APSDS_5.0_User_Manual.pdf

Revision: 5.0.055 9 November, 2010

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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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Contents

How to Start Using APSDS

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

How to Modify the Databases

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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

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Thickness Design Capability ........................................................................................................81 Cost Calculation ...........................................................................................................................82 Calculation of Total Cost....................................................................................................82 Material Costs ....................................................................................................................83 Automatic Parametric Analysis ....................................................................................................84 Example—Cost Optimization .......................................................................................................86

Appendices

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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

Contents

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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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Summary APSDS (Airport Pavement Structural Design System) is for the mechanistic analysis and design 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 and takeoff 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— ƒ

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

ƒ

ability to define and store takeoff weight distributions

APSDS takes account of lateral aircraft wander at a more fundamental level than earlier methods. Lateral aircraft wander is the statistical variation of the paths taken by successive aircraft movements relative to lane centrelines. Increased wander reduces pavement damage 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 layer thicknesses to minimize construction and maintenance costs. APSDS has many other powerful features, including selection of– ƒ

cross-anisotropic and isotropic material properties;

ƒ

fully continuous (rough) or fully frictionless (smooth) layer interfaces;

ƒ

a comprehensive range of load types, including vertical, horizontal, torsional, etc.;

ƒ

non-uniform surface contact stress distributions; and

ƒ

automatic sub-layering of unbound granular materials.

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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 APSDS End 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 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 for any breach of such term shall be limited, at the option of Mincad, 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. 20.2 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 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. Customer warrants that it has not relied on any representation made by Mincad or upon any descriptions or illustrations or specifications contained in any document including any catalogues 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 a substitute in any way for professional advice; (b) APSDS is supplied with certain operating instructions and a failure to follow these instructions carefully could result in erroneous data being produced by APSDS;

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APSDS 5.0 User Manual

(c) Whilst APSDS may be used by persons without a detailed knowledge of computers, APSDS is designed to be used by persons who have a detailed knowledge of, without limitation: (i) the applicable Pavement engineering standards; and (ii) All appropriate legislation and other relevant instruments, including, without limitation the relevant industry recognised engineering design guides; (d) They shall manually check all results provided by APSDS for any anomalies; and (e) They shall obtain professional advice in relation to all results provided by APSDS. 21.2 APSDS is licensed on the basis set out in this Agreement on the understanding that to the extent permitted by law Mincad 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 APSDS. 22. Indemnity Customer warrants that any materials supplied to Mincad 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, its officers, employees and agents, against any loss, costs, expenses, demands, taxes or liability whether direct or indirect arising out of: (a) use of APSDS; (b) a breach of this agreement by Customer; or (c) any wilful, unlawful or negligent act or omission of Customer.

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CHAPTER 1

Introduction Background APSDS (Airport Pavement Structural Design System) is for the mechanistic analysis and design 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 and takeoff weight and to combine the damage using the Cumulative Damage Factor concept. APSDS has unique features to expedite pavement design projects— ƒ

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

ƒ

ability to define and store takeoff weight distributions

APSDS takes account of lateral aircraft wander at a more fundamental level than earlier methods. Lateral aircraft wander is the statistical variation of the paths taken by successive aircraft movements relative to lane centrelines. Increased wander reduces pavement damage 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 all the wheels in all their wandering positions. This contrasts with previous methods which computed single maximum values of the damage indicators. It is this feature that eliminates the need for the pass-to-coverage concept and allows the designer to specify any degree of wander. Successive aircraft movements have been observed to be normally distributed about the pavement centreline. The standard deviation (SD) for a taxiway is typically taken as 773 mm and for a runway as 1546 mm (Ho Sang, 1975). These correspond to wander widths of 1778 mm (70 inches) and 3556 mm (140 inches) where wander width is defined as the zone containing 75% of the aircraft centrelines. For a docking bay, a SD of the order of 200 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 to constantly re-key information. 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. 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.

