

April 2009 © MINCAD Systems Pty. Ltd.

i

Contents

Summary 3

CIRCLY End User Licence Agreement 5

Introduction 7 Overview........................................................................................................................................ 7 Special Features for Pavement Engineering................................................................................. 8

Cumulative Damage Concept ............................................................................................. 8 Material performance .......................................................................................................... 9 Traffic and Loading............................................................................................................ 10 Wheel Loadings................................................................................................................. 10 Automatic thickness design............................................................................................... 10 ESA Multipliers .................................................................................................................. 10 Methods for handling Damage Pulses .............................................................................. 11

Overview of User Interface 13 Introduction.................................................................................................................................. 13 Creating, Opening and Saving Files............................................................................................ 14 Creating and Editing Input Data .................................................................................................. 14

Database Approach........................................................................................................... 15 Running CIRCLY32 Analysis and Plotting Results ..................................................................... 15

Run Analysis ..................................................................................................................... 15 Plot Results ....................................................................................................................... 15

Options ........................................................................................................................................ 16

What's New in Version 5.0 17 Overview...................................................................................................................................... 17 Support of Austroads 2008 Pavement Design Guide ................................................................. 17 New "built-in" Graphics Engine.................................................................................................... 18 Cost Calculation .......................................................................................................................... 21 Automatic Parametric Analysis.................................................................................................... 22

How to Start Using CIRCLY 23 Getting Started: Assembling and Running a Job ........................................................................ 23 Global Coordinate System........................................................................................................... 30

Alternative Calculation Options 33 Overview...................................................................................................................................... 33 Damage Calculation Details ........................................................................................................ 33 Thickness Design Capability ....................................................................................................... 35

ii Contents

Calculating Selected Results at User-defined Z-values (depths)................................................ 36

How to Use Advanced Features 39 Cost Calculation .......................................................................................................................... 39

Calculation of Total Cost ................................................................................................... 39 Material Costs ................................................................................................................... 40

Automatic Parametric Analysis.................................................................................................... 41 Example—Cost Optimization....................................................................................................... 42

How to Modify the Databases 49 Introduction.................................................................................................................................. 49

Units .................................................................................................................................. 49 Sign Convention ................................................................................................................ 51 Overview of Database Approach ...................................................................................... 52

The "Layered System" and "Materials" Databases ..................................................................... 53 Overview of Layered System and Material Properties...................................................... 53 Cross-anisotropy and isotropy in road pavement materials.............................................. 54 Creating a new Layered System....................................................................................... 55 Defining the Layer properties ............................................................................................ 56 Duplicating a Layered System .......................................................................................... 57 Adding a new Elastic Material ........................................................................................... 58 Example: Asphalt tensile strain relationship...................................................................... 60 Adding a new Material Type.............................................................................................. 61

The "Loads" and "Traffic Spectrum" Databases.......................................................................... 62 Introduction........................................................................................................................ 62 Adding a new Traffic Spectrum ......................................................................................... 62 Duplicating a Traffic Spectrum .......................................................................................... 63 Coordinate System for Loads............................................................................................ 64 Adding a new Load Group (i.e., a Vehicle or Axle Group) ................................................ 65 Defining Load Locations (i.e., Wheel positions)................................................................ 67 Important Note about Axle Locations ................................................................................ 67 Important Note about Damage Pulses .............................................................................. 69

Coordinates for Results ............................................................................................................... 71

Appendices 73

Overview of Austroads 2008 Features 75 Model of Standard Axle ..................................................................................................... 75 Project Reliability............................................................................................................... 76 Material Properties ............................................................................................................ 76

How to Use New Austroads 2004/2008 Features 79 Modelling the Standard Axle ............................................................................................. 79 How to Use Project Reliability ........................................................................................... 80 Changes to Materials ........................................................................................................ 82 Austroads 2008 Examples ................................................................................................ 83

References .................................................................................................................................. 85

3

Summary CIRCLY software is for the mechanistic analysis and design of road pavements. CIRCLY uses state-of-the-art material properties and performance models and is continuously being developed and extended. The first mainframe version of CIRCLY was released in 1977 and the current Windows version is Version 5. It is an integral component of the Austroads Pavement Design Guide (Austroads, 2008) that is widely used in Australia and New Zealand. The system calculates the cumulative damage induced by a traffic spectrum consisting of any combination of user-specified vehicle types and load configurations. As well as using the usual 'equivalent' single wheel and axle load approximations, optionally the contribution of each vehicle/load configuration can be explicitly analysed. Other geotechnical applications, such as foundation engineering and settlement analysis, can also be analysed using CIRCLY.

A Parametric Analysis feature can loop through a range of thicknesses for one or two layers, while simultaneously designing the thickness of another layer. This feature will optimise up to three layers. Combining this with a Cost Analysis feature, allows for fine-tuning of layer thicknesses to minimize construction and maintenance costs.

CIRCLY has many other powerful features, including selection of:

cross-anisotropic and isotropic material properties; fully continuous (rough) or fully frictionless (smooth) layer interfaces; a comprehensive range of load types, including vertical, horizontal, torsional, etc.; non-uniform surface contact stress distributions; and automatic sub-layering of unbound granular materials.

5

CIRCLY End User Licence Agreement CIRCLY (c) Mincad Systems Pty Ltd ABN 27 006 782 832. All rights Reserved.

Copyright This manual is copyright and may not be copied, photocopied, reproduced, translated or reduced to any electronic medium or machine readable form, in whole or part, without the prior written consent of Mincad Systems.

This documentation is licensed and sold pursuant to the terms and conditions of the CIRCLY End User Licence Agreement, which appears under the CIRCLY "About" dialogue box which provides (in part).

21.Exclusions and Limitation of Liability

21.1 To the maximum extent permitted by law all warranties whether express, implied, statutory or otherwise, relating in any way to the subject matter of this Agreement or to this Agreement generally, are excluded. Where legislation implies in this Agreement any condition or warranty and that legislation avoids or prohibits provisions in a contract excluding or modifying the application of or the exercise of or liability under such term, such term shall be deemed to be included in this Agreement. However, the liability of Mincad Systems for any breach of such term shall be limited, at the option of Mincad Systems, to any one or more of the following: if the breach related to goods: the replacement of the goods or the supply of equivalent goods; the repair of such goods; the payment of the cost of replacing the goods or of acquiring equivalent goods; or the payment of the cost of having the goods repaired; and if the breach relates to services the supplying of the services again; or the payment of the cost of having the services supplied again.

21.2 To the maximum extent permitted by law and subject only subject only to the warranties and remedies set out in Clause 12 and Sub-clause 21.1, Mincad Systems shall not be under any liability (contractual, tortious or otherwise) to Customer in respect of any loss or damage (including, without limitation, consequential loss or damage) howsoever caused, which may be suffered or incurred or which may arise directly or indirectly in respect to the supply of goods or services pursuant to this Agreement or the act, failure or omission of Mincad Systems.

Customer warrants that it has not relied on any representation made by Mincad Systems or upon any descriptions or illustrations or specifications contained in any document including any catalogues or publicity material produced by Mincad Systems.

