monitoring of an interstate-25 high performance concrete bridge … · 2019-08-24 · monitoring of...

Final Report NM05STR-03

MARCH 2009

NEW MEXICO DEPARTMENT OF TRANSPORTATION

RREESSEEAARRCCHH BBUURREEAAUU

Innovation in Transportation Monitoring of an Interstate-25 High Performance Concrete Bridge with an Embedded Optical Fiber Sensor System Prepared by: New Mexico State University Las Cruces, NM Prepared for: The US Department of Transportation Federal Highway Administration

In Cooperation with: New Mexico Department of Transportation Research Bureau Albuquerque, NM

1. Report No. NM DOT CO4733

2. Government Accession No. 3. Recipient’s Catalog No. 5. Report Date March, 2009

4. Title and Subtitle Monitoring Of An Interstate-25 High Performance Concrete Bridge With An Embedded Optical Fiber Sensor System 6. Performing Organization Code.

7. Author(s) Rola Idriss, Zhiyong Liang.

8. Performing Organization Report No. NMSU 032009 10. Work Unit No. (TRAIS)

9. Performing Organization Name and Address

New Mexico State University Civil Engineering Dept. Box 30001, MSC 3CE Las Cruces, NM 88003-8001

11. Contract or Grant No. CO4733

13. Type of Report and Period Covered FINAL REPORT

12. Sponsoring Agency Name and Address NMDOT Research Bureau 7500B Pan American Freeway PO Box 94690 Albuquerque, NM 87199-4690

14. Sponsoring Agency Code

15. Supplementary Notes 16. Abstract. The I-25/Dona Ana Interchange in Las Cruces NM is a simple span, high performance concrete (HPC) prestressed girder bridge. The girders are six prestressed, BT-63 HPC girders with a span length of 112.5 ft (34.2 m). The bridge was monitored from fabrication through service with an embedded optical fiber sensor system. Thirty two Fiber Bragg Grating (FBG) optical fiber deformation sensors were installed in the beams during fabrication. The strands were 6/10 inch ( 1.5 cm ) low relaxation strands and the concrete had a design compressive strength of 8 ksi (55.2 MPa) at release and 9.5 ksi (66.5 MPa) at 28 days. The bridge was monitored for two years, from transfer of the prestressing force through service. Several topics that are studied in this project: prestress losses, camber, shear and moment girder distribution factors, impact factor, in-situ material properties and serviceability under traffic loads. The results from sensor measurements were compared to the values predicted by the AASTHO codes and other design codes or empirical equations, to check the accuracy of these codes when applied to HPC girder bridges. The project was funded by the FHWA and New Mexico DOT under the FHWA Innovative Bridge Research and Construction Program. 17. Key Words Bridge, High performance Concrete, Optical Fiber, Smart Bridge, Sensors, Monitoring, Prestress Loss, Camber, Girder Distribution Factors, serviceability.

18. Distribution Statement Available from NMDOT Research Bureau

19. Security Classi. (of this report) Unclassified

20. Security Classif. (of this page) Unclassified

21. No. of Pages 223

22. Price

MONITORING OF AN INTERSTATE-25 HIGH PERFORMANCE CONCRETE BRIDGE WITH AN EMBEDDED OPTICAL FIBER SENSOR

SYSTEM

by

Rola L. Idriss Professor

New Mexico State University

Zhiyong Liang Graduate Student

New Mexico State University

A Report on Research Sponsored by

The U.S. Department of Transportation Federal Highway Administration

in Cooperation with

New Mexico Department of Transportation

Research Bureau

March 2009

NMDOT Research Bureau 7500B Pan American Freeway NE

PO Box 94690 Albuquerque, NM 87199-4690

(505) 841-9145

© New Mexico Department of Transportation

i

NOTICE

DISCLAIMER

This report presents the results of research conducted by the author(s) and does not necessarily reflect the views of the New Mexico Department of Transportation. This report does not constitute a standard or specification.

The United States Government and the State of New Mexico do not endorse products or manufacturers. Trade or manufacturers’ names appear herein solely because they are considered essential to the objective of this report. This information is available in alternative accessible formats. To obtain an alternative format, contact the NMDOT Research Bureau, 7500B Pan American Freeway NE, Albuquerque, NM 87109 (PO Box 94690) Albuquerque,

ii

PREFACE

The I-25/Dona Ana Interchange in Las Cruces NM is a simple span, high

performance prestressed concrete (HPC) girder bridge. The girders are six

prestressed, BT-63 HPC girders with a span length of 112.5 ft (34.2 m). The bridge

was monitored from fabrication through service with an embedded optical fiber

sensor system. Thirty two Fiber Bragg Grating (FBG) optical fiber deformation

sensors were installed in the beams during fabrication. The strands were 6/10 inch

( 1.5 cm ) low relaxation strands and the concrete had a design compressive strength

of 8 ksi (55.2 MPa) at release and 9.5 ksi (66.5 MPa) at 28 days. The bridge was

monitored for two years, from transfer of the prestressing force through service.

Several topics that are studied in this project: prestress losses, camber, shear and

moment girder distribution factors, impact factor, in-situ material properties and

serviceability under traffic loads. The results from sensor measurements were

compared to the values predicted by the AASTHO codes and other design codes or

empirical equations, to check the accuracy of these codes when applied to HPC girder

bridges. The project was funded by the FHWA and New Mexico DOT under the

FHWA Innovative Bridge Research and Construction Program.

iii

TABLE OF CONTENTS

LIST OF TABLES............................................................................................................ vii

LIST OF FIGURES ........................................................................................................... ix

CHAPTER 1 INTRODUCTION AND PREVIOUS RESEARCH .............................. 1

1.1 Research Objectives ............................................................................................ 1

1.2 Previous Research on Load Distribution Factors ................................................ 4

1.3 Previous Research on Prestress Losses of HPC .................................................. 9

1.4 Previous Research on Cambers of HPC Bridge Girder..................................... 14

1.5 Previous Research on Modulus of Elasticity of HPC........................................ 18

CHAPTER 2 BRIDGE DESCRIPTION..................................................................... 24

2.1 Overview ........................................................................................................... 24

2.2 Design Data ....................................................................................................... 25

2.3 Girders Details................................................................................................... 26

CHAPTER 3 MONITORING SYSTEM AND EQUIPMENT .................................. 28

3.1 MuST System .................................................................................................... 28

3.2 Sensor Labeling ................................................................................................. 30

3.3 Installation and Other Field Work ..................................................................... 32

CHAPTER 4 DISTRIBUTION FACTORS................................................................ 50

4.1 Overview ........................................................................................................... 50

4.2 Empirical Equations .......................................................................................... 50

4.2.1 AASHTO Standard Specifications ............................................................... 50

4.2.2 AASHTO LRFD Bridge Specifications........................................................ 52

4.2.3 Empirical Equation Results......................................................................... 56

4.3 Finite Element Model ........................................................................................ 57

4.3.1 Sap 2000 ...................................................................................................... 57

4.3.2 Model Description....................................................................................... 58

4.3.3 Method to Calculate GDF Based on Finite Element Results...................... 59

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4.3.4 Finite Element Results................................................................................. 62

4.4 Field Test Using Optical Sensor System ........................................................... 63

4.4.1 Methodology for Calculation of Moment GDF Based on Sensor

Measurements....................................................................................................... 63

4.4.2 Methodology for Calculation of Shear GDF Based on Sensor Measurements

.............................................................................................................................. 66

