Trial structural number 3
At 90% reliability (ZR = −1.282), S0 = 0.45, ΔPSI = 1.7 and MR = 7,500 psi, SN = 3 gives log₁₀W18 = 5.613970, or 0.411121 million ESALs. Solving back for SN should return 3.
Add one row per truck type. Each truck can have multiple axle groups (single, tandem, tridem). LEFs are interpolated live from AASHTO Tables D.1–D.9. Each truck's Adopted Factor starts synced to its computed Composite LEF; setting it higher implies truck loading and/or tyre pressure above the adopted standard/reference conditions.
Note: setting an Adopted value higher than the computed composite LEF implies truck loading and/or tyre pressure above the adopted standard/reference conditions.
| Truck Type | Front Axle | Mid. Axle | Rear1 Axle | Rear2 Axle | Total | Adopted | AADT | Daily ESAL | ||
|---|---|---|---|---|---|---|---|---|---|---|
| Total Daily ESAL | — | |||||||||
| Total Annual ESAL | — | |||||||||
| Growth to opening year (1+g)p | — | |||||||||
| Growth Factor over the design life, GF | — | |||||||||
| Design lane factor DDF × LDF | — | |||||||||
| Design-lane ESALs over the design life, millions | — | |||||||||
| Year | Calendar | Annual ESALs | Cumulative, design lane from opening |
|---|
Evaluate the AASHTO 1993 flexible-pavement equation and compare required and provided structural numbers.
Traffic in millions of 18-kip ESALs; MR in psi. Layer depths cm; coefficients are per cm in this worksheet.
The 1993 empirical equation is solved for SN. Provided SN is the sum of a × thickness × drainage coefficient. This worksheet uses cm-based layer coefficients: an inch-based coefficient must be divided by 2.54. The CBR-to-MR correlation is an estimate; use the measured MR override when available.
Illustrative inputs for checking the method; these are not project records.
At 90% reliability (ZR = −1.282), S0 = 0.45, ΔPSI = 1.7 and MR = 7,500 psi, SN = 3 gives log₁₀W18 = 5.613970, or 0.411121 million ESALs. Solving back for SN should return 3.
At 90% reliability (ZR = −1.282), S0 = 0.45, ΔPSI = 1.7 and MR = 7,500 psi, SN = 4 gives log₁₀W18 = 6.380189, or 2.399877 million ESALs. Solving back for SN should return 4.
Evaluate the AASHTO 1993 flexible-pavement equation and compare required and provided structural numbers.
Traffic in millions of 18-kip ESALs; MR in psi. Layer depths cm; coefficients are per cm in this worksheet. The 1993 empirical equation is solved for SN. Provided SN is the sum of a × thickness × drainage coefficient. This worksheet uses cm-based layer coefficients: an inch-based coefficient must be divided by 2.54. The CBR-to-MR correlation is an estimate; use the measured MR override when available.
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