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APSDS 5.0 User Manual

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. The program allows all of these load types to be simulated for a circular loaded shape. APSDS can also model non-uniform contact stress distributions. APSDS 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. 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. This Australian designed system has been developed by the Melbourne company, MINCAD Systems. APSDS 5.0 is based on APSDS 4.0, CIRCLY 5.0 and HIPAVE 5.0. CIRCLY has been in regular use in Australia and worldwide for more than two decades, proving its worth in thousands of design applications. 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). APSDS 3.0 was first released in 1995 and APSDS 4.0 in 2000. In 2007 Mincad Systems and Pioneer Road Services released the Heavy Duty Industrial Pavement 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 the concepts are directly applicable to the airport pavement design. The Guide is a collaborative effort currently involving Dr. Leigh Wardle of Mincad Systems, Ian Rickards (Pioneer Road Services Pty Ltd, Melbourne, Australia), John Lancaster (VicRoads, Australia) and Dr. Susan Tighe (Dept. Civil Engineering, University of Waterloo, Canada). The Guide presents the author’s attempts to reflect best practice in the design of new construction and rehabilitation of industrial pavements. The Guide steers the designer through all necessary design considerations and suggests external sources for research updates. The Guide is a ‘living document’ that will be regularly updated to reflect advances in pavement technology and made freely available via the Internet at no charge. For further details see http://www.mincad.com.au/hdipdg/.

Chapter 1 Introduction

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Realistic Modelling with APSDS You should be aware of a number of factors, including the accuracy of input material properties and the constraints of the layered elastic model, that will influence the reliability of design 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 the complex and variable properties of the pavement and subgrade materials. Although APSDS can produce what appear to be very accurate solutions to problems, the predictions cannot be any more reliable than indicated by the degree of scatter given by the back-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 consistent with the quality of the input data. Otherwise so many assumptions must be made about the uncertain parameters that the model predictions will be meaningless. The following Sections summarize the "state of the art" with respect to modelling of heavy aircraft loads and the behaviour of pavement materials. Much of this knowledge has been derived from airport pavement research. More detailed advice is given in the Heavy Duty Industrial Pavement Design Guide (Mincad Systems and Pioneer Road Services, 2007). For further details see http://www.mincad.com.au/hdipdg/.

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APSDS 5.0 User Manual

Material Modelling APSDS is an open system that will accommodate material properties and transfer functions for any pavement design methodology. But research has shown that highway pavement design methods such as Austroads (2008) are not applicable to the higher loadings typically applied to heavy duty pavements used at airports (Wardle et al., 2003). The process of establishing a performance relationship entails assigning moduli values to unbound basecourse and sub-base materials in accordance with a particular system of sublayering. Care should be taken to ensure that the sub-layering system used to establish the performance 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 is broken. 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 underdesigned 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. If a failure criterion is used in conjunction with a different design procedure, the vital empirical link between the design and the original performance data used to calibrate the criterion is broken. This issue is discussed in more detail by Wardle et al. (2003). The material performance characteristics recommended for use in APSDS are based on calibrations developed from airport pavement research. The subgrade strains are converted to damage using a performance relationship of the form:

Chapter 1 Introduction

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)

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The preferred subgrade performance relationship for heavy duty airport pavements was developed by Wardle and Rodway (2010). This performance relationship was established by calibrating pavement designs using APSDS against designs based on the US Army Corps of Engineers CBR method (Method S77-1, Pereira 1977). The methodology also incorporates recent ICAO recommendations that impact designs for new generation large aircraft including the Boeing 777 and Airbus A380-800. The relationship was developed using a range of different aircraft with masses varying from 74 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 on the number of wheels on each gear. This calibration gives more reliable predictions for designs involving new generation large aircraft 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 for cement-treated materials:

