Adjacent Box Beam Connections: Performance and Optimization

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FOREWORD

With the ever-increasing congestion and deterioration of the Nation’s highway system, there is a need to develop highly durable and rapidly constructed infrastructure systems. Durable bridge structures that require less intrusive maintenance and exhibit longer life spans, thus maximizing the use of the facilities, are highly desirable. Expediting bridge construction can minimize traffic flow disruptions. The precast prestressed concrete box beam bridge is one type of bridge system that can be constructed in an accelerated process with wide applications in short- and medium-span bridges in the United States.

The study presented herein was completed as part of the Federal Highway Administration’s Structural Concrete Research Program. It investigated the connection design details for this type of bridge, including novel connection details whose performance surpasses common practice. The findings provide an innovative solution that could advance the state of the practice in bridge construction. An executive summary of the information contained in this report has been published as a TechBrief titled Adjacent Box Beam Connections: Performance and Optimization.⁽¹⁾ This report will be of interest to engineers, academics, researchers, and industry partners who are involved the design, fabrication, construction, or maintenance of short- and medium-span bridges.

Cheryl Allen Richter, Ph.D., P.E.
Director, Office of Infrastructure
Research and Development

Form DOT F 1700.7 (8-72) Reproduction of completed page authorized.

SI* (Modern Metric) Conversion Factors

TABLE OF CONTENTS

• CHAPTER 1. INTRODUCTION
  • BACKGROUND
  • OBJECTIVE
  • REPORT ORGANIZATION
    
    
• CHAPTER 2. EXPERIMENTAL INVESTIGATION
  • INTRODUCTION
  • SHEAR KEY AND BOX BEAM DESIGN DETAILS
  • SHEAR KEY MATERIALS
    • Conventional Non-Shrink Grout
    • UHPC
  • SHEAR KEY CONSTRUCTION
  • THERMAL LOADING TEST SETUP
  • CYCLIC STRUCTURAL LOADING TEST SETUP
    • Transverse PT
    • Simply Supported Load and Reaction Arrangement
    • Modified Reactions to Increase System Restraint
    • Loading Protocol
    • Instrumentation
      
      
• CHAPTER 3. ANALYTICAL MODELING OF STRUCTURAL BEHAVIOR
  • PROPORTION OF MOMENT
  • EQUIVALENT MOMENT TRANSFERRED THROUGH THE CONNECTION (M_equivalent)
  • DIFFERENTIAL DEFLECTION (Δ_δ)
  • TRANSVERSE SHEAR IN THE CONNECTION
    
    
• CHAPTER 4. TEST RESULTS
  • EFFECTS FROM THERMAL LOADING
  • EFFECTS FROM CYCLIC STRUCTURAL LOADING
    • Proportion of Moment and Δ_δ Between the Beams
    • Transverse Strain in the Beams
      
      
• CHAPTER 5. DISCUSSION
  • PARTIAL- VERSUS FULL-DEPTH CONNECTION
  • CONDITION OF THE CONNECTION
  • TRANSVERSE PT
  • UHPC VERSUS CONVENTIONAL GROUT
    
