Use of 0.7-in. Diameter Strands in Precast Pretensioned Girders (2022) / Chapter Skim
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Pages 80-102
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From page 80... ...
80 3.1 Introduction The experimental portion of this study was completed in two phases. In phase 1, bond characteristics of unstressed seven-wire prestressing strands, with a particular emphasis on 0.7-in.
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Experimental Research Approach and Findings -- Component Tests 81 0.7 in.
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82 Use of 0.7-in. Diameter Strands in Precast Pretensioned Girders specifically addressing helical deformation patterns; a variation of this ratio is promulgated by Eurocode 2 (British Standards Institution, 2014)
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Experimental Research Approach and Findings -- Component Tests 83 repetitions, sufficient to establish a steady-state load-strain-dilation response. Typically, for a strand that has not been previously stressed, the initial stressing operation is a "shakedown" of sorts, and larger dilation ratios are obtained.
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84 Use of 0.7-in. Diameter Strands in Precast Pretensioned Girders The correction given by Eq.
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Experimental Research Approach and Findings -- Component Tests 85 wires of a seven-wire strand will slip past each other, and thus each wire is bent individually; this permits a smaller diameter to be used without affecting the cracking of the wires. The length of the hook "tail," dimension A in Table 3.4 and Figure 3.4a, was 10 in.
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86 Use of 0.7-in. Diameter Strands in Precast Pretensioned Girders for the samples before their receipt.
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Experimental Research Approach and Findings -- Component Tests 87 3.3.1 Straight Strand Beam-End Test Results All straight strand beam-end tests were compliant with the method of ASTM A944-10 (ASTM, 2015c)
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88 Use of 0.7-in. Diameter Strands in Precast Pretensioned Girders (a)
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Experimental Research Approach and Findings -- Component Tests 89 (Table 3.5) ; thus, the splitting behavior observed is attributable to the nature of the LWC -- likely the relatively brittle nature of the LWC shale aggregate -- rather than to the cylinder-derived strength.
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90 Use of 0.7-in. Diameter Strands in Precast Pretensioned Girders Specimen Concrete Slip >0.0001 in.
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Experimental Research Approach and Findings -- Component Tests 91 Table 3.8. Within the scatter that is expected when measuring a local phenomenon such as a bond, the results do not indicate a significant difference (1)
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92 Use of 0.7-in. Diameter Strands in Precast Pretensioned Girders continued, the region of deteriorated bond progressed toward the hook, and the hook became engaged in sharing the strand pullout force.
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Experimental Research Approach and Findings -- Component Tests 93 Figure 3.10 shows the hooked embedment strand tests following testing. The shear failure of H6-10 and H7-10 is evident as is the shear crack that developed before the splitting failure of H7-20.
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94 Use of 0.7-in. Diameter Strands in Precast Pretensioned Girders and 0.7-in.
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Experimental Research Approach and Findings -- Component Tests 95 0.5 0.5 cot∑ ∑= + ≥ φ + φ + φ − − θT A f A f M d N V V Vs y ps ps u v f u c u v p s Eq. 3.7 where (see Figure 3.12a)
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96 Use of 0.7-in. Diameter Strands in Precast Pretensioned Girders It is unlikely that a short straight strand extension will provide much effect, but providing a hook on this strand may be significant.
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Experimental Research Approach and Findings -- Component Tests 97 Without a hooked embedment, the value of fps,straight = design stress in a straight pretensioned strand at nominal flexural strength at the section under consideration (ksi) is given by AASHTO (2020)
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98 Use of 0.7-in. Diameter Strands in Precast Pretensioned Girders 4.
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Experimental Research Approach and Findings -- Component Tests 99 (a) Case 11 NU-900 girder having fourteen 0.6-in.
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100 Use of 0.7-in. Diameter Strands in Precast Pretensioned Girders The strand is embedded over a length of 16 in.
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Experimental Research Approach and Findings -- Component Tests 101 e device for measuring the slip malfunctioned, and no slip data are available for sample 6. e average load to cause 0.10-in.
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102 Use of 0.7-in. Diameter Strands in Precast Pretensioned Girders 4.
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