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Modelling of Multiple Wheels and Axle Groups APSDS lets you use the actual wheel layouts of the aircraft that operate on the pavement. Care needs to be taken to select which wheels to include in the model. Extensive research gives us guidance on choosing the "right" combination of wheels to include in the model. Using more wheels can lead to inaccurate model predictions. The recommended model for base/sub-base materials and subgrade performance relationship recommended for heavy duty loads was described above. This methodology was derived from full-scale aircraft pavement tests conducted by the US Army Corps of Engineers at their Waterways Experiment Station (WES). These 'WES' tests were essentially conducted using single gear assemblies. No tests were carried out to investigate the increased damage that might result due to interaction effects of adjacent gear assemblies. Considerable uncertainty exists with respect to prediction of damage for aircraft that have main gears in close proximity. APSDS has been used to study multiple gear interaction effects for a Boeing 747 and 777 aircraft using a range of alternative damage models (Rodway 1995a, Wardle and Rodway 1998, Rodway, Wardle and Wickham 1999). Results from these studies show that the successful calibration of simplified design models against the full-scale test data does not create a capability to confidently extrapolate beyond the limits of the test data. The studies showed that simple damage models give unrealistic predictions for the damage caused by all sixteen main wheels of the aircraft when compared to that computed for a single isolated 4wheel gear. Three different performance models, each of which gave a similar 'goodness of fit' to the full-scale test data, gave greatly different predictions of the damage caused by the interactions of the sixteen main wheels. The differences between the alternative predictions increased with increasing depth to subgrade. Given the above comments, as a general rule only groups of wheels that are within 2 metres of each other should be modelled as a single load case. The example shown below is for a Boeing 747 showing the four main gears. In APSDS 5.0 only the gears on the right side of the diagram are modelled. The aircraft is modelled as a single entity with the two gears are modelled as separate components.

Chapter 1 Introduction

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Nature of Damage Pulses The WES tests were performed on relatively thin pavements. In most of the test sections the elastic models predict a distinct strain pulse at subgrade level for each axle of a two-axled gear. For deep pavements (say 1.5 m or more) the models predict a single combined pulse resulting from the entire gear. In other words, a two-axled gear produces two strain pulses per pass for shallow subgrades and one strain pulse, of significantly different shape, for deep subgrades. APSDS uses strain repetitions as the basis for damage predictions, not passes or coverages. Pulse counts and pulse shapes both change with pavement thickness. There is significant uncertainty in the design of thick pavements because data must be extrapolated from 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 damage depends on the transverse and longitudinal widths of the load pulse. The pattern of strains at subgrade level experienced during the passage of a multiple axle gear primarily depends on the pavement depth. The two extremes are: ƒ

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

ƒ

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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CHAPTER 2

Overview APSDS has many features to facilitate pavement analysis and design.

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APSDS 5.0 User Manual

How APSDS handles Traffic Distributions APSDS lets you define your aircraft loadings and traffic in detail. You define the anticipated repetitions over the design period for each aircraft model. You also define a gross weight distribution 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

Chapter 2 Overview

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

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APSDS 5.0 User Manual

APSDS can also generate graphs that show the variation of the damage factor with each aircraft 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 aircraft passes along the pavement. You nominate a standard deviation of aircraft wander about the centreline that is appropriate to the particular aircraft model and pavement. The sophisticated method of handling wander, bypasses the simplified concepts of “coverage” and “pass-to-coverage ratio” (PCR) that have been traditionally used for aircraft pavement design. Some background material to assist with the selection of the standard deviation of wander is given in Wander Statistics (on page 104).

Chapter 2 Overview

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Elastic Properties The elastic material in each layer of the pavement 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. 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 each analysis point by using Miner's hypothesis. The damage factor for any given loading is defined as the number of repetitions (n) of a given response parameter divided by the ‘allowable’ repetitions (N) 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:

where: ƒ

k is summed over M aircraft models

ƒ

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

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APSDS 5.0 User Manual

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— ƒ

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

ƒ

the material performance properties used in the design model.

This approach allows analyses to be conducted by directly using a mix of aircraft models. It is 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 tolerable strain 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)

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. APSDS 5.0 can use performance parameters that depend on the number of wheels on each gear. This approach gives more reliable predictions for designs involving new generation large aircraft including the Boeing 777 and Airbus A380-800. For full details see Wardle and Rodway (2010). APSDS can also handle models of the form:

Chapter 2 Overview

23

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 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 aircraft model and the aircraft weight mix — that is the repetitions for each aircraft weight that is modelled.

