Repair of Cracked Prestressed Concrete Girders, I-565, Huntsville, Alabama

657 Pages·2011·8.05 MB·English

Research Report No. 2F for ALDOT Project 930-601

REPAIR OF CRACKED PRESTRESSED
CONCRETE GIRDERS, I-565,
HUNTSVILLE, ALABAMA

Submitted to

The Alabama Department of Transportation

Prepared by

Wesley O. Bullock
Robert W. Barnes
Anton K. Schindler

JULY 2011
1. Report No. 2. Government Accession No. 3. Recipient Catalog No.
FHWA/ALDOT 930-601-2F
4 Title and Subtitle 5 Report Date
Repair of Cracked Prestressed Concrete Girders, I-565, July 2011
Huntsville, Alabama
6 Performing Organization
Code

7. Author(s) 8 Performing
Organization Report No.
Wesley O. Bullock, Robert W. Barnes, and Anton K. Schindler
FHWA/ALDOT 930-601-2F
9 Performing Organization Name and Address 10 Work Unit No. (TRAIS)
Highway Research Center
Department of Civil Engineering
11 Contract or Grant No.
238 Harbert Engineering Center
Auburn, AL 36849
12 Sponsoring Agency Name and Address 13 Type of Report and Period
Covered
Alabama Department of Transportation
Technical Report
1409 Coliseum Boulevard
Montgomery, Alabama 36130-3050 14 Sponsoring Agency Code

15 Supplementary Notes
Research performed in cooperation with the Alabama Department of Transportation
16 Abstract
Wide cracks were discovered in prestressed concrete bridge girders shortly after their construction in
Huntsville, Alabama. Previous investigations of these continuous-for-live-load girders revealed that the cracking
resulted from restrained thermal deformations and inadequate reinforcement details, and that the cracking
compromised the strength of the girder end regions. A wet-layup fiber-reinforced polymer (FRP) repair system
was installed. To assess the efficacy of the FRP repair solution, load testing and finite-element analyses were
conducted for pre- and post-repair conditions of two repaired spans.
Post-repair testing included controlled truck loading as well as the monitoring of structural response to
diurnal thermal conditions. Results indicate that the girders should be considered simply supported for
conservative strength-limit-state design of the FRP repair system. FRP response to thermal conditions was
accurately estimated using simplified analysis of restrained temperature gradient effects.
A design procedure was developed for FRP repair of similar structures in accordance with AASHTO
LRFD Bridge Design Specifications and the recommendations of ACI 440.2R-08. The reported procedure was
formulated to provide the girder end regions with adequate strength for the combined effects of shear and
flexure, as well as to provide adequate performance under daily truck loads and temperature variations.
17 Key Words 18 Distribution Statement
Bridges, continuity, cracking, damage, fiber- No restrictions. This document is available to the
reinforced polymer reinforcement, repair, restraint public through the National Technical Information
stresses, strengthening, thermal effects Service, Springfield, Virginia 22161
19 Security 20 Security 21 No. of pages 22 Price
Classification (of Classification (of
621
this report) this report)
Unclassified Unclassified
_______________________
Research Report FHWA/ALDOT 930-601-2F

REPAIR OF CRACKED PRESTRESSED
CONCRETE GIRDERS, I-565,
HUNTSVILLE, ALABAMA

Submitted to

The Alabama Department of Transportation

Prepared by

Wesley O. Bullock
Robert W. Barnes
Anton K. Schindler

JULY 2011
DISCLAIMERS

The contents of this report reflect the views of the authors, who are responsible for the facts and
the accuracy of the data presented herein. The contents do not necessarily reflect the official
views or policies of Auburn University or the Federal Highway Administration. This report does
not constitute a standard, specification, or regulation.

NOT INTENDED FOR CONSTRUCTION, BIDDING, OR PERMIT PURPOSES

Robert W. Barnes, Ph.D., P.E.
Anton K. Schindler, Ph.D., P.E.
Research Supervisors

ACKNOWLEDGEMENTS

Material contained herein was obtained in connection with a research project ALDOT 930-601,
conducted by the Auburn University Highway Research Center. Funding for the project was
provided by the Federal Highway Administration (FHWA) and the Alabama Department of
Transportation (ALDOT). The funding, cooperation, and assistance of many individuals from
each of these organizations are gratefully acknowledged. The authors would like to acknowledge
the various contributions of the following individuals:
George H. Conner, State Maintenance Engineer, ALDOT
Robert King, Structural Engineer, FHWA
Eric Christie, Bridge Maintenance Engineer, ALDOT
W. Sean Butler, First Division, ALDOT
Randall Mullins, Section Supervisor, Bridge Bureau, ALDOT
James F. Boyer, Bridge Rating Engineer, ALDOT
Robert A. Fulton, formerly of Maintenance Bureau, ALDOT
Mark Strickland, Specifications Engineer, ALDOT
Lyndi Blackburn, Assistant Materials and Tests Engineer, ALDOT

