Lightweight Concrete for High Strength - Expanded Shale & Clay

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steel and concrete consolidation in the transfer length region. Many experimental programs have focused on the above factors in determining a relation to predict transfer length. The Master’s Thesis by Chris Reutlinger, “Direct Pull-Out Capacity and Transfer Length of 0.6-Inch Diameter Prestressing Strand in High Performance Concrete” provides very thorough coverage of the history and development of equations to predict transfer length. The following is a summary of current code provisions and other proposed equations as determined for NWC. There are no known proposed equations specifically addressing transfer length for HSLC. A.8.1 Janney, 1954 Initial transfer length testing by Janney in 1954 concluded that transfer length and the general shape of the stress transfer distribution were attributable to diameter and surface condition of the prestressing wire and concrete strength. Janney did not suggest a relation for predicting transfer length. A.8.2 Hanson and Kaar, 1959 Although the focus of Hanson and Kaar’s work was on flexural bond, an appendix included comments on an assumed average transfer bond stress of 400 psi. Equation A.3 was proposed as a way to determine the transfer bond stress. u t = A ps Σ f l 0 t se ( A.3) A ps is the area of prestressing strand, f se is the effective prestressing stress at transfer, Σ o is the actual perimeter of the prestressing strand, l t is the transfer length and u t is the transfer bond stress. A.8.3 Kaar, LaFraugh and Mass, 1963 Kaar et al. concluded that transfer length varied directly based on strand diameter for ¼- inch and ½-inch strands but did not follow this same direct proportion for 0.6-inch strand. Kaar et al. found concrete strength did not impact transfer length, but affected the shape of the stress distribution. Higher concrete strength allowed the concrete to pick up stress more quickly when A-10
compared to lower strength specimens. Kaar et al. also reported differences in transfer length between “dead” and “cut” ends. A.8.4 Mattock, 1963 In 1963, Mattock used Equation A.3 with an assumed average transfer bond stress of 400 psi to derive the current ACI-319-99 equation for transfer length. The factors 0.725 and 4/3 were used to determine the actual area and perimeter respectively. l ⎛ 2 d ⎞ ⎜ π b 0.725 ⎟ f ⎜ 4 ⎟ = ⎝ ⎠ ⎛ 4 ⎞ ⎜ π db ⎟0.4 ⎝ 3 ⎠ se t = 1 2.94 f se d b ( A.4) where d b = diameter of prestressing strand f se = effective prestressing stress after losses (psi) Equation A.4 was simplified to Equation A.5, which is the current ACI expression. l t = f se 3 d b ( A.5) Mattock assumed the effective stress, f se , for 250 ksi strand was 150 ksi and further simplified Equation A.5 to Equation A.6, which was adopted by ACI in 1963 and AASHTO 40 in 1973. l t = 50d ( A.6) b Equation A.6, currently maintained by AASHTO, is based on a limited number of tests where strand ultimate strengths were less than products available today. A-11
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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
Page 13 and 14:
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 &
Page 37 and 38: a Creep Coefficient 3.0 2.5 2.0 1.5
Page 39 and 40: Chapter 5. Behavior of AASHTO Type
Page 41 and 42: Portion of Girder Damaged During Te
Page 43 and 44: 2” End Cover (Typ both ends) 4 Sp
Page 45 and 46: 5.3 Instrumentation The surface of
Page 47 and 48: Figure 5.7 Installation of stirrups
Page 49 and 50: Table 5.3 Girder concrete propertie
Page 51 and 52: 120 100 80 Stress (ksi) 60 40 20 0
Page 53 and 54: Table 5.5 -Transfer Length Results
Page 55 and 56: Figure 5.12 Typical flexural failur
Page 57 and 58: Since G2 girders had a higher concr
Page 59 and 60: V " pc cw− Pr ed = ft −Pr ed 1
Page 61 and 62: Test # Table 5.9 Predicted vs. Expe
Page 63 and 64: this research project, modification
Page 65 and 66: Chapter 6. Prestress Losses in HPLC
Page 67 and 68: losses in the 10,000-psi girders to
Page 69 and 70: Microstrains (in/inx10 -6 ) 0 500 1
Page 71 and 72: 6.3 Conclusions Regarding Prestress
Page 73 and 74: 7.3 Transfer Length An evaluation o
Page 75 and 76: Shrinkage after 620 days of drying
Page 77 and 78: More research is required to examin
Page 79 and 80: 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: A.7.2 Strength Ceiling Harmon discu
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 and 134: If significant strand end slip over
Page 135 and 136: CSS at Level of Bottom Strands (µ
Page 137 and 138: Appendix D. Prestress Losses in HPL
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E ps : elastic modulus of prestress
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D.2.2. AASHTO-LRFD Refined Estimate
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∆f log(24 ⋅t) ⎛ f ⎜ ⎞ 55
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P i : initial prestressing force af
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References AASHTO (1996), Standard
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ASTM C 618, Standard Specification
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Guide for Structural Lightweight Ag
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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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