How aircraft characteristics are defined Wheel Loadings Normally a given aircraft type is represented by the main gear as the damage due to the smaller loadings on the nose gear can be ignored. (Nose gears typically take 5% of the aircraft weight). The aircraft loading is defined in terms of the Aircraft Gross Weight, the proportion of Gross Weight 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 the wheels 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. The master 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 the definition of Aircraft loading characteristics. Most importantly, a critical issue is choosing the optimum number of wheels to use in the model - a benefit of of the Standard Aircraft Library is that it takes the worry out of selecting which wheels to model. You will also save time by not 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— ƒ

wheel locations and numbers; and

ƒ

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 the aircraft loading characteristics are specified in terms of the gross weight of the aircraft, the number of axles, the total number of wheels on the aircraft and the tyre pressure. The screendump below shows some sample data:

Chapter 2 Overview

25

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

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APSDS 5.0 User Manual

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 geometry and the points 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 taken as the direction transverse to the runway or taxiway axis. To ensure consistency between results for different aircraft types it is recommended that X=0 corresponds to the runway or taxiway centreline. The Y axis is parallel to the centreline (and the direction of travel of the aircraft!). The Z axis is vertically downwards with Z=0 on the pavement surface.

Chapter 2 Overview

Centreline of Aircraft Direction of Travel

Y

O X

Z

27

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APSDS 5.0 User Manual

Methods for handling Damage Pulses The problems associated with damage pulses were introduced in the Introduction under Nature of 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 surface. The two extremes of behaviour are— ƒ

multiple distinct pulses resulting from each axle, for shallow depths; and

ƒ

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 all wheels 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 generally occur 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 the gear 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 pulse beneath 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.

Chapter 2 Overview

29

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

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APSDS 5.0 User Manual

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

Chapter 2 Overview

31

There are a different number of movements for each gross weight. Commonly only two or three masses are modelled, generally expressed as "% of aircraft operating at a % of MTOW (Maximum Take-Off Weight)". For example, 20% of aircraft operate 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 be provided. 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.

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

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.

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APSDS 5.0 User Manual

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 finetune layer thicknesses to optimise construction cost. For further details see Automatic Parametric Analysis.

Automatically generated plot: Total Cost vs. Layer 3 Thickness

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CHAPTER 3

Overview of User Interface Introduction APSDS has a standard format Microsoft Windows menu, but most commands can be accessed directly from the toolbar as shown below:

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APSDS 5.0 User Manual

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– APSDS data file— this is used to save the details of your job.

Jobname.sds

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 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.

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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 the Analysis and Plotting Results Run Analysis The button invokes the analysis. This invokes the analysis. During a long analysis you can switch to another application (APSDS will continue to run at a lower priority using Microsoft 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 damage factors (CDF) for your pavement. Alternatively, you can calculate results for any given displacement, stress or strain component at selected Z-values (depths below the pavement surface) (see Calculate Selected Results at User-defined Z-Values (see "Calculating Selected 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

1

button.

Two alternative calculation options are available:

ƒ

Calculate damage factors (CDF); or

ƒ

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 108)).

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. 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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Plot Results The icon will generate a graph of the results. Usually, this command will produce a graph of the damage contribution from each aircraft 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 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 surface of the pavement) and results can be plotted for a selected displacement, stress or strain component (see Calculate Selected Results at User-defined Z-Values (see "Calculating Selected Results at User-defined Z-values (depths)" on page 108)).

Options The Options screen allows specification of the following folder: ƒ

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

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CHAPTER 4

How to Start Using APSDS The easiest way of trying APSDS out is to open one of the sample jobs, run the analysis and then graph the results.

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Opening and Running an Existing Job In the interests of providing instant hands-on experience, for this example you simply open an 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 the screen. 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.

Chapter 4 How to Start Using APSDS

3.

41

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, the distance from the centreline of the pavement (i.e. X=0 corresponds the centrelines of the aircraft). 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 Plot Type 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 Aircraft Model and Gross Weight. The two graphs give results for the subgrade layer. If your layered system has other layers that have a performance relationship you can switch to the CDF for the other layers by clicking 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 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 as shown below:

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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.

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Global Coordinate System A global coordinate system is used to define load locations, the layered system geometry and the points below the pavement 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. Two alternative formats are available for specifying the points to be used for results calculation: ƒ

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.

Y

Direction of Travel

X

0

Xmin

Xdel

Xmax Results points

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

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Y

Ymax

Ydel

Ymin X

0

Xmin

Direction of Travel

Xdel

Xmax Results points

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

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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

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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

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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 20 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: ƒ

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

ƒ

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;

Chapter 5 How to Modify the Databases

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.

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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. 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. From a practical standpoint the response of the actual pavement interfaces will be somewhere between these theoretical limits. For design of new pavements the interfaces would be assumed to be fully continuous (rough).

