Road Science Tutorial
On July 20, 2010, in the District of Columbia, the FHWA conducted an accelerated bridge construction workshop using prefabricated bridge components. There, the D.C. DOT was reconstructing its Eastern Avenue Bridge over Kenilworth Avenue using prefabricated components for the pier and superstructure.
Innovative traffic management plans such as the utilization of the service roads in lieu of closing lanes on the main line Kenilworth Avenue were intended to reduce the traffic queuing during construction. The project had a “no-excuse” completion clause of finishing the project within 320 days, and completion was scheduled for October 2010. The contractor was Fort Myer Construction Corp., and the precast sections were manufactured by the Fort Miller Corp.
The project also featured geosynthetic reinforced soil (GRS). Along with precast components, use of GRS can provide a fast, cost-effective bridge support method using alternating layers of compacted fill and sheets of geotextile reinforcement to provide bridge support, said Jim McMinimee, principal engineer, Applied Research Associates, Inc.
GRS, says McMinimee, eliminates the approach slab or construction joint at the bridge-to-road interface, reduces construction time with a complete bridge in about 10 days, costs 25- to 30-percent less than standard pile-capped abutments, results in construction that is less dependent on weather conditions, and provides a flexible design and a bridge that is easier to maintain, built with common equipment and materials.
Nontraditional superstructure construction materials still need to be monitored, the Utah DOT maintains. Utah has been researching methods and products to extend the lives of its bridge decks to match the service life of the entire bridge.
Currently, Utah bridges are designed to a 75-year design life, but the decks are requiring replacement after 30 to 40 years, the state says. Deck replacement projects increase the life-cycle cost of the structure, as well as adding to user delays.
In response, Utah DOT decided to evaluate glass fiber-reinforced polymer (GFRP) reinforcing bars as an alternative to steel rebar in bridge decks, even though there is no significant amount of research regarding precast concrete panels for bridge decks totally reinforced with GFRP bars, says Chris P. Pantelides, Ph.D., S.E., University of Utah Civil & Environmental Engineering Department; Jim Ries, graduate student, University of Utah; and Rebecca Nix, S.E., Utah DOT Structures, in their September, 2010 report, Health Monitoring of Precast GFRP-Reinforced Bridge Deck Panels.
In this application, GFRP reinforcing bars were used in place of traditional epoxy-coated steel rebar in both mats of reinforcing in the deck of the Beaver Creek Bridge on U.S. 6 in rural Utah. The bridge is a single-span creek crossing with access for wildlife passage. The overall span length is 88 feet 2 inches. The girders are AASHTO Type IV prestressed beams.
The deck was constructed using precast deck panels mildly post-tensioned in the longitudinal direction. The bridge was constructed in two phases, which required a closure pour between the east- and west-bound lanes. Pantelides, Ries and Nix believe that this may be the largest bridge utilizing GFRP bars in precast deck panels.
Two GFRP reinforced precast concrete panels were monitored during construction, lifting and placement using electrical strain gauges. In addition, the two panels are being monitored during post-tensioning, truck load testing and long-term using vibrating wire strain gauges. The bridge deck deflections relative to the two diaphragms connecting the prestressed concrete girders were monitored using linear variable differential transformers.
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