apsds 5.0 user manual

8/9/2019 APSDS 5.0 User Manual

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Printed on 9 November, 2010

APSDS 5.0 User ManualRevision: 5.0.055


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i

Contents

Summary 5

APSDS End User Licence Agreement 7

Introduction 9

Background....................................................................................................................................9 Realistic Modelling with APSDS...................................................................................................11

Material Modelling..............................................................................................................12 Modelling of Multiple Wheels and Axle Groups .................................................................14 Nature of Damage Pulses..................................................................................................15

Overview 17

How APSDS handles Traffic Distributions ...................................................................................18 Full Spectral Analysis..................................................................................................................19 Lateral Aircraft Wander ................................................................................................................20 Elastic Properties .........................................................................................................................21

Cumulative Damage Concept ......................................................................................................21

Material Performance...................................................................................................................22 Traffic and Loading.......................................................................................................................23 How aircraft characteristics are defined.......................................................................................23

Wheel Loadings .................................................................................................................23 Standard Aircraft Library ....................................................................................................24 Defining the gear load characteristics................................................................................24 Coordinate System ............................................................................................................26

Methods for handling Damage Pulses.........................................................................................28 Aircraft Weight Distributions.........................................................................................................30 Automatic Thickness Design........................................................................................................31 Cost Calculation ...........................................................................................................................31 Automatic Parametric Analysis ....................................................................................................32

Overview of User Interface 33

Introduction...................................................................................................................................33 Creating, Opening and Saving Files ............................................................................................34 Creating and Editing Input Data...................................................................................................34

Database Approach ...........................................................................................................35 Running the Analysis and Plotting Results ..................................................................................35

Run Analysis ......................................................................................................................35 Damage Calculation Details...............................................................................................36 Plot Results ........................................................................................................................37

Options.........................................................................................................................................37


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ii Contents

How to Start Using APSDS 39

Opening and Running an Existing Job.........................................................................................40 Global Coordinate System...........................................................................................................45

How to Modify the Databases 49

Introduction...................................................................................................................................49 Units...................................................................................................................................49 Sign Convention.................................................................................................................50 Overview of Database Approach.......................................................................................52

The "Layered System" and "Materials" Databases......................................................................54 Overview of Layered System and Material Properties ......................................................54 Creating a new Layered System........................................................................................56

Defining the Layer properties.............................................................................................57 Duplicating a Layered System ...........................................................................................58 Adding a new Performance Criterion.................................................................................59

Example: Asphalt tensile strain relationship........................................................... 59 Example: Log-linear performance relationship....................................................... 61

Adding a new Elastic Material............................................................................................63 Adding a new Material Type ..............................................................................................65

The "Loads" and "Traffic Spectrum" Databases ..........................................................................66 Introduction ........................................................................................................................66 Aircraft Specifications ........................................................................................................67

Automatic Updates for the Standard Aircraft Library.............................................. 67 Adding Aircraft Specifications................................................................................. 68 Defining Load Locations (i.e. Wheel positions) ...................................................... 71

Traffic Spectrums...............................................................................................................72 Creating a new Traffic Spectrum............................................................................ 72 Defining Gross Weight Distributions....................................................................... 74 Duplicating a Traffic Spectrum ............................................................................... 75

Wander Options.................................................................................................................76 Coordinates for Results................................................................................................................79

How to Use Advanced Features 81

Thickness Design Capability ........................................................................................................81 Cost Calculation ...........................................................................................................................82

Calculation of Total Cost ....................................................................................................82 Material Costs ....................................................................................................................83

Automatic Parametric Analysis ....................................................................................................84 Example—Cost Optimization .......................................................................................................86

Appendices 93

What's New in Version 5.0 ...........................................................................................................95 Overview............................................................................................................................97 More convenient definition of Aircraft Loads......................................................................97 Enhanced Spectral Analysis ..............................................................................................98 Standard Aircraft Library ....................................................................................................98 Wander can vary with Aircraft Model .................................................................................99 Reservoir Method...............................................................................................................99

Material Performance depends on Gear Configuration.....................................................99 Reusable Aircraft Gross Weight Distributions....................................................................99


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Contents iii

Cost Optimization............................................................................................................ 100 New "built-in" Graphics Engine....................................................................................... 102 Duplicating Layered Systems and Traffic Spectrums..................................................... 102

Coordinate System for Loads.................................................................................................... 103 Wander Statistics ...................................................................................................................... 104 Cross-anisotropy and isotropy in pavement materials .............................................................. 106 Calculating Selected Results at User-defined Z-values (depths) ............................................. 108 References................................................................................................................................ 111


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5

Summary

APSDS ( Airport P avement Structural Design System) is for the mechanistic analysis anddesign of flexible pavements subjected to the extremely heavy wheel loads associated withlarge aircraft. It is designed to conveniently model each combination of aircraft model andtakeoff weight and to combine the damage using the Cumulative Damage Factor concept.

APSDS 5.0 is based on CIRCLY 5.0 and HIPAVE 5.0. CIRCLY was first released in 1977. APSDS 3.0 was first released in 1995 and APSDS 4.0 in 2000.

APSDS has unique features to expedite pavement design projects—

a standard aircraft model library - that can be automatically updated from our webserver;

ability to define and store takeoff weight distributions

APSDS takes account of lateral aircraft wander at a more fundamental level than earliermethods. Lateral aircraft wander is the statistical variation of the paths taken by successiveaircraft movements relative to lane centrelines. Increased wander reduces pavementdamage by different amounts that depend upon the pavement thickness.

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 layerthicknesses to minimize construction and maintenance costs.

APSDS 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.


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7

APSDS End User Licence Agreement

APSDS © 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.

This documentation is licensed and sold pursuant to the terms and conditions of the APSDSEnd User Licence Agreement, which appears under the APSDS "About" dialogue box which

provides (in part).