iv
ABSTRACT

After the construction of elevated portions of I-565 in Huntsville, Alabama, cracks were
discovered in numerous prestressed concrete bulb-tee bridge girders that were constructed to
exhibit continuous behavior in response to post-construction loads. Previous investigations
conducted by Alabama Department of Transportation (ALDOT) and Auburn University Highway
Research Center (AUHRC) personnel resulted in determinations that the cracking was a result of
restrained thermal deformations and inadequate reinforcement details, and that the cracking
compromised the strength of the girder end regions. A wet-layup fiber-reinforced polymer (FRP)
repair scheme was proposed to address the deficiency. To assess the efficacy of the FRP repair
solution, load testing and finite element model (FEM) analyses were conducted for pre- and post-
repair conditions of Northbound Spans 10 and 11. Pre-repair testing was conducted on June 1
and 2, 2005. The FRP reinforcement system was installed in December 2007. Post-repair
testing was conducted on May 25 and 26, 2010.
Post-repair testing included controlled truck loading as well as the monitoring of structural
response to diurnal thermal conditions. Analysis of pre- and post-repair results indicated that the
efficacy of the repair solution could not be assessed with direct comparisons between pre- and
post-repair measurements due to unforeseen unintentional support conditions that were in effect
during the pre-repair testing. Direct analysis of post-repair behavior indicated that the structure
exhibits continuity degradation in response to heavy truck loads and should be considered simply
supported for conservative strength-limit-state design. Analysis of responses to thermal
conditions indicated the FRP reinforcement exhibits behavior that can be accurately estimated
with simplified analysis of linear temperature gradient effects on restrained girders. Based on
conditions observed after more than 2 years in service, the installed FRP reinforcement system
was determined to be performing appropriately.
Based on the experimental observations, a design procedure was developed for FRP
repair of similar structures with damaged regions near continuous ends of prestressed concrete
bridge girders in accordance with AASHTO LRFD Bridge Design Specifications and the
recommendations of ACI 440.2R-08. The design procedure was formulated to provide the girder
end regions with adequate strength-limit-state resistance for the combined effects of shear and
flexure, as well as to provide adequate performance under service loads—including the effects of
daily temperature variations. A design example is presented.
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TABLE OF CONTENTS
LIST OF TABLES .......................................................................................................................... xvi
LIST OF FIGURES ........................................................................................................................ xx
CHAPTER 1
INTRODUCTION .............................................................................................................................. 1
1.1 Project Overview ............................................................................................................. 1
1.2 Need for Research .......................................................................................................... 3
1.3 Project Objectives ........................................................................................................... 5
1.4 Project Tasks .................................................................................................................. 5
1.4.1 Task 1: Preliminary Engineering for FRP Repair .............................................. 6
1.4.2 Task 2: Literature Review on Current State of the Art ...................................... 6
1.4.3 Task 3: Preliminary Load Testing ..................................................................... 6
1.4.4 Task 4: Construction Monitoring ....................................................................... 6
1.4.5 Task 5: Post-Repair Load Testing .................................................................... 6
1.4.6 Task 6: Performance Monitoring under Traffic Loads ....................................... 7
1.4.7 Task 7: Evaluation of Bridge Performance ....................................................... 7
1.4.8 Task 8: Evaluation of Acoustic Emission Monitoring ........................................ 7
1.4.9 Task 9: Preparation of Final Project Reports .................................................... 7
1.5 Report Organization ........................................................................................................ 7
CHAPTER 2
HISTORY OF THE BRIDGE STRUCTURE AND ASSOCIATED RESEARCH .............................. 9
2.1 Introduction...................................................................................................................... 9
2.2 Bridge Construction ......................................................................................................... 9
2.3 Structural Geometry and Material Properties .................................................................. 9
2.3.1 Spans Investigated ........................................................................................... 10
2.3.2 Girder Types .................................................................................................... 13
2.3.3 Prestressing Strands ........................................................................................ 14
2.3.4 Shear Reinforcement ....................................................................................... 19
2.3.5 Continuity Reinforcement ................................................................................. 23
2.3.6 Bridge Deck ...................................................................................................... 25
2.4 Unexpected Cracking .................................................................................................... 28
2.4.1 Crack Locations ............................................................................................... 28
2.4.2 Previous Repairs and Safety Measures........................................................... 32
2.4.3 Causes for Cracking ......................................................................................... 34
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2.4.3.1 Construction Sequence ................................................................. 34
2.4.3.2 Time-Dependent Effects ................................................................ 35
2.4.3.3 Temperature Effects ...................................................................... 35
2.4.3.4 Internal Reinforcement Details ...................................................... 36
2.4.4 Ramifications of Cracking ................................................................................ 37
2.5 Bridge Behavior Analysis .............................................................................................. 38
2.5.1 Behavior Types Considered ............................................................................. 38
