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AASHTO Rigid PavementDesign Procedure

Reference:AASHTO Guide for the Designof Pavement Structures, 1993

Rigid Pavement Types

JPCP

JRCP

CRCP

Design Methods withProvisions for Establishing

PCC Slab Thickness Reinforcing Steel Requirements Joint Design

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AASHTO Pavement Design

History 1959 (guidelines)

1961, 1972, 1986, 1993, 20XX Basis

AASHO Road Test (1958-60) Ottawa, IL Regression analysis, accelerated loading,flexible & rigid

AASHO Road Test

Experimental design 200 combinations of surfacethickness & subbase Surface: 2.5-12 in Granular subbase: 0-9 in

AASHTO Design

Design criteria smoothness, cracking, & patching

Limitations Pavement materials & subgrade 2 yr testing Identical axle loads & configurations

PSI=5.411.78log(1+SV)0.09(C+P)0.5

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AASHTO Design

Determine Slab Thickness, D D = f(PSI,W18,R,S0,k,Ec,Sc,J,Cd)

D

Subgrade (SG)

PCC surface

SubbaseDsb

Serviceability Concept Pavements ability to Serve the typeof Traffic Using the Facility

PSI = Po - Pt

Time

PSI

Po

Pt

Serviceability Loss (PSI)

PSI = Po - Pt Po = Initial PSI

4.5 for Rigid

Pt = Terminal PSI f(facility classification)

Facility Pt

Interstate 3.0

Urban 2.5

Rural 2.0

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AASHTO Terminology

Performance or design period Initial construction to terminalserviceability

Analysis period Time of design strategy, includes atleast one rehab

High volume 30-40 yr Low volume 15-20 yr

AASHTO Terminology

W18 = Design ESAL See Traffic Notes EALF =f(D and Pt) Recall Lane Distribution Differences

AASHTO Terminology

Reliability (R)

Facility Urban Rural

Interstate 85-99.9 80-99.9

Principal

arterial80-99 75-95

Collectors 80-95 75-95

Local 50-80 50-80

AASHTO Table 2.2

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AASHTO Terminology

Overall Standard Deviation (S0)

Standard error of the estimate fortraffic & performance

Rigid = 0.25 - 0.35

Material Properties

Effective Modulus of SubgradeReaction (k)

Subgrade Resilient Modulus (MR) Subbase Resilient Modulus (Esb) Several Correction Factors

PCC Elastic Modulus (Ec)

PCC Modulus of Rupture (Sc)

Effective Modulus of

Subgrade Reaction f(4 Parameters):

Seasonal effects on subgrade MR Type and thickness of subbase Effect of potential erosion of subbase Depth to bedrock

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Subbase Recommendations

AASHTO Materials -Environmental Effects

Effective modulus of subgradereaction Softer subgrade sustains more damage Recall Relative Damage Ur Similar approach employed

Establishing keff Obtain Seasonal Subgrade and Subbase

Moduli Data Determine Composite k (k)-Figure 3.3 Determine Modified k = f(depth to rigidfoundation)-Figure 3.4

Determine Average Relative Damage(ur)-Figure 3.5

Correct for Loss of Support-Table 2.7and Figure 3.6

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Subgrade and SubbaseModuli

Seasonal Variations Affect Both Measure Over Seasons AASHTO T274 Use Correlations if Necessary

Composite k (k)

Dsb = 6

Esb = 20,000psi

MR = 7,000psi

k = 400pci

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Modify Composite k

Dsg = Distance from top of subgrade toa rigid layer (bedrock)

D

Subgrade (SG)

PCC surface

SubbaseDsb

Dsg

Bedrock

Modify Composite k

Dsg = 5

k = 230pciMR = 4,000psi

k = 300pci

If No Subbase

k =MR

19.4

MR = subgrade resilient modulus

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Relative Damage (ur)

D = 9

k mod = 540pci

ur = 60%

Average Relative Damage

Ur =Urn

Similar to Flexible Subgrade Modulus

See Bottom Figure 3.5

Use Average Relative Damage in Figure 3.5

to Solve for Effective k

Loss of Support Correction

Attempt to Account for Pumping

Potential Apply correction to Effective k

Degree of LS by Material Type (Table2.7)

LS factor (Figure 3.6)

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Loss of Support

SubbaseQuality

Loss of Support

Loss of Support (LS)

Loss of Support

LS = 1.0

keff = 540pci

Corr keff=170pci

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Example keff Determination

Granular Subbase 6 Thick

5 Depth to Rigid Foundation Assumed D = 9