4.4.3 Truck Test .................................................................................................... 70

4.4.4 Static Truck Test Results ............................................................................. 74

4.5 Comparison and Conclusions on GDF .............................................................. 75

4.5.1 Comparison of Load Test to Finite Element Results................................... 75

4.5.2 Comparison of Load Test Results to AASHTO Codes................................. 82

4.5.3 Comparison of FEM Results to AASHTO Codes ........................................ 86

CHAPTER 5 PRESTRESS LOSSES ......................................................................... 97

5.1 Code methods and empirical equations ............................................................. 98

5.1.1 PCI General Method ................................................................................... 99

5.1.2 ACI-ASCE Method .................................................................................... 106

5.1.3 AASHTO LRFD Method............................................................................ 110

5.1.4 AASHTO LRFD Lump Sum Method.......................................................... 112

5.1.5 NCHRP Detailed Method.......................................................................... 113

5.1.6 NCHRP Approximate Method ................................................................... 120

5.1.7 Summary of the Results ............................................................................. 121

5.2 Field Test Using Optical Sensor System ......................................................... 124

5.2.1 Prestress Loss Calculation Based on Sensor Measurements.................... 124

5.2.2 Prestress Losses Result from Sensor Measurements................................. 126

5.3 Prestress Losses: Measured vs. Estimated....................................................... 129

CHAPTER 6 CAMBERS ......................................................................................... 132

6.1 PCI Method for Camber Calculation............................................................... 133

6.2 Camber Based on Sensor Measurements......................................................... 134

6.2.1 Principles to Calculate Cambers Based on Sensor Measurements .......... 134

6.2.2 Sensor Measurement Results..................................................................... 140

v

6.3 Comparison and Conclusions on Cambers...................................................... 144

CHAPTER 7 MODULUS OF ELASTICITY........................................................... 147

7.1 Code Methods and Empirical Equations ......................................................... 147

7.2 Modulus of elasticity based on sensor measurements ..................................... 149

7.2.1 Methodology to Obtain Modulus of Elasticity Using Sensor Measurements

............................................................................................................................ 149

7.2.2 Sensor Measurement Results..................................................................... 151

7.2.3 Laboratory Test Result .............................................................................. 154

7.3 Comparison and Conclusions on Modulus of Elasticity ................................. 159

CHAPTER 8 DYNAMIC TEST WITH CALIBRATION TRUCK............................... 162

8.1 Test Truck........................................................................................................ 162

8.2 Test Plan .......................................................................................................... 163

8.3 Impact Factors ................................................................................................. 166

8.3.1 AASHTO LRFD and Standard Specifications ........................................... 166

8.3.2 Impact Factor from Sensor Measurements ............................................... 167

8.3.3 Comparison and Discussion on Impact Factor......................................... 169

8.4 Girder Distribution Factor ............................................................................... 171

8.4.1 Introduction ............................................................................................... 171

8.4.2 GDF from Sensor Measurements .............................................................. 172

8.4.3 Comparison and Discussion...................................................................... 179

8.5 Deflection under Dynamic Load ..................................................................... 179

CHAPTER 9 DYNAMIC TEST UNDER REGULAR TRAFFIC................................. 183

9.1 Data Filtration.................................................................................................. 183

9.2 Impact Factor................................................................................................... 185

9.3 Girder Distribution Factors.............................................................................. 187

CHAPTER 10 SERVICEABILITY AND LOAD RATING.......................................... 190

10.1 Stress Limit.................................................................................................... 190

10.1.1 Stress Limits by AASHTO Codes............................................................. 190

10.1.2 Stresses from Sensor Measurements ....................................................... 191

10.1.3 Measured Stresses vs. the AASHTO Limits ............................................. 193

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10.2 Moment and Shear Capacity.......................................................................... 195

10.2.1 Moment Capacity by AASHTO Codes..................................................... 195

10.2.2 Shear Capacity by the AASHTO Codes................................................... 197

10.2.3 Moment and Shear from Sensor Measurements...................................... 202

10.2.4 Check the Moment and Shear Capacity by the AASHTO Codes............. 205

10.3 Deflection under Live Load........................................................................... 206

10.3.1 AASHTO Live Load Deflection Limits .................................................... 206

10.3.2 Deflection Obtained from Sensor Measurements.................................... 207

10.4 Bridge Load Rating ....................................................................................... 209

10.4.1 Introduction ............................................................................................. 209

10.4.2 Load Rating Procedures.......................................................................... 209

10.4.3 Results and Discussion............................................................................ 212

CHAPTER 11 CONCLUSIONS .................................................................................... 215

11.1 Prestress Losses ............................................................................................. 215

11.2 Camber........................................................................................................... 216

11.3 Girder Distribution Factors and Impact Factors ............................................ 216

11.4 Modulus of elasticity ..................................................................................... 218

11.5 Serviceability ................................................................................................. 218

11.6 Future Research Recommendations.......................................................... 219

REFERENCE.................................................................................................................. 221

vii

LIST OF TABLES

Table 1.1 Previous research summary on girder distribution factor................................... 9

Table 1.2 Previous research summary on prestress loss ................................................... 13

Table 1.3 Previous research summary on cambers of HPC girders.................................. 19

Table 1.4 Previous research summary on the modulus of elasticity of HPC.................... 23

Table 3.2 Sensor location in girder A, B, and C (1 inch = 25.4 mm) .............................. 37

Table 3.3 Camber after transfer on girder A, B, and C..................................................... 40

Table 3.4 Sensor location in girder D, E, and F (1 inch = 25.4 mm)................................ 42

Table 3.5 Camber after transfer on girder D, E, and F ..................................................... 43

Table 3.6 Camber during storage by laser level. Unit: inch (mm) ................................... 44

Table 4.1 AASHTO Distribution Factors Results ........................................................... 57

Table 5.1 Creep factors for various volume to surface ratios ........................................ 101

Table 5.2 Creep factors for various ages of prestress and periods of cure .................... 102

Table 5.3 Variation of creep with time after prestress transfer...................................... 103

Table 5.4 Shrinkage factors for various volume to surface ratios. ................................. 104

Table 5.5 Shrinkage coefficients for various curing times ............................................. 105

Table 5.6 Values of C .................................................................................................... 109

Table 5.7 Summary of prestress losses estimated by all methods. Unit: ksi(MPa) ........ 123

Table 5.8 Prestress losses at transfer. Unit: ksi(MPa) .................................................... 128

Table 6.1 Summary of cambers at different stages......................................................... 141

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Table 7.1 Modulus of elasticity at transfer based on sensor measurement for the first

pour ................................................................................................................................. 152

Table 7.2 Modulus of elasticity at transfer based on sensor measurement for the

second pour ..................................................................................................................... 153

Table 7.3 Cylinder test results for the first pour at transfer ............................................ 156

Table 7.4 Cylinder test results for the second pour at transfer ....................................... 157

Table 7.5 Cylinder test results at 28 days ....................................................................... 158

Table 7.6 Modulus of elasticity at transfer ..................................................................... 160

Table 7.7 Modulus of elasticity at Deck Pour................................................................. 161

Table 8.1 Truck positions for the dynamic test (ft). 1ft = 0.305 m............................... 164

Table 8.2 Impact factor when the truck moved through the left driving lane ................ 168

Table 8.3 Impact factor when the truck moved through the right driving lane .............. 169

Table 10.1 Stress limits from AASHTO codes............................................................... 191

Table 10.2 Bridge Load Rating Factors.......................................................................... 213

ix

LIST OF FIGURES

Figure 2.1 Bridge Profile ........................................................................................... 24

Figure 2.2 Bridge Cross-section ................................................................................ 25

Figure 2.3 Details of BT-63 Girders (1 inch = 25.4 mm).......................................... 27

Figure 3.1 Layout of all sensors, cables and connection boxes ................................. 29

Figure 3.2 FBG deformation sensor........................................................................... 29

Figure 3.3 Sensor labeling ......................................................................................... 32

Figure 3.4 Fabrication bed layout for the first week................................................... 33

Figure 3.5 Fabrication bed layout for the second week .............................................. 33

Figure 3.6 Fabrication bed .......................................................................................... 34

Figure 3.7 Sensor in the top flange ............................................................................. 35

Figure3.8 Sensor in the bottom................................................................................... 36

Figure 3.9 Crossed sensors ......................................................................................... 36

Figure 3.10 Cable outlet.............................................................................................. 38

Figure 3.11 Girders on the fabrication bed ................................................................. 39

Figure 3.12 Connection boxes .................................................................................... 41

Figure 3.13 Camber measurements using a laser level............................................... 43

Figure 3.14 Girders transported to the bridge site ...................................................... 45

Figure 3.15 Cross-section view of girders on the abutment ....................................... 46

Figure 3.16 Final installation of connection boxes and extension cables................... 46

Figure 3.17 Conduit for the extension cables ............................................................. 47

Figure 3.18 Central cabinet......................................................................................... 48

x

Figure 3.19 Deck pouring ........................................................................................... 49

Figure 4.1 Notional model for applying lever rule to the study bridge. ..................... 52

Figure 4.2 Truck placement for the finite element ..................................................... 59

Figure 4.3 Moment distribution factor by FEM method for the test truck ................ 62

Figure 4.4 Shear distribution factor by FEM method for the test truck..................... 63