22. Acknowledgement

22.1 Customer acknowledges and agrees that:

(a) pavement design and engineering is a complex area and the CIRCLY is not designed as a substitute in any way for professional advice;

6 CIRCLY 5.0 User's Guide

(b) CIRCLY is supplied with certain operating instructions and a failure to follow these instructions carefully could result in erroneous data being produced by CIRCLY;

(c) Whilst CIRCLY may be used by persons without a detailed knowledge of computers, CIRCLY is designed to be used by persons who have a detailed knowledge of, without limitation:

(i) the applicable engineering standards for paving and concrete; and

(ii) All appropriate legislation and other relevant instruments, including, without limitation the relevant industry recognised engineering design guides;

(d) It shall manually check all results provided by CIRCLY for any anomalies; and

(e) It shall obtain professional advice in relation to all results provided by CIRCLY.

22.2 CIRCLY is licensed on the basis set out in this Agreement on the understanding that to the extent permitted by law Mincad Systems is not responsible for the results of any actions taken, either by Customer or a third party relying on figures supplied or not supplied by CIRCLY.

23. Indemnity

Customer warrants that any materials supplied to Mincad Systems by Customer do not infringe Intellectual Property Right of any person.

To the extent permitted by law, Customer shall fully indemnify and keep indemnified Mincad Systems, its officers, employees and agents, against any loss, costs, expenses, demands, taxes or liability whether direct or indirect arising out of:

(a) use of CIRCLY;

(b) a breach of this agreement by Customer; or

(c) any wilful, unlawful or negligent act or omission of Customer.

7

Introduction

Overview CIRCLY is a powerful package that analyses a comprehensive range of load types acting on layered elastic systems. CIRCLY has special features for the convenient mechanistic analysis and design of pavements using state-of-the-art material properties and performance models. CIRCLY is an integral component of the Austroads Pavement Design Guide (2008) that is widely used in Australia and New Zealand. The system calculates the cumulative damage induced by a traffic spectrum consisting of any combination of vehicle types and load configurations. Because the contribution of each vehicle/load configuration can be explicitly considered, it is not necessary to approximate multi-wheel configurations by ‘equivalent’ single loads. CIRCLY can also be used for other geotechnical applications such as foundation engineering and settlement analysis.

CIRCLY has a user-friendly menu-driven interface that runs under Microsoft Windows. Databases are used for material properties and loadings, thus eliminating the need to constantly re-key information. Typical runs take less than a second on Pentium™ PCs. Results can be obtained in tabular form or as report-quality plots on any printer or plotter supported by Microsoft Windows. Results can be easily exported to other application packages such as spreadsheets for further processing.

In many soil and rock engineering problems, loads are applied to the horizontal, or near horizontal, surface of natural or man-made stratified deposits. CIRCLY calculates the stresses, strains and displacements that are developed in these systems, permitting the rational assessment of ultimate stability and the behaviour under working loads.

As well as the usual isotropic properties, cross-anisotropic material properties can also be considered. A cross-anisotropic material is assumed to have a vertical axis of symmetry. Anisotropies of this type have been observed in soil and rock deposits due to processes involved in their formation. The interfaces between the layers can be either fully continuous (rough) or fully frictionless (smooth), or a combination of both types.

In practice, loads may be applied to soil or rock pavement layers in the form of vertical wheel loads, horizontal wheel loads due to traction and braking, torsional wheel loads due to cornering, and the "gripping" load developed by pneumatic tyres on pavements. In addition, foundation loads on footings, piers and rafts may be applied as vertical forces, horizontal forces, moments about horizontal axes or contact stresses due to foundation roughness. The program allows all of these load types to be simulated for a circular loaded shape. CIRCLY can also model non-uniform contact stress distributions.

C H A P T E R 1


CIRCLY is based on integral transform techniques and offers significant advantages over other linear elastic analysis techniques, such as the finite element method. Input data for the program is much simpler than that required for most finite element programs. For most problems the program uses less computer time than a finite element program.

This Australian designed system has been developed by the Melbourne company, MINCAD Systems. It has been in regular use in Australia and worldwide for more than two decades, proving its worth in thousands of design applications. CIRCLY had its genesis in software developed at CSIRO for relatively simple loading cases (Harrison, Wardle and Gerrard 1972). CIRCLY was first released in 1977 and handled polynomial type radial variations in contact stress and multiple loads which provide a much closer representation of the actual loading conditions (Wardle 1977).

CIRCLY was commercialised in 1988 by MINCAD Systems. A limited release of the first Windows version (Version 2.4) was made in early 1996. Version 3.0 was released in late 1996 and included many improvements, including a major re-write of the integration algorithms and automatic sub-layer generation for granular materials. Version 4.0 was released in early 1999 and extended the software to include an automatic thickness design capability. Version 4.1 was released in early 2003. Version 5.0 was released in early 2004. For an overview of the new features of Version 5.0 see What's New in Version 5.0 (see "Overview" on page 17)

Special Features for Pavement Engineering CIRCLY has many features to facilitate pavement analysis and design.

Cumulative Damage Concept The system explicitly accumulates the contribution from each loading in the traffic spectrum at each analysis point by using Miner's hypothesis. The damage factor for the i-th loading is defined as the number of repetitions (ni) of a given response parameter divided by the ‘allowable’ repetitions (Ni) of the response parameter that would cause failure. The Cumulative Damage Factor (CDF) for the parameter is given by summing the damage factors over all the loadings in the traffic spectrum:

Chapter 1 Introduction 9

The system is presumed to have reached its design life when the cumulative damage reaches 1.0. If the cumulative damage is less than 1.0 the system has excess capacity and the cumulative damage represents the proportion of life consumed. If the cumulative damage is greater than 1.0 the system is predicted to ‘fail’ before all of the design traffic has been applied.

The procedure takes account of:

the design repetitions of each vehicle/load condition; and the material performance properties used in the design model.

This approach allows analyses to be conducted by directly using a mix of vehicle or axle types. It is not necessary to approximate passes of different vehicles or axles to passes of an ‘equivalent’ standard load.

The current version of the software uses the cumulative damage concept to sum the damage from multiple vehicle/load cases for one set of layered system material properties. The figure below is a sample cumulative damage plot produced by CIRCLY. CIRCLY generates a file that can be read by most spreadsheet and technical graphics programs.

Material performance Generally most performance models may be represented graphically by a plot of tolerable strain versus load repetitions (generally by a straight line of 'best fit' on a log-log plot). CIRCLY represents models in the form:


where N is the predicted life (repetitions)

k is a material constant

b is the damage exponent of the material

ε is the induced strain (dimensionless strain)

Log-log relationships can be readily converted to the above form.

CIRCLY is supplied with a comprehensive range of published performance models. You can use your own performance equations by specifying values for ‘k’ and ‘b’ and the particular component to be used, for example vertical strain, vertical deflection, maximum tensile strain, etc.

Traffic and Loading You define the anticipated repetitions over the design period for each vehicle or axle group and 'load case'.

The 'load case' allows the loading for a given vehicle or axle group to be treated in more detail if required.

Wheel Loadings The load on each wheel is defined by tyre contact radius and contact pressure (generally assumed to be the tyre inflation pressure).

Although the loads are usually vertical, CIRCLY can compute results from non-vertical loads such as braking and cornering loads.

Automatic thickness design You can automatically determine the optimum thickness of a given layer. This procedure is very fast and takes only a few seconds on a Pentium™ PC. For further details see Thickness Design Capability (on page 35).

ESA Multipliers For design methods such as Austroads that use an equivalent standard wheel approach, the traffic expressed in ESAs must be multiplied by a factor that depends on each material type. You can specify these multipliers (e.g. 1.1, 10) for each material type. For further details see Damage Calculation Details (on page 33).

