Chapter 9 1 Chapter 9. Highway Design for Rideability 1. Determine the loading that vehicles exert...

Chapter 9Chapter 9 11

Chapter 9. Highway Design for RideabilityChapter 9. Highway Design for Rideability

1.1. Determine the loading that vehicles exert Determine the loading that vehicles exert on the highway pavement systemon the highway pavement system

2.2. Design a section of flexible pavementDesign a section of flexible pavement3.3. Evaluate cost tradeoffs between material Evaluate cost tradeoffs between material

attributes and the thickness of pavement attributes and the thickness of pavement layerslayers

4.4. Determine the thickness of a Portland Determine the thickness of a Portland Cement Concrete slab (not covered in Cement Concrete slab (not covered in CE361)CE361)

5.5. Implement a simple pavement Implement a simple pavement management system (9.5.1 – 9.5.3 only)management system (9.5.1 – 9.5.3 only)

Chapter objectives covered by CE361: By the end of this chapter the student will be able to:


9.1 Factors in Pavement Design9.1 Factors in Pavement Design

Objectives of 9.1 & 9.2Objectives of 9.1 & 9.2• List the components in a pavement systemList the components in a pavement system• List the factors that affect pavement designList the factors that affect pavement design• Describe the impacts that trucks have on Describe the impacts that trucks have on

pavementspavements• Explain load equivalency factorsExplain load equivalency factors• Identify truck types by axle configurationsIdentify truck types by axle configurations

By the end of this section, the student will be able to...


9.1 Factors in Pavement Design9.1 Factors in Pavement Design9.1.1 History – Read

9.1.2 Two kinds of pavements

Chapter 9Chapter 944

Measured by Measured by RideabilityRideability (or (or comfort to the rider) and comfort to the rider) and Visual observationVisual observation of faults of faults (distresses such as (distresses such as cracking, rutting, and cracking, rutting, and shoving)shoving)

PSIPSI (present serviceability (present serviceability index 0 -5) – surrogate for index 0 -5) – surrogate for PSR by physical PSR by physical measurementmeasurement

PSRPSR (present serviceability (present serviceability rating 0 – 5) – subjective rating 0 – 5) – subjective rating by expert raters.rating by expert raters.

Terminal serviceability Terminal serviceability index (TSI) PSI index (TSI) PSI = 2.0 to 2.5 = 2.0 to 2.5 (unacceptable ride quality)(unacceptable ride quality)

9.1.4 Measuring pavement quality


IRI (International Roughness Index) IRI (International Roughness Index) – measure of – measure of roughness inches/mile or meters/km – ride-based roughness inches/mile or meters/km – ride-based which is directly a function of pavement distress – which is directly a function of pavement distress – cracking, patching, etc. cracking, patching, etc.

An IRI over 120 in/mi indicates time for rehabilitation and corresponds to a PSI of about 2.2.

Tab 9.3


MMrr: Modulus of resiliency = the elastic properties : Modulus of resiliency = the elastic properties of soil is used in flexible pavement thickness of soil is used in flexible pavement thickness designdesign

When CBR (California bearing ratio) < 6, MWhen CBR (California bearing ratio) < 6, Mrr ≈ ≈ 1500 x CBR1500 x CBR

MMrr has seasonal changes – see the next page. has seasonal changes – see the next page. This chart was omitted in the textbook. Need to This chart was omitted in the textbook. Need to determine an annual average Mdetermine an annual average Mrr to use in to use in pavement design.pavement design.

9.1.5 Soil characteristics

This topic is covered in detail in CEEn563, taught by Dr. Guthrie.


EnvironmentEnvironment Temperature and rainfall

affect the level of strength of the subgrade, reflected on the value of resilient modulus. AASHTO developed a chart that helps you to estimate the effective roadbed soil resilient modulus using the serviceability criteria (in terms of “relative damage, uf.”)