Figure 4.5 Schematic representation of a cell equipped with parallel topology........ 64

Figure 4.6 Sensors in cross topology ........................................................................ 67

Figure 4.7 Dimensions of vehicle used for testing ..................................................... 70

Figure 4.8 Test truck position at midspan and abutment ............................................ 71

Figure 4.9 Moment distribution factors obtained from sensor measurements............ 74

Figure 4.10 Moment distribution factors obtained from sensor measurements.......... 75

Figure 4.11 Comparison of moment GDFs from FEM and field test for girder A..... 76

Figure 4.12 Comparison of moment GDFs from FEM and field test for girder B..... 76

Figure 4.13 Comparison of moment GDFs from FEM and field test for girder C..... 77

Figure 4.14 Comparison of moment GDFs from FEM and field test for girder D..... 77

Figure 4.15 Comparison of moment GDFs from FEM and field test for girder E ..... 78

Figure 4.16 Comparison of moment GDFs from FEM and field test for girder F ..... 78

Figure 4.17 Comparison of shear GDFs from FEM and field test for girder A ......... 79

Figure 4.18 Comparison of shear GDFs from FEM and field test for girder B.......... 80

Figure 4.19 Comparison of shear GDFs from FEM and field test for girder C.......... 80

Figure 4.20 Comparison of shear GDFs from FEM and field test for girder D ......... 81

Figure 4.21 Comparison of shear GDFs from FEM and field test for girder E.......... 81

xi

Figure 4.22 Comparison of shear GDFs from FEM and field test for girder F .......... 82

Figure 4.23 Comparison of measured moment GDFs for interior girders to AASHTO codes................................................................................................................... 83

Figure 4.24 Comparison of measured moment GDFs for exterior girders to AASHTO

codes................................................................................................................... 84 Figure 4.25 Comparison of measured shear GDFs for interior girders to AASHTO

codes................................................................................................................... 85 Figure 4.26 Comparison of measured shear GDFs for exterior girders to AASHTO

codes................................................................................................................... 85 Figure 4.27 Moment GDF from FEM and AASHTO codes for interior girders (1

truck) .................................................................................................................. 87 Figure 4.28 Moment GDF from FEM and AASHTO codes for interior girders (2

trucks)................................................................................................................. 87 Figure 4.29 Moment GDF from FEM and AASHTO codes for interior girders (3

trucks)................................................................................................................. 88 Figure 4.30 Moment GDF from FEM and AASHTO codes for interior girders (4

trucks)................................................................................................................. 88 Figure 4.31 Moment GDF from FEM and AASHTO codes for exterior girders (1

truck) .................................................................................................................. 89 Figure 4.32 Moment GDF from FEM and AASHTO codes for exterior girders (2



trucks)................................................................................................................. 91 Figure 4.35 Shear GDF from FEM and AASHTO codes for interior girders (1 truck)

............................................................................................................................ 92 Figure 4.36 Shear GDF from FEM and AASHTO codes for interior girders (2 trucks)

............................................................................................................................ 92

xii

Figure 4.37 Shear GDF from FEM and AASHTO codes for interior girders (3 trucks)............................................................................................................................ 93

Figure 4.38 Shear GDF from FEM and AASHTO codes for interior girders (4 trucks)

............................................................................................................................ 93 Figure 4.39 Shear GDF from FEM and AASHTO codes for exterior girders (1 truck)

............................................................................................................................ 94 Figure 4.40 Shear GDF from FEM and AASHTO codes for exterior girders (2 trucks)



............................................................................................................................ 96 Figure 5.1 Total prestress losses using the PCI General method.............................. 122

Figure 5.2 Comparison of total prestress losses by all methods ............................... 123

Figure 5.3 Prestress vs. time measured by various sensors for girders A, B, C ....... 126

Figure 5.4 Prestress vs. time measured by various sensors for girders D, E, F ........ 127

Figure 5.5 Prestress losses at transfer ....................................................................... 128

Figure 5.6 Prestress losses PCI method vs. measured .............................................. 130

Figure 5.7 Comparison of the final prestress losses ................................................. 131

Figure 6.1 Schematic Representation of a Cell Equipped with Parallel Topology .. 135

Figure 6.2 Curvature function based on cell measurement....................................... 138

Figure 6.3 Camber history of girder C...................................................................... 142

Figure 6.4 Camber history of girder D...................................................................... 142

Figure 6.5 Camber history of girder D...................................................................... 143

Figure 6.6 Camber history of girder F ...................................................................... 143

xiii

Figure 6.7 Camber sensor measurements vs. laser ................................................... 144

Figure 6.8 Camber at erection................................................................................... 145

Figure 6.9 Camber at two years after fabrication ..................................................... 146

Figure 7.1 Cylinder locations and labels.................................................................. 154

Figure 7.2 Comparison of modulus of elasticity at transfer...................................... 159

Figure 7.3 Comparison of modulus of elasticity at deck pour.................................. 161

Figure 8.1 Dimensions of vehicle used for testing ................................................. 162

Figure 8.2 Sensor measurements vs. time when the truck moved across the bridge near the barrier @ girder A .............................................................................. 165

Figure 8.3 Sensor measurements vs. time when the truck moved across the bridge

along the centerline of the bridge..................................................................... 165 Figure 8.4 Impact factor truck moving through the left driving lane ....................... 170

Figure 8.5 Impact factor truck moving through the right driving lane ..................... 170

Figure 8.6 Moment distribution factors for interior girders for crawl speed ............ 172

Figure 8.7 Moment distribution factors for exterior girders for crawl speed ........... 173

Figure 8.8 Shear distribution factors for interior girders at crawl speed .................. 173

Figure 8.9 Shear distribution factors for exterior girders at crawl speed.................. 174

Figure 8.10 Moment distribution factors for 30mph speed when test truck was moved through the right lane ....................................................................................... 175

Figure 8.11 Moment distribution factors for 30mph speed when test truck was moved

through the left lane.......................................................................................... 175 Figure 8.12 Moment distribution factors for 50mph speed when test truck was moved

through the right lane ....................................................................................... 176 Figure 8.13 Moment distribution factors for 50mph speed when test truck was moved

through the left lane.......................................................................................... 176

xiv

Figure 8.14 Shear distribution factors for 30mph speed when test truck was moved through the right lane ....................................................................................... 177

Figure 8.15 Shear distribution factors for 30mph speed when test truck was moved

through the left lane.......................................................................................... 177 Figure 8.16 Shear distribution factors for 50mph speed when test truck was moved

through the right lane ....................................................................................... 178 Figure 8.17 Shear distribution factors for 50mph speed when test truck was moved

through the left lane.......................................................................................... 178 Figure 8.18 Girder deflections when the test truck was moved through right lane at

30 mph.............................................................................................................. 180 Figure 8.19 Girder deflections when the test truck was moved through left lane at 30

mph................................................................................................................... 181 Figure 8.20 Girder deflections when the test truck was moved through right lane at

50 mph.............................................................................................................. 181 Figure 8.21 Girder deflections when the test truck was moved through left lane at 50

mph................................................................................................................... 182 Figure 9.1 Typical sensor measurements under regular traffic................................. 184

Figure 9.2 Sensor measurements after filtration ....................................................... 184

Figure 9.3 Dynamic and static strain from sensor measurements ............................ 186

Figure 9.4 Impact factors under regular traffic......................................................... 187

Figure 9.5 Moment distribution factors under regular traffic ................................... 188

Figure 9.6 Shear distribution factors under regular traffic ....................................... 188

Figure 10.1 Comparison of the measured stresses to the AASHTO limits at transfer.......................................................................................................................... 194

Figure 10.2 Comparison of the measured stresses to the AASHTO limits at service

.......................................................................................................................... 194 Figure 10.3 Measured moment at midspan under regular traffic.............................. 203

xv

Figure 10.4 Measured moment at midspan caused by dead load ............................. 203

Figure 10.5 Measured shear force caused by regular traffic..................................... 204

Figure 10.6 Measured moment vs. moment capacity by the AASHTO codes ......... 205

Figure 10.7 Measured shear force vs. shear capacity by the AASHTO codes ......... 206

Figure 10.8 Deflection of girders at midspan under regular traffic ......................... 208

Figure 10.9 Deflection measured vs. the AASHTO limits ...................................... 208

1

CHAPTER 1 INTRODUCTION AND PREVIOUS RESEARCH1.1

Research Objectives

High performance concrete (HPC), designed to have a higher strength and better

durability than conventional concrete, is being widely used in prestressed highway

bridges because of its engineering and economic benefits. The use of HPC in

pretensioned concrete bridge girders enables engineers to design bridges with longer

span lengths and fewer supports, shallower sections, and increased girder spacing.

