Alberici Builds New Route 47 Missouri River Bridge with Variable Depth Girders in Tight Spaces
The new Route 47 Missouri River Bridge under construction near Washington, Missouri, sits just 50 feet away from the deteriorating bridge it will replace - a strategy designed to minimize right-of-way acquisition costs and disruptions to the community. To reflect the area's German heritage, the new bridge features variable depth, haunched steel girders and fluted, Gothic-style concrete bridge piers with architectural reveals.
However, as much as those aspects benefit the community, they complicate construction. To build the special piers, General Contractor Alberici Constructors, Inc., of St. Louis needed to purchase custom-made forms. Twin 500-foot spans require crews to place huge girders in extremely tight spaces next to the old structure. However, with strategic planning, two large Manitowoc cranes, and some cooperation from the weather, Alberici plans to set river girders this fall and complete the $63 million project by summer 2019.
Built in 1936, the original through truss bridge links Missouri's Warren and Franklin Counties. With narrow lanes, no shoulders, no bike or pedestrian lanes, and restrictive weight limits, the structure required a regular cycle of rehabilitation. To better accommodate traffic and increase safety, the Missouri Department of Transportation (MoDOT) partnered with the City of Washington, Franklin and Warren Counties, the East West Gateway Council of Governments, and the Boonslick Regional Planning commission to replace the deteriorating bridge.
Construction began in summer 2016. The new 2,560-foot-long bridge - funded by a combination of federal, state, and local money and a TIGER Grant - features 12-foot lanes and 10-foot shoulders. "We used precast concrete girders over the shorter spans on both ends by the land, then once the piers get over the water we changed to steel plate girders," said Judy Wagner, MoDOT's Franklin/Jefferson County Area Engineer.
Placing the new bridge 50 feet upstream from the old structure resulted in an easier realignment of Route 47 and required little right-of-way acquisition, but created other challenges. For instance, when crews drove piles for the bridge bents, "The equipment was too close to have live traffic going past, so we had to temporarily close a lane on the old bridge," Wagner said. "They actually had carpenters on the old structure to mark the piling - that's how close they were."
To ensure vibrations from the new drilled shafts don't cause any damage, "We have a measuring device on the old structure," Wagner added. "When you get down that deep in the rock it's hard to predict what's going to happen, but if anything shifts or changes we'll know immediately."
Huge Girders, Large Cranes
In addition to the tight workspace, the project involves some giant girders as a result of the variable depth design and 500-foot spans. The largest girder measures 16 feet tall and weighs 190,000 pounds. "We try to erect pieces as big as we can so we're out there the minimal amount of time and minimize our risk," said Rob Hartwell, Alberici's Project Director.
To handle the huge loads, Alberici will utilize their Manitowoc 4100 Series-3, 300-ton Ringer Crane, assisted by a Manitowoc 2250 Crawler Crane. "On a few girders it will be a two-crane pick, but for the most part, the 4100 will pick and set the girders then the 2250 will tie in all the bracing between the girders," Hartwell explained.
Industrial Steel Construction, Inc. (ISC), in Gary, Indiana, fabricated the girders. "ISC is a little farther away than what we usually have, but due to these being variable depth and the 16-foot height requirement, it limited the number of bidders who could fabricate that size girder," Hartwell said.
Of the 75 girders, more than 50 will arrive by barge instead of truck. In addition to the difficulty of transporting the large sizes and heavy weights over land, "They can load more onto a barge," Hartwell said. "River traffic is actually the cheaper alternative because we can float them into position exactly where we need them to pick."
With all the barges in the tight workspace, Alberici added a second tugboat to their plans. "We want to make sure our barges don't move or slip toward the existing bridge," Hartwell said. "We'll have one tug stabilizing the crane barge and another going to get the girder barges and switching those out."
Even the smaller girders on land pose their own construction challenges. "On the south end of the project, we'll set the precast girders over the top of an active Union Pacific railroad line," Hartwell explained. "The railroad will supply a flagger, and any time trains are in the vicinity, we'll shut down our work until he tells us we can go again."
Utilities Before Traffic
Once crews set all the girders and pour the bridge deck, they'll move significant amounts of utility lines. "There will be a lot of conduit under the new bridge," Wagner said. "We have 11 utilities going across. On the new bridge, we'll put it all between the girders. We need to maintain service throughout the transfer because if something happens to those utilities, we'll have a lot of people on both sides of the bridge without communications or power."
Since the utility lines will pass through the girder diaphragms, "We'll have the steel pre-drilled," Hartwell said. "We try to have the fabricator do all the prep and put all the holes in so when we come out here we don't have to do any cutting or burning in the field."
Before accomplishing the utilities transfer, "We'll also build vaults on the south bank between the new and old road beds," Wagner said. "We have to finish all that work before we put traffic on the new bridge."
Influenced by Community
Guided by a committee MoDOT formed with local community leaders, the new structure features a number of enhancements. According to Wagner, the committee wanted to reflect the City of Washington's German heritage in a sleek, modern way, so when the architect presented several design options they chose the Gothic-style piers, with a window reminiscent of a cathedral.
Because of the unique pier design, Alberici bought custom forms for many sections. With the added expense, "We try to re-use them as many times as we can," Hartwell said. "That requires careful scheduling and sequencing; until we get done with one we can't finish the next concrete work." To increase efficiency, Alberici rented Doka forms for all the standard pier sections.
In addition to the distinctive pier design, "The committee chose the variable depth girders over the river so we have a curvature to the bottom of the bridge," Wagner said. "The city and both counties added funding to enhance the project, so we'll have girder and pier lighting and a trail that connects the Washington area to the KATY trail." That 10-foot-wide bike/pedestrian path includes a scenic overlook at the center of the bridge.
Under the bridge, $2 million of aesthetic lighting will produce a shadowing effect on the girders. In total, the City of Washington invested in 587 decorative light fixtures comprised of 15,954 individual LED lights to illuminate the bridge piers, girders, and shared-use path for travelers entering the city at night.