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ECGD4228 Transportation Engineering II Summer 2008 Saturdays 15:30-18:30 PM K204. Lecture 6. Pavement Design Methods Design Parameters Flexible Pavement Rigid Pavement. Distribution of Stresses & Temperatures. Present Serviceability Rating (PSR).
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ECGD4228 Transportation Engineering II Summer 2008 Saturdays 15:30-18:30 PM K204 Dr. Wa'el M. Albawwab albawwab@gmail.com
Lecture 6 • Pavement Design Methods • Design Parameters • Flexible Pavement • Rigid Pavement Dr. Wa'el M. Albawwab albawwab@gmail.com
Distribution of Stresses & Temperatures Dr. Wa'el M. Albawwab albawwab@gmail.com
Present Serviceability Rating (PSR) Picture from: Highway Research Board Special Report 61A-G Dr. Wa'el M. Albawwab albawwab@gmail.com
Present Serviceability Index (PSI) • Values from 0 through 5 • Calculated value to match PSR SV = mean of the slope variance in the two wheelpaths (measured with the CHLOE profilometer or BPR Roughometer) C, P = measures of cracking and patching in the pavement surface Dr. Wa'el M. Albawwab albawwab@gmail.com
Present Serviceability Index (PSI) • C = total linear feet of Class 3 and Class 4 cracks per 1000 ft2 of pavement area: • A Class 3 crack is defined as opened or spalled (at the surface) to a width of 0.25 in. or more over a distance equal to at least one-half the crack length. • A Class 4 is defined as any crack which has been sealed. • P = expressed in terms of ft2 per 1000 ft2 of pavement surfacing. Dr. Wa'el M. Albawwab albawwab@gmail.com
Typical LEF’s Notice that cars are insignificant and thus usually ignored in pavement design. Dr. Wa'el M. Albawwab albawwab@gmail.com
Design Catalog Example design catalog from the Washington Asphalt Pavement Association (WAPA) for residential streets Dr. Wa'el M. Albawwab albawwab@gmail.com
AASHTO Flexible PavementDesign Formula Dr. Wa'el M. Albawwab albawwab@gmail.com
AASHTO Rigid PavementDesign Formula Dr. Wa'el M. Albawwab albawwab@gmail.com
Terminologies • W18 (loading) • Predicted number of ESALs over the pavement’s life. • D (slab depth) • Abstract number expressing structural strength • SN = a1D1 + a2D2m2 + a3D3m3 + … • S’c (PCC modulus of rupture) • A measure of PCC flexural strength • Usually between 600 and 850 psi • Cd (drainage coefficient) • Relative loss of strength due to drainage characteristics and the total time it is exposed to near-saturated conditions • Usually taken as 1.0 Dr. Wa'el M. Albawwab albawwab@gmail.com
Terminologies • J (load transfer coefficient) • Accounts for load transfer efficiency • Lower J-factors = better load transfer • Between 3.8 (undoweled JPCP) and 2.3 (CRCP with tied shoulders) • Ec (PCC elastic modulus) • 4,000,000 psi is a good estimate • k (modulus of subgrade reaction) • Estimates the support of the PCC slab by the underlying layers • Usually between 50 and 1000 psi/inch Dr. Wa'el M. Albawwab albawwab@gmail.com
Reliability Reliability = P [Y > X] X = Probability distribution of stress(e.g., from loading, environment, etc.) Y = Probability distribution of strength(variations in construction, material, etc.) Probability Stress/Strength Dr. Wa'el M. Albawwab albawwab@gmail.com
Basic AASHTO Flexible PavementDesign Method Determine the desired terminal serviceability, pt Convert traffic volumes to number of equivalent 18-kip single axle loads (ESAL) Determine the structural number, SN Determine the layer coefficients, ai Solve layer thickness equations for individual layer thickness Dr. Wa'el M. Albawwab albawwab@gmail.com
Basic AASHTO Rigid PavementDesign Method Select terminal serviceability Determine number of ESALs Determine the modulus of sub-grade reaction Determine the slab thickness Dr. Wa'el M. Albawwab albawwab@gmail.com
Economic Analysis Different treatments results in different designs Evaluate cost of different alternatives Dr. Wa'el M. Albawwab albawwab@gmail.com
Sensitivity Analysis Input different values of traffic volume Compare resulting differences in pavement Fairly significant differences in ADT do not yield equally significant differences in pavement thickness Dr. Wa'el M. Albawwab albawwab@gmail.com