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Layer No. 1 Layer No. 2

Layer No. NL

Rough rigid base

Smooth rigid base

∞

Semi-infinite base

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Creating a new Layered System Click on the

button.

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 20 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.

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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, 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. The fully continuous case is always assumed for pavement design.

1

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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:

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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 Performance Criterion APSDS usually represents performance relationships in the form:

(1) 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)

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 a Log-Linear Damage Relationship Type. Before you add a new Performance Criterion you need to choose the appropriate Material Type. For each Material Type, all Performance Criteria use the same Damage Relationship Type.

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 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 'Asphalt1600 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 are more entries than will fit in the listbox, there will be a slider bar on the right hand side. You can move down the list by clicking on the down arrow or by dragging the slider down. For this 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’. For this 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

button.

Click on the Performance tab. You now choose the material type to be used. Click on the material type combo box (as shown 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 = 10 b = 80000 The relevant strain component that is to be used is the maximum horizontal tensile strain at the base (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 adjusted appropriately. Move to the Component field by clicking on it or using the tab key. The screen should now look 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 will be 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 a slider bar on the right hand side. You can move down the list by clicking on the down arrow or 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 the relationship 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

button.

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 'Asphalt' for the 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 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- 1600 MPa, 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 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. 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 SubLayering scheme, click the checkbox next to ‘use sub-layering’, then click on the appropriate sub-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 Adding a new Performance Criterion (on page 59). Depends on Number of Wheels on Gear: if this is set to "Yes", it is assumed that the Performance Relationships for this material type will depend on the number of wheels on each landing gear. 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: ƒ

Traffic Spectrum;

ƒ

Traffic Spectrum Components;

ƒ

Load Groups;

ƒ

Load Group Components;

ƒ

Load Locations;

ƒ

Gross Weight Distributions;

ƒ

Gross Weight Distribution Components.

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

Chapter 5 How to Modify the Databases

Aircraft Specifications The APSDS aircraft library consists of so-called "Standard" aircraft specifications that are provided by Mincad Systems and "Custom" aircraft that you can define. You can browse the aircraft specifications as follows. Click on the

button.

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 Load Components and Locations tab.

Automatic Updates for the Standard Aircraft Library Updates for the Standard Aircraft Library can be automatically imported from the Mincad Systems 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: Click on the

button.

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

Contact Mincad Systems for a Library Update if the combination of Type and Manufacturer that you want to use is not available. 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 20 characters and a descriptive title (up to 72 characters).

Chapter 5 How to Modify the Databases

For this example you can type in 'B787-8 example' as the ID and 'B787-8 example' as the Title. 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 you specify the axle load characteristics and wheel positions. Aircraft are assumed to have equal loads on each axle on the main gears. In this case the loading characteristics are specified in terms of the proportion of gross weight on a single gear, 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 to make 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 Aircraft Models 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 of multiple gears. Click New for each wheel and enter the gear number (1), and the X and Y coordinates of each wheel. See the note Important Note about Axle Locations 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.

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Theta is only used to define the force or moment direction for non-standard loads such as braking 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 of different aircraft models. For each aircraft in the spectrum you specify the number of movements and the gross weight distribution. For each load case the wheel loads are automatically calculated from the aircraft characteristics and the gross weight. For an overview of the concepts see How APSDS handles Traffic Distributions (on page 18).

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 in your ID (index) field of up to 20 characters and a descriptive title (up to 72 characters). For this example you can type in 'TrafficTry' as the ID and 'Example of creating a new Traffic Spectrum' 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 of possible 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 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 aircraft model by double clicking on it. For this example, choose the Boeing 737-600 Max 63t. 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 movements (or passages) over the desired design life. For this example, enter 100,000 movements. The Graph Label is an optional string of up to 20 characters that is appended to the Aircraft Model Plot Label used for the Legend when plotting the results. This is useful when you need to have more than one Spectrum Component that uses the same Aircraft Model, for example 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: ƒ

% Max. Gross Weight - same for all Spectrum Components

ƒ

% Max. Gross Weight - different for each Spectrum Component

Defining Gross Weight Distributions For this example, use the following Gross Weight distribution: % Maximum Gross Weight 80 100