This can decrease the fabrication, transportation, and erection costs of the bridge.

Using HPC in a bridge can be expected to result in significant savings due to the

longer life with less maintenance (Prussack, 2000).

In recent years there has been an ever increasing interest in the use of HPC for

bridge applications. The trend is clear that more and more bridges will be built with

HPC in the foreseeable future as the industry becomes more familiar with the

technology. However, some properties of HPC still remain unknown and under study.

There are factors that need to be further considered due to the new material nature of

HPC.

In this study a fiber optic monitoring system was to be designed and embedded in

a high performance prestressed concrete bridge during construction. The new bridge

was to be monitored from construction through service. Several topics pertaining to

HPC were selected to be further investigated in this project: Prestress losses, camber

as well as in-situ material properties. In addition, the structural performance, load

2

distribution, and load rating of the bridge was to be performed under regular traffic

loading. The main objectives of the study were to:

1. Monitor the prestress losses in the concrete for a period of two years. The

actual prestress losses were obtained from the data collected. The measured

losses were compared to those calculated using the PCI (Prestressed Concrete

Institute) General method, the ACI-ASCE (American Concrete Institute –

American Society for Civil Engineers) method, the AASHTO LRFD (Load

and Resistance Factor Design) method, the AASHTO LRFD Lump Sum

method, and the NCHRP (National Cooperative Highway Research Program)

detailed and approximate method.

2. Obtain cambers of the girders from sensor measurement at different stages.

Then compare the results with the cambers measured using a laser level and

the cambers calculated using the PCI multiplier method and the PCI improved

multiplier method.

3. Obtain in-situ material properties, such as the actual modulus of elasticity at 3

days and 28 days from sensor measurements. The results are then compared

with laboratory cylinder test results and the values calculated using code

methods and various empirical equations.

4. Obtain the moment and shear girder distribution factors (GDF) from sensor

measurements, and compare the results with the values using the AASHTO

Standard and AASHTO LRFD equations.

5. Perform the load rating of the bridge under traffic loading.

3

The tasks to be performed:

1. Install a built-in long gage embeddable MUST optical fiber sensor monitoring

system in the Southbound Bridge. The system will be used to monitor

temperature, short and long term strain, prestressing forces and deflection in

high performance concrete bridge girders.

2. Collect data with the built-in system from the time of fabrication into

construction and service.

3. Perform experimental work that will include both field measurements and

laboratory tests.

4. Perform truck load tests to investigate shear distribution factors and moment

distribution factors in the bridge using the built-in sensor system.

5. In-situ material properties such as the modulus of elasticity obtained at early

age, as well as at 28 days and at the time the deck is cast will be compared

with the modulus of elasticity predicted by formulas used by various codes.

6. Data processing- Data will be analyzed to evaluate prestress losses,

distribution factors in the bridge, camber, material properties, and compare

with predicted results using the AASHTO code.

7. Load rating of the bridge will be performed using data collected under traffic

loading.

8. Final report.

4

1.2 Previous Research on Load Distribution Factors

1.2.1 Barr, Stanton, Eberhard (2000)

The main objective of this study was to evaluate the live load distribution

factors for moment and compare them to the AASHTO LRFD Bridge Specifications.

The study bridge had three spans. Each span had five prestressed high performance

concrete I-girders. The Washington State W74MG cross-section was used for all

girders. The evaluation was performed in several steps. First, a 35 kips (155.7 kN)

truck was placed at several locations along the bridge and the bridge’s response to the

truck load was measured in spans one and two. This measured response was then

compared to a finite element. After the validity of the finite element model was

confirmed, the live load distribution factors for moment were calculated using the

model. The resulting distribution factors were used to evaluate the effects of lifts,

diaphragms, continuity, and skew on the load distribution factors by means of an

analytical parameter study.

The main conclusions from this study were:

1. The distribution factors from the finite element model were lower than those

calculated from the AASHTO LRFD code.

2. The moment distribution factors from the AASHTO LRFD Specifications were

found to be more conservative than those from the Standard Specifications at

low skew angles.

3. The effect of intermediate diaphragms on the distribution factors depended on

the skew for exterior girders. The maximum distribution factors were at a

5

skew angle of 30 degrees. For interior girders the addition of intermediate

diaphragms resulted in more uniform distribution of load at all skew angles,

reducing the distribution factor by an average of 2.5 percent. Overall,

intermediate diaphragms had the smallest effect on the distribution factors of

all the considered parameters.

1.2.2 Stalling, Barnes, Porter (2003)

The purpose of this study was to compare the moment distribution factors,

deflections, and stresses measured during field tests with those calculated using the

AASHTO LRFD and AASHTO Standard Specifications. The study bridge had seven

spans with a total length of 798 feet (243 meters). Span five was chosen for live load

tests. The length of that span was 114 feet (33.7 meters). Five simply supported,

prestressed high performance concrete AASHTO BT-54 girders were used in that

span to support a 7 inch (178 mm) cast-in-place concrete deck. Both static and

dynamic live load tests were conducted on the bridge.

The distribution factors calculated using the AASHTO LRFD and AASHTO

Standard Specifications were found to be conservative. This study also showed that

even though the bridge had diaphragms at the supports and at midspan, it did not

behave as a rigid body when under multiple lane loadings. The diaphragms had very

little effect on the distribution factors. The exterior girders took no more load than the

interior girders.

6

The researchers found that the ratio of dynamic load effects to static load

effects were smaller than the dynamic load allowance factor of 1.33 according to

AASHTO LRFD Specifications. This indicated that the code dynamic load

allowance factor was conservative.

The stresses and strains measured under live load were significantly smaller

than predicted for all girders under different loadings. The researchers concluded that

this difference was due to the added stiffness of the bridge barriers, which were

neglected during design. The deflections measured during the load test were all

within 20 percent of the deflections predicted using AASHTO LRFD Bridge Design

Specifications.

1.2.3 Jauregui, Barr, White (2003)

The purpose of this study was to evaluate the operating load rating of a

precast, prestressed concrete girder bridge over the Rio Grande River on Interstate-40

in Albuquerque, New Mexico. The load rating was defined as the ratio of maximum

allowed moment due to an overweight vehicle to the maximum moment caused by

the HS-20 truck. The bridge consisted of two bounds, and each bound had ten spans

with a total length of 1,240 feet (378 meters). The cross section of the bridges

consisted of twelve prestressed concrete BT-72 girders. The bridges were simply

supported under non-composite dead load, and continuous under composite dead load

and live load. The design of the bridge was according to the AASHTO Standard

Specifications. The original operating load rating of the bridge was 1.67. If a truck

7

caused a moment which is larger than 1.67 multiplied by the moment caused by an

HS-20 truck, the truck would be denied to pass the bridge and had to travel an

additional 100 miles (160 km) to bypass the bridge.

Distribution factors were calculated using the AASHTO Standard

Specifications, as well as using a detailed finite element model from SAP 2000. The

model’s accuracy was confirmed by the live load tests. Span 2 was selected for the

live load test. In order to obtain the maximum moments, the test truck was placed in

several positions along the bridge, and across the width of the bridge. The distribution

factor calculated from the specifications was found to be conservative. The new live

load distribution factor from the finite element model was then used to adjust the load

rating of the bridge. The new load rating was 2.85, increased by a factor of 1.7 from

the old load rating.

1.2.4 Idriss, Hughs (2006)

The purpose of this research was to evaluate the accuracy of girder

distribution factors for a continuous, prestressed concrete, spread box-girder bridge

from AASHTO LRFD and AASHTO Standard Specifications by comparing them with

results from a finite element model verified through field testing. The study bridge

was located in Las Cruces, New Mexico. It consisted of five spans with a total length

of 642 ft (196 m) and has a skew angle of 12 degrees. Each span consisted of six

prestressed high performance concrete spread box-girders. Span 5 was chosen for the

8

live load test. The bridge was designed to be simply supported under dead load, and

continuous under live load.