Determine the average uf. value and obtain Mr from the chart or the equation of uf. . The bar on the right is used twice: Once to read uf value for each month’s sample Mr, then to read annual average Mr using the average uf value.

Step 1

Step 3

Step 2


9.2 Determining Loads from Truck Traffic9.2 Determining Loads from Truck Traffic

Truck traffic is the major cause of pavement Truck traffic is the major cause of pavement damages. And truck loading is converted to damages. And truck loading is converted to ESALs (equivalent single-axle loads) for ESALs (equivalent single-axle loads) for pavement thickness design (the AASHTO design pavement thickness design (the AASHTO design method)method)

The objective is to estimate the ESALs that will The objective is to estimate the ESALs that will cause a degradation of the PSI to 2 or 2.5 from cause a degradation of the PSI to 2 or 2.5 from its initial value of 4.5 to 5. The annual ESALs are its initial value of 4.5 to 5. The annual ESALs are calculated from the expected mix of daily truck calculated from the expected mix of daily truck traffic and summed for the year.traffic and summed for the year.


9.2.1 Determining equivalent single-axle load

4

444

4

44

4

550,47

44.286.038.12.02.33

32

2.33

36

18

12

200,33

4.32.32.018

174

18

12

000,18

lb

WESAL

ESAL

lb

WESAL

ESAL

lb

WESAL

TridemTridem

TandemTandem

SingleSingle

Read 9.2.2 and 9.2.3.

Fig 9.5

Fig 9.6


9.2.4 Determining lifetime ESALs for pavement design

g

gAnnualESALESAL

N 11

This is like calculating a future value of a series of annual payments with interest rate, g.

We will walk through Examples 9.1 and 9.2.

AnnualESAL

Future total ESAL

N years: design horizon


9.3 Flexible Pavement Design9.3 Flexible Pavement Design

9.3.1 The AASHTO Road Test

Read to know the history of the AASHTO flexible pavement thickness design formula,

Done in Ottawa, Ill. 1950 - 1962

9.3.2 Materials for asphalt pavements

Asphalt concrete (surface layer):

• Must resist deformation from loads

• Be skid resistant (even when wet)

• Be impervious to most weather and deicing chemicals


9.3.3 Pavement layers and the structural number

Surface layer of hot Surface layer of hot mix asphalt mix asphalt (typically 3 to 4 (typically 3 to 4 inches)inches)

““black top” = black top” = bitumen + bitumen + aggregatesaggregates

Base course Base course (typically 6 to 12 (typically 6 to 12 inches)inches)

Unbound, untreated Unbound, untreated course aggregate; course aggregate; sometimes treatedsometimes treated

Subbase course Subbase course (depends on the (depends on the subgrade)subgrade)

Right below base Right below base course; heavy course; heavy control of the fines control of the fines

Subgrade – soil Subgrade – soil under pavementunder pavement

Either local material Either local material or replacedor replaced

Structural Number Structural Number (SN)(SN)

Reflects strength of Reflects strength of the total pavement the total pavement thicknessthickness


Structural number of a pavementStructural number of a pavement

SN reflects the total pavement thickness, including the capability of the soil or subgrade to provide sufficient resiliency during the repeated loadings to maintain the desired serviceability (PSI).

subbasebasehmahma mdamdadaSN

mdamdadaSN

)**()**(33322211

a1, a2, a3 = coefficients of relative strength per inch

d1, d2, d3 = thickness in inches, d1 being surface layer

mi = modifiers for more than normal amounts of moisture, mi = 1.0 unless otherwise specified (A table contains m values was omitted in 2nd edition. In this class, m = 1.0 is used.)

hma = hot mix asphalt


Definition of drainage quality and finding Definition of drainage quality and finding recommended recommended mmii values values

Time required to drain the base/subbase layer to 50% saturation of free water.

If “Fair” and 30% exposure, then mi is 0.80.