Count 50 50

For each row in the table, click the New button and enter the % Maximum Gross Weight and Count. Enter the % Maximum Gross Weight in the form of a number less than 1, i.e. 50% is entered 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 from other values. The values in the Gross Weight column are calculated from the Maximum Gross 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 Actual Movements are calculated from the values in the Count column. The Normalized Movements are given by normalizing the values of Count - so that the sum of the Normalized Movements values is 1.0. The Actual Movements values are scaled so that the total matches the total number of movements (1.25E+06 in this example) defined for the current Spectrum 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 historical data or could be simply actual movements. The calculated columns are not updated while you type the data on a particular row - but are updated 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. 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:

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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.

Wander Options If the Traffic Spectrum screen is not already active, click on the Click on the Wander tab. You should now see the alternative Wander options:

button.

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Three alternative Wander options are available: ƒ

No Wander for any Aircraft Model in the Traffic Spectrum;

ƒ

Same Wander for All Aircraft Models in the Traffic Spectrum;

ƒ

Wander varies with Aircraft Model.

If the Wander varies with the Aircraft Model, you specify the Wander in the Spectrum Components 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. Some additional parameters define the numerical approximation used to model the effects of Wander. 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 accuracy XWDEL 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 be 2.7 times the maximum Standard Deviation of wander, or greater. 4500

XWDEL (=100 mm)

4000

Total Movements = 100,000 3500

3000

2500

2000

1500

1000

500

0 20 0 40 0 60 0 80 0 10 00 12 00 14 00 16 00 18 00 20 00 22 00 24 00 26 00 28 00 30 00

0 -8 00 -6 00 -4 00 -2 00

0 -1

00

0 -1

20

0 -1

40

0

60

80

-1

-1

0

0 00

20

-2

-2

0

0 40

-2

-2

60

0 80

-2

00

0

0 -3

Movements in Slot

Standard Deviation = 1000 mm

Lateral Position (mm)

XWMAX (=3000 mm)

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Coordinates for Results Click on the

button.

This screen has fields for specifying the locations for which results are to be computed and the method for treating damage pulses. Two alternative formats are available for specifying the points to be used for results calculation: ƒ

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

ƒ

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 handling Damage 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 multiple distinct pulses for each axle, for shallow depths; or a single combined pulse for large depths.

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How to Use Advanced Features Thickness Design Capability You can automatically determine the optimum thickness of a given layer. This procedure is very 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 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.

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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.

Cost Calculation Calculation of Total Cost APSDS can automatically calculate Total Cost for a pavement from the unit costs of materials in each layer. Click on the

1

button. This will bring up the following screen:

Click on the Calculate Cost checkbox

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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.

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).

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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. Click on the

button. This will bring up the following screen:

1

1

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

1 2 3 4

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.

Chapter 6 How to Use Advanced Features

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 T1maximum in steps of T1step. To use two Independent Variables, click the combo box (

1

on the screenshot below).

1

2 3 4

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 T2maximum in steps of T2step.

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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 3) and to determine which thickness has the minimum Total Cost. For each Layer 3 thickness, you will get APSDS to automatically design the thickness of Layer 2.

¾ Step 1. Open the sample file "Example for Cost Optimization".

Chapter 6 How to Use Advanced Features

¾ Step 2.

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 3.

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3

This lets you choose which layer (thickness) is to be used as the first Independent Variable. For this example change this to "3". (as you are varying the thickness of Layer 3).

4

Here you specify the range of thicknesses to be used for Layer 3:

For this example, you will let Layer 3 vary in thickness from 400 mm to 1000 mm in steps of 20 mm. Enter the following values: Minimum: 400, Maximum: 1000, Step: 20.

¾ Step 3. Now set the automatic thickness design feature to Layer 2. Click on the "Summary" tab (left of the "Variables" tab).

1

Click the check-box labelled 'Design thickness of layer highlighted below'.

2

Click anywhere on the Layer 2 row.

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

to run the analysis.

¾ Step 4- Plot the Total Cost vs Layer 3 thickness. When the analysis is finished, click on

to plot the results.

Chapter 6 How to Use Advanced Features

This plot shows the Minimum Total Cost condition for Layer 3 thickness is 660 mm (to a resolution of 20 mm).

