dowel and tie bars in concrete pavement joints: theory · pdf file2nd international conference...

Dowel and Tie Bars in

Concrete Pavement Joints:

Theory and Practice

Lev Khazanovich

Associate Professor

University of Minnesota

November 2, 2011

2nd International Conference on Best

Practices for Concrete Pavements

• Introduction • Pavement joints, dowels, and tie bars

• Benefits of dowel and tie bars

• Dowel and tie bar design

• Construction

• Summary

Presentation Outline

November 2, 2011



November 2, 2011



Transverse

joints

Longitudinal

joints

• Dowel bars

• Placed across transverse joints at the mid-depth of

the slab

• Transfer load from one slab to another without

preventing the joint from opening

• Commonly made of round, smooth, epoxy coated

steel bars

• Reduce joint faulting and corner cracking

Dowel and Tie Bars

November 2, 2011



• Tie bars

• Placed across longitudinal joints at the mid-depth of the

slab

• Prevent lanes from separation and differential

deflections

• Made of deformed epoxy coated steel

• Reduce transverse cracking

Dowel and Tie Bars

November 2, 2011



Dowels and Tie Bars

November 2, 2011



Transverse contraction

joint

Dower bars

Longitudinal construction

joint

Tie bars

Courtesy of Dr. Darter

• Introduction

• Benefits of dowel and tie bars • Theory

• Mechanism of load transfer

• Effect on deflections and stresses

• Effect on performance

• Practice

• Cost


• Construction

• Summary


November 2, 2011



Why do we need tie bars?

November 2, 2011



Lane separation

None or inadequate tie bar design

Effect of tie bars on pavement responses

November 2, 2011



Aggregate

interlocking No tie bars

High stresses

High deflections

Pavement

distresses

Tie bars

Low stresses

Low deflections Good joint

performance

ISLAB2000 Finite Element Model

November 2, 2011



80 kN single axle load

Deflection

0.0212

0.0194

0.0176

0.0158

0.0140

0.0122

0.0104

0.0086

0.0068

0.0050

0.0032

0.0014

-0.0004

-0.0021

Deflections without Tie Bars

November 2, 2011



Nontied joint

Max Deflection = 0.54 mm

Deflection

0.0128

0.0118

0.0107

0.0096

0.0085

0.0074

0.0064

0.0053

0.0042

0.0031

0.0020

0.0010

-0.0001

-0.0012

Effect of Dowels on Deflections

November 2, 2011



Tied joint


Deflections with Tie Bars

Effect of Tie Bars on PCC Stresses

November 2, 2011



Nontied joint

Max Stress = 2051 kPa

Tied joint


Principal Stresses at the Slab Bottom

X-direction

Y-d

irection

Stresses in Y-direction

293

269

245

222

198

174

151

127

103

80

56

33

9

-15

X-direction

Y-d

irection

Stresses in Y-direction

229

210

192

174

155

137

118

100

81

63

44

26

7

-11

Why do we need dowels?

November 2, 2011



Faulted Joint

None or inadequate dowel bar design

Effect of dowels on pavement responses

November 2, 2011



Traffic direction

Aggregate

interlocking No dowels

High stresses

High deflections

Pavement

distresses

Traffic direction

Aggregate

Interlock

Loss of support

Rapid slab rebound

Rapid movement of

materials backward

Approach slab Leave slab

Effect of dowels on pavement responses

November 2, 2011



Traffic direction No differential deflection,

No faulting

Traffic direction

Dowels

Low stresses

Low deflections Good joint

performance

Effect of Dowels on Stresses and

Deflection

November 2, 2011



ISLAB2000


November 2, 2011



Nondoweled joint



November 2, 2011



Deflection

0.0229

0.0210

0.0191

0.0171

0.0152

0.0133

0.0114

0.0095

0.0076

0.0057

0.0037

0.0018

-0.0001

-0.0020

Doweled joint


Effect of Dowels on Stresses

November 2, 2011



X-direction

Y-d

irection

Principal Stresses

160

142

125

107

89

72

54

37

19

2

-16

-33

-51

-68

X-direction

Y-d

irection

Principal Stresses

116

104

92

80

68

57

45

33

21

9

-3

-15

-26

-38

Nondoweled joint


Doweled joint


Principal Stresses at the Slab Bottom

Federal Highway Administration Long Term

Pavement Performance Studies

1. Evaluation of Joint and Crack Load Transfer

(Khazanovich and Gotlif 2002)

2. Common Characteristics of Good and Poorly

Performing PCC Pavements (Khazanovich et al.

