Asphalt Institute Method

The Asphalt Institute Design Method for Flexible Pavements

The structural design of flexible pavements according to the Asphalt Institute Design Method is not practical to complete by hand. This is because the Asphalt Institute design method requires complex calculations of the horizontal strains induced in the pavement system under load. This requires a multi-layer elastic analysis of the proposed pavement structure which is a complex calculation. The CivilWeb Asphalt Institute Method Spreadsheet includes a spreadsheet which uses elastic theory to complete an elastic analysis of the pavement structure using the Boussinesq method. This spreadsheet calculates the  horizontal tensile strains and vertical compressive strains required as inputs in the Asphalt Institute design method.

Next the spreadsheet suite includes a spreadsheet which follows the Asphalt Institute design method to check the suitability of the proposed pavement design. The inputs from the elastic analysis are used to complete a fatigue and deformation analysis which gives a design number of load repetitions. This can then be checked against the design load required to determine whether the proposed pavement design is suitable or not.

The CivilWeb Asphalt Institute Method Spreadsheet suite also includes an overlay design spreadsheet which can be used to design flexible road overlay repairs. The spreadsheet calculates the estimated design loading which an overlay can be expected to take based on the strength of the overlay and the condition of the existing pavement.

Using the CivilWeb Asphalt Institute Method Spreadsheet allows the designer to complete a flexible pavement design using the Asphalt Institute design method. This design method is not practical to complete by hand, but these powerful spreadsheet tools allow the designer to complete a fully compliant design in minutes.

The Asphalt Institute Method of Flexible Pavement Design - Inputs

Firstly the designer can use the Boussinesq spreadsheet to complete an elastic analysis of the proposed pavement design. The designer inputs a proposed pavement structure including asphalt layers, sub-base layers and a subgrade layer. The designer must input the layer thickness and stiffness which can be taken from experience or from onsite testing.

The Boussinesq analysis spreadsheet then completes a multi-layer elastic analysis of the proposed pavement structure using the Boussinesq method. The spreadsheet calculates the vertical and radial stresses and strains induced in the pavement by the proposed load.

Next the results from the Boussinesq analysis spreadsheet can be input into the Asphalt Institute method spreadsheet. The  designer must input the strains calculated by the Boussinesq analysis spreadsheet and the dynamic modulus of the proposed asphalt. The spreadsheet  then conducts an analysis of the proposed pavement structure against two different failure mechanisms, fatigue failure and deformation failure. The lower of these two values can be taken as the design loading of the pavement.

The CivilWeb Asphalt Institute Method Spreadsheet includes unique design tools which make the optimisation process simple. The spreadsheet produces design graphs which show the effects of different strains on the design loading. The designer can simply read off the required maximum strain from this graph and take this back to the Boussinesq analysis spreadsheet. When the maximum strain is not exceeded, then the pavement will be suitable.

The Asphalt Institute Overlay Design Method

The CivilWeb Asphalt Institute Method Spreadsheet includes an additional spreadsheet which can be used to complete and overlay repair design of a flexible pavement. The spreadsheet takes the proposed loading conditions, the condition and strength of the existing flexible pavement and the thickness of the proposed overlay and uses these inputs to calculate the increase in strength from the overlay. The inputs can be taken from the design conditions and site testing of the existing pavement.

The spreadsheet includes a useful design graph which shows the effects of increasing the thickness of the proposed repair. This makes optimising the repair design easy, the designer can simply read off the graph the overlay thickness required for a particular strength increase.

The CivilWeb Asphalt Institute Method Spreadsheet

The CivilWeb Asphalt Institute Method Spreadsheet suite includes 3 spreadsheets to allow the designer to complete the flexible pavement design. The suite includes;

1. Boussinesq Analysis Spreadsheet - This spreadsheet is used to complete a multi-layer elastic analysis of the proposed pavement design. The results of this spreadsheet are required for the Asphalt Institute design method to be completed.
2. Asphalt Institute Method Spreadsheet - This spreadsheet takes the strains calculated from the elastic analysis and completes the flexible pavement design in accordance with the Asphalt Institute design method.
3. Asphalt Institute Overlay Design Spreadsheet - This spreadsheet completes the design of an overlay repair of a flexible pavement according to the Asphalt Institute overlay design method.

The CivilWeb Asphalt Institute Method Spreadsheet Suite includes all the tools required to complete a structural flexible pavement design in accordance with the Asphalt Institute design method. Unique analysis and optimisation tools allow the design to be complete in minutes. Buy now for only £10.

Asphalt Institute Method Spreadsheet - £10