https://forum.rubicontoolbox.com/pages/topic63-the-axle-spectrum-analysis-tool--how-it-works.aspx Rubicon Online Help - LET Tools: Standard Axle Design, Axle Spectrum and Stress-Strain Calculator - The Axle Spectrum Analysis Tool - How it works - Messages en-us http://blogs.law.harvard.edu/tech/rss Jitbit AspNetForum Fri, 01 Apr 2022 07:57:27 GMT Fri, 01 Apr 2022 07:57:27 GMT https://forum.rubicontoolbox.com/pages/topic63-the-axle-spectrum-analysis-tool--how-it-works.aspx Principles

• Accumulated damage is calculated using Miner’s Linear Damage Rule.

• This rule assumes that damage caused by each load repetition at a given stress level is equal, i.e. the first repetition is as damaging as the last repetition.

• A portion of the useful life is therefore used up by a number of repeated loads (or stress cycles) at a particular level proportional to the total number of load repetitions allowable (until failure) that can be applied at that particular stress level.

• The damage ratio (D) is therefore:

• When 100% of the life is expended, the pavement is expected to fail with D = 1.

• Since D is dimensionless, this ratio can be calculated and summed for different axle loads (or load groups) applied to the same pavement simultaneously.

• For the purpose of damage analysis, the sum of the damage ratios for the spectrum of axle loads can be evaluated at predefined periods per year; each year could be considered as one period with the same material properties throughout the year, or the year could be divided into seasons.

Application

• The Axle Spectrum Analysis Tool applies these principles using mechanistic-empirical (ME) analysis using the same LET model and approach built into the Standard Axle Analysis Tool. The pavement structure is specified in exactly the same way.

• The allowable number of repetitions (to failure) is calculated for each axle load (or load group) for each layer using ME analysis.

• The specified daily number of repetitions and growth rate(s) associated with each axle load (or load group) is used to calculate the actual number of repetitions accumulated to the end of each period for the load (or group) under consideration.

• The accumulated damage ratio at the end of each period is calculated for each axle load (or group) and pavement layer.

• The sum of the accumulated damage ratios across the spectrum of loads (or load groups) at the end of each period is calculated for each pavement layer.

• The layer with accumulated sum of damage ratios that reaches 1 first, is the critical layer representing failure and the accumulated period represents the pavement life in years.

The following schematics present the simplified process of calculating the damage ratios and the life of the critical layer when D = 1.
























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