Lightweight Concrete for High Strength - Expanded Shale & Clay

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Second, in some cases, the length over which the largest amount of prestressing force was transferred appeared to be a distance somewhat less than the original transfer length discussed in Chapter 5. Figure C.26 shows test G1A-East as an example of the strand stress increase in the transfer length region as well as the apparent reduction in transfer length. The embedment length on this test was only 67 inches. The “lone” triangle plots the maximum stress in the strand at the point of loading at the girder’s ultimate load. This actual plot of strand stress differs significantly from the theoretical diagram which would go linearly from “0” to the triangle. 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.26 G1A-East Strand Stress vs. Distance from Girder End Figure C.27 shows typical CSS data corresponding with applied shear levels, the location of shear cracks crossing the bottom strands, and the transfer length region. CSS data was plotted because it provided a measure of crack growth and allowed identification of the cracks that were increasing most significantly in size. Comparing crack locations with the resulting end slip allowed determination of the region where shear cracking most significantly impacted strand slip. Based on crack location, a comparison was made between strand slip in girders with single and double density shear reinforcement. C-17
CSS at Level of Bottom Strands (µε) 4500 4000 3500 3000 2500 2000 1500 1000 500 0 0 10 20 30 40 Crack Lt V=169 K V=242 K V=291 K V=315 K V=339K V=355 K Distance From Girder End (Inches) Shear Crack Data Distance From End (Inches) 5.0 7.0 12.5 20.5 23.5 26.5 34.0 42.0 44.0 47.5 Applied Shear at Cracking (Kips) 169 315 242 339 315 355 339 339 291 355 Figure C.27 G1A-East CSS and Shear Cracking vs. Distance from Girder End Shear cracking across the bottom strands within the transfer length region initiated large increases in strand end slip. Russell (1992) reported this phenomenon. Despite several shear cracks in the transfer length region, tests G1B-West and G2B-West showed no slip because of the double stirrup density. Tests G1A-East and G2A-East showed slip, but at very small or almost acceptable levels. Russell reported that additional bond stresses can be developed beyond initial strand slip and that small slips are not always followed by complete anchorage failure. Russell also reported that closely spaced cracks were an indication of good bond and wide crack spacing indicated poor bond. Both of Russell’s observations were confirmed in the present tests. Concrete grade also played a significant role in determining development length. Table 5.11 clearly demonstrates a reduction in development length based on concrete grade alone. The G1 series girders had compressive strengths on average approximately 1500 psi less than the G2 series girders. The water cement ratios were approximately 0.29 for the G1 series girders and 0.23 for the G2 series girders. A significant difference between the two mix designs was the amount of silica fume. The G1 series girders had 2 percent silica fume by weight of the total C-18
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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
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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
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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 and 132: Figure C.22 Ms. Lyn Clements (GDOT)
Page 133: If significant strand end slip over
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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