Mountaineer State Breaks Record in Segmental Spans
Engineers and contracting crews are breathing easier now that the most complex part has ended in building the $82-million Interstate 64 Kanawha River bridge project near Charleston, W.Va. With more than a year left to meet the project completion deadline, the bridge team already has secured a place in U.S. construction record books with a 760-ft main span of cast-in-place post-tensioned segmental box girders. That span is the longest of its type in the country, surpassing Houston’s Ship Channel Bridge by 10 ft.
General contractor Brayman Construction, Saxonburg, Pa., built the record-setting prestressed span using balanced cantilevered construction, a first in the Mountaineer State. The main span is the first of the bridge’s eight spans to be completed. Segments ranging in depth from 16 ft to 38 ft were constructed using concrete-form travelers extending from the riverbank piers, which rise 108 ft and 88 ft from their concrete footings to the base of the deck.
Brayman project manager Larry Buchheit says the technical demands inherent in erecting a post-tensioned span of such extreme length demanded increasing precision as the sides edged toward each other. “A small variation has greater impact at 300 ft out than it does at 200 ft out,” he says.
State and local officials were on hand to watch the final pour this summer, which “went very smoothly,” according to West Virginia Dept. of Transportation project supervisor John Buchanan. “We had to closely monitor the ambient air temperature through the day and jack the sections horizontally for proper spacing and alignment,” Buchanan adds.
The new 2,975-ft-long bridge is part of a $196.5-million capacity-improvement program for one of the main corridors serving West Virginia’s capital. The structure will take eastbound I-64 traffic off an adjacent 1970s-era steel-plate girder bridge, which currently handles 78,000 vehicles a day, including a significant number of large trucks.
Santiago Rodriguez, project manager and lead bridge designer for T.Y. Lin International, San Francisco, says the choice of a cast-in-place segmental structure reflected both current cost realities and the need for future flexibility. “The segmental bridge was the most economical alternative, allowing us to have longer approach spans at a lower cost,” Rodriguez explains. He adds that WVDOT requested bids for both segmental-concrete and steel-box- girder alternatives to determine the most economical approach. Brayman’s winning bid for the concrete segmental structure was approximately $30 million less than the lowest bid for the steel alternative.
Buchheit notes that the segmental design boosted the area’s economy because the concrete is sourced locally. “It also makes workforce planning easier compared with the variations you go through when erecting a steel structure,” he says.
Over the rest of the year, Brayman will construct the adjoining 460-ft- and 540-ft-long spans and five additional approach spans ranging from 144 ft to 295 ft long, all 16 ft deep. Expansion joints will be located only at the abutments to accommodate the curvature of the approach spans and reduce maintenance needs. Workers will then install parapet walls and a 2-in. overlay of latex modified concrete. Plans call for the new four-lane bridge to open to traffic in late October 2010.
Bucheit says the Kanawha River project has provided valuable insights into the benefits of balanced cantilever construction. “Because there are fewer large cranes, there is far less disruption to road, rail and waterway traffic below the bridge,” he says. “Some people may not even realize there is a bridge being built above them.”
Buchanan also is pleased with the results so far. With the challenging main span completed, “we are through the hardest part,” he says. “The rest of the work will be monotonous by comparison, but a good kind of monotony.”