    
• CHAPTER 6. SUMMARY AND CONCLUSIONS
  • SUMMARY
  • CONCLUSIONS AND RECOMMENDATIONS
    
    
• APPENDIX. BOX BEAM DESIGN DETAILS
  
  
• ACKNOWLEDGEMENTS
  
  
• REFERENCES

LIST OF FIGURES

• Figure 1. Illustration. Partial-depth conventional grout connection
• Figure 2. Illustration. Full-depth conventional grout connection
• Figure 3. Photo. Alignment of the partial-depth conventional grout connection
• Figure 4. Photo. Transverse PT bars after installation
• Figure 5. Illustration. Partial-depth UHPC connection
• Figure 6. Illustration. Full-depth UHPC connection
• Figure 7. Photo. SB surface finish utilized in the conventionally grouted connection
• Figure 8. Photo. EA surface finish utilized in the UHPC connection
• Figure 9. Photo. Alignment of the partial-depth UHPC connection
• Figure 10. Photo. Partial-depth UHPC connection after alignment
• Figure 11. Illustrations. Partial-depth connection details for the conventional and UHPC connections
• Figure 12. Illustrations. Full-depth connection details for the conventional and UHPC connections
• Figure 13. Photo. Partial-depth beams aligned for connection with the conventional grout shear key connection
• Figure 14. Photo. Partial-depth beams aligned for connection with the UHPC shear key connection
• Figure 15. Photo. Pre-wetting the shear key prior to casting the grout
• Figure 16. Photo. Wet burlap curing for the conventionally grouted connection
• Figure 17. Photo. Plastic cover curing for the UHPC connection
• Figure 18. Photo. Comparison of the connection surface and interface between the box beams before and after grinding
• Figure 19. Illustration. Copper tube arrangement within the top flange of the beams
• Figure 20. Photo. Copper tubes in the box beam prior to casting
• Figure 21. Photo. Transverse PT monitored with a load cell
• Figure 22. Illustrations. Loading setup for the simply supported configuration
• Figure 23. Photo. Cyclic structural loading test setup
• Figure 24. Illustrations. Boundary conditions intended to increase structural stiffness
• Figure 25. Photo. Clamping at the beam ends to restrain the transverse rotation
• Figure 26. Photo. Additional support provided at in-span diaphragms
• Figure 27. Graph. Example of force read by the actuator load cells in the simply supported and partially stiffened beam setups
• Figure 28. Graph. Example of force read by the actuator load cells for beams with the fully stiffened boundary condition
• Figure 29. Photo. Load cell under the beam at the west support
• Figure 30. Photo. Five LVDTs (four vertical and one transverse) at the mid-span used to measure vertical deflection of the beams and the transverse connection opening
• Figure 31. Photo. Transverse LVDT and strain gauge on the top surface spanning the connection
• Figure 32. Photo. Longitudinal strain gauge and thermocouple located at the mid-span in the bottom flange of one of the beams
• Figure 33. Illustration. Plan view of instrumentation installed on the test specimens
• Figure 34. Equation. Moment distribution factor for a beam
• Figure 35. Equation. Moment carried by the beam with respect to the mid-span deflection
• Figure 36. Equation. Moment carried by the beam with respect to the longitudinal tensile strain at the mid-span
• Figure 37. Equation. Loaded beam proportion of moment factor with respect to the mid-span deflection
• Figure 38. Equation. Loaded beam proportion of moment factor for the loaded beam with respect to the mid-span longitudinal tensile strain
• Figure 39. Graph. Loaded beam proportion of moment based on deflection and longitudinal tensile strain for unstiffened beams with a partial-depth uncracked conventionally grouted connection
• Figure 40. Graph. Loaded beam proportion of moment based on deflection and longitudinal tensile strain for partially stiffened beams with a partial-depth uncracked conventionally grouted connection
• Figure 41. Equation. Additional strain in beam B due to M_equivalent
• Figure 42. Equation. M_equivalent
• Figure 43. Graph. Longitudinal tensile strain range at the mid-span for unstiffened beams with a partial-depth uncracked conventionally grouted connection
• Figure 44. Graph. Longitudinal tensile strain range at the mid-span for partially stiffened beams with a partial-depth uncracked conventionally grouted connection
• Figure 45. Graph. Tensile strain range at the mid-span for fully stiffened beams with a partial-depth uncracked conventionally grouted connection
• Figure 46. Equation. Δ_δ between the two beams
• Figure 47. Graph. Comparison of Δ_δ and differential rotation for the full-depth UHPC connection
• Figure 48. Illustration. Transverse shear stress distribution through the connection
• Figure 49. Equation. v′_max through the connection
• Figure 50. Graph. Relationship between upward deflection and temperature gradient in beams with conventionally grouted connections
• Figure 51. Graph. Relationship between upward deflection and temperature gradient in beams with UHPC connections