2.5.2 Analysis Methods ............................................................................................. 38
2.5.2.1 Elastic Structural Analysis—Unfactored Demands ........................ 39
2.5.2.2 Sectional Model Analysis—Strength Capacities ............................ 39
2.5.2.3 Strut-and-Tie Analysis—Flow of Forces ........................................ 40
2.6 Design of External Fiber-Reinforced Polymer Strengthening System .......................... 43
2.7 Load Tests Prior to FRP Reinforcement Installation ..................................................... 46
2.7.1 Instrumentation for Pre-Repair Load Testing ................................................... 46
2.7.2 Procedures for Pre-Repair Load Testing ......................................................... 47
2.7.3 Results of Pre-Repair Load Testing ................................................................. 47
2.8 Finite-Element Analysis of Bridge Behavior .................................................................. 48
2.8.1 Uncracked Model ............................................................................................. 48
2.8.2 Cracked Model ................................................................................................. 48
2.8.3 Cracked-with-Reinforcement Model ................................................................. 49
2.8.4 Pre-Repair Model ............................................................................................. 49
2.8.5 Post-Repair Model ........................................................................................... 49
2.9 Installation of External FRP Reinforcement .................................................................. 49
2.9.1 Surface Preparation ......................................................................................... 50
2.9.2 Adhesion Testing ............................................................................................. 53
2.9.3 Tensile Testing ................................................................................................. 54
2.9.4 FRP Fabric Installation Procedures ................................................................. 56
2.9.5 FRP Fabric Installation—First Layer ................................................................ 59
2.9.6 FRP Fabric Installation—Second Layer ........................................................... 59
2.9.7 FRP Fabric Installation—Third Layer ............................................................... 60
2.9.8 FRP Fabric Installation—Fourth Layer ............................................................. 60
2.9.9 Painting of Installed FRP Reinforcement ......................................................... 61
2.9.10 FRP Reinforcement Installation Timeline ......................................................... 62
2.9.10.1 December 11, 2007 ....................................................................... 63
2.9.10.2 December 12, 2007 ....................................................................... 63
2.9.10.3 December 13, 2007 ....................................................................... 63
2.9.10.4 December 14, 2007 ....................................................................... 64
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2.9.10.5 December 15, 2007 ....................................................................... 64
2.9.10.6 December 16, 2007 ....................................................................... 64
2.9.10.7 December 17, 2007 ....................................................................... 64
2.9.10.8 December 18, 2007 ....................................................................... 64
2.9.10.9 December 19, 2007 ....................................................................... 64
2.9.10.10 After December 19, 2007 ............................................................... 64
2.10 Installation and Testing Concerns ................................................................................. 65
2.10.1 FRP Orientation ............................................................................................... 65
2.10.2 FRP Samples for Tensile Testing .................................................................... 65
2.10.3 FRP Tensile Testing Observation .................................................................... 65
2.10.4 FRP Tensile Test Results ................................................................................ 66
2.11 Current Research .......................................................................................................... 67
CHAPTER 3
BRIDGE INSTRUMENTATION ..................................................................................................... 68
3.1 Introduction.................................................................................................................... 68
3.2 Instrumentation Overview ............................................................................................. 68
3.3 Crack-Opening Displacement Gages ........................................................................... 70
3.3.1 COD Gage Locations ....................................................................................... 72
3.3.2 COD Gage Installation ..................................................................................... 72
3.4 Deflectometers .............................................................................................................. 74
3.4.1 Deflectometer Locations .................................................................................. 75
3.4.2 Deflectometer Installation................................................................................. 78
3.5 Strain Gages ................................................................................................................. 81
3.5.1 Strain Gage Locations...................................................................................... 82
3.5.1.1 Cross Section Locations ................................................................ 91
3.5.1.2 Gage Locations within A Typical Cross Section ............................ 92
3.5.1.3 Discontinued, Additional, and Replacement Gages ...................... 92
3.5.2 Concrete Strain Gages..................................................................................... 93
3.5.3 FRP Strain Gages ............................................................................................ 94
3.5.4 Strain Gage Installation .................................................................................... 95
3.6 Data Acquisition System ............................................................................................. 101
3.7 Sensor Notation .......................................................................................................... 102
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CHAPTER 4
BRIDGE TESTING PROCEDURES ............................................................................................ 104
4.1 Introduction.................................................................................................................. 104
