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Sonia Stamatelos Administrator Posts: 25
1/13/2021
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The LET Axle Spectrum Analysis allows you to evaluate the impact of an axle spectrum on a pavement’s design capacity. An axle spectrum can be built and analysed for a specific design situation. The axle spectrum can consist of any number of axle types, or configurations, including aircraft load groups.
Getting Started
The LET Axle Spectrum Analysis Tool is accessed through the Design Tools icon on the Rubicon Toolbox Online Tools.
If this is the first time you are using the Online Tools, you will need to set up a project by clicking on Manage Projects link and create a new project. Alternatively, you can use an existing project if one has already been created.
Once you have created a new project or selected an existing project, click on the Design Tools icon and select LET Axle Spectrum Analysis from the list. A LET Axle Spectrum Analysis page will open. Proceed with the following steps to complete the analysis, working from left to right.
Note, if loads are not available for selection it means that the default loads have not been setup or selected and you will need to pre-define your loads before you can proceed further. Default loads and materials can be defined by clicking on Settings from the left-hand navigation menu.
Defining the Pavement Structure
A default table with five layers will display on-screen, as well as text boxes to input the name of the analysis, a description and notes.
The selection of a predefined or default material automatically populates the Thickness, Stiffness, Poisson’s ratio and Transfer Functions (or Failure Criterion) fields from the default database. These default values and Transfer Functions are merely indicative, to provide guidance, and should be assessed carefully and adjusted if needed to reflect the specific project or design conditions. The actual inputs should be relevant to the project under consideration and should ideally be derived from processing of data collected for the project; e.g. stiffness values can be backcalculated from deflection data and substantiated or validated using other data sources such as dynamic cone penetrometer data, density measurements, moisture measurements, and laboratory test data. Note, if the Material Class is changed after finalization of the thickness, stiffness values etc., these values will change to the default values associated with the new material. Also note, if materials are not available for selection it means that the default materials have not been selected under Settings.
A Phase 1 Pavement Structure table, containing the basic predefined materials, is shown below. The default Transfer Function (or Failure Criterion) is associated with the selected material, and normally a good start. In many cases, one function up or down is selected to meet the required design reliability. In the screen shot below, Cat B represents Category B according to the South African design method associated with a 90% design reliability. It is also possible to select None, implying that the calculated response is not considered in the structural capacity analysis. This does not, however, mean that the entire layer is ignored. The stiffness contribution to the pavement system is still considered.
Once you have changed the default settings to the required project inputs, in Phase 1, proceed with defining Phase 2 of the Pavement Structure or Calculate if the Phase 2 analysis is not applicable.
If Pavement: Phase 2 is selected, the input table, for Phase 2, automatically appears with prepopulated data from Phase 1 and you only need to change the properties that will change for Phase 2. This ascertains accuracy and compatibility between the two phases with only minor changes needed to reflect the change(s) in the relevant layer(s). The screen shots below show the Phase 2 pavement structure, with prepopulated values from the Phase 1 example structure inputs, and highlights the changes required for the Phase 2 setup.
Analysis and Reporting
Once you have completed the Phase 2 setup, proceed with the following steps to generate the analysis report.
Note, for a new analysis, the Save option is initially inactive. Once an analysis is saved for the first time, the save option becomes active. For overwriting an existing saved analysis, click on Save. To save as an alternative analysis, click on Save As. Alternatively you can clone your analysis, from the Online Tools page, and rename it as needed.
The report for each phase can be copied to the clipboard by right clicking on the report and selecting Copy image or Save image as. The image can then be inserted into a document of your choice (Word, Excel etc.).
edited by on 1/22/2023
edited by on 10/17/2023
edited by on 8/29/2024
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