¾ Step 5- Plot the CDF (for Layer 4, Subgrade) vs. Layer 3 thickness. Click on the Parameter combo box.

Select CDF (Select Layer =>). Click on the Layer combo box.

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Select Subgrade - CBR=6 (This is Layer No. 4).

Note that as the thickness of layer no. 3 becomes greater than 660 mm, the CDF becomes less than 1.0 as we have constrained the minimum thickness of layer no. 2 to 100 mm.

¾ Step 6- Plot the Layer 2 thickness (Design Layer) vs. Layer 3 thickness. Click on the Parameter combo box. Select Thickness (Layer used for Thickness Design).

Chapter 6 How to Use Advanced Features

Note that the thickness of layer no. 2 asymptotes to 100 mm as the thickness of layer no. 3 exceeds 660 mm as we have constrained the minimum thickness of layer no. 2 to 100 mm.

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CHAPTER 7

Appendices

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CHAPTER 8

What's New in Version 5.0

97

Overview If you have used APSDS 4.0, you will find many improvements in APSDS 5.0. These improvements include new features to make designing pavements easier and more efficient. This section gives a quick overview of the new and improved features in APSDS 5.0. Crossreferences to the rest of the manual show you where to look for information about most topics. APSDS 5.0 draws on the features that are in HIPAVE 5.0 and CIRCLY 5.0.

More convenient definition of Aircraft Loads Earlier versions of APSDS modelled aircraft with more than one main gear on each side of the aircraft (such as the Boeing 747) as two separate load cases. APSDS 5.0 models these aircraft as a single entity, making it easier to define traffic spectrums that include such aircraft.

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Enhanced Spectral Analysis Like APSDS 4.0, APSDS 5.0 accumulates the contribution from each loading in the traffic spectrum at each analysis point by using Miner's hypothesis. The procedure takes account of— ƒ

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

ƒ

the material performance properties used in the design model.

New to APSDS 5.0 is the way you can define a gross weight distribution for each aircraft model in your traffic spectrum, as shown below: In addition to the usual graphs of damage versus distance, APSDS 5.0 generates spectral damage graphs like this:

Here there is a data point for each combination of aircraft model and gross weight. These graphs let you check the sensitivity of designs to assumptions made about the gross weight distributions.

Standard Aircraft Library APSDS 5.0 comes with a standard aircraft library - that can be automatically updated from our webserver.

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99

Wander can vary with Aircraft Model APSDS 5.0 extends the lateral aircraft wander concept used in earlier versions of APSDS to include the capability of letting the degree of wander vary with each aircraft model in the traffic mix.

Reservoir Method The pattern of strains at subgrade level experienced during the passage of a multiple axle gear primarily depends on the pavement depth. The two extremes are: ƒ

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

ƒ

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.

Material Performance depends on Gear Configuration APSDS 5.0 can use performance parameters that depend on the number of wheels on each gear. This approach gives more reliable predictions for designs involving new generation large aircraft including the Boeing 777 and Airbus A380-800. For full details see Wardle and Rodway (2010).

Reusable Aircraft Gross Weight Distributions APSDS 5.0 lets you specify 'standard' aircraft gross weight distributions that you can conveniently re-use in your traffic spectrums. You can 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.

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Cost Optimization 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. For example, for the pavement structure shown below, you can automatically determine the thicknesses of the Base and Subbase that will minimize the total cost.

Appendices

101

This automatically generated graph shows you the pavement configuration that corresponds to minimum total cost:

Automatically generated plot: Total Cost vs. Layer 3 Thickness

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New "built-in" Graphics Engine APSDS 5.0 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 reanalysing the system. Here is a sample "Three-dimensional" graph of vertical displacement:

You can also copy the graph to the clipboard and then paste it into another application such as Microsoft Word or Powerpoint. Numerical values can also be exported via the clipboard.

Duplicating Layered Systems and Traffic Spectrums APSDS 5.0 lets you duplicate a Layered System or Traffic Spectrum. For example, 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.

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103

Coordinate System for Loads The most common type of load modelled in APSDS 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 aircraft, 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.