The test vehicle used for the live load test was a three-axle dump truck with a

total weight of 56,760 pounds (252.5 kN). Influence lines were used to find the truck

locations for maximum moment and shear. The moment and shear forces were

measured by an optical sensors system embedded in the girders. The results were

compared to those calculated from a finite element model using SAP 2000, and

confirmed its accuracy. It was found in this study that both the AASHTO LRFD and

AASHTO Standard Specifications are conservative in evaluating the moment and

shear distribution factor.

Some of the major points and conclusions from the previous research papers

in this section are summarized in Table 1.1. The table includes the type of bridge, the

method used in each research project, and the conclusions about the girder

distribution factors from finite element model, field test, as well as from the

AASHTO Standard and LRFD codes.

9

Table 1.1 Previous research summary on girder distribution factor SECTION BRIDGE

TYPE METHOD CONCLUSION

1.2.1 Beam and slab, HPC prestressed I-girder

Static load test, FEM

Both AASHTO codes were conservative compared to FEM. Standard was more accurate than LRFD. Intermediate diaphragms had little effect.


Static and dynamic load test, FEM

Both AASHTO codes were conservative. Diaphragms did not make the bridge a rigid body and had little effect on GDF. The impact factor from LRFD was conservative.


Static live load test, FEM

AASHTO Standard was conservative. New GDF from FEM was used to increase the load rating from 1.67 to 2.85.

1.2.4 Beam and slab, HPC prestressed U-girder

Static live load test, FEM

Both AASHTO codes were conservative compared to load test and FEM.

1.3 Previous Research on Prestress Losses of HPC

1.3.1 Naaman, Hamaz (1993)

Antoine E. Naaman and Ali Ml Hamaz conducted a project on the topic of

prestress losses in partially prestressed high strength concrete beams. This project was

focused on the influence of the partial prestressing ratio (from no prestressing to full

prestressing) and the compressive strength of concrete from 6 ksi (41 MPa) up to 10

ksi (69 MPa). Different beam cross-sections, representing building and bridge girders

with various spans and spacing were studied. The conclusions of this project were: 1.

The prestress loss due to creep decreases with a decrease in the partial prestressing

10

ratio: PPR. 2. The loss due to relaxation of the prestressing steel increases with a

decrease in PPR. 3. The time-dependent stress loss in the prestressing steel generally

decreases with an increase in the concrete compressive strength. Up to a 20 percent

decrease was observed when the concrete strength varied from 6-10 ksi (41 to 69

MPa). 4. Time-dependent losses are influenced by the type of cross section. 5. The

loss due to elastic shortening decreases with a decrease in the PPR.

1.3.2 Ahlborn, French, Shield (2000)

Theresa M. Ahlborn, Catherine E. French, and Carol K. Shield, sponsored by

Minnesota Department of Transportation, accomplished a project to study the long

term and flexural behavior of high-strength concrete prestressed bridge girders in

2000. Two standard size Mn/DOT 45M girders were designed, constructed, and

tested to investigate the structural behavior of sections incorporating high strength

concrete. 0.6 in (15.2 mm) diameter 270 ksi (1860 MPa) low-relaxation strands were

chosen for design of the test girders. The design compressive strength of the concrete

was 8925 psi (62 MPa) at release and 10500 psi (73 MPa) at 28-days. The conclusion

about prestress losses of this research project was that the prestress losses predicted

by AASHTO ignore the concrete stress before release and overestimate the high-

strength concrete modulus, which lead to lower initial losses. AASHTO also over-

predicted the creep and shrinkage of the HPC concrete, which led to higher long-term

losses.

11

1.3.3 Kowalsky, Zia, Wagner, Warren (2002)

Mervyn J. Kowalsky, Paul Zia, Matt C. Wagner, and Bruce A. Warren, in a

project sponsored by Federal Highway Administration, used a bridge on U. S.

Highway 401 in Raleigh crossing the Neuse River as a demonstration bridge. The

objective of this research was to monitor the behavior of four prestressed HPC bridge

girders during their casting and study the properties of the concrete used in the

girders. The compressive strength of HPC used in this project was between 10 ksi (69

MPa) and 11 ksi (76 MPa). The structure was a four-span bridge that carried three

lanes of the southbound traffic of the divided highway. HPC was used for both the

girders and the deck. Their conclusion about the prestress loss was: Total prestress

loss was 26.0 ksi (12.9%) for the AASHTO Type III girders and 38.1 ksi (19.1%) for

the AASHTO Type IV girders. Elastic shortening and creep were the major

contributors to the total loss. The loss due to shrinkage was almost insignificant.

1.3.4 Idriss, Solano (2002)

Rola L. Idriss and Amor Solano completed a project on the topic of effects of

steam curing temperature on early prestress losses in high performance concrete

beams in 2002. Four HPC I-beams (type BT-1600) were monitored to calculate the

prestress losses. The compressive strength was found to be 7325 psi (50.5 MPa) at 3

days (strand release), 9076 psi (62.6 MPa) at 28 days, and 10151psi (70.0 MPa) at 56

days according to the cylinder test. The girders were steam-cured and the modulus of

elasticity was 4.9 ksi (34.2 MPa) at 3 days and 5.7 ksi (39.2 MPa) at 60 days. Four

methods where used to predict the prestress losses: the Prestressed Concrete Institute

12

(PCI) General method , the American Concrete Institute – American Society for Civil

Engineers (ACI-ASCE) Method ,the AASHTO LRFD Refined method , and the

AASHTO LRFD Lump Sum method. The research results showed that all four

methods over-predicted the prestress losses for HPC and were found to be very

conservative. The results also showed that the steam curing temperature can have a

significant effect on the early prestress losses in HPC. A lower curing temperature

was associated with larger early prestress losses following transfer. This was most

pronounced in the month following transfer, and tapered with time.

1.3.5 Tadros, Al-Omaishi, Seguirant, Gallt (2003)

Maher K. Tadros, Nabil Al-Omaishi, Stephen J. Seguirant, James G. Gallt,

sponsored by the American Association of State Highway and Transportation

Officials, conducted a project to develop design guidelines for estimating prestress

losses in pretensioned high-strength concrete bridge girders. The research consisted

of experimental and theoretical programs. The experimental program consisted of

measurements of properties of materials and of prestress loss in seven full-scale

bridges girders in four states. It also included the test results previously reported for

31 pretensioned girders in the study. The measured strength of the HPC varied from

9.02 ksi (62.2 MPa) to 10.67 ksi (73.6 MPa). Measured prestress losses were

compared with the estimated prestress losses by AASHTO-LRFD refined and Lump-

sum method. Both of these methods overestimated prestress loss for the instrumented

bridge. This project also proposed an approximated method and a detailed method to

calculate the prestress losses of HPC. The proposed detailed method gave a better

13

correlation with test results than the AASHTO-LRFD refined method and PCI-BDM

method. The proposed approximated method was almost as accurate as the detailed

method and the PCI-BDM method, but was much simpler.

Some of the major points and conclusions from the previous research papers on

prestress losses are summarized in Table 1.2. The table includes the type of bridge,

the concrete strength of the girders, and the conclusions about the prestress losses

from field or laboratory test comparing to the values predicted by different design

codes.

Table 1.2 Previous research summary on prestress loss SECTION

BRIDGE TYPE

CONCRETE STRENGTH

CONCLUSION

1.3.1 Beam and slab, Different beam cross-sections

6 ksi (41MPa) to 10 ksi (69 MPa)

The prestress loss due to creep decreases with a decrease in the PPR; The time dependent loss decreases up to 20% with an increase in the concrete strength

1.3.2 Beam and slab, Standard Mn/DOT 45M girders

10.5 ksi (73 MPa)

AASHTO underestimated the initial loss due to elastic shortening but overestimated the loss due to creep and shrinkage.

1.3.3 Beam and slab, AASHTO Type III and Type IV girders

10 ksi (69 MPa) to 11ksi (76 MPa)

Total loss was 12.9% for the type III girders and 19.1% for the type IV girders. Loss was mainly due to elastic shortening and creep.

1.3.4 Beam and slab, Type BT-1600 I-beams

10.2 ksi (70 MPa)

The PCI General, ACI-ASCE, AASHTO LRFD and Lump Sum methods all overestimated the prestress losses.

1.3.5 Beam and slab, Different beam cross-sections

9.02 ksi (62.2 MPa) to 10.67 ksi (73.6 MPa)

Both AASHTO LRFD and Lump Sum methods overestimated the prestress losses. New methods for the calculation of prestress losses were proposed.

