The structural number SN is defined as: (C.3) Equation (C.2) must be solved implicitly for the structural number SN as a function of the input parameters. The first five parameters typically are the inputs to the design equation, and SN is the output. Structural number (a measure of required structural capacity) Overall standard deviation (function of overall design uncertainty)Īllowable serviceability loss at end of design life Standard normal deviate (function of the design reliability level) Number of 18 kip equivalent single axle loads (ESALs) The empirical expression relating traffic, pavement structure, and pavement performance for flexible pavements is: (C.2) C.2 Flexible Pavement Structural Design Design Equation See the 1993 AASHTO Guide for details of additional procedures ( e.g., determination of remaining structural life for overlay design) relevant to rehabilitation design. The design procedures for reconstruction are similar, except that characterization of recycled materials may be required. For simplicity, only the design procedures for new construction are summarized here. These procedures are summarized below in Sections C.2 and C.3, respectively. The structural design procedures for traffic are different for flexible and rigid pavement types. The structural design procedures for swelling and frost heave are the same for both flexible and rigid pavements these are detailed in Appendix G of the 1993 AASHTO Guide. In which ΔPSI TR, ΔPSI SW and ΔPSI FH are the components of serviceability loss attributable to traffic, swelling, and frost heave, respectively. Serviceability loss at end of design life, ΔPSI, is partitioned between traffic and environmental effects, as follows (see also Figure 3.8): (C.1) Serviceability is defined in terms of the Present Serviceability Index, PSI, which varies between the limits of 5 (best) and 0 (worst). The overall approach of the 1993 AASHTO procedure for both flexible and rigid pavements is to design for a specified serviceability loss at the end of the design life of the pavement. Chapter 6 provides some design examples using the 1993 AASHTO procedures. Geotechnical inputs to the 1993 AASHTO design procedure are detailed in Chapter 5.
All versions of the AASHTO Design Guide are empirical design methods based on field performance data measured at the AASHO Road Test in 1958-60.Ĭhapter 3 of this manual describes the evolution of the various versions of the AASHTO Design Guide. Approximately 80% of all states use the AASHTO pavement design procedures, with the majority using the 1993 version. The AASHTO Guide for Design of Pavement Structures (AASHTO, 1993) is the primary document used to design new and rehabilitated highway pavements. Geotechnical Aspects of Pavements Reference Manual Appendix C: 1993 AASHTO Design Method C.1 Introduction
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