Separate year into time intervals Compute the relative damage value (uf) for each modulus2.32Ģ.4.1 Effective Subgrade Resilient Modulus (cont) PSIt = Terminal serviceability index Major highways: >2.5 Lower volume: 2.0Ģ.4.1 Effective Subgrade Resilient Modulus PSI = PSI0 PSIt PSI0 = Initial serviceability index Rigid: No traffic variation: S0=0.25 With traffic variation: S0=0.35 No traffic variation: S0=0.35 With traffic variation: S0=0.45 Select a standard deviation (S0) Flexible: Select reliability level (R) Table 11.14ģ. Define functional class (Interstate/Local)2. Overall Standard Deviation: Traffic Variation Performance predictionġ. Where:W18 = Design ESALw18 = Predicted ESAL Uncertainty in: Traffic prediction Performance prediction Iii.AASHTO assumes that pavement structural layerswill not be overstressed: Must check that individual layers meet structuralĭesign Life Material Properties Traffic Reliabilityĭegree of certainty that the pavement will lastthe design period Your job as a designer is to select the mosteconomical combination, using available materialsand considering the following: Geometry requirements (Cut/Fill) Drainage requirements Frost requirements Different combination of materials & thicknessesmay result in the same SN Select the performance level (PSI) Solve for the required SN needed to protect the subgrade Structural Coefficient (a):a = fnc (E, position in PVT)īasic Procedure: Determine the traffic (ESAL) Calculate the effective subgrade modulus (MReff) What are the three factors affecting performance (PSI)? PSI = fnc (MReff, SN, ESAL) MReff: Accounts for the environment PSI PSI is such that PSIt is NOT reached before end of design life Terminal PSI (known) Pvt isno longer functional How does the true (user) performancecorrelate to the measured performance?Ĭalculated the regressioncoefficients for the PSI equationġ.3.1 Performance Requirements & Design Life Present Serviceability Index (PSI)PSI = A0 + A1F1 + A2F2 + A3F3Ī0 A3 = Regression CoefficientsF1 = Measure of roughnessF2 = Measure of ruttingF3 = Measure of cracking
Measure of RoughnessMeasure of RuttingMeasure of Cracking Measure of how much slope varies fromhorizontal along the direction of trafficĮstablish correlation between user assessment (ride experience)and performance indicators (measurable characteristics) Measurable characteristics (performance indicators): Visible distress (cracking & rutting) Surface friction Roughness (slope variance) GoodĪ panel of experts drove around in standardvehicles and gave a rating for the pavement Topic 7 - AASHTO Flexible Pavement DesignĪASHO Road Test performance based on user assessment:ĭifficult to quantify (subjective) Highly variable Present Serviceability Rating (PSR)Ġ-1 V. Number of load repetitions with the performance of variouspavements Late 50s road test in Illinois Objective was to determine the relationship between the
#Flexible pavement design aashto profile download
* PAVEXpress download link provides freeware version of the software.Topic 7 - AASHTO Flexible Pavement DesignĪMERICANASSOCIATION OF STATE HIGHWAY AND TRANSPORTATION OFFICIALSġ.2 Performance MeasurementsEstablishment of performance criteria is critical The education modules within PaveInstruct correlate with the design modules in PaveXpress and provide technically sound pavement design and instruction. PaveInstruct, a web-based education system, has been developed with video instruction by leading industry experts on the use of PaveXpress. One exercise was conducted by the Kansas Department of Transportation and the second was performed by Palmer Engineering. There have been two independent verifications confirming PaveXpress calculates pavement designs consistent with the methodologies in AASHTO ’93 and ’98. Since its initial release, PaveXpress has expanded to help users design asphalt overlays, porous asphalt sections, and life cycle cost analyses.
PaveXpress was designed to be an extension of AASHTO 93/98 and has been adopted by public agencies such as the Washington State Department of Transportation as an accepted tool to help assess, scope, and design pavements. PaveXpress creates technically sound pavement structural designs for both asphalt and concrete pavements based on widely accepted industry standards from the American Association of State Highway Transportation Officials (AASHTO).
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PaveXpress is a free web-based pavement design tool available for use by local agencies, engineers and architects who need a reliable way to quickly determine the necessary pavement thickness for a given section of roadway or project.