Chapter 1 Introduction 11

Methods for handling Damage Pulses The damage that a given point in the pavement will experience during the passage of a multiple axle primarily depends on the depth below the road surface. The two extremes of behaviour are–

multiple distinct pulses resulting from each axle, for shallow depths; and a single pulse that reflects the overall loading on the axle group, for large depths.

CIRCLY lets you specify the method to be used to calculate the damage. Further details are given in Important Note about Damage Pulses (on page 69).

13

Overview of User Interface

Introduction CIRCLY has a standard format Microsoft Windows menu, but most commands can be accessed directly from the toolbar as shown below:

C H A P T E R 2


Creating, Opening and Saving Files You supply a 'Jobname' to use as the basis for naming all of the files associated with a 'job' or analysis. If the job name is Jobname the following files are used–

Jobname.cls CIRCLY data file- this is used to save the details of your job.

All the other files are generated automatically by the system:

Jobname.cli CIRCLY32 input data file

Jobname.clo CIRCLY32 'printable' results file

Jobname.prn CIRCLY32 raw results file (i.e., strains, etc.)

Jobname.dam CIRCLY32 cumulative damage results file (for plotting)

Jobname.dmx CIRCLY32 results summary file (damage factors and critical strains)

All of these files are text files that can be opened by standard text editors.

Three icons on the toolbar allow you to create, open and save job files.

Icon Description

Closes the current job, prompting you to save any changes; then creates a new job.

Closes the current job, prompting you to save any changes; then opens an existing job.

Updates the current job file.

You can also save your job under a different name by clicking on the File Menu, then clicking Save As.

Creating and Editing Input Data The following seven icons allow you to create and modify your input data. Each icon corresponds to one of the main groups of data necessary to fully define a Job.

Chapter 2 Overview of User Interface 15

Database Approach Some of the input data items are entered using very simple input forms. Most of the input data is handled using a relational database approach. This is designed to eliminate re-entry of data for design loads and material properties. You can tailor each of the databases to contain specific sets of regularly used data.

The relational database approach gives maximum flexibility in data preparation. For example, the data for a commonly used material need only be entered into the system once. If this data is subsequently modified, all Layered systems that use that material and subsequently all Jobs that use those layered systems will automatically access the modified material properties.

Running CIRCLY32 Analysis and Plotting Results

Run Analysis This invokes the CIRCLY32 analysis. During a long analysis you can switch to another application (CIRCLY will continue to run at a lower priority using Microsoft Windows multi-tasking).

Plot Results Usually, this command will produce a graph of the damage contribution from each vehicle type and the overall total (damage contribution from all the traffic). This graph option shows the variation of the CDF as a function of X, the distance from the centreline of the pavement (i.e. X=0 corresponds the centrelines of the vehicles). Optionally you can graph the maximum CDF as a function of Aircraft Gross Weight.

Alternatively, as an option you can produce a graph of a selected displacement, stress or strain component at your chosen Z-values (i.e., vertical distances/depths below the surface of the pavement) and results can be plotted for a selected displacement, stress or strain component.


Options The Options screen allows specification of the following directory:

location for all data files (Defaults to the sub-folder, "data", in the folder in which CIRCLY has been installed.)

17

What's New in Version 5.0

Overview You will find many improvements in CIRCLY 5.0 if you have used earlier versions such as CIRCLY 4.0 or 4.1. Latest improvements include new features to make designing pavements easier, more transparent and more efficient.

This section gives a quick overview of the new and improved features in CIRCLY 5.0. Cross-references to the rest of the manual show you where to look for information on these topics.

Support of Austroads 2008 Pavement Design Guide The Austroads Pavement Design Guide (the full title is Guide to Pavement Technology - Part 2: Pavement Structural Design) was first published in 1992 (Austroads, 1992). The Guide underwent a major re-write culminating in the 2004 version. In what follows, the new Guide will be referred to as the 2008 Guide.

Briefly, CIRCLY 5.0 implements the following changed features in the Guide:

Standard Axle modelled in full (Austroads 1992 used only one side or half the axle) Project Reliability as chosen by the designer; Changed methodology for sub-layering of unbound granular material; Introduction of Select Fill as a particular type of unbound granular material; Changed Subgrade Performance model for subgrade materials.

These changes are outlined in more detail in Overview of Austroads 2008 Features (on page 75).

Detailed instructions on how to use the new features are given in How to Use New Austroads 2008 Features (see "How to Use New Austroads 2004/2008 Features" on page 79).

C H A P T E R 3


New "built-in" Graphics Engine CIRCLY now uses its own "built-in" Graphics Engine to create on-screen graphics almost instantaneously. The graphics can be customized, exported and printed. In most cases, results for different layers or Z-depths in a layered system can be created without re-analysing the system.

Here is a sample Cumulative Damage graph:

You can choose a graph for a different layer (without re-analysing the system):

Chapter 3 What's New in Version 5.0 19

Here is a sample "Three-dimensional" graph of vertical displacement:


You can customize the graph via the context-sensitive graph menu that drops down when you right click with the mouse pointer anywhere on the graph. Click on “Customization Dialog” to customize the graph:

Chapter 3 What's New in Version 5.0 21

This lets you customize many of the graph parameters such as Minimum and Maximum axis values, etc.

Cost Calculation The unit costs for the materials laid and constructed in the layers can be specified using a combination of both a volumetric (or weight) component and an areal component. The areal component lets you take account of costs that are primarily a function of area, such as surface treatments, subgrade stabilization and the like. The areal component can also be used in circumstances where the relationship between total layer cost and thickness has a non-zero component for zero thickness.


Automatic Parametric Analysis Automatic Parametric Analysis lets you automatically loop through a range of thicknesses for one or two nominated layers. For example, you can have Layer 3 vary from 800 mm to 1000 mm in steps of 10 mm. Additionally, for each combination of those layer thicknesses, you can automatically design the thickness of another layer.

By combining Automatic Parametric Analysis with the Cost Analysis feature you can fine-tune layer thicknesses to optimise construction cost.

Automatically generated plot: Total Cost vs. Layer 3 Thickness

23

How to Start Using CIRCLY

Getting Started: Assembling and Running a Job In the interests of providing instant hands-on experience, this worked example assumes that most of the input data is already in the appropriate databases. You will be using an existing traffic spectrum and an existing layered system.

Follow this procedure:

1. Start a new Job file

Click on the button.

C H A P T E R 4


Enter your Job Name and Job Title (this is used on the graphs).

2. Select Traffic Spectrum


Click on the Spectrum tab.

This will bring up the list of available Traffic Spectra:

If you have not already selected a spectrum the blue highlight will be positioned on the first entry. Select ‘Austroads 2004 - Example 1 - Unbound Granular Pavement’ by moving the mouse pointer to this line and then clicking on it.

3. Specify Layered System


Click on the Layered System tab.

This will bring up the list of available Layered Systems:

Chapter 4 How to Start Using CIRCLY 25

If you have not already selected a Layered System, the blue highlight will be positioned on the first entry. Select ‘Austroads 2004 - Example 1 - Unbound Granular Pavement’ by moving the mouse pointer to this line and then clicking on it.

4. Specify Coordinates for Results


This screen has fields for specifying the locations for which results are to be computed.

Two alternative formats are available for specifying the points to be used for results calculation:

An array of equally spaced points along a line parallel to the X-axis A grid of points with uniform spacing in both the X-direction and the Y-direction

Enter the data as shown below.


The data entered as above will create a line along the X-axis from (0,0) to (165,0) at intervals of 165 mm. To comply with the Austroads Guide, the dimensions are in millimetres (see Units (on page 49) for further details).

