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Structural Number Equation:
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The Structural Number for Surface Course represents the ability of the surface course to withstand axle loads in flexible pavement design. It quantifies the structural capacity of the surface layer based on material properties and thickness.
The calculator uses the Structural Number equation:
Where:
Explanation: The equation multiplies the layer coefficient (material strength factor) by the actual thickness to determine the structural contribution of the surface course.
Details: Accurate structural number calculation is crucial for pavement design, ensuring the surface course can withstand expected traffic loads and environmental conditions throughout its design life.
Tips: Enter the layer coefficient (typically between 0.3-0.5 for asphalt concrete) and actual thickness in millimeters. Both values must be positive numbers.
Q1: What is a typical layer coefficient for asphalt surface courses?
A: Typical layer coefficients range from 0.40 to 0.44 for dense-graded asphalt concrete surface courses.
Q2: How does structural number relate to pavement performance?
A: Higher structural numbers indicate greater load-bearing capacity and better resistance to rutting and fatigue cracking.
Q3: Can this calculator be used for other pavement layers?
A: Yes, the same formula applies to base and subbase layers, though layer coefficient values will differ based on material type.
Q4: What units should be used for thickness?
A: Thickness should be entered in millimeters for consistency with standard pavement design practice.
Q5: How is the total structural number calculated for multi-layer systems?
A: The total structural number is the sum of individual layer structural numbers: SN_total = a₁D₁ + a₂D₂ + a₃D₃ + ...