Precast Bent System for High Seismic Regions: Laboratory Tests of Column-to-Footing Socket Connections
PUBLICATION NO. FHWA-HIF-13-039
June 2013
Notice
This document is disseminated under the sponsorship of the U.S. Department of Transportation in the interest of information exchange. The U.S. Government assumes no liability for the use of the information contained in this document. This report does not constitute a standard, specification, or regulation.
The U.S. Government does not endorse products or manufacturers. Trademarks or manufacturers’ names appear in this report only because they are considered essential to the objective of the document.
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The Federal Highway Administration (FHWA) provides high-quality information to serve Government, industry, and the public in a manner that promotes public understanding. Standards and policies are used to ensure and maximize the quality, objectivity, utility, and integrity of its information. FHWA periodically reviews quality issues and adjusts its programs and processes to ensure continuous quality improvement.
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9. Performing Organization Name and Address 1 University of Washington, Seattle, WA |
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15. Supplementary Notes |
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16. Abstract The tests provide data regarding the performance of the precast column-to-spread footing connection. The results indicate that the connection, when used with a precast column, is sufficiently strong to support the factored design gravity loads and to resist plastic hinging in the column above the footing. The behavior is emulative of cast-in-place performance. However, the precast column also provides an improved load path for lateral force transfer to the footing, owing to the elimination of outwardly hooked column longitudinal reinforcement. Additionally, the connection performance is adequate without reinforcement passing from the footing into the column, thus simplifying construction. |
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Preface
This report provides technical information from the laboratory testing of three precast column-to-spread footing specimens. These tests were conducted to support the development of a precast bent system for use in high seismic regions.
This report consists of seven chapters.
Chapter 1 provides background and overview material, including the spread footing socket connection concept and the research objective and scope.
Chapter 2 covers the design of the test specimens.
Chapter 3 provides a description of the test setup, instrumentation, and the method of control of the testing process.
Chapter 4 provides definition of the damage states that were observed and an overview of the damage progression that occurred during testing.
Chapter 5 provides the measured response of the three specimens, including material strengths, force and moment vs. displacement plots, curvature distributions, displacement histories, and strain histories. Strain histories are provided for all the principal reinforcement types. Also included are the results of the post-seismic tests of the axial capacity of the foundation.
Chapter 6 covers the analysis of the observed and recorded data, and it provides treatment of various modes of potential failure and how the test results compared relative to those failure modes.
Chapter 7 provides a summary, conclusions, and recommendations.
Appendixes are included to report more detailed information that may be useful in understanding the response of the specimens and the progression of damage.
Symbol | When You Know | Multiply By | To Find | Symbol |
---|---|---|---|---|
Length | ||||
in | inches | 25.4 | millimeters | mm |
ft | feet | 0.305 | meters | m |
yd | yards | 0.914 | meters | m |
mi | miles | 1.61 | kilometers | km |
Area | ||||
in2 | square inches | 645.2 | square millimeters | mm2 |
ft2 | square feet | 0.093 | square meters | m2 |
yd2 | square yard | 0.836 | square meters | m2 |
ac | acres | 0.405 | hectares | ha |
mi2 | square miles | 2.59 | square kilometers | km2 |
Volume | ||||
fl oz | fluid ounces | 29.57 | milliliters | mL |
gal | gallons | 3.785 | liters | L |
ft3 | cubic feet | 0.028 | cubic meters | m3 |
yd3 | cubic yards | 0.765 | cubic meters | m3 |
NOTE: volumes greater than 1000 L shall be shown in m3 | ||||
Mass | ||||
oz | ounces | 28.35 | grams | g |
lb | pounds | 0.454 | kilograms | kg |
T | short tons (2000 lb) | 0.907 | megagrams (or "metric ton") | Mg (or "t") |