1997)

Almost 150 pavement sections located

throughout USA

Dowel and Tie Bars?

November 2, 2011



Effect on Load Transfer Efficiency

November 2, 2011



0

10

20

30

40

50

60

70

80

90

100

20 30 40 50 60 70 80 90 100 110

Mean LTE, percentOOOO

Cu

mu

lati

ve

Per

cen

tag

e o

f P

ass

es

Doweled Nondoweled

Good

Poor

nondoweled

doweled

Joint Load Transfer Efficiency, percent

Effect of Dowels on Faulting

November 2, 2011



Faulting (mm)

Cum

ula

tive

pe

rcen

t o

f sectio

ns

Doweled

0

10

20

30

40

50

60

70

80

90

100

0.00 0.05 0.10 0.15 0.20 0.25 0.30 0.35 0.40

Faulting, in

Cum

ula

tive

freq

uen

cy d

istr

ibuti

on (

%)

Nondoweled Doweled

Nondoweled

2.0 4.0 6.0 8.0

Doweled

Good Poor Normal

Smith et al. 1990

Dowels increase the initial cost between

5 and 8 percent, but increase the load

carrying capacity over 100 percent

Gharaibeh and M. I. Darter 2001

The use of dowel bars increases the

initial pavement life by about 60 percent

and results in similar total Life Cycle

Cost reduction than not using dowels.

Benefits of Dowels

November 2, 2011



• Introduction


• Dowel and tie bar design – Diameter

– Length

– Spacing

• Construction

• Summary


November 2, 2011



Germany

25 mm

USA

Concrete thickness Dowel diameter

<200 mm 25 mm

200 - 250 mm 32 mm

>250 mm 38 mm

MEPDG – based on the maximum allowed faulting

Dowel Diameter

November 2, 2011



November 2, 2011



0.00

0.05

0.10

0.15

0.20

0.25

0 50 100 150 200 250 300 350 400 450 500

AADTT in one direction

Fau

ltin

g (

in)

ND

D=1

D=1.25

D=1.5

Nondoweled

DD=25 mm

Design period: 20 years

Slab thickness: 200 mm.

DD=32 mm

DD=38 mm

Faultin

g (

mm

)

Number of Trucks per days

2.50

5.00

Effect of Dowel Diameter on Faulting

Khazanovich et al. 2004

Effect of Dowels Diameter on Bearing

Stresses

November 2, 2011



Dowel Diameter, mm Concrete Bearing Stress, MPa

25 17.3

32 12.7

38 9.3

• Dowel length

Germany: 500 mm

USA: 450 mm

Minnesota: 380 mm

• Dowel spacing

Germany: 250 mm in wheel path

500 mm outside of the wheel path

USA: 300 mm

non-uniform

Dowel Length and Spacing

November 2, 2011



November 2, 2011



Non-uniform Dowels Spacing

5 @ 300 MM 5 @ 300 MM 900 MM

Dowels in the wheel paths only

• Tie bar diameter

Austria: 14 mm

Germany: 20 mm

USA: 12.5 and 16 mm

Tie bar Diameter

November 2, 2011



• Tie bar length

Austria: 700 mm

Germany: 800 mm

USA: 760 mm

• Tie bar spacing

Austria: 3 bars/slab

Germany: construction joints: 5 bars /slab

contraction joints: 3 bars/slab

USA: table

Tie Bar Length and Spacing

November 2, 2011



FHWA Tie Bar Spacing

November 2, 2011



PCC thickness (mm)