The sub-section Assumed number of damage pulses per movement is dealt with later in Important Note about Damage Pulses (on page 69).

5 Run the CIRCLY32 analysis

Click on the button. This invokes the CIRCLY32 analysis.

When the CIRCLY32 analysis starts you may see a blue "progress bar" at the bottom left corner of the screen. Analyses typically take about a second on a Pentium™ PC.

When the CIRCLY32 analysis is complete the results for the damage factor (CDF) will be transferred to the top table on the screen, as shown below.


6. Plot the Results

Click on the button. This will generate a graph of the results:


You can print a copy of the chart by clicking on the Print icon on the toolbar.

You can also copy the graph to the clipboard and then paste into another application such as Microsoft Word or Powerpoint. You do this via the context-sensitive graph menu that drops down when you right click with the mouse pointer anywhere on the graph:


Then click on 'Export Dialog'. The 'Export Dialog' lets you export to a variety of formats, but for most purposes select 'Metafile' to ensure that the graphics are scalable.


Global Coordinate System A global coordinate system is used to define load locations, the layered system geometry and the points below the road surface at which results are required. The global coordinate system is also used to describe the resultant displacements and stress and strain tensors.

The X-axis is usually taken as the direction transverse to the direction of vehicle travel. The Y-axis is then parallel to the direction of vehicle travel.

Figure 1: Global Coordinate System

The Z-axis is vertically downwards with Z = 0 on the pavement surface.


An array of equally spaced points along a line parallel to the X-axis; A grid of points with uniform spacing in both the X-direction and the Y-direction.


X

Y

0

Direction of Travel

Results points

Xmin XmaxXdel

Figure 2: Coordinates for results defined by a line of equally spaced points

X

Y

0

Direction of Travel Results points

Xmin XmaxXdel

Ymax

Ymin

Ydel

Figure 3: Coordinates for results defined by a uniform grid of points

33

Alternative Calculation Options

Overview CIRCLY 5.0 offers a number of calculation options. Normally, you will calculate the damage factors (CDF) for your pavement. You can automatically determine the optimum thickness of a given layer. Alternatively, you can calculate results for any given displacement, stress or strain component at selected Z-values (depths below the road surface).

Damage Calculation Details Typically, between one layer (the subgrade) and three layers (asphalt surfacing, cement-stabilised layer and subgrade) will have performance criteria associated with them.

Click on the button. This will bring up the following screen:

C H A P T E R 5


1 Two alternative calculation options are available:

Calculate damage factors (CDF); Calculate selected results at user-defined Z-values (see Calculate Selected Results at

User-defined Z-Values (see "Calculating Selected Results at User-defined Z-values (depths)" on page 36)).

When operating in 'calculate damage factors' mode, the key features on the screen (the numbers refer to the screenshot above) are:

2 This table is a summary of the layered system including material titles and current thicknesses. Also the current Cumulative Damage Factors (CDFs) will be shown if the problem has been run previously. The current thickness of any layer can be changed from this screen.

3 This table is a summary of the properties for those layers that have a performance criterion.

The Traffic Multipliers are defined in the Austroads Pavement Design Guide (2008) as SAR/ESA for each distress type, where SAR are standard axle repetitions. The multipliers to take account of the material type and the actual traffic mix. The multipliers are simply used to multiply the ESA count that is specified in the Traffic Spectrum screen. The need for multipliers arises only if the actual road traffic spectrum has been represented as ESAs.

Chapter 5 Alternative Calculation Options 35

Thickness Design Capability You can automatically determine the optimum thickness of a given layer. This procedure is very fast, typically taking a few seconds on a Pentium™ PC.

1 The thickness design capability is invoked by clicking on the checkbox that is labelled 'Design thickness of layer highlighted below'.

2 You select the layer you wish to design by moving the mouse pointer to the appropriate layer and clicking the mouse button once. The layer selected will be highlighted in blue.

3 By default, the design will use the maximum damage factor (CDFmax) from all the layers that have a performance criterion. The design involves bringing the maximum damage factor to 1.0 by varying the thickness of the highlighted layer.

In some circumstances, it may be necessary to ignore one or more layers when calculating the maximum damage factor.

Here a tick ( ) denotes that the layer will be included in the maximum damage factor calculation.

The tick-box can be toggled on and off by clicking on it.


Minimum and maximum thicknesses can be specified for each layer, or these fields can be left blank, so that no constraints are applied. If a specified maximum or minimum thickness limit prevents attainment of a CDF of 1.0, the CDF for the thickness limit will be computed.

Calculating Selected Results at User-defined Z-values (depths) In some circumstances, you may need to calculate selected results (displacements, stresses and strains) at selected Z-values (depths). Specify first convenient Z-values and then plot results for a selected displacement, stress or strain component. When you use this option, damage factors are not calculated.


2

1

6

3

45

2

1

6

3

45

22

1

66

33

4455

Chapter 5 Alternative Calculation Options 37

1 This option is invoked by clicking the button that is labelled 'Calculate selected results at user-defined Z-values'.

2 You can choose the component that is to be plotted by first clicking on the 'Component type' tab. You can then define the component type (e.g. displacement, strain etc.) by clicking on the down arrow on the right hand side of the 'component type' combo box. This will invoke this drop down list:

Click on the component type that you wish to use.

3 The actual component (e.g., vertical, etc.) is specified by clicking on the down arrow on the right hand side of the 'Component' combo box. A drop down list of alternatives will appear:

Click on the Component that you wish to use.

4 Now you can define the Z-values. Each Z-value is added by clicking the New button 6 .

You can delete any entry by clicking on it and then clicking the Delete button.

5 When a Z-value coincides with the interface between two layers, you can specify which side of the interface is to be used (i.e. above the interface, or below the interface).

39

How to Use Advanced Features

Cost Calculation

Calculation of Total Cost CIRCLY 5.0 can automatically calculate Total Cost for a pavement from the unit costs of materials in each layer.


1 Click on the Calculate Cost checkbox

C H A P T E R 6


Material Costs The unit costs for the layers can be specified using a combination of both a volumetric (or weight) component and an areal component. The areal component lets you take account of costs that are primarily a function of area such as surface treatments, subgrade stabilization, etc. The areal component can also be used in circumstances where the relationship between total layer cost and thickness has a non-zero component for zero thickness.

Unit Material CostsUnit Material Costs

The Total Cost for a given layer is calculated as follows:

Total Cost (layer no. i) ($/m2) = Unit Volumetric Cost (layer no. i) ($/m3) x Thickness (layer no. i) (mm) + Unit Areal Cost (layer no. i) ($/m2)

The Unit Volumetric Cost can be defined in terms of:

1 Cost/Volume, or

2 Cost/Weight and the density of the material (Weight/Volume).

Chapter 6 How to Use Advanced Features 41

Automatic Parametric Analysis Automatic Parametric Analysis lets you automatically loop through a range of thicknesses for one or two nominated layers. For example, you can have Layer 2 vary from 100 mm to 200 mm in steps of 10 mm. Additionally, for each combination of those layer thicknesses, you can automatically design the thickness of another layer. Combining this with the Cost Analysis feature lets you fine-tune layer thicknesses to optimize construction cost.


111

1 Click to switch on Parametric Analysis. This will bring up the following form:

1

23

4

11

2233

44

1 This combo box lets you specify the number of Independent Variables (i.e. the number of Layers for which you are varying the thickness):

1. One Independent Variable, or

2. Two Independent Variables. 2 This section gives the details of the first Independent Variable. 3 This lets you choose which layer (thickness) is to be used as the first Independent

Variable. 4 Here you specify the range of thicknesses to be used for that layer:

The thickness will range from T1minimum to T1

maximum in steps of T1step.


