1- Analysis & Design of PCCP - Shiraz

7/27/2019 1- Analysis & Design of PCCP - Shiraz

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IMCYCSeminar on Design and Construction

of Concrete Pavements

Mexico City, Mexico

October 22, 2004

Seminar Outline

Welcome, Introductions, Workshop Objectives

Part 1 Analysis & Design of PCCP

Part 2 Concrete Pavement Construction

Part 3 Evaluation of PCCP

Part 4 PCCP Maint., Repair & Rehabilitation

Part 5 New Concrete Pavement Technologies

Analysis and Design of Concrete

Pavements and Overlays


2/25

Concrete Pavement

Fundamentals

Pavement Terminology

crackingPavement thickness

Transverse joint

Dowel bars

Concrete Slab

Subgrade

Base & subbase

Longitudinal joint

Tie bars

And, shoulders PCC or AC

Joint Faulting

PCCP Types

JPCP 14 to 18 ft joint spacing

t = 6 in (streets) to 8 to 10 in (secondaryroads) to 11 to 14 in (primary and interstatesystems)

Dowels & stabilized base formedium/heavy volume of truck traffic

CRCP

Steel: 0.65 to 0.80%

Cracking at 3 to 6 ft, very tight cracks

Terminal joints at structures


3/25

JPCP

(14 to 18 ft)

Transverse Joints

(with or without dowels)

Longitudinal Joint

(with tiebars)

PLAN

VIEW(14 to 18 ft)

CRCP

Longitudinal Joint

(with tiebars)

PLAN

VIEW

Typical Crack Spacing

(3 to 8 ft)

Continuous LongitudinalReinforcement

(Deformed Bars)(0.65 to 0.8%)

Concrete Properties

Strength Flexural: 550+ psi (each 50 psi ~ 1 in)

Compressive: 4,000+ psi

Stiffness/Modulus - E: 4,000,000+ psi

Durability

Free of MRD (eg., ASR, etc)


4/25

Sources of Slab Stresses

Traffic Loads

Thermal Curling (day & night)

Moisture Warping

Shrinkage (early age & later)

Contraction and Expansion from

Temperature Changes (affected by

frictional restraint/bond to base)

Traffic Loading

Major source of stresses in pavements

Traffic load results in bending stress

(tensile stress at top/bottom of the slab)

Repeated applications can result in

fatigue cracking & joint faulting

Critical location for traffic loading is

generally along outside slab edge

Traffic Load Stresses

At slab edge:

Traffic load creates a tensile stress at

bottom of slab

At slab corner

Traffic load creates a tensile stress at top

of slab

Repeated applications can result in fatigue

cracking


5/25

Slab Stress Computation

Stress and deflection for three loading

conditions

Interior

Edge

Corner

PCC Slab

Subbase

Subgrade

PCC Slab

Subbase

PCC Slab

Base/Subbase

PCC SlabPCC SlabPCC Slab

K value

Typical Load Stress Values(Axle Load = 20,000 lb, p = 100 psi)

170240125500/stiff10

200290145100/soft10

12518090500/stiff12

240340180500/stiff8

Corner

Stress,

psi

Edge

Stress,

psi

Interior

Stress,

psi

k, pciSlab t, in.

1

1312

11109

8765

432

Truck Loading (1993Guide):

Truck factors

ESALs


6/25

Temperature Effects

Differentialtemperatures at the

top and bottom of the

PCC slab result in

slab curling Temperature

differentials are

usually expressed as

linear temperature

gradients

Depth,i

n

52 56 60 64 68 72

Temperature, oF

Top of PCC Slab

0

6

3

9

6 AM 11 AM7 PM

3 PM

Linear idealization

of 3 PM gradient

Effect of Temp. Gradients in

PCC Slabs (Curling)

Warmer at top

Cooler at top

TENSION

Slab displacementfor positivegradient

COMPRESSION

Temperature

De

pth

Temperature

Depth

Slab displacementfor negativegradient

Curling Stresses

Positive gradients producetensile stresses at the bottom ofthe pavement slab

Critical when wheel load atslab edge

Negative gradients producetensile stresses at the top of thepavement slab

Critical when wheel load atslab corner

Magnitude depends on slabproperties, support conditions,and thermal gradient


7/25

Typical Curling Stress

Values For long slabs, t = 10 in., a = 0.000005 in./in./F,

E = 4,000,000 psi, temp. diff = 30 F,

then, Edge Curling Stress = 300 psi

For slabs, 12 ft wide & 20 ft long,

then, Edge Curling Stress = 270 psi (long.)

and Edge Curling Stress = 100 psi (trans.)