Step 1

Step 2


9.3.4 Fitting the design variables together

subbasebasehmahma mdamdadaSN

mdamdadaSN

)**()**(33322211

• The properties (i.e. layer coefficients in the equation above) of each layer plays a major role in determining the thickness of each layer.

• Once the required structural number of a pavement section is determined, the layers are computed by using the AASHTO layered analysis method.

• It is assumed that the structural capacity of the pavement is the sum of the structural capacity of each of its layers.

07.8log32.2

)1/(109440.0

)5.12.4/(log

20.01log36.9log

10

19.510

101810

r

oR

M

SN

PSI

SNSZW


Simplify this as f(W18) = f(ZRSo) + f(SN)

We will keep the ESAL value (W18) constant and try to prove whether ZR must be negative or not. Note that So and SN are always positive. Standard deviation is always positive because it is a physical difference from the mean value, and SN is also positive because it implies pavement thickness.

07.8log32.2

)1/(109440.0

)5.12.4/(log

20.01log36.9log

10

19.510

101810

r

oR

M

SN

PSI

SNSZW

ESAL is an estimated value. It may actually more or less. In the design formula, however, the ESAL value is set to a constant. Then, to make sure the pavement survive, you have to have a thicker one than the thickness that the estimated ESAL requires. To make that happen in the design formula, we need to subtract a value from the RHS. Hence, the reliability factor must be negative (see Table 9.7). The only way to make ZRSo a subtraction is to have a negative value of ZR because So is always positive. In return f(SN) must be bigger to make up the difference, resulting in larger SN needed. S0

2 accounts for the chance variation in the traffic forecast and the chance variation in actual pavement performance for a given design period traffic, W18.


Nomograph for the AASHTO flexible Nomograph for the AASHTO flexible pavement design methodpavement design method

Pivot pt.

Finding SN for base course, subbase, & subgrade (see p.9.22).

Data for point D. Mr of subgrade assumed to be 5000 psi


Once the overall structural number for the Once the overall structural number for the pavement has been found, the layered analysis pavement has been found, the layered analysis to find the thickness of each pavement layer to find the thickness of each pavement layer can begin.can begin.

aaii and and mmii values for the layers must be values for the layers must be determined given material strength (determined given material strength (MMrr) and ) and drainage characteristics datadrainage characteristics data

Must meet minimum thickness standardsMust meet minimum thickness standards

9.3.5 Performing the layered analysis

Tab 9.8


Structural layer coefficients (Structural layer coefficients (aaii))

Asphalt Concrete, a1

Granular base layer for untreated, a2

Fig 9.14

Fig 9.15


Structural layer coefficients (cont)Structural layer coefficients (cont)

Cement-treated base, a2 Subbase, a3

OmittedFig 9.15


Determining Determining mmii values ( values (mmii = 1 unless otherwise = 1 unless otherwise

specified)specified)

Time required to drain the base/subbase layer to 50% saturation.

If “Fair” and 30% exposure, then mi is 0.80.

Step 1

Step 2


Problem 9.13 as an exampleProblem 9.13 as an example


Example 9.4: Pavement Design Example 9.4: Pavement Design AlternativesAlternatives

We will walk through this example, We will walk through this example, and you must read it before you and you must read it before you come to class. come to class.

Example 9.4 shows you how we can Example 9.4 shows you how we can minimize the cost of pavement minimize the cost of pavement construction, while meeting SN construction, while meeting SN requirements, by modifying layer requirements, by modifying layer thicknesses.thicknesses.


9.5 Pavement Management System9.5 Pavement Management System PMS = A pavement management system (PMS) is a set of tools PMS = A pavement management system (PMS) is a set of tools

or methods that assist decision makers in finding optimum or methods that assist decision makers in finding optimum strategies for providing and maintaining pavements in a strategies for providing and maintaining pavements in a serviceable condition over a given period of time.serviceable condition over a given period of time.