To use two Independent Variables, click the combo box ( 1 on the screenshot below).

1

23

4

11

2233

44

2 This section gives the additional details for the second Independent Variable 3 Here you specify which layer (thickness) is to be used as the second Independent Variable 4 Here you specify the range of thicknesses to be used for that layer:

The thickness will range from T2minimum to T2

maximum in steps of T2step.

Example—Cost Optimization In this example you will use the Automatic Parametric Analysis feature to automatically loop through a range of thicknesses for one layer (Layer 2) and to determine which thickness has the minimum Total Cost. For each Layer 2 thickness, you will get CIRCLY to automatically design the thickness of Layer 3.

Asphalt: Size 14, Type H

Asphalt: Size 20, Type T

Crushed Rock: 20 mm , Class 4

Subgrade, CBR = 3

Thickness

T1 = 40 mm

T2 = ?

T3 = ?

Unit Cost

$288 / m3

$288 / m3

$50 / m3

Asphalt: Size 14, Type H

Asphalt: Size 20, Type T

Crushed Rock: 20 mm , Class 4

Subgrade, CBR = 3

Thickness

T1 = 40 mm

T2 = ?

T3 = ?

Unit Cost

$288 / m3

$288 / m3

$50 / m3


Step 1. Open the sample file "Economic Analysis - Pavement Option B2".

Step 2.

2

1

22

11

1 Make sure the Calculate Cost check-box is ticked.

2 Click the Parametric Analysis check-box. This will bring up the following form:

1 This combo box lets you specify the number of Independent Variables (i.e. the number of Layers for which you are varying the thickness).

For this example you will use the default, One Independent Variable. 2 This section gives the details of the Independent Variable, the thickness of Layer 2. 3 This lets you choose which layer (thickness) is to be used as the first Independent

Variable.

For this example change this to "2". (as you are varying the thickness of Layer 2). 4 Here you specify the range of thicknesses to be used for Layer 2:


For this example, you will let Layer 2 vary in thickness from 160 mm to 230 mm in steps of 10 mm.

Enter the following values:

Minimum: 160, Maximum: 230, Step: 10.

Step 3. Now set the automatic thickness design feature to Layer 3.

Click on the "Summary" tab (left of the "Variables" tab).

2

1

22

11

1 Click the check-box labelled 'Design thickness of layer highlighted below'. 2 Click anywhere on the Layer 3 row.

Click in the "Minimum Thickness" cell on this row and enter 100 (mm).

Now click on to run the analysis.


Step 4- Plot the Total Cost vs Layer 2 thickness.

When the analysis is finished, click on to plot the results.

Minimum Total Cost

This plot shows the Minimum Total Cost condition for Layer 2 thickness is 220 mm (to a resolution of 10 mm).

Step 5- Plot the CDF (for Layer 2) vs. Layer 2 thickness. Click on the Parameter combo box.

Select CDF (Select Layer =>).

Click on the Layer combo box.


Select Size 20 Type T - 40km/h (This is Layer No. 2)

Step 6- Plot the Layer 3 thickness (Design Layer) vs. Layer 2 thickness. Click on the Parameter combo box.


Select Thickness (Layer used for Thickness Design).

Comments on these results.

If the Layer 2 thickness is 160 mm or less, the "designed" thickness of Layer 3 exceeds 5000 mm. Therefore a Layer 2 thickness of less than 160 is not viable if supported by the Layer 3 material.

If the Layer 2 thickness is 220 mm, the Layer 3 thickness is 100 mm, because of the Minimum Thickness constraint and because the CDF is 0.91.

If there was no Minimum Thickness constraint, the Layer 3 thickness would be 39.6 mm. This would be inconsistent with the Austroads (1992) sub-layering requirement that the minimum thickness of a sub-layer is 50 mm.

49

How to Modify the Databases

Introduction

Units In order for CIRCLY to deliver coherent results, all data must be in a consistent set of units.

The recommended system of units is given below.

Quantity Units

Length, Displacement

mm

Elastic modulus, Pressure

MPa

Force N

Moment N.mm

Strain mm/mm

This system of units is consistent with the Austroads Pavement Design Guide and has been used for all the data files provided with CIRCLY. These units must be used for all Austroads applications involving sub-layering of granular materials.

Other compatible systems of units can be used as shown in the following table, as long as sub-layering of granular materials is not used. Output stresses will have the same units as used to define the loading stresses and the elastic moduli; the strains are dimensionless and the displacements will have the same units as the load dimension and the layer thicknesses.

Quantity Metric* Metric Metric Imperial Imperial

Length, Displacement

mm m m ft in

C H A P T E R 7


Elastic modulus, Pressure

MPa kPa MPa lb/ft2 lb/in2 (psi)

Force N kN MN lbf lbf

Moment N.mm kN.m MN.m lbf.ft lbf.in

Strain mm/mm m/m m/m ft/ft in/in

*This system of units must be used for Austroads applications involving sub-layering of granular materials.

Chapter 7 How to Modify the Databases 51

Sign Convention Compressive direct stresses and strains are considered to be positive. Positive shear stresses are defined on the basis that both the stress and strain tensors obey the right hand rule. Displacements in negative coordinate directions are considered to be positive. Hence a load causing a positive stress acts in the positive coordinate direction. The sign conventions used in the rectangular coordinate system and cylindrical local coordinate system are illustrated below.

Figure 4: Sign Convention


Overview of Database Approach The relational database approach is designed to eliminate re-entry of data for design loads and material properties. For example, the data for a commonly used material need only be entered into the system once. If this data is subsequently modified, all Layered Systems that use that material and subsequently all Jobs that use those Layered Systems will automatically access the modified material properties.

The Figure below illustrates the relational database concept for the elastic material properties. Here, each of the components that make up a Layered System is linked to entries in the Elastic Material Properties database via an ID (index) field of up to 10 characters.

Figure 5: Relationships between elements in Layered System databases

A similar hierarchy applies for the Traffic database. Each load group referenced by the Traffic Spectrum is linked to a record in the Load Group data.

A consequence of the relational database approach is that data should generally be prepared from the 'bottom up'. This means that:

Elastic Materials Properties data must be entered before the Layered System Components data;

Load Group data must be entered before the Traffic Spectrum Components data.

To create a new layered system, these steps must be followed:

1 Create any materials that are not already in the Elastic Materials database;

2 Create a new entry in the Layered Systems database;

3 Define each of the Materials and thicknesses for each of the Layers using the Layered System Components database.

Worked examples in the following sections show how you can create new data.


The "Layered System" and "Materials" Databases

Overview of Layered System and Material Properties CIRCLY models road pavements as a system of layers, each with differing elastic properties. The layered system consists of one or more layers. The layer interface planes are horizontal and each layer is assumed to be of infinite extent in all horizontal directions. The bottom layer may extend to a finite depth or to a semi-infinite depth (see the figure below). If the bottom layer is of finite depth, it is assumed to rest on a rigid base, and the contact can be either fully continuous (i.e., rough) or fully frictionless (i.e., smooth). Interfaces between the layers can be either fully continuous (rough) or fully frictionless (smooth), or a combination of both types.