20.Exclusions and Limitation of Liability

20.1 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 anycondition or warranty and that legislation avoids or prohibits provisions in a contractexcluding or modifying the application of or the exercise of or liability under such term, suchterm shall be deemed to be included in this Agreement. However, the liability of Mincad forany breach of such term shall be limited, at the option of Mincad, to any one or more of thefollowing: if the breach related to goods: the replacement of the goods or the supply ofequivalent goods; the repair of such goods; the payment of the cost of replacing the goods orof acquiring equivalent goods; or the payment of the cost of having the goods repaired; and ifthe breach relates to services the supplying of the services again; or the payment of the costof having the services supplied again.

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

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

21. Acknowledgement

21.1Customer acknowledges and agrees that:

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

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


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9

Introduction

Background

APSDS ( Airport P avement Structural Design System) is for the mechanistic analysis anddesign of flexible pavements subjected to the extremely heavy wheel loads associated with

large aircraft. It is designed to conveniently model each combination of aircraft model andtakeoff weight and to combine the damage using the Cumulative Damage Factor concept.

APSDS has unique features to expedite pavement design projects—

a standard aircraft model library - that can be automatically updated from our webserver;

ability to define and store takeoff weight distributions

APSDS takes account of lateral aircraft wander at a more fundamental level than earliermethods. Lateral aircraft wander is the statistical variation of the paths taken by successiveaircraft movements relative to lane centrelines. Increased wander reduces pavementdamage by different amounts that depend upon the pavement thickness. The important

unique feature in APSDS is that the total damage at any point includes contributions from allthe wheels in all their wandering positions. This contrasts with previous methods whichcomputed single maximum values of the damage indicators. It is this feature that eliminatesthe need for the pass-to-coverage concept and allows the designer to specify any degree ofwander. Successive aircraft movements have been observed to be normally distributedabout the pavement centreline. The standard deviation (SD) for a taxiway is typically takenas 773 mm and for a runway as 1546 mm (Ho Sang, 1975). These correspond to wanderwidths of 1778 mm (70 inches) and 3556 mm (140 inches) where wander width is defined asthe zone containing 75% of the aircraft centrelines. For a docking bay, a SD of the order of200 mm may be appropriate.

APSDS has a user-friendly menu-driven interface that runs under Microsoft Windows.

Databases are used for material properties and loadings, thus eliminating the need toconstantly re-key information. Results can be obtained in tabular form or as report-qualityplots on any printer or plotter supported by Microsoft Windows. Results can be easilyexported to other application packages such as spreadsheets for further processing.

As well as the usual isotropic properties, cross-anisotropic material properties can also beconsidered. 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 processesinvolved in their formation. The interfaces between the layers can be either fully continuous(rough) or fully frictionless (smooth), or a combination of both types.

C H A P T E R 1


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10 APSDS 5.0 User Manual

In practice, loads may be applied to soil or rock pavement layers in the form of vertical wheelloads, horizontal wheel loads due to traction and braking, torsional wheel loads due to

cornering, and the "gripping" load developed by pneumatic tyres on pavements. Theprogram allows all of these load types to be simulated for a circular loaded shape. APSDScan also model non-uniform contact stress distributions.

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

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 tothree layers. Combining this with a Cost Analysis feature, allows for fine-tuning of layer

thicknesses to minimize construction and maintenance costs.

This Australian designed system has been developed by the Melbourne company, MINCADSystems. APSDS 5.0 is based on APSDS 4.0, CIRCLY 5.0 and HIPAVE 5.0. CIRCLY hasbeen in regular use in Australia and worldwide for more than two decades, proving its worthin thousands of design applications. CIRCLY was first released in 1977 and handledpolynomial type radial variations in contact stress and multiple loads which provide a muchcloser representation of the actual loading conditions (Wardle 1977). APSDS 3.0 was firstreleased in 1995 and APSDS 4.0 in 2000.

In 2007 Mincad Systems and Pioneer Road Services released the Heavy Duty IndustrialPavement Design Guide (Mincad Systems and Pioneer Road Services, 2007).

The Guide has been developed to assist users of the APSDS and HIPAVE software. Although the main emphasis of the Guide is on container terminal pavements, all of theconcepts are directly applicable to the airport pavement design. The Guide is a collaborativeeffort currently involving Dr. Leigh Wardle of Mincad Systems, Ian Rickards (Pioneer RoadServices Pty Ltd, Melbourne, Australia), John Lancaster (VicRoads, Australia) and Dr. SusanTighe (Dept. Civil Engineering, University of Waterloo, Canada).

The Guide presents the author’s attempts to reflect best practice in the design of newconstruction and rehabilitation of industrial pavements. The Guide steers the designerthrough all necessary design considerations and suggests external sources for researchupdates.

The Guide is a ‘living document’ that will be regularly updated to reflect advances inpavement technology and made freely available via the Internet at no charge.

For further details see http://www.mincad.com.au/hdipdg/.


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Chapter 1 Introduction 11

Realistic Modelling with APSDS

You should be aware of a number of factors, including the accuracy of input materialproperties and the constraints of the layered elastic model, that will influence the reliability ofdesign predictions made using APSDS, or for that matter, any alternative design software.The design values chosen for material properties are likely to be gross simplifications of thecomplex and variable properties of the pavement and subgrade materials.

Although APSDS can produce what appear to be very accurate solutions to problems, thepredictions cannot be any more reliable than indicated by the degree of scatter given by theback-analysis of the full-scale field tests against which APSDS has been 'calibrated'.

Care must be taken to ensure that the sophistication of the analysis method is consistentwith the quality of the input data. Otherwise so many assumptions must be made about theuncertain parameters that the model predictions will be meaningless.

The following Sections summarize the "state of the art" with respect to modelling of heavyaircraft loads and the behaviour of pavement materials. Much of this knowledge has beenderived from airport pavement research.

More detailed advice is given in the Heavy Duty Industrial Pavement Design Guide (MincadSystems and Pioneer Road Services, 2007). For further details seehttp://www.mincad.com.au/hdipdg/.


