New Features in Version 4

This page is targeted at current users of APSDS Version 3.0, which was released in late 1996.

APSDS 4.0, released in October 2000, includes exciting new features to make designing pavements easier and more efficient. The features are described the following sections:

Automatic thickness design
Simultaneous damage factor calculations
More convenient definition of aircraft loads
New performance relationship forms
Printing
Flexible access to displacements, stresses and strains
Optional smooth interfaces
Online help

Automatic thickness design

Previously you would have to manually adjust the thickness of a given layer until the desired damage factor (typically 1.0) was found. Now you can automatically determine the optimum thickness of a given layer. This procedure is very fast, typically taking about 10 seconds on a Pentium PC.

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

You select the layer you wish to design by moving the mouse pointer to the appropriate layer and clicking the mouse button once. The black highlight will be positioned on that layer.

By default, the design will use the maximum damage factor 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 the box twice.

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.

Simultaneous damage factor calculations

In earlier versions the damage factor could only be calculated for one layer at a time. Version 4.0 simultaneously calculates the damage factor for all layers with a performance model.

Typically between one layer (the subgrade) and three layers (asphalt surfacing, cement-stabilised base, subgrade) will have performance criteria associated with them. APSDS 4.0 allows all criteria to be used for the damage calculation.

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

Two alternative calculation options are available:

calculate damage factors
calculate selected results at user-defined z-values

When operating in 'calculate damage factors' mode, the key features on the screen are:

This table is a summary of the layered system including material titles and current thicknesses. Also the current 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.

More convenient definition of aircraft loads

You can now define aircraft loads in terms of gross weight. This data structure avoids having to completely re-enter all aircraft details such as wheel locations for each gross weight condition needed.

The gross weight of an aircraft can be simply changed in the traffic spectrum components.

New performance relationship forms

In addition to the usual (log-log) performance relationship:

Equation (1)

we now have two new relationship forms:

The log-linear relationship shown below has been used by European designers for cement-treated materials:

A generalised form of Equation (1) has also been implemented where the parameters k and b are dependent on the modulus.
We have used this generalised form to implement a special relationship for light commuter aircraft in the 10-50 tonne range.
We plan to develop a new calibration for medium and heavy aircraft.