The first section of the new Milton-Madison Bridge is ready to be lifted into place onto temporary piers, in an intricate process expected to take three days. The existing bridge will remain open during the span lift, which is currently scheduled to begin June 25, weather permitting. The work is the first of several steps in the replacement of the U.S. 421 bridge, which connects Milton, Ky., and Madison, Ind.
With the help of special hydraulic jacks and the expertise of an international firm, a preassembled 600-ft section of the new bridge—roughly the size of two football fields—will be floated into place on barges and then slowly lifted 85 ft onto temporary piers. The method, called “strand jacking,” is designed to move heavy structures using bundled strands of steel cable.
In order to ensure a safe and efficient operation, project contractor Walsh Construction Co. is using consultant VSL International to lift the 1,776-ton span.
“After the truss has reached the full height of the lift, a massive, 125-ton beam, called a ‘sliding girder,’ will be slid under the truss, supported by the temporary pier and a specially designed concrete pedestal on the existing piers,” explained Charlie Gannon, Walsh Construction project manager. “Eventually, this beam will be used for sliding the new 2,400-ft bridge from the temporary piers to the permanent piers, which are being rehabilitated and strengthened.”
“We’re frequently asked why we’re building the bridge in such a complex manner,” said Kevin Hetrick, Indiana Department of Transportation (INDOT) project manager. “This unique replacement method allows us to keep the bridge open during construction and keep traffic moving.”
While the first section of the new bridge is being lifted, workers will continue to assemble the next span section—a 720-ft-long truss that will be lifted into place in August using the same lifting method. The remainder of the bridge will be “stick built,” meaning it will be assembled in place using cranes.
“Eventually there will be two bridges sitting side-by-side, about 15 ft apart,” explained Project Manager Dav Kessinger with the Kentucky Transportation Cabinet (KYTC). “Then, later this year, we’ll divert traffic onto the new bridge on temporary piers. That gives us time to dismantle the existing truss and get ready for the slide.”
Replacement of the narrow and deteriorating 1929 bridge—a joint effort by INDOT and KYTC—began in early 2011 and is scheduled to be completed in 2013. Because the existing piers are being reused, the new wider bridge will lie within the footprint of the existing bridge.
Time-lapse footage of the span lift will be available on the project website (www.miltonmadisonbridge.com) once the process is complete.