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Material Modelling

APSDS is an open system that will accommodate material properties and transfer functionsfor any pavement design methodology. But research has shown that highway pavementdesign methods such as Austroads (2008) are not applicable to the higher loadings typicallyapplied to heavy duty pavements used at airports (Wardle et al., 2003).

The process of establishing a performance relationship entails assigning moduli values tounbound basecourse and sub-base materials in accordance with a particular system of sub-layering. Care should be taken to ensure that the sub-layering system used to establish theperformance relationship is also used when analysing or designing pavement structures.Unless this is done, the empirical connection between the test data and the new design isbroken. For example, using the Austroads design method for container handling equipment

where the loads can be 20 tonnes per wheel has been shown to lead to grossly under-designed pavements (Rodway and Wardle, 1998).

Because each failure criterion is derived in the context of its own detailed design procedure,it will only produce sensible pavement designs when used as part of that same procedure. Ifa failure criterion is used in conjunction with a different design procedure, the vital empiricallink between the design and the original performance data used to calibrate the criterion isbroken. This issue is discussed in more detail by Wardle et al. (2003).

The material performance characteristics recommended for use in APSDS are based oncalibrations developed from airport pavement research.

The subgrade strains are converted to damage using a performance relationship of the form:


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where N is the predicted life (repetitions of ε)

k is a material constant

b is the damage exponent of the material

ε is the load-induced strain (unitless strain)

The preferred subgrade performance relationship for heavy duty airport pavements wasdeveloped by Wardle and Rodway (2010). This performance relationship was established bycalibrating pavement designs using APSDS against designs based on the US Army Corps ofEngineers CBR method (Method S77-1, Pereira 1977). The methodology also incorporates

recent ICAO recommendations that impact designs for new generation large aircraftincluding the Boeing 777 and Airbus A380-800.

The relationship was developed using a range of different aircraft with masses varying from74 tonnes to 560 tonnes (i.e. Airbus A380-800) and subgrade strengths varying from CBR =3% to CBR = 15%.

The resulting performance parameters k and b depend on the subgrade modulus (E) and onthe number of wheels on each gear.

This calibration gives more reliable predictions for designs involving new generation largeaircraft including the Boeing 777 and Airbus A380-800.

For full details see Wardle and Rodway (2010).

More complex performance relationships can be accommodated by the program if required,for example the log-linear relationship shown below is used by European designers forcement-treated materials:


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Nature of Damage Pulses

The WES tests were performed on relatively thin pavements. In most of the test sections theelastic models predict a distinct strain pulse at subgrade level for each axle of a two-axledgear. For deep pavements (say 1.5 m or more) the models predict a single combined pulseresulting from the entire gear. In other words, a two-axled gear produces two strain pulsesper pass for shallow subgrades and one strain pulse, of significantly different shape, for deepsubgrades. APSDS uses strain repetitions as the basis for damage predictions, not passesor coverages. Pulse counts and pulse shapes both change with pavement thickness. Thereis significant uncertainty in the design of thick pavements because data must be extrapolatedfrom thinner test pavements which have narrower pulses than those expected for the deeper

subgrades. There is still no experimental data to show to what extent pavement damagedepends on the transverse and longitudinal widths of the load pulse.

The pattern of strains at subgrade level experienced during the passage of a multiple axlegear primarily depends on the pavement depth. The two extremes are:

multiple distinct short pulses resulting from each axle, for shallow depths

a single longer pulse that reflects the overall loading on the gear, for large depths

The ‘reservoir’ method, as used in bridge design to handle complex loadings, is used by APSDS 5.0 to ensure a smooth transition between the two extremes.


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17

Overview

APSDS has many features to facilitate pavement analysis and design.

C H A P T E R 2


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How APSDS handles TrafficDistributions

APSDS lets you define your aircraft loadings and traffic in detail. You define the anticipatedrepetitions over the design period for each aircraft model. You also define a gross weightdistribution for each aircraft model.

The following example illustrates the concepts. Here there are two aircraft models, A and B.Each aircraft model is assigned a gross weight distribution.

Aircraft Model A Aircraft Model A - Gross Weight Distribution

Aircraft Model B Aircraft Model B - Gross Weight Distribution


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Chapter 2 Overview 19

Full Spectral Analysis

APSDS does a full spectral analysis of pavement damage by using the cumulative damageconcept to sum the damage from multiple aircraft models and gross weight cases for one setof layered system material properties. The figure below is a sample plot showing thevariation of the damage factor across the pavement:


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APSDS can also generate graphs that show the variation of the damage factor with eachaircraft model / gross weight combination, as shown below:

Note that there is a data point for each combination of aircraft model and gross weight.

Lateral Aircraft Wander

The analysis optionally includes the effect of the lateral distribution of successive aircraftpasses along the pavement. You nominate a standard deviation of aircraft wander about thecentreline that is appropriate to the particular aircraft model and pavement. Thesophisticated method of handling wander, bypasses the simplified concepts of “coverage”and “pass-to-coverage ratio” (PCR) that have been traditionally used for aircraft pavementdesign.

Some background material to assist with the selection of the standard deviation of wander isgiven in Wander Statistics (on page 104).


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Elastic Properties

The elastic material in each layer of the pavement structure is assumed to be homogeneousand of cross-anisotropic or isotropic symmetry.

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

For further background on the elastic properties see Cross-anisotropy and isotropy in pavement materials (on page 106).

Cumulative Damage Concept

The system accumulates the contribution from each loading in the traffic spectrum at eachanalysis point by using Miner's hypothesis.

The damage factor for any given loading is defined as the number of repetitions (n) of agiven response parameter divided by the ‘allowable’ repetitions (N) of the responseparameter that would cause failure:

The Cumulative Damage Factor (CDF) for the parameter is given by summing the damagefactors over all the loadings in the traffic spectrum:

where:

k is summed over M aircraft models

Nk is the number of different gross weight for aircraft model no. k


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The system is presumed to have reached its design life when the cumulative damagereaches 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 cumulativedamage is greater than 1.0 the system is predicted to ‘fail’ before all of the design traffic hasbeen applied.

