ESAL determined using Table 20.13a or 2013b. Note the tables are a function of the structural number SN. When In doubt use 3 and recomputed if necessary.MaterialsMr = 1500*CBRCoefficients for structural number, SN equation areEnvironment`Lecture 23 AASHTO Design ProcedureThis design procedure is based on results determined from the Ottawa test site and modified over the years. The designprocedure accounts for traffic, material and environment as noted belowTrafficESAL determined using Table 20.13a or 2013b. Note the tables are a function of the structural number SN. When In doubt use 3 and recomputed if necessary.MaterialsResilient modulus of the sub grade calculate in the usual way but modified for environmental conditions as noted by the relative damage calculation where each month a modulus value is obtained and the relative damage is calculate using the equation32.281018.1rfMxu Taking the relative damage for each month (uf) an average value is obtained and the effective annual resilient modulus is calculate as431.08)1018.1(avgreffuxM Approximate modulus values are obtained from:Mr = 1500*CBR MI = 1000+555*R (R obtained from Hveentest)Coefficients for structural number, SN equation area1 = asphalt = .44 a2 = base = .14a3 = sub base = .11 EnvironmentAs presented above, determine an effective resilient modulus that take into account seasonal variations of modulus as illustrated in Figure 20.18.Moisture is accounted for by including a coefficient m2 and m3 for the base and sub base terms in the structural number equation. Based on quality of drainage (Table20.14) and percent of time saturated (Table 20.15).ReliabilityIn 1993 the Design guide added some statistical termsto the method including levels of reliability that decreases as functional classification is lowered (Table 20.16), standard deviation (0.4-0.5 for asphalt and 0.3 to 0.4 for concrete) and standard normal deviation (Table 20.17).To quantify pavement performance and determine the ESAL factors a concept known as the present serviceability index was used. This factor relates serviceability to load repetitions and in the design equations the initial value is 4.2 and the final value is 2.5 to 3.0 for major highways and 2.0 for minor roads. The result of the equation is the desired structural number for the given inputs and is relatd to the variouslayers by the equation33322111mDamDbDaSN the terms are defined above. The solution to the equation for structural number is solved using an equation (20.13) or a nomograph as in Fig 20.20. The SN is then use todetermine the thickness of the layers as shown in Lecture 24.A Calculator for asphalt road thickness is available at Calculator for Asphalt Surfaced RoadThe design method described above is in the process of being updated. Additional information about the new procedure and available software can be located at 2002 Guide for Mechanistic Pavement