12 ft

20 ft

Warping Stresses

Moisture difference between top and bottom

of slab

Greater moisture at top of slab results in

downward warping and vice versa

Moisture contents through slab in:

Wet climates fairly constant

Dry climates top is drier that bottom

Warping Stresses

Slab top wetter than bottom

Slab bottom wetter than top


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Drying Shrinkage Stresses

Loss of moisture in hardened concrete leads

to shrinkage of slab

Shrinkage resisted by friction of the base

Slab contractiondue to moisture loss

Base frictional forces

Temperature Shrinkage

Stresses

Daily/seasonal temperature changes cause

PCC slab to expand/contract

Frictional force between slab and base

creates stresses in slab

Slab contractiondue to low temps

Base frictional forces

Shrinkage Stresses (Axial)

(Important for early age)

Frictional force between slab and base

creates stresses in slab

Introduction of joints in slab reduces

magnitude of shrinkage stresses

Joints need to be provided as early as

possible


9/25

Axial Tensile Stresses

(base/subgrade drag)

= (f L )/2

Where: = slab frictional stress, psi

f = slab/base frictional factorL = slab length, ft

PCC Fatigue Damage

Determination of N

log N =f(applied stress level, PCC strength)

Log N

Stress

Level

N1 N2

1

2

Materials characteristic curve

PCCP Deflection/Load Transfer

Load-transfer => abilityto transfer load across

joint/crack

Poor load transferleads to:

Corner Cracking

Pumping of Fines

Faulting

Initial LT ~ 90+%

Need LT > 75 % inservice

Load Transfer = 100% (Good)

L= x

U= 0

Load Transfer = 0% (Poor)

L= x U= x

LT,% = Unloaded/Loaded *100


10/25

Early Age Behavior

Concerns with early age cracking

PCCP Performance Issues

Structural Performance - Ability to

withstand traffic and environmental

loadings over time (30+ years)

Distress types, extent, & severity

Deflection response

Functional Performance - Providing

users safe and comfortable ride

Ride (IRI), Friction, Noise

Operational Issues

Minimal maintenance/repairs for

high volume highways

Functional Pavement

Performance


11/25

Functional Pavement

Performance

Ability of pavement to provide smooth, safe

ride to users

Roughness/Serviceability

Texture/Friction Texture/Noise

Roughness/Smoothness Definitions

Deviations in pavement surface that affect ridequality

Caused by:

Built-in surface irregularities

Distress (traffic, environment, materialproblems)

Smoothness - Lack of roughness

Road Users - I know it when I feel it !!

PCCP Profile Measurement


12/25

Pavements that are Built Smoother

Pavements that are built smoother remain

smoother over time and last longer

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

0 5 10 15 20 25 30

Pavement Age (Years)

IRI(m

/km

)

Achieving Ride

Initial ride (controlled by specification)

In-service changes in ride (controlled by design &specification)

Requirements

Initial ride (Profile Index/IRI)

Profile Index < 12 in./mile

IRI < 75 in./mile

Low rate of degradation in ride quality overtime

IRI increase/year < 3 in./mile (av. over 20years)

Surface Texture

Influences surface friction and noise

Consists of:

Microtexture

Fine scale roughness contributed byfine aggregate in mortar

Macrotexture

Small surface channels, grooves, orindentations formed or cut


13/25

Texturing Methods PCC

Transverse tine

Longitudinal tine

Turf drag

Burlap drag

Diamond grinding

Longitudinal grooving

Exposed aggregate

Surface Friction

Force developed at

pavement-tire interface that

resists sliding

Influenced by:

Surface texture

Surface drainage (cross-

slope)

Locked-wheel trailer tester(f = ??)