Layer No. 2

Rough rigid base

Smooth rigid base

Semi-infinite base

Layer No. NL

Layer No. 1

∞

Layer No. 2

Rough rigid base

Smooth rigid base

Semi-infinite base

Layer No. NL

Layer No. 1

∞


Cross-anisotropy and isotropy in road pavement materials The elastic material in each layer of the pavement/road structure is assumed to be homogeneous and of cross-anisotropic or isotropic symmetry.

A cross-anisotropic material has an axis of symmetry of rotation, which is assumed to be vertical, i.e., the elastic properties are equivalent in all directions perpendicular to the axis of symmetry (in horizontal, radial directions). In general, these properties are different from those in the direction parallel to the axis, whereas isotropic materials have the same elastic properties in both the vertical and horizontal directions.

In the Austroads pavement design method (2004) cross-anisotropic properties are used for subgrade materials and unbound granular aggregates and isotropic properties are used for bound materials such as asphalt and cemented materials.

The stress-strain relations for a cross-anisotropic material in a particular layer are:

εxx = (1/Eh) (σxx - νh σyy - νhv σzz)

εyy = (1/Eh) (- νh σxx + σyy - νhv σzz)

εzz = (1/Ev) (- νvh σxx - νvh σyy + σzz)

εxy = ((1+νh)/Eh) σxy

εxz = (1/f) σxz

εyz = (1/f) σyz

The moduli and Poisson's ratios are related by the following equation:

νvh/Ev = νhv/Eh

The condition that the strain energy must be positive imposes restrictions on the values of the elastic constants:

Eh > 0 Ev > 0 f > 0

1 > νh > -1 1-νh-2νhvnvh > 0

For isotropic materials the restrictions become:

E > 0 0.5 > ν > -1.0

To be able to model a cross-anisotropic material you need to specify five constants: the vertical Elastic modulus (Ev), the horizontal Elastic modulus (Eh), the Poisson’s ratio (νvh), the Poisson’s ratio (νh) and the Shear modulus (f).


Data values for all five constants are rarely available.

The Austroads Pavement Design Guide uses the following simplifications to model subgrade and unbound granular materials:

Eh = 0.5 Ev

νvh = νh = ν

f = Ev/(1+ν)

In this case, the material is defined simply by the vertical Elastic modulus, Ev, and a single Poisson's ratio, ν.

For isotropic materials, only the Elastic modulus and Poisson’s ratio need to be entered, as they are assumed to be the same in all directions.

Creating a new Layered System


Click on the Layered System tab.

Click on the New button. A dialog box will appear as shown below. You should now type in your ID (index) field of up to 10 characters and a descriptive title (up to 72 characters). For this example you can type in 'MyLayers' as the ID and 'Example of creating a new Layered System' as the Title. Click the OK button.

Now you can define the details of the layers in your layered system.


Defining the Layer properties You add the layers working from the top of your pavement system, i.e., starting with typically asphalt or cemented material, and working downwards through the pavement.

Click on the New button. A pop-up list will appear, as shown below.

You will now choose the Material Type. To select the Material Type, click on the appropriate line then click the OK button.

A list of available materials will now appear. Select the required material by clicking on the appropriate line, then click on the OK button.

A new record will be added at the bottom of the table and the cursor will be positioned in the Thickness column. Enter the layer thickness. You repeat this process to add as many layers as you require. The subgrade will extend to an infinite depth if you enter the thickness as 0.0.

As explained in Overview of Layered System and Material Properties (on page 53), interfaces between the layers can be either fully continuous (rough) or fully frictionless (smooth), or a combination of both types. You can specify any interfaces as fully frictionless.

1


1 By default, all interfaces are assumed to be rough. You can change the condition for the interface at the bottom of a given layer by clicking in the 'Interface Type' cell. You can then click on the down arrow at the right of the cell to select a 'Smooth' interface. Note that for a semi-infinite subgrade both 'Rough' and 'Smooth' are equivalent.

Duplicating a Layered System Sometimes you may want to create a Layered System that is similar to an existing one. The Duplicate function lets you duplicate an existing Layered System. Then you can change the settings that need to be different.

Move the blue highlight to the Layered System that you want to duplicate:

Then click the Duplicate button. You will then see a form that will let you define the ID and Title of the newly duplicated Layered System:


The ID and Title that are provided are based on the original Layered System - make sure that you modify the Title.

After you click the OK button you will be taken to the Layered System Components table so that you can make your changes.

Adding a new Elastic Material


Click on the Elastic Materials tab.

You now choose the material type to be used. Click on the material type combo box as shown below to select from the available material types. Click on 'Subgrade (Austroads 2004)' for the Material Type.

Click here to select Material TypeClick here to select Material Type

Click on the New button. A dialog box will appear, as shown below. You should now type in your ID (index) field of up to 10 characters. As you can see from the example below, the ID is used to sort the data. For this example, you can type in 'Sub_CBR2.5'. Type in 'Subgrade, CBR=2.5' for the Title. Click the OK button.


You will now be given an opportunity to select a Performance Criterion. To select a Performance Criterion make sure the checkbox next to ‘Use performance criterion’ is checked, then click on the appropriate performance criterion. Click on the OK button.

A new record will be added to the table. Select 'Anisotropic' in the column headed 'Aniso?'. Then type in the moduli and Poisson's ratios as follows:

Ev = 25.0

Eh = 12.5 (= 0.5 Ev)

νvh = νh = 0.45 (= ν)

f = 17.24 (= Ev/(1+ν))

The new record should be as shown below:


Example: Asphalt tensile strain relationship For this example we consider the Shell asphalt fatigue criterion:

where RF is the Reliability Factor

µε = maximum tensile strain (in units of microstrain),

VB = percentage by volume of bitumen in the asphalt,

and Smix= mix stiffness (Elastic modulus) in MPa.

The value of the Reliability Factor is automatically handled by your choice of Project Reliability (see How to Use Project Reliability (on page 80)).

For this example, assume VB = 12.9 and Smix = 1600 MPa, so that the above equation simplifies to:

N = [ 5889 / µε]5

To enter this data click on the button.

Click on the Performance tab.

You now choose the material type to be used. Click on the material type combo box (as shown on the first screenshot in Adding a new Elastic Material) to select from the available material types. For this example click on 'Asphalt'.

Click on the New button. Now type in your ID (index) field of up to 10 characters and the Title (up to 72 characters). For this example type in 'Asph1600' for the ID. Type in 'Asphalt- 1600 MPa, Vb=12.9%' for the Title. Click the OK button.


Adding a new Material Type

You can add new material types. To add a new material type, Click on the button.

Click on the Material Types tab.

Click New to create a new entry. A dialog box will now appear and you can enter the ID (index) field of up to 10 characters and Title field (up to 72 characters). Click the OK button.

You will now choose the Generic Material Type for your new Material Type:

You will now be given an opportunity to select a Sub-Layering scheme. To select a Sub-Layering scheme, click the checkbox next to ‘use sub-layering’, then click on the appropriate sub-layering scheme. Click on the OK button.


The "Loads" and "Traffic Spectrum" Databases

Introduction Four inter-related databases are used for the Traffic data. The databases form a hierarchy:

Traffic Spectrum; Traffic Spectrum Components; Load Groups; Load Locations.

Depending on whether or not the components you need already exist, the steps required are described in the following sub-sections.

Adding a new Traffic Spectrum

If the Traffic screen is not already active, click on the button.

Click on the Spectrum tab.

Click New to create a new entry. A dialog box will now appear and you can enter the ID (index) field of up to 10 characters and Title field (up to 72 characters). Click the OK button. The Spectrum Components Table will now appear.

