Lecture 14 - The Pennsylvania State University Department of Civil and Environmental Engineering Lecture 14 Rigid Pavement Design CE 321 Highway

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Unformatted text preview: The Pennsylvania State University Department of Civil and Environmental Engineering Lecture 14 Rigid Pavement Design CE 321: Highway Engineering Fall 2007 Design Principles Rigid pavements distribute wheel loads by beam action of PCC slab. Material has high elasticity modulus Beam action distributes wheel loads over large area of pavement. Reduces high stresses to subgrade soil. Beam Action of Pavement AASHTO Design Procedure Based on AASHO Road Test results. Reduction in serviceability. Applicable to following: Jointed plain (no steel reinforcement). Reinforced (welded wire fabric). Continuously reinforced (steel bars both longitudinal and transverse). PCC slab thickness is measure of pavement strength. AASHTO Rigid Pavement Design Equation log10 W18 = Z R So + 7.35[log10 (D + 1)] - 0.06 + log10 [PSI/(3.0)] 1 + [1.624 X 10 7 /(D + 1)8.46 ] Sc ' C d [ D 0.75 - 1.132] + (4.22 - 0.32TSI) log10 215.63 J D 0.75 - 18.42 /( E / k ) 0.25 c { [ } W18 = ZR = D= TSI = 18k equivalent single axle load reliability PCC slab thickness in inches pavement's terminal serviceability index Sc' = Cd = J= Ec = MR = concrete modulus of rupture (psi) drainage coefficient load transfer coefficient concrete elastic modulus in psi resilient modulus of subgrade soil So = overall standard deviation PSI = design present serviceability "loss" AASHTO Rigid Pavement Design Equation Traffic ESALs (W18) Function of slab thickness Tables 4.7, 4.8, and 4.9 Reliability (ZR) Probability that serviceability is maintained at adequate levels; denoted "R" in nomograph Standard Deviation (So) Engineer's inability to accurately estimate future 18-kip ESALs, variability in materials and construction practices Assume 0.45 if unknown AASHTO Rigid Pavement Design Equation 2 Terminal Serviceability Index (TSI) Pavement no longer performs in serviceable manner Amount of serviceability loss (PSI) Initial PSI TSI Concrete modulus of rupture, Sc' Measure of concrete tensile strength (avg. 28-day strength) Ranges from 500 to 1,200 psi Drainage coefficient (Cd) Drainage characteristics of subgrade "Good" drainage, Cd = 1.0 (sandy soil) AASHTO Rigid Pavement Design Equation 3 Load transfer coefficient (J) Accounts for ability of PCC slab to transfer load to another PCC slab across joints J = 3.2 (d'less) with dowel bars at joints Concrete modulus of elasticity (Ec) Use E = 3 to 7 M psi Modulus of subgrade reaction (k) Moisture content and density of soil Range: 100 to 800 pci Relationship between CBR and k Relationship of CBR and k CBR 2 10 20 25 40 50 75 100 k (pci) 100 200 250 290 420 500 680 800 Directional W18 in Design Lane Number of Directional Lanes 1 2 3 4 Proportion of Direction W18 in Design Lane (PDL) 1.00 0.80 1.00 0.60 0.80 0.50 0.75 Design chart for rigid pavement based on input variables Segment #1 Design chart for rigid pavement based on input variables Segment #2 Example Problem #1 Traffic = use 26,000,000 ESAL for 20 yr. Design Life Reliability = 90% Standard Deviation = 0.45 7,000 psi compressive strength 10% = 700 psi modulus of rupture Subgrade = 300 pci Example Problem #1 (con't) E concrete = 6 x 106 psi J = 3.2 Cd = 1.0 psi (4.5 to 2.5) use 2.0 Example Problem #1 (con't) Segment #1 Ec = 6 x 106 psi Sc' = 700 psi Cd = 1.0 J = 3.2 k = 300 pci Match Line = 65 Example Problem #1 Segment #2 From nomograph: Need 11.5 in. Use 12 in. slab Match Line = 65 PSI = 2.0 18k = 26 Std. Dev. = 0.45 Reliability = 90 % ...
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This note was uploaded on 04/11/2008 for the course C E 321 taught by Professor Pietrucha,martinkeller,michaelwi during the Spring '07 term at Pennsylvania State University, University Park.

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Lecture 14 - The Pennsylvania State University Department of Civil and Environmental Engineering Lecture 14 Rigid Pavement Design CE 321 Highway

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