14

1.4 Previous Research on Cambers of HPC Bridge Girder

1.4.1 Byle, Burns, Carrasquillo (1997)

K. A. Byle, Ned H. Burns, and Ramon L. Carrasquillo in a project sponsored

by the Texas Department of Transportation and the Federal Highway Administration

investigated time-dependent deformation behavior of prestressed high performance

concrete bridge beams in 1997. Twelve full-scale prestressed high performance

concrete Texas type U54 bridge beams with span lengths ranging from 116.63 ft

(35.55 m) to 135.33 ft (41.25 m) were instrumented and monitored in the field. The

design compressive strengths of the concrete were between 11.6 ksi and 13.1 ksi

(80.0 and 90.3 MPa). The modulus of elasticity was varied from 5580 ksi to 6150 ksi

(38.5 Gpa to 42.4 Gpa) at release and from 6550 ksi to 7290 ksi (45.2GPa to

50.3GPa) at 56 days. Cambers were measured from transfer of the prestressing force

until 5 months after the deck placement. The cambers predicted by the PCI method

were found to be 0.60, 0.56, 0.57 inch (15.3, 14.1, and 14.6 mm) larger than the

measured cambers at release, erection, and long-term respectively. This was due to

the inability to precisely predict the material properties, prestressing force, and

movements induced by temperature change.

A set of new multipliers were proposed in this project and were found to

predict the measured camber and deflection of the U-beams with reasonable accuracy.

These proposed multipliers were sensitive to the effective prestressing force, the

creep coefficient function, and the modulus of elasticity at release. The long-term

deflection of the U-beams due to the superimposed deck load was projected to be

15

very small because the composite section was nearly three times as stiff as the

noncomposite section and because a majority of the ultimate creep deformation

occurred during storage. The authors also found that the temperature gradients on

sunny days could cause thermal movements of at least 0.43 in (12 mm) in the

noncomposite U-beams and at least 0.32 in (8 mm) in the composite U-beams.

1.4.2 Barr, Fekete, Eberhard, Stanton, Khaleghi, Hsieh (2000)

P. Barr, E. Fekete, M. Eberhard, J. Stanton, B. Khaleghi, and J.C.Hsieh,

sponsored by Federal Highway Administration, conducted a research on the

effectiveness of using HPC in prestressed precast concrete girders on a bridge in the

state of Washington. Fifteen bridge girders were fabricated for the three-span bridge.

Ten had length of 80 ft (24.4 m) in span 1 and 3, and five had length of 137 ft (41.8 m)

in span 2. The Washington W74G cross-section was used for all girders, which were

made composite with the 7.5 in (190 mm) deck slab. The strength of HPC was 10 ksi

(68.9 MPa) at 56 days. Camber was monitored with a stretched-wire system and a

supplementary surveyor’s level. The predicted camber by the PCI method was found

to be 37.5 percent higher than the measured camber at transfer. Out of the five girders

in span 2, the predicted camber before the deck pour was close to the measured

cambers for three girders, while the other two girders had lower cambers than

predicted. The predicted camber after the deck pour was higher than the measured

cambers for all girders except one. The average camber at day 200 was 5.4 inch (138

mm). The camber was also found to vary by approximately 0.8 in (20 mm) in a

16

typical day for the girders in span 2. The maximum and minimum camber readings

occurred at 3:00 PM and 6:00 AM respectively. The variation was attributed to

thermal effects.

1.4.3 Slapkus (2002)

The Jonesboro Road Bridge located at Henry County, Georgia was the

demonstration bridge for this project discussed by Slapkus. The bridge consisted of

four spans, using both Type II and Type IV precast, prestressed HPC girders, with a

cast-in-place composite deck. Span 2 was simply supported with a span length of 124

ft-1 in. and was an instrumented span. The 56-day compressive strength for the HPC

prestressed girders and the composite deck were 12,050 psi (83 MPa) and 7,311 psi

(50 MPa), respectively. The 56- day modulus of elasticity was 4,911 ksi (33.9 MPa)

and 3,600 ksi (24.8 MPa) respectively for the Type IV girders and deck. The initial

deflection from the dead load (DL) of the deck was an average of 2.53 in (64.3 mm)

for the three girders measured. During deck hydration, at a peak temperature of

107.8°F (42°C), the bridge experienced an average upward displacement of

approximately 0.43 in (10.9 mm). At approximately two days after casting, the

average deck temperature returned to ambient condition; and the average downward

deflection was approximately 0.68 in. (17.3 mm) from the point of peak temperature

(total deflection of 2.92 in, 74.2 mm). With the additional DL of the barriers, the

average bridge deflection was 3.187 in. (2.3 mm), with individual deflections of

2.973 in. (75.5 mm), 3.171 in. (80.5 mm) and 3.418 in. (86.8 mm) for the north (G

17

2.9), center (G2.10) and south girder (G 2.11), respectively. The deflections varied

between girders due to the uneven barrier weight distribution and bridge skew. At 70

days from the time of casting, the average bridge deflection measured was 3.266 in

(82.9 mm), 0.55 in. (14 mm) greater than the total DL deflection from the deck self

weight and barrier weight. In analyzing deflections from this project, Slapkus found

the actual deflections to be greater than those predicted. The predicted deflections

resulted in an upward camber of 0.71 in (18.0 mm), whereas the actual measured

deflections after one year translated into a downward deflection of 1.3 in (33.0 mm).

1.4.4 Idriss, Liang (2004)

The bridge under investigation was the I-10 bridge over University Avenue

and Main Street in Las Cruces, New Mexico. The bridge consisted of two parts:

westbound and eastbound. A total of 72 deformation sensors were installed in span 5

of the westbound bridge to monitor the bridge. The span length was 132.25 ft (40.13

m). The primary members of the bridge consisted of six U54b HPC beams. The

strength of the concrete was 8 ksi at release and 10 ksi at 28 days. Cambers of the

girders were obtained from sensor measurements and were measured using a laser

level, and also calculated using the methods in PCI design manual section 8.7.1. The

following conclusions were reached based on the result of this project:

1. Both the PCI multiplier method and the PCI improved multiplier method over-

predicted the camber at erection. This led to additional concrete and a thicker

18

haunch needed to correct for the lack of girder camber. It also led to a downward

deflection after the pouring of the slab.

2. The lack of camber growth during storage was attributed to the lower creep

properties of the HPC.

3. When in-situ modulus of elasticity is used, the PCI multiplier method and the PCI

improved multiplier method accurately predicted the elastic deflection at prestress

transfer and deck pour.

4. The PCI improved multiplier method yielded more accurate results than The PCI

multiplier method in predicting the time-dependent growth of camber.

5. Only a small increase of 0.40 in (10.1 mm) of downward deflection was measured

during the six month after deck pour.


cambers of HPC girders are summarized in Table 1.3. The table includes the type of

bridge, the concrete strength of the girders, and the conclusions about the measured

cambers comparing to the predicted values by the PCI methods.

1.5 Previous Research on Modulus of Elasticity of HPC

1.5.1 Fekete, Barr, Stanton, Eberhard, Janssen (2001)

E. Fekete, P. Barr, J. Stanton, M. Eberhard, D. Janssen [8], sponsored by Federal

Highway Administration, conducted a research on the topic of the creep properties of

HPC. The creep properties strongly affect the prestressing losses in a prestressed

19

girder. This paper presented preliminary test results from the first year of the

materials testing program of the HPC mix used in the prestressed precast concrete

girders on a bridge in the state of Washington. The bridge utilizes WSDOT 74G

pretensioned I-girders with a 190 mm cast-in-place composite deck. The girders were

designed for a concrete compressive strength of 10 ksi (69 MPa) at 56 days. The

Table 1.3 Previous research summary on cambers of HPC girders SECTION BRIDGE

TYPE CONCRETE STRENGTH

CONCLUSION

1.4.1 Beam and slab, Texas U54 girders

11.6 ksi (80 MPa) to 13.1 ksi (90.3 MPa)

The PCI method overestimate the cambers at transfer, erection, and long-term. Long-term camber caused by the superimposed deck load was small.

1.4.2 Beam and slab, Washington W74G girders

10 ksi (68.9 MPa)

The predicted camber by PCI method was higher than the measured camber at transfer, before and after deck placement. Cambers varied by 0.8 in (20 mm) in a typical day due to thermal effect.