Temperature (exact degrees) | ||||
°F | Fahrenheit | 5 (F-32)/9 or (F-32)/1.8 |
Celsius | °C |
Illumination | ||||
fc | foot-candles | 10.76 | lux | lx |
fl | foot-Lamberts | 3.426 | candela/m2 | cd/m2 |
Force and Pressure or Stress | ||||
lbf | poundforce | 4.45 | newtons | N |
lbf/in2 | poundforce per square inch | 6.89 | kilopascals | kPa |
Table of Contents
CHAPTER 1. INTRODUCTION
Need for Rapid Construction
Socket Connection Concept
Objectives and Scope
CHAPTER 2. DESIGN OF TEST SPECIMENS
Design of Prototype and Test Columns
Design of Prototype and Test Specimen Column-to-Footing Connection
Specimens SF-1 and SF-2
Specimen SF-3
CHAPTER 3. EXPERIMENTAL PROGRAM
Loading Setup
Instrumentation
Testing Protocol
CHAPTER 4. DAMAGE PROGRESSION
Definitions of Damage States
Preliminary Test Cycles
Factored Axial-Load Tests
Lateral-Load Tests (up to yielding)
Lateral-Load Tests (after yielding)
Axial-Load Testing to Collapse
CHAPTER 5. MEASURED RESPONSE
Material Properties
Concrete Strength
Grout Strength
Reinforcement
Friction Correction
Moment-Drift Response
Effective Force
Distribution of Column Curvature
Column Splice
Strains in Column Longitudinal Bars
Strain Profiles along the Height of Specimen
Strain Histories for Bars near Splice
Column Longitudinal Bar Strain Histories in Footing
Footing Strain Corrections
Strains in Bottom Mat of Footing Reinforcement
Strains in Bottom Bars in the North-South Direction (Loading Direction)
Implication of the Effective Width
Strains in Bottom Bars in the East-West Direction
Strains in Diagonal Bars
Strains in Footing Ties
Axial Load-Response
Factored Axial Loading
Ultimate Axial-Load Capacities
CHAPTER 6. ANALYSIS OF MEASURED RESPONSE
Footing OverturningFooting Response
Footing Flexural Strength
Footing One-Way Shear Strength
Combined Punching Shear and Moment Transfer
Footing Punching Shear Strength
Footing Shear-Friction Strength
Footing Joint Shear
Column Response
Column Axial-Load Capacity
Column Flexural Strength
Column Shear Strength
Column Splice in Specimens SF-1 and SF-2
Damage Progression Models
Effective Stiffness Model
Normalized Moment-Drift Response
Strength Degradation
Energy Dissipation
CHAPTER 7. SUMMARY AND CONCLUSIONS
SummarySystem Concept
Design of Test Specimens
Experimental Testing
Experimental Analysis
Conclusions
Recommendations
APPENDIX A: SPECIMEN CONSTRUCTION DRAWINGS
Specimen SF-1Specimen SF-2
Specimen SF-3
Concrete Strength
Grout Strength
Reinforcement
Stress-Strain Plots for Specimens SF-1 and SF-2
Stress-Strain Plots for Specimen SF-3
Corrugated Metal Ducts
APPENDIX C: DAMAGE PROGRESSION
Specimen SF-1Specimen SF-2
Specimen SF-3
APPENDIX D: CONSTRUCTION SEQUENCE
Specimen Construction SequenceColumns with Projecting Bars
Columns without Projecting Bars
Socket Columns
Long Struts
Short Struts
List of Figures
Figure 1. Diagram. Rapid construction sequence
Figure 2. Diagram. Strut-and-tie models for (a) bent out bars and (b) headed bars
Figure 4. Diagram. Precast column elevation for specimens SF-1 and SF-2
Figure 5. Diagram. Specimen SF-1 footing steel arrangement
Figure 6. Diagrams. Spread footing cross section for (a) SF-1 and (b) SF-2 (section A-4)
Figure 7. Graph. Final criteria design space for specimen SF-3
Figure 8. Diagram. Specimen SF-3 footing steel arrangement
Figure 9. Diagram. Specimen SF-3 spread footing cross-section (section A-5)
Figure 10. Diagram. Specimen SF-3 longitudinal section (section A-7)
Figure 11. Diagram. Test setup
Figure 12. Diagram. Locations of external instruments
Figure 13. Diagram. Locations of strain gauges in the three specimens
Figure 14. Diagram. Locations of strain gauges in the three specimens' cast-in-place footings
Figure 15. Graph. Lateral loading displacement history
Figure 16. Chart. Comparison of specimens' drift ratios for the major damage states
Figure 17. Diagram. Column vertical bar naming convention
Figure 18. Photos. Test specimens after a cycle of maximum drift ratio of 4.28 percent
Figure 20. Photo. Specimen SF-3 footing failure
Figure 21. Photo. Damage on top of footing after test
Figure 22. Diagram. Punching shear profile in the north-south direction (loading direction)
Figure 23. Photos. Specimens at the end of the test program
Figure 24. Equation. Coefficient of friction
Figure 25. Equation. Calculation of the moment at the base of the column
Figure 26. Diagram. Displacements and forces on test specimen used in figure 25
Figure 27. Graph. Specimen SF-1 moment-drift response
Figure 28. Graph. Specimen SF-2 moment-drift response
Figure 29. Graph. Specimen SF-3 moment-drift response
Figure 30. Equation. Effective lateral force
