However, ESALs may be estimated using the following equation: (C.4)ĮSAL = ( ADT 0 ) ( T ) ( T f ) ( G ) ( D ) ( L ) ( 365 ) ( Y )Īverage daily traffic at the start of the design period Detailed traffic analysis is beyond the scope of this reference manual.
The AASHTO Design Guide is based on cumulative 18 kip (80 KN) equivalent single-axle loads (ESALs). Traffic analysis requires the evaluation of initial traffic volume, traffic growth, directional distribution, and traffic type. Traffic is one of the most important factors in pavement design, and every effort should be made to collect accurate data specific to each project. Guidelines for length of analysis period (AASHTO, 1993). AASHTO recommendations for analysis periods for different types of roads are summarized in Table C-1. Analysis period in this context is synonymous with design life in the 1993 AASHTO Guide. However, realistic performance limitations may require planned rehabilitation within the desired analysis period, in which case, the analysis period may encompass multiple performance periods. It may be identical to the performance period. The term "analysis period" refers to the overall duration that the design strategy must cover. It is equivalent to the time elapsed as a new, reconstructed, or rehabilitated pavement structure deteriorates from its initial serviceability to its terminal serviceability. Performance period refers to the time that a pavement design is intended to last before it needs rehabilitation. Note that there may be many combinations of layer thicknesses that can provide satisfactory SN values cost and other issues must be considered to determine the optimal final design. Equation (C.3) can be generalized for additional bound and/or unbound layers. In which D 1, D 2, and D 3 are the thicknesses (inches) of the surface, base, and subbase layers, respectively, a 1, a 2, and a 3 are corresponding structural layer coefficients, and m 2 and m 3 are drainage coefficients for the base and subbase layers, respectively. 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.
1993 AASHTO GUIDE FOR DESIGN OF PAVEMENT STRUCTURES MANUAL
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
0 kommentar(er)