1.4.3 Beam and slab, AASHTO Type II and Type IV girders

12 ksi (83 MPa)

The actual deflections are greater than those predicted. Final deflection after one year was 1.3 in (33 mm) downward. The maximum seasonal variation was 0.25 in (5.3 mm).

1.4.4 Beam and slab, Texas U54B girders

10 ksi (68.9 MPa)

PCI methods accurately predicted the elastic deflection at transfer if in-situ modulus of elasticity was used, but overestimated the cambers at erection. Small increase of 0.40 in (10.1 mm) downward deflection was measured during the six month after deck pour.

20

girders were also steam-cured. The concrete had a modulus of elasticity of 5500 ksi

(37.9 Gpa). The material testing program included determining compressive and

tensile strengths, elastic modulus, long term creep, shrinkage, and thermal expansion

properties of the HPC girder. They also monitored the compressive and tensile

strengths, and elastic modulus variations of the deck concrete. The conclusion of this

paper was: The total measured creep coefficient after 6 months of testing ranged from

1.64 to 2.72 for a total creep of 6 in (152 mm) diameter cylinders. These values

significantly exceeded the value of 1.60 suggested for 10,000 psi (68.9 MPa) concrete

as given by Nilson (1987).

1.5.2 Ramakrishnan, Sigl (2001)

V. Ramakrishnan and Arden Sigl, in cooperation with the South Dakota

Department of Transportation, constructed a research on the twin prestressed girder

bridges located along Interstate 29 near Sioux Falls, South Dakota. Each bridge had

three spans with four AASHTO Type II prestressed girders in each span. The design

compressive concrete strength was 9.9 ksi (68.3 MPa) at 28 days. Laboratory trial

batches were made and tested to optimize HPC mix designs for the girders and the

decks. For the high performance bridge deck concrete two different coarse aggregates

were used (quartzite and limestone) and ten mixes were cast with each aggregate. In

each mix the percentage replacement of cement by weight with silica fume and fly

ash was varied, keeping the w/c ratio constant. For the high-strength bridge girder

concrete, twelve mixes were cast varying both the percentage replacement of cement

21

with silica fume and the w/c ratios. The percentage replacements of silica fume

investigated were 7%, 10% and 12% and the w/c ratios investigated were 0.28, 0.30,

and 0.32. All concretes were tested for compressive strength, static modulus, modulus

of rupture and chloride permeability. Tests to determine the modulus of elasticity for

both the girder and deck concrete were conducted at selected ages up to one year. The

authors found that the equation currently recommended for calculation of the

modulus of elasticity for HPC (the ACI 363 equation:

5.1' )145)(000,000,1000,40( ccc wfE += ) did not yield the correct results. Based on

the modulus of elasticity tests conducted as part of this research and limited to mixes

containing Sioux Quartzite aggregate, the authors recommended that the above

equation be modified by changing the 1,000,000 constant to 2,000,000. It was also

recommended that the ACI 363 equation be used without modification for mixes

containing limestone aggregates since the research was not conducted on mixes

containing limestone aggregate.

1.5.3 Hughs, Liang, Idriss, Newtson (2005)

Erin A. Hughs, Zhiyong Liang, Rola L. Idriss, and Craig M. Newtson

conducted a research project on an evaluation of Young’s modulus of elasticity (Ec)

for a new, prestressed, high performance concrete, spread box-girder bridge. The

design compressive strength of the HPC was 8ksi (55.2 MPa) at transfer and 10 ksi

(68.9 MPa) at 28 days. The modulus of elasticity was measured using sample

concrete cylinders obtained during concrete placement of the study bridge girders as

22

well as through embedded fiber optic sensors which were placed inside the bridge

girders. The measured modulus of elasticity was then compared with several well-

known empirical equations used to predict Ec during the design process. The

coefficient of thermal expansion (α) was also measured using the deformation

sensors.

The following conclusions were drawn based on the results of this

experimental investigation of the modulus of elasticity and the coefficient of thermal

expansion for high performance concrete:

1. Empirical equations originally created for regular strength concrete are not

necessarily applicable to high performance concrete.

2. For the study bridge the ACI 363 revised equation for HPC and the PCI Design

Handbook equation for HPC were found to be the most accurate to the true value.

3. All other empirical equations investigated did not predict a value for Ec that fell

within an acceptable range of error.

4. The coefficient of thermal expansion for the HPC study bridge fell within the

accepted range for regular strength concrete, supporting its use for HPC.

5. More on-site and laboratory testing should be done to find Ec for other HPC bridges.

Also, an empirical equation developed specifically for HPC should be required to

use for design of HPC bridges.


the modulus of elasticity of HPC are summarized in Table 1.4. The table includes the

type of bridge, the concrete strength of the girders, and the conclusions about the

23

modulus of elasticity of HPC from field or laboratory test comparing to the values

predicted by different design codes.

Table 1.4 Previous research summary on the modulus of elasticity of HPC Section Bridge Type Concrete

Strength Conclusion

1.5.1 Beam and slab, WSDOT 74G I-girder

10 ksi (68.9 MPa)

The total measured creep coefficients after 6 months of testing were significantly exceeded the value suggest for 10 ksi (68.9 MPa) by Nilson (1987)

1.5.2 Beam and slab, AASHTO Type II girders

9.9 ksi (68.3 MPa)

The ACI 363 equation did not yield the correct results for the modulus of elasticity of HPC. It was recommended that the constant 1,000,000 in the ACI 363 equation be modified to 2,000,000

1.5.3 Beam and slab, AASHTO Type II and Type IV girders

12 ksi (83 MPa)

Empirical equations originally created for regular strength concrete are not necessarily applicable to HPC. The ACI 363 revised equation for HPC and the PCI equation for HPC were found to be the most accurate to the measured value.

24

CHAPTER 2 BRIDGE DESCRIPTION

2.1 Overview

The bridge studied in this project is the I-25 bridge at the Dona Ana

interchange in Las Cruces, New Mexico. The structure consists of two parts,

northbound and southbound. The northbound was selected for evaluation. As shown

in Figure 2.1, the bridge has one simple span with a length of 112.5 ft (34.3 m). The

primary members of the bridge consist of six BT-63 prestressed high performance

concrete (HPC) girders. The bridge cross section is shown in Figure 2.2. Concrete

diaphragms were used to transfer the load from one beam to another and to assist in

the stability of the bridge. The deck was fabricated with concrete reinforced with

Grade 60 steel. The deck is 7.5 in (191 mm) thick and has a slope of 2%.

Figure 2.1 Bridge Profile

112’-6” (34.3 m) between Abutments

6 BT-63 Girders

25

Figure 2.2 Bridge Cross-section

2.2 Design Data

The bridge design was in accordance with AASHTO Standard Specifications

2002, seventeenth edition and current interims.

The concrete compressive strength for the girders:

f’ci = 8,000 psi (55.2 MPa) at time of initial prestress transfer

f’c = 9,500 psi (65.5 MPa) at 28 days

Prestressing Steel:

6/10” (15.2 mm) diameter seven wire low relaxation strands

Ultimate strength fs = 58.6 kips (261 kN) /strand

5 Spaces @ 7’-3” (2.2 m) = 36’-3” (11.0 m)

43’-0” (13.1 m)

A B C D E F

Right Driving Lane 12 ft (3.66 m)

Left Driving Lane 12 ft (3.66 m)

Shoulder 10 ft (3.05 m)

Shoulder 6 ft (1.83 m)

7 ½” (191 mm) Deck Thickness

26

Yield strength fy = 52.7 kips (234 kN)/strand

Conventional Reinforcing Bars:

Yield strength fy = 60,000 psi (414 MPa)

The concrete compressive strength for the composite slab:

f’c = 4,000 psi (27.6 MPa)

Loads:

Allowance for future overlay = 30 psf (1436 Pa)

Allowance for stay-in-place deck forms = 15 psf (718 Pa)

Live load = HS-25-44

2.3 Girders Details

There were six I-beam type BT-63 high performance concrete girders in the

bridge, spaced at 7’3” (2.2 m). Hooked epoxy coated grade 60 reinforcing bars

protruding through the top of the girders provided a connection between the girders

and the deck. The girders were prestressed by 30 Grade 270 steel tendons: 24 straight

and 6 draped. The tendon configuration as well as the dimensions of the girder cross

section can be seen in Figure 2.3. The design was based on the use of 6/10” (15.2

mm) diameter low-relaxation strands meeting the requirements of AASHTO M-203

(grade 270). Initial prestressing force was 43.9 kips (195.3 kN) per strand. Slight

overstressing up to 46.9 kips (208.6 kN) per strand was allowed to offset seating

losses.