The procedure takes account of—

the design repetitions of each aircraft model/takeoff weight combination; and

the material performance properties used in the design model.

This approach allows analyses to be conducted by directly using a mix of aircraft models. Itis not necessary to approximate passes of different aircraft or axles to passes of an‘equivalent’ standard load or "design aircraft".

Material Performance

Generally most performance models may be represented graphically by a plot of tolerablestrain versus load repetitions (generally by a straight line of 'best fit' on a log-log plot).Usually the models are represented in the form:

where N is the predicted life (repetitions)



ε is the induced strain (dimensionless strain)

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

APSDS 5.0 can use performance parameters that depend on the number of wheels on eachgear.

This approach gives more reliable predictions for designs involving new generation largeaircraft including the Boeing 777 and Airbus A380-800.

For full details see Wardle and Rodway (2010).

APSDS can also handle models of the form:


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This log-linear relationship is used by European designers for cement-treated materials.

APSDS is supplied with a comprehensive range of published performance models. You canuse your own performance equations by specifying values for ‘k’ and ‘b’ and the particularcomponent 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 aircraft model and theaircraft weight mix — that is the repetitions for each aircraft weight that is modelled.

How aircraft characteristics aredefined

Wheel Loadings

Normally a given aircraft type is represented by the main gear as the damage due to thesmaller loadings on the nose gear can be ignored. (Nose gears typically take 5% of theaircraft weight).

The aircraft loading is defined in terms of the Aircraft Gross Weight, the proportion of GrossWeight on a single gear, the number of wheels on a main gear and the tyre contact pressure(generally assumed to be the tyre inflation pressure). The detailed contact radius for thewheels is calculated from the other parameters.


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Standard Aircraft Library

In designing APSDS we have introduced the concept of a Standard Aircraft Library. Themaster version is maintained on our webserver. You can obtain updates (new Aircraft)automatically by clicking the "Import" icon on the toolbar.

In designing APSDS account has been taken of a number of important issues relating to thedefinition of Aircraft loading characteristics. Most importantly, a critical issue is choosing theoptimum number of wheels to use in the model - a benefit of of the Standard Aircraft Libraryis that it takes the worry out of selecting which wheels to model. You will also save time bynot having to seek aircraft specifications from manufacturers or airport operators. Of course,you can define your own aircraft models directly in APSDS.

APSDS uses the following aircraft data—

wheel locations and numbers; and

axle mass characteristics.

Defining the gear load characteristics

The aircraft are assumed to have equal loads on each axle of the main gear. In this case theaircraft loading characteristics are specified in terms of the gross weight of the aircraft, thenumber of axles, the total number of wheels on the aircraft and the tyre pressure.

The screendump below shows some sample data:


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If you now click on the Load Components and Locations tab, you will see more details for thecurrently selected Airdraft Model :


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Coordinate System

The Figure below shows the coordinate system that is used.

This global coordinate system is used to define load locations, the layered system geometryand the points at which results are required. The global coordinate system is also used todescribe the resultant displacements and stress and strain tensors.

The X axis is taken as the direction transverse to the runway or taxiway axis. To ensureconsistency between results for different aircraft types it is recommended that X=0corresponds to the runway or taxiway centreline. The Y axis is parallel to the centreline (andthe direction of travel of the aircraft!).

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


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Z

Direction of Travel

Centreline of Aircraft

O

X

Y


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Methods for handling DamagePulses

The problems associated with damage pulses were introduced in the Introduction underNature of damage pulses.

The damage that a given point in the pavement will experience during the passage of amultiple axle primarily depends on the depth below surface. The two extremes of behaviourare—

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.

For shallow pavement depths compared to axle spacing one ‘pulse per axle’ is selected. APSDS then computes the damage beneath that axle due to the strain contributions for allwheels of the aircraft, then multiplies the computed damage by the number of axle rows (i.e.the number of axles seen from one side of the aircraft).

APSDS relies on you specifying one set of axles at Y=0 [see Defining Load Locations (i.e.Wheel positions) (on page 71)].

However, for large depths relative to the axle spacing the maximum strain will generallyoccur under the centroid of the gear. In this case you specify 'combined pulse for gear' and

APSDS will automatically shift the load coordinates so that the origin is at the centroid of thegear as shown on Automatic shift of Y-coordinates for 'combined pulse for gear' case (on page Error! Bookmark not defined.). APSDS then computes the damage pulsebeneath the centroid of the gear due to the strain contributions for all wheels of the aircraft,and ignores the number of axles in the group.


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The ‘reservoir’ method, as used in bridge design to handle complex loadings, is used by APSDS 5.0 to ensure a smooth transition between the two extremes.

APSDS automatically shifts the position of the load coordinates if you specify 'combinedpulse for gear'.

For compatibility with legacy projects, you can still choose the method to be used to calculatethe damage - either multiple distinct pulses for each axle, for shallow depths; or a singlecombined pulse for large depths.


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Aircraft Weight Distributions APSDS lets you specify detailed aircraft gross weight distributions. For example, the Figurebelow shows two Gross Weight conditions for a single aircraft model.


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There are a different number of movements for each gross weight.

Commonly only two or three masses are modelled, generally expressed as "% of aircraftoperating at a % of MTOW (Maximum Take-Off Weight)". For example, 20% of aircraftoperate at 70% of MTOW. In practice, estimates of this nature are provided by airports. Although airlines are often required to record this data, it is rare for this information to beprovided.

APSDS lets you use a single % Gross Weight "mix" for all aircraft models, or if more detailedinformation is available, the mix can be different for each aircraft model.

Automatic Thickness Design

You can automatically determine the optimum thickness of a given layer. For further detailssee Thickness Design Capability (on page 81).

Cost Calculation

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


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Automatic Parametric Analysis Automatic Parametric Analysis lets you automatically loop through a range of thicknesses forone or two nominated layers. For example, you can have Layer 3 vary from 800 mm to1000 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. For further details see AutomaticParametric Analysis.