Now define your spectrum components:

Click New for each vehicle model you wish to include. This will activate a pop-up list of possible choices. You can move the highlight to the vehicle that you wish to use by positioning the mouse pointer on it and clicking once. If there are more entries than will fit in the listbox there will be a slider bar on the right. You can move down the list by clicking on the down arrow or by dragging the slider down. You finally select the vehicle by double clicking on it.

A new record will be added at the bottom of the table and the cursor will be positioned in the Movements column. Enter the number of vehicle movements (or passages) over the desired design life.


Duplicating a Traffic Spectrum Sometimes you may want to create a Traffic Spectrum that is similar to an existing one. The Duplicate function lets you duplicate an existing Traffic Spectrum. Then you can change the settings that need to be different.

Move the blue highlight to the Traffic Spectrum that you want to duplicate:

Then click the Duplicate button. You will then see a form that will let you define the ID and Title of the newly duplicated Traffic Spectrum:

The ID and Title that are provided are based on the original Traffic Spectrum - make sure that you modify the Title.

After you click the OK button you will be taken to the Traffic Spectrum Components table so that you can make your changes.


Coordinate System for Loads The most common type of load modelled in CIRCLY is a circular area over which a uniform vertical pressure is applied. This load typically represents the contact of a tyre on the surface of the pavement. However, it is possible to model more complex loads induced by breaking and turning movements of vehicles, which is dealt with in Wardle (2004).

The location of the circular load is described by a ‘global’ coordinate system, while 'local' coordinate systems are used to describe each of the loads. The 'global' system is cartesian, with axes X, Y, Z. Note the use of uppercase X, Y, Z for Global coordinates and lowercase x, y, z for Local coordinates. You can choose the origin of the 'global' coordinate system to be any point on the upper surface of the layered system and the X and Y axes as any two mutually perpendicular axes that lie in this horizontal plane. The Z-axis in the positive direction is taken as vertically downwards.

Each 'local' coordinate system may be cartesian (x, y, z) or cylindrical (r, θ, z) and has its origin at the centre of the load it describes. In terms of the 'global' coordinate system the origin of each 'local' coordinate system is specified by Xload, Yload. For loads that are symmetrical about a horizontal axis this axis is taken as the x-axis. The orientation of the load is defined by the angle (θload) between the directions of the X-axis and the x-axis. For loads that are symmetrical about their centre point the x-axis may have any orientation, though, for convenience, it may be taken as parallel to the X-axis so that θload is then zero. The location and orientation of a load are therefore specified by Xload, Yload and θload.

Figure 6: Global and Local Coordinate Systems


Adding a new Load Group (i.e., a Vehicle or Axle Group)


Click on the Load Groups tab.

The example given here is for a tandem axle with dual wheels. Click on the New button. A dialog box will appear as shown below. Type in your ID (index) field of up to 10 characters and a descriptive title (up to 72 characters). For this example type in 'TA-DW' as the ID and 'Tandem axle with dual wheels' as the Title. Click the OK button.


A record will be added to the table and you can enter the relevant data as follows:

Field name (Heading) Value Explanation

Plot Label TA-DW Label used by legend in graphs (Up to 72 characters)

Rows 2 Number of rows (axles) in main gear (this is the NROWS parameter described in Important Note about Damage Pulses (on page 69))

Type 1 A flag to indicate type of load (1=Vertical, for other values see Program CIRCLY Theory and Background Manual)

Radius 92.1 Radius of tyre contact area (mm)

Stress 0.75 For Vertical loads (Type=1) use the tyre contact pressure, generally assumed to be the tyre inflation pressure (MPa). If you are using an advanced load type, enter the reference stress referred to in the Program CIRCLY Theory and Background Manual.

Exponent 0.0 If this parameter is zero the contact stress will be uniform. Non-zero values give non-uniform contact pressure distributions as described in Program CIRCLY Theory and Background Manual.

The entries should look like this:

You should now specify the wheel locations.


Defining Load Locations (i.e., Wheel positions)

If the Load Groups screen is not already active, click on the button.

Click on the Load Locations tab. Check the descriptive title above the table to make sure that you are referring to the correct Load Group. If it is not the one you have just defined, click on the Load Groups tab, click on the appropriate record within the Load Groups table and click on Load Locations again.

Click New for each wheel and enter the gear number, and the X and Y coordinates of each wheel. See the note Important Note about Axle Locations (on page 67) below for special information about defining axle locations.

The scaling factor is normally 1.0 - other values allow for a variation in contact pressure from wheel to wheel.

Theta is only used to define the force or moment direction for non-standard loads such as braking loads. Theta corresponds to θLOAD in Figure: Global and Local Coordinate Systems.

Important Note about Axle Locations Make sure gear number 1 has an axle on Y = 0.

It is essential that the gear numbers are correctly specified. The gear numbers are used for calculating the centroid of gear number 1. This is used to shift the Y-coordinates of the wheels for the combined pulse option, as described, so that the gear centroid of gear number 1 is on Y = 0 (see Important Note about Damage Pulses (on page 69) for further details).

For the Tandem axle, dual wheels gear layout (TA-DW) shown above, the entries in the table should be similar to the table below. Note that the wheels making up a given gear can be in any order.


(165,0)

X

Y

0

Direction of Travel

Axle 1

Axle 2(165,-1320)(-165,-1320)

(-165,0)

Figure 7: Example wheel layout (Tandem axle, dual wheels)


Important Note about Damage Pulses The damage that a given point in the pavement will experience during the passage of a multiple axle will primarily depend on the depth that the given point is below the road surface. For shallow pavement depths, relative to axle spacing, one ‘pulse per axle’ is selected. CIRCLY then computes the damage beneath that axle due to the strain contributions for all wheels of the vehicle, then multiplies the computed damage by the number of axles in the axle group (NROWS). NROWS refers to the number of axles in the gear, which is specified in the ROWS column of the Load Groups section of the Loads database.

CIRCLY relies on you to specify one set of axles at Y = 0 as shown on Figure: Example wheel layout (Tandem axle, dual wheels).

However, for large depths, relative to the axle spacing, the maximum strain will generally occur under the centroid of the gear. In this case, you specify 'combined pulse for gear' and CIRCLY will automatically shift the load coordinates so that the origin is at the centroid of the gear, as shown in the Figure below. CIRCLY then computes the damage pulse beneath the centroid of the gear due to the strain contributions for all wheels of the vehicle, and ignores the number of axles in the group.


X

Y

0

Direction of Travel

Axle 1

Axle 2

Figure 8: Automatic shift of Y-coordinates for ‘combined pulse for gear’ case

You must decide whether the pavement is deep or shallow relative to the axle spacing. CIRCLY automatically shifts the position of the load coordinates if you specify 'combined

pulse for gear'. You specify how to deal with the gear by clicking on the button to open the Coordinates for Results screen. This screen has a sub-section for specifying the locations at which results are to be computed and the method for treating the damage pulses.

Computation of the damage at intermediate depths requires judgement based on a knowledge of the strain pattern, regardless of whether CIRCLY or other analysis methods are used.


Coordinates for Results


This screen has fields for specifying the locations for which results are to be computed and the method for treating damage pulses.


An array of equally spaced points along a line parallel to the x-axis; or A grid of points with uniform spacing in both the x-direction and the y-direction.

