THE CONCRETE BRIDGE MAGAZINE

WINTER 2018

ASPIRE is a quarterly magazine published by PCI in cooperation with the associations of the National Concrete Bridge Council. The editorial content focuses on the latest technology and key issues in the Concrete Bridge Industry.

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ASPIRE Winter 2018 | 35 tendons and the reinforcing bar projected through sleeves in the girder webs to tie the diaphragm and girder together, developing integral action for the final design loadings. The diaphragm was designed with conventional reinforcement and three post-tensioning tendons with twelve 0.6-in.-diameter, 270-ksi strands each, which were tensioned prior to casting the deck and would resist the noncomposite dead load of the wet concrete deck as well as the composite dead and live loads of the final structure. Conclusion By using precast concrete pier caps in the design of the Southbound I-95 to Eastbound SR 202 Flyover Bridge, the designer and contractor overcame significant issues during construction. The caps were designed as a complementary piece of the structure that helped enhance the aesthetics of the bridge, and they were an integral part of the collaborative process that made this project a success. EDITOR'S NOTE A version of this project article was originally published by Bridge Design & Engineering magazine (www.bridgeweb.com) in Bd&e | ISSUE 88 | 2017. ASPIRE's editors have received permission to reprint in whole or in part this article. _____________ Andrew Mish is a project manager at Summit Engineering Group (a Modjeski and Masters company) in Littleton, Colo. four post-tensioning tendons with twelve 0.6-in.-diameter, 270-ksi strands each. All four tendons are located at the top of the section to provide negative moment reinforcement and control stresses. The tendons in the caps were tensioned in two phases to accommodate multiple loading conditions through several stages of construction. After the column-to-cap connection concrete was cast and cured, the first two tendons were tensioned and grouted. Next, the precast concrete girders were erected and the final two tendons in the precast concrete cap were tensioned and grouted. During the design review process, the design team and FDOT discussed whether the CIP column-to-cap connection would behave in a fully composite fashion with the cap. To account for the range of various possible behaviors, the designer bounded the solution by considering both fully composite action and zero- composite action at the connection. This approach gave the owner confidence in the construction method. The phased post-tensioning was designed to work with both solutions. Diaphragm Composite Action After erec ting the pier girders, the in t e gra l di a p h ra g m w a s c a s t . Th e CIP diaphragm was designed to act compositely with the precast concrete pier cap. To ensure composite action, the tops of the precast concrete caps were roughened to ¼-in. amplitude and reinforcement projected from the cap into the diaphragm. Both post-tensioning Plan view of the precast concrete pier cap showing the column blockout, horizontal post-tensioning tendon layout, and shear key. Figure: Modjeski and Masters. The design stages of the precast concrete pier cap were: • Stage 1: Handling and erection of the cap as a mildly reinforced component • Stage 2: Installing and casting of the cast-in-place (CIP) column-to-cap connection • Stage 3: Phase 1 post-tensioning of the pier cap including tendon grouting • Stage 4: Erection of precast concrete curved, spliced pier girders considering out-of-balance loading with only the first girder erected • Stage 5: Phase 2 post-tensioning of the pier cap including tendon grouting • Stage 6: Casting of the CIP diaphragm for composite action with the precast concrete pier cap • Stage 7: Applying post-tensioning to the CIP diaphragm/cap for composite action • Stage 8: Erection of drop-in girders and completion of longitudinal post- tensioning of the structure • Stage 9: Casting of the CIP deck • Stage 10: Applying composite dead loads • Stage 11: Aging of the structure to 30 years to account for time-dependent effects • Stage 12: Applying vehicle live loads Design Stages of the Precast Concrete Pier Caps

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