4.2 Traffic Control .............................................................................................................. 104
4.3 Load Testing Trucks .................................................................................................... 105
4.3.1 Load Truck Block Configurations ................................................................... 109
4.3.2 Resultant Force Comparisons—Pre- and Post-Repair .................................. 113
4.3.3 Night 1—AE Preloading—LC-6.5 ................................................................... 114
4.3.4 Night 2—AE Loading and Multiposition Load Test—LC-6 ............................. 115
4.3.5 Truck Weight Limits ........................................................................................ 115
4.4 Load Testing Traverse Lanes and Stop Positions ...................................................... 115
4.4.1 Traverse Lanes .............................................................................................. 116
4.4.2 Stop Positions ................................................................................................ 118
4.5 Acoustic Emissions Load Testing ............................................................................... 120
4.6 Bridge Monitoring ........................................................................................................ 122
4.6.1 Weather Conditions during Pre-Repair Testing ............................................. 123
4.6.2 Weather Conditions during Post-Repair Testing ........................................... 123
4.7 Multiposition Load Testing .......................................................................................... 125
4.8 Superposition Testing ................................................................................................. 126
4.9 Data Reduction and Analysis ...................................................................................... 129
CHAPTER 5
RESULTS AND DISCUSSION .................................................................................................... 130
5.1 Introduction.................................................................................................................. 130
5.2 Bearing Pad Effects .................................................................................................... 130
5.3 Bridge Response to Truck Loads—Post-Repair ......................................................... 136
5.3.1 Response to Different Horizontal Truck Alignments ...................................... 136
5.3.2 Indications of Damage to Instrumented Girders ............................................ 141
5.3.2.1 Crack-Opening Displacements .................................................... 141
5.3.2.2 Crack-Opening Displacement Observations ............................... 144
5.3.2.3 Bottom-Fiber Strains .................................................................... 145
5.3.2.4 Bottom-Fiber Strain Observations ............................................... 150
5.3.2.5 COD and Bottom-Fiber Strain Comparisons ............................... 150
5.3.2.6 Damage Indication Conclusions .................................................. 154
5.3.3 Post-Repair Continuity Behavior Assessment ............................................... 154
5.3.3.1 Deflections ................................................................................... 154
5.3.3.2 Bottom-Fiber Strains .................................................................... 159
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5.3.3.3 Crack Behavior ............................................................................ 170
5.3.3.4 Continuity Behavior Conclusions ................................................. 177
5.3.4 Linear-Elastic Behavior .................................................................................. 178
5.3.4.1 Linear-Elastic Behavior Assessment—Two-Span Structure ....... 178
5.3.4.2 Linear-Elastic Behavior Assessment—Damaged Regions ......... 180
5.3.4.3 Linear-Elastic Behavior Conclusions ........................................... 185
5.3.5 Relationship between Truck Position and FRP Tensile Demand .................. 185
5.4 Bridge Response to Ambient Thermal Conditions ...................................................... 193
5.4.1 Theoretical Response to Ambient Thermal Conditions ................................. 193
5.4.1.1 Structural Analysis ....................................................................... 194
5.4.1.2 Expected Behavior ....................................................................... 198
5.4.2 Measured Responses to Ambient Thermal Conditions ................................. 206
5.4.2.1 Deflections ................................................................................... 207
5.4.2.2 Bottom-Fiber Strains .................................................................... 213
5.4.2.3 Crack-Opening Displacements .................................................... 231
5.5 Performance of FRP Reinforcement ........................................................................... 238
5.6 Conclusions ................................................................................................................. 239
CHAPTER 6
FRP REINFORCEMENT DESIGN ............................................................................................... 241
6.1 Introduction.................................................................................................................. 241
6.2 Necessity of FRP Reinforcement ................................................................................ 241
6.3 FRP Reinforcement Product Selection ....................................................................... 242
6.4 Strength-Limit-State Design ........................................................................................ 243
6.4.1 Critical Cross-Section Locations .................................................................... 244
6.4.2 Critical Load Conditions ................................................................................. 244
6.4.3 Strength-Limit-State Temperature Demands ................................................. 245
6.4.4 Material Properties ......................................................................................... 245
6.4.4.1 Concrete ...................................................................................... 245
6.4.4.2 Steel Reinforcement .................................................................... 246
6.4.4.3 FRP Reinforcement ..................................................................... 246
6.4.5 Dimensional Properties .................................................................................. 247
6.4.5.1 Cross-Section Dimensions .......................................................... 248
6.4.5.2 Reinforcement Dimensions .......................................................... 248
6.4.6 Initial Estimate of Required FRP Layers ........................................................ 250
6.4.7 Vertical Shear Strength Resistance ............................................................... 251
6.4.7.1 Nominal Strength for Bending Moment Resistance ..................... 252
x