Lightweight Concrete for High Strength - Expanded Shale & Clay

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ar graph shows the actual strand slip values. Figure C.24 shows a bar graph for all G2 girder tests that compares average strand end slip with embedment length. Strand Slip (in) 0.020 0.018 0.016 0.014 0.012 0.010 0.008 0.006 0.004 0.002 0.000 67 81 91 96 G1 1X Stirrups 0.7350 0.1988 0.0000 0.0000 G1 2X Stirrups 0.0102 0.0007 Strand Embedment Length (in) Figure C.23 G1 Series Girder Average Strand End Slip vs Embedment Length Values 0.008 Strand Slip (in) 0.006 0.004 0.002 0.000 67 81 91 96 G2 1X Stirrups 0.0065 0.0041 0.0000 0.0000 G2 2X Stirrups 0.0033 0.0000 Strand Embedment Length (in) Figure C.24 G2 Series Girder Average Strand End Slip vs Embedment Length Values C-15
If significant strand end slip over occurred during the test, it was impossible to accurately estimate what the level of stress was at a point along the strand based on CSS data. Strand end slip indicates there is a lack of adequate bond between the strand and concrete; near perfect bond is necessary for CSS to be a meaningful predictor of an increase in strand stress. A telling depiction of the effect of strand end slip can be seen in Figure C.25 for test G1B-East, which shows the stress level in the strand to be 260 ksi near the end of the girder and only 227 ksi at the point of load application. Extensive shear cracking in the transfer length region during test G1B- East initiated a strand slip failure resulting in strand end slip of 0.75 inches. The slip allowed the shear cracks to expand causing CSS values in that region to become extremely large. When used to predict strand strain, the values were found to be erroneous. 300 Stress in Strands (ksi) 250 200 150 100 50 0 0 10 20 30 40 50 60 70 80 Distance From Girder End (Inches) Strand Yield Stress at Load Point Strand Maximum Stress at Load Point Strand Maximum Stress Effective Prestress Crack Locations Figure C.25 G1B-East Strand Stress vs. Distance from Girder end In tests where strand slip was less than 0.01 inches, the CSS data appeared consistent and was used to determine the strain and the stress in the prestressing strand. Two trends became evident in examining these plots. First, in every case where strand slip was under 0.01 inches, there was an observed increase in strand stress in the transfer length region above the level of effective prestress. The effect was far more pronounced with shorter embedment lengths. C-16
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School of Civil and Environmental E
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ACKNOWLEDGMENTS The research presen
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A statistical evaluation based on f
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5.6 - Transfer Length 5-13 5.7 - Gi
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Report ACI 318- 99 AASHTO Standard
Page 11 and 12:
Chapter 1. Introduction 1.1 Purpose
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Long term properties including pret
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ottom flange. Prestressing strands
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12500 12000 Concrete Strength, fc'
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Chapter 3. Mix Designs, Field Evalu
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Variation of coarse-to-fine aggrega
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3.2.1 Compressive Strength Figure 3
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Table 3.5 Chloride Permeability --
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12,000 11,500 11,000 Compressive St
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1,400 1,300 1,200 1,100 Experimenta
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strength (10L made in the laborator
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The 50% and 90% of the 620-day cree
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700 600 10,000-psi Measured Shams &
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a Creep Coefficient 3.0 2.5 2.0 1.5
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Chapter 5. Behavior of AASHTO Type
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Portion of Girder Damaged During Te
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2” End Cover (Typ both ends) 4 Sp
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5.3 Instrumentation The surface of
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Figure 5.7 Installation of stirrups
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Table 5.3 Girder concrete propertie
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120 100 80 Stress (ksi) 60 40 20 0
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Table 5.5 -Transfer Length Results
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Figure 5.12 Typical flexural failur
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Since G2 girders had a higher concr
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V " pc cw− Pr ed = ft −Pr ed 1
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Test # Table 5.9 Predicted vs. Expe
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this research project, modification
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Chapter 6. Prestress Losses in HPLC
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losses in the 10,000-psi girders to
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Microstrains (in/inx10 -6 ) 0 500 1
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6.3 Conclusions Regarding Prestress
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7.3 Transfer Length An evaluation o
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Shrinkage after 620 days of drying
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More research is required to examin
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Appendix A. Background A.1 Introduc
Page 81 and 82: Raithby and Lydon described the use
Page 83 and 84: are normally recognized as being on
Page 85 and 86: aggregate must be saturated by pres
Page 87 and 88: A.7.2 Strength Ceiling Harmon discu
Page 89 and 90: compared to lower strength specimen
Page 91 and 92: A.8.8 Deatherage, Burdette and Chew
Page 93 and 94: 3. Concrete compressive strength at
Page 95 and 96: findings were comments that the AAS
Page 97 and 98: including strand diameter, embedmen
Page 99 and 100: l d = l t + l fb = f si 3 d b + 1.5
Page 101 and 102: l d = l t + l fb ⎛ = ⎜ ⎝ f d
Page 103 and 104: Table A.1 Summary of Development Le
Page 105 and 106: strand release, the strand attempts
Page 107 and 108: Appendix B. Creep and Shrinkage B.1
Page 109 and 110: Changes in moisture migration: the
Page 111 and 112: t′: age of concrete at loading (d
Page 113 and 114: s: slump (in) γ ψ ⎧ 0.30 −1.4
Page 115 and 116: t: age of concrete (days) t 0 : age
Page 117 and 118: where ε sh ∞ ⎧ 510 µε for st
Page 119 and 120: left girder-end. The dimension L wa
Page 121 and 122: 6” 85” 50” Segment of girder
Page 123 and 124: 146” 89” 96” 137” Stirrups
Page 125 and 126: were added in a specific sequence f
Page 127 and 128: C.2.3 Formwork Removal, Detensionin
Page 129 and 130: Figure C.19 Mostafa Prestressing St
Page 131: Figure C.22 Ms. Lyn Clements (GDOT)
Page 135 and 136: CSS at Level of Bottom Strands (µ
Page 137 and 138: Appendix D. Prestress Losses in HPL
Page 139 and 140: E ps : elastic modulus of prestress
Page 141 and 142: D.2.2. AASHTO-LRFD Refined Estimate
Page 143 and 144: ∆f log(24 ⋅t) ⎛ f ⎜ ⎞ 55
Page 145 and 146: P i : initial prestressing force af
Page 147 and 148: References AASHTO (1996), Standard
Page 149 and 150: ASTM C 618, Standard Specification
Page 151 and 152: Guide for Structural Lightweight Ag
Page 153 and 154: Martin, L. D., Scott, N. L., “Dev
Page 155: Shahawy, M. A., Batchelor, B., “S
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Lightweight Concrete for High Strength - Expanded Shale & Clay

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