Location: Milton, Kentucky, to Madison, Indiana
The rehabilitation of the 83-year-old, structurally deficient Milton-Madison Bridge is an excellent example of creative and innovative engineering solutions applied to a serious and costly transportation challenge.
Constructed in 1929, the 3,180-foot-long, steel, seven-span cantilever through-truss bridge carried more than 10,000 vehicles per day on U.S. 421 over the Ohio River between Milton, Kentucky, and Madison, Indiana. It had two 10-foot-wide travel lanes with no shoulders, and no longer met state or national bridge standards. The narrow lane widths, inadequate sight distances, and driveway configurations to access commercial properties adjacent to the bridge approaches posed safety concerns. A 2006 fracture-critical inspection rated the condition of the bridge's main truss members and floor beams as poor. The bridge is located 26 miles away from the nearest Ohio River crossing and is one of only two Ohio River crossings between Louisville, Kentucky, and Cincinnati, Ohio.
In August 2008, the Kentucky Transportation Cabinet, the Indiana Department of Transportation, and the Federal Highway Administration established the Milton-Madison Management Team (M3T) to explore options for the replacement of the bridge. As a subconsultant to another engineering firm, Michael Baker International conducted a year-long investigation and alternatives analysis to rehabilitate or replace the bridge. Michael Baker explored the possibility of replacing the bridge's superstructure on its existing piers, and developed a sophisticated three-dimensional model and finite-element analysis to assess the stability of the soil, bedrock, caissons, and piers. This advanced analysis and modeling proved the feasibility of reuse of the existing piers. Replacing the superstructure on the existing piers, instead of constructing a new bridge on a new alignment, saved $50 million and reduced construction time by four to five years, allowing M3T to secure a $20 million Transportation Investment Generating Economic Recovery Discretionary Grant, which required substantial completion of the project during 2012.
Michael Baker developed bid documents that included specific scour mitigation and pier strengthening plans, and a maximum permissible bridge closure time of one year, and the design-build team committed to reduce the expected one-year closure of the bridge to 10 days by using prefabrication methods and accelerated bridge construction techniques. The reconstructed bridge features a 40-foot-wide deck with two 12-foot-wide lanes, 8-foot-wide shoulders, and a 5-foot-wide cantilevered sidewalk on the downstream side of the trusses. Crews assembled the prefabricated steel components of a new 2,427-foot-long truss on barges beside the bridge while other crews strengthened and widened the piers and constructed temporary approach ramps. The construction team floated two of the preassembled spans into place alongside the existing bridge and used jacks to lift them onto temporary towers. After construction of the new bridge on the temporary piers, traffic resumed on the new bridge, followed by removal of the old bridge. Crews then slid the new bridge from the temporary towers onto the reinforced piers. Michael Baker provided project management, design review, and construction management and inspection throughout the superstructure replacement.
The project has won numerous awards, including the American Council of Engineering Companies (ACEC) Kentucky Chapter’s Grand Award February 8, 2011; the ACEC Indiana Chapters' Engineering Excellence Award March 5, 2011; and an ACEC National Recognition Award in the national excellence awards competition in April 2011.