Automatically generated plot: Total Cost vs. Layer 3 Thickness


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33

Overview of User Interface

Introduction

APSDS has a standard format Microsoft Windows menu, but most commands can beaccessed directly from the toolbar as shown below:

C H A P T E R 3


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Creating, Opening and Saving FilesYou 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.sds APSDS data file— this is used to save the details of your job.

All the other files are generated automatically by the system:

Jobname.cli APSDS32 input data file

Jobname.clo APSDS32 'printable' results file

Jobname.prn APSDS32 raw results file(i.e., strains, etc.)

Jobname.dam APSDS32 cumulative damage results file (for plotting)

Jobname.dmx APSDS32 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 createsa new job.

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

Updates the current job file.

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

Creating and Editing Input Data

The following seven icons allow you to create and modify your input data. Each iconcorresponds to one of the main groups of data necessary to fully define a Job.


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Chapter 3 Overview of User Interface 35

Database Approach

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

The relational database approach gives maximum flexibility in data preparation. Forexample, 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 andsubsequently all Jobs that use those layered systems will automatically access the modified

material properties.

Running the Analysis and PlottingResults

Run Analysis

The button invokes the analysis. This invokes the analysis. During a long analysis youcan switch to another application (APSDS will continue to run at a lower priority usingMicrosoft Windows multi-tasking).

When the analysis is complete you will see a screen with the damage calculation details.

APSDS offers a number of calculation options. Normally, you will calculate the damagefactors (CDF) for your pavement. Alternatively, you can calculate results for any givendisplacement, stress or strain component at selected Z-values (depths below the pavementsurface) (see Calculate Selected Results at User-defined Z-Values (see "CalculatingSelected Results at User-defined Z-values (depths)" on page 108)).


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Damage Calculation Details

This screen will be displayed when the Analysis is complete. You can navigate to this screen

without running an analysis by clicking on the button.

1 Two alternative calculation options are available: Calculate damage factors (CDF); or

Calculate selected results at user-defined Z-values (see Calculate Selected Results atUser-defined Z-Values (see "Calculating Selected Results at User-defined Z-values(depths)" on page 108)).

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

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

3 This table is a summary of the properties for those layers that have a performancecriterion. Typically, between one layer (the subgrade) and three layers (asphalt surfacing,cement-stabilised layer and subgrade) will have performance criteria associated with them.


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Chapter 3 Overview of User Interface 37

Plot Results

The icon will generate a graph of the results. Usually, this command will produce agraph of the damage contribution from each aircraft type and the overall total (damagecontribution from all the traffic). This graph option shows the variation of the CDF as afunction of X, the distance from the centreline of the pavement (i.e. X=0 corresponds thecentrelines of the aircraft). 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 surfaceof the pavement) and results can be plotted for a selected displacement, stress or straincomponent (see Calculate Selected Results at User-defined Z-Values (see "CalculatingSelected Results at User-defined Z-values (depths)" on page 108)).

Options

The Options screen allows specification of the following folder:

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


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39

How to Start Using APSDS

The easiest way of trying APSDS out is to open one of the sample jobs, run the analysis andthen graph the results.

C H A P T E R 4


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Opening and Running an ExistingJob

In the interests of providing instant hands-on experience, for this example you simply openan existing job, run the analsis and inspect the results.

1 Open the Job

Click on the button.

Select the job "Example - Large Indian Airport".

2 Run the Analysis

Click on the button. This invokes the analysis.

When the analysis starts you will see a blue "progress bar" at the bottom left corner of thescreen.

When the analysis is complete the results for the damage factor (CDF) will be transferred to

the top table on the screen, as shown below.


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Chapter 4 How to Start Using APSDS 41

3. Plot the Results

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

This graph option shows the variation of the CDF for the subgrade as a function of X, thedistance from the centreline of the pavement (i.e. X=0 corresponds the centrelines of theaircraft). Note that the results for the different aircraft Gross Weights have been aggregated.

Optionally you can graph the maximum CDF as a function of Gross Weight. Click on the PlotType combo box then click on CDF vs. Gross Weight .


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This graph option shows the maximum CDF for each Aircraft Model and Gross Weight:


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As can be seen from the graph there is one result point for each combination of AircraftModel and Gross Weight.

The two graphs give results for the subgrade layer. If your layered system has other layersthat have a performance relationship you can switch to the CDF for the other layers byclicking on the combo box in the top left-hand corner.

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 asMicrosoft 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 as shown below:


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


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Global Coordinate System

A global coordinate system is used to define load locations, the layered system geometryand the points below the pavement surface at which results are required. The globalcoordinate system is also used to describe the resultant displacements and stress and straintensors.

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

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

An array of equally spaced points along a line parallel to the X-axis;


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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


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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


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49

How to Modify the Databases

Introduction

Units

In order for APSDS to deliver coherent results, all data must use this system of units:

Quantity Units

Length,Displacement

mm

Elastic modulus,Pressure

MPa

Weight tonne

Force N

Moment N.mm

Strain mm/mm

C H A P T E R 5


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Sign Convention

Compressive direct stresses and strains are considered to be positive. Positive shearstresses are defined on the basis that both the stress and strain tensors obey the right handrule. Displacements in negative coordinate directions are considered to be positive. Hencea load causing a positive stress acts in the positive coordinate direction. The signconventions used in the rectangular coordinate system and cylindrical local coordinatesystem are illustrated below.

Figure 4: Sign Convention


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Chapter 5 How to Modify the Databases 51


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Overview of Database Approach

The relational database approach is designed to eliminate re-entry of data for design loadsand material properties. For example, the data for a commonly used material need only beentered into the system once. If this data is subsequently modified, all Layered Systems thatuse that material and subsequently all Jobs that use those Layered Systems willautomatically access the modified material properties.

The Figure below illustrates the relational database concept for the elastic materialproperties. Here, each of the components that make up a Layered System is linked toentries in the Elastic Material Properties database via an ID (index) field of up to 20characters.