Figure 31. Graph. Specimen SF-1 effective force-displacement response
Figure 32. Graph. Specimen SF-2 effective force-displacement response
Figure 33. Graph. Specimen SF-3 effective force-displacement response
Figure 34. Equation. Calculating the average curvature
Figure 35. Graph. Specimen SF-1 average column curvature
Figure 36. Graph. Specimen SF-2 average column curvature
Figure 37. Graph. Specimen SF-3 average column curvature
Figure 38. Photo. Crack opening measurement pot
Figure 39. Graph. Specimen SF-1 splice interface opening
Figure 40. Graph. Specimen SF-2 splice interface opening
Figure 41. Graph. Strain profiles in S-SW bar in specimen SF-1
Figure 42. Graph. Strain profiles in S-SW bar in specimen SF-2
Figure 43. Graph. Strain profiles in S-SW bar in specimen SF-3
Figure 44. Graphs. Strain-drift relationship 2 inches below the column splice interface
Figure 48. Graph. Thermal effects in strain gauges
Figure 49. Graph. Specimen SF-1 strain profiles in bottom mat of the footing
Figure 50. Graph. Specimen SF-2 strain profiles in bottom mat of the footing
Figure 51. Graph. Specimen SF-3 strain profiles in bottom of the footing
Figure 52. Graph. Specimen SF-1 transverse strains in bottom mat of the footing
Figure 53. Graph. Specimen SF-2 transverse strains in bottom mat of the footing
Figure 54. Graph. Specimen SF-3 transverse strains in bottom mat of the footing
Figure 55. Graph. Specimen SF-1 strains in diagonal steel in footing
Figure 56. Graph. Specimen SF-2 strains in diagonal steel in footing
Figure 57. Graph. Specimen SF-3 strains in diagonal steel in footing
Figure 58. Graph. Specimen SF-1 strains in ties
Figure 59. Graph. Specimen SF-2 strains in ties
Figure 60. Graph. Specimen SF-3 strains in ties
Figure 61. Graph. Column vertical displacement vs. cumulative column drift
Figure 62. Graph. Axial response of specimens SF-1 and SF-2
Figure 63. Photo. Specimen SF-2 after axial load of 817 kips
Figure 64. Diagram. Support conditions
Figure 65. Equation. Shear stress demand
Figure 66. Equation. Nominal shear capacity
Figure 67. Equation. Nominal punching shear capacity including transverse steel
Figure 68. Equation. Nominal punching shear capacity excluding transverse steel
Figure 69. Equation. Nominal shear friction resistance
Figure 70. Equation. Maximum principal compressive stress
Figure 71. Equation. Maximum principal tensile stress
Figure 72. Equation. Principal tensile stress
Figure 73. Equation. Principal compressive stress
Figure 74. Diagrams. Strut and tie models for bent-out bars (left) and headed bars (right)
Figure 75. Photo. Joint region of specimen SF-3 after failure
Figure 76. Equation. Nominal axial-load capacity of the column
Figure 77. Graph. Moment-curvature model.(15)
Figure 78. Equation. Plastic overstrength shear demand
Figure 79. Equation. Nominal shear resistance
Figure 80. Equation. Component of total shear resistance due to concrete strength
Figure 81. Equation. Concrete shear resistance
Figure 82. Equation. Contribution of total shear resistance due to transverse steel strength
Figure 83. Equation. Analytical plastic hinge length
Figure 84. Equation. Damage model for spalling
Figure 85. Equation. Damage model for bar buckling
Figure 86. Equation. Damage model for bar fracture
Figure 87. Equation. Effective modulus of rigidity
Figure 88. Graphs. Normalized equivalent moment-drift response
Figure 89. Graph. Comparison of effective force vs. drift
Figure 90. Equation. Energy dissipation
Figure 92. Graph. Equivalent viscous damping calculated per cycle
Figure 93. Equation. Equivalent viscous damping
Figure 94. Graph. Equivalent viscous damping vs. drift
Figure 95. Photos. Specimen SF-1 (left) and specimen SF-2 (right)
Figure 96. Diagram. Specimen SF-1 column elevation and sections
Figure 97. Diagram. Specimen SF-1 top mat plan view
Figure 98. Diagram. Specimen SF-1 bottom mat plan view
Figure 99. Diagram. Specimen SF-1 sections
Figure 100. Diagram. Specimen SF-2 column elevation and sections
Figure 101. Diagram. Specimen SF-2 top mat plan view
Figure 102. Diagram. Specimen SF-2 bottom mat plan view
Figure 103. Diagram. Specimen SF-2 sections
Figure 104. Diagram. Specimen SF-3 column sections
Figure 105. Diagram. Specimen SF-3 column elevation
Figure 106. Diagram. Specimen SF-3 bottom mat plan view
Figure 107. Diagram. Specimen SF-3 footing sections A7 and A6
Figure 108. Diagram. Specimen SF-3 footing sections A5 and B5
Figure 109. Equation. Calculating yield strain
Figure 110. Graph. Specimens SF-1/SF-2 stress-strain curves for No. 6 bars
Figure 111. Graph. Specimens SF-1/SF-2 stress-strain curve for No. 5 bar