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Figure 6: Global and Local Coordinate Systems

Wander Statistics Field observations (HoSang, 1975) show that the lateral distribution of aircraft wheel paths can be represented by a theoretical normal (bell-shaped) distribution. HoSang's results can be summarised as follows: Standard Deviation

Appendices

Pavement Type

Minimum mm (ft)

Maximum mm (ft)

Runways

1800 (6.0)

3400 (11.2)

Taxiways

800 (2.5)

1800 (6.0)

Runway Exits

2400 (8.0)

3200 (10.5)

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In much of the design literature the term “wander width” is used. This is defined as the width of the zone over which the centreline of aircraft traffic is distributed 75% of the time. If the normal distribution is used it can be shown that (Pereira, 1977): Wander width = 2.30 x Standard deviation of wander The U.S. Army/Air Force Design Manual Flexible Pavement Design for Airfields (Elastic Layered Method) (Army TM 5-825-2-1, Air Force AFM 88-6, Chap. 2, Section A) uses the following wander statistics: Pavement Type

Wander Width mm (in.)

Standard Deviation mm (in.)

Taxiways First 300 m (1000 feet) of runway ends

1800 (70)

770 (30)

Runways

3600 (140)

1550 (60)

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Cross-anisotropy and isotropy in pavement materials The elastic material in each layer of the pavement 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

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

- νh σyy - νhv σzz)

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

Ef > 0 v

> 0 1 > νh > -1

1-νh-2νhvnvh > 0

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107

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.

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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. Click on the

1

2 3 4 5

6

button. This will bring up the following screen:

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109

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 6

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

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References Austroads (1992). Pavement Design – A Guide to the Structural Design of Road Pavements. Austroads Publication No. AP-17/92. Austroads (2008). Guide to Pavement Technology - Part 2: Pavement Structural Design. Austroads Publication No. AGPT02/08. Barker, W. and Brabston, W. (1975). Development of a structural design procedure for flexible airport pavements. Report No. S-75-17. US Army Corps of Engineers, Waterways Experiment Station, Vicksburg, Miss. British Ports Association/Interpave (1996). The Structural Design of Heavy Duty Pavements for Ports and other Industries, 3rd ed., Interpave, Leicester. HoSang, V.A. (1975). Field survey and analysis of aircraft distribution on airport pavements. Report No. FAA-RD-74-36. U.S. Federal Aviation Administration. Mincad Systems and Pioneer Road Services (2007). Heavy Duty Industrial Pavement Design Guide. (Web: http://www.mincad.com.au/hdipdg/). Pereira, A. T. (1977). Procedures for development of CBR design curves. Instruction Report S-77-1, US Army Corps of Engineers, Waterways Experiment Station, Vicksburg, Miss. Rodway, B. (1995a). Design Of Flexible Pavements For Large Multiwheeled Aircraft. Int. Conf. on Road & Pavement Technology, Singapore, 27-29 September, 1995. Rodway, B. and Wardle, L.J. (1998). Layered Elastic Design of Heavy Duty and Industrial Pavements. Proc. AAPA Pavements Industry Conf., Surfers Paradise, Australia. Rodway, B., Wardle, L.J. and Wickham, G. (1999). Interaction between wheels and wheel groups of new large aircraft. Airport Technology Transfer Conference, Atlantic City, U.S.A., April 1999, Federal Aviation Administration. 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. Wardle, L.J. and Rodway, B. (1998). Recent Developments in Flexible Aircraft Pavement Design using the Layered Elastic Method. Third Int. Conf. on Road and Airfield Pavement Technology, Beijing, April 1998. Wardle, L.J. and Rodway, B. (2010). Calibration of Advanced Flexible Aircraft Pavement Design Method. to be published.

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Wardle, L.J., Rodway, B. and Rickards, I. (2001). Calibration of Advanced Flexible Aircraft Pavement Design Method to S77-1 Method. in Advancing Airfield Pavements, American Society of Civil Engineers, 2001 Airfield Pavement Specialty Conference, Chicago, Illinois, 58 August 2001 (Buttlar, W.G. and Naughton, J.E, eds.), pp. 192-201. Wardle, L.J., Youdale, G. and Rodway, B. (2003). Current Issues For Mechanistic Pavement Design. in 21st ARRB and 11th REAAA Conference, Cairns, Australia, 18 - 23 May, 2003, Session S32, ARRB Transport Research.