Figure 5: Relationships between elements in Layered System databases

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

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

Elastic Materials Properties data must be entered before the Layered SystemComponents data;

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

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

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

2 Create a new entry in the Layered Systems database;


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

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


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The "Layered System" and"Materials" Databases

Overview of Layered System and Material Properties

APSDS models pavements as a system of layers, each with differing elastic properties. Thelayered system consists of one or more layers. The layer interface planes are horizontal andeach layer is assumed to be of infinite extent in all horizontal directions. The bottom layermay 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 eitherfully continuous (i.e., rough) or fully frictionless (i.e., smooth). Interfaces between the layerscan be either fully continuous (rough) or fully frictionless (smooth), or a combination of bothtypes. From a practical standpoint the response of the actual pavement interfaces will besomewhere between these theoretical limits. For design of new pavements the interfaceswould be assumed to be fully continuous (rough).


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Layer No. 2

Rough rigidbase

Smooth rigidbase

Semi-infinitebase

Layer No. NL

Layer No. 1

∞

Layer No. 2

Rough rigidbase

Smooth rigidbase

Semi-infinitebase

Layer No. NL

Layer No. 1

∞


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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 inyour ID (index) field of up to 20 characters and a descriptive title (up to 72 characters). Forthis example you can type in 'MyLayers' as the ID and 'Example of creating a new LayeredSystem' as the Title. Click the OK button.

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


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Defining the Layer properties

You add the layers working from the top of your pavement system, i.e., starting with typicallyasphalt 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 appropriateline then click the OK button.

A list of available materials will now appear. Select the required material by clicking on theappropriate 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 theThickness column. Enter the layer thickness. You repeat this process to add as many layersas you require. The subgrade will extend to an infinite depth if you enter the thicknessas 0.0 .

As explained in Overview of Layered System and Material Properties, interfaces between thelayers can be either fully continuous (rough) or fully frictionless (smooth), or a combination ofboth types. You can specify any interfaces as fully frictionless. The fully continuous case isalways assumed for pavement design.

1


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1 By default, all interfaces are assumed to be rough. You can change the condition forthe interface at the bottom of a given layer by clicking in the 'Interface Type' cell. You canthen click on the down arrow at the right of the cell to select a 'Smooth' interface. Note thatfor 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. TheDuplicate function lets you duplicate an existing Layered System. Then you can change thesettings 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:


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

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

Adding a new Performance Criterion

APSDS usually represents performance relationships in the form:

(1)

where N is the predicted life (repetitions)



ε is the induced strain (dimensionless strain)

APSDS can also handle log-linear models of the form:

(2)

Equation (1) is called a Standard Damage Relationship Type and Equation (2) is called aLog-Linear Damage Relationship Type.

Before you add a new Performance Criterion you need to choose the appropriate MaterialType. For each Material Type, all Performance Criteria use the same Damage RelationshipType.

Example: Asphalt tensile strain relationship

For this example we consider the Shell asphalt fatigue criterion:

where 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.


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For this example, assume VB = 12.9 and Smix = 1600 MPa, so that the above equationsimplifies 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 (asshown on the first screenshot in Adding a new Elastic Material) to select from the availablematerial 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 theTitle (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.

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

The cursor will now be in the component field.

Here you specify the particular displacement, stress or strain component to be used. You

can select the component from a dropdown list by clicking on the button. If there aremore entries than will fit in the listbox, there will be a slider bar on the right hand side. Youcan move down the list by clicking on the down arrow or by dragging the slider down. Forthis example select the ‘Max. Horizontal Tensile Strain’ (maximum horizontal tensile strain).

The Location field defines the location (relative to a layer of this material) at which the

criterion is to be applied. Click on the button to choose between ‘Top’ and ‘Bottom’ . Forthis example Location should be 'Bottom' .

The entries for the remaining two parameters define the fatigue relationship N = [5889 / µε]5.


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Note carefully that strains in APSDS must be specified in dimensionless units (i.e.,length/length, mm/mm). As APSDS assumes that the fatigue relationship is of the form N =[k / ε]b , the parameter µ (micro) must be replaced by 10-6 giving:

N = [k / ε]b

So Constant (k) will be 0.005889 and Exponent (b) will be 5.0.

The new record should be identical to the bottom row in the figure below:

Example: Log-linear performance relationship


Click on the Performance tab.

You now choose the material type to be used. Click on the material type combo box (asshown below) to select Cemented (Log-Linear) from the available material types.

Click on the New button. Now type in your ID (index) field of up to 20 characters and the Title(up to 72 characters). For this example type in 'CTB15000' for the ID. Type in ' CTB,E=15000MPa' for the Title. Click the OK button.

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


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For this example assume that equation (2) is used with:

k = 10b = 80000

The relevant strain component that is to be used is the maximum horizontal tensile strain at thebase (bottom) of the layer.

Note: Equation (2) expresses the strain component as a unitless (i.e. length/length, mm/mm)quantity. If you are converting from an expression that uses microstrain, b must be adjustedappropriately.

Move to the Component field by clicking on it or using the tab key. The screen should nowlook like this (the black highlight is on the new entry):

Here you specify the particular strain or stress component to be used (in this example it willbe the maximum horizontal tensile strain. You select the component from the drop-down list by

clicking on the button. If there are more entries than will fit in the list box there will be aslider bar on the right hand side. You can move down the list by clicking on the down arrowor by dragging the slider down.

Select the entry Max. Horizontal Tensile Strain.

The location field defines the location (relative to a layer of this material) at which therelationship is to be applied.

Click on the button to choose Bottom.

Now enter the values for k (= 10) and b (= 80000).

The screen below shows the completed entries:


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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 asshown below to select from the available material types. Click on 'Asphalt' for the MaterialType.

