Bridges for Service Life Beyond 100 Years: Innovative Systems, Subsystems, and Components (2014) / Chapter Skim
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Pages 160-172
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From page 160... ...
160 A p p e n d i x C This appendix presents details of the experimental testing performed on a precast adjacent box beam system with transverse posttensioning. Additional information describing the development of the system can be found in the following PCI journal articles: Simplified Transverse Post-Tensioning Construction and Maintenance of Adjacent Box Girders (Hansen et al.
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161 Wide Joint System The wide joint system developed by UNL does not use a topping or diaphragms. Top and bottom transverse reinforcement is used in a wide shear key filled with concrete to connect adjacent boxes instead of the reinforced concrete composite topping.
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162 fabricated with a plastic duct at the top and bottom flanges to create openings for the threaded rods, as shown in Figure C.6. The bottom duct is inserted between the two layers of prestressing strands, and the top plastic duct is located 3 in.
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163 to the appropriate dimensions. Reinforcement should be provided for confinement about these locations.
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164 Construction Overview Construction of the 16 ft × 8 ft × 27 in. specimen mentioned in the system analysis began by tying together the reinforcement and building the interior and exterior wooden forms.
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165 Once reinforcement preparations were complete, exterior supports for the interior form were built to connect the top and bottom cages. Interior forms had been constructed before this part of the experimental setup was executed.
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166 of 12 ksi, which is much higher than the expected 8 ksi ordered. Burlap sacks were used to provide moisture as the specimen cured.
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167 where an actual girder is most susceptible to environmental corrosion. Cracks were monitored by leakage from a dam built around the middle joint, as well as white latex paint to aid with visibility.
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168 Loading The loads for testing were determined by using the theory of the previously developed 3-D models of the adjacent box girder system. The first model was used to determine the axial force produced by ultimate and fatigue loads in the transverse direction of a 52-ft × 64-ft × 27-in.
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169 Analysis showed that the axial forces due to dead weight for the bottom and top tension setups were 4.9 and 21.4 kips, respectively. A load equal to 17.4 kips brings the axial force to fatigue conditions for the bottom tension setup; however, the fatigue load is already surpassed by the top tension setup.
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170 Both north strain gauges and the southwest strain gauge had to be replaced before obtaining their final readings. Once more, results suggested that the parallel crack caused the changes in strain.
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171 production, improving the rate of construction, allowing easier inspection of voids, and reducing projects costs. It was found that posttensioning also increases the capacity and efficiency of the section because joints are placed under compression and are less likely to experience reflective cracking and leakage.
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From page 172... ...
172 Figure C.27. Total load versus deflection of specimen.
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