International Friction Index

Achieving Safety By specification

Materials (e.g., concrete)

Finishing operations

Requirements

Initial friction characteristics (eg. FN > 50?)

Long-term friction characteristics (eg., FN > 35?)

Minimize hydro-planning potential


14/25

Texture and Noise

Motor and exhaust control noise levels for

vehicles under 35 mph

Tire-pavement interaction primary source at

greater speeds

Mainly a concern in urban areas

Factors affecting noise

Tine or groove depth

Width

Spacing

Orientation

PCC typically 3 dB(A) > AC

Proposed Texture Guidelines

Tining

3mm width

3mm depth

Random transverse spacing

10/14/16/11/10/13/15/16/11/10/21/13/10

24/27/23/31/21/34

19mm longitudinal

Concrete Pavement

Design Considerations


15/25

Concrete Pavement

Performance Requirements

Structural performance

Long life - no major distresses

Functional performance

Safety very few wet weather accidents Smoothness good ride

( A well constructed pavement with the best

materials WILL fail early if it is not designed

correctly)

Pavement Performance

Time or Traffic

Serviceability

Enhanced

Design

Standard

Design

Performance

Benefit vs.

Incremental Cost

Deficient

Design &

Constructio

nThreshold

Level

Pavement Design

Considerations Minimize failure conditions & costs

Understand typical failure mechanisms

How does a concrete pavement crack?

How does a concrete pavement fault?

How does a concrete pavement get rough?

Are there other local failure conditions that

need to be addressed?

Understand impact of design features

Minimize costs by optimizing design features


16/25

How do Concrete Pavements Fail?

Transverse

Cracking

Smoothness

(IRI)

FaultingAnd, localized

distresses (spalling)

and materials

related distresses

Allowable Distress

At end of service life

40 years for primary system (US)

20+ years for secondary system (US)

2.5 to 3.0Smoothness (IRI),

m/km

6 7Faulting, mm

10 - 15Cracked Slabs, %

ValueDistress

Concrete Pavement Design Elements

Pavement system Slab geometry & boundary conditions

Jointing and load transfer

Pavement layers (slab, base/subbase, subgrade)

Material characteristics (strength, stiffness)

Loading

Truck loading (a wide range of truck traffic & axleloadings)

Environmental (slab temp. & moisture effects)

Climatic (seasonal variations & drainage needs)

Ability to consider applicable failure modes


17/25

Developing Failure (Design) Models

- Early Testing of PCCP 1920s

Developing Failure (Design) Models

- AASHO Road Test (late 1950s)

The AASHO Road

Test equations &

design procedure

used for > 30 years,but are no longer

considered suitable

for current levels of

heavy truck traffic

conditions

Accelerated Testing &Instrumented Test Highways

Instrumented Test Sections to

calibrate/validate analysis

models >>


18/25

CC Pavement Analysis1920s to 1950s

Prof. Westergaard established techniques for

computing slab stresses & deflections

Equations developed for curling stresses due

to temperature gradients in the slab

(Bradburys chart)

Current -- 2D Finite Element Analysis

Deflections

0.0535

0.0512

0.0477

0.0442

0.0407

0.0371

0.0336

0.0301

0.0266

0.0231

0.0196

0.0161

0.0126

0.0091

0.0079

Flat Slab Condition, Tridem Axle Loading

Stresses in Y-direction

360.2

340.7

311.5

282.2

253.0

223.8

194.5

165.3

136.0

106.8

77.6

48.3

19.1

-10.1

-19.9

Load Transfer Considerations inDesign

Load-transfer is a slabs

ability to transfer part of its

load to the adjacent slab

Poor load transfer leads to:

Corner Cracking

Pumping & Faulting

Also, need to consider dowel

bearing stresses

(dowel looseness

concerns?) >>>

Load Transfer = 100% (Good)

