This document outlines the specifications for a Microsoft Excel spreadsheet tool created to automate the design of flexible (asphalt) pavements. The tool utilizes the AASHTO 1993 Design Equation to calculate the required Structural Number ($SN$) and subsequently determines the thickness of individual pavement layers (Surface, Base, and Sub-base). The spreadsheet includes input sections for traffic data, material properties, environmental factors, reliability parameters, and an output summary with a design check.
is determined, you can design the individual layer thicknesses using the following relationship:
log10(W) = Zr * S0 + 9.36 * log10(SN+1) - 4.14 - 0.20 - 0.372 * (SN+1)^(1/3) / (p+1)
Enter the layer coefficients (a) and drainage coefficients (m) into the appropriate cells alongside trial thicknesses. aashto flexible pavement design excel spreadsheet
(Overall Standard Deviation): Typically ranges from for flexible pavements to account for variability in materials and traffic. ΔPSIcap delta cap P cap S cap I (Serviceability Loss): The difference between initial ( ) and terminal ( ) serviceability. MRcap M sub cap R
Use =NORM.S.INV(R%) to automatically calculate ZRcap Z sub cap R from the reliability percentage. The Iteration Loop: Since SNcap S cap N must be solved iteratively, you have two options in Excel:
An effective AASHTO spreadsheet typically processes several critical engineering inputs: Design Traffic ( W18cap W sub 18 This document outlines the specifications for a Microsoft
The core of flexible pavement design is a predictive equation that determines the required to support a specific traffic volume over a set design life. Because the SN appears on both sides of the equation in a non-linear format, it requires a trial-and-error approach or a "Goal Seek" function in Excel to solve. The fundamental equation is:
automatically without requiring the user to manually trigger Goal Seek. 3. Layer Design & Optimization Output This section takes the calculated target SNcap S cap N and allows the engineer to input structural coefficients ( ), drainage coefficients ( ), and trial layer thicknesses ( Dicap D sub i The spreadsheet computes the .
is the probability that the pavement will perform as intended; it is converted into ZRcap Z sub cap R for the equation. Overall Standard Deviation ( S0cap S sub 0 is determined, you can design the individual layer
The total number of 18,000-lb equivalent single axle loads (ESALs).
| Layer | Material | a-coeff | m-coeff | Thickness (in) | SN Contribution | |-------|----------|---------|---------|----------------|-----------------| | Surface | Hot-Mix Asphalt | 0.44 | 1.0 | 4.0 | 1.76 | | Base | Crushed Aggregate | 0.14 | 1.0 | 8.0 | 1.12 | | Subbase | Gravel | 0.11 | 0.9 | 10.0 | 0.99 | | | - | - | - | 22.0 | 3.87 |