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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Page 31 of 55

CONCRETE BRIDGE TECHNOLOGY Design Considerations for Horizontally Curved Precast Concrete U-Girders by Thomas W. Stelmack, Parsons Plant produced horizontally curved, precast concrete U-girders began in Colorado about 10 years ago with the Ramp K flyover ramp linking Interstate 25 (I-25) and State Highway 270 (SH 270) in Denver. This generated interest in the precast industry and led to the development of the PCI Zone 6 concept plans in 2012. A full discussion of the history of the curved U-girder development may be found in the Summer 2015 issue of ASPIRE.™ Several more similar structures were constructed in Colorado, all being contractor-developed alternate designs or value-engineering change proposals. The SR 417/Boggy Creek Road interchange in Orlando was the first standard design-bid-build project in the United States to use the curved precast concrete U-girder concept (see article beginning on page 14). This milestone project illustrates that the concept is viable for typical project delivery, in addition to contractor alternate designs and design-build. Applications While most curved bridge structures can be designed and constructed with the precast concrete curved U-girders, the most common application has been interchange flyover ramps where aesthetics are important, the curve makes chorded girders impractical, and highways and ramps below make precast concrete construction advantageous. The girders are also well suited to rail structures with a girder line below each track. Special Design Considerations One of the most critical and limiting aspects of this girder type is the girder weight. When possible, additional dead loads such as diaphragms, lid slabs, and bottom slab thickening, should be designed such that they can be cast after the girders are erected at the site. This requires analyzing the casting sequence, checking stresses, and providing the necessary details in the plans.

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