Distance to free edge (mm)

3000 3600 4800 7200

225 650 550 400 275

250 600 500 400 250

275 550 450 350 225

300 500 400 325 225

Bar diameter: 12.5 mm

Steel yield strength: 280 MPA

FHWA Tie Bar Spacing

November 2, 2011



PCC thickness (mm)

Distance to free edge (mm)

3000 3600 4800 7200

225 1050 875 650 425

250 950 775 600 400

275 850 725 525 350

300 775 650 500 325

Bar diameter: 16 mm

Steel yield strength: 280 MPa)

• Introduction



• Construction – Installation

– Common problems

– Evaluation

– Fixing

• Summary


November 2, 2011



Installation

November 2, 2011



• Dower bars

– Dowel baskets

– Dowel bar inserter (DBI)

A bond breaker (typically, grease) must be

applied prior to placement

• Tie bars

– Machine-place

– Placed by hand

– Chairs

– Drilled and grouted

Dowel Baskets

November 2, 2011



Dowel Bar Inserter

November 2, 2011



NHI

Tie Bar Installation

November 2, 2011



Tie bar chairs Drilled

Common Installation Problems

November 2, 2011



Happy families are all alike;

every unhappy family is unhappy in its

own way.

Todas as famílias felizes são iguais.

Todas as famílias infelizes são diferentes.

Lev Tolstoy “Anna Karenina”

Common Installation Problems

November 2, 2011



• Bars are missing or misplaced

•Poorly adjusted equipment

•Damaged dowel baskets

•Improper basket anchoring

• Concrete around bars is poorly consolidated

•Poorly adjusted equipment

•Too stiff mix (often caused by mix delays)

Common Problems Problems

November 2, 2011



– Dowel and tie bar misplacement

– Dowel and tie bars are too close to each other

– Poor consolidation of concrete around dowels

and tie bars

Vertical Position Problem

November 2, 2011



Dowel Installation

A tie bar is too far from the

mid-depth.

Concrete cover is too low.


November 2, 2011



Dowel Installation

If a bar is too close to the

top surface


November 2, 2011



Dowel Installation

Cracking occurred near the joint the next

morning

Common Problems

November 2, 2011



Dowel Installation

Common Problems

November 2, 2011



Dowel Installation

The tie is too close to the dowel

Poor Consolidation of Concrete

November 2, 2011



Dowel Installation

Dowel bar

Entrapped air

The PCC mix was way too stiff

due to paving delays.

300 meters had to be

removed and replaced.

Three Ways to Achieve Good

Placement

• Inspection

• Inspection

• Inspection

How to Avoid Problems

November 2, 2011



NDT for Bar Placement

November 2, 2011



Non-destructive Methods for Bar Location

• Magnetic (MIT SCAN)

• Ground-penetrating radar (GPR)

• Ultrasound tomography

MIT SCAN

November 2, 2011



•Advantages

• Simple

• Accurate

• Relatively fast

•Disadvantages

• Must be calibrated for specific dowels and tie bars

• May be have problems when dowel baskets are used

• Cannot determine condition of concrete around dowel or

tie bars

MIT SCAN

November 2, 2011



Ground-Penetrating Radar (GPR)

November 2, 2011



Advantages

• Fast – can be used for initial screening/gross bar

misplacements

Disadvantages

• Data interpretation is time-consuming

•Resolution is not very high

Rister and Graves 2011

Ultrasound Tomography

November 2, 2011



Advantages

• Determines not only bar

position but also condition of

concrete around dowel/tie bar

Disadvantages

• Relatively slow


November 2, 2011



Lane 3

Shoulder

Longitudinal Joint

Measurement Point

18 in.

