Use of 0.7-in. Diameter Strands in Precast Pretensioned Girders (2022) / Chapter Skim
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103 Experimental Research Approach and Findings 4.1 Introduction This chapter reports the second phase of the experimental study in which full-scale girders having 0.7-in. strands were cast and tested.
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104 Use of 0.7-in. Diameter Strands in Precast Pretensioned Girders Girder ID Length (ft)
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Experimental Research Approach and Findings 105 With the exception of girders G1–G4 (T-beams) and G9 and G10 (box girders)
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106 Use of 0.7-in. Diameter Strands in Precast Pretensioned Girders Figure 4.5.
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Experimental Research Approach and Findings 107 Figure 4.8. Specimen details -- G9 and G10.
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108 Use of 0.7-in. Diameter Strands in Precast Pretensioned Girders Girder ID Release At girder test Age (days)
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Experimental Research Approach and Findings 109 Reported nominal specimen capacity is based on measured values of material properties (mill report values are used in the cases in which measured values for reinforcing steel were not obtained)
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110 Use of 0.7-in. Diameter Strands in Precast Pretensioned Girders the smooth strains at location i (εismooth)
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Experimental Research Approach and Findings 111 Transfer lengths were also computed using the equation from NCHRP Report 603 (Ramirez and Russell, 2008) as shown in Eq.
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112 Use of 0.7-in. Diameter Strands in Precast Pretensioned Girders The location of load (Le measured from the end of the girder)
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Experimental Research Approach and Findings 113 were used. Except for girders G3, G4, and G5, for which the bearing pad extended over only 53% of the bottom flange width, at least 75% of the bottom flange width of the other single- web girders was supported, as shown in Figure 4.14.
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114 Use of 0.7-in. Diameter Strands in Precast Pretensioned Girders 4.5 Instrumentation In each beam, strain gauges were bonded to multiple strands as well as confining and shear reinforcement.
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Experimental Research Approach and Findings 115 (a) Measurement of support vertical deformation.
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116 Use of 0.7-in. Diameter Strands in Precast Pretensioned Girders The applied shear or load point deflections corresponding to slip of full-length bonded or partially debonded strands are presented in the following discussions.
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Experimental Research Approach and Findings 117 The applied shear versus deflection at the point of load application is compared for all tests in Group 1 in Figure 4.18. The capacities based on Method 1 (labeled AASHTO capacity)
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118 Use of 0.7-in. Diameter Strands in Precast Pretensioned Girders 2.
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120 Use of 0.7-in. Diameter Strands in Precast Pretensioned Girders a ductile behavior in test G4B, i.e., the capacity did not drop as the deflection continued to increase.
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Experimental Research Approach and Findings 121 (a) G3A (detailed based on AASHTO)
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122 Use of 0.7-in. Diameter Strands in Precast Pretensioned Girders these girders experienced extensive cracking and damage.
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Experimental Research Approach and Findings 123 Side (a)
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124 Use of 0.7-in. Diameter Strands in Precast Pretensioned Girders Side (a)
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Experimental Research Approach and Findings 125 (a)
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126 Use of 0.7-in. Diameter Strands in Precast Pretensioned Girders (a)
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Experimental Research Approach and Findings 127 (a)
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128 Use of 0.7-in. Diameter Strands in Precast Pretensioned Girders The failure mode of Girder G8 was a "typical" flexural failure, i.e., exhibiting large deflection before compression failure of the top flange as shown in Figure 4.30.
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Experimental Research Approach and Findings 129 The force in the confinement reinforcement was determined from the strain data (from which stress was calculated as discussed in Appendix F)
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130 Use of 0.7-in. Diameter Strands in Precast Pretensioned Girders The spike for girder G7 occurred within the region with 33% debonded strands whereas in girder G8 the confinement reinforcement force spiked once all the strands were bonded.
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Experimental Research Approach and Findings 131 Nevertheless, the actual girder capacity was 99% of the All-strands capacity and 1.38 times AASHTO capacity. Considering the challenges of modeling the shear behavior of pretensioned girders, a 1% difference between the measured and calculated shear capacities is not considered significant.
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132 Use of 0.7-in. Diameter Strands in Precast Pretensioned Girders The applied shear-load deflection curves (Figure 4.36a)
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Experimental Research Approach and Findings 133 (a) Girder G11.
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134 Use of 0.7-in. Diameter Strands in Precast Pretensioned Girders interaction by using longitudinal strain to determine β and θ for calculating concrete shear strength and θ for the shear resistance of transverse reinforcement.
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Experimental Research Approach and Findings 135 Assuming all the strands are fully developed, the ratio of measured to calculated capacity is greater than 1 for all the tests except for G2B, G9, and G12; however, the average value of this ratio is 1.04 with a coefficient of variation of 7.4%. On other hand, the calculated capacities based on the AASHTO development length equation underestimated the specimen capacity resulting in the measured to calculated capacity ratio being above 1 for all the tests including G2B, G9, and G12.
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136 Use of 0.7-in. Diameter Strands in Precast Pretensioned Girders (a)
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Experimental Research Approach and Findings 137 of the girder. Slippage of strands debonded for 3 ft and 6 or 6.5 ft from the end of the girder was also delayed by extending the bottom flange confinement beyond AASHTO LRFD Bridge Design Specifications Article 5.9.4.4.2 (AASHTO, 2020)
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138 Use of 0.7-in. Diameter Strands in Precast Pretensioned Girders Figure 4.40.
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Experimental Research Approach and Findings 139 the calculations based on a larger transfer length indicate the stresses are within the limits specified in AASHTO LRFD Bridge Design Specifications (AASHTO, 2020)
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140 Use of 0.7-in. Diameter Strands in Precast Pretensioned Girders greater of that determined using the strut-and-tie approach and that required by AASHTO LRFD Bridge Design Specifications Article 5.9.4.4.2 (AASHTO, 2020)
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