• Figure 52. Photo. Representative cracking observed in the partial-depth conventional grout connection after thermal loading
• Figure 53. Graph. Longitudinal tensile strain measured at the mid-span in unstiffened beams with a partial-depth uncracked conventionally grouted connection
• Figure 54. Graph. Proportion of moment based on the mid-span strain and deflection for unstiffened beams with a partial-depth uncracked conventionally grouted connection
• Figure 55. Graph. Δ_δ measured at the mid-span in unstiffened beams with a partial-depth uncracked conventionally grouted connection
• Figure 56. Graph. Longitudinal tensile strain measured at the mid-span in partially stiffened beams with a partial-depth uncracked conventionally grouted connection
• Figure 57. Graph. Loaded proportion of moment based on the mid-span strain and deflection for partially stiffened beams with a partial-depth uncracked conventionally grouted connection
• Figure 58. Graph. Δ_δ measured at the mid-span in partially stiffened beams with a partial-depth uncracked conventionally grouted connection
• Figure 59. Graph. Longitudinal tensile strain range measured at the mid-span in fully stiffened beams with a partial-depth uncracked conventionally grouted connection
• Figure 60. Graph. Δ_δ measured at the mid-span in fully stiffened beams with a partial-depth uncracked conventionally grouted connection
• Figure 61. Photos. Mechanical cracking of the partial-depth conventionally grouted connection, including the cracking setup and the cracked connection
• Figure 62. Photos. Propagation of the end of the connection crack induced by cyclic structural loading
• Figure 63. Graph. Longitudinal tensile strain range measured at the mid-span in fully stiffened beams with a partial-depth partially cracked conventionally grouted connection
• Figure 64. Graph. Δ_δ measured at the mid-span in fully stiffened beams with a partial-depth partially cracked conventionally grouted connection
• Figure 65. Graph. Longitudinal tensile strain range measured at the mid-span in fully stiffened beams with a partial-depth fully cracked conventionally grouted connection
• Figure 66. Graph. Δ_δ measured at the mid-span in fully stiffened beams with a partial-depth fully cracked conventionally grouted connection
• Figure 67. Illustration. Exaggerated transverse curve in box beams
• Figure 68. Graph. Tensile strain at the mid-span showing full-depth connection, conventional grout, unstiffened boundary, and partially and fully cracked conditions
• Figure 69. Graph. Proportion of moment carried by the loaded beam based on the mid-span strain and deflection for the full-depth partially and fully cracked conventionally grouted connections
• Figure 70. Graph. Δ_δ measured at the mid-span in the full-depth partially and fully cracked conventionally grouted connections
• Figure 71. Graph. Longitudinal tensile strain measured at the mid-span in partially and fully stiffened beams with a partial-depth UHPC connection
• Figure 72. Graph. Proportion of moment carried by the loaded beam based on the mid-span strain and deflection for partially stiffened beams with a partial-depth UHPC connection
• Figure 73. Graph. Δ_δ measured at the mid-span in partially and fully stiffened beams with a partial-depth UHPC connection
• Figure 74. Photo. Crack development in the box beam during an attempt to mechanically induce a crack in the UHPC connection
• Figure 75. Graph. Longitudinal tensile strain measured at the mid-span in unstiffened and partially stiffened beams with a full-depth UHPC connection
• Figure 76. Graph. Proportion of the moment carried by the loaded beam based on the mid-span strain and deflection for unstiffened and partially stiffened beams with a full-depth UHPC connection
• Figure 77. Graph. Δ_δ measured at the mid-span in unstiffened and partially stiffened beams with a full-depth UHPC connection
• Figure 78. Graph. Longitudinal tensile strain range measured at the mid-span in fully stiffened beams with a full-depth UHPC connection
• Figure 79. Graph. Δ_δ measured at the mid-span in fully stiffened beams with a full-depth UHPC connection
• Figure 80. Illustration. Location of all possible transverse strain gauges in this study
• Figure 81. Graph. Top transverse strain ranges recorded by internal strain gauges in two beams for unstiffened beams with a partial-depth uncracked conventionally grouted connection
• Figure 82. Graph. Top transverse strain ranges recorded at the mid-span for fully stiffened beams with a partial-depth uncracked conventionally grouted connection
• Figure 83. Graph. Top transverse strain ranges recorded 6 ft (1.8 m) east of the mid-span for fully stiffened beams with a partial-depth uncracked conventionally grouted connection
• Figure 84. Graph. Top transverse strain ranges recorded at the mid-span for partially and fully stiffened beams with a partial-depth uncracked UHPC connection
• Figure 85. Graph. Top transverse strain ranges recorded 6 ft (1.8 m) east of the mid-span for partially and fully stiffened beams with a partial-depth uncracked UHPC connection