Intermodal Surface Transportation Efficiency Act of 1991 (ISTEA Intermodal Surface Transportation Efficiency Act of 1991 (ISTEA 91) required all States to have a PMS that covered all Federal-91) required all States to have a PMS that covered all Federal-Aid highways; but this requirement was rescinded in 1995.Aid highways; but this requirement was rescinded in 1995.

“A Pavement Management System is designed to provide objective information and useful data for analysis so that highway managers can make consistent, cost-effective, and defensible decisions related to the preservation of a pavement network.”

1990 AASHTO Guidelines for PMS1990 AASHTO Guidelines for PMS


Performance AnalysisPerformance Analysis

Fig. 9.27

With routine maintenance

Without routine maintenance, but with reconstruction every 5 years.


Three components of a PMSThree components of a PMS

• database which contains, as a minimum, the data required for PMS analysis:

• analysis methods to generate products useful for decision making: and,

• feedback process which

uses ongoing field observations to improve the reliability of PMS analysis.

Figure 1.2 Database as a central feature of the PMS (Haas/Hudson/Zaniewski, 63)

Planning & Programming

Project Selection

Design

Data Base Elements

Section Description

Performance-related History-related Policy-related

Geometry-related Environment-related

Cost-related

Construction Maintenance Research


Data collection componentsData collection components

Inventory:Inventory: physical pavement features including the physical pavement features including the number of lanes, length, width, surface type, functional number of lanes, length, width, surface type, functional classification, and shoulder informationclassification, and shoulder information

History:History: project dates and types of construction, project dates and types of construction, reconstruction, rehabilitation, and preventive maintenance, reconstruction, rehabilitation, and preventive maintenance, and their costsand their costs

Condition survey:Condition survey: roughness or ride, pavement distress, roughness or ride, pavement distress, rutting, and surface frictionrutting, and surface friction

Traffic:Traffic: volume, vehicle type, and load data volume, vehicle type, and load data

Data base:Data base: compilation of all data files in the PMS compilation of all data files in the PMS


Analysis ComponentsAnalysis Components Condition analysisCondition analysis: ride (PSI, IRI), distress (see Figures 9.29 : ride (PSI, IRI), distress (see Figures 9.29

and 9.30), rutting, and surface frictionand 9.30), rutting, and surface friction

Performance analysisPerformance analysis: pavement performance analysis and : pavement performance analysis and an estimate of remaining service lifean estimate of remaining service life

Investment analysisInvestment analysis: an estimate of network and project : an estimate of network and project level investment strategies (single- and multi-year period level investment strategies (single- and multi-year period analyses and life-cycle cost evaluation analyses and life-cycle cost evaluation (trade-offs analysis, (trade-offs analysis, e.g. rehabilitation or maintenance)e.g. rehabilitation or maintenance)

Engineering analysisEngineering analysis: evaluation of design, construction, : evaluation of design, construction, rehabilitation, materials, mix design, and maintenancerehabilitation, materials, mix design, and maintenance

Feedback analysisFeedback analysis: evaluation and updating of procedures : evaluation and updating of procedures and calibration of relationships using PMS performance data and calibration of relationships using PMS performance data and current engineering criteriaand current engineering criteria


Pictures from the UP North SLC Intermodal Pictures from the UP North SLC Intermodal Transfer YardTransfer Yard

Cracks Joint failures & corner cracks

Potholes Alligator cracks


Condition Analysis OutputsCondition Analysis Outputs The outputs from this module can include:

(1) ranking of all pavement segments according to types of distress and condition scores as a function of traffic or road classification;

(2) identification of MR&R strategies, which define a set of criteria (e.g., combinations of different distress levels and traffic) for assigning a particular action to each pavement segment; and

(3) estimates of funding needs for the selected treatments. The outputs are indicative of current needs based on current conditions.

Chapter 9 1 Chapter 9. Highway Design for Rideability 1. Determine the loading that vehicles exert...

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