Figure 112. Graph. Specimens SF-1/SF-2 stress-strain curve for No. 4 bar
Figure 113. Graph. Specimens SF-1/SF-2 stress-strain curves for No. 3 bar
Figure 114. Graph. Specimens SF-1/SF-2 stress-strain curves for stirrups (2-gauge wire)
Figure 115. Graph. Specimens SF-1/SF-2 stress-strain curves for spiral reinforcement (3-gauge wire)
Figure 116. Graph. Specimen SF-3 stress-strain curve for No. 7 bar
Figure 117. Graph. Specimen SF-3 stress-strain curve for No. 6 bar
Figure 118. Graph. Specimen SF-3 stress-strain curve for No. 5 bar
Figure 119. Graph. Specimen SF-3 stress-strain curve for No. 4 bar
Figure 120. Graph. Specimen SF-3 stress-strain curve for No. 3 bar
Figure 121. Photo. Corrugated metal duct used in test specimens
Figure 122. Photo. Specimen SF-1 flexural cracks after cycle 4-1 (+1.00/-1.00 target drift ratio)
Figure 127. Photo. Specimen SF-1: damage after the cyclic testing
Figure 128. Photo. Specimen SF-1: no damage to the footing was observed after the cyclic testing
Figure 130. Photo. Specimen SF-2: flexural cracks after cycle 3-2 (+0.83/-0.83 target drift ratio)
Figure 135. Photo. Specimen SF-2: damage after the cyclic testing
Figure 136. Photo. Specimen SF-2: no damage to the footing was observed after the cyclic testing
Figure 145. Photo. Specimen SF-3: full column spalling in cycle 9-1 (+6.16/-6.16 target drift ratio)
Figure 152. Photo. Specimen SF-3: condition of specimen just before last cycle
Figure 156. Photo. Roughened surface of octagonal, bottom portion of column
Figure 157. Photo. Specimens SF-1 and SF-2, column segments formed and ready to be cast
Figure 158. Photo. Specimen SF-3, column formed and ready to be cast
Figure 159. Photo. Specimen SF-1 footing ready to be cast
Figure 160. Photo. Specimen SF-3 footing formwork and reinforcement
Figure 161. Photo. Specimen SF-3 column inserted into footing that is ready to cast
Figure 162. Photo. Specimen SF-3: finishing the footing surface
Figure 163. Diagram. Column detail with projecting bars
Figure 164. Diagram. Socket column concept
Figure 165. Diagram. Long struts concept
Figure 166. Diagram. Short struts concept
List of Tables
Table 1. Strain gauge types used in the specimens
Table 2. Target displacement history
Table 3. Damage state description
Table 4. Damage milestones for all three specimens
Table 5. Average concrete strength on test day
Table 6. Average grout strength on test day
Table 7. Measured mild reinforcement properties
Table 8. Moments and drift ratios at maximum and 80 percent of maximum resistance
Table 9. Effective force and displacement at maximum and 80 percent of maximum resistance
Table 10. Axial load and strains across and near splice interfaces
Table 11. Axial load combinations on the test specimens
Table 12. External forces, displacements, and estimated reactions.
Table 13. Footing flexural capacities and demands
Table 14. Footing one-way strength capacities and demands
Table 15. Combined punching shear and moment transfer capacities and demands
Table 16. Punching shear capacities and demands
Table 17. Footing shear-friction capacities and demands
Table 18. Footing joint shear stress capacities and demands
Table 19. Column axial-load capacities and demands
Table 20. Column flexural capacities and demands
Table 21. Column shear capacities and demands
Table 22. Comparison of damage model predictions and observed occurrences
Table 23. Comparison of model prediction and measured effective modulus of rigidity
Table 24. Summary of ratios of footing demands to calculated capacities
Table 25. Slump and air content test results
Table 26. Concrete compressive strengths up to 28 days
Table 27. Concrete compressive strengths on test day
Table 28. Concrete split cylinder strengths on test day.1
Table 29. Grout cube strength on test day
Table 30. Measured mild reinforcement properties
AASHTO | American Association of State Highway and Transportation Officials |
ABC | Accelerated Bridge Construction |
ACI | American Concrete Institute |
ASCE | American Society of Civil Engineers |
BDM | Bridge Design Manual |
Caltrans | California Department of Transportation |
CCC | Compression-compression-compression |
DL | Dead load |
HSS | Hollow structural section |
LL | Live load |
LRFD | Load and Resistance Factor Design |
LVDT | Linear variable differential transformer |
MEF | Maximum effective force |
NEHRP | National Earthquake Hazards Reduction Program |
o.c. | On center |
o.d. | Outside diameter |
OT | Overturning |
PEER | Pacific Earthquake Engineering Research |
PTFE | Polytetrafluoroethylene |
SDC | Seismic Design Criteria |
WSDOT | Washington State Department of Transportation |