Pavement-Base Interface

Dowels


November 2, 2011



Crack Reflection

Dep

th,

mm

0

150

300

dowels joint

Alignment Tolerances

November 2, 2011



Washington DOT tolerances for tie bars

• Vertical translation: 25-mm

• Horizontal translation: 25-mm

• Vertical tilt: 25 mm

• Horizontal skew: 25 mm


November 2, 2011



Ministry of Transportation of Ontario (MTO 2007)

tolerances for tie bars

• Depth tolerance

– PCC thickness 200 mm : -6 mm / +12 mm

– PCC thickness 250 mm : -15 mm/ +25 mm

• Longitudinal translation: 50-mm

• Vertical tilt: 15 mm

• Horizontal skew: 15 mm


November 2, 2011



http://onlinepubs.trb.org/onlinepubs/nchrp/nchrp_rpt_637.p

df

NCHRP 10-69 Study

University of Minnesota (Prime Contractor)

Lev Khazanovich

Kyle Hoegh

Mark Snyder


November 2, 2011



Field Testing of 60 pavement sections across USA

The majority of joints had dowel misalignments

within the following limits:

Vertical translation – +/- 13 mm

Horizontal skew – +/- 13 mm

Vertical tilt - +/- 13 mm

Longitudinal translation - +/- 50 mm

Dowel misalignment within these limits does not

appear to significantly affect pavement

performance.

Laboratory Testing

November 2, 2011



Pullout Test Shear Test

Dowel Installation

• 16 beams ,64 dowels with

precise misalignments

• Pullout test

• Shear test

• Ultimate one time load

application

• Repeated load application

Analytical Modeling

November 2, 2011



Dowel Installation

Joint

Plane of Symmetry

60”

180”

8”

Exaggerated joint opening

Analytical and Laboratory Results

November 2, 2011



Good Bad

Vertical position Mid-depth +/- 13 mm Concrete cover <50

mm

Concrete cover < saw

cut depth

Embedment length >175 mm < 50 mm

Rotation < 25 mm/450 mm > 75 / 450 mm

• Dowel greasing is very important!

• Dowel alignment

• Dowel misalignment has the same apparent effect

on joint performance as a reduction in dowel

diameter

Equivalent Dowel Diameter Concept

November 2, 2011



0drrrrd hsvtccembeq

remb <1 if longitudinal translation is greater than 50 mm

rcc <1 if vertical translation is greater than 12.5 mm

rvt < 1 if vertical tilt is greater than 12.5 mm

rhs <1 if horizontal skew is greater 12.5 mm

d0 = nominal dowel diameter Predicted Faulting

0.00

0.02

0.04

0.06

0.08

0.10

0.12

0.14

0 2 4 6 8 10 12 14 16 18 20 22

Pavement age, years

Faultin

g, in

Equivalent dowel diameter=1.32 in

Nominal dowel diameter=1.5 in

Faulting Limit

D=38 mm

D=33 mm

1

1 mm

2 mm

3 mm

MEPDG Faulting Prediction, mm

If the Bars Misplaced ..

November 2, 2011



•It is NOT OK to have dowel positioned out of specification

•Do not harm – try to minimize invasive treatment

•How to react

•Carefully evaluate the problem (determine actual bar

location)

• Evaluate short-term and long-term effects

•Develop remedy plan

If the Bars are Misplaced ..

November 2, 2011



•Case A: a dowel or tie bar is to close to the top surface

(<50 mm)

•Cut the dowel through

•Develop penalty and/or retrofit dowels or tie bars

•Case B: Other types of misplacements

•Evaluate effective dowel/tie bar diameter

•Predict performance

•Develop penalty and/or retrofit dowel or tie bar

Summary

November 2, 2011



• If properly designed and installed, dowels and tie bars

significantly improve performance of pavement joints

• Although they increase the initial cost, dowel and tie bars

reduce Life Cycle Cost

• Both dowel baskets and dowel bar inserters are good

installation alternatives

• Improper dowel installation may reduce effectiveness of

the dowels and tie bars

•Nondestructive testing methods give an opportunity to

trouble shoot the problems and determine their extent

• The best approach is to use NDT during construction to

identify and fix the problem

dowel and tie bars in concrete pavement joints: theory · pdf file2nd international conference...

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