Click on the New button. A dialog box will appear, as shown below. You should now type inyour ID (index) field of up to 20 characters. As you can see from the example below, the ID is used to sort the data. For this example, you can type in ' Asph1600' . Type in 'Asphalt- 1600MPa, Vb=12.9%' for the Title. Click the OK button.


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You will now be given an opportunity to select a Performance Criterion. To select aPerformance 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. Type in the modulus and Poisson's ratio as follows:

E = 1600

ν = 0.4

The new record should be as shown below:


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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 20 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 appropriatesub-layering scheme. Click on the OK button.


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A new record will be added to the table.

The other parameters that can be defined are:

Damage Relationship Type: this can be set to "Standard" or "Log-Linear", as defined in Addinga new Performance Criterion (on page 59).

Depends on Number of Wheels on Gear: if this is set to "Yes", it is assumed that the PerformanceRelationships for this material type will depend on the number of wheels on each landinggear.

The new record will look something like the last record shown below:

The "Loads" and "Traffic Spectrum"Databases

Introduction

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

Traffic Spectrum;

Traffic Spectrum Components;

Load Groups;

Load Group Components;

Load Locations;

Gross Weight Distributions;

Gross Weight Distribution Components.

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


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Aircraft Specifications

The APSDS aircraft library consists of so-called "Standard" aircraft specifications that areprovided by Mincad Systems and "Custom" aircraft that you can define.

You can browse the aircraft specifications as follows.


Click on the Aircraft Models tab.

You can browse by clicking on the Type and Manufacturer combo boxes.

To see the specifications for any listed aircraft click on that row, then click on the LoadComponents and Locations tab.

Automatic Updates for the Standard Aircraft Library

Updates for the Standard Aircraft Library can be automatically imported from the MincadSystems webserver.

To do this, click on the icon. You will then see a status screen like the one below.

The status screen shows the number of Aircraft records that have been imported/updated.


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Adding Aircraft Specifications

Here are details on how you define your own aircraft models directly:


Make sure you make the correct choices for the Type and Manufacturer combo boxes, asshown below:

Contact Mincad Systems for a Library Update if the combination of Type and Manufacturer thatyou want to use is not available.

Click on the New button. A dialog box will appear as shown below. You should now type inyour ID (index) field of up to 20 characters and a descriptive title (up to 72 characters).


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For this example you can type in 'B787-8 example' as the ID and 'B787-8 example' as theTitle. Click the OK button.

Now type 'B787-8 example' as the Plot Label and 228.40 as the Gross Weight :


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Now click on the Load Components and Locations tab. This will bring up a form that lets youspecify the axle load characteristics and wheel positions.

Aircraft are assumed to have equal loads on each axle on the main gears. In this case theloading characteristics are specified in terms of the proportion of gross weight on a singlegear, the number of axle rows (i.e. the number of axles seen from one side of the aircraft),the total number of wheels on the gear and the tyre pressure.

For this example, assume the following values:

Number of Axle Rows 2

Total Number of Wheels on Gear 4

Tyre Pressure 1.52 MPa

Proportion of Gross Weight on a Single Gear 0.475

After you enter these axle load characteristics the screen will look like this:

You can now add the Wheel Locations.


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Defining Load Locations (i.e. Wheel positions)

Example wheel layout(Boeing 787-8)

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

Click on the Load Components and Locations tab. Check the descriptive title above the table tomake sure that you are referring to the correct aircraft model. If it is not the one you have

just defined, click on the Load Groups tab, click on the appropriate record within the AircraftModels table and click on Load Components and Locations tab again.

Only one main gear (Gear 1) is included in the model, as discussed in Interaction effects ofmultiple gears.

Click New for each wheel and enter the gear number (1), and the X and Y coordinates ofeach wheel. See the note Important Note about Axle Locations below for special informationabout defining axle locations.

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


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Theta is only used to define the force or moment direction for non-standard loads such asbraking loads. Theta corresponds to θLOAD see Coordinate System for Loads.

Traffic Spectrums

APSDS is designed to let you conveniently specify a Traffic Spectrum in terms of a mix ofdifferent aircraft models. For each aircraft in the spectrum you specify the number ofmovements and the gross weight distribution. For each load case the wheel loads areautomatically calculated from the aircraft characteristics and the gross weight.

For an overview of the concepts see How APSDS handles Traffic Distributions (on page18).

Creating a new Traffic Spectrum

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

Click on the Spectrum tab.

Click on the New button. A dialog box will appear as shown below. You should now type inyour ID (index) field of up to 20 characters and a descriptive title (up to 72 characters). Forthis example you can type in 'TrafficTry' as the ID and 'Example of creating a new TrafficSpectrum' as the Title. Click the OK button.


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The Spectrum Components form will now appear.

Now define your Spectrum Components:

Click New for each aircraft model you wish to include. This will activate a pop-up list ofpossible choices:

You can browse by clicking on the Type and Manufacturer combo boxes.

You can move the highlight to the aircraft model that you wish to use by positioning themouse pointer on it and clicking once. If there are more entries than will fit in the listbox therewill 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 aircraft model by double clicking on it.

For this example, choose the Boeing 737-600 Max 63t . A new record will be added at thebottom of the table and the cursor will be positioned in the Movements column.

Enter the number of movements (or passages) over the desired design life. For thisexample, enter 100,000 movements.

The Graph Label is an optional string of up to 20 characters that is appended to the AircraftModel Plot Label used for the Legend when plotting the results. This is useful when youneed to have more than one Spectrum Component that uses the same Aircraft Model, forexample your spectrum may include the same model twice, each with a different Gross

Weight.


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

Click on the Spectrum tab and choose the Traffic Spectrum.

Now click the Spectrum Components tab.

As mentioned earlier, APSDS lets you use a single Gross Weight "mix" for all aircraft models,or if more detailed information is available, the mix can be different for each aircraft model.