• Figure 86. Graph. Top transverse strain ranges recorded along the length of the connection for partially and fully stiffened beams with a partial-depth uncracked UHPC connection
• Figure 87. Graph. Distribution of top transverse strain ranges recorded along the top of the unstiffened and partially stiffened beams with a full-depth uncracked UHPC connection at the mid-span
• Figure 88. Graph. Top transverse strain ranges recorded along the top of unstiffened and partially stiffened beams with a full-depth uncracked UHPC connection 6 ft (1.8 m) from the mid-span
• Figure 89. Graph. Top transverse strain ranges recorded along the top of fully stiffened beams with a full-depth uncracked UHPC connection at the mid-span
• Figure 90. Graph. Top transverse strain ranges recorded along the top of fully stiffened beams with a full-depth uncracked UHPC connection 6 ft (1.8 m) east of the mid-span
• Figure 91. Graph. Comparison of the longitudinal strain ranges for the partial- and full-depth UHPC connections
• Figure 92. Graph. Comparison of the loaded beam proportion of moment between the partial- and full-depth UHPC connections
• Figure 93. Graph. Comparison of Δ_δ of the partial- and full-depth UHPC connections
• Figure 94. Graph. Comparison of the top transverse strain ranges in the partial- and full-depth UHPC connections
• Figure 95. Graph. Comparison of longitudinal strain ranges based on the extent of cracking in the connection
• Figure 96. Graph. Comparison of Δ_δ between the beams based on the extent of cracking in the connection
• Figure 97. Graph. Comparison of the top transverse strain ranges at the mid-span in the connection based on the extent of cracking in the connection
• Figure 98. Graph. Comparison of the top transverse strain ranges in the beams based on the extent of cracking in the connection
• Figure 99. Comparison of the longitudinal strain ranges for the unloaded and loaded beams with unstiffened uncracked partial-depth conventional connections based on the level of PT
• Figure 100. Graph. Comparison of the loaded beam proportion of moment in the beams with unstiffened uncracked partial-depth connections based on the level of PT force
• Figure 101. Graph. Comparison of Δ_δ in the beams with unstiffened uncracked partial-depth connections based on the level of PT force
• Figure 102. Graph. Comparison of longitudinal strain ranges in beams with fully stiffened partial-depth connections based on the level of PT force
• Figure 103. Graph. Comparison of Δ_δ in beams with fully stiffened partial-depth connections based on the level of PT force
• Figure 104. Graph. Comparison of longitudinal strain ranges in beams with partially cracked unstiffened full-depth conventional connections based on the level of PT force
• Figure 105. Graph. Comparison of loaded beam proportion of moment in beams with partially cracked unstiffened full-depth conventional connections based on the level of PT force
• Figure 106. Comparison of Δ_δ in beams with partially cracked unstiffened full-depth conventional connections based on the level of PT force
• Figure 107. Graph. Connection compressive strain recorded during PT operation
• Figure 108. Graph. Comparison of the longitudinal strain ranges in the fully stiffened beams with a partial-depth connection
• Figure 109. Graph. Comparison of the longitudinal strain ranges in the unstiffened beams with a full-depth connection
• Figure 110. Graph. Comparison of the loaded beam proportion of moment in the unstiffened beams with a full-depth connection
• Figure 111. Graph. Comparison of Δ_δ of the fully stiffened beams with a partial-depth connection
• Figure 112. Graph. Comparison of Δ_δ of the unstiffened beams with a full-depth connection
• Figure 113. Drawing. Box design with partial-depth shear keys showing plan, elevation, section, and shear key details
• Figure 114. Drawing. Box design with partial-depth shear keys showing notes, details, and reinforcement schedule
• Figure 115. Drawing. Box design with full-depth shear keys showing plan, elevation, section, and shear key details
• Figure 116. Drawing. Box design with full-depth shear keys showing notes, details, and reinforcement schedule

LIST OF TABLES

• Table 1. Typical material properties of the utilized conventional non-shrink grout
• Table 2. Typical field-cast UHPC material properties
• Table 3. UHPC mix design
• Table 4. Summary of structural loading scenarios for the partial-depth conventional shear key connections
• Table 5. Summary of structural loading scenarios for the full-depth conventional shear key connections
• Table 6. Summary of structural loading scenarios for the partial-depth UHPC shear key connections
• Table 7. Summary of structural loading scenarios for the full-depth UHPC shear key connections
• Table 8. Strain gauges used in the test setups
• Table 9. Beam stiffness calculation
• Table 10. Data summary of the thermal tests

LIST OF ABBREVIATIONS AND SYMBOLS