27

Figure 2.3 Details of BT-63 Girders (1 inch = 25.4 mm)

16 SP.@11”=6’-5” 16 SP. @ 2’-0” = 32’-0” 10” 12 SP. @ 8”

= 8’-0”

8 SP.@1 1/2” = 1’-0” 56’-3”

(6) Draped Strands

3’-6” 3’-6”

2’-2” 2’-2”

1’-0

”

3’-9

”

5’-3

”

4½”

5”2” 2

”3½

”

SECTION NEAR END SECTION NEAR MIDSPAN

11’-4 3/16”

28

CHAPTER 3 MONITORING SYSTEM AND EQUIPMENT

3.1 MuST System

The monitoring system used in this project is the MuST (Multiplexed Strain

and Temperature) Monitoring System, which was designed by the SMARTEC Co.

The system consists of a MuST reading unit with 16 channels, 6 connection boxes, 32

Fiber Bragg Grating (FBG) sensors, and extension cables whose function is to

connect the sensors to the connection box and reading unit. Figure 3.1 shows the

layout of all the equipments.

The FBG deformation sensor is 3.28 ft (1 meter) long, single end deformation

sensor with an integrated temperature sensor, which can compensate for the

deformation caused by temperature changes. As shown in figure 3.2, the sensor is

composed of two parts: the active part and the passive part. The active part contains

the measurement fiber and measures the deformations between its two ends. The FBG

sensor measures the deformation by transforming a static or dynamic distance

variation into a change in reflected wavelength of a pre-stressed Fiber Bragg Grating

that can be measured with the reading unit. The passive part is an optical cable which

is insensitive to the deformations and used to connect the sensor to the connection

box or reading unit.

29

Figure 3.1 Layout of sensors, cables and connection boxes

Figure 3.2 FBG deformation sensor

Optic cable Active part

FBG Deformation Sensors FBG Deformation Sensors in crossed configuration Connection Box

113’-6”

28’- 4.5” 28’- 4.5”

F

E

D

C

B

A

C.C.B 7’

30

A temperature sensor is integrated in the passive part of the FBG sensor, 4 in

(10 cm) away from the active part. Each pair of crossed sensors shares the same

temperature sensor, while each parallel sensor has its own temperature sensor.

The MuST Reading Unit is a FBG demodulator based on the Micron Optics

engine. It simultaneously measures the deformation of all the FBG sensors and

therefore allows for dynamic testing to be performed using the system.

The main technical characteristics of the system are listed below (Smartec,

2004):

• Average strain resolution: 0.2 μm (0.0002 mm/m)

• Average strain repeatability: 2 μm (0.002 mm/m)

• Measurement range 0.5 % in shortening, 0.75 % in elongation

• Temperature resolution: 0.02°C

• Average strain repeatability: 0.2°C

• Frequency: 62.5 Hz (250/4)

3.2 Sensor Labeling

Each sensor has its own specific label according to its location. As shown in

Table 3.1, each label consists of three letters or digits. The first letter represents the

label of the girder, from A to F. The second letter represents the location of the sensor

along the girder, at midspan, quarter span, or the end. The third letter represents the

location of the sensor in the cross-section of the girder, at top or bottom. For the

sensors in crossed configuration, the end close to the abutment is chosen to represent

31

the “top” and “bottom” position, as shown in Figure 3.3. For example, sensor “BMT”

is located in girder B, at midspan in the top flange. The sensor labels are shown in

Figure 3.3.

Table 3.1 Sensor Label Description

SYMBOL DESCRIPTION

A

B

C

D

E

F

Girder A

Girder B

Girder C

Girder D

Girder E

Girder F

E

Q

M

End

Quarter span

Midspan

B

T

Bottom

Top

32

Figure 3.3 Sensor labels

3.3 Installation and Other Field Work

All girders were prefabricated at Core slab Structures in Albuquerque, NM.

Three girders were fabricated simultaneously on one long fabrication bed each week.

The bed layouts for each week are shown in Figures 3.4 and 3.5.

F

E

D

C

B

A AMTAM

BBMTBMB

CMT CMB

DMT DMB

EMTEMB

FMTFMB

CQTCQB

DQTDQB

EQTEQB

FQTFQB

AEB AET

BEB BET

CEBCET

DEB DET

EEB EET

FEB FET

33

Figure 3.4 Fabrication bed layout for the first week

Figure 3.5 Fabrication bed layout for the second week

Marked End Marked End

Girder A Girder B

Extension cables Computer and reading unit

Marked End

Girder C

Girder F Girder D Girder E Marked End Marked End Marked End

Computer and reading unit

Extension cables

34

Figure 3.6 Fabrication bed

All the sensors in girder A, B and C were installed on June 6 and 7. The sensors

were placed along dummy rebars. A dummy rebar was placed for each longitudinal

sensor and a dummy rebar was used for each crossed sensor. The dummy rebars for

the crossed sensor were placed so the center of the cross was 8 ft (2.4 m) away from

the marked ends. A four feet long level was used to make sure the dummy rebars

were placed at a 45 degree angle. Figures 3.7 to 3.9 show the sensors and dummy

rebars in the top flange, bottom flange, and crossed sensors respectively. The exact

location of each sensor was measured after installing all the sensors and is shown in

Table 3.2.

35

Figure 3.7 Sensor in the top flange

36

Figure3.8 Sensor in the bottom

Figure 3.9 Crossed sensors

37

Table 3.2 Sensor location in girder A, B, and C (1 inch = 25.4 mm) Sensor Type Away from bottom/top Away from CL*

AMB Parallel 2.36 in 2 in

AMT Parallel 3.25 in 0

AEB Cross

AET Cross

8 ft away from the end

2’ 7” away from the bottom

BMB Parallel 2.46 in 2 in

BMT Parallel 2 in 0

BEB Cross

BET Cross


2’ 6.5” away from the bottom

CMB Parallel 2.36 in 2.36 in

CMT Parallel 3.25 in 0

CQB Parallel 2.75 in 0

CQT Parallel 3 in 0

CEB Cross

CET Cross


2’ 7” away from the bottom

* On the side of the connection box

The sensors were attached to the dummy rebars using plastic zipper fasteners.

The optical cables were then guided to an outlet located in the top flange 5 ft (1.5 m)

away from the girder end. All the sensors were tested before the forms were installed.

During the test, the sensors were stretched if necessary to make sure the readings

were in the range of 200 um/m to 1000 um/m. The sensors are capable of taking

measurements in the range of -3500 um/m to 6500um/m, which is -0.0035 to

0.0065 in strain. This is a good measurement range for concrete.

38

Figure 3.10 Cable outlet in the girder top flange

The concrete of girder A, B and C was poured on June 13, 2004, starting at 1:15

pm with a temperature at 109.4°F (43.0°C) and finished at 4:25 pm with a

temperature at 106.3°F (41.3°C). Measurements were taken every one minute to

monitor the girders during the pouring of concrete. Vibration of the concrete was

provided using a vibrator attached on the outside of the forms. Twenty-four cylinder

samples were taken during the pouring of girder B. The girders were covered

immediately after the pouring.

39

The formworks were removed on June 14 in the morning. The strands were

cut from 12:40 pm to 1:15 pm, starting from the top row to the bottom row. All

strands were cut simultaneously at the ends of the bed and between the girders. Ten

measurements were taken after the cut of each row. There were six rows of strands

including the harped strands. After the cutting of all strands, the reading unit was set

to take measurements every one minute until the girder was stabilized. The camber

was measured at the mid-span of each girder and is shown in Table 3.3.

Figure 3.11 Girders on the fabrication bed

40

Table 3.3 Camber after transfer on girder A, B, and C GIRDER CAMBER

A 2.76 in (70.10 mm)

B 2.95 in (74.93 mm)

C 3.15 in (80.01 mm)

The reading unit and switch were disconnected and the girders were

transported to a secure location at the manufacturing site that afternoon. One

connection box for each girder was permanently installed on the girder web under the

top flange, as shown in Figure 3.12. All the sensor cables were connected to their own

connection box in each girder. Each connection box had an exten

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