73

Appendices

C H A P T E R 8

75

Overview of Austroads 2008 Features The Austroads Pavement Design Guide (the full title is Guide to Pavement Technology - Part 2: Pavement Structural Design) was first published in 1992 (Austroads, 1992). The Guide underwent a major re-write culminating in the 2004 version. For convenience, we use the convention that Austroads 1992 is the original Guide and that Austroads 2008 is the new Guide.

The following notes assume that you are already familiar with the original Guide. These notes should be read in conjunction with Austroads 2008. No attempt is made to comprehensively describe all the features, but the main differences with the original Guide are highlighted.

Model of Standard Axle The Standard Axle Load consists of a dual-wheeled single axle, applying a load of 80 kN.

Austroads 2008 uses a full Standard Axle Loading.

This figure shows the layout of the wheels and their respective positions along the CIRCLY x-axis.

Figure 9: Model of Standard Axle


Project Reliability The Project Reliability is defined as follows (Austroads 2008):

The Project Reliability is the probability that the pavement when constructed to the chosen design will outlast its Design Traffic before major rehabilitation is required. In regard to these reliability procedures, a project is defined as a portion from a uniformly designed and (nominally) uniformly constructed road pavement which is subsequently rehabilitated as an entity.

The desired project reliability is chosen by the designer. Typical project reliability levels are given as follows (Austroads 2008):

Road Class Project Reliability (%)

Freeway 95 - 97.5

Highway: lane AADT>2,000 90 - 97.5

Highway: lane AADT<2,000 85 - 95

Main Road: lane AADT>500 85 - 95

Other Roads: lane AADT<500 80 - 90

Material Properties Sub-layering Unbound Granular Materials Sub-layering is required for granular materials placed directly on the subgrade.

Austroads 2008 always uses 5 equi-thick sub-layers [with Austroads 1992, the number of sub-layers were dependent on the thickness and elastic properties of the layers].

The procedure is:

a Divide the total depth of unbound granular materials into 5 equi-thick sub-layers.

b The vertical Elastic modulus of the top sub-layer is the minimum of the value specified in the CIRCLY input (indicative values are given in Table 6.3 of Austroads 2008) and that determined using:

Chapter 8 Overview of Austroads 2008 Features 77

c The ratio of Elastic moduli of adjacent sub-layers is given by:

d The Elastic modulus of each sub-layer may then be calculated from the Elastic modulus of

the adjacent underlying sub-layer, beginning with the subgrade or upper sub-layer of selected subgrade material as appropriate, the Elastic modulus of which is known.

Selected Subgrade Materials Selected subgrade materials are a special case of unbound granular material.

The total (i.e. combined) thickness of all selected materials is divided into five sub-layers and each assigned an Elastic modulus value according to the following guidelines:

a Divide the total depth of all selected subgrade materials into 5 equi-thick sub-layers.

The vertical Elastic modulus of the top sub-layer of selected subgrade is the minimum of 10 times the design CBR of the selected subgrade material and that determined using:

b The ratio of Elastic moduli of adjacent sub-layers is given by:

c The Elastic modulus of each sub-layer may then be calculated from the Elastic modulus of

the adjacent underlying sub-layer, beginning with the insitu subgrade, the Elastic modulus of which is known.

d If the pavement includes more than one type of selected subgrade material, a check needs to be made that the vertical Elastic modulus calculated for each sub-layer (step a) does not exceed 10 times the design CBR of each selected subgrade material within the sub-layer. If this condition is not met, an alternative trial selected subgrade configuration needs to be selected.

Performance Models

The main change to the Performance Models is the introduction of a Reliability Factor, RF.


The Performance models for Cemented and Asphalt Materials are the same as for Austroads 1992, apart from the introduction of the Reliability Factor.

Cemented Materials

Suggested Reliability Factors (RF) for Cemented Materials Fatigue (Austroads 2004)

Desired Project Reliability

80% 85% 90% 95% 97.5%

Reliability Factor (RF) 4.7 3.3 2.0 1.0 0.5

Asphalt

Suggested Reliability Factors (RF) for Asphalt Fatigue (Austroads 2004)

Desired Project Reliability

80% 85% 90% 95% 97.5%

Reliability Factor (RF) 2.5 2.0 1.5 1.0 0.67

Subgrade

The subgrade Performance Model used in Austroads 2008 is:

Note that a Reliability Factor is not used for the subgrade.

79

How to Use New Austroads 2004/2008 Features The previous Section provided an Overview of the new features in the Austroads 2004/2008 Guide.

This Section shows how to use the new Austroads features in CIRCLY 5.0.

The following notes assume that you are already familiar with using CIRCLY 4.0 or 4.1 in conjunction with the original Guide.

Modelling the Standard Axle The layout of the four wheels used to model the Standard Axle is shown in the earlier section (see "Model of Standard Axle" on page 75).

The design tyre pressure for pavement analysis is taken as 750 kPa (Chapter 7, Austroads 2008).

This Standard Axle is provided in the Load Groups database with the ID given by "ESA75-Full".


How to Use Project Reliability


111

1 Click the Reliability tab to switch to the Reliability form. This will bring up the following form:

22

Chapter 8 How to Use New Austroads 2004/2008 Features 81

2 Click on Use Project Reliability Factors.

333

3 In the Project Reliability list, click the desired Project Reliability.

444

4 This Table shows the Reliability Factor for each Material Type.


Changes to Materials The Materials database in CIRCLY is affected by the Austroads 2004 changes in three main areas:

1 Unbound Granular Materials

2 Subgrade Materials

3 Select Subgrade Materials

To ensure that pavements can be handled using either the Austroads 1992 or Austroads 2004 methods, separate Material Types are used for variants of these materials:

Material Type

Design Method: Austroads 1992 Austroads 2004

Unbound Granular Material Unbound Granular (Austroads 1992 sub-layering)

Unbound Granular (Austroads 2004 sub-layering)

Subgrade Subgrade (Austroads 1992) Subgrade (Austroads 2004)

Select Subgrade Material n/a Subgrade (Selected Material)

n/a = not applicable

Chapter 8 How to Use New Austroads 2004/2008 Features 83

Austroads 2008 Examples Appendix 8.3 (Austroads 2008) outlines three worked examples that apply a mechanistic design procedure for flexible road pavements.

Copies of these examples are provided in the CIRCLY database:

CIRCLY Job Name Pavement Description

Austroads 2004 - Example 1 - Unbound Granular Pavement

Sprayed Seal Surfaced Unbound Granular Pavement

Austroads 2004 - Example 2- Asphalt Pavement with CT Subbase

Asphalt Pavement containing a Cemented Material Subbase (pre-cracking phase)

Austroads 2004 - Example 2- Asphalt Pavement with CT Subbase- Post-Cracked

Asphalt Pavement containing a Cemented Material Subbase (post-cracking phase)

Austroads 2004 - Example 3 - Full Depth Asphalt Pavement

Full Depth Asphalt Pavement

CT = Cement Treated

See Appendix 8.3 (Austroads 2008) for full details of the parameters used.

85

References Austroads (1992). Pavement Design – A Guide to the Structural Design of Road Pavements. Austroads Publication No. AP-17/92. (Austroads: Sydney).

Austroads (2008). Guide to Pavement Technology - Part 2: Pavement Structural Design, Austroads Publication No. AGPT02/08.

Wardle, L.J. (1977). Program CIRCLY User’s Manual. CSIRO Australia. Division of Applied Geomechanics, Geomechanics Computer Program. No. 2.

Wardle, L.J. (2004). Program CIRCLY Theory and Background Manual. Mincad Systems, Australia.

CIRCLY 5.0 User Manual

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