If you click the Distribution Type combo you will see two options:

% Max. Gross Weight - same for all Spectrum Components

% Max. Gross Weight - different for each Spectrum Component

Defining Gross Weight Distributions

For this example, use the following Gross Weight distribution:

% Maximum Gross Weight

Count

80 50

100 50

For each row in the table, click the New button and enter the % Maximum Gross Weight andCount . Enter the % Maximum Gross Weight in the form of a number less than 1, i.e. 50% isentered as 0.5.

After you enter the last row of data, the screen should look like this:


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As shown above, values in some of the columns are grey - these values are calculated fromother values. The values in the Gross Weight column are calculated from the MaximumGross Weight cell for the currently selected Aircraft Model given in the Spectrum Component table above. Values in the columns that are labelled Normalized Movements and ActualMovements are calculated from the values in the Count column. The NormalizedMovements are given by normalizing the values of Count - so that the sum of the NormalizedMovements values is 1.0. The Actual Movements values are scaled so that the totalmatches the total number of movements (1.25E+06 in this example) defined for the currentSpectrum Component .

The absolute magnitude of the Count values is not important, as they are normalized (i.e.scaled so that they add up to 1.0) when you run a APSDS analysis. This gives you a lot of

flexibility in how you define your Count values - for example they could be based on historicaldata or could be simply actual movements.

The calculated columns are not updated while you type the data on a particular row - but areupdated when you press the Enter key when in the Count cell.

Duplicating a Traffic Spectrum

Sometimes you may want to create a Traffic Spectrum that is similar to an existing one. TheDuplicate function lets you duplicate an existing Traffic Spectrum. Then you can change thesettings that need to be different.

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


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Three alternative Wander options are available: No Wander for any Aircraft Model in the Traffic Spectrum;

Same Wander for All Aircraft Models in the Traffic Spectrum;

Wander varies with Aircraft Model.

If the Wander varies with the Aircraft Model, you specify the Wander in the SpectrumComponents table (accessed by clicking on the Spectrum Components tab):

The wander is assumed to follow the bell-shaped frequency distribution given by the Normal(or Gaussian) distribution. The degree of wander is given by the Standard Deviation. Someadditional parameters define the numerical approximation used to model the effects ofWander. Normally the default values of these can be used.


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The parameter XWDEL is used to subdivide the wander distribution. For acceptable accuracyXWDEL must be no greater than 100 mm. The parameter XWMAX sets the limiting value used to

approximate the Normal distribution. For acceptable numerical accuracy XWMAX needs to be2.7 times the maximum Standard Deviation of wander, or greater.

0

500

1000

1500

2000

2500

3000

3500

4000

4500

- 3 0 0

0

- 2 8 0

0

- 2 6 0

0

- 2 4 0

0

- 2 2 0

0

- 2 0 0

0

- 1 8 0

0

- 1 6 0

0

- 1 4 0

0

- 1 2 0

0

- 1 0 0

0 - 8

0 0 - 6

0 0 - 4

0 0 - 2

0 0 0 2 0 0

4 0 0

6 0 0

8 0 0

1 0 0 0

1 2 0 0

1 4 0 0

1 6 0 0

1 8 0 0

2 0 0 0

2 2 0 0

2 4 0 0

2 6 0 0

2 8 0 0

3 0 0 0

Lateral Position (mm)

M o v e m e n t s i n S l o t

Total Movements = 100,000

Standard Deviation = 1000 mm

XWMAX(=3000 mm)

XWDEL (=100 mm)

0

500

1000

1500

2000

2500

3000

3500

4000

4500

- 3 0 0

0

- 2 8 0

0

- 2 6 0

0

- 2 4 0

0

- 2 2 0

0

- 2 0 0

0

- 1 8 0

0

- 1 6 0

0

- 1 4 0

0

- 1 2 0

0

- 1 0 0

0 - 8

0 0 - 6

0 0 - 4

0 0 - 2

0 0 0 2 0 0

4 0 0

6 0 0

8 0 0

1 0 0 0

1 2 0 0

1 4 0 0

1 6 0 0

1 8 0 0

2 0 0 0

2 2 0 0

2 4 0 0

2 6 0 0

2 8 0 0

3 0 0 0

Lateral Position (mm)

M o v e m e n t s i n S l o t

Total Movements = 100,000

Standard Deviation = 1000 mm

XWMAX(=3000 mm)

XWDEL (=100 mm)


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Coordinates for Results


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

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

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.

The section labelled Assumed number of damage pulses per movement lets you define how APSDS will calculate the damage from gears with multiple axles (see Methods for handlingDamage Pulses (on page 28)). The recommended choice is to use the Reservoir Method.The other two options are provided for compatibility with legacy projects: either multipledistinct pulses for each axle, for shallow depths; or a single combined pulse for large depths.


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81

How to Use Advanced Features

Thickness Design Capability

You can automatically determine the optimum thickness of a given layer. This procedure isvery fast, typically taking 4-5 times the usual analysis time.

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 theappropriate layer and clicking the mouse button once. The layer selected will be highlightedin 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 maximumdamage 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 whencalculating the maximum damage factor.

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

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

C H A P T E R 6


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

Cost Calculation

Calculation of Total Cost

APSDS can automatically calculate Total Cost for a pavement from the unit costs ofmaterials in each layer.

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

1 Click on the Calculate Cost checkbox


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Chapter 6 How to Use Advanced Features 83

Material Costs

The unit costs for the layers can be specified using a combination of both a volumetric (orweight) component and an areal component. The areal component lets you take account ofcosts 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 relationshipbetween total layer cost and thickness has a non-zero component for zero thickness.

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

Total Cost (layer no. i) ($/m2) = Unit Volumetric Cost (layer no. i) ($/m

3) 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).


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Automatic Parametric Analysis Automatic Parametric Analysis lets you automatically loop through a range of thicknesses forone or two nominated layers. For example, you can have Layer 2 vary from 100 mm to200 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.

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

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

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2

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1 This combo box lets you specify the number of Independent Variables (i.e. the numberof 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.


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Chapter 6 How to Use Advanced Features 85

3 This lets you choose which layer (thickness) is to be used as the first Indepe

apsds 5.0 user manual

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