L= x

U= 0

Load Transfer = 0% (Poor)

L= x U= x

P (


19/25

Mechanistic-Empirical

Design Procedures (US)

PCA (1984)/IRC:58-2002

200X Design Guide (Future US

AASHTO)

(New M-E procedures allow consideration of a

broad range of design features)

PCA Thickness Design

Procedure (1984)

Mechanistic stress

analysis

Calibrated to field tests,

test roads

Control criteria are:

Fatigue (cracking)

Erosion (pumping)

Windows-based computer

program (Streetpave)

Fatigue (IRC also)

Midslab loading away

from transverse joint

produces critical edge

stresses

Erosion

Corner loading

produces critical

pavement deflections

Transverse joint Transverse joint

Critical Loading Positions


20/25

Basics of Thickness Design(PCA Edge Stress & Fatigue)

Compressive strength: ~ 280

kg/cm2(4000 psi)

Flexural strength: ~ 45 kg/cm2 (650 psi)

T

C

Basics of Thickness Design (PCA)Corner Deflection / Erosion (pumping)/Faulting

Higher k-value (stiffer support) will lowerdeflections

Load transfer (dowel bars) will lowerdeflections

Non-erodible base much better

The 200X M-E Design Process

ClimateTraffic

Materials

Structure

DistressResponse

Time

Damage

Damage

Accumulation

Iterations


21/25

200X Design Inputs(3 Main Categories & 3 Levels)

Traffic

Volume

Axle load distribution

Axle configuration Climate (site specific)

Latitude, longitude, elevation, etc.

Structure

Layers, thicknesses, and materialproperties

Features joint spacing, shouldertype, layer interface, etc.

Distress Types Considered

Faulting

Transverse Cracking

Edge Punchout in CRCP

IRI for Rigid Pavements [=f(distresses)]

IRI prediction accuracy depends upon

predictive accuracy of all other Distress

Smoothness/IRISmoothness/IRI

Joint FaultingJoint Faulting

TransverseTransverse

CrackingCracking


22/25

Design Parameters Over Pavement Life

Incremental Damage Concept

Time, years

Traffic

PQC Modulus

Granular BaseModulus

DLC Modulus

Each loadapplication

2 8640

SubgradeModulus

Typical 200X Design Guide Results

Allowable 200X Guide Distress

At end of service life 40 years for primary system (US)

20+ years for secondary system (US)

2.5Smoothness (IRI)

6 7 mmFaulting

10 - 15 %Cracked Slabs

ValueDistress


23/25

Joint Spacing

0.33 0.34

0.70

0.83

0.93 0.95

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

Joint 15' Joint 17'

Design Variables

DistressRati

o

(to

Reference)

Cracking

Faulting

IRI

Reference Design

Joint Spacing = 20 ft

Cracking = 18.1%, Faulting = 0.23 in.,IRI = 192.1 in/mile

PCC Properties

0.41

3.86

1.0 1.0 1.05

1.45

0.971.18 1.08

1.60

5.52

2.00

0.0

1.0

2.0

3.0

4.0

5.0

6.0

MOR 700psi MOR 500psi Poisson's Ratio

0.2

Siliceous Gravel

(CTE=7e-6/F)

Design Variables

DistressRatio(toReference) Cracking

Faulting

IRI

Reference Design

28day MOR= 600 psi

Poisson's Ratio= 0.15

Aggregate: Limestone (CTE=5.5e-6/F)

Slab Thickness

0.35

1.23

0.80

1.37

0.87

5.00

0.0

1.0

2.0

3.0

4.0

5.0

Slab Thickness 10" Slab Thickness 14"

Design Variables

DistressRatio

(to

Reference)

CrackingFaulting

IRI

Reference DesignSlab Thickness = 12"

Cracking = 18.1%

Faulting = 0.23 in.

IRI = 192.1 in/mile


24/25

Some Recommendations

Establish national goals for NHS PCC pavements

Service life 40 years (low maintenance)

Smoothness (IRI, m/km) New:


25/25

Review & QuestionsReview & Questions

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